Means and methods for treating castration-resistant prostate cancer

Abstract

The present invention relates to the field of therapeutic antibodies for the treatment of subjects with castration-resistant prostate cancer. More specifically, it relates to the treatment of castration-resistant prostate cancer using a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3. It also relates to the treatment of castration-resistant prostate cancer using an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3. The present invention also relates to the treatment of castration-resistant prostate cancer using a combination of one of the antibodies and an androgen receptor axis targeting agent.

Description

[Background technology]

[0001] The present invention relates to the field of antibodies, particularly to the field of therapeutic (human) antibodies for the treatment of castration-resistant prostate cancer, more particularly to antibodies that bind to ERBB3, and antibodies that bind to ERBB2 and ERBB3, and their use in the treatment of cancer in combination or combined therapy with androgen receptor axis targeting agents.

[0002] In 2020, prostate cancer was the second most common malignant tumor in men worldwide and the fifth leading cause of cancer death (Sung et al., “Global Cancer Statistics 2020: GLOBOCAN Estimates of Incidence and Mortality Worldwide for 36 Cancers in 185 Countries,” CA Cancer J Clin 71(3):209-249, 2021). In 2021, the number of cases of advanced prostate cancer in the United States is estimated to be approximately 250,000 (Siegel et al., "Cancer Statistics, 2021," CA Cancer J Clin 71(1):7-33, 2021), including a subpopulation of 30,000 men with castration-resistant prostate cancer (CRPC) (Scher et al., Prostate Cancer Clinical Trials Working (2016) "Trial Design and Objectives for Castration-Resistant Prostate Cancer: Updated Recommendations From the Prostate Cancer Clinical Trials Working Group 3," J Clin Oncol 34(12):1402-1418, 2015). For patients with locally advanced, recurrent, or metastatic tumors, current therapy goals include extending survival and progression-free intervals while maintaining a good quality of life.

[0003] Since 1940, the primary therapy for men with metastatic prostate cancer has been androgen deprivation therapy (ADT), which suppresses testosterone production using either surgical or chemical castration. Chemotherapy is typically initiated only after patients no longer respond to ADT alone, when the disease is considered castration-resistant.

[0004] The androgen receptor (AR) is a lineage survival factor for luminal cancer cells in prostate tumors that plays a role in cancer. ADT remains the primary treatment modality for advanced / metastatic disease, targeting AR signaling. Next-generation AR signaling inhibitors approved for first-line treatment include abiraterone and enzalutamide (Swami et al. 2020, “Advanced Prostate Cancer: Treatment Advances and Future Directions.” Trends Cancer 6(8):702-715). These inhibitors enable stronger blockade of the androgen receptor (AR) axis and longer survival for men with CRPC. However, the degree of improved survival remains insufficient, and most patients eventually develop resistance to these novel agents. The mechanisms of resistance to next-generation hormonal agents are complex and may or may not be dependent on AR signaling, and the AR axis may remain an important driver in advanced / metastatic CRPC after progression (Verma et al. 2020, “Resistance to second-generation antiandrogens in prostate cancer: pathways and mechanisms.” Cancer Drug Resist 3(4):742-761).

[0005] Although preclinical studies have suggested the involvement of the ERBB signaling pathway in the progression of CRPC (Craft et al., 1999. A mechanism for hormone-independent prostate cancer through modulation of androgen receptor signaling by the HER-2 / neu tyrosine kinase. Nat Med 5(3):280-285), successful targeting of this pathway has not yet been realized in the clinical setting, due to the failure to demonstrate the antitumor activity of ERBB2-targeting agents, including trastuzumab and afatinib (Ziada et al., 2004. The use of trastuzumab in the treatment of hormone-refractory prostate cancer; phase II trial. Prostate 60(4):332-337. Molife et al., 2014. Randomized Phase II trial of nintedanib, afatinib, and sequential combination in castration-resistant prostate cancer. Future Oncol 10(2):219-231).

[0006] More than 30,000 patients with metastatic CRPC (mCRPC) are currently receiving first- or second-line systemic therapy but continue to progress and require subsequent lines of therapy. Thus, there is a significant unmet medical need for additional treatment options for patients who progress after treatment with AR signaling inhibitors. Furthermore, an increasing number of patients with non-metastatic prostate cancer currently being treated with AR signaling inhibitors are progressing, expanding the pool of patients after AR signaling inhibitors for CRPC. Thus, there is a need in the field for the treatment of castration-resistant prostate cancer. Summary of the Invention

[0007] The present disclosure provides a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3 for use in a method of treating castration-resistant prostate cancer in a subject. The method comprises administering to the subject an effective amount of a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3. In certain embodiments, the method of treatment further comprises the use of an androgen receptor axis targeting agent.

[0008] The present disclosure provides methods for treating castration-resistant prostate cancer in a subject, the method comprising administering to the subject a therapeutically effective amount of a bispecific antibody comprising an antigen-binding site capable of binding to an extracellular portion of ERBB2 and an antigen-binding site capable of binding to an extracellular portion of ERBB3. In certain aspects, the method comprises selecting a subject who has or is suspected of having castration-resistant prostate cancer before being treated for the castration-resistant prostate cancer.

[0009] The present disclosure provides an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3 for use in a method for treating castration-resistant prostate cancer in a subject. The method comprises administering to the subject a therapeutically effective amount of an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3. In certain embodiments, the method further comprises the use of an androgen receptor axis targeting agent. In certain embodiments, the antibody is a monospecific antibody.

[0010] The present disclosure provides methods for treating castration-resistant prostate cancer in a subject, the method comprising administering to the subject a therapeutically effective amount of a bispecific antibody comprising an antigen-binding site capable of binding to an extracellular portion of ERBB3. In certain embodiments, the method comprises selecting a subject with castration-resistant prostate cancer or a subject suspected of having castration-resistant prostate cancer before treating the subject for castration-resistant prostate cancer. In certain embodiments, the antibody is a monospecific antibody.

[0011] In certain embodiments, the treatment method further comprises screening patients suspected of having castration-resistant prostate cancer according to certain inclusion and exclusion criteria.

[0012] In certain aspects, the method of treatment further comprises administering to the subject an androgen receptor axis targeting agent.

[0013] The present disclosure provides use of a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3 for the manufacture of a medicament for treating castration-resistant prostate cancer in a subject. In certain embodiments, the treatment or use further comprises use of an androgen receptor axis targeting agent.

[0014] In certain embodiments, the castration-resistant prostate cancer has progressed after previous treatment with an androgen receptor axis targeting agent. In certain embodiments, the castration-resistant prostate cancer has progressed after previous treatment with an androgen receptor antagonist, such as a second-generation androgen receptor antagonist, or after previous treatment with an androgen synthesis inhibitor, such as abiraterone acetate. In certain embodiments, the castration-resistant prostate cancer has progressed after previous treatment with enzalutamide.

[0015] In certain embodiments, a treatment method comprising the use or administration of a bispecific antibody of the present disclosure further comprises the use or administration of an androgen receptor axis targeting agent. In certain embodiments, the bispecific antibody and the androgen receptor axis targeting agent are administered within the same time period. The time period typically comprises a 28-day cycle, during which the bispecific antibody is typically administered twice, on days 1 and 15 of the cycle (i.e., Q2W), and the androgen receptor axis targeting agent is administered on each day of the cycle (i.e., QD). Administration of the bispecific antibody and / or the androgen receptor axis targeting agent is continued until a decision is made to discontinue treatment, although treatment may proceed as long as deemed clinically relevant or as long as a clinically relevant effect is observed.

[0016] Thus, in certain embodiments, the cancer has progressed after previous treatment with an androgen receptor axis targeting agent. In certain embodiments, if the cancer has progressed after previous treatment with an androgen receptor antagonist, the use of a bispecific antibody in a treatment method according to the present disclosure further comprises the use of an androgen receptor antagonist. In certain embodiments, if the cancer has progressed after previous treatment with an androgen receptor antagonist, the bispecific antibody treatment method according to the present disclosure further comprises the administration of an androgen receptor antagonist. Thus, combined use is envisioned, where a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3 is used during the same treatment period as an androgen receptor antagonist.

[0017] Thus, in certain embodiments, the present disclosure provides a combination therapy comprising a first container containing an antibody described herein together with a second container containing an androgen receptor axis targeting agent. The two components may be formulated as separate pharmaceutical compositions (e.g., as a kit of parts) and may be administered simultaneously, separately, or sequentially in any order. As will be understood by those skilled in the art, the two components may be provided at different times during the same treatment cycle. In certain embodiments, the treatment cycle consists of 28 days. In certain embodiments, the bispecific antibody of the present disclosure is administered twice during the treatment cycle (e.g., Q2W), and the androgen receptor axis targeting agent is administered every day during the treatment cycle.

[0018] In certain embodiments, the androgen receptor antagonist used in the previous cancer treatment is the same androgen receptor antagonist used in the treatment method in combination with the bispecific antibody of the present disclosure. In certain embodiments, the androgen receptor antagonist used in the previous cancer treatment and the androgen receptor antagonist used in combination with the bispecific antibody of the present disclosure are both enzalutamide. Accordingly, in these embodiments, the present disclosure provides combination treatments or therapies in which a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, e.g., zenocutuzumab, is used together with an androgen receptor antagonist, e.g., enzalutamide.

[0019] In certain embodiments, enzalutamide is administered at a daily dose of 160 mg.

[0020] In certain embodiments, the cancer has progressed after previous treatment with an androgen synthesis inhibitor. In certain embodiments, if the cancer has progressed after previous treatment with an androgen synthesis inhibitor, the use of a bispecific antibody in a treatment method according to the present disclosure further comprises the use of an androgen synthesis inhibitor. In certain embodiments, if the cancer has progressed after previous treatment with an androgen synthesis inhibitor, the treatment method according to the present disclosure using a bispecific antibody further comprises the administration of an androgen synthesis inhibitor. Thus, combined use is envisioned, where a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3 is used during the same treatment period as an androgen synthesis inhibitor.

[0021] In certain embodiments, the androgen synthesis inhibitor used in the previous cancer treatment is the same androgen synthesis inhibitor used in the treatment method in combination with the bispecific antibody of the present disclosure. In certain embodiments, the androgen synthesis inhibitor used in the previous cancer treatment and the androgen synthesis inhibitor used in combination with the bispecific antibody of the present disclosure are both abiraterone acetate, e.g., ZYTIGA®. Thus, in this embodiment, the present disclosure provides a combination treatment or therapy in which a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, e.g., xenocutuzumab, is used during the same treatment period as an androgen synthesis inhibitor, e.g., abiraterone acetate, e.g., ZYTIGA®.

[0022] In certain embodiments, abiraterone acetate, e.g., ZYTIGA®, is administered at a daily dose of 1000 mg. In certain embodiments, abiraterone acetate is used in combination with oral administration of 5 mg prednisone twice daily.

[0023] In certain embodiments, the bispecific antibody of the disclosure is administered or used in an amount of 750 mg once every two weeks. In certain embodiments, the bispecific antibody is xenoctuzumab.

[0024] In certain embodiments, the antibodies of the present disclosure comprise an antigen-binding site capable of binding to the extracellular portion of ERBB3, which blocks both ERBB3 and its ligand, heregulin. In certain embodiments, the antibodies bind to domain III of ERBB3. In certain embodiments, the antibodies also comprise an antigen-binding site capable of binding to the extracellular portion of ERBB2. In certain embodiments, the antibodies comprise an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3. In certain embodiments, the antibodies are bispecific antibodies. In certain embodiments, the bispecific antibodies of the present disclosure comprise a first antigen-binding site capable of binding to the extracellular portion of ERBB2 and a second antigen-binding site capable of binding to the extracellular portion of ERBB3. In certain embodiments, the bispecific antibodies have a first antigen-binding site capable of binding to domain I of ERBB2 and a second antigen-binding site capable of binding to domain III of ERBB3. In certain embodiments, the affinity of the first antigen-binding site for ERBB2 is lower than the affinity of the second antigen-binding site for ERBB3, hi certain embodiments, the antibody is or comprises xenoctuzumab.

[0025] In certain aspects, the present disclosure provides therapeutic methods as disclosed herein, in which an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3 is used. In certain aspects, the antibody is a monospecific antibody.

[0026] In certain aspects, the present disclosure provides a method of treating a subject with castration-resistant prostate cancer, the method comprising administering to the subject an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3. In certain aspects, the antibody comprises an antigen-binding site capable of binding to domain III of ERBB3.

[0027] In certain aspects, the present disclosure provides use of an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3 for the manufacture of a medicament for treating castration-resistant prostate cancer in a subject. In certain aspects, the antibody comprises an antigen-binding site capable of binding to domain III of ERBB3.

[0028] In certain aspects, antibodies of the present disclosure, including but not limited to bispecific antibodies, comprise an antigen-binding site capable of binding to the extracellular portion of ERBB3, blocking both ERBB3 and its ligand, heregulin. In certain aspects, the antibody also comprises an antigen-binding site capable of binding to the extracellular portion of ERBB3. In certain aspects, the antibody comprises an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3. In certain aspects, the antibody is or comprises xenoctuzumab.

[0029] Also provided is a method for selecting a subject with castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or for treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the subject for the treatment if the sample does not show PTEN loss.

[0030] Also provided is a method for establishing whether a subject with castration-resistant prostate cancer is likely to respond to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or whether a subject with castration-resistant prostate cancer is likely to respond to treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the samples for not showing PTEN loss, thereby establishing which subject the sample was derived from, or whose sample was derived from, is likely to respond to the treatment.

[0031] Also provided is a method for classifying a subject with castration-resistant prostate cancer based on PTEN status prior to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or prior to treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) if the sample does not show PTEN loss, classifying the subject from whom the sample was obtained, or from whom the sample was obtained, as eligible for the treatment.

[0032] Also provided is a method for selecting a subject with castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or for treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the subject for the treatment if the sample shows PTEN loss.

[0033] Also provided is a method for establishing whether a subject with castration-resistant prostate cancer is likely to respond to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or whether a subject with castration-resistant prostate cancer is likely to respond to treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the sample for showing PTEN loss, thereby establishing which subject the sample was derived from, or whose sample was derived from, is likely to respond to the treatment.

[0034] Also provided is a method for classifying a subject with castration-resistant prostate cancer based on PTEN status prior to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or prior to treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) if the sample shows PTEN loss, classifying the subject from which the sample was obtained, or from whom the sample was obtained, as eligible for the treatment.

[0035] In certain embodiments, the subject is a human subject. The human subject has or is at risk of developing castration-resistant prostate cancer. In certain embodiments, the subject has or is at risk of developing metastatic castration-resistant prostate cancer. Thus, the subject is in need of treatment for castration-resistant prostate cancer or metastatic castration-resistant prostate cancer. [Brief explanation of the drawings]

[0036] [Figure 1]a) Lists the amino acid sequence of the consensus light chain variable region (VL+CL sequence), b) the amino acid sequence of the consensus light chain variable region DNA sequence and its translation (IGKV1-39 / jk1), c) the consensus light chain constant region DNA sequence and translation, d) the IGKV1-39 / jk5 consensus light chain variable region translation, e) V region IGKV1-39A, f) consensus light chain CDR1, CDR2, and CDR3 sequences (all according to IMGT). [Figure 2] The IgG heavy chain sequences for the generation of bispecific molecules are listed below: a) CH1 region, b) hinge region, c) CH2 region, d) CH3 domain containing variations L351K and T366K (KK), e) CH3 domain containing variations L351D and L368E (DE). [Figure 3] The nucleic acid and amino acid sequences of the heavy chain variable regions are listed below. The CDR1, CDR2, and CDR3 sequences of each heavy chain variable region are also provided according to the Kabat numbering system. DETAILED DESCRIPTION OF THE INVENTION

[0037] A proportion of CRPC patients exhibit primary resistance, and ultimately, nearly all patients develop resistance. The development of CRPC resistance is thought to be a subclonal phenomenon, with a proportion of tumor cells remaining sensitive to androgen deprivation therapy despite the emergence of resistant clones. Without being bound by theory, the inventors believe that preventing paracrine activation of NRG1 / ERBB3 signaling to blunt the drivers of antiandrogen resistance in CRPC is an option for treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3 in domain III, or an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3 in domain III and an antigen-binding site capable of binding to the extracellular portion of ERBB2 in domain I, as disclosed herein for use in a method of treating castration-resistant prostate cancer in a subject.

[0038] The ERBB family of tyrosine kinase transmembrane receptors is also referred to as the human epidermal growth factor (EGF) receptor family (HER). The family includes ERBB (erythroblastoma)-1, ERBB2, ERBB3, and ERBB4. Receptors (reviewed in Yarden and Pines 2012) are widely expressed on epithelial cells. Upregulation of HER receptors or their ligands, such as neuregulin (NRG) (also known as heregulin (HRG)) or epidermal growth factor (EGF), is a frequent event in human cancers (Wilson, Timothy R et al. Nature, vol. 487, 7408 (2012): 505-9). Specifically, overexpression of ERBB1 and ERBB2 occurs in epithelial tumors and is associated with tumor invasion, metastasis, resistance to chemotherapy, and poor prognosis (Zhang, Hongtao et al., The Journal of Clinical Investigation, vol. 117, 8 (2007): 2051-8). In normal breast tissue, ERBB3 has been shown to be important for the growth and differentiation of luminal epithelium. For example, loss / inhibition of ERBB3 causes selective basal expansion on luminal epithelium (Balko, Justin M et al., Proceedings of the National Academy of Sciences, vol. 109, 1 (2012): 221-6). Ligand binding to the extracellular domain of RTK induces receptor dimerization of both the same (homodimerization) and different (heterodimerization) receptor subtypes. Dimerization can activate the intracellular tyrosine kinase domain, which undergoes autophosphorylation and can then activate several downstream growth-promoting signaling pathways, including those mediated by mitogen-activated protein kinases (MAPKs) and the pro-survival pathway Akt (reviewed in Yarden, Yosef, and Gur Pines. Nature reviews. Cancer, vol. 12, 8 553-63).No specific endogenous ligand for ERBB2 has been identified, and therefore it is assumed that it normally signals via heterodimerization (Sergina, Natalia V et al. Nature, vol. 445, 7126 (2007): 437-41). ERBB3 can be activated by the engagement of its ligand. These ligands include, but are not limited to, neuregulin (NRG) (also known as heregulin (HRG)).

[0039] ERBB1 is known by various synonyms, the most common of which is EGFR. EGFR has an extracellular domain (ECD) composed of four subdomains, two of which are involved in ligand binding and two of which are involved in homodimerization and heterodimerization. EGFR integrates extracellular signals from various ligands, resulting in diverse intracellular responses. EGFR is involved in several human epithelial malignancies, particularly cancers of the breast, bladder, non-small cell lung cancer, lung, colon, ovary, head and neck, and brain. Activating mutations in the gene and overexpression of the receptor and its ligands have been found, resulting in an autocrine activation loop. This receptor tyrosine kinase (RTK) is widely used as a target for cancer therapy. Both small molecule inhibitors targeting the RTK and monoclonal antibodies (mAbs) (monospecific bivalent) directed against the extracellular ligand-binding domain have been developed and have shown some clinical success. The database accession number for the human EGFR protein and the gene encoding it is (GenBank NM_005228.3). This accession number is provided primarily to provide further means of specifying the EGFR protein as a target; the actual sequence of the EGFR protein bound by an antibody may vary due to mutations in the encoding gene, such as those that occur in some cancers.

