Bicyclic peptide

Abstract

The invention relates to a compound comprising a bicyclic peptide attached to a molecular scaffold. The bicyclic peptide may be functionalised by attachment of an imaging agent and / or therapeutic agent. Pharmaceutical compositions comprising the compound, and various uses thereof, are also described.

Description

FIELD OF THE INVENTION The present invention relates to bicyclic peptides and their use, particularly when comprised in radiopharmaceuticals including imaging methods and radiotherapy (e.g. in targeted radionuclide therapy). In particular, the disclosed bicyclic peptides and compounds comprising such are useful in targeting erythropoietin-producing hepatocellular receptor A2 (EphA2), a tyrosine kinase involved in cell-cell interactions known to be overexpressed in various tumors and associated with poor prognosis. The disclosed bicyclic peptides and compounds comprising them are useful in therapy, such as in cancer therapy, and diagnostics. BACKGROUND OF THE INVENTION Cyclic peptides are able to bind with high affinity and specificity to protein targets and hence are an attractive molecule class for the development of therapeutics. Several cyclic peptides are already successfully used in the clinic, as for example the antibacterial peptide vancomycin, the immunosuppressant drug cyclosporine and the anti-cancer drug octreotide (Driggers etal. (2008), Nat. Rev. Drug. Discov.7(7), 608-24). Good binding properties result from a relatively large interaction surface formed between the peptide and the target as well as the reduced conformational flexibility of the cyclic structures. Typically, macrocycles bind to surfaces of several hundred square angstrom, as for example the cyclic peptide CXCR4 antagonist CVX15 (400 A2 ; Wu etal. (2007), Science 330, 1066-71), a cyclic peptide with the Arg-Gly-Asp motif binding to integrin aVb3 (355 A2 ) (Xiong etal. (2002), Science 296(5565), 151-5) or the cyclic peptide inhibitor upain-1 binding to urokinase-type plasminogen activator (603 A2 ; Zhao et al. (2007), J. Struct. Biol.160(1), 1-10). Due to their cyclic configuration, peptide macrocycles are less flexible than linear peptides, leading to a smaller loss of entropy upon binding to targets and resulting in a higher binding affinity. The reduced flexibility also leads to locking target-specific conformations, increasing binding specificity compared to linear peptides. This effect has been exemplified by a potent and selective inhibitor of matrix metalloproteinase 8 (MMP-8) which lost its selectivity over other MMPs when its ring was opened (Chemey et al. (1998), J. Med. Chern.41(11), 1749- 51). The favourable binding properties achieved through macrocyclization are even more pronounced in multicyclic peptides having more than one peptide ring as for example in vancomycin, nisin and actinomycin. Different research teams have previously tethered polypeptides with cysteine residues to a synthetic molecular structure (Kemp and McNamara (1985), J. Org. Chern; Timmerman etal. (2005), ChemBioChem). Meloen and co-workers had used tris(bromomethyl)benzene and related molecules for rapid and quantitative cyclisation of multiple peptide loops onto synthetic scaffolds for structural mimicry of protein surfaces (Timmerman et al. (2005), ChemBioChem). Methods for the generation of candidate drug compounds wherein said compounds are generated by linking cysteine containing polypeptides to a molecular scaffold as for example l,T,l"-(l,3,5-triazinane-l,3,5-triyl)triprop-2-en-l-one (TATA) (Heinis et « / .(2014) Angewandte Chemie, International Edition 53(6) 1602-1606). Phage display-based combinatorial approaches have been developed to generate and screen large libraries of bicyclic peptides to targets of interest (Heinis et al. (2009), Nat. Chern. Biol. 5(7), 502-7 and WO 2009 / 098450). Briefly, combinatorial libraries of linear peptides containing three cysteine residues and two regions of six random amino acids (Cys-(Xaa)6-Cys-(Xaa)e- Cys) were displayed on phage and cyclised by covalently linking the cysteine side chains to a small molecule scaffold. Erythropoietin-producing hepatocellular receptor A2 (EphA2) is a transmembrane glycoprotein and part of the tyrosine kinase receptor family. It is involved in multiple cellular processes such as cell migration, adhesion, differentiation and death. In healthy adult tissues EphA2 expression is generally low, but the receptor has been found to be upregulated in numerous solid tumors. Moreover, expression of EphA2 has been associated with increased carcinogenesis, metastatic disease and poor clinical prognosis. SUMMARY OF THE INVENTION The present inventors have developed bicyclic peptides capable of binding strongly to EphA2. The bicyclic peptides can thus be used in the targeting of EphA2, with particular application (among others) in the field of cancer therapeutics and diagnostics, and particularly in targeted radionuclide therapy and imaging. One such bicyclic peptide developed by the present inventors is provided by the polypeptide of SEQ ID NO: 1 attached to a l,r,l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-l-one) (TATA) molecular scaffold. In the provided compounds, the cysteine (C) groups in SEQ ID NO: 1 are covalently bonded to the scaffold such that a plurality of peptide loops are subtended between the attachment points. The provided bicyclic peptide has a strong affinity for EphA2 and thus has numerous applications in the fields of pharmaceuticals and diagnostics, among others. The inventors have found that the provided bicyclic peptide’s strong affinity for EphA2 renders it highly appropriate for delivery of therapeutic and / or imaging agents to targets which are rich in EphA2 , such as cells which overexpress EphA2. The bicyclic peptide may be readily functionalised by attachment of agents such as imaging agents and therapeutic agents. In such a manner, the bicyclic peptide may be used to selectively deliver such agents to the target, to achieve selective therapeutic applications (e.g. selective cell-killing) or to facilitate imaging of EphA2 rich regions within a subject. Such agents may be attached directly to the provided bicyclic peptide or, more commonly, may be attached to the provided bicyclic peptide using a spacer. Accordingly, provided herein is a compound comprising a bicyclic peptide comprising a polypeptide of SEQ ID NO: 1: A[HArg]DC[HyP][Cba]VNPLCLHP[dD]W[HArg]C-AH2 (SEQ ID NO: 1) attached to a molecular scaffold; wherein - [HArg] is homoarginine, [HyP] is (2S,4R)-4-hydroxypyrrolidine-2-carboxylic acid, [Cba] is beta-cyclobutyl alanine, and [dD] is D-aspartic acid; - the molecular scaffold is l,r,l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-l-one) (TATA); and - each C group is a cysteine group comprising a sulfur atom which is covalently attached to the molecular scaffold; or a pharmaceutically acceptable salt thereof; wherein the bicyclic peptide further comprises an imaging agent and / or therapeutic agent. In some embodiments the imaging agent and / or therapeutic agent is attached to SEQ ID NO: 1. In some embodiments the bicyclic peptide is linked to the imaging agent or therapeutic agent at the N terminus of SEQ ID NO: 1. In this way, the bicyclic peptide can be functionalised by the imaging agent and / or the therapeutic agent. Also provided herein is a compound of formula I: [Formula (I)] wherein - Bicycle is a peptide ligand comprising a polypeptide of SEQ ID NO: 1: A[HArg]DC[HyP][Cba]VNPLCLHP[dD]W[HArg]C-W2 (SEQ ID NO: 1) attached to a molecular scaffold; wherein [HArg] is homoarginine, [HyP] is (2S,4R)-4-hydroxypyrrolidine-2-carboxylic acid, [Cba] is beta-cyclobutyl alanine, and [dD] is D-aspartic acid; the molecular scaffold is l,r,l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-l-one) (TATA); and each C group is a cysteine group comprising a sulfur atom which is covalently attached to the molecular scaffold; - Spacer is a bivalent moiety that connects the Bicycle moiety to the Z moiety; and - Z is an imaging and / or therapeutic agent or a ligand thereto. In some embodiments the compound further comprises one or more additional Z moieties such that the compound comprises two or more Z moieties. In some embodiments each Z is independently a chelator, a chromophore, a fluorescent moiety, a luminescent moiety and / or a phosphorescent moiety. In some embodiments, Z is a metal chelator. In some embodiments, Z is a polycarboxylic acid or a polyphosphonic acid, preferably an amino polycarboxylic acid. In some embodiments, Z is selected from DOTA, DTP A, NOTA and TETA. In some embodiments, Z is DOTA. In some embodiments Z is complexed to a radioisotope. In some embodiments the radioisotope is 225Ac, 227Ac, 241Am, 72As, 74As, 211At, 198Au, nB, 7Be, 212Bi, 213Bi, 75Br, 77Br, nC, 14C, 48Ca, 109Cd, 139Ce, 141Ce, 252Cf, 55Co, 57Co, 60Co, 51Cr, 130Cs, 131Cs, 137Cs, 61Cu, 62Cu, 64Cu, 67Cu, 165Dy, 152Eu, 155Eu, 18F, 55Fe, 59Fe, 64Ga, 67Ga, 68Ga, 153Gd, 68Ge, 122j 123j 124j 125j 131j 132j 111^ 114111^ llim^ 191mjr 192^         177j^u 51jjn 52jjn "Mo, 13N, 95Nb, 15O, 191Os, 1940s, 32P, 33P, 203Pb, 212Pb, 103Pd, 109Pd, 238Pu, 223Ra, 226Ra, 82Rb, 186Re, 188Re, 105Rh, 97Ru, 103Ru, 35S, 44Sc, 46Sc, 47Sc, 72Se, 75Se, 28Si, 145Sm, 153Sm, 117mSn, 85Sr, 89Sr, 90Sr, 178Ta, 179Ta, 182Ta, 149Tb, 96Tc, "mTc, 228Th, 229Th, 2O1T1, 170Tm, 171Tm, 188W, 127Xe, 133Xe, 86Y, 88Y, 90Y 91Y, 169Yb, 62Zn, 65Zn, 89Zr or 95Zr. In some embodiments the radioisotope is [64Cu], [67Ga], [68Ga], [177Lu], [90Y], [213Bi], [212Pb], [niIn] or [225Ac], In some embodiments the radioisotope is [68Ga], [177Lu], [inIn] or [225Ac], In some embodiments Spacer is a bidentate group having a length of from about 0.3 nm to about 300 nm. In some embodiments Spacer comprises one or more linking moieties, wherein each linking moiety is an amino acid or amino acid derivative, preferably a polypeptide; an alkylene group; an alkenylene group; an alkynylene group; a poly(alkyleneglycol), preferably poly(ethyleneglycol) or poly(propyleneglycol); an amide group; a carbamate group; an ether group; an ester group; a disulphide bond; a hydrazone group; a sulfonamide group; a thioether group; an amine group; or a cyclic group, preferably a 4-12 membered carbocyclic or heterocyclic group, a 5-12 membered heteroaryl group or a Ce-12 aryl group; wherein said alkylene, alkenylene, alkynylene, poly(alkyleneglycol), amine and cyclic group is each independently optionally substituted. In some embodiments Spacer comprises an oligopeptide moiety, preferably wherein said oligopeptide moiety comprises from about 2 to about 20 amino acids or amino acid analogs. In some embodiments Spacer comprises one or more sarcosine residues, one or more polyethyleneglycol (PEG) residues and / or one or more amide groups. In some embodiments Spacer is -[P-Ala]-[Sar]io-, wherein [P-Ala] is beta-alanine. In some embodiments the compound is Compound 1 as described in more detail herein. In some embodiments compound I is complexed to a radioisotope as described in more detail herein. Also provided is a pharmaceutical composition comprising a compound as provided herein, in combination with one or more pharmaceutically acceptable excipients. Also provided is a compound as provided herein, or a composition as provided herein, for use in a method of treatment or diagnosis of the human or animal body. Also provided is a compound as provided herein, or a composition as provided herein, for use in a method of treatment or diagnosis of cancer. Also provided is a method of imaging an EphA2-associated disorder, disease or condition in a subject, the method comprising administering to said subject a compound as provided herein, or a composition as provided herein. Also provided is a method of imaging a subject or part thereof or an organ of a subject, wherein the subject has or is suspected of having an EphA2-associated disorder, disease or condition, the method comprising administering to the subject a compound as provided herein, or a composition as provided herein and taking one or more images of said subject. In some embodiments the imaging is PET or SPECT imaging. Also provided is a compound as provided herein, or a composition as provided herein, for use in treating, preventing or suppressing an EphA2-associated disorder, disease or condition. Further provided is a method of treating, preventing or suppressing an EphA2-associated disorder, disease or condition in a subject comprising administering a compound as provided herein or a composition as provided herein to the subject. In some embodiments the disorder, disease or condition is a cancer. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1. SPR sensograms of Compound 1 binding to (A) human EphA2 (up to 100 nM) and (B) mouse EphA2 (up to 300 nM). See example 2 for details. Figure 2. Cell surface binding (B) and internalization (A) of 68Ga / 177Lu-labeled Compound 1. Specificity of internalization was determined by blocking with an excess of non-labeled compound (200 pM) and by incubation at 4 °C. Data expressed as % applied activity / 105 cells (n = 3). Figure 3. PET / MRI imaging of [68Ga] Ga-Compound 1. A) PET / MR Maximum Intensity Projection (MIP) 2 h p.i. of 150 pmol of [68Ga]Ga-Compound 1; B) Time-activity-curve (TAC) for organs of interest from 0 to 60 min p.i. of 150 pmol of [68Ga]Ga-Compound 1; C) Detailed TAC of tumor and muscle (background). Figure 4. Coronal slices of dynamic PET imaging. Imaging at various time points after injection of 150 pmol (8.98 MBq) [68Ga]Ga-Compound 1. H: heart; T: tumor; L: liver; K: kidney. Figure 5. Biodistribution of [177Lu]Lu-Compound 1. A) After injection of 150 pmol of peptide at 1, 2, 6 and 24 h p.i. B) Tumor-to-organ ratios at 1, 2, 6 and 24 h p.i. Data expressed as mean %injected dose(ID) / g tissue ± SD (n = 3) Figure 6. SPECT / CT imaging of [inIn]In-Compound 1. A) Maximum intensity projection at 1 h and B) 24 h p.i. of 230 pmol of ['11 In] In-Compound 1. C) Quantified data (%ID / g) of [niIn]In-Compound 1 SPECT imaging. Figure 7. HPLC UV-chromatogram (top - UV at 220 nm) and radio HPLC (bottom) of a ‘spiked’ sample of [68Ga]Ga-Compound 1. Radiolabeled compound was co-injected with 10 pL of 1 mg / mL solution of non-labeled Compound 1. Figure 8. Radio HPLC of [177Lu]Lu-Compound 1. Figure 9. Radio iTLC analysis of [68Ga] Ga-Compound 1 (A) and [177Lu]Lu-Compound 1 (right). Figure 10. A. Phosphor image of radio iTLC of ['11 In] In-Compound 1 reaction mixture before purification. Percentage at origin 91.8%. B. HPLC chromatogram of [inIn]In-Compound 1 post purification, purity = 100%. Figure 11. In vitro stability of [177Lu]Lu-Compound 1 in mouse plasma (grey line) and human plasma (black line). Determined over 72-h incubation by HPLC. Figure 12. Plasma concentration - time profile following intravenous administration of Compound 1 (1 mg / kg). Figure 13. SPR sensograms of Compound 1 against EphAl, EphA3, EphA4, EphA5, EphA6, EphA7. Figure 14. PET / MRI imaging of [68Ga] Ga-Compound 1. A) PET / MR Maximum Intensity Projection (MIP) 2 h p.i. of 150 pmol of [68Ga]Ga-Compound 1 in an HT1080 (left) and EphA2 negative MCF-7 xenograft (middle), and 2 h p.i. of 300 pmol of [68Ga]Ga-Compound 1 after 15 nmol of Compound 1 in an HT1080 xenograft (right). T: tumor, K: kidney, B: bladder; B) Time-activity-curve (TAC) for organs of interest from 0 to 60 min p.i. of 150 pmol of [68Ga]Ga-Compound 1 in the HT1080 xenograft; C) Detailed TACs of tumor (T) and muscle (M, background). Figure 15. A) Internalization and cell surface binding of [68Ga]Ga-Compound 1 in iPyMT 1312 cells. Specificity was determined by blocking with non-labeled compound in excess (200 pM) (n = 3). B) Western Blot of EphA2+ HT1080 cell protein extract and iPyMT 1312 cell protein extract. Figure 16. A) Exemplary PET coronal slices at 1 h p.i. of 150 pmol of [68Ga]Ga-Compound 1 overlaid with MR maximum intensity projections of longitudinal imaging in an MMTV-PyMT mouse, from week 4 to week 14. B) MR coronal and transversal plane images (left) of the week 14 mouse, PET / MR overlaid images of the same coronal and transversal plane slices (right). PET / MR Coronal slices at 1 h p.i. of a necrotic tumor of C) [68Ga]Ga-Compound 1 and D) 2-[18F]FDG showing necrotic tissue and differential uptake with the radiolabeled peptide. Figure 17. A) Biodistribution after PET / MR imaging at 1 h p.i. of 150 pmol of [68Ga]Ga-Compound 1 in MMTV-PyMT mice (n = 5). B) Biodistribution after PET / MR imaging at 1 h p.i. of 150 pmol of [68Ga]Ga-Compound 1 in wild-type mice (n = 4). DETAILED DESCRIPTION OF THE INVENTION The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. Any reference signs in the claims shall not be construed as limiting the scope. Of course, it is to be understood that not necessarily all aspects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may be taught or suggested herein. The invention, both as to organization and method of operation, together with features and advantages thereof, may best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings. The aspects and advantages of the invention will be apparent from and elucidated with reference to the embodiments) described hereinafter. Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. It should be appreciated that “embodiments” of the disclosure can be specifically combined together unless the context indicates otherwise. The specific combinations of all disclosed embodiments (unless implied otherwise by the context) are further disclosed embodiments of the claimed invention. All publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety. Where an indefinite or definite article is used when referring to a singular noun e.g. "a" or "an", "the", this includes a plural of that noun unless something else is specifically stated. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. The following terms or definitions are provided solely to aid in the understanding of the invention. Unless specifically defined herein, all terms used herein have the same meaning as they would to one skilled in the art of the present invention. Practitioners are particularly directed to Sambrook et al., Molecular Cloning: A Laboratory Manual, 4th ed., Cold Spring Harbor Press, Plainsview, New York (2012); and Ausubel et al., Current Protocols in Molecular Biology (Supplement 114), John Wiley & Sons, New York (2016), for definitions and terms of the art. The definitions provided herein should not be construed to have a scope less than understood by a person of ordinary skill in the art. "About" as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ± 20 % or ± 10 %, more preferably ± 5 %, even more preferably ± 1 %, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods. The term “amino acid” in the context of the present disclosure is used in its broadest sense and is meant to include organic compounds containing amine (NH2) and carboxyl (COOH) functional groups, along with a side chain (e.g., a R group) specific to each amino acid. In some embodiments, the amino acids refer to naturally occurring L a-amino acids or residues. The commonly used one and three letter abbreviations for naturally occurring amino acids are used herein: A=Ala; C=Cys; D=Asp; E=Glu; F=Phe; G=Gly; H=His; I=Ile; K=Lys; L=Leu; M=Met; N=Asn; P=Pro; Q=Gln; R=Arg; S=Ser; T=Thr; V=Val; W=Trp; and Y=Tyr (Lehninger, A. L., (1975) Biochemistry, 2d ed., pp. 71-92, Worth Publishers, New York). The general term “amino acid” further includes D- amino acids, retro-inverso amino acids as well as chemically modified amino acids such as amino acid analogues, naturally occurring amino acids that are not usually incorporated into proteins such as norleucine, and chemically synthesised compounds having properties known in the art to be characteristic of an amino acid, such as P-amino acids. For example, analogues or mimetics of phenylalanine or proline, which allow the same conformational restriction of the peptide compounds as do natural Phe or Pro, are included within the definition of amino acid. Other examples of amino acid analogues include [24MePro] (2,4-methanoproline), [HArg] (homoarginine), and [tBuAla] (tert-butyl alanine). Such analogues and mimetics are also referred to herein as "functional equivalents" of the respective amino acid. Other examples of amino acids are listed by Roberts and Vellaccio, The Peptides: Analysis, Synthesis, Biology, Gross and Meiehofer, eds., Vol. 5 p. 341, Academic Press, Inc., N.Y. 1983, which is incorporated herein by reference. The terms “polypeptide”, and “peptide” are interchangeably used herein to refer to a polymer of amino acid residues and to variants and synthetic analogues of the same. Thus, these terms apply to amino acid polymers in which one or more amino acid residues is a synthetic non-naturally occurring amino acid, such as a chemical analogue of a corresponding naturally occurring amino acid, as well as to naturally-occurring amino acid polymers. Polypeptides can be synthesized synthetically or biologically. Solid phase synthesis is well known to those skilled in the art; practitioners are referred to reference texts such as Peptide Synthesis: Methods and Protocols (Springer, 2020) and Peptide Synthesis and Applications (ed. Howl, Humana Press 2010). Biological synthesis includes expression from appropriate organisms. A peptide can be made using recombinant techniques, e.g., through the expression of a recombinant or synthetic polynucleotide. A recombinantly produced peptide it typically substantially free of culture medium, e.g., culture medium represents less than about 20 %, more preferably less than about 10 %, and most preferably less than about 5 % of the volume of the protein preparation. Peptides, especially biologically produced peptides, can undergo maturation or post-translational modification processes that may include, but are not limited to: glycosylation, proteolytic cleavage, lipidization, signal peptide cleavage, propeptide cleavage, phosphorylation, and such like. The term “protein” is used to describe a folded polypeptide having a secondary or tertiary structure. The protein may be composed of a single polypeptide, or may comprise multiple polypeptides that are assembled to form a multimer. The multimer may be a homooligomer, or a heterooligmer. The protein may be a naturally occurring, or wild type protein, or a modified, or non-naturally, occurring protein. The protein may, for example, differ from a wild type protein by the addition, substitution or deletion of one or more amino acids. A “variant” of a peptide or protein encompass peptides, oligopeptides, polypeptides, proteins and enzymes having amino acid substitutions, deletions and / or insertions relative to the unmodified or wild-type protein in question and having similar biological and functional activity as the unmodified protein from which they are derived. The term "amino acid identity" as used herein refers to the extent that sequences are identical on an amino acid-by-amino acid basis over a window of comparison. Thus, a "percentage of sequence identity" is calculated by comparing two optimally aligned sequences over the window of comparison, determining the number of positions at which the identical amino acid residue (e.g., Ala, Pro, Ser, Thr, Gly, Vai, Leu, He, Phe, Tyr, Trp, Lys, Arg, His, Asp, Glu, Asn, Gin, Cys and Met) occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison (i.e., the window size), and multiplying the result by 100 to yield the percentage of sequence identity. For all aspects and embodiments of the present invention, a “variant” typically has at least 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98% or 99% complete sequence identity to the amino acid sequence of the corresponding peptide. Sequence identity can also be to a fragment or portion of the full length polypeptide; e.g. to at least 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98% or 99% of the full length polypeptide. Conservative substitutions replace amino acids with other amino acids of similar chemical structure, similar chemical properties or similar side-chain volume. The amino acids introduced may have similar polarity, hydrophilicity, hydrophobicity, basicity, acidity, neutrality or charge to the amino acids they replace. Alternatively, the conservative substitution may introduce another amino acid that is aromatic or aliphatic in the place of a pre-existing aromatic or aliphatic amino acid. Conservative amino acid changes are well-known in the art and may be selected in accordance with the properties of the 20 main amino acids as defined in Table 1 below. Where amino acids have similar polarity, this can also be determined by reference to the