P2.03b-072 Resistance to BET Inhibitors in Lung Adenocarcinoma is Mediated through a MYC Independent Mechanism: Topic: Biomarkers

Abstract

JQ1 is an inhibitor of the bromodomain and extraterminal (BET) family proteins, which function as important reader molecules of acetylated histones and recruit transcriptional activators to specific promoter sites. BET proteins have been shown to control the expression of numerous genes involved in cell cycle, cell growth, and cancer. The down-regulation of c-MYChas been linked to JQ1 inhibition in many non-lung cancer cell lines, while reactivation of c-MYC expression, through co-regulation by GLI2 or activation of Wnt signaling, has been shown to induce JQ1 resistance. However, our lab has previously shown that lung adenocarcima (LAC) cells are inhibited by JQ1 through a mechanism independent of c-MYC down-regulation,identifying FOSL1 as a possible target in LAC cells. This suggests that the epigenetic landscape of cells from different origins and differentiation states influences response to JQ1. This study aims to identify potential mechanisms regulating resistance to JQ1 in LAC in order to determine if the epigenome affects this process in different cancer types. LAC cell lines sensitive to JQ1 treatment, H23 and H1975, were passaged with increasing concentrations of JQ1 until the cells were resistant to high doses of the drug. Expression profiles were generated for parental and resistant cells using Affymetrix Human PrimeView Arrays and genes differentially expressed between the states for each cell line were identified and compared across both H23 and H1975 to identify candidate genes. Protein expression was evaluated through Western Blot analysis to confirm gene changes associated with resistance. Initial morphological and western blot analysis showed resistant H1975 cells underwent EMT transition with significant decrease in E-cadherin and increase in Vimentin. Analysis of differentially expressed genes between the parental and resistant pairs identified 101 significantly differentially expressed genes (Benjamini-Hochberg corrected p-value <0.005) common between the H1975 and H23 lines; however, MYC was not significantly altered nor was FOSL1 expression reactivated. Preliminary findings indicate that AXL and SPOCK1 up-regulation in H1975 and H23, respectively, may be driving resistance in each LAC cell line. The discovery and optimization of small-molecule inhibitors of epigenetic targets is a major focus of current biomedical research. We determined that LAC cells, unlike those from other cancers, develop JQ1 resistance through mechanisms independent of c-MYC, suggesting the epigenomic landscape of a cell can influence both sensitivity and resistance to BET inhibitors. Together, this work will lead to the development of more efficient therapies for lung cancer treatment.