A polypeptide targeting and stabilizing BRD7 tumor suppressor protein and its application in preparing drugs for treating solid tumors

Abstract

The present invention discloses a polypeptide that targets and stabilizes the BRD7 tumor suppressor protein and its application in the preparation of drugs for treating solid tumors, belonging to the field of medical treatment. The present invention screened and determined CC2 (299-349aa), the structural basis for the interaction between TRIM28 and BRD7, and screened and identified a polypeptide TAB12 containing 12 amino acids and capable of increasing the stability of the BRD7 protein from two polypeptide structures with α-helices, and confirmed that the polypeptide exerts an anti-tumor effect in multiple tumors such as breast cancer and nasopharyngeal carcinoma, and can be used for the research and development of anti-tumor targeted drugs. The polypeptide drug TAB12 described in the present invention has been proven to be able to competitively block the binding of TRIM28 to BRD7, inhibit the ubiquitination degradation of BRD7, has good anti-solid tumor activity, and is expected to become a new anti-tumor targeted drug.

Description

Technical Field

[0001] The present invention belongs to the field of medical treatment, and specifically relates to the screening and determination of a polypeptide drug that targets and blocks the binding of E3 ubiquitin ligase TRIM28 to tumor suppressor protein BRD7, increases the stability of BRD7 protein, and thus exerts an anti-tumor effect in various tumor types such as nasopharyngeal carcinoma and breast cancer, and its application. Background Art

[0002] Targeted therapy is a treatment method that achieves precise killing of tumor cells by specifically binding drugs to specific molecular targets of tumor cells. Currently, the targeted drugs used in clinical practice are mainly small molecule inhibitors and antibody drugs that target tumor gene inactivation, such as EGFR tyrosine kinase inhibitors that target tumor genes, and monoclonal antibody drugs that target HER2. Peptide drugs are a new generation of targeted drug development strategies after small molecule drugs and antibody-drug conjugates. They can competitively destroy protein-protein interactions by simulating peptide binding epitopes, affecting the stability or function of target proteins, thereby achieving specific killing or inhibition of tumor cells. However, peptide drugs are currently basically in the laboratory research or preclinical trial stage in the study of clinical anti-tumor treatment. Therefore, peptide drugs for tumor genes or tumor suppressor genes for targeted tumor treatment still need to be developed in depth.

[0003] BRD7 is a highly unstable protein, and its reduced protein stability is an important molecular mechanism leading to tumorigenesis and malignant progression. At the same time, TRIM28 is a potential E3 ubiquitin ligase of BRD7, which can induce the degradation of BRD7 protein through the ubiquitin-proteasome pathway, thereby leading to the malignant progression of solid tumors such as breast cancer and nasopharyngeal carcinoma. Therefore, the present invention is based on blocking the binding of TRIM28 / BRD7 to reverse the ubiquitination degradation of BRD7 and increase its protein stability, which is an important new molecular strategy for the clinical treatment of tumors. The present invention has developed a polypeptide that can target and block the binding of TRIM28 to BRD7 and increase the stability of BRD7 protein, and it is confirmed that the polypeptide can play an anti-tumor effect in various tumors such as breast cancer and nasopharyngeal carcinoma by increasing the stability of BRD7 tumor suppressor protein. The development of this polypeptide drug is expected to fill the gap in tumor polypeptide drugs under this mechanism and has very good application prospects. Summary of the invention

[0004] The primary purpose of the present invention is to provide a polypeptide that can target and block the binding of TRIM28 to BRD7 protein and stabilize BRD7 protein. The polypeptide drug is designed and obtained by screening and finely locating the sites where TRIM28 and BRD7 proteins interact, and screening and identifying them in terms of function and biological phenotype. The present invention confirms the anti-tumor effect and biosafety of the polypeptide drug in multiple tumors such as breast cancer and nasopharyngeal carcinoma.

[0005] The second objective of the present invention is to provide the use of the above polypeptide in drugs for treating solid tumors.

