Our group has demonstrated that ectopic expression of murine GRM1 results in transformation of mouse melanocyte cells, and we have found that human GRM1 is ectopically expressed in more than 60% human melanomas. We recently reported on the results of a Phase 0 preclinical trial targeting GRM1 signaling using a glutamate release-inhibitor, Riluzole. We demonstrated inhibition of signaling through the PI3K/AKT and MAPK pathways and a reduction in tumor size in 40% of patients treated. To better examine the mechanisms of Riluzole treatment effect and to begin to understand the function of GRM1 signal transduction in melanoma, cell lines that over-express GRM1 (UACC903 G2 and UACC903G4) were constructed using the native, low GRM1-expressing, UACC903 human melanoma cell line. We found that UACC903G2 and G4 cells produce elevated levels of GRM1 and were much more sensitive to treatment with 25uM Riluzole than the vector transfected control cell line UACC903V1. We also found that UACC903G2 and G4 cells produced much larger tumors in nude mice than the vector control cells. Tumors formed by UACC903G2 and G4 xenografts also do not demonstrate areas of hemorrhage necrosis as is found in UACC903V1 xenografts, and there are significantly more tumor blood vessels in the GRM1-overexpressing xenograft tumors. To confirm the angiogenic effect of GRM1 over-expression in UACC903 cells, an endothelial cell migration assay was performed. We found that culturing UACC903G2 and G4 cells in serum-free basic medium stimulated HMVECnd endothelial cell migration, an effect not seen with the vector control UACC903V1 cells. We next examined whether increased GRM1 expression in UACC903 cells resulted in the release of angiogenesis factor(s) from these cells. An angiogenesis antibody array (from Affymetrix) experiment was performed and we found that the conditioned medium from UACC903G2 and G4 cells had significantly higher levels of IL8 and VEGF (angiogenesis promoters), but decreased level of TIMP-2 and TIMP-1 (angiogenesis inhibitors) as compared to the conditioned medium from the UACC903V1 vector control cells. We conclude that over-expression of human GRM1 promotes proliferation, activates angiogenesis signaling, and renders cells more susceptible to the inhibitory effects of the glutamate-release inhibitor Riluzole. Further experiments examining the molecular mechanism of GRM1 in cell survival and angiogenesis are need to better understand the mechanisms at work.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 315. doi:10.1158/1538-7445.AM2011-315