hydropathy scale for amino acid side chains in Table 2. Table 1 - Chemical properties of amino acids Ala aliphatic, hydrophobic, neutral Met hydrophobic, neutral Cys polar, hydrophobic, neutral Asn polar, hydrophilic, neutral Asp polar, hydrophilic, charged (-) Pro hydrophobic, neutral Glu polar, hydrophilic, charged (-) Gin polar, hydrophilic, neutral Phe aromatic, hydrophobic, neutral Arg polar, hydrophilic, charged (+) Gly aliphatic, neutral Ser polar, hydrophilic, neutral His aromatic, polar, hydrophilic, charged (+) Thr polar, hydrophilic, neutral He aliphatic, hydrophobic, neutral Vai aliphatic, hydrophobic, neutral Lys polar, hydrophilic, charged(+) Trp aromatic, hydrophobic, neutral Leu aliphatic, hydrophobic, neutral Tyr aromatic, polar, hydrophobic Table 2 - Hydropathy scale Side Chain Hydropathy He 4.5 Vai 4.2 Leu 3.8 Phe 2.8 Cys 2.5 Met 1.9 Ala 1.8 Gly -0.4 Thr -0.7 Ser -0.8 Trp -0.9 Tyr -1.3 Pro -1.6 His -3.2 Glu -3.5 Gin -3.5 Asp -3.5 Asn -3.5 Lys -3.9 Arg -4.5 A peptide can also be chemically modified in any way. A modified peptide can be chemically modified by attachment of a molecule to one or more cysteines (cysteine linkage), attachment of a molecule to one or more lysines, attachment of a molecule to one 5 or more non-natural amino acids, enzyme modification of an epitope or modification of a terminus. Suitable methods for carrying out such modifications are well-known in the art. A peptide can be modified at the N and / or C terminus. For example, the N terminus can be acylated and / or the C terminus can be amidated. Specificity, in the context herein, typically refers to the ability of a ligand to bind or otherwise interact with its cognate target to the exclusion of entities which are dissimilar or partially similar to the target. Specificity is not intended to be synonymous with activity, affinity or avidity, and the potency of the action of a ligand on its target (such as, for example, binding affinity or level of inhibition) are not necessarily related to its specificity. Binding activity, as used herein, refers to quantitative binding measurements taken from binding assays, for example as described herein. Therefore, binding activity refers to the amount of peptide ligand which is bound at a given target concentration. Multispecificity is the ability to bind to two or more targets. Typically, binding peptides are capable of binding to a single target, such as an epitope in the case of an antibody, due to their conformational properties. However, peptides can be developed which can bind to two or more targets; dual specific antibodies, for example, as known in the art as referred to above. A peptide ligand may be capable of binding to two or more targets and therefore be multispecific (e.g. it may bind to two targets, and be dual specific). Binding in this way may be independent, such that the binding sites for targets on the peptide are not structurally hindered by binding other targets; however more generally binding of one target may at least partially impede the binding of another. A dual specific ligand may be specific for two targets individually, and interact with each in a specific manner. For example, in a bicyclic peptide a first loop may bind to a first target, and a second loop to a second target. A ligand with specificity which encompasses two related targets may interact with an epitope of the targets which is common to both. A ligand with activity in respect of, for example, a target and an orthologue, could be a bispecific ligand. Alternatively the ligand could be not bispecific and have a less precise specificity such that it binds both the target and one or more orthologues. The loop length in the bicyclic peptide may be decisive in providing a tailored binding surface such that good target and orthologue cross-reactivity can be obtained, while maintaining high selectivity towards less related homologues. A target is a molecule or part thereof to which the peptide ligands bind or otherwise interact with. Although binding is seen as a prerequisite to activity of most kinds, and may be an activity in itself, other activities are envisaged. Thus, the compounds and methods disclosed herein do not require the measurement of binding directly or indirectly. As used herein, a Ci-io alkyl group is a linear or branched alkyl group containing from 1 to 10 carbon atoms. A Ci-io alkyl group is often a Ci-6 alkyl group or a Ci-4 alkyl group, such as a C1-3 alkyl group. Examples of C1-4 alkyl groups include methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, and tert-butyl. A C1-3 alkyl group is typically a C1-2 alkyl group, such as methyl or ethyl, typically methyl. For the avoidance of doubt, where two alkyl groups are present, the alkyl groups may be the same or different. As used herein, an alkoxy group is typically a said alkyl group attached to an oxygen atom. Thus, a C1-10 alkoxy group is a C1-10 alkyl group attached to an oxygen atom. A Ci-10 alkoxy group is often a C1-6 alkoxy group or a C1-4 alkoxy group, such as a C1-3 alkoxy group. Examples of C1-4 alkyl groups include methoxy, ethoxy, n-propyoxy, isopropoxy, n-butoxy, sec-butoxy, and tert-butoxy. Typically, a C1-3 to C3 alkoxy group is a C1-2 alkoxy group such as a methoxy or ethoxy group. For the avoidance of doubt, where two alkoxy groups are present, the alkoxy groups may be the same or different. As used herein, a C2-10 alkenyl group is a linear or branched alkenyl group containing from 2 to 4 carbon atoms and having one or more, e.g. one or two, typically one double bonds. Typically a C2-10 alkenyl group is C2-6 alkenyl group or a C2-4 alkenyl groups such as a C2-3 alkenyl group. Examples of C2-4 alkenyl groups include ethenyl, propenyl and butenyl. For the avoidance of doubt, where two alkenyl groups are present, the alkenyl groups may be the same or different. As used herein, a C2-10 alkynyl group is a linear or branched alkynyl group containing from 2 to 4 carbon atoms and having one or more, e.g. one or two, typically one triple bonds. Typically a C2-10 alkynyl group is C2-6 alkynyl group or a C2-4 alkynyl groups such as a C2-3 alkynyl group. Examples of C2-4 alkynyl groups include ethynyl, propynyl and butynyl. For the avoidance of doubt, where two alkynyl groups are present, the alkenyl groups may be the same or different. Unless otherwise stated, an alkyl, alkoxy, alkenyl or alkynyl group as defined herein may be unsubstituted or substituted as provided herein. The substituents on a substituted alkyl, alkenyl, alkynyl or alkoxy group are typically themselves unsubstituted. Where more than one substituent is present, these may be the same or different. As used herein, a halogen is typically chlorine, fluorine, bromine or iodine and is preferably chlorine, bromine or fluorine, especially chorine or fluorine. A 4- to 12- membered carbocyclic group is a cyclic hydrocarbon containing from 4 to 12 carbon atoms. A carbocyclic group may be saturated or partially unsaturated, but is typically saturated. A 4- to 12- membered carbocyclic group may be a fused bicyclic group or a spiro bicyclic group, as defined herein. A 4- to 12- membered carbocyclic group is typically a 5- to 10- membered carbocyclic group such as a 5-6 membered carbocyclic group; or a 4- to 6-membered, preferably 5- or 6- membered carbocyclic group. Examples of 4- to 6- membered saturated carbocyclic groups include cyclobutyl, cyclopentyl and cyclohexyl groups. A 4- to 12- membered heterocyclic group is a cyclic group containing from 4 to 12 atoms selected from C, O, N and S in the ring, including at least one heteroatom, and typically one or two heteroatoms. The heteroatom or heteroatoms are typically selected from O, N, and S, most typically from O and N, especially N. A heterocyclic group may be saturated or partially unsaturated, but is typically saturated. A 4- to 12- membered heterocyclic group may be a fused bicyclic group or a spiro bicyclic group, as defined herein. A 4- to 12- membered heterocyclic group is typically a 5- to 10- membered heterocyclic group such as a 5-6 membered heterocyclic group. References herein to heterocyclic group(s) include quatemised derivatives thereof, as defined herein. Preferred nitrogen-containing heterocyclic groups include azetidine, morpholine, 1,4-oxazepane, octahydropyrrolo[3,4-c]pyrrole, piperazine, piperidine, and pyrrolidine, including quatemised derivatives thereof, as defined herein. As used herein, a Ce-12 aryl group is a substituted or unsubstituted, monocyclic or fused polycyclic aromatic group containing from 6 to 12 carbon atoms in the ring portion. Examples include monocyclic groups such as phenyl and fused bicyclic groups such as naphthyl and indenyl. Phenyl (benzene) is preferred. As used herein, a 5- to 12- membered heteroaryl group is a substituted or unsubstituted monocyclic or fused polycyclic aromatic group containing from 5 to 10 atoms in the ring portion, including at least one heteroatom, for example 1, 2 or 3 heteroatoms, typically selected from O, S and N. A 4- to 12- membered heteroaryl group is typically a 5- to 10- membered heteroaryl group such as a 5-6 membered heteroaryl group. References herein to heteroaryl group(s) include quatemised derivatives thereof, as defined herein. Preferred nitrogen-containing heteroaryl groups include imidazole, pyridine, pyrimidine and pyrazine, including quatemised derivatives thereof, as defined herein. As used herein, a fused bicyclic group is a group comprising two cyclic moieties sharing a common bond between two atoms. A spiro bicyclic group is a group comprising two cyclic moieties sharing a common atom. A carbocyclic, heterocyclic, aryl or heteroaryl group may be unsubstituted or substituted as described herein. The substituents on a substituted carbocyclic, heterocyclic, aryl or heteroaryl group are typically themselves unsubstituted, unless otherwise stated. A compound may comprise heterocyclic or heteroaryl groups comprising at least one nitrogen atom. In such compounds, said nitrogen atom(s) are independently selected from secondary, tertiary and quaternary nitrogen atom(s). As used herein, a quaternised derivative of a moiety such as a cyclic moiety is formed by bonding an additional alkyl group to a nitrogen atom in the moiety such that the valency of the said nitrogen atom increases from 3 to 4 and the nitrogen atom is positively charged. The stereochemistry of a compound as provided herein is typically as depicted. Amino acids are typically L-amino acids unless implied otherwise by the context. Typically, an agent or composition described herein contains at least 50%, preferably at least 60, 75%, 90% or 95% of a compound provided herein which is enantiomerically or diasteriomerically pure. Thus, the compound is preferably substantially optically pure. Salt forms It will be appreciated that salt forms are provided herein, and references to peptides (e.g. bicyclic peptides) and compounds comprising them include the salt forms of said compounds. Salt forms can be synthesized from the parent compound that contains a basic or acidic moiety by conventional chemical methods such as methods described in Pharmaceutical Salts: Properties, Selection, and Use, P. Heinrich Stahl (Editor), Camille G. Wermuth (Editor), ISBN: 3-90639-026-8, Hardcover, 388 pages, August 2002. Generally, such salts can be prepared by reacting the free acid or base forms of these compounds with the appropriate base or acid in water or in an organic solvent, or in a mixture of the two. Acid addition salts (mono- or di-salts) may be formed with a wide variety of acids, both inorganic and organic. Examples of acid addition salts include mono- or di-salts formed with an acid selected from the group consisting of acetic, 2,2-dichloroacetic, trifluoroacetic, adipic, alginic, ascorbic (e.g. L-ascorbic), L-aspartic, benzenesulfonic, benzoic, 4-acetamidobenzoic, butanoic, (+) camphoric, camphor-sulfonic, (+)-(1 S)- camphor-1 O-sulfonic, capric, caproic, caprylic, cinnamic, citric, cyclamic, dodecylsulfuric, ethane-1,2-disulfonic, ethanesulfonic, 2- hydroxy ethanesulfonic, formic, fumaric, galactaric, gentisic, glucoheptonic, D-gluconic, glucuronic (e.g. D-glucuronic), glutamic (e.g. L-glutamic), a-oxoglutaric, glycolic, hippuric, hydrohalic acids (e.g. hydrobromic, hydrochloric, hydriodic), isethionic, lactic (e.g. (+)-L-lactic, (±)-DL-lactic), lactobionic, maleic, malic, (-)-L-malic, malonic, (±)-DL-mandelic, methanesulfonic, naphthalene-2-sulfonic, naphthalene-l,5-disulfonic, l-hydroxy-2-naphthoic, nicotinic, nitric, oleic, orotic, oxalic, palmitic, pamoic, phosphoric, propionic, pyruvic, L-pyroglutamic, salicylic, 4-amino-salicylic, sebacic, stearic, succinic, sulfuric, tannic, (+)-L-tartaric, thiocyanic, p-toluenesulfonic, undecylenic and valeric acids, as well as acylated amino acids and cation exchange resins. Pharmaceutically acceptable acids include both inorganic acids such as hydrochloric, sulphuric, phosphoric, diphosphoric, hydrobromic or nitric acid and organic acids such as oxalic, citric, fumaric, maleic, malic, ascorbic, succinic, tartaric, palmitic, benzoic, acetic, triphenyl acetic, methanesulphonic, ethanesulphonic, l-hydroxy-2-naphthenoic, isethionic, benzenesulphonic or / ?-toluenesulphonic acid. Pharmaceutically acceptable bases include alkali metal (e.g. sodium or potassium), alkali earth metal (e.g. calcium or magnesium) and zinc bases, for example hydroxides, carbonates, and bicarbonates, and organic bases such as alkyl amines, aralkyl (i.e. aryl-substituted alkyl; e.g. benzyl) amines and heterocyclic amines. One particular group of salts consists of salts formed from acetic, hydrochloric, hydriodic, phosphoric, nitric, sulfuric, citric, lactic, succinic, maleic, malic, isethionic, fumaric, benzenesulfonic, toluenesulfonic, sulfuric, methanesulfonic (mesylate), ethanesulfonic, naphthalenesulfonic, valeric, propanoic, butanoic, malonic, glucuronic and lactobionic acids. One particular salt is the hydrochloride salt. Another particular salt is the acetate salt. A yet further particular salt is the trifluoroacetate salt. If the compound is anionic, or has a functional group which may be anionic (e.g., -COOH may be -COO'), then a salt may be formed with an organic or inorganic base, generating a suitable cation. Examples of suitable inorganic cations include, but are not limited to, alkali metal ions such as Li+, Na+ and K+, alkaline earth metal cations such as Ca2+ and Mg2+, and other cations such as Al3+ or Zn+. Examples of suitable organic cations include, but are not limited to, ammonium ion (i.e., NELT) and substituted ammonium ions (e.g., NEER4, NH2R2+, NHR3+, NFV; for example R may be alkyl e.g. C1-3 alkyl). Examples of some suitable substituted ammonium ions are those derived from: methylamine, ethylamine, diethylamine, propylamine, dicyclohexylamine, triethylamine, butylamine, ethylenediamine, ethanolamine, diethanolamine, piperazine, benzylamine, phenylbenzylamine, choline, meglumine, and tromethamine, as well as amino acids, such as lysine and arginine. An example of a common quaternary ammonium ion is N(CHs)4+. Where the compounds provided herein contain an amine function, these may form quaternary ammonium salts, for example by reaction with an alkylating agent according to methods well known to the skilled person. Such quaternary ammonium compounds are also provided herein. In some embodiments (e.g. where the compounds provided herein contain a positively charged nitrogen atom), the compound may exist as a zwitterion. Such compounds may also be provided in the form of a pharmaceutically acceptable salt. Suitable salts include those formed with pharmaceutically acceptable acids, which can provide a proton to a COO' group, and a counter-ion to balance the positive charge on a quaternary nitrogen atom. Suitable pharmaceutically acceptable acids include hydrochloric acid, sulphonic acids including methanesulphonic acid and toluene sulphonic acid, ascorbic acid and citric acid. Hydrochloric acid and sulphonic acids are preferred, in particular hydrochloric acid. Alternatively, zwitterions can be combined with pharmaceutically acceptable bases as mentioned above, for example, alkali metal (e.g. sodium or potassium) and alkali earth metal (e.g. calcium or magnesium) hydroxides. Bicyclic peptide The invention relates to a polypeptide of SEQ ID NO: 1 and to compounds comprising such a polypeptide, as well as uses thereof. SEQ ID NO: 1 has the sequence A[HArg]DC[HyP][Cba]VNPLCLHP[dD]W[HArg]C-W2 The amino acid sequence in SEQ ID NO: 1 should be understood as relating to the sequence of the peptide in the direction from the N-terminus to the C-terminus. In SEQ ID NO: 1, the C terminal cysteine residue is amidated; i.e. the C terminal free carboxylic acid group is amidated to modify the -C(O)OH moiety to form a -C(O)NH2 moiety. This is indicated by the notation -NH2 and can also be denoted using the notation -[CONH2] or -[CONH2]. In other words, SEQ ID NO: 1 can also be written as: A[HArg]DC[HyP] [Cba]VNPLCLHP[dD]W[HArg]C[CONH2]. In SEQ ID NO: 1, non-coding amino acids are shown in square brackets. In SEQ ID NO: 1, [HArg] is homoarginine. Homoarginine (HArg) has the structure: In SEQ ID NO: 1, [HyP] is (2S,4R)-4-hydroxypyrrolidine-2-carboxylic acid. (2S,4R)-4-hydroxypyrrolidine-2-carboxylic acid (HyP) has the structure: In SEQ ID NO: 1, [Cba] is beta-cyclobutyl alanine. Beta-cyclobutyl alanine (Cba) has the structure: In SEQ ID NO: 1, [dD] is D-aspartic acid. D-aspartic acid (dD) has the structure: Those skilled in the art will appreciate that modifications can be made to the sequence of SEQ ID NO: 1. Exemplary modifications are described herein. In some embodiments a modified form of SEQ ID NO: 1 contains one or more amino acid modifications (e.g. amino acid substitutions). The one or more amino acid substitutions may relate to one or more coding amino acids and / or one or more non-coding amino acids in SEQ ID NO: 1. In some embodiments, a modified form of SEQ ID NO: 1 involves replacement of one, two or three of the cysteine residues with a reactive group (RG). The reactive group may be any suitable reactive group which is capable of forming covalent bonds to the molecular scaffold. Where a peptide sequence contains more than one reactive group, each reactive group may be the same or different. In one embodiment, a modified form of SEQ ID NO: 1 involves replacement of the central cysteine with a reactive group as defined herein. In some embodiments, the reactive group is an amino acid that comprises a reactive side chain. In some embodiments, said reactive groups are selected from cysteine, d-cysteine (dC), cysteamine (Cysam), homocysteine (hCys, (S)-2-Amino-4-sulfanylbutanoic acid), pCys ((R)-3-amino-3-mercaptopropanoic acid), penicillamine (Pen, (R)-2-amino-3-mercapto-3-methylbutanoic acid), Dap ((S)-2,3-diaminopropanoic acid) and N-alkyl-Dap (e.g. N-methyl-Dap, (S)-2-amino-3-(methylamino)propanoic acid). In some embodiments said reactive groups are isoelectronic and / or isosteric with cysteine. In one embodiment, said reactive groups are cysteine residues. A compound comprising a polypeptide having the amino acid sequence of SEQ ID NO: 1 can be provided in the form of a salt such as a pharmaceutically acceptable salt. Pharmaceutically acceptable salts are described herein. For avoidance of doubt, a compound comprising a polypeptide having the amino acid sequence of SEQ ID NO: 1 can be a zwitterion (also known as an “inner salt”). In compounds provided herein, the polypeptide of SEQ ID NO: 1 is attached to a molecular scaffold. The molecular scaffold is any molecule which is able to connect the polypeptide at multiple points to impart one or more structural features to the polypeptide. Preferably, the molecular scaffold comprises at least three attachment points for the polypeptide, referred to as scaffold reactive groups. These groups are typically capable of reacting with the cysteine residues on the polypeptide to form a covalent bond. In some embodiments the scaffold reactive groups form covalent thioether linkages with the polypeptide. Molecular scaffolds are described in, for example, WO 2009 / 098450 and references cited therein, particularly WO 2004 / 077062 and WO 2006 / 078161. In compounds provided herein, the molecular scaffold is l,r,l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-l-one) (TATA). Those skilled in the art will appreciate that the scaffold can also be considered as a group (e.g. a radical) to which the polypeptide is bonded; for example a TATA scaffold may be considered as l,l',l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-l-on-3-yl). In other words, in some embodiments the scaffold has the form: wherein s is the point of attachment to the C residues of SEQ ID NO: 1. The attachment of SEQ ID NO: 1 typically comprises one or more covalent bonds to the TATA scaffold. The attachment of SEQ ID NO: 1 typically comprises one or more covalent bonds between the cysteine residues in SEQ ID NO: 1 and the TATA scaffold. Typically, each cysteine residue comprises a sulfur atom (e.g. comprises a thiol or thiolate side chain) and a covalent attachment (e.g. a covalent bond) is formed between the sulfur atom and the TATA scaffold. In some embodiments each C group in SEQ ID NO: 1 is a cysteine group comprising a sulfur atom which is covalently attached to the molecular scaffold. In some embodiments the attachment of the polypeptide of SEQ ID NO: 1 to the scaffold forms a plurality of polypeptide loops on the molecular scaffold. In some embodiments the attachment of the polypeptide of SEQ ID NO: 1 to the scaffold forms two polypeptide loops on the molecular scaffold. In some embodiments the polypeptide of SEQ ID NO: 1 is covalently bound to the molecular scaffold such that a plurality (e.g. two) peptide loops are subtended between attachment points to the scaffold Any suitable precursor can be used in synthesizing the scaffold. In some embodiments the precursor comprises one or more groups selected from amines, thiols, alcohols, ketones, aldehydes, nitriles, carboxylic acids, esters, alkenes, alkynes, azides, anhydrides, succinimides, maleimides, alkyl halides and acyl halides. In some embodiments the polypeptide of SEQ ID NO: 1 is attached to the TATA scaffold by reaction of the polypeptide of SEQ ID NO: 1 with l,3,5-triacryloylhexahydro-l,3,5-tri azine. The bicyclic peptide moiety provided herein may be referred to as a “peptide ligand”. The term “peptide ligand” as used herein thus refers to a polypeptide covalently bound to a molecular scaffold. In particular, the bicyclic peptide moiety has a high affinity for erythropoietin-producing hepatocellular receptor A2 (EphA2) and thus may be described as a peptide ligand for EphA2. Affinity for a target such as EphA2 may be determined by affinity maturation studies. The examples describe experiments using SPR to determine the binding affinity of compounds of the invention for EphA2. In one embodiment, the bicyclic peptide of the invention is specific for mammalian EphA2. In one embodiment, the bicyclic peptide of the invention is specific for human EphA2. In a further embodiment, the bicyclic peptide of the invention is specific for mouse EphA2. In a yet further embodiment, the bicyclic peptide of the invention is specific for human and mouse EphA2. In a yet further embodiment, the bicyclic peptide of the invention is specific for human, mouse and dog EphA2. In some embodiments the bicyclic peptide moiety of the compounds provided herein is cross-reactive with murine, dog, cynomolgus and human EphA2. In some embodiments the bicyclic peptide moiety is selective for EphA2 over other Eph receptor tyrosine kinases, such as EphAl , EphA3, EphA4, EphA5, EphA6, EphA7 and EphBl and factor XIIA, carbonic anhydrase 9 and CD38. In some embodiments, the bicyclic peptide moiety is selective for human EphA2 over human EphAl, EphA3, EphA4, EphA5, EphA6, and EphA7. In one embodiment, the bicyclic peptide moiety is at least 10 fold, preferably at least 100 fold, and more preferably at least 1000 fold, more selective for human EphA2 as compared to one or more of, and preferably all of, human EphAl, EphA3, EphA4, EphA5, EphA6, and EphA7. In some embodiments, the bicyclic peptide moiety has a binding affinity to EphA2 of less than about IpM, preferably less than 100 nM, more preferably less than 10 nM and yet further preferably less than 5 nM. In some embodiments, the bicyclic peptide moiety has a binding affinity to human EphA2 of less than about IpM, preferably less than 100 nM, more preferably less than 10 nM and yet further preferably less than 5 nM. In some embodiments, the bicyclic peptide moiety has a binding affinity to human