Abstract 2399: System analysis of adapted and quiescent/dormancy(QD) models of drug resistance in melanoma cell lines

The biological basis for inherent and acquired drug resistance in melanoma is a prominent issue, highlighted by the recent discovery of various pathways leading to acquired resistance to the mutant BRAF inhibitor Vemurafenib (Plx4032). In order to dissect patterns of drug resistance, we treated 3 melanoma cell lines (A375, 1205Lu and SK-Mel28) under 2 diverse conditions: (1) Increasing drug concentrations over time(4 months)- Melanoma cells treated with increasing concentrations of Plx4032 (initial and increasing concentrations of 0.1, 0.5, 1 and 5 μM PLx4032) exhibited an adaptation response. After an initial pause in proliferation, these cells proliferated in the continuing presence of the drug. Cells able to grow in the presence of 10 or 20 μM of Plx4032 were cultured as pools. RNA-Seq profiling and system biology analysis comparing the gene expression in the parental SK-Mel28 cells and adapted A2-1 revealed three major altered pathways: the PDGF-MAPK-DUSP-HIF2α, TGF-β-SMAD9-FGF1 and EDNRB-GNAI2-PLCB4-PKA-MITF pathway. Our qRT-PCR and western blot experiments have confirmed an up-regulation of PDGF which by-passed the BRAF gene and activated ERK1/2 kinases. These changes were accompanied by increase of NRAS accumulation in the adapted cells. (2) Using high initial drug concentrations of PLx4032 (>10 μM), > 99.9 of cells were killed, but some single cells (Q/D) survived for at least 4 weeks in the continuous presence of drug. After the drug was removed cellular proliferation reoccured 2-3 weeks later (designated post-dormant cells 1, PD1 cells). These cells did not show increased IC50s to Plx4032 after 72 hour of retreatment. However, when treated with high dose of drug again, the PD1 cells produced more dormant cells (PD2 cells), suggesting inheritance of the DQ trait. RNA-Seq profiling studies of the DQ cells are underway. The drug-induced dormancy/quiescence and adaptive response represent 2 different pathways of how cells survive treatment and develop resistance and provide a beginning to understanding the biological basis of the well established clinical phenomenon of long term clinical dormancy of melanoma and potentially other cancers. Citation Format: Feng Liu, Parvita Paresh Panchal, Zi Wang, Ahmed Farhat, Angela Garcia, Tcharles Fagundes, Fabian Filipp, Frank L. Meyskens. System analysis of adapted and quiescent/dormancy(QD) models of drug resistance in melanoma cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2399.