Table 1.

Some representative peptides, receptors and corresponding imaging applications.

Peptide designation	Key sequence	Receptor	Indication	Subject studied	Reference
RGD	Arg-Gly-Asp	Integrin	Angiogenesis	In vitro Rodents Humans	[28–32]
Bombesin/gastrin-releasing peptide	Share sequence of Trp-Ala-Val-Gly-His-Leu-Met	GRPR	Prostate cancer; breast cancer; glioma	In vitro Rodents Humans	[33–36]
CCK/gastrin	Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe	CCK2R	Medullary thyroid cancer	In vitro Rodents	[37–39]
VIP	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	VPAC1/2	Primary and metastatic lesions of breast, ovarian, prostate, colon and urinary bladder carcinomas, and meningiomas	In vitro Rodents Humans	[13,40,41]
NT	pGlu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu	NTSR1	Tumor progression (lung cancer/breast cancer/prostate cancer)	In vitro Rodents	[42,43]
Somatostatin	Ala-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys (Disulfide bridge Cys3-Cys14)	SSTR1–5	Neuroendocrine tumors	In vitro Rodents Humans	[14,44–46]
α-MSH	Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val	Melanocortin-1 receptor	Melanogenesis	In vitro Rodents	[47,48]
T140	Arg-Arg-Nal-Cys-Tyr-Arg-Lys-D-Lys-Pro-Tyr-Arg-Cit-Cys-Arg	CXCR4	Tumor aggressiveness, invasiveness, and metastasis formation	In vitro Rodents	[49,50]
Exendin-4	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	GLP-1R	Insulinomas	In vitro Rodents Humans	[51–53]
NPY	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	NPY1R	Breast cancer; sarcomas	In vitro Rodents	[54,55]
Substance P	Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met	NK1R	Glioblastoma	In vitro Rodents	[56,57]
TMTP1	Asn-Val-Val-Arg-Gln	Unclear	Highly metastatic cancer cells	In vitro Rodents	[58,59]