EphAl, EphA3, EphA4, EphA5, EphA6, and EphA7 of greater than 100 nM, preferably greater than 1 pM, and more preferably greater than 5pM. In some embodiments, the bicyclic peptide moiety has a binding affinity to EphA2 of less than about IpM, preferably less than 100 nM, more preferably less than 10 nM and yet further preferably less than 5 nM; and the bicyclic peptide moiety has a binding affinity to human EphAl, EphA3, EphA4, EphA5, EphA6, and EphA7 of greater than 100 nM, preferably greater than 1 pM, and more preferably greater than 5pM. In one embodiment, the bicyclic peptide moiety does not bind to human EphAl, EphA3, EphA4, EphA5, EphA6, and EphA7. Binding affinity may be expressed as a Kd value, as measured by SPR assays as described in the examples. The selectivity of the compounds provided herein for EphA2 is advantageous. It allows specific delivery of the compounds provided herein to targets (e.g. one or more regions of a subject’s body; one or more organs of a subject; one or more surface regions of an organ; one or more cellular targets such as cell masses (including tumors); cell clusters etc). In particular, it allows specific delivery of the compounds provided herein to targets that are rich in (e.g. that overexpress) EphA2. In a particular aspect, the invention describes bicyclic peptide ligands useful for selectively delivering the linked detectable moiety to cancer cells. Spacer In some embodiments the bicyclic peptide of the compounds provided herein is functionalised by attachment of one or more imaging agents and / or therapeutic agents to SEQ ID NO: 1. Accordingly in some embodiments the bicyclic peptide further comprises one or more imaging agents and / or therapeutic agents. In some embodiments the bicyclic peptide comprises an imaging agent and / or a therapeutic agent. An imaging and / or therapeutic agent can be attached to the bicyclic peptide at any suitable position. In some embodiments an imaging and / or therapeutic agent is attached to the N terminus and / or the C terminus of SEQ ID NO: 1. In some embodiments an imaging and / or therapeutic agent is attached to the N terminus or the C terminus of SEQ ID NO: 1. In some embodiments an imaging and / or therapeutic agent is attached to SEQ ID NO: 1 at one of the amino acids of SEQ ID NO: 1, such as for example, by attachment to a side chain of an amino acid of SEQ ID NO: 1 or to the polypeptide backbone of SEQ ID NO: 1. In some embodiments an imaging and / or therapeutic agent is attached to SEQ ID NO: 1 by being linked to SEQ ID NO: 1, e.g. via a spacer. In some embodiments the or each imaging agent or therapeutic agent is attached to the N terminus of SEQ ID NO: 1. In some embodiments the or each imaging agent or therapeutic agent is linked to the N terminus of SEQ ID NO: 1. In some embodiments the or each imaging agent or therapeutic agent is linked to the N terminus of SEQ ID NO: 1 via a spacer. Accordingly, in some embodiments the compound provided herein is of the formula (I): [Formula (I)] wherein Bicycle is a peptide ligand comprising a polypeptide of SEQ ID NO: 1 attached to 5 a molecular scaffold as described herein; Spacer is a bivalent moiety that connects the Bicycle moiety to the Z moiety; and Z is an imaging and / or therapeutic agent or a ligand thereto. In some embodiments, therefore, Bicycle is 10 wherein s is the point of attachment to the imaging agent and / or therapeutic agent. The attachment may be via a spacer moiety as described herein; in such embodiments is typically the point of attachment to the Spacer. In some embodiments, Spacer is a bidentate group having a length of from about 0.3 nm to about 300 nm. In some embodiments Spacer has a length of from about 0.5 nm 15 to about 200 nm, such as from about 1 nm to about 100 nm, e.g. from about 1.5 nm to about 50 nm, e.g. from about 2 nm to about 20 nm, such as from about 3 nm to about 10 nm, e.g. about 3.5 to about 5 nm, such as about 4 nm. In some embodiments the length is the persistence length. In some embodiments the length is determined when the compound of Formula (I) is in aqueous solution under physiological conditions, e.g. phosphate buffered saline, pH 7.4 at 37 °C). In some embodiments the persistence length can be determined using atomic force microscopy. In some embodiments, Spacer comprises or consists of one or more linking moieties, wherein each linking moieties is an amino acid or amino acid derivative, preferably a polypeptide; an alkylene group; an alkenylene group; an alkynylene group; a poly(alkyleneglycol), preferably poly(ethyleneglycol) or poly(propyleneglycol); an amide group; a carbamate group; an ether group; an ester group; a disulphide bond; a hydrazone group; a sulfonamide group; a thioether group; an amine group; or a cyclic group, preferably a 4-12 membered carbocyclic or heterocyclic group, a 5-12 membered heteroaryl group or a Ce-12 aryl group; wherein said alkylene, alkenylene, alkynylene, poly(alkyleneglycol), amine and cyclic group is each independently optionally substituted. In some embodiments Spacer comprises or consists of one or more amino acids or amino acid derivatives (e.g. one or more polypeptides), one or more glycol and / or polyglycol moieties, one or more alkylene and / or alkenylene moieties, one or more amide moieties, and / or one or more triazolylene moieties. In some embodiments Spacer comprises or consists of one or more amino acids or amino acid derivatives (e.g. one or more polypeptides), one or more glycol and / or polyglycol moieties, and / or one or more amide moieties. In some embodiments Spacer comprises or consists of one or more amino acids or amino acid derivatives (e.g. one or more polypeptides) and / or one or more glycol and / or polyglycol moieties. In some embodiments when Spacer comprises an alkylene group, said alkylene group is a Ci-io alkylene group. Exemplary alkylene groups are described in more detail herein. In some embodiments when Spacer comprises an alkenylene group, said alkenylene group is a C2-10 alkenylene group. Exemplary alkenylene groups are described in more detail herein. In some embodiments when Spacer comprises an alkynylene group, said alkynylene group is a C2-10 alkynylene group. Exemplary alkynylene groups are described in more detail herein. In some embodiments when Spacer comprises a poly(alkyleneglycol), the poly(alkyleneglycol) is poly(ethyleneglycol) (PEG) or poly(propyleneglycol) (PPG). In some embodiments Spacer comprises a poly(alkyleneglycol) having an average molecular weight (e.g. a number average molecular weight) of from about 100 to about 5000, e.g. from about 200 to about 1000, such as from about 300 to about 600. In some embodiments when Spacer comprises a poly(alkyleneglycol), Spacer comprises (alkyleneglycol) is (PEG)n, wherein n represents the number of contiguous ethyleneglycol units in said PEG. In some embodiments n is an integer from about 2 to about 50, such as about 3 to about 30, e.g. about 4 to about 10. In some embodiments when Spacer comprises a poly(alkyleneglycol), Spacer comprises (alkyleneglycol) is (PPG)m, wherein m represents the number of contiguous propyleneglycol units in said PPG. In some embodiments m is an integer from about 2 to about 50, such as about 3 to about 30, e.g. about 4 to about 10. In some embodiments when Spacer comprises an amide group, said amide group is of formula -NR10C(O)- or -C(O)NR10-. In some embodiments when Spacer comprises a carbamate group, said carbamate group is of formula -NR10C(O)NR10-. In some embodiments when Spacer comprises an ether group the ether group is of formula -O-. In some embodiments when Spacer comprises an ester group the ester group is of formula -C(O)O- or -OC(O)-. In some embodiments when Spacer comprises a disulphide bond the disulphide bond is -S-S-; e.g. a disulphide bond may be formed between two cysteine amino acids. In some embodiments when Spacer comprises a hydrazone group, the hydrazone group is of formula -C(N=NR10)-. In some embodiments when Spacer comprises a sulfonamide group, the sulphonamide group is of form -SO2-NR10-. In some embodiments when Spacer comprises a thioether group, the thioether group is of form -S-. In some embodiments when Spacer comprises an amine group, the amine group is of form -NR10- or -N+(R10)2-. In some embodiments when Spacer comprises a cyclic group, the cyclic group is a cyclic group as described in more detail herein. In some embodiments the cyclic group is a 4-12 membered carbocyclic or heterocyclic group, a 5-12 membered heteroaryl group or a C6-12 aryl group. In some embodiments when the cyclic group is a carbocyclic or heterocyclic group, the cyclic group is a 5-10 membered carbocyclic or heterocyclic group such as a 5-6 membered carbocyclic or heterocyclic group. In some embodiments when the cyclic group is a 5-12 membered heteroaryl group, the cyclic group is a 5-10 membered heteroaryl group, such as a 5-6 membered heteroaryl group. In some embodiments when the cyclic group is a Ce-12 aryl group the cyclic group is a Ce aryl group. In some embodiments when Spacer comprises a substituted group, said group is substituted with 1, 2 or 3, typically 1 or 2, more typically 1 substituent. Substituents may be independently selected from halogen atoms (e.g. F, Cl, Br and I), halomethyl groups such as CF3 and CCI3; oxygen containing groups such as oxo, hydroxy, carboxy, carboxyCi-ealkyl, alkoxy, alkoyl, alkoyloxy, aryl oxy, aryloyl and aryl oyl oxy; nitrogen containing groups such as amino, Ci-ealkylamino, diCi-ealkylamino, cyano, azide and nitro; sulphur containing groups such as thiol, Ci-ealkylthiol, sulphonyl and sulphoxide; heterocyclic groups which may themselves be substituted; alkyl groups as defined above, which may themselves be substituted; and aryl groups as defined above, which may themselves be substituted, such as phenyl and substituted phenyl. Substituents on said heterocyclic, alkyl and aryl groups are as defined immediately above. Typically each R10 is independently H or C1-3 alkyl, typically H or methyl, most typically H. In some embodiments, Spacer comprises or consists of an oligopeptide moiety. In some embodiments the oligopeptide moiety comprises from about 2 to about 20 amino acids or amino acid analogs or derivatives (such as non-coding and / or non-canonical amino acids, such as artificial amino acids) which may be the same or different. In some embodiments the oligopeptide moiety comprises from about 5 to about 15 amino acids or amino acid analogs or derivatives, such as from about 8 to about 12 amino acids or amino acid analogs or derivatives, each of which may be the same or different. In some embodiments, when Spacer comprises one or more amino acid analogs or derivatives, said amino acid analogs are selected from sarcosine ([Sar]) and beta-alanine ([P-Ala]). Other non-natural amino acids include D-Aspartate, homophenylalanine, pentafluoro-phenylalanine, 3-pyridylalanine, 4-pyridylalanine, D-Proline, 2-aminoisobutyric acid, D-Alanine, D-Arginine, D-Glutamine, D-Histidine, hydroxyproline, D-Leucine, homoarginine, 4,4-biphenylalanine, 3,3-diphenylalanine, dipropylglycine, 1-napthylalanine, 2-napthylalanine, pipecolic acid, azeitidine-2-carboxylic acid, betacyclohexyl-L-alanine, 4-fluoro-pyrrolidine-2-carboxylic acid, D-Asp(tBu), u-tert-butylglycine, cyclohexylglycine, and phenylglycine-OH. In some embodiments, Spacer comprises or consists of one or more sarcosine residues and / or one or more beta-alanine residues and / or one or more polyethyleneglycol (PEG) residues and / or one or more amide groups. In some embodiments Spacer comprises or consists of one or more sarcosine residues and / or one or more polyethyleneglycol (PEG) residues and / or one or more amide groups. In some embodiments, Spacer comprises or consists of one or more sarcosine residues and / or one or more beta-alanine residues. In some embodiments, Spacer comprises or consists of [Sar]2-2o wherein Sar is sarcosine. In some embodiments Spacer comprises [Sar]s-i5 such as [Sar]s-i2e.g. [Sar]w. In some embodiments Spacer comprises [Sar]2-2o and further comprises one or more betaalanine residues. In some embodiments, Spacer comprises or consists of a moiety -([P-Ala]p-[Sar]q)r-, wherein each p is independently from about 1 to about 5; each q is independently from about 5 to about 15; and r is an integer of from about 1 to about 5. In some embodiments Spacer comprises or consists of a moiety -([P-Ala]p-[Sar]q)r-, wherein each p is independently from about 1 to about 3; each q is independently from about 8 to about 12; and r is an integer of from about 1 to about 2. In some embodiments Spacer comprises or consists of a moiety -([P-Ala]p-[Sar]q)r-, wherein each p is independently from about 1 to about 2; each q is independently about 10; and r is an integer of from about 1 to about 2, typically 1. In some embodiments Spacer is —[P-Ala]—[Sar]io~. For the avoidance of doubt, if two or more Spacer groups are present the two or more Spacer groups may be the same or different. In some embodiments Spacer is absent, such that Bicycle is bonded directly to group Z. Furthermore, it will readily be appreciated that such embodiments can equivalently be regarded as embodiments in which Spacer is simply a (direct) bond between Bicycle and group Z. Thus, in some embodiments, Spacer is a bond that connects the Bicycle moiety to the Z moiety. Modified derivatives As mentioned above, in some embodiments provided herein is a compound as described herein, comprising a modified form of SEQ ID NO: 1. Accordingly, in some embodiments provided herein is a compound comprising a bicyclic peptide comprising a polypeptide comprising a modified form of SEQ ID NO: 1 attached to a molecular scaffold; wherein the molecular scaffold is l,l',l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-1-one) (TATA); or a pharmaceutically acceptable salt thereof. Also provided is a compound of formula I: [Formula (I)] wherein Bicycle is a peptide ligand comprising a polypeptide comprising a modified form of SEQ ID NO: 1 attached to a molecular scaffold; wherein the molecular scaffold is l,r,l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-l-one) (TATA); and wherein Spacer and Z are as described herein; or a pharmaceutically acceptable salt thereof. In some embodiments the modified form of SEQ ID NO: 1 comprises one or more cysteine groups (e.g. 3 cysteine groups) each comprising a sulfur atom which is covalently attached to the molecular scaffold. In some embodiments the modified form of SEQ ID NO: 1 comprises cysteine residues at positions corresponding to the positions of the cysteine residues in SEQ ID NO: 1; i.e., in some embodiments the cysteine residues in SEQ ID NO: 1 are invariant. Many different peptide modifications are known to those skilled in the art and include modifications to introduce new functionalities to amino acid residues, modifications to protect reactive amino acid residues or modifications to couple amino acid residues to chemical moieties such as reactive functional groups. A modified peptide as disclosed herein may be referred to as a variant. In some embodiments modified peptides include addition variants wherein one or more, such as at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acids are added or introduced into the reference sequence. Addition may occur at the C- terminus or N-terminus of the native sequence or within the reference sequence. In some embodiments modified peptides include deletion variants wherein one or more, such as at least 1, 2, 3, 4, or 5 amino acids are removed from the reference sequence. Deletion may occur at the C- terminus or N-terminus of the native sequence or within the reference sequence. In some embodiments modified peptides include substitution variants wherein one or more, such as at least 1, 2, 3, 4, or 5 amino acids are substituted in the reference sequence. Substitution may occur at the C- terminus or N-terminus of the native sequence or within the reference sequence. Exemplary modifications include modifications selected from: N-terminal and / or C-terminal modifications; replacement of one or more amino acid residues with one or more non-natural amino acid residues (such as replacement of one or more polar amino acid residues with one or more isosteric or isoelectronic amino acids; replacement of one or more non-polar amino acid residues with other non-natural isosteric or isoelectronic amino acids); addition of a spacer group; replacement of one or more oxidation sensitive amino acid residues with one or more oxidation resistant amino acid residues; replacement of one or more amino acid residues with an alanine; replacement of one or more L-amino acid residues with one or more D-amino acid residues; N-alkylation of one or more amide bonds within the bicyclic peptide ligand; replacement of one or more peptide bonds with a surrogate bond; peptide backbone length modification; substitution of the hydrogen on the alpha-carbon of one or more amino acid residues with another chemical group, modification of amino acids such as cysteine, lysine, glutamate / aspartate and tyrosine with suitable amine, thiol, carboxylic acid and phenol-reactive reagents so as to functionalise said amino acids, and introduction or replacement of amino acids that introduce orthogonal reactivities that are suitable for functionalisation, for example azide or alkyne-group bearing amino acids that allow functionalisation with alkyne or azide-bearing moieties, respectively. A modified derivative may comprise an N-terminal and / or C-terminal modification. A modified derivative may comprise an N-terminal modification using suitable aminoreactive chemistry, and / or C-terminal modification using suitable carboxy-reactive chemistry. The N-terminal or C-terminal modification may comprise addition of an effector group, including but not limited to a cytotoxic agent, a radiochelator or a chromophore. A modified derivative may comprise an N-terminal modification. An exemplary N-terminal modification comprises an N-terminal acetyl group. The N-terminal cysteine group may be capped with acetic anhydride or other appropriate reagents during peptide synthesis leading to a molecule which is N-terminally acetylated. This provides the advantage of removing a potential recognition point for aminopeptidases and avoids the potential for degradation of the bicyclic peptide. Alternatively, an N-terminal modification may comprise the addition of a molecular spacer group which facilitates the conjugation of effector groups and retention of potency of the bicyclic peptide to its target. The compounds disclosed herein typically comprise an N-terminal attachment to a spacer and Z-moiety as described herein. A modified derivative may comprise a C-terminal modification. The C-terminal modification may comprise an amide group. The C-terminal group may be synthesized as an amide during peptide synthesis leading to a molecule which is C-terminally amidated. This provides the advantage of removing a potential recognition point for carboxy peptidase and reduces the potential for proteolytic degradation of the bicyclic peptide. A modified derivative may comprise replacement of one or more amino acid residues with one or more non-natural amino acid residues. Non-natural amino acids may be selected having isosteric / isoelectronic side chains which are neither recognised by degradative proteases nor have any adverse effect upon target potency. Alternatively, non-natural amino acids may be used having constrained amino acid side chains, such that proteolytic hydrolysis of the nearby peptide bond is conformationally and sterically impeded. In particular, these concern proline analogues, bulky sidechains, Ca-disubstituted derivatives (for example, aminoisobutyric acid, Aib), and cyclo amino acids, a simple derivative being amino-cyclopropylcarboxylic acid. A modified derivative may comprise a plurality of the above mentioned modifications, such as 2, 3, 4 or 5 or more modifications. A modified derivative may comprise the addition of a spacer group. A modified derivative may comprise the addition of a spacer group to the N-terminal amino acid and / or the C-terminal amino acid. A modified derivative may comprise replacement of one or more oxidation sensitive amino acid residues with one or more oxidation resistant amino acid residues. For example, a modified derivative may comprise replacement of a tryptophan residue with a naphthylalanine or alanine residue. This provides the advantage of improving the pharmaceutical stability profile of the resultant bicyclic peptide ligand. A modified derivative may comprise replacement of one or more hydrophilic (e.g. charged) amino acid residues with one or more hydrophobic amino acid residues. Alternatively, a modified derivative may comprise replacement of one or more hydrophobic amino acid residues with one or more hydrophilic (e.g. charged) amino acid residues. The correct balance of charged versus hydrophobic amino acid residues is an important characteristic of the bicyclic peptide ligands. For example, hydrophobic amino acid residues influence the degree of plasma protein binding and thus the concentration of the free available fraction in plasma, while charged amino acid residues (in particular arginine) may influence the interaction of the peptide with the phospholipid membranes on cell surfaces. The two in combination may influence half-life, volume of distribution and exposure of the peptide in vivo, and can be tailored according to the clinical endpoint. In addition, the correct combination and number of charged versus hydrophobic amino acid residues may reduce irritation at the administration site. A modified derivative may comprises replacement of one or more L-amino acid residues with one or more D-amino acid residues. This is believed to increase proteolytic stability by steric hindrance and by a propensity of D-amino acids to stabilise P-tum conformations (Tugyi et al (2005) PNAS, 102(2), 413-418). A modified derivative may comprise removal of any amino acid residues and substitution with alanines. This embodiment provides the advantage of removing potential proteolytic attack site(s). It should be noted that each of the above mentioned modifications serve to deliberately improve the potency or stability of the peptide. Further potency improvements based on modifications may be achieved through the following mechanisms: - Incorporating hydrophobic moieties that exploit the hydrophobic effect and lead to lower off rates, such that higher affinities are achieved; - Incorporating charged groups that exploit long-range ionic interactions, leading to faster on rates and to higher affinities (see for example Schreiber et al, Rapid, electrostatically assisted association of proteins (1996), Nature Struct. Biol. 3, 42731); and - Incorporating additional constraint into the peptide, by for example constraining side chains of amino acids correctly such that loss in entropy is minimal upon target binding, constraining the torsional angles of the backbone such that loss in entropy is minimal upon target binding and introducing additional cyclisations in the molecule for identical reasons. (for reviews see Gentilucci et al, Curr. Pharmaceutical Design, (2010), 16, 3185-203, and Nestor et al, Curr. Medicinal Chern (2009), 16, 4399-418). A compound provided herein may comprise a half-life extending moiety. In some embodiments a half-life extending moiety prolongs the circulating half-life of the compound. In some embodiments the half-life extending moiety comprises a reversible albumin binding motif. In some embodiments the half-life extending moiety binds to albumin. In some embodiments the half-life extending moiety reversibly (e.g. non-covalently) binds to albumin. In some embodiments the half-life extending moiety is a lipid such as a palmitoyl group. A lipid can be incorporated by reaction of the compound with a fatty acid. For example, a palmitoyl group can be incorporated by reaction of the compound with palmitoic acid. In some embodiments the half-life extending moiety is attached to a Spacer group of a compound of Formula (I) as described herein. In some embodiments the compound (e.g. the Spacer group) comprises a reactive functional group such as an amine group (e.g. provided by a lysine residue) that is capable of reacting with a reactive functional group of the half-life extending moiety (e.g. to the acid group of a fatty acid), thereby attaching the half-life extending moiety to the compound (e.g. to the Spacer). Isotopic variations As explained in more detail herein, many of the compounds provided herein comprise a radionuclide, for example, for use in radiotherapy (e.g. in targeted radionuclide therapy) and / or imaging. This is described in more detail herein. More generally, provided herein are all pharmaceutically acceptable (radio)isotope-labelled compounds of the invention, wherein one or more atoms are replaced by atoms having the same atomic number, but an atomic mass or mass number different from the atomic mass or mass number usually found in nature; and compounds wherein metal chelating groups are attached that are capable of holding relevant (radio)isotopes; and compounds wherein certain functional groups are covalently replaced with relevant (radio)isotopes or isotopically labelled functional groups. For example, in some embodiments the compound provided herein comprises one or more amino acids or amino acid analogs comprising one or more (radio)isotopes. Examples of isotopes suitable for inclusion in the compounds of the invention comprise isotopes of hydrogen, such as 2H (D) and 3H (T), carbon, such as nC, 13C and 14C, chlorine, such as 36C1, fluorine, such as 18F, iodine, such as 123I, 125I and 131I, nitrogen, such as 13N and 15N, oxygen, such as 15O, 17O and 18O, phosphorus, such as 32P, and sulfur, such as 35S. As discussed in more detail herein, certain isotopically-labelled compounds, for example, those incorporating a radioactive isotope, are useful in drug and / or substrate tissue distribution studies, and to clinically assess the presence and / or absence of the EphA2 target on diseased tissues such as tumours and elsewhere. The compounds of formula (I) can further have valuable diagnostic properties in that they can be used for detecting or identifying the formation of a complex between a labelled compound and other molecules, peptides, proteins, enzymes or receptors. The detecting or identifying methods can use compounds that are labelled with labelling agents such as radioisotopes, enzymes, fluorescent substances, luminous substances (for example, luminol, luminol derivatives, luciferin, aequorin and luciferase), etc. The radioactive isotopes tritium, i.e. 3H (T), and carbon-14, i.e. 14C, are particularly useful for this purpose in view of their ease of incorporation and ready means of detection. Incorporation of heavier isotopes such as deuterium, i.e. 2H (D), may afford certain therapeutic advantages resulting from greater metabolic stability, for example, increased in vivo half-life or reduced dosage requirements, and hence may be preferred in some circumstances. Incorporation of positron emitting isotopes, such as nC, 18F, 15O and 13N, can be useful in Positron Emission Topography (PET) studies for examining target occupancy. Such isotopes can be incorporated in any suitable manner. In some embodiments an isotope is incorporated by substitution of one or more atoms of the compound with one or more isotopic equivalents. For example, in some embodiments 1H can be substituted with 2H, 12C can be substituted with nC, 19F can be substituted with 18F, 16O can be substituted with 15O, and / or 14N can be substituted with 13N, etc. In some embodiments the compound is labelled with a group comprising an isotope. In some embodiments the compound is conjugated to an isotopically-labelled moiety. Any suitable conjugation method can be used. In some embodiments the compound is conjugated to an isotopically-labelled moiety via a Spacer group as described herein (for avoidance of doubt, if multiple Spacer groups are present in a compound provided herein then said Spacer groups may be the same or different). In some embodiments a compound of formula (I) is bonded, e.g. via an amide bond, to an isotopically-labelled moiety. In some embodiments the isotopically-labelled moiety is an isotopically-labelled organic group such as an amino acid or analog thereof. In some embodiments the isotopically-labelled moiety comprises one or more of 2H (D), nC, 18F, 15O and 13N. Isotopically-labelled compounds of formula (I) can generally be prepared by conventional techniques known to those skilled in the art or by processes analogous to those described in the accompanying Examples using an appropriate isotopically-labelled reagent in place of the non-labelled reagent previously employed. Effector moieties In some embodiments the provided compounds comprise a bicyclic peptide as described herein attached (e.g via a spacer group as described herein) to an imaging agent and / or therapeutic agent or a ligand thereto. In some embodiments the compound is a compound of formula [Formula (I)] wherein Bicycle and Spacer are as described herein, and Z is an imaging and / or therapeutic agent or a ligand thereto. Imaging agents and therapeutic agents suitable for use in the disclosed compounds may also be referred to as “effector moieties”. Also provided is a compound as set forth in Formula (I) and comprising one or more additional Z moieties, such that the compound comprises two or more (e.g. two) Z moieties, each of which may be the same or different. In some embodiments each Z moiety is attached to the Bicycle moiety by a Spacer moiety as described herein, wherein the Spacer moieties may be the same or different. In some embodiments the or each effector moiety (e.g. Z) is independently a chelator, a chromophore, a fluorescent moiety, a luminescent moiety and / or a phosphorescent moiety. In some embodiments therefore the bicyclic peptide is attached to a group Z and Z is a chelator, a chromophore, a fluorescent moiety, a luminescent moiety and / or a phosphorescent moiety. In some compounds provided herein the bicyclic peptide is attached to one or more, e.g. to two or more, e.g. 1 or 2 groups Z and each Z is independently a chelator, a chromophore, a fluorescent moiety, a luminescent moiety and / or a phosphorescent moiety. For avoidance of doubt, if two or more Z moieties are present, the Z moieties may be the same or different. In some embodiments when Z is a chromophore, Z is a dye such as a monoazo dye (e.g. diamine scarlet B), a diazo dye (e.g. Congo red), a triazo dye (e.g. Direct brown), a polyazo dye (e.g. a chlorazol dye), a stilbene dye or a thiazole derivative dye (e.g. primuline). In some embodiments when Z is a fluorescent moiety, Z is a fluorescent dye. In some embodiments Z is a fluorophore. In some embodiments Z is selected from: Alexa Fluor dyes (Alexa Fluor 350, Alexa Fluor 488, Alexa Fluor 532, Alexa Fluor 546, Alexa Fluor 568, Alexa Fluor 594, Alexa Fluor 633, Alexa Fluor 647, Alexa Fluor 660 and Alexa Fluor 680), AMCA, AMCA-S, BODIPY dyes (BODIPY FL, BODIPY R6G, BODIPY TMR, BODIPY TR, BODIPY 530 / 550, BODIPY 558 / 568, BODIPY 564 / 570, BODIPY 576 / 589, BODIPY 581 / 591, BODIPY 630 / 650, BODIPY 650 / 665), Carboxyrhodamine 6G, carboxy-X-rhodamine (ROX), Cascade Blue, Cascade Yellow, Coumarin 343, Cyanine dyes (Cy3, Cy5, Cy3.5, Cy5.5, Cy7, Cy7.5), Dansyl, Dapoxyl, Dialkylaminocoumarin, 4',5'-Dichloro-2',7'-dimethoxy-fluorescein, DM-NERF, Eosin, Erythrosin, Fluorescein, FAM, Hydroxycoumarin, IRDyes (IRD40, IRD 700, IRD 800), JOE, Lissamine rhodamine B, Marina Blue, Methoxy coumarin, Naphthofluorescein, Oregon Green 488, Oregon Green 500, Oregon Green 514, Pacific Blue, PyMPO, Pyrene, Rhodamine B, Rhodamine 6G, Rhodamine Green, Rhodamine Red, Rhodol Green, 2',4',5',7'-Tetra-bromosulfone-fluorescein, Tetramethyl-rhodamine (TMR), Carboxytetramethylrhodamine (TAMRA), Texas Red, and Texas Red-X. In some embodiments when Z is a luminescent moiety, Z is a luminescent semiconductor nanocrystal. In some embodiments Z is a zincsulfide-capped cadmium selenide nanocrystal. Such nanocrystals are known as quantum dots. In some embodiments Z is a quantum dot. The synthesis and utility of quantum dots is described in United States Patents 6,326,144, 6,468,808, 7,192,785, 7,151,047, and in the scientific literature (see: Chan and Nie (1998) Science 281(5385) 2016-2018). In some embodiments when Z is a luminescent dye, Z is selected from an Atto dye (e.g. Atto 490LS); a Lumilux dye (e.g. Luminux Green D 254); Acridine; 8-Hydroxy-N,N,N',N',N'',N"-hexamethylpyrene-l,3,6-trisulfonamide; 5-Cyano-2,3-di-(p-tolyl)tetrazolium chloride; a Protoporphyrin (e.g, Protoporphyrin IX dimethyl ester); Chloro(2,2':6',2''-terpyridine)platinum(II) chloride dihydrate; an Abberior® dye (e.g. Abberior® STAR 635, Abberior® STAR 440SXP, Abberior® STAR 512, Abberior® STAR 580, Abberior® FLIP 565, Abberior® STAR 635P); Acridine Mutagen ICR 191; 5(6)-Carboxynaphthofluorescein; TpOx (2,3,6,1 l,12-pentakis(pentyloxy)triphenyleno[l,2-d]oxazole and derivatives thereof); and 7-Hydroxycoumarin-3-carboxylic acid. In some embodiments Z is selected from luminol, luminol derivatives, luciferin, aequorin and luciferase. In some embodiments when Z is a phosphorescent moiety, Z is a metal complex (e.g. a palladium or iridium complex) such as 5,10,15,20-Tetrakis(pentafluorophenyl)-21H,23H-porphine palladium(II). In some embodiments when Z is a chelator, Z is a metal chelator. As used herein a chelator is a complexing agent (ligand) capable of forming a complex with a metal ion; typically via electron donation from the complexing agent to the metal ion. Examples of groups that are suitable for electron donation from the complexing agent to the metal ion include carbonyl groups (C=O), amine groups (-N(R10)2, e.g. NH2) and carboxyl groups (e g. C(O)O-). When Z is a metal chelator Z is typically chosen or designed in order to provide a strong coordination bond to the metal. The rational choice of chelators for metals is within the skill of one in the art. Practitioners are referred to Price and Orvig; Chern. Soc. Rev. 2014 (43) 260-290 (2013), the entire contents of which are hereby incorporated by reference. In some embodiments Z is a clathrate. In some embodiments Z is a cryptand. In some embodiments Z is an organic acid chelator. In some embodiments Z is SarAr (1-N-(4-aminobenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]-eicosane-l,8-diamine). In some embodiments Z is a polycarboxylic acid or a polyphosphonic acid. In some embodiments Z is an amino polycarboxylic acid. In some embodiments Z is selected from 2-(Carboxymethylamino)acetic acid (IDA); 2,2',2''-Nitrilotriacetic acid (NTA); 2-({2-[Bis(carboxymethyl)amino]ethyl}(carboxymethyl)amino) acetic acid (EDTA); N,N'-{[(Carboxymethyl)azanediyl]di(ethane-2,l-diyl)}bis[N-(carboxymethyl)glycine] (DTPA); ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetra acetic acid (EGTA); l,2-bis(o-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid (BAPTA); diethylenetriaminepentaacetic anhydride (DTPA); l,4,7-triazacyclononane-N,N’,N”-triacetic acid (NOTA); 1,4,7,10-tetraazacyclododecane-l,4,7,10-tetraacetic acid (DOTA); 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA); ethylenediamine-N,N'-disuccinic acid (EDDS); 2,2',2",2"',2"",2.....-(1,4,7,10,13,16-hexaazacyclooctadecane-l,4,7,10,13,16-hexayl)hexaacetic acid (HEHA); 2,2',2",2"',2""-(l,4,7,10,13-pentaazacyclopentadecane-l,4,7,10,13-pentayl)pentaacetic acid (PEPA); 3,3',3",3"'-(1,5,9,13-tetraazacyclohexadecane-l,5,9,13-tetrayl)tetrapropionic acid (TETPA); 3,3 ',3",3"'-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetrapropionic acid (DOTPA); 2-[4,7,10-tris(2-amino-2-oxoethyl)-l,4,7,10-tetrazacyclododec-l-yl]acetamide (DOTAM) (also known as TCMC); 6,6'-((l,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)bis(methylene))dipicolinic acid (MACROPA); l,4,7,10-tetraazacyclododececane,l-(glutaric acid)-4,7,l O-triacetic acid (DOTAGA) and 2,2',2”-(l,4,7,10-tetraazacyclododecane-l,4,7-triyl)triacetamide (DO3AM). In some embodiments Z is selected from DOTA, NOTA, EDTA, DTP A, HEHA, and SarAr (Targeted Radionuclide therapy, Tod Speer, Wolters / Kluver Lippincott Williams & Wilkins, 2011). In some embodiments Z is selected from DOTA, DTP A, NOTA and TETA. In some embodiments Z is DOTA. Those skilled in the art will appreciate that when Z is a chelator such as chelator as described herein, the chelator is attached (typically covalently attached) to the bicyclic peptide (e.g. via a Spacer group as described herein). The attachment chemistry between the chelator and the bicycle peptide (e.g. to the Spacer) is not particularly limited. Any suitable attachment means can be used. In some embodiments a reactive functional group on the chelator is reacted with a complementary reactive functional group on the Spacer. Some exemplary reactive groups and their corresponding targets include amines which may react with carboxylic acids (e.g. the N-terminus amino group of a peptide may react with a carboxylic acid group of a chelator as described in the examples), aryl azides which may react with amine, carbodiimides which may react with amines and carboxyl groups, hydrazides which may react with carbohydrates, hydroxmethyl phosphines which may react with amines, imidoesters which may react with amines, isocyanates which may react with hydroxyl groups, carbonyls which may react with hydrazines, maleimides which may react with sulfhydryl groups, NHS-esters which may react with amines, PFP-esters which may react with amines, psoralens which may react with thymine, pyridyl disulfides which may react with sulfhydryl groups, vinyl sulfones which may react with sulfhydryl amines and hydroxyl groups, and the like. In some embodiments a chelator is attached to a Spacer group via a click chemistry reaction, e.g. between a click group on the Spacer and a complementary click group on the chelator. Click chemistry reactions include coppery-catalyzed cycloadditions between azides and alkynes (azide alkyne Huisgen cycloadditions); strain-promoted cycloadditions between azides and alkynes, including alkene and azide [3+2] cycloadditions; alkene and tetrazine inverse-demand Diels-Alder reactions; and alkene and tetrazole photoclick reactions; copper-free variants of the 1,3 dipolar cycloaddition reaction, where an azide reacts with an alkyne under strain, for example in a cyclooctane ring; the reaction of an oxygen nucleophile with an epoxide or aziridine reactive moiety; and the Staudinger ligation between an aryl phosphine and an azide to give an amide bond. Typically, Z is covalently attached by removing (abstracting) a hydrogen atom from the free chelator molecule such that Z is monodentate and capable of binding to the bicyclic peptide (e.g. via Spacer). Those skilled in the art will appreciate that the references to Z groups above embrace the forms of those groups wherein an atom such as a hydrogen atom is abstracted and replaced by a bond such as a covalent bond to the bicyclic peptide or to a Spacer attached thereto. Similarly, when Z is a chromophore, a fluorescent moiety, a luminescent moiety and / or a phosphorescent moiety the Z group is typically attached to Spacer by abstraction of a hydrogen atom from the molecular structure of the chromophore, a fluorescent moiety, a luminescent moiety and / or a phosphorescent moiety and bonding of the resultant group to an atom (e.g. a reactive functional group) of the Spacer. For example, in some embodiments Z is DOTA having the structure: wherein s is the point of attachment to the rest of the molecule (e.g. in some embodiments ? is the point of attachment to Spacer). In some embodiments Z is complexed to a radioisotope. In some embodiments Z is complexed to a metal radioisotope. Any suitable radioisotope can be used. Many metal radioisotopes (including 64Cu, 67Ga, 68Ga, and 177Lu) are useful for visualizing tumour specific antigens employing PET or SPECT (e.g. SPECT / CT) imaging. Example 3 describes the use of a 11 'in-labelled compound described herein in SPECT imaging and a 68Ga-labelled compound described herein in PET imaging. Many metal radioisotopes (including 90Y, 177Lu, and 213Bi) can present the option of targeted radiotherapy, whereby metal-chelator-bearing compounds carry the therapeutic radionuclide towards the target protein and site of action. In some embodiments Z is selected from 225Ac, 227Ac,241 Am, 72As, 74As,211 At, 198Au, nB, 7Be, 212Bi, 213Bi, 75Br, 77Br, nC, 14C, 48Ca, 109Cd, 139Ce, 141Ce, 252Cf, 55Co, 57Co, 60Co, 51Cr, 130Cs, 131Cs, 137Cs, 61Cu, 62Cu, 64Cu, 67Cu, 165Dy, 152Eu, 155Eu, 18F, 55Fe, 59Fe, 64Ga, 67Ga, 68Ga, 153Gd, 68Ge, 122I, 123I, 124I, 125I, 131I, 132I, mIn, 114mIn, 115mIn, 191mIr, 192Ir, 5 81mKr, 177Lu, 51Mn, 52Mn, "Mo, 13N, 95Nb, 15O, 1910s, 1940s, 32P, 33P, 203Pb, 212Pb, 103Pd, 109Pd, 238Pu, 223Ra, 226Ra, 82Rb, 186Re, 188Re, 105Rh, 97Ru, 103Ru, 35S, 44Sc, 46Sc, 47Sc, 72Se, 75Se, 28Si, 145Sm, 153Sm, 117mSn, 85Sr, 89Sr, 90Sr, 178Ta, 179Ta, 182Ta, 149Tb, 96Tc, "mTc, 228Th, 229Th, 2O1T1, 170Tm, 171Tm, 188W, 127Xe, 133Xe, 86Y, 88Y, 90Y91Y, 169Yb, 62Zn, 65Zn, 89Zr and 95Zr. 10           In some embodiments Z is selected from [64Cu], [67Ga], [68Ga], [177Lu], [90Y], [213Bi], [212Pb], [U1ln] and [225Ac], In some embodiments Z is [68Ga], [177Lu], [niIn] or [225Ac], Specific aspects 15          In some embodiments the compound is of the structure: wherein Spacer and Z are as described herein. (For avoidance of doubt, in the structure above the bond to the Spacer-Z moiety may derive from any atom of any amino acid in SEQ ID NO: 1. In some embodiments the bond to the Spacer-Z moiety is at the N terminus of SEQ ID NO: 1). In some embodiments Z is a metal chelator and is complexed to a radioisotope such as a metal radioisotope as described herein. In some embodiments the compound is of the structure: 5                                      nh wherein Spacer and Z are as described herein. In some embodiments Z is a metal chelator and is complexed to a radioisotope such as a metal radioisotope as described herein. In some embodiments the compound is of the structure: wherein Z is as described herein. In some embodiments Z is a metal chelator and is complexed to a radioisotope such as a metal radioisotope as described herein. 5          In some embodiments the compound is of the structure: HO wherein Spacer is as described herein. In some embodiments the moiety is complexed to a metal radioisotope, such as a metal radioisotope as described 5 herein. In some embodiments the metal radioisotope is 225Ac, 227Ac, 241Am, 72As, 74As, 211At, 198Au, nB, 7Be, 212Bi, 213Bi, 75Br, 77Br, nC, 14C, 48Ca, 109Cd, 139Ce, 141Ce, 252Cf, 55Co, 57Co, 60Co, 51Cr, 130Cs, 131Cs, 137Cs, 61Cu, 62Cu, 64Cu, 67Cu, 165Dy, 152Eu, 155Eu, 18F, 55Fe, 59Fe, 64(^ 67(^ 68^ 153^ 68(^ 122^ 123^ 124^ 125^ 131^ 132^ 111^ 114^ 115™^ 191mir3 192^ 81mKl. 177Lu, 51^ 52^ 99^ 13^ 95^ 15q 191(^ 194(^ 32p 33p 203pb, 10    212Pb, 103Pd, 109Pd, 238Pu, 223Ra, 226Ra, 82Rb, 186Re, 188Re, 105Rh, 97Ru, 103Ru, 35S, 44Sc, 46Sc, 47Sc, 72Se, 75Se, 28Si, 145Sm, 153Sm, 117mSn, 85Sr, 89Sr, 90Sr, 178Ta, 179Ta, 182Ta, 149Tb, 96Tc, "mTC, 228^ 229^, 201^ 170^ 171Tm 188^ 127^ 133^ 86^ 88^ 90y 91^ 169^, 62^ 65Zn, 89Zr or 95Zr. In some embodiments the compound is of the structure (Compound 1): HO and the moiety is complexed to a metal radioisotope. In some embodiments the metal radioisotope is 225Ac, 227Ac, 241Am, 72As, 74As, 211At, 198Au, nB, 7Be, 212Bi, 213Bi, 75Br, 77Br, nC, 14C, 48Ca, 109Cd, 139Ce, 141Ce, 252Cf, 55Co, 57Co, 60Co, 51Cr, 130Cs, 131Cs, 137Cs, 61Cu, 62Cu, 64Cu, 67Cu, 165Dy, 152Eu, 155Eu, 18F, 55Fe, 59Fe, 64Ga, 67Ga, 68Ga, 153Gd, 68Ge, 122I, 123I, 124I, 125I, 131I 132j llljH IMmj 115min 191mj  192^ 81mK 17?L  51M  52M  99M  13N 95^ 15q 191Os, 1940s, 32P, 33P, 203Pb, 212Pb, 103Pd, 109Pd, 238Pu, 223Ra, 226Ra, 82Rb, 186Re, 188Re, 105Rh, 97Ru, 103Ru, 35S, 44Sc, 46Sc, 47Sc, 72Se, 75Se, 28Si, 145Sm, 153Sm, 117mSn, 85Sr, 89Sr, 90Sr, 178Ta, 179Ta, 182Ta, 149Tb, 96Tc, "mTc, 228Th, 229Th, 2O1T1, 170Tm, 171Tm, 188W, 127Xe, 133Xe, 86Y, 88Y, 90Y 91Y, 169Yb, 62Zn, 65Zn, 89Zr or 95Zr. In some embodiments the metal radioisotope is [64Cu], [67Ga], [68Ga], [177Lu], [90Y], [213Bi], [212Pb], [mIn] or [225Ac], In some embodiments the metal radioisotope is [68Ga], [177Lu], [inIn] or [225Ac], The bicyclic peptides of the present invention have advantageous properties which enables them to be considered as suitable drug-like molecules for injection, inhalation, nasal, ocular, oral or topical administration. Such advantageous properties may typically include some or all of: - Species cross-reactivity. This is a typical requirement for preclinical pharmacodynamics and pharmacokinetic evaluation; - Protease stability. Bicyclic peptide ligands should ideally demonstrate stability to plasma proteases, epithelial ("membrane-anchored") proteases, gastric and intestinal proteases, lung surface proteases, intracellular proteases and the like. Protease stability should be maintained between different species such that a bicycle lead candidate can be developed in animal models as well as administered with confidence to humans; - Desirable solubility profile. This is a function of the proportion of charged and hydrophilic versus hydrophobic residues and intra / inter-molecular H-bonding, which is important for formulation and absorption purposes; and - An optimal plasma half-life in the circulation. Depending upon the clinical indication and treatment regimen, it may be required to develop a bicyclic peptide for short exposure in an acute illness management setting, or develop a bicyclic peptide with enhanced retention in the circulation, and is therefore optimal for the management of more chronic disease states. Other factors driving the desirable plasma half-life are requirements of sustained exposure for maximal therapeutic efficiency versus the accompanying toxicology due to sustained exposure of the agent. - Selectivity, such as selectivity for EphA2 (e.g. without cross-reactivity with other Eph receptor tyrosine kinases, such as EphAl , EphA3, EphA4, EphA5, EphA6, EphA7 and EphBl and factor XIIA, carbonic anhydrase 9 and CD38). - Safety, such as improved safety compared with EphA2-targeting antibody-drug conjugates such as MEDI-547, a phase 1 open label study with which was halted due to bleeding and coagulation events that occurred in 5 of 6 patients (Annunziata et ai, Invest New Drugs (2013) 31 :77-84). Synthesis The compounds described herein may be made by any suitable technique. The compounds may be manufactured synthetically by standard techniques for peptide synthesis followed by reaction with a molecular scaffold. When this is performed, standard chemistry may be used. This enables the rapid large scale preparation of soluble material for further downstream experiments or validation. Such methods could be accomplished using conventional chemistry such as that disclosed in Timmerman et al (supra). Thus, the invention also relates to manufacture of polypeptides or conjugates selected as set out herein, wherein the manufacture comprises optional further steps as explained below. In one embodiment, these steps are carried out on the end product polypeptide / conjugate made by chemical synthesis. Optionally amino acid residues in the polypeptide of interest may be substituted when manufacturing a conjugate or complex. Peptides can also be extended, to incorporate for example another loop and therefore introduce multiple specificities. To extend the peptide, it may simply be extended chemically at its N-terminus or C-terminus or within the loops using orthogonally protected lysines (and analogues) using standard solid phase or solution phase chemistry. Standard (bio)conjugation techniques may be used to introduce an activated or activatable N- or C-terminus. Alternatively additions may be made by fragment condensation or native chemical ligation e.g. as described in (Dawson et al. 1994. Synthesis of Proteins by Native Chemical Ligation. Science 266:776-779), or by enzymes, for example using subtiligase as described in (Chang et al Proc Natl Acad Sci USA. 1994 Dec 20; 91 (26): 12544-8 or in Hikari et al Bioorganic & Medicinal Chemistry Letters Volume 18, Issue 22, 15 November 2008, Pages 6000-6003). Alternatively, the peptides may be extended or modified by further conjugation through disulphide bonds. Such bonds may be configured to dissociate from each other once within the reducing environment of the cell. In this case, the molecular scaffold (e.g. TATA) could be added during the chemical synthesis of the peptide so as to react with the three cysteine groups. Optionally, a further cysteine or thiol could then be appended to the N or C-terminus of the peptide, so that this cysteine or thiol only reacted with a free cysteine or thiol of a second peptide, forming a disulfide -linked bicyclic peptide-peptide conjugate. Similar techniques apply equally to the synthesis / coupling of two bicyclic and bispecific macrocycles, potentially creating a tetraspecific molecule. Furthermore, addition of other functional groups or effector groups may be accomplished in the same manner, using appropriate chemistry, coupling at the N- or C-termini or via side chains. In one embodiment, the coupling is