[0006] The present invention provides a polypeptide TAB12 for targeting and stabilizing BRD7 protein based on TRIM28, and its amino acid sequence is IQKHQEHILRFA, or further includes a pharmaceutically acceptable polypeptide modification type.

[0007] Further,

[0008] The polypeptide modification types include at least one of C-terminal modification, N-terminal modification, intermediate residue modification and cyclization modification.

[0009] Furthermore,

[0010] The modification includes, but is not limited to, at least one of lipidation modification, acetylation modification, phosphorylation modification, glycosylation modification, polyethylene glycol modification, methylation modification, amidation modification, and D-amino acid substitution.

[0011] In the present invention, based on the interaction region of TRIM28 and BRD7, blocking peptides are prepared and screened to find polypeptides that prevent TRIM28 from binding to BRD7 protein and enhance the stability of BRD7 protein, thereby inhibiting the ubiquitination degradation of BRD7 protein as anti-tumor drugs.

[0012] Specifically, the polypeptide drug can target and inhibit the binding of TRIM28 to BRD7 protein, thereby increasing the stability of BRD7 protein.

[0013] In particular, it can prevent the Coiled-Coil domain of TRIM28 from binding to the BRD7 protein, thereby inhibiting the ubiquitination and degradation of the BRD7 protein, and can be used as a tumor treatment drug.

[0014] The solid tumor described in the present invention is a solid tumor with low expression of BRD7, including one or more of breast cancer, nasopharyngeal cancer, lung cancer, liver cancer, and ovarian cancer.

[0015] The breast cancer cells include at least one of MDA-MB-231 and MCF7; the nasopharyngeal cancer cells include at least one of CNE2 and 5-8F.

[0016] In the application of the present invention, the dosage form is an oral dosage form or an injectable dosage form, including but not limited to tablets, pills, capsules, sprays, granules, powder injections, injections, etc. The dosage of the drug is a pharmaceutically acceptable dosage, and the administration method includes but is not limited to tumor injection, intravenous injection, intraperitoneal injection and oral administration.

[0017] The drug for treating tumors of the present invention also includes a drug combination and further includes pharmaceutically acceptable excipients.

[0018] Preferably, the drug is in a pharmaceutically acceptable dosage form.

[0019] Beneficial effects of the present invention

[0020] The polypeptide TAB12 provided by the present invention blocks the binding of TRIM28 to BRD7 in breast cancer and nasopharyngeal cancer cells and reverses the ubiquitination of BRD7 mediated by TRIM28 overexpression, and increases the stability of BRD7 protein in a dose-dependent manner. TAB12 inhibits the proliferation, invasion, migration and tumor growth of tumor cells in vivo, thereby exerting an anti-tumor effect in tumors such as breast cancer and nasopharyngeal carcinoma, and has no obvious toxic side effects in mice. Therefore, TAB12 is expected to become a potential anti-solid tumor drug targeting BRD7 protein. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 :The results of TRIM28 negatively regulating BRD7 protein stability through the ubiquitin-proteasome pathway;

[0022] Figure 1 A: Treatment with the proteasome inhibitor MG132 reversed the inhibitory effect of TRIM28 overexpression on BRD7 protein; Figure 1 B: Effect of TRIM28 overexpression on polyubiquitination of BRD7 in MDA-MB-231 and MCF7 cells; Figure 1 C: Effect of silencing TRIM28 expression on the ubiquitination level of BRD7.

[0023] Figure 2 :TRIM28 relies on its Coiled-Coil domain to recognize and reduce the stability of BRD7 protein;

[0024] Figure 2 A: full-length and truncated versions of TRIM28; Figure 2 B: Co-immunoprecipitation (Co-IP) experiment results showing interaction between TRIM28 Coiled-Coil domain and BRD7 in breast cancer cell MCF7; Figure 2 C: Co-IP experimental results of the interaction between TRIM28-CC region and BRD7; Figure 2 D: Detection results of BRD7 protein expression level after overexpression of TRIM28-CC region in two breast cancer cell lines, MDA-MB-231 and MCF7.