[0040] As used herein, the term "ERBB2" refers to the protein encoded by the ERBB2 gene in humans. Alternative names for the gene or protein include CD340, HER2, HER-2 / neu, MLN19, NEU, NGL, and TKR1. The ERBB2 gene is often referred to as HER2 (for human epidermal growth factor receptor 2). When ERBB2 is referred to herein, the reference refers to human ERBB2. Antibodies containing an antigen-binding site that binds to ERBB2 bind to human ERBB2. Due to sequence and tertiary structure similarities between human and other mammalian orthologs, ERBB2 antigen-binding sites may, but do not necessarily, also bind to such orthologs. The database accession numbers for the human ERBB2 protein and its encoding gene are (NP_001005862.1, NP_004439.2, NC_000017.10, NT_010783.15, and NC_018928.2). The accession numbers are provided primarily to provide a means of further characterization of ERBB2 as a target; the actual sequence of the antibody that binds to the ERBB2 protein may vary due to mutations in the encoding gene, such as those that occur in some cancers. The ERBB2 antigen-binding site binds to ERBB2 and its various variants, such as those expressed by some ERBB2-positive tumor cells. The antigen-binding site that binds to ERBB2 preferably binds to domain I of ERBB2.

[0041] As used herein, the term "ERBB3" refers to the protein encoded by the ERBB3 gene in humans. Alternative names for the gene or protein are HER3, LCCS2, MDA-BF-1, c-ERBB3, c-ERBB3, ERBB3-S, p180-ERBB3, p45-sERBB3, and p85-sERBB3. When ERBB3 is referred to herein, the reference refers to human ERBB3. Antibodies comprising an antigen-binding site that binds to ERBB3 bind to human ERBB3. Due to similarities in sequence and tertiary structure between humans and other mammalian orthologs, the ERBB3 antigen-binding site may, but does not necessarily, also bind to such orthologs. The database accession numbers for the human ERBB3 protein and the gene encoding it disclosed herein are NP_001973.2 and NC_000012.11, which include the genomic location of the ERBB3 gene on chromosome 12 (56473892-56497289). The accession numbers are provided primarily to provide a method for further specification of ERBB3 as a target, and the actual sequence of the ERBB3 protein bound by the antibody may vary due to mutations in the encoding gene, such as those that occur in some cancers. The ERBB3 antigen-binding site binds to ERBB3 and its various variants, such as those expressed by some ERBB3-positive tumor cells. The antigen-binding site that binds to ERBB3 preferably binds to domain III of ERBB3.

[0042] When ERBB1, ERBB2 or ERBB3 or alternative names for these are mentioned, the reference is to human ERBB1, ERBB2 or ERBB3. The antibodies referred to herein bind to ERBB1, ERBB2 or ERBB3, and many mutant ERBB1, ERBB2 or ERBB3 proteins, such as those found in cancers.

[0043] The present disclosure provides a bispecific antibody comprising an antigen-binding site that binds to or is capable of binding to the extracellular portion of ERBB2 and an antigen-binding site that binds to or is capable of binding to the extracellular portion of ERBB3 for use in a method of treating castration-resistant prostate cancer in a subject. The method comprises administering to the subject an effective amount of a bispecific antibody comprising an antigen-binding site that binds to or is capable of binding to the extracellular portion of ERBB2 and an antigen-binding site that binds to or is capable of binding to the extracellular portion of ERBB3. In certain embodiments, the method of treatment further comprises the use of an androgen receptor axis targeting agent.

[0044] The present disclosure provides a method for treating castration-resistant prostate cancer in a subject, the method comprising administering to the subject an effective amount of a bispecific antibody comprising an antigen-binding site that binds to or is capable of binding to an extracellular portion of ERBB2 and an antigen-binding site that binds to or is capable of binding to an extracellular portion of ERBB3. In certain embodiments, the method comprises selecting a subject who has castration-resistant prostate cancer or a subject suspected of having castration-resistant prostate cancer before treating the subject for castration-resistant prostate cancer. In certain embodiments, the treatment method further comprises administering to the subject an androgen receptor axis targeting agent.

[0045] The present disclosure provides use of a bispecific antibody comprising an antigen-binding site that binds to or is capable of binding to an extracellular portion of ERBB2 and an antigen-binding site that binds to or is capable of binding to an extracellular portion of ERBB3 for the manufacture of a medicament for treating castration-resistant prostate cancer in a subject. In certain embodiments, the treatment or use further comprises use of an androgen receptor axis targeting agent.

[0046] Endocrine and metabolic outcomes represent the major adverse effects associated with the safety profile of hormone therapy directed against prostate cancer. For example, treatment with abiraterone acetate induces mineralocorticoid excess, hypokalemia, hypertension, elevated liver function tests, insulin resistance, and hyperglycemia. Enzalutamide is known to induce or exacerbate hypertension and is associated with increased falls and fractures in elderly patients. Therefore, limited overlapping toxicities with xenoctuzumab are expected given the safety profiles associated with abiraterone acetate and enzalutamide. The very well-tolerated safety profile of xenoctuzumab makes it a particularly good candidate for combination therapy in this advanced, often previously treated elderly patient population. Continued blockade of CRPC with AR signaling inhibitors while simultaneously blocking the HER3 / NRG1 resistance signaling pathway manages patients after failure of next-generation AR agents. Continuous treatment of CRPC with an androgen-targeting agent while simultaneously using an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3 in domain III, or an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3 in domain III and an antigen-binding site capable of binding to the extracellular portion of ERBB2 in domain I, is disclosed herein for use in a method of treating castration-resistant prostate cancer in a subject.

[0047] In certain embodiments, the castration-resistant prostate cancer has progressed after a previous cancer treatment. Such previous treatment is also known as anti-cancer therapy or treatment, and in some embodiments, includes an androgen receptor axis targeting agent. In certain embodiments, the cancer has progressed after a previous treatment with an androgen receptor antagonist, e.g., a second-generation androgen receptor antagonist. In certain embodiments, the cancer has progressed after a previous treatment with a first-generation androgen receptor antagonist, e.g., flutamide, bicalutamide, nilutamide, or a second-generation androgen receptor antagonist, e.g., apalutamide, darolutamide, or enzalutamide, or an androgen receptor antagonist known to those skilled in the art, e.g., proxalutamide, BMS-641988, TQB3720, SHR3680, or TRC-253. In certain aspects, the cancer has progressed after prior treatment with enzalutamide.

[0048] In certain embodiments, the castration-resistant prostate cancer is metastatic castration-resistant prostate cancer (mCRPC).

[0049] In certain aspects, the therapeutic methods comprising the use or administration of a bispecific antibody of the present disclosure further comprise the use or administration of an androgen receptor axis targeting agent.

[0050] Thus, in certain embodiments, the cancer has progressed after previous treatment with an androgen receptor axis targeting agent. In certain embodiments, if the cancer has progressed after previous treatment with an androgen receptor antagonist, the use of a bispecific antibody in a treatment method according to the present disclosure further comprises the use of an androgen receptor antagonist. In certain embodiments, if the cancer has progressed after previous treatment with an androgen receptor antagonist, the bispecific antibody treatment method according to the present disclosure further comprises the administration of an androgen receptor antagonist. Thus, combined use is envisioned, where a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3 is used during the same treatment period as an androgen receptor antagonist. Thus, in certain embodiments, the cancer has progressed after previous treatment with an androgen receptor antagonist, and the antibody treatment method further comprises the use of an androgen receptor antagonist.

[0051] In certain embodiments, the androgen receptor antagonist used in the previous cancer treatment is the same androgen receptor antagonist used in the treatment method in combination with the bispecific antibody of the present disclosure. In certain embodiments, the androgen receptor antagonist used in the previous cancer treatment and the androgen receptor antagonist used in combination with the bispecific antibody of the present disclosure are both apalutamide, darolutamide, or enzalutamide. In certain embodiments, the androgen receptor antagonist used in the previous cancer treatment and the androgen receptor antagonist used in combination with the antibody of the present disclosure are both enzalutamide. Thus, in this embodiment, the present disclosure provides a combination treatment or therapy in which a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, e.g., xenoctuzumab, is used together with an androgen receptor antagonist, e.g., enzalutamide.

[0052] In certain aspects, an antibody of the disclosure is combined with an androgen receptor antagonist, including flutamide, bicalutamide, nilutamide, a second generation androgen receptor antagonist, such as apalutamide, darolutamide, or enzalutamide, or an androgen receptor antagonist known to those of skill in the art, such as proxalutamide, BMS-641988, TQB3720, SHR3680, or TRC-253.

[0053] In certain embodiments, enzalutamide is administered at a daily dose of 160 mg. In certain embodiments, enzalutamide is administered at a daily dose of 160 mg, and the bispecific antibody of the present disclosure is administered in an amount of 750 mg once every two weeks. In certain embodiments, the bispecific antibody is xenoctuzumab. Thus, treatment of the subject includes administration of both enzalutamide and xenoctuzumab. In certain embodiments, enzalutamide, which has been used in previous cancer treatment and is further included in the treatment method, is administered at a daily dose of 160 mg.

[0054] In certain embodiments, the cancer has progressed after previous treatment with an androgen synthesis inhibitor. In certain embodiments, if the cancer has progressed after previous treatment with an androgen synthesis inhibitor, the use of a bispecific antibody in a treatment method according to the present disclosure further comprises the use of an androgen synthesis inhibitor. In certain embodiments, if the cancer has progressed after previous treatment with an androgen synthesis inhibitor, the bispecific antibody treatment method according to the present disclosure further comprises the administration of an androgen synthesis inhibitor. Thus, combined use is envisioned, where a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3 is used during the same treatment period as an androgen synthesis inhibitor. Thus, in certain embodiments, the cancer has progressed after previous treatment with an androgen synthesis inhibitor, and the antibody treatment method further comprises the use of an androgen synthesis inhibitor.

[0055] In certain embodiments, the androgen synthesis inhibitor used in the previous cancer treatment is the same androgen synthesis inhibitor used in the treatment method in combination with the bispecific antibody of the present disclosure. In certain embodiments, the androgen synthesis inhibitor used in the previous cancer treatment and the androgen synthesis inhibitor used in combination with the bispecific antibody of the present disclosure are both abiraterone acetate, e.g., ZYTIGA®. Thus, in this embodiment, the present disclosure provides a combination treatment or therapy in which a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, e.g., xenocutuzumab, is used during the same treatment period as an androgen synthesis inhibitor, e.g., abiraterone acetate, e.g., ZYTIGA®.

[0056] In certain embodiments, the antibody of the present disclosure is combined with an androgen synthesis inhibitor, such as abiraterone acetate. In certain embodiments, the antibody is a bispecific antibody disclosed herein. In certain embodiments, abiraterone acetate, which has been used in previous cancer treatments and is further included in the treatment method, is administered at a daily dose of 1000 mg.

[0057] In certain embodiments, abiraterone acetate, e.g., ZYTIGA®, is administered at a daily dose of 1000 mg. In certain embodiments, abiraterone acetate is used in combination with oral administration of 5 mg of prednisone twice daily. In certain embodiments, abiraterone acetate, e.g., ZYTIGA®, is administered at a daily dose of 1000 mg, and the bispecific antibody of the present disclosure is administered in an amount of 750 mg once every two weeks. In certain embodiments, the bispecific antibody is xenoctuzumab. Thus, treatment of the subject includes administration of both abiraterone acetate and xenoctuzumab during the same treatment period.

[0058] Furthermore, the subject may have received additional prior treatment for prostate cancer, including taxane-based chemotherapy, e.g., docetaxel or cabazitaxel. Additionally, or alternatively, the subject may have also received prior treatment with sipuleucel-T or a radiopharmaceutical, e.g., radium-223 or lutetium LU 177.

[0059] Radiopharmaceuticals, or pharmaceutical radioactive compounds, are a group of pharmaceuticals that contain radioisotopes. Examples include radium-223 and lutetium (177Lu) oxodotreotide. 177 Lu) oxodotreotide (International Nonproprietary Name, or INN), or 177 Lu DOTA-TATE, trade name Lutathera®, is a chelated complex of a radioisotope of the element lutetium with DOTA-TATE, used in peptide receptor radionuclide therapy.

[0060] As used herein, the terms "subject" and "patient" are used interchangeably and refer to a mammal (e.g., a patient, such as a human, mouse, rat, hamster, guinea pig, rabbit, cat, dog, monkey, cow, horse, pig, etc.) having cancer. In certain embodiments, the subject is a human subject. As used herein, the subject has or is at risk of developing castration-resistant prostate cancer.

[0061] As used herein, castration-resistant prostate cancer (CRPC) refers to a subject with prostate cancer that has progressed after previous prostate treatment and has testosterone levels below the level detected after the subject has undergone castration (also referred to as "castration level testosterone").In certain embodiments, the subject has an increase in serum prostate-specific antigen and / or develops new metastases and / or progression of existing metastases while undergoing androgen deprivation therapy (ADT).In certain embodiments, the subject with CRPC has a serum testosterone level of less than 50 ng / dL.

[0062] Castration serves to suppress the production of androgens, such as testosterone, and is one method used in the treatment of prostate cancer to reduce circulating androgen levels. Castration is typically achieved using surgical (orchiectomy) or chemical means. Such chemical means include androgen deprivation therapy (ADT), chemotherapy (including but not limited to docetaxel (Taxotere®) or cabazitaxel (Jevtana®)), androgen receptor axis targeting (ARAT) agents, androgen synthesis inhibitors, and (second-generation) androgen receptor antagonists. Examples include, but are not limited to, abiraterone, enzalutamide, apalutamide, and darolutamide. Further examples of AR antagonists are included in Table 1.

[0063] [Table 1]

[0064] In certain embodiments, castration-resistant prostate cancer is cancer that has progressed after receiving a second-generation hormone drug of choice for the treatment of castration-resistant prostate cancer. In certain embodiments, castration-resistant prostate cancer is cancer that has progressed after receiving two or fewer second-generation hormone drugs of choice for the treatment of castration-resistant prostate cancer. Such second-generation hormone drugs include, but are not limited to, androgen receptor antagonists (including, but not limited to, enzalutamide) or androgen synthesis inhibitors (including, but not limited to, abiraterone).

[0065] In certain embodiments, the subject to be treated shows an increase in the level of prostate-specific antigen (PSA), which is defined as two increases in PSA reaching a minimum value of 1 ng / mL or more before the start of treatment.In certain embodiments, the increase exceeds the previous reference value.The increase in the level of prostate-specific antigen (PSA) is typically a PSA increase of 25% or more from the minimum point, and a PSA increase of more than 2 ng / mL from the minimum point, and is confirmed by progression at two time points at least 3 weeks apart.

[0066] In certain embodiments, a patient may have discontinued administration of an androgen receptor axis targeting agent, e.g., abiraterone or enzalutamide, for more than 14 days, after which an increase in PSA levels is documented after resuming the agent.

[0067] As used herein, the term "androgen receptor axis targeting agent" includes androgen synthesis inhibitors and androgen receptor antagonists. Thus, an androgen receptor axis targeting agent as used herein prevents, blocks, or reduces the signaling activity of the androgen receptor. Androgen receptor axis activity is involved in the progression to castration-resistant prostate cancer. This effect on the androgen receptor axis can be achieved using an androgen synthesis inhibitor, such as abiraterone acetate, which affects serum androgen levels, such as testosterone, thereby preventing, blocking, or reducing androgen receptor activity. Alternatively, this effect on the androgen receptor axis can be achieved by using an androgen receptor antagonist, such as enzalutamide, which can prevent, block, or reduce the binding of ligands to the androgen receptor and its activation.

[0068] At the start of treatment, at least one, more than one, or all of the following inclusion factors IF1-IF7 apply to the subject of treatment. In certain embodiments, the subject includes or complies with all of inclusion factors IF1-IF7.

[0069] IF1. Be 18 years of age or older.

[0070] Have an Eastern Cooperative Oncology Group performance status (ECOG) of IF2.0 or 1.

[0071] IF3. Having an estimated life expectancy of 12 weeks or more.

[0072] IF4. A minimum of 3 weeks has elapsed since completion of any major surgery, radiation, and all prior systemic anticancer therapy, or, if the prior therapy was a single-agent small molecule therapeutic, at least 5 half-lives have elapsed and sufficient recovery from acute toxicity of any prior therapy to Grade 1 or less according to the National Cancer Institute (NCI)-Common Terminology Criteria for AEs (CTCAE) v. 5.0, except for alopecia or neuropathy. Such single-agent small molecule therapeutics may be flutamide, ketoconazole, etc.

[0073] IF5. Left ventricular ejection fraction (LVEF) of 50% or greater by echocardiogram (ECHO) or multi-gated acquisition scan (MUGA).

[0074] IF6. Have adequate organ function as established by: IF6.1.1.5×10 9 Absolute neutrophil count ≥ 1 / L.

[0075] IF 6. Hemoglobin level above 2.9 g / dL.

[0076] IF6.3.100×10 9 Platelet count of ≥ 1 / L.

[0077] IF6.4. Serum calcium within normal range (or corrected with supplements).

[0078] IF6.5.2. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) less than or equal to 5 × upper limit of normal (ULN), except in cases involving hepatic malignancy, where ALT / AST is less than or equal to 5 × ULN.

[0079] IF6.6 Total bilirubin level of 1.5 x ULN or less, except in Gilbert's disease, where the total bilirubin level is 3 x ULN or less.

[0080] IF6.7 Estimated glomerular filtration rate greater than 30 mL / min based on the Cockroft-Gault formula, and IF6.8 Serum albumin greater than 3.0 g / dL.

[0081] IF7. Have a formalin-fixed, paraffin-embedded (FFPE) tumor specimen. The specimen may be a freshly collected archival FFPE tumor sample, preferably collected within 2 years of treatment initiation.

[0082] In certain embodiments, all values for organ function measurements by IF6 have upper limits observed in healthy subjects.

[0083] In certain embodiments, the treatment target includes one or more factors selected from the group consisting of IF1-IF7. In certain embodiments, the treatment target includes factors IF2, IF3, IF5, and IF6. In certain embodiments, the treatment target includes all of factors IF1-IF7.

[0084] As used herein, the definitions of the ECOG performance status scoring grades are as follows: 0 Fully active and able to perform all pre-disease activities without limitation. 1 Limited physically strenuous activity but ambulatory and able to perform light or sedentary tasks such as light housework and office work. 2 Ambulatory and able to care for all self but unable to perform any work activities. Able to sit and move around more than 50% of waking hours. 3 Only able to care for self limited and confined to a bed or chair more than 50% of waking hours. 4 Totally disabled. Unable to care for self. Totally confined to a bed or chair. 5 Death.

[0085] In certain embodiments, the subject being treated has histologically confirmed adenocarcinoma of the prostate, which in certain embodiments does not have features of neuroendocrine differentiation or small cell carcinoma.