conducted in such a manner that it does not block the activity of either entity. Compositions The compounds provided herein are useful in a range of pharmaceutical applications as described in more detail herein. In some aspects a compound provided herein is utilised in the form of a pharmaceutical composition. Accordingly, provided herein is a pharmaceutical composition comprising a compound as provided herein (e.g. a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide) and one or more pharmaceutically acceptable excipients. Also provided is a pharmaceutical composition comprising a compound as provided herein (e.g. a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide) and one or more pharmaceutically acceptable carriers or diluents. Typically, the composition contains up to 85 wt% of a compound as provided herein. More typically, it contains up to 50 wt% of a compound as provided herein. Preferred pharmaceutical compositions are sterile and pyrogen free. Generally, the compounds provided herein will be utilised in purified form together with pharmacologically appropriate excipients or carriers. Typically, these excipients or carriers include aqueous or alcoholic / aqueous solutions, emulsions or suspensions, including saline and / or buffered media. Parenteral vehicles include sodium chloride solution, Ringer's dextrose, dextrose and sodium chloride and lactated Ringer's. Suitable physiologically-acceptable adjuvants, if necessary to keep a polypeptide complex in suspension, may be chosen from thickeners such as carboxymethylcellulose, polyvinylpyrrolidone, gelatin and alginates. Intravenous vehicles include fluid and nutrient replenishers and electrolyte replenishers, such as those based on Ringer's dextrose. Preservatives and other additives, such as antimicrobials, antioxidants, chelating agents and inert gases, may also be present (Mack (1982) Remington's Pharmaceutical Sciences, 16th Edition). This is described in further detail herein The peptide ligands of this invention can be lyophilised for storage and reconstituted in a suitable carrier prior to use. This technique has been shown to be effective and art-known lyophilisation and reconstitution techniques can be employed. It will be appreciated by those skilled in the art that lyophilisation and reconstitution can lead to varying degrees of activity loss and that levels may have to be adjusted upward to compensate. The peptide ligands of the present invention may be used as separately administered compositions or in conjunction with other agents. These can include antibodies, antibody fragments and various immunotherapeutic drugs, such as cyclosporine, methotrexate, adriamycin or cisplatinum and immunotoxins. Pharmaceutical compositions can include "cocktails" of various cytotoxic or other agents in conjunction with the protein ligands of the present invention, or even combinations of selected polypeptides according to the present invention having different specificities, such as polypeptides selected using different target ligands, whether or not they are pooled prior to administration. A composition as provided herein may be provided as a kit comprising instructions to enable the kit to be used in the methods described herein or details regarding which subjects the method may be used for. Therapeutic efficacy As explained above, the bicyclic peptides of the invention have utility as high affinity binders of erythropoietin-producing hepatocellular receptor A2 (EphA2). EphA2 is a transmembrane glycoprotein and part of the tyrosine kinase receptor family. It is involved in multiple cellular processes such as cell migration, adhesion, differentiation and death. In healthy adult tissues EphA2 expression is generally low, but the receptor has been found to be upregulated in numerous solid tumors such as breast cancer, colon cancer, prostate cancer and lung cancer. Moreover, expression of EphA2 has been associated with increased carcinogenesis, metastatic disease and poor clinical prognosis. Therefore, due to its overexpression in cancerous cells, in combination with low expression in healthy tissues, it represents an ideal target for radiotheranostic applications. EphA2 has been previously targeted in non-radioactive-based approaches in both clinical and preclinical settings, both by small molecule drugs and by antibody-drug conjugates such as MEDI547, which showed sufficient preclinical efficacy against EphA2-expressing tumors but resulted in non-satisfactory outcomes in a Phase I clinical trial. An EphA2-targeting bicyclic peptide carrying a cytotoxic payload, BT5528, is currently being tested in a Phase VII clinical trial. The applications of such compounds are not limited, however, and in addition to in vivo therapeutic and prophylactic applications they are also useful in in vitro and in vivo diagnostic applications, also including in vitro assay and reagent applications, and the like. Ligands having selected levels of specificity are useful in applications which involve testing in non-human animals, where cross-reactivity is desirable, or in diagnostic applications, where cross-reactivity with homologues or paralogues needs to be carefully controlled. In some applications, such as vaccine applications, the ability to elicit an immune response to predetermined ranges of antigens can be exploited to tailor a vaccine to specific diseases and pathogens. Animal model systems which can be used to screen the effectiveness of peptide ligands in protecting against or treating diseases are available. The use of animal model systems is facilitated by the present disclosure, which allows the development of polypeptide ligands which can cross react with human and animal targets, to allow the use of animal models. Substantially pure peptide ligands of at least 90 to 95% homogeneity are preferred for administration to a mammal, and 98 to 99% or more homogeneity is most preferred for pharmaceutical uses, especially when the mammal is a human. Once purified, partially or to homogeneity as desired, the selected polypeptides may be used diagnostically or therapeutically (including extracorporeally) or in developing and performing assay procedures, immunofluorescent stainings and the like (Lefkovite and Pernis, (1979 and 1981) Immunological Methods, Volumes I and II, Academic Press, NY). In one aspect, therefore, provided herein is a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein, for use in medicine. Also provided is a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein, for use in treating the human or animal body. Still further provided is use of a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein, in the manufacture of a medicament. Still further provided is a method (e.g. a method of treating a subject in need of such treatment), the method comprising administering to the subject a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein. In some embodiments the subject suffers from or is at risk of suffering from one of the disorders disclosed herein. As explained above, the compounds and compositions provided herein are useful in treating or preventing various disorders. As noted, they are particularly useful as binders of EphA2. Accordingly, the compounds and compositions provided herein are useful in treating or preventing disorders, diseases or conditions associated with EphA2. In some embodiments the disorder, disease or condition associated with EphA2 is a disorder, disease or condition characterised by expression (e.g. by over-expression) of EphA2. In some embodiments the disorder, disease or condition associated with EphA2 is a disorder, disease or condition associated with EphA2 expression (e.g. overexpression). In some embodiments the disorder, disease or condition associated with EphA2 is an EphA2-mediated disorder, disease or condition. For example, in some embodiments the disorder, disease or condition associated with EphA2 is an EphA2-expressing cancer (e.g. an EphA2-overexpressing cancer). In one aspect, therefore, provided herein is a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein, for use in treating, preventing or suppressing an EphA2-associated disorder, disease or condition. Also provided is use of a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein, in the manufacture of a medicament for treating, preventing or suppressing an EphA2-associated disorder, disease or condition. Still further provided is a method of treating, preventing or suppressing an EphA2-associated disorder, disease or condition in a subject in need thereof, the method comprising administering to the subject a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein. In some embodiments the EphA2-associated disorder, disease or condition is a cancer. Accordingly, in one aspect a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein is useful in the treatment, prevention or suppression of cancer. As used herein, the term "prevention" involves administration of the protective composition prior to the induction of the disease. "Suppression" refers to administration of the composition after an inductive event, but prior to the clinical appearance of the disease. "Treatment" involves administration of the protective composition after disease symptoms become manifest. Accordingly, provided herein is a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein for use in the treatment, prevention or suppression of cancer, such as a cancer described in more detail herein. Also provided is a method of treating, preventing or suppressing a cancer, such as a cancer described herein, the method comprising administering to a subject having or suspected of having such a cancer a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein. Further provided is use of a bicyclic peptide as provided herein or a compound comprising such a bicyclic peptide, or a pharmaceutical composition as described herein in the manufacture of a medicament for the treatment, prevention or suppression of cancer, such as a cancer as described herein. In some embodiments a cancer is a carcinoma or adenocarcinoma (such as bladder cancer, prostate cancer, breast cancer, lung (e.g. non-small cell) cancer, kidney (e.g. renal cell) cancer, pancreatic cancer, thyroid cancer, uterine cancer, and colorectal cancer); or a sarcoma (e.g. soft tissue sarcoma). In some embodiments the cancer is marked by solid tumours. In some embodiments the cancer is breast cancer. In some embodiments the cancer is associated with EphA2 expression (e.g. with EphA2 over-expression). In some embodiments the cancer is an EphA2-expressing cancer. The compounds and compositions provided herein may be used as standalone therapeutic agents. Alternatively, they may be used in combination with other active agents such as chemotherapeutic agents. For example, they may be used in combination with an EGFR inhibitor (for instance erlotinib, gefitinib, lapatinib or cetuximab), an immunotherapy (for instance pembrolizumab or nivolumab), a tumour-agnostic therapy (for instance larotrectinib) or a chemotherapy (for instance 5-fluorouracil, cisplatin or docetaxel). The compounds and compositions may be used in combination with agents such as radiosensitizing agents. As used herein, a radiosensitizing agent is typically an agent that improves the efficacy of radiotherapy (e.g. targeted radionuclide therapy as described herein), e.g. in killing cells such as cancer cells. In some embodiments a radiosensitizing agent induces DNA damage and / or inhibits DNA damage repair in irradiated cells. In some embodiments a DNA damage repair inhibitor is a PARP inhibitor. In some embodiments a radiosensitizing agent is selected from the group consisting of thiol group suppressors, compounds forming cytotoxic radiolytic by-products, post-irradiation cell process inhibitors, DNA binding thymine analogs, and radical stabilizers such as oxygen and oxygen mimics. When two or more active agents are administered to a subject, they may be administered simultaneously, separately or sequentially. When used to treat a cancer, the compounds and compositions provided herein may be used in alleviating, ameliorating or preventing aggravation of the symptoms of the cancer. Typically, treating a cancer may comprise reducing progression of the cancer, e.g. increasing progression free survival. Treating a cancer may comprise preventing or inhibiting growth of a tumour associated with the cancer. Treating a cancer may comprise preventing metastasis of the cancer. Preferably, treating a cancer may comprise reducing the size of a tumour associated with the cancer. As such, the treatment may cause tumour regression in the cancer. Treating a cancer may comprise reducing the number of tumours or lesions present in the patient. When the treatment reduces the size of a tumour associated with the cancer, the size of the tumour is typically reduced from base line by at least 10%. Base line is the size of the tumour at the date treatment with the compound is first started. The size of the tumour is typically as measured in accordance with version 1.1 of the RECIST criteria (for instance as described in Eisenhauer et al, European Journal of Cancer 45 (2009) 228-247). The response to the treatment with the compound may be complete response, partial response or stable disease, in accordance with version 1.1 of the RECIST criteria. Preferably, the response is partial response or complete response. The treatment may achieve progression free survival for at least 60 days, at least 120 days or at least 180 days. The reduction in tumour size may be greater 20%, greater than 30% or greater than 50% reduction relative to base line. The reduction in tumour size may be observed after 30 days of treatment or after 60 days of treatment. In one aspect, the subject is a mammal, in particular a human. However, it may be non-human. Preferred non-human animals include, but are not limited to, primates, such as marmosets or monkeys, commercially farmed animals, such as horses, cows, sheep or pigs, and pets, such as dogs, cats, mice, rats, guinea pigs, ferrets, gerbils or hamsters. The subject can be any animal that is capable of being infected by a bacterium. A subject is typically a human patient. The patient may be male or female. The age of the patient is typically at least 18 years, for instance from 30 to 70 years or from 40 to 60 years. A compound or composition as provided herein may be utilised in prophylactic and therapeutic settings to aid in the alteration, inactivation, killing or removal of a select target cell population in a mammal. In addition, the compound or composition may be used extracorporeally or in vitro selectively to kill, deplete or otherwise effectively remove a target cell population from a heterogeneous collection of cells. Blood from a mammal may be combined extracorporeally with the selected compound or composition whereby the undesired cells are killed or otherwise removed from the blood for return to the mammal in accordance with standard techniques. A compound or composition as provided herein can be administered to the subject in order to prevent the onset or reoccurrence of one or more symptoms of the disorder. This is prophylaxis. In this embodiment, the subject can be asymptomatic. A prophylactically effective amount of the compound or composition is administered to such a subject. A prophylactically effective amount is an amount which prevents the onset of one or more symptoms of the disorder. A compound or composition as provided herein can be administered to the subject in order to treat one or more symptoms of the disorder. In this embodiment, the subject is typically symptomatic. A therapeutically effective amount of the compound or composition is administered to such a subject. A therapeutically effective amount is an amount effective to ameliorate one or more symptoms of the disorder. A compound or composition described herein may be administered in a variety of dosage forms. The administration can be by any appropriate mode, including orally, parenterally, subcutaneously, intravenously, intravesically, intramuscularly, intraperitoneally, intrasternally, transdermally, via the pulmonary route, by direct infusion with a catheter, as a suppository, or by inhalation. The dosage and frequency of administration will depend on the age, sex and condition of the patient, concurrent administration of other drugs, counterindications and other parameters to be taken into account by the clinician. The compound or composition is typically formulated for administration with a pharmaceutically acceptable excipient, carrier or diluent. Solid oral forms may contain, together with the active compound, diluents, e.g. lactose, dextrose, saccharose, cellulose, corn starch or potato starch; lubricants, e.g. silica, talc, stearic acid, magnesium or calcium stearate, and / or polyethylene glycols; binding agents; e.g. starches, arabic gums, gelatin, methylcellulose, carboxymethylcellulose or polyvinyl pyrrolidone; disaggregating agents, e.g. starch, alginic acid, alginates or sodium starch glycolate; effervescing mixtures; dyestuffs; sweeteners; wetting agents, such as lecithin, polysorbates, laurylsulphates; and, in general, non toxic and pharmacologically inactive substances used in pharmaceutical formulations. Such pharmaceutical preparations may be manufactured in known manner, for example, by means of mixing, granulating, tableting, sugar coating, or film coating processes. Liquid dispersions for oral administration may be syrups, emulsions and suspensions. The syrups may contain as carriers, for example, saccharose or saccharose with glycerine and / or mannitol and / or sorbitol. Inhaled (aerosolised) forms may be administered as a solution or suspension, e.g. by a metered dose inhaler (MD I) or a nebulizer such as an electronic or jet nebulizer, or alternatively as a powdered drug, such formulations may be administered from a dry powder inhaler (DPI). When formulated for inhaled administration, the compound or composition may be delivered in the form of particles which have a mass median aerodynamic diameter (MMAD) of from 1 to 100 pm, preferably from 1 to 50 pm, more preferably from 1 to 20 pm such as from 3 to 10 pm, e.g. from 4 to 6 pm. When the compound or composition is delivered as a nebulized aerosol, the reference to particle diameters defines the MMAD of the droplets of the aerosol. The MMAD can be measured by any suitable technique such as laser diffraction. Suspensions and emulsions may contain as carrier, for example a natural gum, agar, sodium alginate, pectin, methylcellulose, carboxymethylcellulose, or polyvinyl alcohol. Suspension or solutions may contain, together with the active compound, a pharmaceutically acceptable carrier, e.g. sterile water, olive oil, ethyl oleate, glycols, e.g. propylene glycol, and if desired, a suitable amount of lidocaine hydrochloride. Typically solutions may contain as carrier, for example, sterile water or preferably they may be in the form of sterile, aqueous, isotonic saline solutions. A therapeutically or prophylactically effective amount of the compound or composition may be administered to a subject. In certain therapeutic applications, an adequate amount to accomplish at least partial inhibition, suppression, modulation, killing, or some other measurable parameter, of a population of selected cells is defined as a "therapeutically-effective dose". The dose may be determined according to various parameters, especially according to the compound used; the age, weight and condition of the subject to be treated; the severity of the disease and the general state of the patient's own immune system; the route of administration; and the required regimen. Again, a physician will be able to determine the required route of administration and dosage for any particular subject. A typical daily dose is from about 0.005 to 10 mg per kg, more often from about 0.005 mg / kg to about 5 mg / kg, or from about 0.005 mg / kg to about 2 mg / kg, according to the activity of the specific inhibitor, the age, weight and conditions of the subject to be treated, the type and severity of the disease and the frequency and route of administration. For prophylactic applications, compositions containing the present peptide ligands or cocktails thereof may also be administered in similar or slightly lower dosages. As will be appreciated from the above, in some embodiments the compound or composition comprises a radionuclide and may be applied in radiotherapy (e.g. targeted radionuclide therapy and / or theranostics). In some embodiments the radiotherapy (e.g. targeted radionuclide therapy) is a therapy for a condition or disorder such as a condition or disorder associated with EphA2 expression, such as a disorder described herein, e.g. a cancer described herein. In some such embodiments, the dose of the compound or composition provided herein contains between about 5 mCi and about 200 mCi radioactivity, such as between about 10 mCi and about 150 mCi, e.g. between about 20 mCi and about 100 mCi, such as between about 25 mCi, about 50 mCi. In some embodiments, the dose of the compound or composition does not cause an adverse event (AE) in the subject, such as, e.g., an AE greater than or equal to grade 3 (i.e., severe AE). In some embodiments, the dose does not exceed a radiation dose of about 23 Gy to the kidneys and / or a radiation dose of about 1.5 Gy to the bone marrow. In some embodiments, the dosimetry and / or biodistribution of a compound as provided herein is evaluated following administration of the compound to the subject. For example, dosimetry and biodistribution can be evaluated using nuclear imaging at from about 1 to about 7 days after administration to the subject. Nuclear imaging methods are described in more detail herein. Methods for dosimetry analysis are known in the art and include, but are not limited to, descriptive statistics (e.g., mean, median, standard deviation, etc.) reported for AUC based on activity concentration-time curves of the compound (e.g., separately for discernible thoracic and abdominal organs, target lesion, and blood), maximum uptake (e.g., achieved in %) at the target lesion and in discernible organs, specific absorbed dose per organ (pGy / MBq), and cumulative absorbed organ doses (Gy). In some cases, organs receiving the highest absorbed dose assessed by equivalent dose to tissue are tabulated using frequency and proportion. In some cases, graphic tools are used to describe the endpoints. When the compound or composition is administered to a subject in combination with another active agent, the dose of the other active agent can be determined as described above. The dose may be determined according to various parameters, especially according to the agent used; the age, weight and condition of the subject to be treated; the route of administration; and the required regimen. Again, a physician will be able to determine the required route of administration and dosage for any particular subject. A typical daily dose is from about 0.01 to 100 mg per kg, preferably from about 0.1 mg / kg to 50 mg / kg, e.g. from about 1 to 10 mg / kg of body weight, according to the activity of the specific agent, the age, weight and conditions of the subject to be treated, the type and severity of the disease and the frequency and route of administration. Imaging methods The compounds and compositions provided herein are also useful in imaging methods. In some embodiments the provided methods of diagnosis comprise imaging a subject having or suspected of having a disease, disorder or condition such as a disease, disorder or condition associated with EphA2 expression as described in more detail herein, such as a cancer. Accordingly, provided herein is a method of imaging a subject comprising administering to the subject a compound or composition as provided herein, and taking one or more images of the subject. With reference to compounds and compositions provided herein, wherein the compound comprises a radioisotope (i.e. wherein the compound is radiolabelled), any device or method known in the art for detecting the radioactive emissions of radionuclides in a subject may be used. For example, single photon emission computerized tomography (SPECT), which detects the radiation from a single photon gamma-emitting radionuclide using a rotating gamma camera, and radionuclide scintigraphy, which obtains an image or series of sequential images of the distribution of a radionuclide in tissues, organs, or body systems using a scintillation gamma camera, may be used for detecting the radiation emitted from a radiolabeled compound described herein. Positron emission tomography (PET) is another suitable technique for detecting radiation in a subject. Laparoscopic probes for detecting radiation concentrated in solid tissue tumors have been described (e.g. U.S. Patent No. 5,429,133). Nuclear magnetic resonance (NMR)-based methods (e.g., magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI)) or any other imaging technique known to one of skill in the art (including, but not limited to, computed tomography (CT)) may be combined with methods that are suitable for detecting the radioactive emissions of radionuclides. In some embodiments the one or more images are PET or SPECT images. Accordingly, in some embodiments the method comprises administering to the subject a compound or composition as provided herein and taking one or more PET or SPECT images of the subject. In some embodiments a SPECT image is obtained by single photon emission computerized tomography / computed tomography (SPECT / CT). In some embodiments the methods can be used to image a subject in circumstances wherein the subject can be asymptomatic. In some embodiments the subject is suffering or is suspected of suffering from a disease, disorder or condition such as a disease, disorder or condition associated with EphA2 expression such as a disorder described in more detail herein, such as cancer. In some embodiments, radiation from a radionuclide is used to determine where the radiolabelled compound is concentrated in a subject, with such concentration typically being an indicator of the location of a tumor or tumor cells (e.g. the location of a solid tumor). In some embodiments the method is a method of imaging a disorder, disease or condition associated with EphA2 expression in a subject. In some embodiments the method is a method of imaging a subject or a part thereof or an organ of a subject, wherein the subject has or is suspected of having a disorder, disease or condition associated with EphA2 expression. In some embodiments the method comprises administering to the subject a compound or composition as provided herein and taking one or more images of the subject, such as one or more PET or SPECT images. In some embodiments the disorder, disease or condition associated with EphA2 expression is cancer. In some embodiments the method is a method of imaging a cancer, pre-cancerous or benign tumour or growth. Such a method is particularly valuable when the subject (i) has suffered from or is suffering from cancer, or (ii) is susceptible to cancer. Cancers are described in more detail herein. In some embodiments the method is a method of imaging a solid tumor. In some embodiments the subject may undergo whole body planar imaging (e.g., anterior and posterior view) and SPECT (e.g. SPECT / CT) (e.g., skull vertex extending through the perineum, terminating at the proximal thighs; approx. 