It has become increasingly important to identify targeted therapy in a defined molecular context. Here we will present our data which suggests TERT, a telomerase reverse transcriptase, serves as a novel drug target in melanoma in the context of PTEN mutation. PTEN is mutated in ∼15% of melanoma patients. Genomic RNA-interference (RNAi) technology was applied for synthetic lethality screens in an effort to identify the targets which upon knock-down significantly decrease cell viability specifically in the context of somatic mutations of the PTEN gene. We carried out such screen in a panel of 15 melanoma cell lines, including four PTEN mutated cell lines, against an siRNA library covering the kinome (∼700 genes with 4 siRNA per target) using CellTiter Glo as the endpoint to measure cell viability. Lethal genes, which decreased cell viability significantly upon knockdown, were initially identified for each cell line. Then the hit lists were compared between wild-type PTEN and mutant PTEN using a chi-square test, a statistical analysis. 29 gene candidates were selected for hit confirmation using the same set of siRNA, among which 24 genes were confirmed as potential PTEN synthetic lethal candidates, this results in a high confirmation rate of 83%. Based upon its association with melanoma risk (Law et al, J Invest Dermatol, 2012), We further validated TERT using a commercially available small molecule inhibitor. This inhibitor has significantly higherpotency in the PTEN mutant context (average IC50 of 0.34uM) compared to PTEN wild-type background (average IC50 of 0.75uM). This result both validates our RNAi screening results, but more importantly, this compound can serve as an initial structure scaffold for further optimization towards development as a novel drug for metastatic melanoma patients who carry PTEN mutations. Evaluation of more TERT inhibitors in a diverse panel of melanoma cell lines is presently underway.

Citation Format: Holly Yin, Donald Chow, Chris Sereduk, Meraj Aziz, Seungchan Kim, Kevin M. Brown, Jeffrey M. Trent. High-throughput RNAi screening identifies a novel metastatic melanoma drug target in the context of PTEN mutation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3151. doi:10.1158/1538-7445.AM2013-3151