The biological activity of peptides is regulated through their binding to corresponding receptors. Peptides that target receptors overexpressed on tumor cells—but not on normal cells—are excellent candidates for in vivo tumor imaging. To date, many peptides and their analogs have been identified for disease detection. Some representative peptides are summarized below:
1. RGD
The tripeptide RGD can specifically bind to integrin receptors. Integrins are composed of two subunits (α and β). The integrin family, especially αVβ3, plays a crucial role in tumor angiogenesis and metastasis. During angiogenesis, these receptors are overexpressed on endothelial cells but are barely detectable in most normal organs. Therefore, they are widely used in diagnostic imaging.
Single-letter code: H2N-RGD-OH
Three-letter code: H2N-Arg-Gly-Asp-OH
Number of amino acids: 3
Molecular formula: C12H22N6O6
Average molecular weight (MW): 346.34
2. Bombesin (BBN) / Gastrin-Releasing Peptide (GRP)
BBN and its related peptides from amphibians form a neuropeptide family with multiple physiological effects, such as exocrine and endocrine secretion, thermoregulation, sucrose regulation, and cell growth. Bombesin-like peptide receptors have four subtypes: neuromedin B receptor, bombesin receptor subtype 3, gastrin-releasing peptide receptor (GRPR), and bombesin receptor subtype 4. These receptors are overexpressed in various tumors, including breast cancer, ovarian cancer, and gastrointestinal stromal tumors.
| CAT# | Product Name |
| B07004 | Bombesin (8-14) |
| B07010 | [Lys3]-Bombesin |
| B07011 | [Tyr4, D-Phe12]-Bombesin |
| B07015 | (D-Cys6,Asn7,D-Ala11,Cys14)-Bombesin (6-14) |
| B07016 | (D-Phe12)-Bombesin |
| B07017 | (D-Phe12,Leu14)-Bombesin |
| B07019 | (D-Phe6,Leu-NHEt13,des-Met14)-Bombesin (6-14) |
| B07020 | (D-Tyr6,betaPhe11,Phe13,Nle14)-Bombesin (6-14) (free acid) |
| B07022 | (Tyr4)-Bombesin |
| B07023 | Cyclo(-D-Phe-His-Trp-Ala-Val-Gly-His-Leu-Leu) |
| B07024 | Biotin – Bombesin |
| B07025 | Biotin – LC – LC – Bombesin |
| B07026 | Bombesin, FAM – labeled |
Gastrin-Releasing Peptide (GRP)
3. Somatostatin (SST) Peptides
Somatostatins (SSTs) are naturally occurring cyclic peptide hormones composed of either 14 or 28 amino acids. They inhibit the secretion of insulin, glucagon, and several other hormones. Their biological effects are mediated by binding to specific high-affinity somatostatin receptors (SSTRs), of which there are five subtypes: SSTR1 to SSTR5. These receptors are overexpressed in a variety of neuroendocrine tumors, such as pancreatic neuroendocrine tumors, small cell lung cancer, and thyroid carcinoma. Synthetic somatostatin analogs are widely used in imaging and therapy of tumors that express these receptors.
| CAT# | Product Name |
| 10-101-169 | Pasireotide |
| 10-101-26 | Octreotide Acetate |
| 10-101-44 | Vapreotide Acetate |
| M34140635H | [Nal3]Octreotide acetate |
| M34140636H | TETA-Octreotide acetate |
| M34140637H | NOTA-Octreotide trifluoroacetate |
| M34140643H | DOTA-Lanreotide acetate |
| M34140653H | [Tyr3,Lys5(Boc)]octreotide acetate |
| M34140655H | [Lys5(Boc)]lanreotide acetate |
| O1003 | ([ring-D5]Phe3)-Octreotide |
| S07018 | (D-2-Nal5,Cys6·11,Tyr7,D-Trp8,Val10,2-Nal12)-Somatostatin-14 (5-12) amide |
| S07041 | Tyr-(D-Dab4,Arg5,D-Trp8)-cyclo-Somatostatin-14 (4-11) |
| S07043 | Vapreotide |
4. Vasoactive Intestinal Peptide (VIP)
VIP is a neuropeptide consisting of 28 amino acids. It not only promotes vasodilation but also stimulates cell growth and proliferation through cell surface receptor-mediated signaling pathways. Its effects are primarily regulated by two receptor subtypes, VPAC1 and VPAC2. VIP receptors are highly expressed in a variety of tumors, including but not limited to brain tumors, pancreatic adenocarcinomas, and neuroendocrine tumors. Notably, VIP is also considered a potential therapeutic agent; however, toxicity may occur even at sub-microgram doses.