2-4 bed positions) following administration of the compound or composition. In some embodiments, the distribution of the compound in the subject may be determined using e.g. whole-body planar SPECT (e.g. SPECT / CT) imaging. In some embodiments the distribution of the compound in a tumor (e.g., a primary tumor or cancerous lesion), blood, gall bladder, liver, heart, lung, spleen, kidneys, pancreas, stomach, small intestines, bladder, skin, muscle, bone, large intestines, and / or brain of a subject is determined. As a non-limiting example, radiation-absorbed doses to kidneys, stomach, uninvolved liver, bone marrow and the whole body together with any other organs displaying accumulation of the therapeutic conjugate may be calculated based on the analysis of serial blood counts and SPECT (e.g. SPECT / CT) scans. In some cases, the SPECT (e.g. SPECT / CT) images are used to compute the volumetric absorbed radiation dose in the diseased and healthy tissues, e.g., activity concentration-time curves for normal tissues can be generated from region-of-interest (ROI) analysis from the SPECT (e.g. SPECT / CT) scans, activity concentration-time curves for red marrow and heart can be generated from blood activity concentration measured by a well scintillation counter, and / or volumes of interest (VOI) can be generated for each patient. In some cases, the activity concentration in red bone marrow is equal to that in blood. In some cases, activity concentration-time curves are integrated (e.g., either analytically or numerically as appropriate) to yield AUC values from which so-called residence times are generated. In some cases, these data are inputted into an organ dosimetry software (e.g., OLINDA / EXM) to generate absorbed dose estimates for normal tissues. In some cases, a supplementary dosimetry assessment is performed including, e.g., lesion absorbed dose estimates based on image ROI analysis. In some cases, absorbed doses are normalized to administered activity and expressed in terms of mGy / MBq. Diagnosis The compounds and compositions provided herein may be used in methods of diagnosis. The methods of diagnosis may comprise taking one or more images as described herein, e.g. one or more images of a subject or a part of a subject wherein the subject has or is suspected of having a disease, disorder or condition as described herein, such as a disease, disorder or condition associated with EphA2 expression. Accordingly, provided herein is a compound or composition as described herein for use in a method of diagnosing a pathology in a subject. The subject may be a subject as described in more detail herein. The pathology may be a pathology as described herein, such as a disease, disorder or condition associated with EphA2 expression. In some embodiments the method may comprise contacting the compound or composition with a sample obtained from the subject (e.g. a biological fluid such as blood, serum, urine, or cerebrospinal fluid; and virology swab samples, biopsy and necropsy tissues) and detecting a change characteristic of the pathology in the sample in the presence of the compound or composition. In some embodiments the method may comprise administering the compound or composition to a subject and taking one or more images of the subject or a portion thereof (e.g. an organ or body region thereof). In some embodiments the one or more images are one or more PET or SPECT (e.g. SPECT / CT) images. In some embodiments the method comprises (a) administering to the subject a compound or composition as described herein, wherein said compound or composition comprises a radionuclide; (b) imaging the subject by PET or SPECT (e.g. SPECT / CT); and (c) determining whether or not the subject has a disorder such as a disorder described in more detail herein, e.g. a cancer, or quantifying the extent of the disorder. Also provided is a compound or composition as described herein, wherein said compound or composition comprises a radionuclide, for use in a method of diagnosing a disorder (e.g. a disease, disorder or condition associated with EphA2 expression, e.g. cancer) in a subject; the method comprising (a) administering to the subject the compound or composition, (b) imaging the subject by PET or SPECT (e.g. SPECT / CT); and (c) determining whether or not the subject has the disorder or quantifying the extent of the disorder. Also provided is a method of diagnosing a disease, disorder or condition (e.g. disease, disorder or condition associated with EphA2 expression, e.g. cancer) in a subject, the method comprising (a) administering to the subject a compound or composition as described herein, wherein said compound or composition comprises a radionuclide, (b) imaging the subject by PET or SPECT (e.g. SPECT / CT); and (c) determining whether or not the subject has the disorder or quantifying the extent of the disorder. Determining whether or not the subject has a disorder such as cancer can be conducted according to any suitable technique. For example, the skilled person may associate accumulation of the compound or composition (also referred to as a tracer) as a marker for cancer. Determining accumulation of the compound, composition or tracer may be conducted relative to a standard such as an image obtained from a different subject or from a panel of different subjects, or from the same subject at a different time, or from a different part of the body of the same subject. In some embodiments the diagnostic method comprises (a) administering to the subject a compound or composition as described herein, wherein said compound or composition comprises a radionuclide, (b) imaging the subject by PET or SPECT (e.g. SPECT / CT); (cl) comparing the images with a standard (e.g. an image obtained from a different subject or from a panel of different subjects, or from the same subject at a different time, or from a different part of the body of the same subject); and (c2) determining whether or not the subject has the disorder or quantifying the extent of the disorder based on differences between the obtained image and the standard. In some embodiments provided herein, a disease, disorder or condition is diagnosed as described herein, and is also treated as described herein. For avoidance of doubt, when a compound as described herein is used to diagnose a disease, disorder or condition as described herein and a compound as described herein is used to treat a disease, disorder or condition as described herein, the compounds may be the same or different. In some embodiments, a disease, disorder or condition is diagnosed as described herein, and is treated using a compound that has therapeutic efficacy against the disease, disorder or condition. In some embodiments, the compound that has therapeutic efficacy against the disease, disorder or condition is a compound that binds to EphA2. In some embodiments, said compound comprises a bicyclic peptide (for example a bicyclic peptide that binds to EphA2) and a toxin. The following examples illustrate the invention. They do not however limit the invention in any way. In particular, there are many assays for protein binding and so a negative 5 result in any specific assay is not determinative. The invention is defined according to the claims. Examples 10   Example 1 — Experimental methods and synthesis of a bicyclic compound as provided herein Nine phage libraries with random residues between the three bicyclic peptide-linking cysteine residues were panned against EphA2 using a hydrophilic TATA scaffold. From this panning, six distinct chemical families were identified. The abundantly occurring sequences 15 were submitted to affinity maturation, giving a lead series with high affinity for EphA2 (Ki <10 nM). Chemical modifications to increase the hydrophilic character of the Bicycle series as well as increase the stability towards plasma proteases were performed. Based on this, a bicycle having the structure shown below (Compound 1) was synthesized HO The peptide chain, [DOTA][B-Ala][SarlO]A[HArg]DC[HyP][Cba]VNPLCLHP[dD]W[HArg]C[CONH2] 5 contains both coding and non-coding amino acids, with coding amino acids shown as their single letter code, and non-coding amino acids shown in square brackets. The C-terminus terminates as a primary amide. The peptide sequence was cyclised using TATA (1,3,5-triacryloylhexahydro-l,3,5-triazine). The non-coding building blocks have the following identities: Code     Name [B-Ala]     Beta-alanine [Sar]        Sarcosine [HArg]     Homoarginine [HyP]       (2S,4R)-4-hydroxypyrrolidine-2-carboxylic acid [Cba]       Beta-cyclobutyl alanine [dD]        D-aspartic acid [DOTA]    l,4,7,10-Tetraazacyclododecane-l,4,7,10-tetraacetic acid Compound 1 is designed to improve proteolytic stability, while retaining affinity for EphA2. Without being bound by theory, the inventors believe that incorporation of an additional non-natural amino acid, cyclobutyl alanine at the position above, is beneficial is this regard. Compound 1 was synthesised using solid phase peptide synthesis and cyclized according to previously described methods (see, Mudd GE, Brown A, Chen L, et al. Identification and Optimization of EphA2-Selective Bicycles for the Delivery of Cytotoxic Payloads. J Med Chern 2020; 63: 4107-16, the entire contents of which are hereby incorporated by reference). In brief, bicyclic peptide was synthesized on Rink amide MBHA resin using standard Fmoc (9-fluorenylmethyloxycarbonyl) solid-phase peptide synthesis, either by manual coupling (for large scale) or using a Biotage Syro II automated peptide synthesizer (for small scale). Following TFA-based cleavage from the resin, the peptide was precipitated in cold isopropyl ether and centrifuged (3 min at 3000 rpm). The solid was washed with isopropyl ether for two additional times, dried under vacuum for 2 hours and dissolved in 40:60 acetonitrile / water. The crude peptide (at ~1 mM concentration) was then cyclized with 1.0 equiv of TATA scaffold, using ammonium bicarbonate in water (1.0 M) as a base to adjust to pH 8. Completion of cyclization was determined by LC-MS. Once complete, the cyclization reaction was quenched using a cysteine solution (10 equiv. with respect to the peptide), and the solution was adjusted to pH 7 using IM HC1 before lyophilization. Afterwards, the residue was dissolved in an appropriate solvent and purified by RP-HPLC. Peptide fractions of sufficient purity and the correct molecular weight (verified by either MALDI-TOF and HPLC or LC-MS) were pooled and lyophilized. DOTA was coupled to the peptide chain during solid phase peptide synthesis using the protected precursor DOTA(tBu)3 (GL Biochem, CAS 13707654-1). Rink resin (1.85 g, 0.54 mmol / g) was used to generate 1312.4 mg of Compound 1 (36.7% yield). MS (ESI): exact mass calcd, 3581.11; found, m / z 1791.5 ([M + 2H]2+), 1194.7 ([M + 3H]3+). Purity >95% by HPLC. 68Ga was obtained from a commercially available TiO2-based 68Ge / 68Ga generator (Eckert & Ziegler Radiopharma GmbH, Berlin, Germany). The generator was eluted with 0.1 M HCl(aq.), the 68Ga was then trapped via SCX cartridge and eluted as [68Ga]GaCh for further use in radiolabeling reactions. Lutetium-177 was purchased from Isotope Technologies Munich (ITM, Munich, Germany) as carrier-free [177Lu]LuC13 in 0.05 M HCl(aq.). Radiolabeling with 68Ga was performed by mixing equal parts (40 - 150 pL) of 1.0 M HEPES buffer (4-(2-hydroxyethyl)-1 -piper-azineethanesulfonic acid, pH = 4.03) and 68Ga-eluate (40 - 150 pL, 30 - 120 MBq), pH of the mixture was adjusted to 4.00 whenever needed by addition of 10 % NaOH(aq.). Thereafter, 2-5 nmol (2 - 5 pL of a 1 mM solution) of precursor in DMSO was added. The mixture was heated to 95 °C for 5 minutes, thereafter HPLC and iTLC analyses were carried out (Figures 7 and 9). The labeled compound was always used without further purification and only when the amount of free ionic and colloidal 68Ga (determined by HPLC and TLC) was < 2%. For in vivo applications, the labeling was diluted to the required concentration with 0.9% NaCl and adjusted to pH ~7 with 30% NaOH(aq.). Similarly, radiolabeling with 177Lu was performed by mixing 50 pL of NaOAc buffer (sodium acetate, pH = 5.4), 2-5 nmol (2 - 5 pL of a 1 mM solution) of precursor in DMSO, and 2 - 15 pL of [177Lu]LuCl3 (~ 20- 100 MBq) diluted in 10 - 20 pL of 0.05 M HCl(aq.). The mixture was heated to 95 °C for 15 minutes and analyzed by HPLC and iTLC (Figures 8 and 9). Like the 68Ga-labeled compound, the 177Lu-labeled peptide was used without further purification. Indium-111 was purchased from Curium (London, UK) as carrier-free [inIn]InC13 in 0.05 M HCl(aq.). Radiolabeling was performed by adding 65 MBq of In-111 stock to an Eppendorf containing 144 pl of 0.1 M ammonium acetate pH 5.5 and 5 pl (5 pg) of test article. The reaction was heated at 90 °C with vigorous shaking (500 rpm) for ~10 min. Labelling efficiency for the crude material was assessed using iTLC and HPLC. iTLC was performed using iTLC-SG plates which were spotted with 0.5 pL of reaction mixture 10 mm higher than the bottom of the plate. The plates were allowed to develop using a mobile phase of ammonium acetate (0.1 mM) with EDTA (25 nM) buffer. iTLC strips were visualised on a cyclone phosphor imager. For HPLC ~ 500kBq was injected onto a Jupiter Cl8 column and eluted using H2O (0.1% TFA) and CH3CN (0.1% TFA), 5% - 80% over 20 minutes. After iTLC and HPLC analysis (Figure 10) the preparation was purified on a pre-activated Cl8 Sep-Pak cartridge (flushed with 1 mL ethanol, followed by 5 mL PBS buffer and left wet) by syringe addition. Activities contained in the empty reaction vessel, tC18 cartridge, non-retained fraction and reception vial were measured in a dose calibrator and recorded. The product was eluted with 200 pL of 50% ethanol / PBS buffer followed by 800 pL of PBS buffer to bring the final formulation up to 1 mL (ethanol content -10%). The resulting ['11 In]Compound 1 was formulated in PBS with 5 mg sodium ascorbate, 0.05% v / v Tween-20 and 10% ethanol for administration to animals. Physicochemical properties For the determination of the lipophilicity (logDoct / PBS) of Compound 1, labeling was performed with 68Ga (apparent molar activity 1 GBq / pmol). Thereafter an aliquot of 10 pL was added into a 1:1 mixture of n-octanol:PBS (500 pL total volume). After shaking and centrifugation at 9,000 rpm for 10 min, a 20 pL fraction of each phase was collected and analyzed in a gamma counter (Wizard2, Perkin Elmer, Germany). Subsequently, the counts of each phase were used to calculate the partition coefficient. To determine binding to plasma proteins, Compound 1 was labeled with 68Ga (apparent molar activity 1 GBq / pmol). Thereafter, 10 pL of the labeling mixture were added to 100 pL of mouse or human plasma (mouse: BioIVT, United Kingdom, human: Sigma Aldrich, Germany). The mixture was left for 15 min at room temperature. Afterwards, the plasma was loaded into an ultrafiltration device (Amicon Ultra 0.5ml - 30 kDa, Merck, Germany) and centrifuged at 14,000 rpm for 30 min at r.t. The filtrate and the membrane were measured in a gamma counter (Wizard2, Perkin Elmer, Germany). The amount of plasma-bound compound was calculated based on the counts in the filtrate relative to the total counts (filtrate + membrane). Determination of stability in plasma was performed with the 177Lu-labeled peptide. 10 pL of the labeled compound were added into human or mouse plasma (mouse: BioIVT, United Kingdom, human: Sigma Aldrich, Germany) and incubated at 37 °C. Aliquots were taken at different time points during incubation (1, 6, 24, 48 and 72 h) to which acetonitrile (30 uL) was added in order to precipitate plasma proteins. After centrifugation at 13,000 rpm for 5 min at r.t. the supernatant was taken and analyzed via HPLC. Cell culture and in vitro assays For the in vitro evaluation of the novel compound, EphA2-expressing HT1080 cells (CCL-121, ATCC, last authentication April 2023) and MCF-7 cells (HTB-22, ATCC) were cultured in MEM modified with Earle’s Balanced Salt Solution (EMEM, Sigma Aldrich, Germany), non-essential amino acids, 2 mM L-glutamine, 1500 mg / L sodium bicarbonate, 10 % FBS, 1 % sodium pyruvate and 1 % pen / strep. PC-3 cells (CRL-1435, ATCC) were cultured in F-12K medium supplemented with 10% Foetal Bovine Serum (FBS). Cells were cultured at 37 °C in humidified air supplemented with 5 % CO2. When the cells reached a confluence > 80 %, they were harvested using trypsin-EDTA and subsequently processed. Binding and internalization properties Protein production method Cloning: Human EphA2 (residues 27-529), was cloned into pEXPR-IBA44 between the 5' Nhel and 3' Bsal sites to make constructs expressing a BM40 signal sequence and C-terminal 6xHIS tag. Expression and purification: HEK293 f / s cells at 1 x 106 mL'1 in freestyle media (Thermo Fisher) were transfected with 1 pg DNA per million cells by PEI either 2:1 or 3:1 PEI:DNA ratio. On day 2 valproic acid was added to 2.2 mM. Supernatant was harvested 5 days post transfection and loaded on a 1 ml Ni-NTA agarose resin (Thermo Fisher) (wash buffer: 20 mM HEPES pH7.6, 0.5 M NaCl, 5 mM imidazole, 0.01% Tween-20 buffer; elution buffer: 20 mM HEPES pH 7.6, 0.5 M NaCl, 300 mM imidazole, 0.01% Tween-20). Protein was concentrated to a volume of 2 mL and loaded onto an S-200 Superdex column (GE Healthcare) in 20 mM HEPES pH7.6, 150 mM NaCl, 0.01% Tween-20 at 1 mL / min. 2 mL fractions were collected and those containing EphA2 protein were concentrated. Mouse EphA2 was purchased from R&D Systems, product number 639-A2. Human EphAl was purchased from Sino Biological, product number 15789-H02H. Human EphA3, EphA6 and EphA7 were purchased from R&D Systems, product numbers 644-A3, 5606-A6, and 6756-A7, respectively. 2-Deoxy-2-[18F]fluoroglucose (2 -[18F]FDG) was provided by EuroPET GmbH (Freiburg, Germany) as a ready-to-inject solution. EphA2 SPR method SPR experiments were performed on a Biacore 8K+ instrument, with methods matched for both human and mouse EphA2 protein. Protein was captured on to a Cytiva NTA sensor chip, via the expressed His-tag; this was followed by primary amine coupling chemistry to covalently immobilise the protein to the chip at 25°C. Initially the surface was injected with 0.5mM NiCh for 2 minutes, followed by activation of the carboxymethyl dextran surface for 7 minutes using an injection of a 1:1 ratio of 0.4 M l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) / 0.1 M N-hydroxy succinimide (NHS) at a flow rate of 10 pl / min. Human EphA2 protein was captured to the Ni-NTA surface to a level of 200-300RU and mouse EphA2 captured to 500-800RU; the residual activated groups were then blocked with a 7 minute injection of 1 M ethanolamine (pH 8.5):HBS-N (1:1). Finally, the Ni-NTA surface was chelated with a 1-minute injection of 350mM EDTA. Peptide was prepared in PBS / 0.05% Tween 20 with a final DMSO concentration of 0.5% with a top peptide concentration was 100 or 500nM and 5 further 3-fold dilutions. The peptide was titrated over the chip using single cycle kinetics at 25°C at a flow rate of 75pl / min with 60 seconds association and 4000 seconds dissociation. Data were corrected for DMSO excluded volume effects. All data were double referenced for blank injections and reference surface using standard processing procedures. Data were characterised with a 1:1 kinetic binding model to determine ka (M-1sl), kd (s'1) and Kd (nM), compensating for mass transport limitations where appropriate. All data processing was performed using Cytiva insight evaluation software. In vitro cell binding and internalization Binding affinity was determined through saturation binding experiments. On an ice-cold pre-conditioned 96-well plate (MultiScreen-DV, 0,65 pm, Merck KGaA, Germany), HT1080 cells were added in each well (105 cell / well). This was followed by addition of 177Lu-labeled peptide (apparent molar activity of 5 GBq / pmol) in increasing concentrations (1, 2.5, 5, 10, 25, 50, 75, 100, 250, 500, 750 and 1000 nM, in cell culture media + 0.01% Tween 20) for every row of the plate, for a total volume of 200 pL. The plate was left on ice for 2 h. Thereafter, the liquids were removed via vacuum manifold and each well washed with ice-cold PBS (5 x 100 pL), after removal of PBS and drying of the membranes the 96-well plate was pierced, the membranes collected and measured in a gamma counter (Perkin Elmer Wizard2, Germany). Thereafter, the counts were fitted into a non-linear regression algorithm (Prism 8.0.1, GraphPad) to obtain the Kd. To assess internalization and specificity, HT1080 cells (105 cells / well) were seeded in a 24-well plate coated with poly-L-lysine one day before the experiment. Previous to the experiment, the culture medium was aspirated, the 68Ga-labeled compound (apparent molar activity of 2 GBq / pmol) diluted in 250 pL of growth medium + 0.01% Tween 20 (c = 32 nM) was added and incubated at 37°C for 45 minutes. To determine specific uptake, 'cold' (non-radiolabeled) Compound 1 was added to half of the wells at an excess concentration of 200 pM / well or, alternatively, the cells were kept at 4 °C during the experiment. Following the incubation, the cells were thoroughly rinsed with cold PBS (3x1 mL). Subsequently, surface bound radioactivity was removed by washing with 50 mM glycine (pH 2.8, 2 x 500 pL). Finally, the internalized fraction was determined by lysing the cells with 0.5 M NaOH (500 pL). All fractions were collected and measured using a gamma counter (Perkin Elmer Wizard2, Germany). All counts were standardized to the initial activity, and specific surface binding as well as specific internalization were calculated by subtracting the non-specific binding values obtained from the wells treated with an excess of‘cold’ compound. Results were calculated and expressed as %AA / 105 cells (% applied activity / 105 cells). The same procedure was followed using MMTV-pyMT cells. In vivo evaluation In vivo pharmacokinetic studies were conducted in male CD-I (ICR) mice, 7-9 weeks of age. Three animals were administered 1 mg / kg of Compound 1 in 25 mM Histidine HC1 and 10% sucrose (pH 7) by intravenous bolus. Serial blood samples were taken at 5 min, 15 min, 30 min, 45 min, 1 h, 2h and 4h post injection. Samples were immediately transferred into low-binding microcentrifuge tubes containing 2 pL K2-EDTA (0.5 M) as anti-coagulant and kept on ice until processed by centrifugation at 4°C, 3200 g for 10 min. The resulting plasma was transferred into low-binding tubes and the protein precipitated by addition of methanol containing 0.5% Triton X-100 and internal standards (100 ng / mL each of labetalol, tolbutamide, verapamil, dexamethasone, glyburide and celecoxib). Samples were centrifuged at 4°C, 12000 g for 15 min and the supernatant removed, frozen over dry ice and stored at -70°C until LC-MS / MS analysis. A calibration curve and quality control samples were prepared in the same matrix. Pharmacokinetic parameters were derived from noncompartmental analysis using the intravenous-noncompartmental model 201 (IV bolus input) in Phoenix WinNonlin version 8.3.5 (Certara, USA). PET / MR imaging PET / MR imaging was performed in 7- to 8-week-old female BALC / c nu / nu mice (Charles River, Germany) which were subcutaneously inoculated on the right flank with 106 HT1080 cells (1:1 in PBS:Matrigel). Tumor growth was monitored, and once size was approx. 