[0086] In certain embodiments, the subject being treated has metastatic disease documented by at least two bone lesions on whole-body bone scintigraphy or soft tissue disease documented by computed tomography (CT) scan / magnetic resonance imaging (MRI).

[0087] In certain embodiments, the subject to be treated has a serum testosterone level of 1.73 nmol / L or less (50 ng / dL or less) before the start of treatment. In certain embodiments, the subject to be treated is undergoing androgen deprivation therapy. In certain embodiments, the subject to be treated is undergoing androgen deprivation therapy and has a serum testosterone level of 1.73 nmol / L or less (50 ng / dL or less) before the treatment. Thus, in certain embodiments, the treatment method is preceded by a step of determining the serum testosterone level in a sample obtained from the subject. If the serum testosterone level is then 1.73 nmol / L or less (50 ng / dL or less), the subject can be selected for treatment. When determining serum testosterone levels, the PCWG3 guidelines recommend the use of a testosterone detection assay with a sensitivity of 1-2 ng / dL, and such detection assays are readily available.

[0088] In certain embodiments, prior treatment with an androgen receptor axis targeting agent was initiated at least 90 days or at least 118 days prior to initiation of treatment according to the present disclosure. A break in administration of up to 30 days is permitted between at least 90 days or 118 days.

[0089] In certain embodiments, the subject being treated has CRPC or progressive CRPC disease according to Prostate Cancer Working Group 3 (PCWG3) criteria. In certain embodiments, progressive CRPC disease is established according to at least one or more of the following criteria: 1. An increase in prostate-specific antigen (PSA) levels is defined as two increases in PSA reaching a nadir of 1 ng / mL or greater before the start of treatment compared to the previous reference value, except that if the patient discontinues administration of an androgen receptor axis targeting agent, e.g., abiraterone or enzalutamide, for longer than 14 days, an increase in PSA levels is documented after the agent is restarted. 2. Progression of soft tissue disease as defined by RECIST v1.1. 3. Progression of previously normal (less than 10 mm) lymph nodes (determined by growth of 5 mm or more across the short axis). 4. Progression of bone disease defined by two or more new lesions demonstrated by whole-body bone scintigraphy.

[0090] An increase in prostate-specific antigen (PSA) levels, or its determination, is defined as a PSA increase of greater than 25% above the nadir and a PSA increase of more than 2 ng / ml above the nadir, confirmed by progression at two time points at least 3 weeks apart. (See Scher et al., 2016, "Trial Design and Objectives for Castration-Resistant Prostate Cancer: Updated Recommendations From the Prostate Cancer Clinical Trials Working Group 3." J Clin Oncol 34(12):1402-1418.)

[0091] In certain embodiments, the subject being treated is receiving a stable dose of a bisphosphonate or denosumab for a period of at least four weeks, which may be provided to maintain or improve bone health.

[0092] In certain embodiments, the subject to be treated is able to swallow oral medication and is free of gastrointestinal conditions (eg, malabsorption, resection) that are considered to compromise intestinal absorption.

[0093] In certain embodiments, premedication with the following substances is provided: -Aracetamol / acetaminophen 1000 mg PO or IV. -Dexchlorpheniramine 5 mg IV (or other anti-H1 equivalent, PO or IV) Dexamethasone 10 mg IV (or equivalent, PO or IV). If needed, corticosteroids should be administered prior to the Cycle 1 Day 1 dose and, at the investigator's discretion, used for subsequent injections to manage infusion-related reactions (IRR). -H2 antagonists may be given at the investigator's discretion.

[0094] In certain embodiments, the subject being treated has not received more than two second-generation hormonal agents for metastatic disease. Such agents include abiraterone and enzalutamide. In certain embodiments, the subject being treated has not received more than two systemic chemotherapy regimens for metastatic disease. Such chemotherapy regimens include docetaxel (Taxotere®) and cabazitaxel (Jevtana®). In certain embodiments, the subject being treated has not received previous anti-HER3-directed therapy.

[0095] In certain embodiments, a subject exhibits clinical efficacy according to PCWG3-modified RECIST v1.1 criteria after receiving an anti-CRPC treatment according to the present disclosure. In certain embodiments, the patient exhibits progression-free survival (PFS), non-progressive disease (non-PD), no evidence of disease (NED), stable disease (SD), partial response (PR), or complete response (CR) according to PCWG3-modified RECIST v1.1 criteria. In certain embodiments, the patient exhibits measurable radiological disease control for lymph node, visceral tissue, and / or bone tissue according to PCWG3 or PCWG3-modified RECIST v1.1 criteria. In certain embodiments, the subject exhibits such clinical efficacy after receiving treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3. In certain aspects, the method of treatment further comprises administering to the subject an androgen receptor axis targeting agent, such as abiraterone or enzalutamide.

[0096] As used herein, the terms "treat," "treating," and "treatment" refer to any type of intervention or process performed on a subject or administering to a subject an active agent or combination of active agents for the purpose of curing or ameliorating a disease or its symptoms, including reversing, alleviating, ameliorating, suppressing, or delaying symptoms, complications, conditions, or biochemical manifestations associated with a disease, as well as preventing the onset, progression, occurrence, severity, or recurrence of symptoms, complications, conditions, or biochemical manifestations associated with a disease.

[0097] Any embodiment disclosed herein that is mentioned in relation to any use in a method of treatment according to the present disclosure applies equally to any method of treatment according to the present disclosure, and vice versa.

[0098] Any embodiment disclosed herein that is mentioned in relation to any use in a method of treatment according to the present disclosure applies equally to any use for the manufacture of a medicament for treatment according to the present disclosure, and vice versa.

[0099] Any embodiment disclosed herein that is mentioned in relation to any use in a method of treatment according to the present disclosure applies equally to any use for the manufacture of a medicament for treatment according to the present disclosure, and vice versa.

[0100] As used herein, "effective treatment" or "positive therapeutic response" refers to treatment that results in a beneficial effect, e.g., an improvement in at least one symptom of a disease or disorder, e.g., cancer. A beneficial effect can take the form of an improvement over a baseline, including an improvement over measurements or observations made before initiating therapy according to the method. For example, a beneficial effect can take the form of slowing, stabilizing, halting, or reversing the progression of cancer in a subject at any clinical stage, as evidenced by a reduction or elimination of clinical or diagnostic symptoms of the disease or markers of cancer. Effective treatment can, for example, reduce tumor size, reduce the presence of circulating tumor cells, reduce or prevent tumor metastasis, slow or halt tumor growth, and / or prevent or delay tumor recurrence or relapse.

[0101] The term "therapeutic amount" or "effective amount" refers to that amount of an agent or combination of agents that provides a desired biological, therapeutic, and / or prophylactic result. That result can be reduction, improvement, amelioration, relief, delay, and / or alleviation of one or more of the signs, symptoms, or causes of a disease, or any other desired alteration of a biological system. In certain aspects, a therapeutic amount is an amount sufficient to delay tumor development. In certain aspects, a therapeutic amount is an amount sufficient to prevent or delay tumor recurrence.

[0102] A therapeutic amount of a drug or composition may (i) reduce the number of cancer cells, (ii) reduce tumor size, (iii) inhibit, prevent, delay to some extent, and stop the invasion of cancer cells into peripheral organs, (iv) inhibit tumor metastasis, (v) inhibit tumor growth, (vi) prevent or delay the onset and / or recurrence of tumors, and / or (vii) relieve to some extent one or more symptoms associated with cancer.

[0103] Therapeutic amounts may vary depending on factors such as the disease state, age, sex, and weight of the individual being treated, and the ability of the agent or agent combination to elicit a desired response in the individual.

[0104] A therapeutic amount can be administered in one or more administrations.

[0105] A therapeutic amount also includes an amount that balances any toxic or detrimental effects of a drug or drug combination with a therapeutically beneficial effect." Notably, loss of tumor suppressor genes is particularly common in CPC and is associated with aggressive disease and poor prognosis. For effective tumor growth inhibition mediated by the bispecific antibodies disclosed herein, such as xenoctuzumab, or the ERBB3-specific antibodies disclosed herein, intact signaling pathways downstream of the PI3K pathway may be required. Thus, in certain embodiments, the castration-resistant prostate cancer being treated does not have PTEN loss or PTEN deficiency. In certain embodiments, cancers treated according to the present disclosure are characterized as having wild-type PTEN status. In certain embodiments, the cancer does not have PTEN loss. In certain embodiments, the cancer is wild-type for PTEN. In certain embodiments, the cancer does not exhibit PTEN loss. Without being bound by theory, in certain embodiments, classifying subjects based on PTEN status is useful before initiating the treatments disclosed herein, as cancers with appropriate PTEN status may benefit more from the treatment. Subjects whose PTEN status is determined to be either wild-type PTEN or not have PTEN loss may be selected for or classified as eligible for the treatments disclosed herein.

[0106] Alternatively, in certain embodiments, castration-resistant prostate cancer treated according to the present disclosure exhibits PTEN loss or PTEN deficiency. In certain embodiments, cancer treated according to the present disclosure is characterized as having PTEN loss status. In certain embodiments, the cancer has PTEN loss. In certain embodiments, the cancer is not wild-type for PTEN. In certain embodiments, the cancer exhibits PTEN loss. Without being bound by theory, in certain embodiments, classifying subjects based on PTEN status is useful before initiating the treatments disclosed herein, as cancers with appropriate PTEN status may benefit more from the treatments. Subjects whose PTEN status is determined to be either not wild-type for PTEN or has PTEN loss may be selected for or classified as eligible for the treatments disclosed herein.

[0107] PTEN status can be determined by means known to those skilled in the art, and any suitable means can be used in combination with the antibody-based treatment methods or uses of the present disclosure, including combination therapies described herein. In certain embodiments, PTEN status is determined using IHC. In certain embodiments, PTEN status is determined using a liquid biopsy assay.

[0108] Determining PTEN status can be performed, for example, using commercially available PTEN genetic testing on cells from a biopsy or blood sample. Various methods are available, and many are known in the art. One method is PCR amplification using primers spanning PTEN cDNA or genomic DNA, followed by sequencing of the amplified nucleotide molecules. This can be performed for mutations known to cause or affect PTEN activity. New mutations can also be easily detected through techniques known to those skilled in the art, including next-generation DNA or RNA sequencing. Another method for determining PTEN status is by ELISA.

[0109] Available nucleic acid-based techniques for determining PTEN status include RT-PCR, real-time PCR, transcriptome analysis, anchored multiplex PCR, nCounter, allele-specific RNA-based methodologies including FISH, hybrid capture-based next-generation sequencing (NGS), and DNA-based methodologies including amplicon-based NGS, among other commercially available techniques. PTEN loss can also be established using protein-based assays such as immunohistochemistry, IHC, and FISH. To date, robust clinical assays exist that reproducibly measure PTEN protein and gene loss using immunohistochemistry and fluorescent in situ hybridization (FISH) in diagnostic tissue biopsies and circulating tumor cells from plasma. Notably, IHC protocols have been successfully validated on the Ventana Benchmark platform in Clinical Laboratory Improvement Amendments-certified laboratories with high inter-observer reproducibility in the scoring system.

[0110] One example of a commercially available kit for establishing PTEN status is through the use of Guardant360® TissueNext®, an analytically validated tissue-wide genomic profiling panel that includes TMB, MSI status, and PD-L1 IHC. The Guardant360 TissueNext report includes 84 genes. This kit allows for the identification of genotyping point mutations (SNVs) and deletion variants (indels) of 84 genes, including PTEN, amplifications of 20 genes, and fusions of 12 genes. A further example of a commercially available kit that can be used to establish PTEN status is the Roche Ventana Optiview kit DAB, which uses the SP218 PTEN antibody.

[0111] Accordingly, the present disclosure also provides a method for selecting a subject having castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the subject for the treatment if the sample does not show PTEN loss.

[0112] Alternatively, the present disclosure provides a method for establishing whether a subject with castration-resistant prostate cancer is likely to respond to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the samples for not showing PTEN loss, thereby establishing which subject the sample is derived from, or whose subject the sample is derived from, is likely to respond to the treatment.

[0113] Alternatively, the present disclosure provides a method for classifying a subject with castration-resistant prostate cancer based on PTEN status prior to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) if the sample does not show PTEN loss, classifying the subject from which the sample was obtained, or from whom the sample was obtained, as eligible for the treatment.

[0114] The present disclosure also provides a method for selecting a subject having castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the subject for the treatment if the sample shows PTEN loss.

[0115] Alternatively, the present disclosure provides a method for establishing whether a subject with castration-resistant prostate cancer is likely to respond to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the sample for showing PTEN loss, thereby establishing which subject the sample was derived from, or whose sample was derived from, is likely to respond to the treatment.

[0116] Alternatively, the present disclosure provides a method for classifying a subject with castration-resistant prostate cancer based on PTEN status prior to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) if the sample shows PTEN loss, classifying the subject from which the sample was obtained, or from whom the sample was obtained, as eligible for the treatment.

[0117] In certain embodiments, PTEN loss or PTEN status is determined using IHC. In other embodiments, PTEN status is determined using a liquid biopsy assay including DNA sequencing.

[0118] In certain embodiments, the cancer or subject to be treated according to the present disclosure does not have an oncogenic driver mutation. In certain embodiments, the cancer or subject does not have an oncogenic driver mutation in the PI3K, AKT, or mTOR pathway. In certain embodiments, the cancer or subject does not have upregulation of such pathways. In certain embodiments, the cancer or subject does not have a mutation in any one of EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET, and ROS1. In certain embodiments, the cancer or subject does not have a mutation in known tumor-associated genes or proteins encoded therefrom, such as EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET, and ROS1.

[0119] In certain aspects, the subject's cancer is examined by next generation sequencing (e.g., DNA, RNA, or whole transcriptome), and the cancer or subject is then selected for treatment with a bispecific antibody comprising an antigen binding site capable of binding to the extracellular portion of ERBB2 and an antigen binding site capable of binding to the extracellular portion of ERBB3 using a method comprising: a) determining the presence of oncogenic driver mutations in a sample obtained from the subject, in certain aspects, mutations modulating the PI3K, AKT, and / or mTOR pathways; and b) if the sample lacks the presence of oncogenic driver mutations, in certain aspects, mutations modulating the PI3K, AKT, and / or mTOR pathways, classifying the subject from which the sample was obtained, or from whom the sample was obtained, as eligible for the treatment.

[0120] In certain aspects, the subject's cancer is tested by next generation sequencing (e.g., DNA, RNA, or whole transcriptome sequencing), and the cancer or subject is thereafter selected for treatment with a bispecific antibody comprising an antigen binding site capable of binding to an extracellular portion of ERBB2 and an antigen binding site capable of binding to an extracellular portion of ERBB3 using a method comprising: a) determining the presence of an oncogenic driver mutation, in a sample from the cancer of the subject, in certain aspects an oncogenic driver mutation in any one of EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET, and ROS1; and b) if the sample lacks the presence of an oncogenic driver mutation, in certain aspects EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET, and ROS1, classifying the subject from whom the sample was obtained as eligible for the treatment.

[0121] In certain aspects, CRPC, or a subject having CRPC, is selected for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to an extracellular portion of ERBB2 and an antigen-binding site capable of binding to an extracellular portion of ERBB3 using a method comprising the steps of: a) determining the presence of oncogenic driver mutations, in certain aspects, mutations modulating the PI3K, AKT, and / or mTOR pathways, in a sample obtained from the subject's CRPC; and b) classifying the subject from whom the sample was obtained, or from whom the sample was obtained, as eligible for the treatment if the sample lacks the presence of oncogenic driver mutations, in certain aspects, mutations modulating the PI3K, AKT, and / or mTOR pathways.

[0122] In certain aspects, CRPC, or a subject having CRPC, is selected for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to an extracellular portion of ERBB2 and an antigen-binding site capable of binding to an extracellular portion of ERBB3 using a method comprising: a) determining the presence of an oncogenic driver mutation, in a sample obtained from the subject's CRPC, in certain aspects an oncogenic driver mutation in any one of EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET, and ROS1; and b) if the sample lacks the presence of an oncogenic driver mutation, in certain aspects EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET, and ROS1, classifying the subject from whom the sample was obtained as eligible for the treatment.

[0123] In certain embodiments, the sample obtained from the subject is a sample taken from a tumor or cancer prior to the anti-CRPC treatment of the present disclosure. In certain embodiments, the sample obtained from the subject is a sample comprising tumor or cancer cells from a tumor or cancer from which the subject being treated is afflicted. In certain embodiments, the sample taken from the tumor or cancer is obtained prior to initiating the anti-CRPC treatment of the present disclosure.

[0124] As used herein, the term "antigen-binding site" refers to a site derived from, and preferably present in, a bispecific antibody that is capable of binding to an antigen. An antigen-binding site is typically formed by and present in the variable domains of an antibody. The variable domains contain the antigen-binding site. An antigen-binding site is capable of binding to an antigen under normal physiological conditions. This is often also referred to as the antigen-binding site "binding" to the antigen.

[0125] In one embodiment, an antibody variable domain comprises a heavy chain variable region (VH) and a light chain variable region (VL). The antigen-binding site may be present in the combined VH / VL variable domains, or in the VH region alone, or in the VL region alone. When the antigen-binding site is present in only one of the two regions of the variable domain, the corresponding variable region may contribute to folding and / or stability of the combined variable region, but does not contribute significantly to antigen binding itself.

[0126] As used herein, antigen binding refers to the typical binding ability of an antibody to its antigen. An antibody comprising an antigen-binding site that binds to ERBB2 binds to ERBB2 and, under otherwise identical conditions, binds to the homologous receptors ERBB1 and ERBB4 of the same species at least 100-fold less. An antibody comprising an antigen-binding site that binds to ERBB3 binds to ERBB3 and, under otherwise identical conditions, does not bind to the homologous receptors ERBB1 and ERBB4 of the same species.

[0127] Considering that the ERBB family is a family of cell surface receptors, binding is typically evaluated against cells that express the receptor.The binding of antibody to antigen can be evaluated in various ways.One method is to incubate antibody with antigen (preferably, cells that express the antigen), remove unbound antibody (preferably by washing step), and detect bound antibody by labeled antibody that binds to the bound antibody.

[0128] Antigen binding by an antibody is typically mediated through the complementary regions of the antibody and the specific three-dimensional structure of both the antigen and variable domains, allowing these two structures to bind together with precision (an interaction similar to a lock and key), as opposed to random, nonspecific attachment of the antibody. Because antibodies typically recognize an epitope of an antigen, and such epitopes may also exist in other compounds, antibodies according to the present invention that bind to ERBB2 and / or ERBB3 may also recognize other proteins if such other compounds contain the same epitope. Thus, the term "bind" does not exclude the binding of the antibody to one or more other proteins containing the same epitope. Such other proteins are preferably not human proteins. The ERBB2 antigen-binding site and ERBB3 antigen-binding site defined herein typically do not bind to other proteins on the membranes of cells in postnatal, preferably adult, humans.

[0129] As used herein, the term "interferes with binding" means that the antibody is directed to an epitope on ERBB3 and competes with the ligand for binding to ERBB3. The antibody may weaken ligand binding, displace the ligand if it is already bound to ERBB3, or at least partially prevent the ligand from binding to ERBB3, for example, through steric hindrance.