[0025] Figure 3 :Results of designing ɑ-helix blocking peptides based on the amino acid sequence of the minimal binding region of TRIM28 and BRD7;

[0026] Figure 3 A: Schematic diagram of the ɑ-helix in the CC region of TRIM28; Figure 3 B: TRIM28 △CC1, △CC2 vector map; Figure 3 C: Co-IP experimental results showing that the TRIM28 299-349aa region is the structural basis for the interaction between TRIM28 and BRD7 protein; Figure 3 D: Two interfering peptides designed and synthesized based on the secondary structure characteristics of the amino acid sequence.

[0027] Figure 4 : The peptide drug TAB12 derived from the coiled-coil region of TRIM28 competitively inhibits the binding of TRIM28 to BRD7 and increases the stability of BRD7 protein;

[0028] Figure 4 A: Effects of TAB12 and TAB14 on BRD7 protein expression in breast cancer cell line MDA-MB-231; Figure 4 B: Effects of TAB12 and TAB14 on BRD7 protein expression in breast cancer cell line MCF7; Figure 4 C: Co-IP experimental results of the effect of TAB14 and TAB12 treatment on the binding ability of TRIM28 and BRD7 protein in breast cancer MCF7; Figure 4 D: Effects of TAB14 and TAB12 treatment on TRIM28-mediated BRD7 ubiquitination levels.

[0029] Figure 5 : The results of the TAT-TAB12 peptide drug TAB12's TAT-modified peptide exerting anti-tumor effects in various tumors such as breast cancer and nasopharyngeal carcinoma;

[0030] Figure 5 A: CCK8 experimental results of the effect of TAT-TAB12 treatment on the proliferation of breast cancer cells (MDA-MB-231, MCF7) and nasopharyngeal carcinoma cells (CNE2, 5-8F); Figure 5 B: The results of the effect of TAT-TAB12 on the clone-forming ability of breast cancer cells.

[0031] Figure 6 :The results of TAT-TAB12 exerting anti-tumor effects in mice by stabilizing BRD7 protein;

[0032] Figure 6 A: Appearance morphology of tumor-bearing mice after being treated with peptide drugs; Figure 6 B: Comparison of tumor sizes of mice in the three treatment groups; Figure 6 C: Effect of TAT-TAB12 on tumor growth; Figure 6D: Effect of TAT-TAB12 on tumor weight; Figure 6 E: Effect of TAT-TAB12 on the body weight of mice.

[0033] Figure 7 : The results showed that the peptide drug TAT-TAB12 had no obvious toxic side effects on important organs of mice. DETAILED DESCRIPTION

[0034] The following examples are intended to further illustrate the present invention, but are not intended to limit the present invention.

[0035] The MDA-MB-231, MCF7, 5-8F, and CNE2 cell lines used in the present invention were purchased from the Biomedical Center of the Advanced Research Center of Central South University. The cell culture conditions were: DMEM liquid culture medium plus 10% fetal bovine serum (FBS) and 1% double antibody (penicillin and streptomycin), placed in a constant temperature incubator at 37°C and 5% CO2 concentration.

[0036] Example 1 TRIM28 negatively regulates BRD7 protein stability through the ubiquitin-proteasome pathway

[0037] 1.1 Experimental plan:

[0038] (1) The control plasmid and TRIM28 overexpression plasmid were transfected into two breast cancer cell lines, MDA-MB-231 and MCF7, respectively. After 48 h of transfection, the complete culture medium was replaced and the proteasome inhibitor MG132 (20 µM) was added for 4 h. Subsequently, the cells were collected and proteins were extracted, and the expression of TRIM28 and BRD7 proteins was detected by Western Blot.

