UNLABELLED:The synthetic laminin pentapeptide tyrosyl-isoleucyl-glycyl-seryl-arginine (YIGSR) binds to a metastasis associated high-affinity laminin receptor. The aim of this study was to investigate if the radiolabeled peptide can be considered as a basis for a potential tumor-imaging radiopharmaceutical. METHODS:Iodine-131-labeled YIGSR was injected in mice inoculated with Lewis Lung carcinoma, as well as in normal controls. The experimental animals were imaged on a gamma camera 10 hr after peptide administration. The same peptide was also labeled with 125I and administered to tumor-bearing and normal mice. At various time-points after peptide administration, the experimental animals were killed, and the radioactivity in the tumor, lung, liver and spleen was measured. Microscopic autoradiography was performed in histological sections of the same tissues. RESULTS:The tumor and the spleen of tumor-bearing animals were imaged on a gamma camera. No significant blood-pool background was detected. No other organ except urinary bladder and thyroid was imaged in normal animals. The peptide was retained on tumor and spleen of tumor-bearing animals. Twenty-four hours after peptide administration, the tumor, lung, liver and spleen of animals with tumors contained significantly more radioactivity than the same tissues of equally treated normal controls. The radiolabeled peptide YIGSR was detected by microscopic autoradiography on the surface of certain tumor cells, but not on the surface of any normal cell. CONCLUSION:Although extensive research is still required, the peptide YIGSR can be considered as a basis for the development of a receptor specific radiopharmaceutical useful for the in vivo estimation of the metastatic potential of tumors. This radiopharmaceutical may be helpful in staging and prognostic-related decisions on cancer treatment.

It has been reported that metastatic melanoma cell lines selectively bind in vitro with the synthetic laminin pentapeptide tyrosyl-isoleucyl-glycyl-seryl-arginine (YIGSR). The aim of this study was to investigate whether the same peptide can bind on melanoma cells in vivo as well. Iodine-125-labeled YIGSR was administered to B16 melanoma-bearing animals. Microscopic autoradiography of tumor and organ sections taken 24 h after peptide administration showed that the peptide did accumulate on the surface of certain tumor cells. The peptide binding cells were frequent in metastatic sites and tumors grown for 24 days and rare in tumors grown for 10 days. A similarly radiolabeled control pentapeptide (peptide DRLKY) did not bind to any tumor cell. It is suggested that the YIGSR binding tumor cells may represent a distinct melanoma cell population with a high metastatic potential.