Autophagy inhibitors increase the susceptibility of KRAS-mutant human colorectal cancer cells to a combined treatment of 2-deoxy-D-glucose and lovastatin

RAS-driven colorectal cancer relies on glucose metabolism to support uncontrolled growth. However, monotherapy with glycolysis inhibitors like 2-deoxy-D-glucose causes limited effectiveness. Recent studies suggest that anti-tumor effects of glycolysis inhibition could be improved by combination treatment with inhibitors of oxidative phosphorylation. In this study we investigated the effect of a combination of 2-deoxy-D-glucose with lovastatin (a known inhibitor of mevalonate pathway and oxidative phosphorylation) on growth of KRAS-mutant human colorectal cancer cell lines HCT116 and LoVo. A combination of lovastatin (>3.75 μM) and 2- deoxy-D-glucose (>1.25 mM) synergistically reduced cell viability, arrested cells in the G2/M phase, and induced apoptosis. The combined treatment also reduced cellular oxygen consumption and extracellular acidification rate, resulting in decreased production of ATP and lower steady-state ATP levels. Energy depletion markedly activated AMPK, inhibited mTOR and RAS signaling pathways, eventually inducing autophagy, the cellular pro-survival process under metabolic stress, whereas inhibition of autophagy by chloroquine (6.25 μM) enhanced the cytotoxic effect of the combination of lovastatin and 2-deoxy-D-glucose. These in vitro experiment results were reproduced in a nude mouse xenograft model of HCT116 cells. Our findings suggest that concurrently targeting glycolysis, oxidative phosphorylation, and autophagy may be a promising regimen for the management of RAS-driven colorectal cancers.