[0130] The term "antibody" as used herein preferably refers to a protein molecule belonging to the immunoglobulin class of proteins containing one or more variable domains that bind to an epitope on an antigen, such domains being derived from or sharing sequence homology with the variable domains of an antibody. Antibodies for therapeutic use are preferably as close as possible to the natural antibody of the subject to be treated (e.g., human antibodies for human subjects). Antibody binding can be expressed in terms of specificity and affinity. Specificity determines which antigen or its epitope is specifically bound by a binding domain. Affinity is a measure of the strength of binding to a particular antigen or epitope. Antibodies such as bispecific antibodies of the present invention comprise the constant domain (Fc portion) of a natural antibody. Antibodies of the present invention are typically bispecific full-length antibodies, preferably of the human IgG subclass. Preferably, the antibodies disclosed herein are of the human IgG1 subclass. Such antibodies have favorable half-lives upon in vivo administration to humans and have excellent ADCC properties, with CH3 engineering that can provide modified heavy chains that form heterodimers preferentially over homodimers upon co-expression in clonal cells.

[0131] The antibodies disclosed herein are preferably "full-length" antibodies. The term "full-length" is defined to include essentially the entire antibody, but not necessarily possessing all of the functions of an intact antibody. For the avoidance of doubt, a full-length antibody contains two heavy chains and two light chains. Each chain contains a constant (C) region and a variable (V) region, which can be divided into domains designated CH1, CH2, CH3, VH, and CL, VL (suitable amino acid sequences for each domain are shown in Figures 1 and 2). Antibodies bind to antigens via the variable domains contained in the Fab portion, and after binding, can interact with molecules and cells of the immune system via the constant domains, primarily via the Fc portion. The terms "variable domain," "VH / VL pair," and "VH / VL" are used interchangeably herein. Full-length antibodies according to the invention may contain mutations that provide desired characteristics. The term "full-length antibody" encompasses antibodies with a deletion of one or more amino acid residues without substantially altering the binding properties of the resulting antibody. Such mutations should not involve the deletion of a substantial portion of any of the regions. However, antibodies with one or more amino acid residues deleted without essentially altering the binding properties of the resulting antibody are encompassed within the term "full-length antibody." For example, an IgG antibody may have 1 to 20 amino acid residues inserted, deleted, or a combination thereof in the constant region. For example, if an antibody itself has low ADCC activity, the ADCC activity of the antibody can be improved by slightly modifying the antibody's constant region (Junttila, T.T., K. Parsons, et al. (2010) "Superior In Vivo Efficacy of Afucosylated Trastuzumab in the Treatment of HER2-Amplified Breast Cancer," Cancer Research 70(11):4481-4489).

[0132] Full-length IgG antibodies are preferred due to their favorable half-life and the need to remain close to fully self (human) molecules for immunogenicity reasons. The antibodies disclosed herein are preferably bispecific IgG antibodies, preferably bispecific full-length IgG1 antibodies. IgG1 is preferred due to its long circulating half-life in humans. To prevent any immunogenicity in humans, it is preferred that the bispecific IgG antibody is human IgG1.

[0133] The term "bispecific" (bs) means that one part of an antibody (defined above) binds to one epitope on an antigen, while a second part binds to a different epitope. The different epitopes are typically present on different antigens. The heavy chain variable regions of a bispecific antibody are typically different from each other, while the light chain variable regions are preferably the same. Bispecific antibodies in which different heavy chain variable regions are associated with the same or a common light chain are also referred to as bispecific antibodies with a common light chain. The bispecific antibodies described herein typically comprise one variable domain that binds to ERBB2 and another variable domain that binds to ERBB3.

[0134] Preferred bispecific antibodies can be obtained by coexpression of two different heavy chains and a common light chain in a single cell. When using wild-type CH3 domains, coexpression of two different heavy chains and a common light chain will result in three different species: AA, AB, and BB. To increase the percentage of the desired bispecific product (AB), CH3 engineering can be used, or in other words, heavy chains with compatible heterodimerization domains can be used, as defined herein below. Suitable compatible CH3 heterodimerization domains are shown in Figures 2d and 2e.

[0135] As used herein, the term "compatible heterodimerization domain" refers to a protein domain that has been engineered such that engineered domain A' preferentially forms heterodimers with engineered domain B', and vice versa, but with reduced homodimerization between A'-A' and B'-B'.

[0136] The term "common light chain" refers to a light chain that may be identical or may have some amino acid sequence differences, but the binding specificity of the full-length antibody is not affected. For example, it is possible to prepare or find a non-identical but still functionally equivalent light chain by introducing and testing conservative amino acid changes, amino acid changes in regions that do not contribute, or only partially contribute, to binding specificity when paired with a heavy chain, and the like. The terms "common light chain," "common VL," "single light chain," and "single VL," with or without the addition of the term "rearranged," are all used interchangeably herein.

[0137] The common light chain (variable region) preferably has a germline sequence. Preferred germline sequences are light chain variable regions that are frequently used in the human repertoire and have good thermodynamic stability, yield, and solubility. In a preferred embodiment, the light chain comprises a light chain region comprising the amino acid sequence of the IgVκ1-39*01 gene segment, as shown in FIG. 1, more preferably the common light chain IGKV1-39 / jk1, with 0 to 10, preferably 0 to 5, amino acid insertions, deletions, substitutions, additions, or combinations thereof. IgVκ1-39 is an abbreviation for immunoglobulin variable kappa 1-39 gene. This gene is also known as immunoglobulin kappa variable 1-39, IGKV139, or IGKV1-39. The external identifiers for this gene are HGNC: 5740, Entrez Gene: 28930, and Ensembl: ENSG00000242371. The variable regions of IGKV1-39 are listed in Figure 1. The V regions can be combined with one of five J regions. Figure 1 describes two preferred sequences of IgVκ1-39 combined with a J region. The combined sequences are designated IGKV1-39 / jk1 and IGKV1-39 / jk5, with alternative names being IgVκ1-39*01 / IGJκ1*01 or IgVκ1-39*01 / IGJκ5*01 (designation according to the IMGT database world wide web at imgt.org).

[0138] Preferably, the IgVκ1-39*01 comprising the light chain variable region is a germline sequence. More preferably, the IGJκ1*01 or / IGJκ5*01 comprising the light chain variable region is a germline sequence. In a preferred embodiment, the IGKV1-39 / jk1 or IGKV1-39 / jk5 light chain variable region is a germline sequence.

[0139] In a preferred embodiment, the light chain variable region comprises germline IgVκ1-39*01. In a preferred embodiment, the light chain variable region comprises kappa light chain IgVκ1-39*01 / IGJκ1*01 or IgVκ1-39*01 / IGJκ5*01. In a preferred embodiment, IgVκ1-39*01 / IGJκ1*01. The light chain variable region preferably comprises germline kappa light chain IgVκ1-39*01 / IGJκ1*01 or germline kappa light chain IgVκ1-39*01 / IGJκ5*01, preferably germline IgVκ1-39*01 / IGJκ1*01.

[0140] Those skilled in the art will recognize that "common" also refers to functional equivalents of light chains that do not have identical amino acid sequences. Many variants of such light chains exist in which mutations (deletions, substitutions, additions) exist that do not substantially affect the formation of a functional binding region. The light chain may also be a light chain identified herein above with one to five amino acid insertions, deletions, substitutions, or combinations thereof.

[0141] Preferably, the first antigen-binding site and the second antigen-binding site both comprise a light chain variable region comprising a CDR1 having the sequence (RASQSISSYLN), a CDR2 having the sequence (AASSLQS) and a CDR3 having the sequence (QQSYSTPPT) according to the KABAT numbering or according to the IMGT numbering system, wherein the CDRs are QSISSY, AAS and QQSYSTPPT, respectively.

[0142] The antibodies disclosed herein can reduce the ligand-induced receptor function of ERBB3 on ERBB2- and ERBB3-positive cells. In the presence of excess ERBB2, the ERBB2 / ERBB3 heterodimer can provide growth signals to expressing cells in the absence of detectable ligands for the ERBB3 chains in the heterodimer. This ERBB3 receptor function is referred to herein as the ligand-independent receptor function of ERBB3. The ERBB2 / ERBB3 heterodimer also provides growth signals to expressing cells in the presence of an ERBB3 ligand. This ERBB3 receptor function is referred to herein as the ligand-induced receptor function of ERBB3.

[0143] As used herein, the term "ERBB3 ligand" refers to a polypeptide that binds to and activates ERBB3. Examples of ERBB3 ligands include, but are not limited to, neuregulin 1 (NRG) and neuregulin 2, betacellulin, heparin-binding epidermal growth factor, and epiregulin. The term includes biologically active fragments and / or variants of naturally occurring polypeptides.

[0144] Preferably, the ligand-induced receptor function of ERBB3 is ERBB3 ligand-induced growth of ERBB2- and ERBB3-positive cells. In a preferred embodiment, the cells are MCF-7 cells (ATCC® HTB-22™), SKBR3 (ATCC® HTB-30™), NCI-87 (ATCC® CRL-5822™), BxPC-3-luc2 cells (Perkin Elmer 125058), BT-474 cells (ATCC® HTB-20™), or JIMT1 cells (DSMZ number: ACC589).

[0145] The ERBB2 protein contains several domains (see Figure 1 in Landgraf, R Breast Cancer Res. 2007;9(1):202- for reference). The extracellular domains are designated domains I to IV. The binding locations of the antigen-binding sites of the antibodies described herein to each domain have been mapped. Bispecific antibodies having an antigen-binding site (first antigen-binding site) that binds to domain I or domain IV of ERBB2 (first antigen-binding site) contain heavy chain variable regions that maintain significant binding specificity and affinity for ERBB2 when combined with various light chains. Bispecific antibodies having an antigen-binding site (first antigen-binding site) that binds to domain I or domain IV of ERBB2 (first antigen-binding site) and an antigen-binding site (second antigen-binding site) for ERBB3 are more effective at reducing ligand-induced receptor function of ERBB3 than bispecific antibodies containing an antigen-binding site (first antigen-binding site) that binds to a different extracellular domain of ERBB2. A bispecific antibody comprising an antigen-binding site (first antigen-binding site) that binds to ERBB2, preferably to domain I or domain IV of ERBB2. Preferably, the antigen-binding site binds to domain IV of ERBB2. A preferred antibody comprises a first antigen-binding site that binds to domain I of ERBB2 and a second antigen-binding site that binds to domain III of ERBB3.

[0146] In a preferred embodiment, the antibody comprises an antigen-binding site that binds to at least one amino acid in Domain I of ERBB2 selected from the group consisting of T144, T164, R166, P172, G179, S180, and R181, and a surface-exposed amino acid residue located within about 5 amino acid positions of T144, T164, R166, P172, G179, S180, or R181.

[0147] In a preferred embodiment, the antibody comprises an antigen-binding site that binds to at least one amino acid in domain III of ERBB3, preferably selected from the group including R426, and a surface-exposed amino acid residue located within 11.2 Å of R426 in the native ERBB3 protein.

[0148] Bispecific antibodies that bind to ERBB2 and have an antigen-binding site (first antigen-binding site) that also contains ADCC are more effective, particularly in vivo, than other ERBB2-binding antibodies that do not have significant ADCC activity. Therefore, bispecific antibodies that exhibit ADCC are preferred. By engineering the Fc region (by introducing amino acid substitutions) to bind to activating receptors with greater selectivity, antibodies can be generated that have a greater ability to mediate the cytotoxic activity desired by anti-cancer Mabs.

[0149] One technique for enhancing the ADCC of antibodies is afucosylation. (See, e.g., Junttila, T.T., K. Parsons, et al. (2010) "Superior In vivo Efficacy of Afucosylated Trastuzumab in the Treatment of HER2-Amplified Breast Cancer." Cancer Research 70(11): 4481-4489.) Accordingly, afucosylated bispecific antibodies disclosed herein are further provided. Alternatively, or additionally, several other strategies can be used to achieve enhanced ADCC, including, for example, glycoengineering and mutagenesis, all of which aim to improve Fc binding to the low-affinity activating FcγRIIIa and / or reduce binding to the low-affinity inhibitory FcγRIIb.

[0150] Several in vitro methods exist for determining the effectiveness of antibodies or effector cells in inducing ADCC. These include the chromium-51 [Cr51] release assay, europium [Eu] release assay, and sulfur-35 [S35] release assay. Typically, a labeled target cell line expressing a particular surface-exposed antigen is incubated with an antibody specific for that antigen. After washing, effector cells expressing the Fc receptor CD16 are typically co-incubated with the antibody-labeled target cells. Target cell lysis is then typically measured by the release of intracellular label, for example, by scintillation counting or spectrophotometry.

[0151] The antibodies disclosed herein are, in certain embodiments, intended for use in humans. Thus, in certain embodiments, the antibodies are human or humanized. Human tolerance to a polypeptide is governed by many different factors. T cell-mediated, B cell-mediated, or other immunity is one of the variables involved in human tolerance to a polypeptide. The constant regions of bispecific antibodies are preferably human constant regions. The constant regions may contain one or more, preferably ten or fewer, and preferably five or fewer amino acid differences from the constant regions of naturally occurring human antibodies. Preferably, the constant portions are derived entirely from naturally occurring human antibodies. The various antibodies produced herein are derived from a human antibody variable domain library. Thus, these variable domains are human. The unique CDR regions may be derived from humans, synthetically produced, or from another organism. A variable region is considered human if it has an amino acid sequence identical to that of a naturally occurring human antibody variable region, but the CDR regions are not. The variable region of the ERBB2-binding VH, ERBB3-binding VH, or light chain in the antibody may contain one or more, preferably ten or fewer, preferably five or fewer amino acid differences from the variable region of a naturally occurring human antibody, not counting possible differences in the amino acid sequence of the CDR regions. Such variations also occur naturally in the context of somatic hypermutation.

[0152] Antibodies, at least for their heavy chain variable regions, can be derived from various animal species. For example, it is common practice to humanize mouse heavy chain variable regions. This can be achieved by various methods, including CDR grafting onto a human heavy chain variable region having a 3D structure that matches that of the mouse heavy chain variable region; preferably, deimmunization of the mouse heavy chain variable region, which is carried out by removing known or suspected T-cell or B-cell epitopes from the mouse heavy chain variable region. This removal is typically achieved by substituting one or more amino acids in the epitope with another (typically conservative) amino acid, such that the sequence of the epitope is altered so that it is no longer a T-cell or B-cell epitope.

[0153] Such deimmunized mouse heavy chain variable regions are less immunogenic in humans than the original mouse heavy chain variable regions. Preferably, the variable regions or domains are further humanized, e.g., veneering. Using veneering techniques, exterior residues that are easily encountered by the immune system are selectively replaced with human residues to provide hybrid molecules containing either weakly immunogenic or substantially non-immunogenic veneering surfaces. The animals used in the present invention are preferably mammals, more preferably primates, and most preferably humans.

[0154] In certain embodiments, the antibodies disclosed herein comprise a human antibody constant region. Based on differences in the heavy chain constant domain, antibodies are grouped into five classes or isotypes: IgG, IgA, IgM, IgD, and IgE. These classes or isotypes comprise at least one of the heavy chains designated by the corresponding Greek letter. In certain embodiments, the constant region comprises an IgG constant region, and in certain embodiments, an IgG1 constant region, and in certain embodiments, a mutant IgG1 constant region. Some variations in the IgG1 constant region, such as allotypes G1m1, 17, and G1m3, occur naturally and / or are tolerated without altering the immunological properties of the resulting antibody. Typically, approximately 1-10 amino acid insertions, deletions, substitutions, or combinations thereof, are tolerated within the constant region.

[0155] In certain embodiments, antibodies of the present disclosure, including but not limited to bispecific antibodies, comprise an antigen-binding site capable of binding to the extracellular portion of ERBB3, blocking both ERBB3 and its ligand, heregulin. In certain embodiments, the antibodies also comprise an antigen-binding site capable of binding to the extracellular portion of ERBB3 at domain III. In certain embodiments, the antibodies also comprise an antigen-binding site capable of binding to the extracellular portion of ERBB2. In certain embodiments, the antibodies comprise an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3. Bispecific antibodies of the present disclosure comprise a first antigen-binding site that binds to the extracellular portion of ERBB2 and a second antigen-binding site that binds to the extracellular portion of ERBB3. In certain embodiments, the bispecific antibodies have a first antigen-binding site that binds to domain I of ERBB2 and a second antigen-binding site that binds to domain III of ERBB3. In certain embodiments, the affinity of the first antigen-binding site for ERBB2 is lower than the affinity of the second antigen-binding site for ERBB3. In certain embodiments, the bispecific antibody is or comprises xenoctuzumab (International Nonproprietary Name).

[0156] In certain embodiments, the cancer is not NRG1 fusion-positive. Not being NRG1 fusion-positive or NRG1 fusion-negative means that any cancer or subject referred to herein does not contain an NRG1 fusion gene, specifically, that the subject or cancer does not contain an NRG fusion gene that expresses a protein containing the NRG1 EGF-like domain. In certain embodiments, the subject contains cancer-associated cells, such as cancer-associated fibroblasts, that are not NRG1 fusion-positive. The cancer-associated cells are typically located in the human prostate.

[0157] The bispecific antibodies of the present disclosure comprise a first antigen-binding site that binds to the extracellular portion of ERBB2 and a second antigen-binding site that binds to the extracellular portion of ERBB3. In certain embodiments, the bispecific antibodies have a first antigen-binding site that binds to domain I of ERBB2 and a second antigen-binding site that binds to domain III of ERBB3. In certain embodiments, the affinity of the first antigen-binding site for ERBB2 is lower than the affinity of the second antigen-binding site for ERBB3.

[0158] In certain embodiments, the bispecific antibody i) comprises at least the CDR1, CDR2 and CDR3 sequences of an ERBB2-specific heavy chain variable region selected from the group consisting of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031 and MF3003, or the antibody comprises CDR sequences which differ by at most three amino acids, preferably at most two amino acids, preferably at most one amino acid from the CDR1, CDR2 and CDR3 sequences of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031 or MF3003; and / or the bispecific antibody ii) comprises at least the CDR1, CDR2 and CDR3 sequences of an ERBB3-specific heavy chain variable region selected from the group consisting of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 and MF6074; or MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073, or MF6074.

[0159] In certain embodiments, the bispecific antibody i) comprises an ERBB2-specific heavy chain variable region sequence selected from the group consisting of: MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031, and MF3003, or the antibody comprises a heavy chain variable region sequence that differs by at most 15 amino acids from the heavy chain variable region sequence of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031, or MF3003; and / or the bispecific antibody comprises ii) an ERBB3-specific heavy chain variable region sequence selected from the group consisting of the heavy chain variable region sequences of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073, and MF6074. or the antibody comprises a heavy chain variable region sequence that differs by at most 15 amino acids from the heavy chain variable region sequence of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073, or MF6074.

