Gastrin-releasing peptide receptors in the tumor vascular bed of various human cancers: high incidence in urinary tract cancers

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e14575 Background: Tumoral Gastrin-releasing peptide (GRP) receptors are potential targets for diagnosis and therapy using radiolabeled or cytotoxic GRP analogs. GRP-receptor overexpression has been detected in cancer cells and, more recently, also in the vascular bed of selected tumors. More information on vascular GRP-receptors in cancer is required to asses their potential for vascular targeting applications. Methods: Frequent human cancers from the breast (n=134), lung (n=57), prostate (n=50), kidney (n=32), colon (n=46), urinary tract (n=26) and biliary tract (n=23) were analyzed using in vitro GRP-receptor autoradiography on tissue sections with the 125I-[Tyr4]-bombesin radioligand and/or the universal radioligand 125I-[D-Tyr6, ß-Ala11, Phe13, Nle14]-bombesin(6–14). GRP-receptor expressing tumoral vessels were evaluated in each tumor group for prevalence, quantity (vascular score) and GRP-receptor density. Results: Prevalence of vascular GRP-receptors is variable, ranging from 13% (prostate cancer) to 92% (urinary tract cancer). Different tumor-types within a given site may have divergent prevalence of vascular GRP-receptors (e.g. lung: small cell cancer: 0%; adenocarcinoma: 59%; squamous carcinoma: 83%). Also the vascular score varies widely, with highest score in urinary tract cancer (1.69), moderate scores in lung (0.91), colon (0.88), kidney (0.84) and biliary tract (0.69) cancers and low scores in breast (0.39) and prostate (0.14) cancers. Vascular GRP-receptors are expressed in the muscular vessel wall in moderate to high densities. Normal non- neoplastic control tissues from these organs lack vascular GRP-receptors. Conclusions: Tumoral vessels in all evaluated sites overexpress GRP-receptors, suggesting a major biological function of GRP-receptors in the tumor vascular bed. Vascular GRP-receptor expression varies between the tumor-types indicating tumor-specific mechanisms in their regulation. Urinary tract cancers express vascular GRP-receptors so abundantly, that they are promising candidates for vascular targeting applications. No significant financial relationships to disclose.