Purpose: Metastasis and drug resistance are the major limitations in the survival and management of patients with cancer. This study aimed to identify the mechanisms underlying HT29 colon cancer cell chemoresistance acquired after sequential exposure to 5-fluorouracil (5FU), a classical anticancer drug for treatment of epithelial solid tumors. We examined its clinical relevance in a cohort of patients with colon cancer with liver metastases after 5FU-based neoadjuvant chemotherapy and surgery. Results: We show that a clonal 5F31 cell population, resistant to 1 μmol/L 5FU, express a typical cancer stem cell–like phenotype and enter into a reversible quiescent G₀ state upon reexposure to higher 5FU concentrations. These quiescent cells overexpressed the tyrosine kinase c-Yes that became activated and membrane-associated upon 5FU exposure. This enhanced signaling pathway induced the dissociation of the Yes/YAP (Yes-associated protein) molecular complex and depleted nuclear YAP levels. Consistently, YES1 silencing decreased nuclear YAP accumulation and induced cellular quiescence in 5F31 cells cultured in 5FU-free medium. Importantly, YES1 and YAP transcript levels were higher in liver metastases of patients with colon cancer after 5FU-based neoadjuvant chemotherapy. Moreover, the YES1 and YAP transcript levels positively correlated with colon cancer relapse and shorter patient survival (P < 0.05 and P < 0.025, respectively). Conclusions: We identified c-Yes and YAP as potential molecular targets to eradicate quiescent cancer cells and dormant micrometastases during 5FU chemotherapy and resistance and as predictive survival markers for colon cancer. Clin Cancer Res; 20(4); 837–46. ©2013 AACR.

Cancer cells can undergo a metabolic reprogramming from oxidative phosphorylation to glycolysis that allows them to adapt to nutrient-poor microenvironments, thereby imposing a selection for aggressive variants. However, the mechanisms underlying this reprogramming are not fully understood. Using complementary approaches in validated cell lines and freshly obtained human specimens, we report here that mitochondrial respiration and oxidative phosphorylation are slowed in metastatic melanomas, even under normoxic conditions due to the persistence of a high nuclear expression of hypoxia-inducible factor-1α (HIF-1α). Pharmacologic or genetic blockades of the HIF-1α pathway decreased glycolysis and promoted mitochondrial respiration via specific reduction in the expression of pyruvate dehydrogenase kinase-3 (PDK3). Inhibiting PDK3 activity by dichloroacetate (DCA) or siRNA-mediated attenuation was sufficient to increase pyruvate dehydrogenase activity, oxidative phosphorylation, and mitochondrial reactive oxygen species generation. Notably, DCA potentiated the antitumor effects of elesclomol, a pro-oxidative drug currently in clinical development, both by limiting cell proliferation and promoting cell death. Interestingly, this combination was also effective against BRAF V600E-mutant melanoma cells that were resistant to the BRAF inhibitor vemurafenib. Cotreatment of melanomas with DCA and elesclomol in vivo achieved a more durable response than single agent alone. Our findings offer a preclinical validation of the HIF-1/PDK3 bioenergetic pathway as a new target for therapeutic intervention in metastatic melanoma, opening the door to innovative combinations that might eradicate this disease. Cancer Res; 72(19); 5035–47. ©2012 AACR.