Abstract 3708: microRNAs involved in BRAF inhibitor resistance

Abstract

Abstract BRAF inhibitors (BRAFi) have shown remarkable clinical activity in advanced metastatic melanomas with mutant BRAF(V600E). However, there is considerable variability in both the extent and the duration of patient responses, and acquired resistance invariably emerges. To date, a number of mechanisms underlying acquired resistance to BRAF inhibitors have been identified, most of which reactivate ERK signaling while simultaneously engaging parallel survival pathways. However, these mechanisms account for only a fraction of progressed melanoma and do not explain the large variability of initial response rates and time to progression of melanoma patients subjected to these therapies. We hypothesize that in addition to genetic events, non-genetic alterations such as microRNA changes are critical in mediating time to progression in melanoma tumors treated with BRAF inhibitors. In order to identify microRNAs involved in BRAF inhibitor resistance we performed a functional screen approach utilizing a novel lentiviral-based library of microRNA ‘decoys’. These constructs are better able to stably suppress endogenous microRNA activity than the hairpin RNAs traditionally used. This pooled parallel loss-of-microRNA function analysis in BRAF(V600E) mutant melanoma cells showed enrichment and loss of specific decoys after drug treatment, corresponding to microRNAs that may enhance or compromise the response, respectively. MicroRNA decoys that are positively or negatively selected during drug treatment are being validated using single decoy constructs for their ability to modulate BRAFi response. MicroRNA target genes will be determined by a combination of microarray analysis, in silico predictive algorithms, and 3′UTR-luciferase reporter assay. MicroRNAs and target genes are being validated on human samples from treated patients. Those potentially involved in processes/pathways known to influence drug resistance (i.e. survival genes) will be examined for their ability to mimic or counteract microRNA effects in BRAFi resistance when silenced or overexpressed, respectively. Identification of novel modulators of drug resistance provides the opportunity to design rational combinatorial approaches that will enhance and prolong the effect of these therapies, with the ultimate goal of achieving cures. Citation Format: Lisa Koetz, Elena Sokolova, Brian D. Brown, Eva Hernando. microRNAs involved in BRAF inhibitor resistance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3708. doi:10.1158/1538-7445.AM2014-3708