1cm3, mice were injected intravenously via tail vein with 150 pmol of the 68Ga-labeled compound (8.98 MBq). For the PET imaging experiments with blocking, an excess (15 nmol) of non-radiolab eled Compound 1 was injected 5 mins before the injection of 300 pmol (4 MBq) of the 68Ga-labeled compound. PET scan consisted of a dynamic scan from 0 to 60 min p.i. (30 frames), followed by non-triggered localizer and a 3-step whole body Tl-weighed 3D MR-scan (PET / MR 3T, Bruker BioSpin, Germany). Additionally, a 2 h p.i. static image (10 min scan) was recorded, followed by the same MR scan protocol. Data was obtained via ParaVision 3.0 and reconstructed using a Maximum-Likelihood Expectation-Maximization (MLEM) algorithm at 0.5 mm for 18 iterations. Reconstructed data was analyzed on PMOD 3.7. For imaging of MMTV-PyMT, MMTV-PyMT female mice (n = 6) were scanned every two weeks, starting on week 4 until week 14 (defined end-point according to termination criteria) of their life span. Mice were injected via the tail vein with 150 pmol of the 68Ga-labeled compound (5.4 ± 2.5 MBq). After 1-hour, mice were anaesthetized (2 % isoflurane in air) and a PET static image (10 min scan) was recorded, followed by a 3-step whole body Tl-weighed 3D MR-scan (PET / MR 3T, Bruker BioSpin, Germany). Additionally, as negative control, wild-type (wt) female mice (n = 4) from the same strain were imaged in matching points employing the identical imaging protocol. Further control experiments with 2-[18F]FDG were performed, in all the mice, at weeks 6, 10 and 14. Mice were injected via the tail vein with 10.4 ±1.0 MBq of 2-[18F]FDG and submitted to the imaging protocol described above. In all cases, data was obtained via Para Vision 3.0 and reconstructed using a Maximum-Likelihood Expectation-Maximization (MLEM) algorithm at 0.5 mm for 18 iterations. Reconstructed data was analyzed on PMOD 3.7. Cut and count biodistribution study For the cut and count biodistribution study of [177Lu]Lu-Compound 1, the HT1080 xenograft model was used. Once tumors reached a comparable size to the PET imaging study, mice were injected via the tail vein with 150 pmol of the 177Lu-labeled bicyclic peptide and sacrificed at 1, 2, 6 and 24 h p.i. (n = 3 mice per time point). Thereafter, mice were dissected, and organs of interest harvested, which included: blood, heart, lung, spleen, liver, kidneys, muscle (quadriceps), intestine, brain, tail, bone (femur) and grafted tumor. SPECT / CT imaging SPECT / CT imaging was performed in 5- to 8-week-old male athymic nude mice (Janvier Labs, UK) which were subcutaneously inoculated on the right upper flank with 5 x 106 PC-3 cells (1:1 in PBS:Matrigel). Tumor growth was monitored, and once size was approx. 200-500 mm3, mice were injected intravenously via tail vein with 0.83 ±0.02 pg (232 pmol) of the [inIn]Compound 1 (5.3 ± 0.2 MBq). Mice were imaged using wholebody static SPECT followed by a CT (VECTor6-CT, Milabs) at each timepoint (30-minute SPECT scan time starting at Ih and 24h post injection). During the scan, mouse temperature was maintained at 37 °C, respiration was monitored, and anaesthesia was maintained using isoflurane in oxygen. Reconstructed images were generated in units of activity, namely, the values assigned to the voxels (volume elements) comprising the 3D reconstructed SPECT images were in units of MBq or equivalent. Reconstructed images were processed with VivoQuant (Invicro) including co-registration of SPECT and CT, resampling to 0.8 mm isotropic voxels, and cropping to a uniform size for presentation and further analysis. ROIs for the left ventricle, liver, spleen, lungs, and muscle were generated by placing fixed volume spheres to encompass areas of representative concentration for each respective region. The bladder ROI was segmented through manual thresholding of the SPECT signal. Fixed volume, encompassing phantoms were placed on both kidneys, and the tumor ROI was drawn manually to encompass the entirety of the tumor. Whole body maximum intensity projection (MIP) images were generated using VivoQuant. SPECT / CT MIP images were generated for each animal at each time point and a color scale adjusted to the range 0-10 %ID / g. Animal experiments were performed according to the directive 2010 / 63ZEU of the European Parliament and the European Council on the protection of animals used for scientific purposes and approved by the Federal Republic of Germany, Regional Council Freiburg (G-17 / 142); or according to United Kingdom’s Guidance on the Operation of Animals (Scientific Procedures) Act of 1986, under Home Office Project License number PP6127261. Statistics All experiments were performed at least in triplicate, with exception of the PET / MR imaging (n = 1). All multiple measurement results are expressed as value ± SD. Data was analyzed and plotted using Prism (version 8.0.1, GraphPad Software), when applicable P values were determined by Student's t-test and were considered significant when smaller than 0.05. Example 2 —In vitro cell binding and internalisation Determination of physicochemical properties of Compound 1 confirmed its hydrophilic nature with a remarkably low logD pH 7.4 in n-octanol / PBS. Furthermore, [68Ga]Ga-Compound 1 showed moderate binding to human and mouse plasma proteins as well as high serum stability, with 94 % of peptide remaining intact after 72 h in human plasma and 40 % in mouse (Figure 11). Compound 1 binds with high affinity to recombinant human EphA2 (hEphA2), as determined by surface plasmon resonance (KD 1.93 ± 0.35 nM, n=2). Importantly, cross reactivity with recombinant mouse EphA2 protein (mEphA2) was also demonstrated (KD 3.82 ± 0.56 nM, n=2), allowing for the detection of any EphA2 mediated uptake in nontumor tissue. See Figure 1 and Table 3. Table 3. Affinity values of Compound 1 obtained from SPR on mouse and human EphA2. Human EphA2, n=2 Mouse EphA2, n=2 KD (M) 1.93E-09 ± 3.54E-10 3.82E-09 ± 5.59E-10 ka (1 / Ms) 1.82E+06 ± 4.24E+04 4.19E+05 ± 9.33E+04 kd (1 / s) 3.52E-03 ± 7.21 E-04 1.57E-03 ± 1.27E-04 Internalization experiments of [68Ga]Ga-Compound 1 revealed specific binding towards EphA2 expressing HT1080 cells 45 min post incubation (Figure 2). The uptake was proven to be specific by blocking with an excess of non-labeled peptide. Additionally, internalization at 4 °C, a temperature in which endocytosis processes are dormant, was decreased and similar to blocked uptakes at 37 °C, further confirming the specificity of the binding to EphA2. Example 3 — PET / SPECT imaging and cut and count biodistribution studies PK parameters of Compound 1 were assessed following intravenous bolus administration to mice at 1 mg / kg (Table 4; Figure 12). Relatively high plasma clearance (24 ml / min / kg, greater than glomerular filtration) and low volume of distribution at steady state (0.39 L / kg) were observed, resulting in a short terminal half-life (0.24 h). Table 4 - Average PK parameters for Compound 1 in mouse following intravenous bolus administration at 1 mg / kg. Abbreviations: AUC = area under the plasma concentration time curve, CLp = plasma clearance, Cmax = maximum mean plasma concentration, ti / 2 = half-life, Vdss = volume of distribution at steady state PK Parameter Compound 1 Cmax (ng / mL) 3322 ti / 2 (h) 0.24 Vdss (L / kg) 0.39 CLp (mL / min / kg) 23.9 AUCo-iast (ng.h / mL) 700 AUCo-inf (ng.h / mL) 701 PET / MR imaging of [68Ga] Ga-Compound 1 in HT1080 mouse xenograft showed high tumor accumulation along with rapid clearance of non-tumor bound peptide through renal pathways as shown by the time-activity-curve (Figure 3). Peak tumor accumulation of 1.70 SUVbw (g / mL) was observed within 60 min p.i.. Tumor-to-muscle ratio at 1 h p.i. and 2 h p.i. proved very high imaging contrast, which is further demonstrated by the maximum intensity projection images and coronal slices (Figure 4). Consistently, imaging of the EphA2-negative MCF-7 xenograft showed no uptake of [68Ga]Ga-Compound 1 in the tumor proving the compound’s specificity. This finding was confirmed by PET imaging in the HT1080 xenograft when blocking with an excess of non-labeled compound (Figure 14). Uptake values for [68Ga]Ga-Compound 1 are shown in Tables 5 and 6. Table 5 - Uptake values of [68Ga] Ga-Compound 1 over 60 minp.i. (in SUVbw) in PET / MRI after injection of 150 pmol in an HT1080 tumor xenograft. Minutes p.i. Tumor Bladder Kidneys Heart Liver Muscle 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.67 0.21 1.64 6.48 1.56 0.08 0.3 0.54 0.25 1.87 4.94 1.45 0.13 0.4 0.53 0.28 1.94 4.11 1.46 0.14 0.5 0.53 0.28 1.93 3.62 1.49 0.16 0.7 0.56 0.27 1.89 3.46 1.53 0.15 0.8 0.56 0.30 1.83 3.18 1.61 0.17 0.9 0.58 0.30 1.75 2.93 1.76 0.19 1.1 0.58 0.30 1.68 2.74 1.76 0.20 1.2 0.61 0.31 1.63 2.59 1.79 0.19 1.3 0.60 0.34 1.59 2.42 1.82 0.22 1.5 0.66 0.37 1.57 2.37 1.73 0.22 1.6 0.67 0.38 1.62 2.26 1.63 0.23 1.7 0.69 0.41 1.70 2.13 1.59 0.24 1.9 0.69 0.40 1.81 2.02 1.49 0.26 2.0 0.70 0.42 1.89 1.94 1.46 0.25 3.0 0.73 0.40 2.29 1.67 1.30 0.27 4.0 0.82 0.40 2.81 1.35 1.13 0.27 5.0 0.91 0.41 3.15 1.16 1.04 0.27 7.0 1.03 0.44 3.54 0.98 0.94 0.28 9.0 1.17 0.51 3.92 0.82 0.86 0.27 11.0 1.27 0.60 4.20 0.74 0.81 0.27 13.0 1.36 0.69 4.42 0.69 0.77 0.25 15.0 1.42 0.76 4.61 0.64 0.74 0.25 20.0 1.51 0.80 4.92 0.58 0.70 0.24 25.0 1.58 0.80 5.29 0.53 0.66 0.22 30.0 1.63 0.79 5.61 0.49 0.64 0.20 35.0 1.67 0.77 5.92 0.45 0.61 0.19 40.0 1.70 0.76 6.18 0.43 0.60 0.18 45.0 1.71 0.75 6.44 0.40 0.59 0.17 60.0 1.71 0.74 6.83 0.35 0.56 0.15 Table 6 - Uptake values of [68Ga]Ga-Compound 1 over 60 minp.i. (in %ID / g) in PET / MRI after injection of 150 pmol in an HT1080 tumor xenograft. Minutes p.i. Tumor Bladder Kidneys Heart Liver Muscle 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 3.2 1.0 7.0 31.3 7.6 0.4 0.3 2.6 1.2 8.3 23.9 7.0 0.6 0.4 2.6 1.3 8.7 19.9 7.0 0.7 0.5 2.6 1.4 8.7 17.5 7.2 0.8 0.7 2.7 1.3 8.5 16.7 7.4 0.7 0.8 2.7 1.4 8.2 15.4 7.8 0.8 0.9 2.8 1.4 7.8 14.2 8.5 0.9 1.1 2.8 1.4 7.6 13.2 8.5 1.0 1.2 3.0 1.5 7.3 12.5 8.7 0.9 1.3 2.9 1.6 7.1 11.7 8.8 1.0 1.5 3.2 1.8 7.0 11.4 8.3 1.1 1.6 3.2 1.9 7.2 10.9 7.9 1.1 1.7 3.3 2.0 7.6 10.3 7.7 1.1 1.9 3.3 2.0 8.2 9.7 7.2 1.3 2.0 3.4 2.0 8.7 9.4 7.1 1.2 3.0 3.5 1.9 10.7 8.0 6.3 1.3 4.0 3.9 1.9 13.3 6.5 5.5 1.3 5.0 4.4 2.0 15.1 5.6 5.0 1.3 7.0 5.0 2.1 16.9 4.7 4.6 1.3 9.0 5.7 2.5 18.7 4.0 4.2 1.3 11.0 6.1 2.9 20.1 3.6 3.9 1.3 13.0 6.5 3.4 21.3 3.3 3.7 1.2 15.0 6.9 3.7 22.3 3.1 3.6 1.2 20.0 7.3 3.9 23.9 2.8 3.4 1.1 25.0 7.6 3.9 25.7 2.6 3.2 1.1 30.0 7.9 3.8 27.3 2.4 3.1 1.0 35.0 8.1 3.7 28.7 2.2 3.0 0.9 40.0 8.2 3.7 29.9 2.1 2.9 0.9 45.0 8.2 3.6 31.1 1.9 2.8 0.8 60.0 8.3 3.6 32.9 1.7 2.7 0.7 Cut and count biodistribution of [177Lu]Lu-Compound 1 confirmed the PET / MRI findings. Tumor enrichment within 1 h p.i. was high with 19.50 ± 3.50 %ID / g (Figure 5). The tumor uptake decreased over time with 5.56 ± 1.24 %ID / g at 6 h p.i. and 1.77 ± 0.51 5 %ID / g at 24 h p.i., however the difference between the tumor uptake at 6 and 24 h p.i. was non-significant (P > 0.05). Non-target organs showed negligible uptake (< 1 %ID / g) throughout all time points. Due to the renal excretion pathway [177Lu]Lu-Compound 1 uptake in kidneys persisted high with 54.86 ± 17.12 %ID / g at 24 h p.i.. Biodistribution values are shown in Tables 7 and 8. 0 Table 7 - Biodistribution values of177Lu-Compound 1 (in %ID / g) at different time points after injection of 150 pmol in an HT1080 tumor xenograft. 177Lu-Compound 1 Organ 1 h p.i. 2 h p.i. 6 h p.i. 24 h p.i. Mean SD n Mean SD n Mean SD n Mean SD n Blood 0.2 0.06 3 0.03 0.01 3 0.02 0 3 0.01 0 3 Heart 0.1 0.03 3 0.03 0 3 0.05 0.01 3 0.03 0.01 3 Lung 0.7 0.3 3 0.19 0.04 3 0.28 0.09 3 0.13 0.05 3 Spleen 0.6 0.1 3 0.16 0.02 3 0.4 0.01 3 0.31 0.08 3 Liver 0.25 0 3 0.15 0.02 3 0.6 0.03 3 0.53 0.15 3 Kidneys 65.3 15.1 3 47.23 1.68 3 62.6 15.28 3 54.86 17.12 3 Muscle 0.06 0 3 0.02 0 3 0.03 0.01 3 0.02 0 3 Intestine 0.34 0.1 3 0.16 0.1 3 0.15 0.01 3 0.1 0.01 3 Brain 0 0 3 0.01 0 3 0.01 0 3 0 0 3 Tumor 19.5 3.5 3 9.99 1.24 3 5.56 1.84 3 1.77 0.51 3 Tail 1.8 0.6 3 0.7 0.42 3 0.83 0.47 3 0.38 0.21 3 Bone 0.3 0.1 3 0.21 0.15 3 0.56 0.02 3 0.44 0.08 3 Table 8 - Tumor-to-organ ratios in selected organs of [I7 / Lu]Lu-Compound 1 at different time points after injection of 150 pmol in an HT1080 tumor xenograft. 1 h p.i. 2 h p.i. 6 h p.i. 24 h p.i. Mean SD n Mean SD n Mean SD n Mean SD n Blood 97.5 26.28 3 333 78.33 3 278 92 3 177 51 3 Heart 195 52.55 3 333 41.33 3 111.2 41.25 3 59 23.56 3 Lung 27.86 10.12 3 52.58 8.86 3 19.86 8.62 3 13.62 5.94 3 Spleen 32.5 6.74 3 62.44 8.73 3 13.9 4.61 3 5.71 2.03 3 Liver 78 14 3 66.6 9.45 3 9.27 3.09 3 3.34 1.23 3 Kidneys 0.3 0.07 3 0.21 0.03 3 0.09 0.03 3 0.03 0.01 3 Muscle 325 58.33 3 499.5 62 3 185.33 81.93 3 88.5 25.5 3 Intestine 57.35 15.26 3 62.44 32.14 3 37.07 12.43 3 17.7 5.28 3 Tail 10.83 3.15 3 14.27 6.91 3 6.7 4.36 3 4.66 2.76 3 5          SPECT / CT imaging with [niIn]In-Compound 1 in PC-3 tumor bearing mice was in line with the previous findings through PET and biodistribution experiments in HT1080 tumor bearing mice (Figure 6). SPECT imaging at 1 h p.i. further confirmed the good tumor uptake at early time-points with 5.72 ± 1.47 %ID / g. At 24 h p.i., it showed sufficient contrast and an uptake of 2.32 ± 0.50 %ID / g. Furthermore, non-target organs had 10 negligible uptakes (< 1 %ID / g) and the excretion through renal pathways was comparable to the PET findings at 1 h p.i. (31.9 ± 3.4 %ID / g in kidney). Biodistribution values are shown in Table 10. Table 10 - Uptake values of f11 In]In-Compound 1 (in %ID / g) at different time points after injection of230 pmol in an PC-3 tumor xenograft. 111ln-Compound 1 Organ 1 h p.i. 24 h p.i. Mean SD n Mean SD n Bladder 206.7 119.2 3 4.2 0.5 3 Kidneys 32.0 3.4 3 17.0 2.5 3 Heart 0.03 0.01 3 0.03 0.02 3 Liver 0.13 0.09 3 0.05 0.03 3 Lungs 0.12 0.02 3 0.01 0.00 3 Muscle 0.27 0.25 3 0.02 0.02 3 Spleen 0.27 0.19 3 0.40 0.19 3 Tail 0.28 0.09 3 0.07 0.01 3 Tumor 5.7 1.5 3 2.3 0.5 3 Example 4 — Selectivity The binding of Compound 1 to a panel of closely related homologues of EphA2 was assessed by SPR (as outlined in Example 1). Compound 1 showed a high degree of selectivity, with no binding observed to the homologues. The results are shown in Table 11, and Figure 13. Table 11 - Affinity values of Compound 1 obtainedfrom SPR against a panel of close homologues ofEphA2. Protein Kd(M) Human EphA1, n=1 No binding up to 5 pM Human EphA3, n=1 No binding up to 5 pM Human EphA4, n=1 No binding up to 5 pM Human EphA5, n=1 No binding up to 5 pM Human EphA6, n=1 No binding up to 5 pM Human EphA7, n=1 No binding up to 5 pM Example 5 - MMTV-PyMT breast cancer model: in vitro assays and disease progression The internalization assay on tumor-derived iPyMT 1312 cells showed specific binding of [68Ga]Ga-Compound 1 towards the EphA2 receptor when incubated for 45 minutes (Figure 15 A). Western Blot of cell protein extracts revealed that the tumor-derived cells expressed the EphA2 receptor, however in a lower concentration than the control cell line, HT1080. In both cell lines, different isoforms of the receptor could be detected, whereas for the control HT1080 the dominant band was for the 54 kDa isoform of EphA2, for the iPyMT 1312, it was the 108kDa isoform (Figure 15B). Tumors could be detected in the MMTV-PyMT mouse model through [68Ga]Ga-Compound 1, starting at week 8 as shown by exemplary coronal slices in Figure 16. The first palpable hardened nodules in the mammary glands were felt between weeks 7 and 8. Figure 16 also shows that the 68Ga-labelled peptide was able to detect mammary tumors over a lapse of 6 weeks, until week 14. Tumor uptakes of [68Ga]Ga-Compound 1 increased over time and with it the imaging contrast (tumor-to-muscle ratios). Additionally, [68Ga]Ga-Compound 1 uptake in tumors overlaid the MRI detection of the lesions. There was a moderate positive correlation (r = 0.546) between tumor uptakes of [68Ga]Ga-Compound 1 and tumor volume (as determined by 2-[18F]FDG uptake), thus the uptake of [68Ga]Ga-Compound 1 increased slightly as the tumors developed with time. Imaging with 2-[18F]FDG starting at week 6 and every 4th week until week 14 could detect, as expected, the formation and progression of the mammary gland tumors. However, radiotracer uptake did not significantly change with disease progression. 2-[18F]FDG tumor uptake and size had low correlation (r = 0.268). When comparing the tumor-to-background (muscle) ratios to the [68Ga]Ga-Compound 1 there was no significant difference at week 10 (p > 0.05) neither at week 14 (p > 0.05). The ex vivo biodistribution after the last PET / MR scan at week 14 confirmed the findings of the imaging study, with uptake in the multiple tumors of the MMTV-PyMT model ranging from 2.3 to 4.5 %ID / g (Figure 17). Not every tumor could be individually delineated upon dissection, with close-by lesions that were fused being dissected as a single tumor and grouped. Lung uptake was higher than background (muscle = 0.4 ± 0.3 %ID / g) in some mice (ranging from 1.6 to 3.3 % ID / g with an average of 2.7 ± 0.7 %ID / g) indicating the possible presence of lung metastases. Discussion of Examples 1-5 As described above, a novel EphA2-targeting bicyclic peptide was developed through phage display aiming at an optimization for future clinical translation as a radiotheranostic agent. The best candidate from successive rounds of panning was affinity matured and modified chemically to further increase its affinity and proteolytic stability. After introduction of the metal-chelating moiety DOTA, Compound 1 was identified as the lead candidate with nanomolar affinity towards human EphA2 (Kd = 1.93 ± 0.35 nM) and good cross reactivity with mouse EphA2 (Kd = 3.82 ± 0.56 nM). Compound 1 was successfully radiolabeled with three clinically relevant radionuclides, 68Ga, suitable for molecular imaging with PET, 177Lu, suitable for therapy and inIn for SPECT imaging. The radiolabeling under the described conditions did not result in any degradation; demonstrating the chemical robustness of this bicyclic peptide. Additionally, [177Lu]Lu-Compound 1 showed minimal degradation in human plasma over 72 hours, following chemical optimization aiming to reduce metabolic susceptibility. Although [177Lu]Lu-Compound 1 was degraded to a greater degree in mouse plasma over 72 hours, with 40% of parental compound remaining, this was deemed to be acceptable given the typically short circulating half-life of bicyclic peptides, as exemplified by the PK studies of Compound 1 (t% = 0.24 h). Furthermore, [68Ga]Ga-Compound 1 showed modest plasma protein binding of around 50%, which is consistent with the rapid clearance observed in the in vivo biodistribution and PK studies. Further in vitro testing of Compound 1 ensured high affinity and specificity towards EphA2 in both isolated protein and cell-bound receptor. These results were comparable to recently reported 18F-labeled bicyclic peptides (~ 0.2 % AA / 105 cells) although work was performed in PC-3 cells, which expresses EphA2 in a higher degree compared to HT1080. The promising in vitro performance of both the 68Ga and 177Lu-labeled versions of Compound 1 allowed for its progression into preclinical in vivo testing. [68Ga]Ga-Compound 1 was used in PET-imaging studies in an HT1080 mouse xenograft. PET / MRI revealed fast renal elimination, resulting in sufficient imaging contrast as early as 5 minutes p.i.. At 2 h p.i. a static scan confirmed the findings from the dynamic imaging, proving once more high uptake of [68Ga]Ga-Compound 1 in the tumor at early time points, as well as excellent tumor-to-background contrast. The in vivo specificity of Compound 1 towards EphA2 was proven by both PET imaging in an EphA2-negative cell line (MCF-7) and blocking with an excess on non-radiolab eled Compound 1, with both experiments showing no significant uptake and no tumor-to-background contrast. To further confirm the data from the PET / MR imaging, biodistribution studies with [177Lu]Lu-Compound 1 were performed in the same mouse xenograft model. A high tumor uptake at 1- and 2-hour p.i. was observed, while after 24 hours a significant decrease in the retained activity was detected. This decrease in tumor retained activity at later time points correlates with the low internalization ratios determined in the in vitro assays. Low internalization leads to the majority of the peptide being surface-bound and not able to enter the tumor cell, allowing faster washout of the activity. Notably, the majority of non-tumor bound radioactivity was cleared rapidly, with no activity detected in any other organ than kidney by 1 h p.i. Tumor-to-background (muscle) ratios were high through all time points with an impressively high ratio of 325 at 1 h p.i. and ending with a ratio of 88 at 24 h p.i.. SPECT imaging with [niIn]In-Compound 1 was also in line with the findings in the PET and biodistribution studies, and further confirmed the excellent selectivity of Compound 1 towards EphA2 as well as the rapid tumor uptake and clearance. Notably, the SPECT / CT imaging was carried out employing the PC-3 cell line as an alternative to the HT1080. This allowed for the validation of Compound 1 in an additional cell line, with satisfactory and comparable results, confirming the positive performance of the bicyclic peptide across cell lines. Furthermore, the performance of the bicyclic peptide was tested in the immunocompetent MMTV-PyMT BC model, which provides an additional layer of physiological relevance. The MMT-PyMT model mirrors human carcinogenesis stages, with orthotopic and ductal tumors in the mouse breast within 3 months of its lifespan. In vitro and in vivo experiments confirmed that the peptide was specific in its binding towards the cell-expressed EphA2 receptor, and allowed for detection of tumors over the whole lifespan of the genetically modified BC model. This allowed for the further validation of Compound 1 in an immunocompetent model, yet further confirming the positive performance of the bicyclic peptide. The relatively low retention of activity in late time points makes Compound 1 a very good candidate for imaging as well as therapy with short-lived isotopes. The excellent performance of Compound 1 in detecting EphA2-positive tumors in preclinical settings postulates it as an encouraging candidate for clinical translation, especially in cancer entities where specific biomarkers for molecular imaging have yet not been discovered e.g. pancreatic, bladder, gastric / esophageal, non-small cell lung and head and neck cancers. In addition, the implication of having sufficient imaging contrast, in a mouse xenograft, as early as 5 minutes p.i. could significantly increase outputs and reduce given doses in clinical imaging practices. In summary, Compound 1 was identified via phage display and was chemically optimized to give a high affinity, biologically stable bicyclic peptide targeting EphA2. The bicyclic peptide was radiolabeled with clinically relevant radionuclides and evaluated both in vitro and in vivo. Compound 1 showed high affinities, EphA2 specificity, and a favorable biodistribution profile with excellent tumor targeting properties and adequate renal-mediated clearance.