[0160] In certain embodiments, a bispecific antibody for use in the present invention is MF3958xMF3178, comprising the heavy chain variable regions MF3958 (anti-ERBB2) and MF3178 (anti-ERBB3). MF3958xMF3178 has been shown to be well tolerated as a single agent, with a low risk of immunogenicity in treatment of over 100 patients, making it an excellent agent for combination therapy and offering advantages over other anti-ERBB2 and / or anti-ERBB3 targeted agents. Without being bound by any theory, it is believed that the efficacy of MF3958×MF3178 in treating patients with cancers that have ERBB2 and ERBB3-positive cells with ERBB3 mutations is based on the imbalance in epitope specificity and affinity of MF3958×MF3178, which allows MF3958×MF3178 to dock to domain 1 of ERBB2 and block ERBB3 from dimerizing with ERBB2 at domain 3, thereby disrupting activation of the PI3K pathway.

[0161] The variable domain comprising the first antigen-binding site and the variable domain comprising the second antigen-binding site of the bispecific antibody preferably comprise a light chain variable region comprising a CDR1 having the sequence (RASQSISSYLN), a CDR2 having the sequence (AASSLQS) and a CDR3 having the sequence (QQSYSTPPT) according to the KABAT numbering or according to the IMGT numbering system, wherein the CDRs are QSISSY, AAS and QQSYSTPPT, respectively.

[0162] The variable domain comprising the first antigen-binding site and the variable domain comprising the second antigen-binding site of the bispecific antibody preferably comprise the light chain variable region of Figure 1a or Figure 1b and / or the CDR1, CDR2 and CDR3 sequences QSISSY, AAS and QQSYSTPPT, respectively, according to the IMGT numbering system (Figure 1f).

[0163] The amount of bispecific antibody administered to a subject typically falls within the therapeutic window, meaning that an amount sufficient to achieve a therapeutic effect is used without exceeding the threshold for unacceptable side effects. The selected dosage level depends on various factors, including the route of administration, time of administration, excretion rate of the specific compound used, duration of treatment, other drugs, compounds, and / or materials used in combination, the age, sex, weight, condition, general health, and past medical history of the subject being treated, as well as similar factors well known in the medical field. Dosage amounts range from 200 to 1000 mg weekly, every other week, or every three weeks. Preferably, the therapeutic agent of the present disclosure targeting ERBB2×ERBB3 follows a weekly, every other week, or every three weeks dosing regimen of 750 mg, preferably every two weeks or every three weeks. This dosing is preferably in subjects with cancer having solid tumors harboring an ERBB3 mutation, and the dosing regimen then includes weekly fixed doses of 400 mg, preferably starting after a single dose of 800 mg. Following this alternative dosing regimen, the bispecific antibody of the present invention is preferably administered at a weekly dose of 400 mg for three weeks, followed by one week without administration. This is then followed by one or more cycles of a four-week period consisting of a flat dose of 400 mg every three weeks, followed by one week without administration. This preferably continues until a therapeutic effect is observed. The dosing regimen of the present disclosure includes a biweekly cycle of a flat dose of 750 mg starting after an initial administration of a 750 mg infusion over four hours, followed by a two-hour infusion of 750 mg every other week for four-week cycles. This preferably continues until a therapeutic effect is observed.

[0164] Dosing preferably involves intravenous injection of two infusions of the bispecific antibody of the invention to reach the full dose, preferably when dosing more than 360 mg of antibody. Alternatively, for lower dosages, e.g., when dosing 360 mg or less of antibody, a single infusion of the full dose may be given. Premedication may be included in the dosing regimen to mitigate infusion-related reactions.

[0165] Preferably, treatment involves stabilization of tumor size or lesions, or prevention of further tumor growth, including tumor reduction. Preferably, treatment or administration is with a bispecific antibody according to the invention on a weekly regimen, progressing for at least 1, 2, 4, 8, or at least 12 months. Preferably, a dosing regimen is followed, comprising a weekly cycle of 400 mg flat doses starting after an initial dose of 800 mg. From week 3, the bispecific antibody of the invention is administered at a weekly dose of 400 mg for three weeks, followed by one week without administration of the bispecific antibody of the invention. Alternatively, a dosing regimen is followed, comprising a biweekly cycle of 750 mg flat doses starting after an initial dose of 750 mg infusion over four hours, followed by a two-hour infusion of 750 mg every other week for four-week cycles. A further alternative involves the administration of a 750 mg flat dose per subject every three weeks.

[0166] Preferably, a bispecific antibody having a first antigen-binding site that binds or is capable of binding to the extracellular portion of ERBB2 and a second antigen-binding site that binds or is capable of binding to the extracellular portion of ERBB3, particularly MF3958xMF3178, stabilizes castration-resistant prostate cancer tumors in terms of size or pathology, or the treatment prevents further castration-resistant prostate cancer tumor growth.

[0167] The antibodies of the present disclosure can be formulated as pharmaceutical compositions comprising a pharmaceutically acceptable carrier, diluent, or excipient, and additional optional active agents. Antibodies and compositions comprising the antibodies can be administered by any route, including parenteral, enteral, and topical administration. Parenteral administration is typically by injection, and includes, for example, intravenous, intramuscular, intraarterial, intrathecal, intraventricular, intracapsular, intraorbital, intracardiac, intradermal, intraperitoneal, transtracheal, subcutaneous, subcuticular, intraarticular, subcapsular, intraarachnoid, intraspinal, intracranial, intratumoral, and intrasternal injection and infusion.

[0168] The present disclosure provides bispecific antibodies for use in the methods and treatments described herein. Suitable bispecific antibodies comprise a first antigen-binding site that binds or is capable of binding to ERBB2 and a second antigen-binding site that binds or is capable of binding to ERBB3. The bispecific antibodies reduce or are capable of reducing ligand-induced receptor function of ERBB3 on ERBB2- and ERBB3-positive cells and / or disrupt ERBB2 and ERBB3 heterodimerization. Preferred antibodies and their preparation are disclosed in WO2015 / 130173, which is incorporated herein by reference. The Examples in WO2015 / 130173 further describe some properties of the antibodies, such as ligand binding and epitope mapping.

[0169] In certain aspects, the present disclosure provides antibodies that bind to or are capable of binding to ERBB3. In certain aspects, the antibodies bind to domain III of ERBB3 and comprise the CDR1, CDR2, and CDR3 sequences disclosed herein. In certain aspects, the antibodies are monospecific antibodies, such as patritumab (U3-1287 / A888), seribantumab (MM-121), lumuletuzumab (RG7116, RO-5479599), elgemtumab (LJM716), AV-203, KTN3379 (CDX-3379), or GSK2849330. In certain aspects, the antibodies are antibody-drug conjugates, such as patritumab deruxtecan (U3-1402). In certain aspects, the antibodies are monospecific bivalent antibodies.

[0170] In one particular embodiment, patritumab is administered at 18 mg / kg once every 21 days, followed by 9 mg / kg once every 21 days.

[0171] In certain embodiments, seribantumab is administered at a loading dose of 40 mg / kg once a week, followed by a maintenance dose of 20 mg / kg (40 / 20 mg / kg). The dose or schedule can be adjusted at the discretion of the treating physician. In certain embodiments, seribantumab is administered at a dose of 3 g once a week, administered via intravenous infusion (IV).

[0172] In certain embodiments, lumuletuzumab is administered at 500 mg or 1000 mg once every three weeks via IV infusion in combination with pertuzumab, which is administered as an initial loading dose of 840 mg once every three weeks via IV infusion, followed by a maintenance dose of 420 mg once every three weeks via IV infusion.

[0173] In one particular embodiment, patritumab deruxtecan is administered as an intravenous dose of 5.6 mg / kg once every three weeks (q3W).

[0174] In certain embodiments, KTN3379 / CDX-3379 is administered as an intravenous dose of 20 mg / kg once every three weeks (q3W). Alternatively, CDX-3379 is administered at 400 mg / m on the first day. 2 of cetuximab, then 250 mg / m 2 It is administered at a dose of 12 mg / kg once every three weeks in combination with cetuximab at a dose of 12 mg / kg once every three weeks.

[0175] In certain embodiments, AV-203 is administered as an intravenous dose of 20 mg / kg once every two weeks (q2W).

[0176] In certain embodiments, GSK2849330 is administered at a dose of 30 mg / kg once weekly.

[0177] In certain aspects, the bispecific antibodies disclosed herein comprise: - comprising at least the CDR3 sequence, preferably at least the CDR1, CDR2 and CDR3 sequences, or at least a heavy chain variable region sequence of an ERBB2-specific heavy chain variable region selected from the group consisting of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031 and MF3003, or a heavy chain variable region sequence that differs by at most 15 amino acids, preferably by at most 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acids, more preferably by at most 1, 2, 3, 4 or 5 amino acids from the listed heavy chain variable region sequences; and / or Bispecific antibodies are - at least the CDR1, CDR2 and CDR3 sequences, or at least a heavy chain variable region sequence of an ERBB3-specific heavy chain variable region selected from the group consisting of: MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 and MF6074, or a heavy chain variable region sequence that differs by at most 15 amino acids, preferably by at most 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acids, more preferably by at most 1, 2, 3, 4 or 5 amino acids, from the listed heavy chain variable region sequence.

[0178] In certain embodiments, the antibodies disclosed herein that bind to ERBB3, but not necessarily to ERBB2, are - at least the CDR1, CDR2 and CDR3 sequences, or at least a heavy chain variable region sequence of an ERBB3-specific heavy chain variable region selected from the group consisting of: MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 and MF6074, or a heavy chain variable region sequence that differs by at most 15 amino acids, preferably by at most 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acids, more preferably by at most 1, 2, 3, 4 or 5 amino acids, from the listed heavy chain variable region sequence.

[0179] The CDR sequences are altered, for example, for optimization purposes, preferably to improve the binding efficacy or stability of the antibody. Optimization is performed, for example, by mutagenesis procedures, after which the stability and / or binding affinity of the resulting antibody are preferably tested and improved ERBB2 or ERBB3-specific CDR sequences are preferably selected. Those skilled in the art can easily generate antibody variants containing at least one modified CDR sequence. For example, conservative amino acid substitutions are applied. Examples of conservative amino acid substitutions include the substitution of one hydrophobic residue, such as isoleucine, valine, leucine, or methionine, for another hydrophobic residue, and the substitution of one polar residue for another, such as arginine for lysine, glutamic acid for aspartic acid, or glutamine for asparagine.

[0180] In certain embodiments, the antibody comprises a variable domain that binds to ERBB2, wherein the VH chain of said variable domain comprises the amino acid sequence of VH chain MF2973, MF3004, MF3958 (which is humanized MF2971), MF2971, MF3025, MF2916, MF3991 (which is humanized MF3004), MF3031, or MF3003, or at most 15, preferably 10, of the above VH chain sequences. , 2, 3, 4, 5, 6, 7, 8, 9, or 10, more preferably at most 1, 2, 3, 4, or 5, amino acid insertions, deletions, substitutions, or a combination thereof. The VH chain of the variable domain that binds to ERBB2 preferably comprises the amino acid sequence: MF2971 or a humanized version thereof, said humanized version preferably comprising the amino acid sequence of MF3958, or -MF3004 or a humanized version thereof, wherein the humanized version preferably comprises the amino acid sequence of MF3991. In one embodiment, the VH chain of the variable domain that binds to ERBB2 comprises the amino acid sequence of VH chain MF2971 or a humanized version thereof, wherein the humanized version preferably comprises the amino acid sequence of MF3958, or MF3004 or a humanized version thereof, wherein the recited VH sequences have, with respect to each sequence, at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, more preferably at most 1, 2, 3, 4 or 5 amino acid insertions, deletions, substitutions or combinations thereof. In a preferred embodiment, the VH chain of the variable domain that binds to ERBB2 comprises the amino acid sequence of MF3958 or comprises the amino acid sequence of MF3958 with at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, more preferably at most 1, 2, 3, 4 or 5 amino acid insertions, deletions, substitutions or combinations thereof relative to the VH chain sequence.

[0181] The VH chain of the variable domain that binds to ERBB3 preferably comprises the amino acid sequence of VH chain MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074, or has at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, more preferably at most 1, 2, 3, 4 or 5 amino acid insertions, deletions, substitutions or combinations thereof with respect to the VH chain sequence. and a VH chain having the amino acid sequence of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073, or MF6074. The VH chain of the variable domain that binds to ERBB3 preferably comprises the amino acid sequence of MF3178, MF3176, MF3163, MF6058, MF6061, or MF6065, or comprises the amino acid sequence of MF3178, MF3176, MF3163, MF6058, MF6061, or MF6065 with at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, more preferably at most 1, 2, 3, 4, or 5, amino acid insertions, deletions, substitutions, or combinations thereof, with respect to each VH chain sequence. In a preferred embodiment, the VH chain of the variable domain that binds to ERBB3 comprises the amino acid sequence of MF3178 or comprises the amino acid sequence of MF3178 with at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, more preferably at most 1, 2, 3, 4, or 5, amino acid insertions, deletions, substitutions, or a combination thereof, relative to the VH chain sequence. Preferably, the amino acid insertions, deletions, and substitutions are not in the CDR3 region. The amino acid insertions, deletions, and substitutions are also preferably not in the CDR1 and CDR2 regions.The above amino acid insertions, deletions and substitutions are also preferably not present in the FR4 region.

[0182] In certain embodiments, the antibody comprises at least the CDR1, CDR2, and CDR3 sequences of MF2971, MF3958, MF3004, or MF3991, most preferably at least the CDR1, CDR2, and CDR3 sequences of MF3958. The antibody preferably comprises at least the CDR1, CDR2, and CDR3 sequences of MF3178, MF3176, MF3163, MF6058, MF6061, or MF6065, most preferably at least the CDR1, CDR2, and CDR3 sequences of MF3178.

[0183] In certain embodiments, the ERBB2-specific heavy chain variable region comprises the amino acid sequence of VH chain MF3958 with at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, more preferably at most 1, 2, 3, 4, or 5, amino acid insertions, deletions, substitutions, or a combination thereof for the VH (preferably, the insertions, deletions, or substitutions are not in CDR1, CDR2, or CDR3). In certain embodiments, these are not in the FR4 region. The amino acid substitutions are, in certain embodiments, conservative amino acid substitutions.

[0184] In a specific embodiment, the ERBB3-specific heavy chain variable region comprises the amino acid sequence of VH chain MF3178, with at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, more preferably at most 1, 2, 3, 4, or 5, amino acid insertions, deletions, substitutions, or a combination thereof, for the VH. The one or more amino acid insertions, deletions, substitutions, or a combination thereof are preferably not present in the CDR1, CDR2, and CDR3 regions of the VH chain. They are preferably not present in the FR4 region. The amino acid substitutions are preferably conservative amino acid substitutions.

[0185] In a specific embodiment, the ERBB2-specific heavy chain variable region comprises the amino acid sequence of VH chain MF3991 with at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, more preferably at most 1, 2, 3, 4, or 5, amino acid insertions, deletions, substitutions, or a combination thereof for the VH (preferably, the insertions, deletions, or substitutions are not in CDR1, CDR2, or CDR3). These preferably are not in the FR4 region. The amino acid substitutions are preferably conservative amino acid substitutions.

[0186] In a specific embodiment, the ERBB3-specific heavy chain variable region comprises the amino acid sequence of VH chain MF3178, with at most 15, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, more preferably at most 1, 2, 3, 4, or 5, amino acid insertions, deletions, substitutions, or a combination thereof, for the VH. The one or more amino acid insertions, deletions, substitutions, or a combination thereof are preferably not present in the CDR1, CDR2, and CDR3 regions of the VH chain. They are preferably not present in the FR4 region. The amino acid substitutions are preferably conservative amino acid substitutions.

[0187] In certain aspects, the first antigen-binding site of the antibody comprises at least the CDR1, CDR2, and CDR3 sequences of MF3958, or CDR1, CDR2, and CDR3 sequences that differ by at most three, preferably at most two, and preferably at most one amino acid from the CDR1, CDR2, and CDR3 sequences of MF3958, and the second antigen-binding site comprises at least the CDR1, CDR2, and CDR3 sequences of MF3178, or CDR1, CDR2, and CDR3 sequences that differ by at most three, preferably at most two, and preferably at most one amino acid from the CDR1, CDR2, and CDR3 sequences of MF3178.

[0188] In certain embodiments, the bispecific antibody comprises i) a first antigen-binding site comprising an ERBB2-specific heavy and light chain variable region comprising the CDR1, CDR2, and CDR3 sequences of MF3958, and ii) a second antigen-binding site comprising an ERBB3-specific heavy and light chain variable region comprising the CDR1, CDR2, and CDR3 sequences of MF3178.

[0189] In a specific embodiment, the ERBB2-specific heavy chain variable region has the MF3958 sequence and the ERBB3-specific heavy chain variable region has the MF3178 sequence. This combination is also referred to as the PB4188 antibody. Preferably, the PB4188 antibody is afucosylated.

[0190] In one particular embodiment, the bispecific antibody comprises a "heavy chain for ERBB2 binding" as shown in Figure 3a and a "heavy chain for ERBB3 binding" as shown in Figure 3b.

[0191] In certain embodiments, the antigen-binding site of the bispecific antibody comprises a common light chain as defined herein, preferably a germline common light chain, preferably a rearranged germline human kappa light chain IgVκ1-39*01 / IGJκ1*01, or a fragment or functional derivative thereof (as designated by the IMGT database World Wide Web at imgt.org). The terms rearranged germline human kappa light chain IgVκ1-39*01 / IGJκ1*01, IGKV1-39 / IGKJ1, huVκ1-39 light chain or short huVκ1-39 are used. The light chain may have 1, 2, 3, 4, or 5 amino acid insertions, deletions, substitutions, or a combination thereof. The 1, 2, 3, 4, or 5 amino acid substitutions mentioned are preferably conservative amino acid substitutions, and the insertions, deletions, substitutions, or combinations thereof are preferably not present in the CDR3 region of the VL chain, and preferably not present in the CDR1, CDR2, or CDR3 region or the FR4 region of the VL chain. Preferably, the first antigen-binding site and the second antigen-binding site comprise the same light chain variable region, or rather a common light chain. In certain embodiments, the light chain variable region comprises CDR1 having the sequence (RASQSISSYLN), CDR2 having the sequence (AASSLQS), and CDR3 having the sequence (QQSYSTPPT) according to the KABAT numbering or IMGT numbering system, where the CDRs are QSISSY, AAS, and QQSYSTPPT, respectively. Preferably, the light chain variable region comprises the common light chain sequence shown in Figure 1.

[0192] Various methods for producing bispecific antibodies are available and are discussed in WO2015 / 130173. One method involves expressing two different heavy chains and two different light chains in cells and collecting the antibodies produced by the cells. The antibodies produced in this manner typically contain a collection of antibodies with different combinations of heavy and light chains, some of which are the desired bispecific antibodies. The bispecific antibodies can then be purified from the collection.

[0193] The ratio of bispecific antibodies relative to other antibodies produced by a cell can be increased in various ways. Preferably, the ratio is increased by expressing two essentially identical light chains in the cell, rather than two different light chains. This concept is also referred to in the art as the "common light chain" method. When an essentially identical light chain works with two different heavy chains, allowing the formation of variable domains with different antigen-binding sites and concurrently different binding properties, the ratio of bispecific antibodies relative to other antibodies produced by the cell is significantly improved by expressing two different light chains. The ratio of bispecific antibodies produced by the cell can be further improved by encouraging the pairing of two different heavy chains with each other rather than the pairing of two identical heavy chains. Various methods by which such heavy chain heterodimerization can be achieved have been described in the art. A preferred method is described in PCT Application No. PCT / NL2013 / 050294 (WO2013 / 157954A1), which is incorporated herein by reference. Methods and means for producing bispecific antibodies from a single cell are disclosed, thereby providing a means to favor the formation of bispecific antibodies over the formation of monospecific antibodies.