[0039] (2) Vector or TRIM28 and Ub expression plasmids were co-transfected into breast cancer cells MDA-MB-231 and MCF7 to explore the effect of TRIM28 overexpression on the ubiquitination level of BRD7. After 48 h of transfection, the culture medium was replaced and MG132 (20 µM) was added for a further 4 h. Cell samples were collected and proteins were extracted. Co-IP was performed using BRD7 antibody, and then Western Blot experiments were performed using Ub antibody to detect the ubiquitination of BRD7. Similarly, control siNC or siTRIM28#1 or siTRIM28#2 and Ub expression plasmids were co-transfected into breast cancer cells MDA-MB-231 and MCF7, respectively. After 48 h of transfection, culture medium containing MG132 (20 µM) was added, and the cells were placed in an incubator for a further 4 h. Cells were collected and proteins were extracted. Co-immunoprecipitation (Co-IP) experiments were performed using BRD7 antibody to enrich proteins that bind to BRD7. Western Blot experiments were then performed to detect the ubiquitination level of BRD7 protein using Ub antibody.

[0040] 1.2 Experimental results:

[0041] In the two breast cancer cell lines without MG132, overexpression of TRIM28 significantly inhibited the protein expression level of BRD7, while in the MG132-treated group, the inhibitory effect of TRIM28 overexpression on the protein expression level of BRD7 was reversed ( Figure 1 A). Ubiquitination assay results showed that TRIM28 overexpression increased the polyubiquitination of BRD7 in MDA-MB-231 and MCF7 cells ( Figure 1 B). In addition, compared with the control siNC, silencing expression of TRIM28 significantly downregulated the ubiquitination level of BRD7 (Figure 1C). These results indicate that TRIM28 promotes protein degradation by increasing the ubiquitination modification of BRD7 protein.

[0042] Example 2 TRIM28 relies on its Coiled-Coil domain to recognize BRD7 and reduce BRD7 protein stability

[0043] 2.1 Experimental plan:

[0044] (1) Based on the protein domain of TRIM28, a series of Flag-TRIM28 domain deletion vectors were constructed, including TRIM28-△RING (RING domain deletion), TRIM28-△BB (B-BOX domain deletion), TRIM28-△CC (Coiled-Coil domain deletion), TRIM28-△PHD (PHD domain deletion) and TRIM28-△BROMO (BROMO domain deletion). The Flag-TRIM28 series truncated vectors and the HA-BRD7 full-length plasmid were co-transfected into the breast cancer cell line MCF7, and Co-IP experiments were performed using anti-HA to explore the domains of TRIM28 and BRD7 that interact with each other.

[0045] (2) An expression vector Flag-TRIM28-CC containing the Coiled-Coil domain of TRIM28 was constructed. Flag-TRIM28-CC and HA-BRD7 plasmids were co-transfected into the breast cancer cell line MCF7. Flag and HA antibodies were used for forward and reverse Co-IP experiments. Next, anti-Flag and anti-HA were used to detect whether TRIM28-CC and BRD7 interacted by Western Blot.

[0046] (3) TRIM28-CC plasmid was transfected into two breast cancer cell lines, MDA-MB-231 and MCF7. After 48 hours, the cells were harvested for protein extraction and the expression level of BRD7 protein was detected by Western Blot.

[0047] 2.2 Experimental results:

[0048] Co-IP and Western Blot results showed that there was an interaction between TRIM28 Coiled-Coil domain and BRD7 in breast cancer cells MCF ( Figure 2 A, B). Subsequently, a TRIM28-CC truncation was constructed and the interaction between the two was further confirmed by Co-IP ( Figure 2 C). Overexpression of TRIM28-CC truncations in two breast cancer cell lines, MDA-MB-231 and MCF7, significantly increased the expression level of BRD7 protein ( Figure 2 D), indicating that the Coiled-Coil domain of TRIM28 is very likely to be a target for peptide-based BRD7 protein activation.