Claims

1. A compound comprising a bicyclic peptide comprising a polypeptide of SEQ ID NO: 1:A[HArg]DC[HyP][Cba]VNPLCLHP[dD]W[HArg]C-W2(SEQ ID NO: 1)attached to a molecular scaffold; wherein- [HArg] is homoarginine, [HyP] is (2S,4R)-4-hydroxypyrrolidine-2-carboxylic acid, [Cba] is beta-cyclobutyl alanine, and [dD] is D-aspartic acid;- the molecular scaffold is l,r,l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-l-one) (TATA); and- each C group is a cysteine group comprising a sulfur atom which is covalently attached to the molecular scaffold;or a pharmaceutically acceptable salt thereof;wherein the bicyclic peptide further comprises one or more imaging agents and / or therapeutic agents.

2. A compound according to claim 1, wherein the imaging agent or therapeutic agent is attached to the N terminus of SEQ ID NO: 1.

3. A compound of formula I:BicycleSpacer \ Z[Formula (I)]wherein- Bicycle is a peptide ligand comprising a polypeptide of SEQ ID NO: 1:A[HArg]DC[HyP][Cba]VNPLCLHP[dD]W[HArg]C-W2(SEQ ID NO: 1)attached to a molecular scaffold; wherein[HArg] is homoarginine, [HyP] is (2S,4R)-4-hydroxypyrrolidine-2-carboxylic acid, [Cba] is beta-cyclobutyl alanine, and [dD] is D-aspartic acid; the molecular scaffold is l,l',l"-(l,3,5-triazinane-l,3,5-triyl)tris(propan-l-one) (TATA); and each C group is a cysteine groupcomprising a sulfur atom which is covalently attached to the molecular scaffold;- Spacer is a bivalent moiety that connects the Bicycle moiety to the Z moiety; and- Z is an imaging and / or therapeutic agent or a ligand thereto.

4. A compound according to claim 3, wherein Bicycle iswherein s is the point of attachment to Spacer.

5. A compound according to claim 3 or 4, wherein Z is a chelator, a chromophore, a fluorescent moiety, a luminescent moiety and / or a phosphorescent moiety.

6. A compound according to any one of claims 3 to 5, wherein Z is a metal chelator.

7. A compound according to any one of claims 3 to 6, wherein Z is a polycarboxylicacid or a polyphosphonic acid, preferably an amino polycarboxylic acid.

8. A compound according to any one of claims 3 to 7, wherein Z is selected from 2-(Carboxymethylamino)acetic acid (IDA); 2,2',2''-Nitrilotriacetic acid (NTA); 2-({2-[Bis(carboxymethyl)amino]ethyl}(carboxymethyl)amino) acetic acid (EDTA); N,N'-{[(Carboxymethyl)azanediyl]di(ethane-2,l-diyl)}bis[N-(carboxymethyl)glycine] (DTPA); ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetra acetic acid (EGTA); l,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA); di ethylenetriaminepentaacetic anhydride (DTP A); 1,4,7-triazacyclononane-N,N’,N”-triacetic acid (NOTA); 1,4,7,10-tetraazacyclododecane-l,4,7,10-tetraacetic acid (DOTA); 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA); ethylenediamine-N,N'-disuccinic acid (EDDS); 2,2',2",2"',2"",2.....-(1,4,7,10,13,16-hexaazacyclooctadecane-1,4,7,10,13,16-hexayl)hexaacetic acid (HEHA);2,2',2" ,2"',2"" -(1,4,7,10,13 -pentaazacyclopentadecane-1,4,7,10,13-pentayl)pentaacetic acid (PEPA); 3,3',3",3"'-(l,5,9,13-tetraazacyclohexadecane-1,5,9,13-tetrayl)tetrapropionic acid (TETPA); and 3,3',3",3"'-(l,4,7,10-tetraazacyclododecane-l,4,7,10-tetrayl)tetrapropionic acid (DOTPA).

9. A compound according to any one of claims 3 to 8, wherein Z is selected from DOTA, DTP A, NOTA and TETA.

10. A compound according to any one of claims 3 to 9, wherein Z is DOTA having thestructure:wherein s is the point of attachment to Spacer.

11. A compound according to any one of claims 3 to 10, wherein Z is complexed to aradioisotope.

12. A compound according to claim 11, wherein the radioisotope is 225Ac, 227Ac,241 Am, 72As, 74As, 211At, 198Au, nB, 7Be, 212Bi, 213Bi, 75Br, 77Br, nC, 14C, 48Ca, 109Cd, 139Ce, 141Ce, 252Cf, 55Co, 57Co, 60Co, 51Cr, 130Cs, 131Cs, 137Cs, 61Cu, 62Cu, 64Cu, 67Cu, 165Dy, 152Eu, 155Eu, 18F, 55Fe, 59Fe, 64Ga, 67Ga, 68Ga, 153Gd, 68Ge, 122I, 123j 124j 125j 131j 132j 111 jn 114111^ 115mjn 191mjj. 192^ Slm^ 177j^u 51jjn 52Mn "Mo, 13N, 95Nb, 150, 1910s, 1940s, 32P, 33P, 203Pb, 212Pb, 103Pd, 109Pd, 238Pu, 223Ra, 226Ra, 82Rb, 186Re, 188Re, 105Rh, 97Ru, 103Ru, 35S, 44Sc, 46Sc, 47Sc, 72Se, 75Se, 28Si, 145Sm, 153Sm, 117mSn, 85Sr, 89Sr, 90Sr, 178Ta, 179Ta, 182Ta, 149Tb, 96Tc, "mTc, 228Th, 229Th, 2O1T1, 170Tm, 171Tm, 188W, 127Xe, 133Xe, 86Y, 88Y, 90Y91Y, 169Yb, 62Zn, 65Zn, 89Zr or 95Zr.

13. A compound according to claim 11 or 12, wherein the radioisotope is [64Cu], [67Ga], [68Ga], [177Lu], [90Y], [213Bi], [niIn] or [225Ac], preferably [68Ga], [177Lu], [niIn] or [225Ac],14. A compound according to any one claims 3 to 13, wherein Spacer is a bidentate group having a length of from about 0.3 nm to about 300 nm.

15. A compound according to any one of claims 3 to 14, wherein Spacer comprises one or more linking moieties, wherein each linking moiety is an amino acid or amino acid derivative, preferably a polypeptide; an alkylene group; an alkenylene group; an alkynylene group; a poly(alkyleneglycol), preferably poly(ethyleneglycol) or poly(propyleneglycol); an amide group; a carbamate group; an ether group; an ester group; a disulphide bond; a hydrazone group; a sulfonamide group; a thioether group; an amine group; or a cyclic group, preferably a 4-12 membered carbocyclic or heterocyclic group, a 5-12 membered heteroaryl group or a Ce-12 aryl group; wherein said alkylene, alkenylene, alkynylene, poly(alkyleneglycol), amine and cyclic group is each independently optionally substituted.

16. A compound according to any one of claims 3 to 15, wherein Spacer comprises an oligopeptide moiety, preferably wherein said oligopeptide moiety comprises from about 2 to about 20 amino acids or amino acid analogs.

17. A compound according to any one of claims 3 to 16, wherein Spacer comprises an oligopeptide moiety comprising from about 5 to about 15 canonical or non-canonical amino acids; preferably wherein Spacer comprises an oligopeptide moiety comprising from about 5 to about 15 groups each independently selected from sarcosine and beta-alanine.

18. A compound according to any one of claims 3 to 17, wherein Spacer comprises one or more sarcosine residues, one or more polyethyleneglycol (PEG) residues and / or one or more amide groups.

19. A compound according to any one of claims 3 to 18, wherein Spacer comprises [Sar]8-i2, preferably wherein Spacer comprises [Sar]io, wherein Sar is sarcosine.

20. A compound according to any one of claims 3 to 19, wherein Spacer is -[P-Ala]-[Sar]io—, wherein [P-Ala] is beta-alanine.

21. A compound according to any one of the preceding claims, wherein(i) the compound is of the structure:HOpreferably wherein the compound is of the structuremoiety is preferably complexed to a radioisotope; more preferably to a radioisotope as defined in claim 12 or 13.

22. A pharmaceutical composition comprising a compound according to any one of thepreceding claims, in combination with one or more pharmaceutically acceptable excipients.

23. A compound according to any one of claims 1 to 21, or a composition according to claim 22, for use in a method of treatment or diagnosis of the human or animal body.

24. A method of imaging an EphA2-associated disorder, disease or condition in a subject, the method comprising administering to said subject a compound according to any one of claims 1 to 21, or a composition according to claim 22;preferably wherein said imaging is PET or SPECT imaging.

25. A method of imaging a subject or part thereof or an organ of a subject, wherein the subject has or is suspected of having an EphA2-associated disorder, disease or condition, the method comprising administering to the subject a compound according to any one of claims 1 to 21, or a composition according to claim 22 and taking one or more images of said subject;preferably wherein said imaging is PET or SPECT imaging.

26. A compound according to any one of claims 1 to 21, or a composition according to claim 22, for use in treating, preventing or suppressing an EphA2-associated disorder, disease or condition.

27. A method of treating, preventing or suppressing an EphA2-associated disorder,disease or condition in a subject, comprising administering to the subject a compound according to any one of claims 1 to 21 or a composition according to claim 22.

28. A compound for use or composition for use according to claim 26 or a method according to claim 27, wherein the EphA2-associated disorder, disease or condition is a cancer.

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