[0194] For purposes of clarity and concise description, features may be described herein as part of the same or separate embodiments, but it will be understood that the scope of the invention may include embodiments having all or any combination of the described features. Also, any aspect disclosed herein as being related to any use in a method of treatment according to the present disclosure applies equally to the method of treatment according to the present disclosure, and vice versa.

[0195] Terms 1. A bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, for use in a method of treating castration-resistant prostate cancer in a subject. 2. The bispecific antibody for use according to clause 1, wherein the cancer has progressed after previous treatment with an androgen receptor axis targeting agent. 3. The bispecific antibody for use according to clause 2, wherein the androgen receptor axis targeting agent is an androgen receptor antagonist, for example a second generation androgen receptor antagonist. 4. The bispecific antibody for use according to clause 3, wherein the androgen receptor antagonist is enzalutamide. 5. The bispecific antibody for use according to clause 2, wherein the androgen receptor axis targeting agent is an androgen synthesis inhibitor, for example, abiraterone acetate. 6. The bispecific antibody for use according to any one of the preceding clauses, wherein the method of treatment further comprises use of an androgen receptor axis targeting agent. 7. The bispecific antibody for use according to any one of clauses 1 to 5, wherein the method of treatment further comprises the use of an androgen receptor antagonist, such as a second generation androgen receptor antagonist, such as enzalutamide. 8. The bispecific antibody for use according to any one of clauses 1 to 5, wherein the method of treatment further comprises the use of an androgen synthesis inhibitor, for example abiraterone acetate. 9. The bispecific antibody for use according to any one of clauses 1-4 or 6-7, wherein if the cancer has progressed after previous treatment with an androgen receptor antagonist, the method of treatment with the bispecific antibody further comprises the use of an androgen receptor antagonist. 10. A bispecific antibody for use according to clause 9, wherein the androgen receptor antagonist used in the previous treatment and the androgen receptor antagonist further used in the bispecific antibody treatment method are the same. 11. The bispecific antibody for use according to clause 9 or 10, wherein the androgen receptor antagonist used in the previous treatment and the androgen receptor antagonist further used in the bispecific antibody treatment method are both enzalutamide. 12. The bispecific antibody for use according to any one of clauses 4, 7 or 11, wherein enzalutamide is administered at 160 mg once daily. 13. The bispecific antibody for use according to any one of clauses 1, 2, 5, 6 or 8, wherein if the cancer has progressed after previous treatment with an androgen synthesis inhibitor, the method of treatment with the bispecific antibody further comprises the use of an androgen synthesis inhibitor. 14. A bispecific antibody for use according to clause 13, wherein the androgen synthesis inhibitor used in the previous treatment and the androgen synthesis inhibitor further used in the method of treatment with the bispecific antibody are the same. 15. The bispecific antibody for use according to clause 13 or 14, wherein the androgen synthesis inhibitor used in the previous treatment and the androgen synthesis inhibitor further used in the bispecific antibody treatment method are both abiraterone acetate. 16. The bispecific antibody for use according to any one of clauses 5, 8 or 15, wherein abiraterone acetate is administered at 1000 mg once daily. 17. The bispecific antibody for use according to clause 16, wherein abiraterone acetate is administered in combination with 5 mg of prednisone twice daily. 18. A method of treating a subject with castration-resistant prostate cancer, the method comprising administering to the subject a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3. 19. Use of a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3 for the manufacture of a medicament for the treatment of castration-resistant prostate cancer in a subject. 20. The method of treatment or use according to clause 18 or 19, wherein the cancer has progressed after previous treatment with an androgen receptor axis targeting agent. 21. The method of treatment or use according to clause 20, wherein the androgen receptor axis targeting agent is an androgen receptor antagonist, for example a second generation androgen receptor antagonist. 22. The method of treatment or use according to clause 21, wherein the androgen receptor antagonist is enzalutamide. 23. The method of treatment or use according to clause 20, wherein the androgen receptor axis targeting agent is an androgen synthesis inhibitor, for example, abiraterone acetate. 24. The method of treatment or use according to any one of clauses 18 to 23, wherein the bispecific antibody treatment or use for the manufacture of a medicament further comprises the administration or use of an androgen receptor axis targeting agent. 25. The method of treatment or use according to any one of clauses 18 to 23, wherein the bispecific antibody treatment or use for the manufacture of a medicament further comprises the administration or use of an androgen receptor antagonist, such as a second generation androgen receptor antagonist, such as enzalutamide. 26. The method of treatment or use according to any one of clauses 18 to 23, wherein the bispecific antibody treatment or use for the manufacture of a medicament further comprises the administration or use of an androgen synthesis inhibitor, for example abiraterone acetate. 27. The method of treatment or use according to any one of clauses 18 to 26, wherein if the cancer has progressed after previous treatment with an androgen receptor antagonist, the method of treatment or use for the manufacture of a medicament with the bispecific antibody further comprises the administration or use of an androgen receptor antagonist. 28. The method of treatment or use according to clause 27, wherein the androgen receptor antagonist used in the previous treatment and the androgen receptor antagonist further used in the method of treatment with the bispecific antibody or used for the manufacture of the medicament are the same. 29. The method or use of treatment according to clause 27 or 28, wherein the androgen receptor antagonist used in the previous treatment and the androgen receptor antagonist further used in the bispecific antibody treatment method or used for the manufacture of the medicament are both enzalutamide. 30. The method of treatment or use according to any one of clauses 22, 25 or 29, wherein enzalutamide is or will be administered at 160 mg once daily. 31. The method of treatment or use of any one of clauses 18, 19, 23, 24 or 26, wherein if the cancer has progressed after previous treatment with an androgen synthesis inhibitor, the bispecific antibody method of treatment or use for the manufacture of a medicament further comprises the administration or use of an androgen synthesis inhibitor. 32. The method of treatment or use according to clause 31, wherein the androgen synthesis inhibitor used in the previous treatment and the androgen synthesis inhibitor further used in the method of treatment with the bispecific antibody or used for the manufacture of the medicament are the same. 33. The method or use according to clause 31 or 32, wherein the androgen synthesis inhibitor used in the previous treatment and the androgen synthesis inhibitor further used in the method of treatment with the bispecific antibody or used for the manufacture of the medicament are both abiraterone acetate. 34. The method of treatment or use according to any one of clauses 23, 26 or 33, wherein abiraterone acetate is or will be administered at 1000 mg once daily. 35. The method of treatment or use according to clause 34, wherein abiraterone acetate is or will be administered in combination with prednisone 5 mg twice daily. 36. The bispecific antibody for use according to any one of clauses 1 to 17, or the method of treatment or use according to any one of clauses 18 to 35, wherein the method of treatment comprises administering the bispecific antibody in an amount of 750 mg once every two weeks. 37. The bispecific antibody for use according to any one of clauses 1 to 17 or 36, or the method of treatment or use according to any one of clauses 18 to 36, wherein the subject or cancer has PTEN wild-type status. 38. The bispecific antibody for use according to any one of clauses 1 to 17 or 36, or the method of treatment or use according to any one of clauses 18 to 36, wherein the subject or cancer does not exhibit PTEN loss. 39. A bispecific antibody for use according to any one of clauses 1 to 17 or any one of clauses 36 to 38, or a method of treatment or use according to any one of clauses 18 to 38, wherein the method of treatment comprises administering to a subject in need thereof a therapeutically effective amount of a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular part of ERBB2 and an antigen-binding site capable of binding to the extracellular part of ERBB3. 40. The bispecific antibody for use according to any one of clauses 6 to 17 or any one of clauses 36 to 39 or the method of treatment or use according to any one of clauses 24 to 39, wherein the androgen receptor axis targeting agent is or will be administered in accordance with medical prescribing instructions established by a medical authority such as the FDA. 41. The bispecific antibody for use according to any one of clauses 1 to 17 or any one of clauses 36 to 40, or the method of treatment or use according to any one of clauses 18 to 40, wherein the cancer is characterised in one particular embodiment by histologically confirmed adenocarcinoma of the prostate without features of neuroendocrine differentiation or small cell carcinoma. 42. A bispecific antibody for use according to any one of clauses 1 to 17 or any one of clauses 36 to 41 or a method of treatment or use according to any one of clauses 18 to 41, wherein the bispecific antibody comprises a first antigen-binding site which binds to, or is capable of binding to, domain I of ERBB2 and a second antigen-binding site which binds to, or is capable of binding to domain III of ERBB3. 43. A bispecific antibody is i) comprises at least the CDR1, CDR2 and CDR3 sequences of an ERBB2-specific heavy chain variable region selected from the group consisting of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031 and MF3003, or the antibody comprises CDR sequences that differ by at most three amino acids, preferably at most two amino acids, preferably at most one amino acid from the CDR1, CDR2 and CDR3 sequences of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031 or MF3003; and / or ii)MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062 , MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 & M or the antibody comprises at least CDR1, CDR2 and CDR3 sequences of an ERBB3-specific heavy chain variable region selected from the group consisting of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074, comprising a CDR sequence that differs by at most three amino acids, preferably at most two amino acids, preferably at most one amino acid, from the CDR1, CDR2 and CDR3 sequences of MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074. 44. A bispecific antibody is i) comprises an ERBB2-specific heavy chain variable region sequence selected from the group consisting of the heavy chain variable region sequences of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031, and MF3003, or the antibody comprises a heavy chain variable region sequence that differs by at most 15 amino acids from the heavy chain variable region sequence of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031, or MF3003; and / or ii) the antibody comprises an ERBB3-specific heavy chain variable region sequence selected from the group consisting of the heavy chain variable region sequences of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073, and MF6074, or the antibody comprises an ERBB3-specific heavy chain variable region sequence selected from the group consisting of the heavy chain variable region sequences of MF3178, MF3176, MF3163, MF6055, MF6056 MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074, or the method of treatment or use of any one of clauses 18 to 43, wherein the bispecific antibody for use according to any one of clauses 1 to 17 or any one of clauses 36 to 43 comprises a heavy chain variable region sequence which differs by at most 15 amino acids from the heavy chain variable region sequence of MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074. 45. The bispecific antibody for use according to any one of clauses 1 to 17 or any one of clauses 36 to 44, or the method of treatment or use according to any one of clauses 18 to 44, wherein the bispecific antibody comprises the heavy chain variable regions MF3958 and MF3178. 46. A bispecific antibody for use according to any one of clauses 1 to 17 or any one of clauses 36 to 45, or a method of treatment or use according to any one of clauses 18 to 45, wherein the bispecific antibody comprises a variable domain comprising the first antigen-binding site and a variable domain comprising the second antigen-binding site, and wherein the first and second antigen-binding sites comprise a light chain variable region comprising CDR1 comprising the sequence QSISSY, CDR2 comprising the sequence AAS, and CDR3 comprising the sequence QQSYSTPPT. 47. An antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3 for use in a method for treating castration-resistant prostate cancer in a subject. 48. A method for treating a subject having castration-resistant prostate cancer, the method comprising administering to the subject an effective amount of an antibody comprising an antigen-binding site capable of binding to an extracellular portion of ERBB3. 49. Use of an antibody comprising an antigen-binding site capable of binding to an extracellular portion of ERBB3 for the manufacture of a medicament for the treatment of castration-resistant prostate cancer in a subject. 50. An antibody for use according to clause 47, a method of treatment according to clause 48 or a use according to clause 49, wherein the antibody comprises an antigen binding site that binds to domain III of ERBB3. 51.Antibodies i) the antibody comprises at least the CDR1, CDR2 and CDR3 sequences of an ERBB3-specific heavy chain variable region selected from the group consisting of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 and MF6074, or MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074, 52.Antibodies i) the antibody comprises an ERBB3-specific heavy chain variable region sequence selected from the group consisting of the heavy chain variable region sequences of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073, and MF6074, or the antibody comprises an ERBB3-specific heavy chain variable region sequence selected from the group consisting of the heavy chain variable region sequences of MF3178, MF3176, MF3163, MF6055, MF6056, MF MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074, 53. The antibody for use according to any one of clauses 47 or 50 to 52, the method of treatment according to any one of clauses 48 or 50 to 52 or the use according to any one of clauses 49 to 52, wherein the antibody comprises the heavy chain variable region MF3178. 54. The antibody for use according to any one of clauses 47 or 50 to 53, the method of treatment according to any one of clauses 48 or 50 to 53 or the use according to any one of clauses 49 to 53, wherein the antibody comprises a variable domain comprising an antigen-binding site capable of binding to the extracellular part of ERBB3, and wherein the antigen-binding site comprises a light chain variable region comprising CDR1 comprising the sequence QSISSY, CDR2 comprising the sequence AAS, and CDR3 comprising the sequence QQSYSTPPT. 55. The antibody for use according to any one of clauses 47 or 50 to 54, the method of treatment according to any one of clauses 48 or 50 to 54 or the use according to any one of clauses 49 to 54, wherein the antibody is a monospecific antibody, e.g. a monospecific bivalent antibody, that binds to ERBB3. 56. The antibody for use according to any one of clauses 47 or 50 to 55, the method of treatment according to any one of clauses 48 or 50 to 55 or the use according to any one of clauses 49 to 55, wherein the antibody comprises patritumab (U3-1287 / A888), seribantumab (MM-121), lumletuzumab (RG7116, RO-5479599), elgemtumab (LJM716), AV-203, KTN3379 / CDX-3379, GSK2849330, or an antibody-drug conjugate such as patritumab deruxtecan (U3-1402). 57. The antibody for use according to any one of clauses 47 or 50 to 55, the method of treatment according to any one of clauses 48 or 50 to 55 or the use according to any one of clauses 49 to 55, wherein the antibody is capable of reducing or reduces ligand-induced receptor function of ERBB3. 58. The antibody for use according to any one of clauses 47 or 50 to 55, the method of treatment according to any one of clauses 48 or 50 to 55 or the use according to any one of clauses 49 to 55, wherein the antibody comprises an antigen binding site capable of binding to an extracellular portion of ERBB3 that blocks both ERBB3 and its ligand heregulin. 59. The antibody for use according to any one of clauses 47 or 50-58, the method of treatment according to any one of clauses 48 or 50-58 or the use according to any one of clauses 49-58, wherein the cancer has progressed after previous treatment with an androgen receptor axis targeting agent. 60. The antibody for use according to clause 59, the method of treatment according to clause 59 or the use according to clause 59, wherein the androgen receptor axis targeting agent is an androgen receptor antagonist, for example a second generation androgen receptor antagonist. 61. The antibody for use according to clause 60, the method of treatment according to clause 60 or the use according to clause 60, wherein the androgen receptor antagonist is enzalutamide. 62. The antibody for use according to clause 59, the method of treatment according to clause 59 or the use according to clause 59, wherein the androgen receptor axis targeting agent is an androgen synthesis inhibitor, for example abiraterone acetate. 63. The antibody for use according to any one of clauses 47 or 50-62, the method of treatment according to any one of clauses 48 or 50-62 or the use according to any one of clauses 49-62, wherein the method of treatment further comprises use of an androgen receptor axis targeting agent. 64. The antibody for use according to any one of clauses 47 or 50 to 62, the method of treatment according to any one of clauses 48 or 50 to 62 or the use according to any one of clauses 49 to 62, wherein the method of treatment further comprises the use of an androgen receptor antagonist, such as a second generation androgen receptor antagonist, such as enzalutamide. 65. The antibody for use according to any one of clauses 47 or 50 to 62, the method of treatment according to any one of clauses 48 or 50 to 62 or the use according to any one of clauses 49 to 62, wherein the method of treatment further comprises the use of an androgen synthesis inhibitor, for example abiraterone acetate. 66. The antibody for use according to any one of clauses 47, 50-61 or 63-64, the method of treatment according to any one of clauses 48, 50-61 or 63-64 or the use according to any one of clauses 49-61 or 63-64, wherein if the cancer has progressed after previous treatment with an androgen receptor antagonist, the method of treatment with the bispecific antibody further comprises the use of an androgen receptor antagonist. 67. The antibody for use according to clause 66, the method of treatment according to clause 66 or the use according to clause 66, wherein the androgen receptor antagonist used in the previous treatment and the androgen receptor antagonist further used in the method of treatment with the bispecific antibody are the same. 68. The antibody for use according to clause 66 or 67, the method of treatment according to clause 66 or 67 or the use according to clause 66 or 67, wherein the androgen receptor antagonist used in the previous treatment and the androgen receptor antagonist further used in the method of treatment with the bispecific antibody are both enzalutamide. 68. The antibody for use according to any one of clauses 61, 64 or 68, the method of treatment according to any one of clauses 61, 64 or 68 or the use according to any one of clauses 61, 64 or 68, wherein enzalutamide is administered at 160 mg once daily. 70. The antibody for use according to any one of clauses 47 or 50-59, 62, 63 or 65, the method of treatment according to any one of clauses 48 or 50-59, 62, 63 or 65 or the use according to any one of clauses 49-59, 62, 63 or 65, wherein the method of treatment with the bispecific antibody further comprises the use of an androgen synthesis inhibitor if the cancer has progressed after previous treatment with an androgen synthesis inhibitor. 71. The antibody for use according to clause 70, the method of treatment according to clause 70 or the use according to clause 70, wherein the androgen synthesis inhibitor used in the previous treatment and the androgen synthesis inhibitor further used in the method of treatment with the bispecific antibody are the same. 72. The antibody for use according to clause 70 or 71, the method of treatment according to clause 70 or 71 or the use according to clause 70 or 71, wherein the androgen synthesis inhibitor used in the previous treatment and the androgen synthesis inhibitor further used in the method of treatment with the bispecific antibody are both abiraterone acetate. 73. The antibody for use according to any one of clauses 62, 65 or 72, the method of treatment according to any one of clauses 62, 65 or 72 or the use according to any one of clauses 62, 65 or 72, wherein abiraterone acetate is administered at 1000 mg once daily. 74. The antibody for use according to clause 73, the method of treatment according to clause 73 or the use according to clause 73, wherein abiraterone acetate is administered in combination with 5 mg of prednisone twice daily. 75. The antibody for use according to any one of clauses 47 or 50 to 74, the method of treatment according to any one of clauses 48 or 50 to 74 or the use according to any one of clauses 49 to 74, wherein the method of treatment comprises administering the bispecific antibody in an amount of 750 mg once every two weeks. 76. The antibody for use according to any one of clauses 47 or 50-75, the method of treatment according to any one of clauses 48 or 50-75 or the use according to any one of clauses 49-75, wherein the subject or cancer has PTEN wild-type status. 77. The antibody for use according to any one of clauses 47 or 50-76, the method of treatment according to any one of clauses 48 or 50-76 or the use according to any one of clauses 49-76, wherein the subject or cancer does not exhibit PTEN loss. 78. The antibody for use according to any one of clauses 47 or 50 to 77, the method of treatment according to any one of clauses 48 or 50 to 77 or the use according to any one of clauses 49 to 77, wherein the method of treatment comprises administering a therapeutically effective amount of the antibody to a subject in need thereof. 79. The antibody for use according to any one of clauses 47 or 50-78, the method of treatment according to any one of clauses 48 or 50-78 or the use according to any one of clauses 49-78, wherein the androgen receptor axis targeting agent is administered or will be administered in accordance with medical prescribing instructions established by a medical authority such as the FDA. 80. The antibody for use according to any one of clauses 47 or 50 to 79, the method of treatment according to any one of clauses 48 or 50 to 79 or the use according to any one of clauses 49 to 79, wherein the cancer is characterized in one particular embodiment by histologically confirmed adenocarcinoma of the prostate without features of neuroendocrine differentiation or small cell carcinoma. 81. A method for selecting a subject with castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or for treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting the subject for the treatment if the sample does not show PTEN loss. 82. A method for establishing whether a subject with castration-resistant prostate cancer is likely to respond to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or whether a subject with castration-resistant prostate cancer is likely to respond to treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining PTEN status in a sample obtained from the subject; and b) selecting samples for not showing PTEN loss, thereby establishing which subjects from which the samples were derived are likely to respond to the treatment. 83. A method for classifying a subject with castration-resistant prostate cancer based on PTEN status prior to treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or prior to treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining the PTEN status in a sample obtained from the subject; and b) if the sample does not show PTEN loss, classifying the subject from whom the sample was obtained or from whom the sample was obtained as eligible for the treatment. 84. The method of any one of clauses 81 to 83, wherein the PTEN status is determined using IHC. 85. The method of any one of clauses 81 to 83, wherein the PTEN status is determined using a liquid biopsy. 86. A kit of parts comprising a bispecific antibody comprising an antigen binding site capable of binding to the extracellular portion of ERBB2 and an antigen binding site capable of binding to the extracellular portion of ERBB3, and an androgen receptor axis targeting agent. 87. A kit of parts as described in clause 86, further comprising instructions for use. 88. The kit of parts according to clause 86 or 87, wherein the instructions for use comprise instructions for administration of the bispecific antibody and administration of the androgen receptor axis targeting agent. 89. A kit of parts according to any one of clauses 86 to 88, wherein the androgen receptor axis targeting agent comprises an androgen receptor antagonist, for example a second generation androgen receptor antagonist, for example enzalutamide, or an androgen synthesis inhibitor, for example abiraterone acetate, and the bispecific antibody comprises xenoctuzumab. 90. The kit of parts according to clause 89, wherein the instructions for use include administration of 1000 mg of abiraterone acetate once a day in combination with 5 mg of prednisone twice a day, and administration of the bispecific antibody in an amount of 750 mg once every two weeks. 91. The kit of parts according to clause 89, wherein the instructions for use include administration of 160 mg of enzalutamide once daily and administration of the bispecific antibody in an amount of 750 mg once every two weeks. 92. The kit of parts according to clause 90 or 91, wherein the instructions for use of abiraterone acetate or enzalutamide comprise oral administration instructions and the administration of the bispecific antibody comprises intravenous injection instructions. 93. A kit of parts comprising an antibody comprising an antigen binding site capable of binding to an extracellular portion of ERBB3, and an androgen receptor axis targeting agent. 94. A kit of parts according to clause 93, further comprising instructions for use. 95. The kit of parts according to clause 93 or 94, wherein the instructions for use comprise instructions for administration of the antibody and administration of the androgen receptor axis targeting agent. 96. A kit of parts according to any one of clauses 93 to 95, wherein the androgen receptor axis targeting agent comprises an androgen receptor antagonist, for example a second generation androgen receptor antagonist, for example enzalutamide, or an androgen synthesis inhibitor, for example abiraterone acetate, and the antibody comprises xenoctuzumab. 97. A kit of parts according to clause 96, the instructions for use comprising administration of 1000 mg of abiraterone acetate once daily in combination with 5 mg of prednisone twice daily, and administration of the antibody in an amount of 750 mg once every two weeks. 98. The kit of parts according to clause 96, wherein the instructions for use include administration of 160 mg of enzalutamide once daily and administration of the antibody in an amount of 750 mg once every two weeks. 99. The kit of parts according to clause 97 or 98, wherein the instructions for use of abiraterone acetate or enzalutamide include instructions for oral administration and the administration of the antibody includes instructions for intravenous injection. 100. The bispecific antibody for use according to any one of clauses 1 to 17 or 36, or the method of treatment or use according to any one of clauses 18 to 36, wherein the subject or cancer has PTEN loss status. 101. The bispecific antibody for use according to any one of clauses 1 to 17 or 36, or the method of treatment or use according to any one of clauses 18 to 36, wherein the subject or cancer exhibits PTEN loss. 102. The bispecific antibody for use according to any one of clauses 1 to 17 or 36, or the method of treatment or use according to any one of clauses 18 to 36, wherein the subject or cancer does not have an oncogenic driver mutation in any of the PI3K, AKT, and / or mTOR pathways, or wherein the subject or cancer does not have upregulation of any of said pathways. 103. The bispecific antibody for use according to any one of clauses 1 to 17 or 36, or the method of treatment or use according to any one of clauses 18 to 36, wherein the subject or cancer does not exhibit oncogenic driver mutations in any of the PI3K, AKT, and / or mTOR pathways, or wherein the subject or cancer does not exhibit upregulation of any of said pathways. 104. The bispecific antibody for use according to any one of clauses 1 to 17 or 36, or the method of treatment or use according to any one of clauses 18 to 36, wherein the subject or cancer does not have an oncogenic driver mutation in any known tumor-associated gene such as EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET and ROS1 or in proteins encoded therefrom. 105. The bispecific antibody for use according to any one of clauses 1 to 17 or 36, or the method of treatment or use according to any one of clauses 18 to 36, wherein the subject or cancer does not display oncogenic driver mutations in any known tumor-associated genes such as EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET and ROS1 or proteins encoded therefrom. 106. The antibody for use according to any one of clauses 47 or 50-75, the method of treatment according to any one of clauses 48 or 50-75 or the use according to any one of clauses 49-75, wherein the subject or cancer has PTEN loss status. 107. The antibody for use according to any one of clauses 47 or 50-75, the method of treatment according to any one of clauses 48 or 50-75 or the use according to any one of clauses 49-75, wherein the subject or cancer exhibits PTEN loss. 108. The antibody for use according to any one of clauses 47 or 50-75, the method of treatment according to any one of clauses 48 or 50-75 or the use according to any one of clauses 49-75, wherein the subject or cancer does not have an oncogenic driver mutation in any known tumor-associated gene such as EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET and ROS1 or in the proteins encoded therefrom. 109. The antibody for use according to any one of clauses 47 or 50 to 75, the method of treatment according to any one of clauses 48 or 50 to 75 or the use according to any one of clauses 49 to 75, wherein the subject or cancer does not display oncogenic driver mutations in any known tumor-associated genes such as EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET and ROS1 or proteins encoded therefrom. 110. A method for selecting a subject with castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or for treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining the presence of oncogenic driver mutations in any one of the PI3K, AKT, and / or mTOR pathways, or mutations regulating the PI3K, AKT, and / or mTOR pathways, in a sample obtained from the subject's cancer; and b) selecting the subject for the treatment if the sample lacks the presence of oncogenic driver mutations in the PI3K, AKT, and / or mTOR pathways, or mutations regulating the PI3K, AKT, and / or mTOR pathways. 111. The method of clause 110, wherein the subject's cancer is tested by next generation sequencing, e.g., DNA, RNA, or whole transcriptome sequencing. 112. A method for selecting a subject with castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or for treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) determining the presence of an oncogenic driver mutation in any one of EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET, and ROS1 in a sample obtained from the subject's cancer; and b) selecting the subject for the treatment if the sample lacks the presence of the oncogenic driver mutation. 113. The method of clause 110, wherein the subject's cancer is tested by next generation sequencing, e.g., DNA, RNA, or whole transcriptome sequencing. 114. A method for selecting a subject with castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or for treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) testing the subject's cancer for the presence of an oncogenic driver mutation that modulates any one of the PI3K, AKT, and / or mTOR pathways in a sample obtained from the subject by next-generation sequencing; and b) if the sample lacks the presence of the oncogenic driver mutation, classifying the subject from whom the sample was obtained, or from whom the sample was obtained, as eligible for the treatment. 115. A method of selecting a subject with castration-resistant prostate cancer for treatment with a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, or for treatment with an antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB3, the method comprising: a) testing the subject's cancer for the presence of an oncogenic driver mutation, in a sample obtained from the subject, by next-generation sequencing, and in certain embodiments, an oncogenic driver mutation in any one of EGFR, cMET, ALK, BRAF, KRAS, NRAS, RET, and ROS1; and b) if the sample lacks the presence of the oncogenic driver mutation, classifying the subject from whom the sample was obtained, or from whom the sample was obtained, as eligible for the treatment. 116. The method of any one of clauses 110-115, wherein the subject or cancer further has PTEN wild-type status. [Example]