[0049] Example 3 Design of α-helix-based blocking peptides based on the amino acid sequence of the minimal binding region of TRIM28 and BRD7

[0050] 3.1 Experimental plan:

[0051] α-helix is ​​the basic recognition element of protein-protein interaction. Therefore, α-helical peptides designed based on protein-protein interaction are ideal blockers of biomacromolecule interactions. According to the crystal structure of TRIM28 RBCC in the PDB database (PDB: 6QU1), it was found that there are three α-helical structures in the TRIM28 CC domain. According to the characteristics of the TRIM28 CC domain, two TRIM28 CC domain deletion vectors were constructed, namely TRIM28-△CC1 (deletion of 246-295aa) and TRIM28-△CC2 (deletion of 299-349aa); through Co-IP and Western Blot experiments, the region where TRIM28 binds to BRD7 was further shortened. The full-length HA-BRD7 expression plasmid and the full-length Flag-TRIM28 (i.e. Figure 3 C), Flag-TRIM28-△CC1 or △CC2 expression plasmids, Co-IP was performed using anti-Flag, and the level of BRD7 bound to Flag was detected by Western Blot to find the part of TRIM28-CC region that binds to BRD7. Subsequently, an α-helix blocking peptide was designed and synthesized based on the amino acid sequence of the minimum region where TRIM28 binds to BRD7.

[0052] 3.2 Experimental results:

[0053] The results of the Co-IP experiment showed that the TRIM28△CC1 truncation was still able to bind to and pull down the BRD7 protein, while the TRIM28△CC2 truncation lost its ability to bind to the BRD7 protein, supporting that the CC2 region (299-349aa) of TRIM28 is the structural basis for the interaction between TRIM28 and BRD7 protein ( Figure 3 AC). Based on the crystal structure characteristics of TRIM28 RBCC, we found that the CC2 region of TRIM28 contains two α-helical structures. Therefore, we designed and synthesized two interfering peptides based on its amino acid sequence ( Figure 3 D), 14 peptides and 12 peptides, respectively, were named TAB14 (sequence: LNKRGRVLVNDAQK) and TAB12 (sequence: IQKHQEHILRFA). In the future, it is necessary to further screen out the peptides that can block the binding of TRIM28 to BRD7 and stabilize the BRD7 protein.

[0054] Example 4 The peptide TAB12 derived from the coiled-coil region of TRIM28 competitively inhibits the binding of TRIM28 to BRD7 and increases the stability of BRD7 protein

[0055] 4.1 Experimental plan:

[0056] (1) When the cell density reached 80-90%, breast cancer cells MDA-MB-231 and MCF7 were treated with different concentrations of TAB14 and TAB12 (0µM, 5µM, 10µM, 20µM, 40µM), respectively. After 24 hours, the cells were collected and proteins were extracted. Western Blot experiments were performed to explore the effects of TAB14 and TAB12 treatment on the protein expression level of BRD7.

[0057] (2) TRIM28 and BRD7 plasmids were transfected into breast cancer MCF7 cells. 24 h after transfection, 20 µM TAB14 or TAB12 was added and cultured for another 24 h. Co-IP was performed using anti-Flag, and the effects of TAB14 and TAB12 treatment on the binding of TRIM28 and BRD7 were detected by Western Blot experiments.

[0058] (3) TRIM28, BRD7 and Ub plasmids were co-transfected into breast cancer MCF7 cells. After 24 hours, the culture medium was replaced with 20 μM TAB14 or TAB12 and cultured for another 24 hours. Then MG132 was added for 4 hours. Co-IP was performed using anti-BRD7, and the ubiquitination level of BRD7 was detected using anti-Ub antibody.

[0059] 4.2 Experimental results:

[0060] In two breast cancer cell lines, MDA-MB-231 and MCF7, TAB12 increased the expression level of BRD7 protein in a dose-dependent manner, while TAB14 had no significant effect on BRD7 protein expression ( Figure 4 A, B). In breast cancer MCF7, the results of Co-IP experiments showed that compared with the TAB14 treatment group, TAB12 treatment caused a significant weakening of the binding ability of TRIM28 and BRD7 protein ( Figure 4 C) Similarly, TAB12 treatment can significantly reverse the increase in BRD7 ubiquitination levels mediated by TRIM28 ( Figure 4 D). The above results indicate that TAB12 can inhibit the interaction between TRIM28 and BRD7 and the ubiquitination degradation of BRD7 mediated by TRIM28, thereby increasing the stability of BRD7 protein.