Single-letter sequence: H2N-HSDAVFTDNYTRLRKQMAVKKYLNSILN-OH
Three-letter sequence: H2N-His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr-Thr-Arg-Leu-Arg-Lys-Gln-Met-Ala-Val-Lys-Lys-Tyr-Leu-Asn-Ser-Ile-Leu-Asn-OH
Number of amino acids: 28
Molecular formula: C147H237N43O43S1
Average molecular weight (MW): 3326.78
Vasoactive Intestinal Peptides (VIPs)
- Cholecystokinin (CCK) / Gastrin Peptide
Cholecystokinin (CCK) and gastrin are structurally and functionally related peptides that play multiple physiological roles in the gastrointestinal tract and central nervous system. They share an identical sequence in their bioactive region, differing only in the site of tyrosine sulfation—position 6 in gastrin and position 7 in CCK. To date, three CCK receptors have been identified: CCK1, CCK2, and CCK2i4sv, all of which belong to the G protein-coupled receptor (GPCR) superfamily. Among them, the CCK2/gastrin receptor is frequently implicated in human cancers, such as ovarian stromal tumors and astrocytomas.
Single-letter sequence: H2N-D-sTyr-MGWMDF-OH
Three-letter sequence: H2N-Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-OH
Number of amino acids: 8
Molecular formula: C49H61N9O17S3
Average molecular weight (MW): 1144.25
6. Alpha-Melanocyte-Stimulating Hormone (α-MSH)
Alpha-Melanocyte-Stimulating Hormone (α-MSH) is a linear tridecapeptide primarily responsible for regulating skin pigmentation. α-MSH and its analogs exhibit extremely high binding affinity to the melanocortin-1 receptor (MC-1R), which is expressed in over 80% of human melanoma metastases. Therefore, α-MSH is widely used as a carrier for targeted imaging and radiotherapy of melanoma.
Single-letter sequence: H2N-SYSMEHFRWGKPV-OH
Three-letter sequence: H2N-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-OH
Number of amino acids: 13
Molecular formula: C75H106N20O19S1
Average molecular weight (MW): 1623.83
Melanocyte-Stimulating Hormone (MSH)
| CAT# | Product Name |
| M09001 | a-MSH, amide |
| M09002 | a-MSH, Free Acid |
| M09003 | [Des-Ac] a-MSH, amide |
| M09004 | g-MSH |
| M09005 | g-1-MSH, amide |
| M09006 | MSH Release Inhibiting Factor, amide |
| M09007 | b-MSH, porcine |
| M09009 | [Lys0]-γ-1-MSH (41-58), amide |
| M09010 | Melanocyte Associated Antigen gp 100 (17-25) |
| M09011 | Melanotropin-Potentiating Factor, MPF |
| M09012 | RAB38/NY-MEL-1 (50-58) |
| M09013 | Acetyl-(D-Val13)-a-MSH (11-13) |
7. Neurotensin (NT)
Neurotensin (NT) is a peptide consisting of 13 amino acids that acts on neurotensin receptors, which have been identified in various tumors, such as ductal pancreatic adenocarcinoma, small-cell lung carcinoma, and medullary thyroid carcinoma. Thus, NT is considered a highly promising candidate for cancer imaging applications.
Single-letter sequence: Pyr-LYENKPRRPYIL-OH\
Three-letter sequence: Pyr-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu-OH
Number of amino acids: 12
Molecular formula: C78H121N21O20
Average molecular weight (MW): 1672.92
Neurotensins and Related Peptides
| CAT# | Product Name |
| N05044 | (Dab9)-Neurotensin (8-13) |
| N05045 | (D-Trp11)-Neurotensin |
| N05046 | (D-Tyr11)-Neurotensin |
| N05048 | (Lys9,Trp11,Glu12)-Neurotensin (8-13) (Cyclic Analog) |
| N05049 | Acetyl-Neurotensin (8-13) |
| N05050 | Boc-(Lys9)-Neurotensin (9-13)-methyl ester |
| N05051 | Neurotensin (1-11) |
| N05052 | Neurotensin (1-6) |
| N06001 | (Lys8,Lys9)-Neurotensin (8-13) |
| N06002 | [Lys8,Asn9] Neurotensin LANT-6 (8-13) |
| N06003 | [Trp11] Neurotensin (8-13) |
| N06004 | [Trp11]-Neurotensin |
| N06006 | Neurotensin (1-8) |
| N06008 | Neurotensin (9-13) |
| N06009 | [Gln4]-Neurotensin |
8. T140
T140 is a peptide composed of 14 amino acids and one disulfide bond. It is an antagonist of chemokine receptor 4 (CXCR4). Its derivatives have been widely used as imaging agents targeting CXCR4.
Single-letter sequence: H2N-RR-2Nal-CYRKkPYR-Cit-CR-OH
Three-letter sequence: H2N-Arg-Arg-2Nal-Cys-Tyr-Arg-Lys-DLys-Pro-Tyr-Arg-Cit-Cys-Arg-OH
Number of amino acids: 14
Molecular formula: C90H143N33O18S2
Average molecular weight (MW): 2039.44
9. Exendin-4
Exendin-4 is a peptide hormone consisting of 39 amino acids. It shares 50% sequence homology with the natural glucagon-like peptide-1 (GLP-1) and has been identified as an agonist of the GLP-1 receptor. Exendin-4 has been clinically used for the treatment of insulinomas and type 2 diabetes.
