Identification of anti-renal cell carcinoma agents using pharmacological synthetic lethal screening

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Renal cell carcinoma (RCC) is the most common malignant lesion of the kidney, comprising approximately 3% of all adult cancers. The primary treatment for clinically localized RCC is surgical removal of the lesion. There are some promising new approaches with VEGF/PDGF interactive agents. Remissions to these agents have been seen in a significant percentage of patients. One of the most significant advances in the past decade in our understanding of RCC is the identification of the von Hippel-Lindau disease (VHL) gene. The VHL gene is a tumor suppressor gene that has been found to be disabled either through mutations or through hypermethylation in over 75% of all RCC cases. Although it has been proven difficult for small molecule based cancer therapies to exclusively target a loss-of-function mutation like the VHL gene, recent advances in the drug development field provides new prospective for such strategy. In this study, we used a pharmacological synthetic lethal screening approach (Wang et al, Proc. AACR, 45:1421, 2004) to identify new agents that target specifically renal cancer cells with VHL deficiency. To do so, a pair of isogenic cell lines (786-O-vector and 786-O-VHL) for the VHL gene were generated and used to screen chemical libraries using the standard MTS-based cell proliferation assay. After screening about 10,000 compounds (the NCI diversity set and a subset of the NanoSyn Pharm library), we identified 3 potential leads that showed greater than 2 fold selectivity against the renal cancer cell line with inactivated VHL gene (786-O-vector), compared to the cell line with wildtype VHL (786-O-VHL). The IC50s of the compounds in the VHL deficient cell line range from low nanomolar to low micromolar. The selectivity of the compounds was further confirmed in a second pair of VHL isogenic cell lines. We are currently characterizing the potential mechanism of action of these compounds using flow cytometry and apoptosis assays. Further development of these leads can potentially lead to new therapies for the treatment of patients with RCC. (This work was supported by a grant from the Arizona Biomedical Research Commission)