[0196] As used herein, "MFXXXX," where X is independently a number from 0 to 9, refers to a Fab comprising a variable domain, and a VH having the amino acid sequence identified by the four digits shown in Figure 3. Unless otherwise indicated, the light chain variable region typically has the sequence of Figure 1b. In the examples, the light chain constant region has the sequence shown in Figure 1c. "MFXXXX VH" refers to the amino acid sequence of the VH identified by the four digits. The MF further comprises a light chain constant region and a heavy chain constant region that typically interacts with the light chain constant region. The heavy chain VH / variable regions differ, and typically the CH3 regions also differ, with one heavy chain having a KK mutation in its CH3 domain and the other having a complementary DE mutation in its CH3 domain (see PCT / NL2013 / 050294 (published as WO2013 / 157954) and Figures 2d and 2e for reference). In the examples, the bispecific antibody has an Fc tail with a KK / DE CH3 heterodimerization domain, a CH2 domain, and a CH1 domain as shown in Figure 2, a common light chain as shown in Figure 1a, and a VH designated by the MF number.

[0197] Example 1: Multispecific antibody binding to domain I of ERBB2 and domain III of ERBB3. Bimultispecific antibodies comprising the heavy chain variable regions described in Tables 2 and 3 were obtained as described in WO2015 / 130173. The ERBB3 binding domains shown can also be used to provide monospecific antibodies. [Table 2] [Table 3-1] [Table 3-2]

[0198] Example 2: A clinical study using xenoctuzumab, a full-length IgG1 bispecific antibody containing MF3958 x MF3178 targeting ERBB2 and ERBB3, in patients with castration-resistant prostate cancer.

[0199] This is a phase II, open-label, multicenter, international study designed to evaluate the efficacy of xenoctuzumab in patients with metastatic mCRPC who have evidence of disease progression according to Prostate Cancer Clinical Trials Working Group 3 (PCWG3) criteria on previous last-line hormonal therapy, including either the second-generation AR antagonist enzalutamide or the androgen synthesis inhibitor abiraterone acetate. Patients will be enrolled and receive xenoctuzumab in combination with an AR-targeting agent who experienced disease progression immediately prior to study enrollment. A cohort of patients with phosphate and tensin homolog (PTEN) wild-type status will be enrolled. Safety run-in will be conducted in the first 4-6 patients.

[0200] Investigational Drugs Xenoctuzumab is an investigational drug, and its companion drug, an AR signaling inhibitor, is considered a non-investigational drug. Xenoctuzumab, a bispecific humanized full-length IgG1 antibody, is formulated at 20 mg / mL.

[0201] Zenoctuzumab Xenoctuzumab will be administered as a 2-hour IV infusion on Day 1, then Q2W every 28-day cycle. A fixed dose of 750 mg will be administered.

[0202] Patients receive xenoctuzumab in combination with other medications. Premedication is required before each xenoctuzumab infusion. The required premedication regimen is as follows: · Paracetamol / acetaminophen 1000mg PO or IV. ·Dexchlorpheniramine 5 mg IV (or other anti-H1 equivalent, PO or IV). Dexamethasone 10 mg IV (or equivalent, PO or IV). Corticosteroids are required only prior to the administration on Day 1 of Cycle 1 and should be used for subsequent injections to manage infusion-related reactions (IRR), at the investigator's discretion. Use of H2 antagonists is optional and may be performed at the investigator's discretion.

[0203] Next-generation AR signaling inhibitors Patients will receive xenoctuzumab in combination with one of the following next-generation AR signaling inhibitors that the patient was receiving immediately before entering the study: Abiraterone acetate (ZYTIGA®) 1000 mg PO QD in combination with prednisone 5 mg twice daily (BID). · Enzalutamide (XTANDI®) 160 mg PO QD.

[0204] Administration of enzalutamide or abiraterone acetate will begin on day 1 of cycle 1.

[0205] Abiraterone acetate: Abiraterone acetate is taken in combination with prednisone and should be taken on an empty stomach. No food should be consumed at least two hours before and at least one hour after each dose. Tablets should be swallowed whole with water. Abiraterone acetate is available as 250 mg tablets, which are white to off-white in color, oval in shape, and debossed with AA250 on one side. Tablets should be stored at 20°C to 25°C (68°F to 77°F). Temperature fluctuations of 15°C to 30°C (59°F to 86°F) are permitted.

[0206] Enzalutamide: Enzalutamide may be taken with or without food. Capsules should be swallowed whole. Enzalutamide is supplied as 40 mg white to off-white oblong soft gelatin capsules imprinted with "MDV" in black ink. Capsules should be stored in a tightly closed container in a dry place at 20°C to 25°C (68°F to 77°F). Temperature fluctuations of 15°C to 30°C (59°F to 86°F) are permitted.

[0207] Treatment indications Next-generation AR signaling inhibitors will be administered according to the local prescribing information for each drug. Dose adjustments of enzalutamide or abiraterone acetate are permitted based on clinical judgment for drug-related toxicity. Abiraterone acetate: Treatment should be interrupted in patients who develop hepatotoxicity during treatment (ALT and / or AST >5xULN or total bilirubin >3xULN). Once liver function tests return to the patient's baseline or ALT and AST values ≤2.5xULN and total bilirubin ≤1.5xULN, treatment may be resumed at a reduced dose of 750mg QD. Once the patient resumes treatment, serum transaminases and bilirubin should be monitored at least every 2 weeks for 3 months, then monthly. If hepatotoxicity recurs at the 750mg QD dose, treatment may be resumed at a reduced dose of 500mg QD once function tests return to the patient's baseline or ALT and AST <2.5xULN and total bilirubin ≤1.5xULN. If hepatotoxicity recurs at the reduced dose of 500mg QD, treatment should be discontinued.

[0208] Enzalutamide: If a patient experiences Grade ≥ 3 toxicity or intolerable side effects, withhold administration for 1 week or until symptoms improve to Grade ≤ 2, then resume at the same dose or at a reduced dose (120 mg or 80 mg) as needed.

[0209] Treatment discontinued Zenoctuzumab will be administered until one of the following occurs, at which point it will be definitively discontinued unless benefit is recognized and agreed with the sponsor. Continuation of monotherapy if benefit occurs will be discussed on a case-by-case basis in agreement with the sponsor.

[0210] ·Progressive disease. ·AE / Unacceptable toxicity. Withdrawal of consent. · Patient non-compliance. Investigator decision (e.g., clinical deterioration). -Continuous treatment interruption for more than 6 weeks. Discontinuation of any concomitant therapeutic medications.

[0211] Eligible patients will be enrolled and receive successive treatment cycles, each lasting 4 weeks (28 days). All patients will receive xenoctuzumab at a fixed dose of 750 mg IV Q2W.

[0212] Study population Inclusion criteria Patients must meet all of the following requirements to participate in the study: 1. Signed informed consent prior to the start of any study procedures. 2. Be 18 years of age or older at the time of signing the informed consent. Eastern Cooperative Oncology Group (ECOG) performance status of 3.0 or 1. 4. Estimated lifespan of 12 weeks or more. 5. A minimum of 3 weeks since any major surgery, completion of radiation, completion of all prior systemic anticancer therapy, or at least 5 half-lives if the prior therapy was a single-agent small molecule therapeutic, and sufficient recovery from acute toxicity of any prior therapy to Grade 1 or less according to the National Cancer Institute (NCI)-Common Terminology Criteria for AEs (CTCAE) v. 5.0, except in the case of alopecia or neuropathy. 6. Left ventricular ejection fraction (LVEF) of 50% or more by echocardiogram (ECHO) or multi-gated acquisition scan (MUGA). 7. Proper organ function: Absolute neutrophil count (ANC) ≥ 1.5 × 10 9 / L. Hemoglobin ≥ 9g / dL. Platelets ≥ 100 × 10 9 / L. Serum calcium within normal range (or corrected with supplements). Alanine aminotransferase (ALT), aspartate aminotransferase (AST) ≤ 2.5 × upper limit of normal (ULN) (ALT / AST ≤ 5 × ULN is acceptable in cases of hepatic involvement by malignancy). · Total bilirubin ≤ 1.5 x ULN (in Gilbert's disease, a total bilirubin level ≤ 3 x ULN is acceptable). ·Estimated glomerular filtration rate greater than 30 mL / min based on the Cockroft-Gault formula. · Serum albumin > 3.0 g / dL. 8. Availability of a representative tumor specimen, preferably either formalin-fixed, paraffin-embedded (FFPE) in de novo form (i.e., obtained no more than 2 months prior to signing of the informed consent form) collected within 2 years of the start of study treatment, or an FFPE archival tumor sample. Fresh FFPE samples are preferred. 9. Sexually active male and female patients of childbearing potential must agree to use one of the following highly effective methods of contraception throughout the study and for 6 months after the last dose of xenoctocog alfa: ·Combined (estrogen- and progestogen-containing) hormonal contraception associated with the inhibition of ovulation: oral, intravaginal, transdermal. · Progestogen-only hormonal contraception associated with inhibition of ovulation: oral, injectable, implantable, intrauterine device, intrauterine hormone-releasing system, bilateral tubal occlusion, vasectomized partner, sexual abstinence.

[0213] Additional inclusion criteria: Patients must meet all of the following requirements to participate in the study: B1. Histologically confirmed adenocarcinoma of the prostate without neuroendocrine differentiation or small cell features. B2. Metastatic disease documented by at least two bone lesions on whole-body bone scintigraphy or soft tissue disease documented by computed tomography (CT) scan / magnetic resonance imaging (MRI). B3. Continuous androgen deprivation with serum testosterone levels ≤ 1.73 nmol / L (≤ 50 ng / dL) at screening and before initiation of treatment. B4. Ongoing therapy with a next-generation AR signaling inhibitor (enzalutamide or abiraterone) was initiated at least 90 days prior to screening and before treatment initiation. A dose interruption of up to 30 days is permitted before resuming the drug. B5. Progressive disease per PCWG3 criteria for study enrollment defined as one of the following: Prostate-specific antigen (PSA) progression, defined as two increases in PSA reaching a minimum of ≥1 ng / mL compared to the previous reference value at screening and before treatment initiation (if the patient discontinues abiraterone or enzalutamide for longer than 14 days, a PSA rise must be documented after restarting the drug). · Progression of soft tissue disease as defined by RECIST v1.1. · A previously normal (less than 10mm) lymph node must grow more than 5mm in its short axis to be considered advanced). Progression of bone disease as defined by two or more new lesions on whole-body bone scintigraphy. B6. Patients receiving bisphosphonates or denosumab for bone health must be on a stable dose for at least 4 weeks prior to starting study treatment. B7. Able to swallow oral medications and no gastrointestinal conditions (e.g., malabsorption, resection) that would compromise intestinal absorption are present.