[0061] Example 5 The TAT-modified peptide TAT-TAB12 of the peptide drug TAB12 exerts anti-tumor effects in various tumors such as breast cancer and nasopharyngeal carcinoma

[0062] 5.1 Experimental plan:

[0063] We have screened TAB12 to increase the stability of BRD7 protein in breast cancer cells, so we fused TAB12 with the classic cell-penetrating peptide TAT (GRKKRRQRRRPP) to form TAT-TAB12, the sequence is: GRKKRRQRRRPP-IQKHQEHILRFA, to enhance its cell penetration. We then explored the anti-tumor effect of the peptide drug TAT-TAB12 through CCK8 experiments and clone formation experiments.

[0064] (1) CCK8 experiment: Breast cancer cells MDA-MB-231, MCF7 and nasopharyngeal carcinoma cells 5-8F and CNE2 were collected and the cell density was measured by blood cell counting. The cells were diluted and inoculated into 96-well plates at 3000 cells / well. Six time points were set at 0d, 1d, 2d, 3d, 4d and 5d, and five replicates were set for each time point. The 96-well plate was placed in a cell culture incubator for continued culture. After the cells adhered to the wall, MDA-MB-231, MCF7, CNE2 and 5-8F cells were treated with 80µM TAT-TAB12. The control group was the TAT treatment group. Discard the original culture medium in the 0 d well, add 100 μL of culture medium containing 10% CCK8 reagent, place it in a 37°C incubator for 2-3 h, and use a microplate reader to detect the absorbance value at 450 nm. This time point is 0 d, and the absorbance value of the cells is measured every other day (CCK8 incubation time remains the same). Analyze the absorbance values ​​at 6 time points and draw the cell proliferation curve using GraphPad.

[0065] (2) Clone formation experiment: Breast cancer cells (MDA-MB-231, MCF7) with good growth status were inoculated at a density of 1500 cells / well in a 6-well plate. TAT control group and TAT-TAB12 treatment group were set up respectively, with 3 replicates in each group. After small clones grew out, 80μM TAT and TAT-TAB12 were co-cultured with the cells for 3 days, and then the normal culture medium was replaced and continued to be cultured until more obvious clones were observed with the naked eye. After rinsing with 1×PBS 1-2 times, 4% paraformaldehyde was added to fix the cells for 30-60 min. After fixation, they were washed with 1×PBS 2-3 times, stained with crystal violet solution, stained for 10-15 minutes, and then the crystal violet was washed off. After drying, the cells were photographed. Finally, the number of clones formed in each group was analyzed and counted.

[0066] 5.2 Experimental results:

[0067] The results of CCK8 experiments showed that compared with the control TAT group, TAT-TAB12 treatment could significantly inhibit the proliferation of breast cancer cells (MDA-MB-231, MCF7) and nasopharyngeal carcinoma cells (CNE2, 5-8F). Figure 5 A). The clone formation experiment showed that TAT-TAB12 could inhibit the clone formation ability of breast cancer cells compared with the TAT group ( Figure 5 B). This indicates that TAT-TAB12 can significantly inhibit the growth of tumor cells in vitro and exhibits a good anti-tumor effect.

