Abstract 2894: Overcoming intrinsic resistance to BRAF-inhibitors by modulating redox balance inBRAF-mutated melanoma cells
Authors: Paudel B. Bishal , Harris Leonard A. , Hardeman Keisha N. , Hayford Corey E. , Meyer Christian T. , Abugable Arwa A. , Tyson Darren R. , Fessel Joshua P. , Quaranta Vito 
Published: August 2019

Abstract
Post-resistant tumor analyses or static measurements provide most of our current knowledge of tumor recurrence. Unfortunately, these studies neither elucidate critical events that precede resistance nor explain the dynamics of drug response in cancer cells. Filling this knowledge gap may engender key advances in cancer therapy. Therefore, we coupled single-cell time-lapse microscopy, bioinformatics, and mathematical modeling to study the dynamics of drug response in BRAF-mutated melanoma cells. We recently reported a novel non-quiescent idling state that melanoma cells exhibit under continued drug exposure. Although Idling cells exhibit a constant population size, they continue to divide and die at the level of the single cell. We speculate that idling state, primed to acquire resistance, could be a new type of drug tolerance, and may constitute the bulk of minimum residual disease (MRD)often seen in the clinic in remission. Melanoma cells we considered, exhibited heterogeneous responses prior to convergence to idling state. These differential responses in melanoma can be defined within a mathematical framework of epigenetic landscape: initial heterogeneity reflects an early re-equilibration among distinct phenotypic basins while idling is a final equilibrated state. Thus, describing the molecular signatures that define basins in BRAF-mutated melanoma landscape, both drug-naïve and drug-induced, would provide rational strategies to alter the landscape and enhance the clinical benefits. To this end, we utilized single-cell-derived clones to find gene-signatures that correlate to drug-sensitivity and discovered that drug-naïve landscape could be defined with respect to distinct redox metabolism. We further confirmed and validated these signatures in CCLE dataset across a range of BRAF-mutated melanoma cells. Specifically, the antioxidants such as NADPH and GSH provide an early survival advantage to melanoma cells under BRAF-inhibition. We show that modulating expression of these metabolic genes changes the initial landscape, and synergizes with BRAF-inhibitors. The enhanced effects of combination can be mitigated by antioxidants specific to glutathione redox balance. These observations suggest that disruption of redox balance, in combination with BRAF-inhibition, may improve the outcomes of BRAF-targeted therapy. Additionally, this strategy will maximize initial cell killing, and hence reduce the number of cells that constitute MRD or idling state. Taken together, our work provides a unifying view of how melanomas respond to BRAF-inhibition and suggest that targeted landscaping is a rational way to suppress both an initial tumor and idling cells.
Citation Format: B. Bishal Paudel, Leonard A. Harris, Keisha N. Hardeman, Corey E. Hayford, Christian T. Meyer, Arwa A. Abugable, Darren R. Tyson, Joshua P. Fessel, Vito Quaranta. Overcoming intrinsic resistance to BRAF-inhibitors by modulating redox balance inBRAF-mutated melanoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2894.