Single-letter sequence: H2N-HGEGTFTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-OH
Three-letter sequence: H2N-His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-OH
Number of amino acids: 39
Molecular formula: C184H281N49O61S1
Average molecular weight (MW): 4187.56
| CAT# | Product Name |
| 10-101-83 | Exendin (9-39) Acetate |
| E10001 | Exendin (9-39) |
| E10005 | Exendin-4 (3-39) |
| E10007 | Exendin (10-39) |
| E10008 | Exendin (4-39) |
| E10009 | Exendin (5-39) |
| E10010 | Exendin (7-39) |
| E10013 | Exendin-4 (1-8) |
| E10014 | Exendin 4 (5-39)amide |
| R1346 | Exendin derivative 1 |
| R1347 | Exendin-3 |
| R1827 | Exendin 3 (9-39) |
| R2090 | Exendin-4 |
| E10004 | Des His1, Glu8 Exendin-4 |
| E10006 | [Des-His1, Glu8]-Exendin-4 |
| 10-101-16 | Exenatide |
| CAD-110 | Endo-38a-Pro-Exenatide |
| PI-019 | Heliodermin |
| R1484 | Lixisenatide |
10. Neuropeptide Y (NPY)
Neuropeptide Y (NPY) is a peptide composed of 36 amino acids and belongs to the pancreatic polypeptide family. NPY receptors are overexpressed in various tumors, including neuroblastoma, sarcoma, and breast cancer. Many NPY analogs have been evaluated in animal models.
Single-letter sequence: H2N-YPSKPDNPGEDAPAEDLARYYSALRHYINLITRQRY-OH
Three-letter sequence: H2N-Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu-Asp-Ala-Pro-Ala-Glu-Asp-Leu-Ala-Arg-Tyr-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Thr-Arg-Gln-Arg-Tyr-OH
Number of amino acids: 36
Molecular formula: C190H286N54O58
Average molecular weight (MW): 4254.63
Neuropeptide Y (NPY), Analogs and Fragments
11. Substance P
Substance P is an eleven-amino acid peptide belonging to the tachykinin family of neuropeptides. Substance P is a specific endogenous ligand of the neurokinin 1 receptor (NK1R), which is expressed in various cancer cells. Substance P analogs have been synthesized and used for positive detection of NK1R-positive tumors.
Single-letter sequence: H2N-RPKPQQFFGLM-OH
Three-letter sequence: H2N-Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-OH
Number of amino acids: 11
Molecular formula: C63H97N17O14S1
Average molecular weight (MW): 1348.61
| CAT# | Product Name | CAT# | Product Name |
| R0901 | alfa-Bungarotoxin | R0950 | Galanin (1-15) (porcine, rat) |
| R0903 | RLLFT-NH2 | R0954 | GLYX 13 |
| R0905 | Ac9-25 | R0956 | BAM (8-22) |
| R0906 | Alpha-Conotoxin PIA | R0957 | RS 09 |
| R0909 | CH 275 | R0958 | Spexin |
| R09100 | Spexin-2 (53-70), human/mouse/rat | R0959 | Lauryl-LF 11 |
| R0913 | Caffeic acid-pYEEIE | R0962 | ELA-14 (human) |
| R0914 | Xenin 8 | R0963 | Histone H3 (1-34) |
| R0916 | [D-Trp7,9,10]-Substance P | R0964 | H3K4(Me2) (1-20) |
| R0917 | N-Acetyl-O-phosphono-Tyr-Glu Dipentylamide | R0966 | d[Cha4]-AVP |
| R0923 | [cPP1-7,NPY19-23,Ala31,Aib32,Gln34] – hPancreatic Polypeptide | R0968 | Acein |
| R0925 | Kisspeptin 10 (dog) | R0969 | TT 232 |
| R0926 | RFRP 3 (human) | R0973 | RFRP-1 (human) |
| R0930 | Galanin (2-29) (rat) | R0986 | Pam2CSK4 Biotin |
| R0931 | Nocistatin (human) | R0988 | Pam3CSK4 Biotin |
| R0934 | [Leu31,Pro34]-Neuropeptide Y (porcine) | R0989 | LF 11 |
| R0940 | Neuropeptide SF (mouse, rat) | R0990 | [D-Trp8]-γ-MSH |
| R0943 | Apelin-17 (human, bovine) | R0992 | M 1145 |
| R0944 | A-71623 | R0994 | MMK 1 |
| R0947 | Pseudo RACK1 | R0996 | CRSP-1 |
12. Tumor Molecular Targeting Peptide 1 (TMTP1)
TMTP1 is a five-amino acid peptide that has been found to specifically bind to highly metastatic cancer cells, especially those from typical liver micrometastatic foci. However, high concentrations of TMTP1 can mediate tumor cell apoptosis. Therefore, appropriately labeled TMTP1 has been used in preclinical trials for imaging and therapeutic applications.
Single-letter sequence: H2N-NVVRQ-OH
Three-letter sequence: H2N-Asn-Val-Val-Arg-Gln-OH
Number of amino acids: 5
Molecular formula: C25H46N10O8
Average molecular weight (MW): 614.69