[0214] Exclusion criteria Exclusion criteria: Patients will be excluded from participation in the study if any of the following criteria are present: 1. Central nervous system metastases that are untreated or symptomatic or require radiation, surgery, or continuous steroid therapy to control symptoms within 14 days of study enrollment. 2. Previous exposure to anti-ERBB3 directed therapy. 3. Known leptomeningeal involvement. 4. Participation in another interventional clinical trial or treatment with any investigational drug within 4 weeks prior to study enrollment. 5. Chronic use of high-dose oral corticosteroid therapy (more than 10 mg prednisone equivalent daily). 6. Uncontrolled hypertension (systolic blood pressure >150mmHg and / or diastolic blood pressure >100mmHg) or unstable angina. 7. History of congestive heart failure according to New York Heart Association criteria, Class II-IV, or severe cardiac arrhythmia requiring treatment (excluding atrial fibrillation or paroxysmal supraventricular tachycardia). 8. History of myocardial infarction within 6 months of study enrollment. 9. History of previous or concurrent malignancy (excluding resected non-melanoma skin cancer, in situ cured cervical cancer, or low-grade Ta or T1 urothelial carcinoma of the bladder that has undergone potentially curative therapy) within 3 years of study enrollment. 10. Current serious illness or psychiatric disorder, including but not limited to uncontrolled active infection and clinically significant pulmonary, metabolic, or psychiatric disease. 11. Patients with any of the following known infections: Known active hepatitis B infection (hepatitis B surface antigen [HBsAg] positive) without antiviral therapy. Note: Patients with active hepatitis B (HbsAg positive) must be on antiviral treatment with lamivudine, tenofovir, entecavir, or other antiviral agents starting at least 7 days before the start of study treatment. Patients with prior hepatitis B (anti-HBc positive, HbsAg and hepatitis B virus [HBV] DNA negative) are eligible. 12. Known human immunodeficiency virus (HIV) positive patients unless the CD4+ count is ≥ 300 / μL, the viral load is undetectable, and the patient is currently receiving highly active antiretroviral therapy. Further exclusion criteria that will exclude patients from participating in the study are the presence of any of the following criteria: 13. More than two second-generation hormonal agents for metastatic disease. 14. More than two lines of systemic chemotherapy for metastatic disease. 15. Patients with only non-measurable lesions other than bone metastases (e.g., pleural effusion, ascites, other visceral sites). 16. Any condition that could cause a patient to have a seizure within 12 months prior to study treatment, including a history of seizures in patients receiving enzalutamide, or a history of unexplained loss of consciousness or transient ischemic attack.

[0215] Management of infusion-related reactions Patients will be closely monitored during the study treatment period. Patients must be premedicated with antihistamines, paracetamol / acetaminophen, and corticosteroids before each infusion of zenoctuzumab.

[0216] Prophylactic and concomitant medications Accepted medications All medications necessary for the patient's well-being and not expected to interfere with the evaluation of the investigational product, including supplemental treatment for symptoms and AEs or standard treatment for comorbid conditions, may be administered at the investigator's discretion.

[0217] Luteinizing hormone-releasing hormone (LHRH) agonists or antagonists are permitted in patients who have not previously undergone bilateral orchiectomy.

[0218] Prohibited drugs · Concomitant chronic oral corticosteroids (prednisone equivalents greater than 10 mg / day), tumor necrosis factor (TNF)-α inhibitors, and anti-T-cell antibodies (due to the risk of immunosuppression). Any investigational drug during the study or within 4 weeks prior to the first dose of study treatment. It is recommended to refrain from starting any new investigational medication for at least 4 weeks after the last dose of investigational medication. Systemic anti-cancer therapy. Note: For patients in Group B, next-generation AR signaling inhibitors that the patient was receiving immediately prior to study entry are allowed.

[0219] Efficacy assessment: response measures, tumor measurements Radiographic measurements of tumors to assess the antitumor effect of zenoctuzumab will be performed by CT scan or MRI. Imaging will be performed according to local standard practice, and data will be collected on computerized case report forms. Imaging of all patients will be reviewed by a local investigator.

[0220] Brain MRI or CT scans should be performed with the same frequency as CT / MRI of the chest, abdomen, and pelvis, and only if brain metastases are detected on screening scans. Depending on the patient's tumor type, additional imaging of anatomical sites (e.g., head, neck) should be performed. Note that if there is evidence of bone lesion evaluation, these evaluations are performed as part of the CT or MRI evaluation; additional radiological bone scan evaluations are not required.

[0221] Additional scans may be performed to confirm response as needed. Any requirement for a confirmatory scan will typically be performed at the next protocol-required evaluation or follow-up visit. A period of +3 days is allowed for the initial tumor evaluation only. Thereafter, a period of ±3 days is allowed but must occur prior to the start of the next treatment cycle. Patients who discontinue treatment for reasons other than disease progression and do not withdraw consent will have their disease status evaluated every 8 weeks for up to 12 months until disease progression and / or initiation of new anti-cancer treatment or withdrawal of consent, whichever occurs first.

[0222] Whole-body bone scans will be performed every 8 weeks for the first 12 months of treatment and every 12 weeks thereafter. Tumor assessments will be completed according to PCWG3-modified RECIST criteria.

[0223] Tumor markers PSA levels will be assessed before treatment initiation and on day 1 of each cycle (every 4 weeks ± 3 days). The same laboratory must be used for repeat assessments.

[0224] The evolution of tumor marker levels will be followed throughout treatment.

[0225] Tumor tissue sample evaluation PTEN analysis is performed on a baseline biopsy (preferably fresh; archival samples collected within 2 years are acceptable, provided the biopsy is collected after castration resistance has been established) by IHC (local or central) or next-generation sequencing to identify patients with PTEN wild-type status.

[0226] Example 3 Following the clinical trial protocol described in Example 2, patients with histologically confirmed mCRPC and prostate adenocarcinoma were enrolled. Patients who progressed on either abiraterone acetate or enzalutamide continued their background AR axis-targeting agent after study enrollment and received concomitant xenoctuzumab treatment. Sites of metastatic involvement included lymph nodes, bone, and / or visceral organs. Tumor PTEN status was established in patients by IHC using the Roche Ventana Optiview DAB kit and SP218 PTEN antibody on a Benchmark Ultra immunohistochemistry automated slide stainer when sufficient biological material was available. The OptiView DAB IHC Detection Kit (OptiView) is an indirect, biotin-free system for detecting mouse IgG, mouse IgM, and rabbit primary antibodies. This kit is intended for identifying targets by IHC in formalin-fixed, paraffin-embedded frozen tissue sections stained with the Ventana automated slide stainer and visualized by light microscopy. Clinical interpretation of any staining, or absence of staining, is complemented by morphologic studies and evaluation of appropriate controls.

[0227] Among the cohort of 10 treated patients, no treatment-emergent adverse events (TEAEs) related to the study treatment classified as Grade 3 or higher TEAEs were observed. Furthermore, the combination of xenoctuzumab and abiraterone acetate or enzalutamide was very well tolerated, with no safety concerns identified. Furthermore, no treatment discontinuations due to adverse events occurred, and no unexpected toxicity signals were reported. Only a single IRR (i.e., Grade 2, related) was reported.

[0228] Example 4 Following the clinical trial protocol of Example 2, an 85-year-old man with mCRPC was treated with a combination of xenoctuzumab and enzalutamide. The patient had received multiple prior systemic therapies, including two androgen receptor axis-targeting agents (i.e., abiraterone and enzalutamide) and two chemotherapy regimens (e.g., docetaxel and cabazitaxel), but showed progressive disease after these treatments. Blood-based next-generation sequencing revealed nonsense mutations in NF1 (L1201*) and ERRFI1 (Y403*) and a missense mutation in TP53 (V172D). According to investigator reports, the patient had slow radiological progression of lymph node (LN) (target lesion) prior to study enrollment. On study treatment, the patient had a best overall response of stable disease by RECIST (6 months) and no evidence of disease by bone scan (NED) by PCWG3 (6 months), with overall stable disease. After 6 months of ongoing treatment, no evidence of lymph node progression consistent with radiological disease control was reported.

[0229] Example 5 Following the clinical trial protocol described in Example 2, a 77-year-old man with mCRPC was treated with a combination of xenoctuzumab and abiraterone acetate / prednisone. The patient had received four prior systemic therapies, including one chemotherapy and two androgen receptor axis-targeting agents (i.e., darolutamide and abiraterone), but showed progressive disease after these treatments. PTEN loss was observed by IHC testing performed on an archival prostate biopsy specimen. No tumor-associated somatic alterations or mutations were detected by blood-based next-generation sequencing. According to the investigator's report, the patient had LN progression (non-targeted) and bone metastases prior to enrollment. On study treatment, the patient had a best overall response of stable disease by RECIST (4 months) and stable disease by bone scan by PCWG3 (4 months), with overall stable disease. After 5 months of ongoing treatment, no evidence of lymph node or bone progression consistent with radiological disease control was reported.

[0230] Example 6 Following the clinical trial protocol of Example 2, a 77-year-old man with mCRPC was treated with a combination of xenoctuzumab and enzalutamide. The patient had received multiple prior systemic therapies, including chemotherapy, radiopharmaceuticals (Xofigo®), and androgen receptor axis-targeting agents such as docetaxel, abiraterone (in combination with prednisone), and enzalutamide, but showed progressive disease after these treatments. The patient's tumor was shown to be PTEN wild-type by IHC testing performed on an archival tumor sample from a previous prostate biopsy. Blood-based next-generation sequencing detected only a missense mutation in TP53 (A161T) and a nonsense mutation in APC (K139*). On investigational treatment, the patient had a best overall response of stable disease as measured by target lesions (lymph nodes) under RECIST v1.1 per investigator. The patient discontinued treatment in light of a skeletal-related event.

[0231] Example 7 Following the clinical study protocol of Example 2, two additional patients with wild-type PTEN status established using IHC testing were treated with a combination of xenoctuzumab and enzalutamide. According to PCWG3 criteria, PSA levels were assessed for at least 12 weeks after treatment initiation and showed a trend toward improvement. Imaging studies were performed at pre-specified time points within the same time frame to assess radiographic disease control. These patients had previously received multiple prior systemic therapies, including chemotherapy and androgen receptor axis-targeting agents such as abiraterone, docetaxel in combination with bicalutamide, cabazitaxel in combination with enzalutamide, or prednisone, but both showed progressive disease after these treatments.

Claims

1. A bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3, for use in a method for treating castration-resistant prostate cancer in a subject.

2. A method of treating a subject with castration-resistant prostate cancer, said method comprising administering to said subject a therapeutically effective amount of a bispecific antibody comprising an antigen-binding site capable of binding to the extracellular portion of ERBB2 and an antigen-binding site capable of binding to the extracellular portion of ERBB3.

3. 3. The bispecific antibody for the use or method of claim 1 or 2, wherein the cancer has progressed after previous treatment with an androgen receptor axis targeting agent.

4. 4. The bispecific antibody for the use or method of claim 3, wherein the androgen receptor axis targeting agent is an androgen receptor antagonist, such as a second generation androgen receptor antagonist.

5. 5. The bispecific antibody for the use or method of claim 4, wherein the androgen receptor antagonist is enzalutamide.

6. 4. The bispecific antibody for the use or method of claim 3, wherein the androgen receptor axis targeting agent is an androgen synthesis inhibitor, such as abiraterone acetate.

7. 10. The bispecific antibody for use or method according to any one of the preceding claims, wherein said method of treatment further comprises the use of an androgen receptor axis targeting agent.

8. 7. The bispecific antibody for use or method according to any one of claims 1 to 6, wherein the method of treatment further comprises the use of an androgen receptor antagonist, such as a second generation androgen receptor antagonist, such as enzalutamide.

9. 7. The bispecific antibody for use or method according to any one of claims 1 to 6, wherein the method of treatment further comprises the use of an androgen synthesis inhibitor, such as abiraterone acetate.

10. 5. The bispecific antibody for use or method according to any one of claims 1 to 4, wherein the cancer has progressed after previous treatment with an androgen receptor antagonist, and the method of treatment with the bispecific antibody further comprises the use of an androgen receptor antagonist.

11. 11. The bispecific antibody for use or method according to claim 10, wherein the androgen receptor antagonist used in the previous treatment and the androgen receptor antagonist further used in the method of treatment with the bispecific antibody are the same.

12. 12. The bispecific antibody for use or method according to claim 10 or 11, wherein the androgen receptor antagonist used in the previous treatment and the androgen receptor antagonist further used in the method of treatment with the bispecific antibody are both enzalutamide.

13. 13. The bispecific antibody for the use or method of claim 8 or 12, wherein enzalutamide is administered at 160 mg once daily.

14. 10. The bispecific antibody for use or method of any one of claims 1 to 3 or 6, wherein the cancer has progressed after previous treatment with an androgen synthesis inhibitor, and the method of treatment with the bispecific antibody further comprises the use of an androgen synthesis inhibitor.

15. 15. The bispecific antibody for use or method according to claim 14, wherein the androgen synthesis inhibitor used in the previous treatment and the androgen synthesis inhibitor further used in the method of treatment with the bispecific antibody are the same.

16. 16. The bispecific antibody for use or method according to claim 14 or 15, wherein the androgen synthesis inhibitor used in the previous treatment and the androgen synthesis inhibitor further used in the method of treatment with the bispecific antibody are both abiraterone acetate.

17. 17. The bispecific antibody for the use or method of claim 9 or 16, wherein abiraterone acetate is administered at 1000 mg once daily.

18. 18. The bispecific antibody for the use or method of claim 17, wherein abiraterone acetate is administered in combination with 5 mg prednisone twice daily.

19. 10. The bispecific antibody for use or method according to any one of the preceding claims, wherein said method of treatment comprises administering said bispecific antibody in an amount of 750 mg once every two weeks.

20. 10. The bispecific antibody for the use or method according to any one of the preceding claims, wherein said cancer is not NRG1 fusion positive.

21. 8. The bispecific antibody for use or method of claim 7, wherein said androgen receptor axis targeting agent is administered in accordance with medical prescribing instructions established by a medical authority such as the FDA.

22. 10. The bispecific antibody for use or method according to any one of the preceding claims, wherein said cancer is characterized by histologically confirmed adenocarcinoma of the prostate without features of neuroendocrine differentiation or small cell carcinoma.

23. 10. A bispecific antibody for use or method according to any one of the preceding claims, wherein said bispecific antibody comprises a first antigen-binding site capable of binding to domain I of ERBB2 and a second antigen-binding site capable of binding to domain III of ERBB3.

24. the bispecific antibody i) comprises at least the CDR1, CDR2 and CDR3 sequences of an ERBB2-specific heavy chain variable region selected from the group consisting of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031 and MF3003, or the antibody comprises CDR sequences which differ by at most 3 amino acids, preferably by at most 2 amino acids, preferably by at most 1 amino acid from the CDR1, CDR2 and CDR3 sequences of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031 or MF3003; and / or the bispecific antibody ii) comprises at least the CDR1, CDR2 and CDR3 sequences of an ERBB3-specific heavy chain variable region selected from the group consisting of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 and MF6074; or the antibody 3. The bispecific antibody for the use or method according to any one of the preceding claims, comprising CDR sequences which differ by at most 3 amino acids, preferably by at most 2 amino acids, preferably by at most 1 amino acid from the CDR1, CDR2 and CDR3 sequences of MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074.

25. the bispecific antibody i) comprises an ERBB2-specific heavy chain variable region sequence selected from the group consisting of: MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031, and MF3003, or the antibody comprises a heavy chain variable region sequence that differs by at most 15 amino acids from the heavy chain variable region sequence of MF2973, MF3004, MF3958, MF2971, MF3025, MF2916, MF3991, MF3031, or MF3003; and / or The bispecific antibody is selected from the group consisting of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073, MF6074, MF6075, MF6076, MF6077, MF6078, MF6079, MF6080, MF6081, MF6082, MF6083, MF6084, MF6085, MF6086 or the antibody comprises an ERBB3-specific heavy chain variable region sequence selected from the group consisting of the heavy chain variable region sequences of MF3178, MF3176, MF3163, MF6055, MF6056, MF6057, MF6058, MF6059, MF6060, MF6061, MF6062, MF6063, MF6064, MF 6065, MF6066, MF6067, MF6068, MF6069, MF6070, MF6071, MF6072, MF6073 or MF6074,

26. 10. The bispecific antibody for use or method according to any one of the preceding claims, wherein said bispecific antibody comprises the heavy chain variable region sequences of MF3958 and MF3178.

27. 10. The bispecific antibody for use or method according to any one of the preceding claims, wherein the bispecific antibody comprises a variable domain comprising the first antigen-binding site and a variable domain comprising the second antigen-binding site, wherein the first and second antigen-binding sites comprise a light chain variable region comprising CDR1 comprising the sequence QSISSY, CDR2 comprising the sequence AAS, and CDR3 comprising the sequence QQSYSTPPT.

28. 10. The bispecific antibody for use or method according to any one of the preceding claims, wherein the subject is a human subject.

29. 10. The bispecific antibody for use or method according to any one of the preceding claims, wherein the cancer is metastatic castration-resistant prostate cancer or the subject is at risk of developing metastatic castration-resistant prostate cancer.

30. A kit of parts comprising a bispecific antibody comprising an antigen binding site capable of binding to the extracellular portion of ERBB2 and an antigen binding site capable of binding to the extracellular portion of ERBB3, and an androgen receptor axis targeting agent.

31. 31. The kit of parts of claim 30, further comprising instructions for use.

32. 32. The kit of parts of claim 30 or 31, wherein the instructions for use comprise instructions for administration of the bispecific antibody and administration of the androgen receptor axis targeting agent.

33. 33. The kit of parts of any one of claims 30 to 32, wherein the androgen receptor axis targeting agent comprises an androgen receptor antagonist, such as a second generation androgen receptor antagonist, such as enzalutamide, or comprises an androgen synthesis inhibitor, such as abiraterone acetate, and the bispecific antibody comprises zenocutuzumab.

34. 34. The kit of parts of claim 33, wherein the instructions for use comprise administration of 1000 mg of abiraterone acetate once daily in combination with 5 mg of prednisone twice daily, and administration of the bispecific antibody in an amount of 750 mg once every two weeks.

35. 34. The kit of parts of claim 33, wherein the instructions for use comprise administering 160 mg of enzalutamide once daily and administering the bispecific antibody in an amount of 750 mg once every two weeks.

36. 36. The kit of parts of claim 34 or 35, wherein the instructions for use of abiraterone acetate or enzalutamide comprise oral administration instructions and the administration of the bispecific antibody comprises intravenous injection instructions.

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