Orphan G-protein coupled receptor GPCR-X as a novel cancer drug target: validation and mechanistic studies

Proc Amer Assoc Cancer Res, Volume 46, 2005 960 GPCR-X is an orphan G-protein coupled receptor widely expressed in many tissues, but with higher expression levels in several cancer tissues. High expression levels have also been found to be associated with cellular transformation, implying a potential oncogenic function for this gene. Here, we show that siRNA mediated GPCR-X silencing in cancer cells reduced anchorage-independent growth, at least partly due to increased anoikis. GPCR-X silencing also led to induction of intrinsic apoptosis in several cancer cells, but not in normal primary cells. Using regulated GPCR-X siRNA expression in prostate cancer line PC3 in an athymic xenograft tumor model, we observed 100% tumor free regression in response to GPCR-X inactivation for the early staged tumors. Even with the later staged PC3 tumors, 80% of tumors also regressed and 17% became tumor free, suggesting the potential of an efficacious targeted therapy. The expression profiles between A2058 cells containing either the control siRNA or siRNA against GPCR-X were compared in an attempt to elucidate downstream pathways. Genes involved in several known pathways were affected by GPCR-X gene silencing. In particular, a number of genes involved in integrin-mediated signaling and cell adhesion were down-regulated, indicating a potential role for GPCR-X in the cell adhesion pathway. This hypothesis was further validated by cell adhesion experiments which demonstrated reduced adhesion of cells silenced for GPCR-X. Thus, the role of GPCR-X in cell transformation is likely via an integrin-mediated cell adhesion pathway. The apparent absence of physiological defects in adult human tissues lacking GPCR-X and the specificity of apoptotic induction by GPCR-X-silencing in cancer cells suggest an interesting drug target for cancer therapeutics with low toxicity.