Abstract 665: Inhibition of mitochondrial complex I enhances the therapeutic benefit of BRAF inhibition in mutant melanoma cell lines

Abstract

Abstract Metabolic reprogramming is considered to be one of the major hallmarks of cancer. Selective inhibitors of mutant BRAFV600E, are a widely used targeted therapy for melanoma. Unfortunately, acquired drug resistance, which commonly occurs, represents a major limitation to clinical efficacy. Recent studies have highlighted the role of BRAF inhibition in promoting oxidative phosphorylation (OXPHOS), over glycolysis, in BRAFV600E melanomas, a switch commonly seen in conjunction with development of drug resistance. This metabolic switch occurs at the transcriptional level, indicated by the up-regulation of PGC1α through the lineage-specific transcription factor MITF. Based on these data, we propose that increased OXPHOS is required for melanoma cells to acquire resistance against the BRAF inhibition, which supports our investigation of the therapeutic benefit of combining BRAF and OXPHOS inhibitors. For the latter, respiratory Complex I, an essential enzyme in the mitochondrial respiratory chain, is a logical target for OXPHOS inhibition. We investigated the molecular, metabolic and bioenergetic effects of a selective mutant BRAF inhibitor (Vemurafenib/PLX4032) and BAY 87-2243, a small molecule inhibiting respiratory Complex I, in vitro using various BRAF-mutant melanoma cell lines. First, our study revealed that BRAF inhibition increased the expression of mitochondrial genes and mitochondrial respiration, which is associated with elevated mitochondrial oxidative stress, independent of the expression of PGC1α. Furthermore, BAY 87-2243 inhibited OXPHOS, down-regulated the expression of mitochondrial genes and increased reactive oxygen species (ROS) production. We also demonstrated that inhibition of BRAF increased the OXPHOS phenotype and therefore enhanced the effect of BAY 87-2243 on mitochondrial metabolism; the combination of both inhibitors showed synergistic effects in vitro.Interestingly, long term BRAF inhibition resulted in BRAFV600E melanoma cells to become resistant to BAY 87-2243. Preliminary studies suggest that melanoma cells pretreated with a BRAF inhibitor, with higher rates of mitochondrial respiration and elevated ROS levels, are prone to cell death when targeted by pro-oxidants. Further studies are currently ongoing to understand this resistance phenotype as well as the underlying mechanism which drives the synergistic drug effect. Citation Format: Laura Schoeckel, Katharina Bitschar, Mélanie Héroult, Charlotte Kopitz, Andrea Hägebarth. Inhibition of mitochondrial complex I enhances the therapeutic benefit of BRAF inhibition in mutant melanoma cell lines. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 665. doi:10.1158/1538-7445.AM2015-665