[0068] Example 6 TAT-TAB12 exerts anti-tumor effects in vivo by stabilizing BRD7

[0069] 6.1 Experimental plan:

[0070] The BALB / c female nude mice used to construct the transplanted tumor model were purchased from Hunan Slake Jingda Experimental Animal Co., Ltd., a total of 21 mice, aged 4-5 weeks, weighing 16 ± 2 g, and passed the animal quality inspection. Animal breeding and related operations were completed under specific pathogen-free (SPF) conditions at the Animal Experiment Center of Hunan Cancer Hospital. The following are the specific steps for constructing nude mouse transplanted tumors:

[0071] (1) Use breast cancer MCF7 cells that are in good growth condition, wash them 2-3 times with D-Hanks, digest them, and centrifuge them. Add physiological saline to wash the cells 2-3 times, and add 2 mL of physiological saline to resuspend the cells.

[0072] (2) Count the cells and dilute the cell density to 3×10 cells per 100 μL. 6 MCF7 cells were added to the cell suspension at a ratio of 2:1, and the matrix gel was pipetted and mixed for later use.

[0073] (3) Each nude mouse was subcutaneously inoculated with 150 μL of MCF7 cell suspension (3×10 6 The tumor growth of mice was observed regularly.

[0074] (4) Starting from the fourth day when a visible tumor appeared, the length (L) and width (W) of the tumor and the weight of the mouse were measured every 2 days. The tumor volume was calculated according to the formula (volume = L × W 2 / 2) Calculate tumor volume.

[0075] (5) When the tumor volume grows to 40-100 mm 3 The nude mice were randomly divided into three groups, each with 7 mice, namely saline treatment group, TAT treatment group and TAT-TAB12 treatment group. Tumor-bearing mice were injected with 100μL TAT, TAT-TAB12 (30mg / kg) or saline every two days, by intratumoral injection, for a total of 6 injections.

[0076] (6) On the 18th day, the nude mice were euthanized, and the changes in tumor volume were statistically analyzed and the tumor growth curve was drawn. The tumor-bearing mice were photographed and recorded, and then the tumor was removed, photographed and weighed.

[0077] 6.2 Experimental results:

[0078] The results of the nude mouse subcutaneous transplant tumor model showed that compared with the saline-treated group and the TAT-treated group, TAT-TAB12 treatment significantly inhibited the growth rate of mouse tumors and significantly reduced the tumor volume and weight ( Figure 6 CD). Body weights were not affected in all groups throughout the treatment period ( Figure 6 E). The above results indicate that TAT-TAB12 can inhibit the growth of tumors in vivo and play an anti-tumor role in breast cancer.

[0079] Example 7 The peptide drug TAT-TAB12 has no obvious toxic side effects on important organs of mice

[0080] 7.1 Experimental plan:

[0081] In the transplanted tumor model of Example 6, 3 mice were randomly selected from each group, and their important organs, including heart, liver, spleen, lung and kidney, were removed and fixed, paraffin-embedded, sectioned and HE-stained to observe the tissue status of each organ, analyze whether there were obvious abnormalities or lesions, and explore the in vivo toxicity of the polypeptide drug.

[0082] 7.2 Experimental results:

[0083] The results of histopathological examination of mouse organs (heart, liver, spleen, lung, and kidney) showed that no obvious abnormalities or lesions were found in the important organs of the saline-treated group, the TAT-treated group, and the TAT-TAB12-treated group ( Figure 7 ), indicating that the peptide drug TAT-TAB12 had no obvious toxicity to tumor-bearing mice.

Claims

1. A polypeptide targeting and stabilizing BRD7 tumor suppressor protein, characterized in that: The amino acid sequence of the polypeptide is: IQKHQEHILRFA.

2. Use of the polypeptide according to claim 1 in preparing a drug for treating solid tumors, characterized in that: The solid tumor is breast cancer or nasopharyngeal carcinoma.

3. The use according to claim 2, characterized in that: The polypeptide can target and inhibit the binding of TRIM28 to BRD7 protein, thereby increasing the stability of BRD7 protein.

4. The use according to claim 2, characterized in that: The breast cancer cells include at least one of MDA-MB-231 and MCF7; the nasopharyngeal cancer cells include at least one of CNE2 and 5-8F.

5. The use according to claim 2, characterized in that: The medicine also includes pharmaceutically acceptable excipients.

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