Fatty acid synthase (FASN) inhibition cooperates with BH3 mimetic drugs to overcome resistance to mitochondrial apoptosis in pancreatic cancer

Abstract

Resistance to mitochondrial apoptosis is a major driver of chemoresistance in pancreatic ductal adenocarcinoma (PDAC). However, pharmacological manipulation of the mitochondrial apoptosis threshold in PDAC cells remains an unmet therapeutic goal. We hypothesized that fatty acid synthase inhibitors (FASNis), a family of targeted metabolic therapeutics recently entering the clinic, could lower the apoptotic threshold in chemoresistant PDAC cells and be synergistic with BH3 mimetics that neutralize anti-apoptotic proteins. Computational studies with TVB-3166 and TVB-3664, two analogues of the clinical-grade FASNi TVB-2640 (denifanstat), confirmed their uncompetitive behavior towards NADPH when bound to the FASN ketoacyl reductase domain. The extent of NADPH accumulation, a consequence of FASN inhibition, paralleled the sensitivity of PDAC cells to the apoptotic effects of TVB FASNis in conventional PDAC cell lines that naturally express varying levels of FASN. FASN inhibition dramatically increased the sensitivity of “FASN-high” expressing PDAC cells to the BCL2/BCL-X_L/BCL-W inhibitor ABT-263/navitoclax and the BCL2-selective inhibitor ABT-199/venetoclax, both in vitro and in in vivo xenografted tumors. The ability of TVB FASNis to shift the balance of pro- and anti-apoptotic proteins and thereby push PDAC cells closer to the apoptotic threshold was also observed in cell lines developed from patient-derived xenografts (PDXs) representative of the classical (pancreatic) transcriptomic subtype of PDAC. Experiments in PDAC PDXs in vivo confirmed the synergistic antitumor activity of TVB-3664 with navitoclax and venetoclax, independent of the nature of the replication stress signature of patient-derived PDAC cells. The discovery that targeted inhibition of FASN is a metabolic perturbation that sensitizes PDAC cells to BH3 mimetics warrants further investigation to overcome resistance to mitochondrial apoptosis in PDAC patients.