Biology of Human Tumors SIRT1/PGC1a-Dependent Increase in Oxidative Phosphorylation Supports Chemotherapy Resistance of Colon Cancer

Purpose: Chemotherapy treatment of metastatic colon cancer ultimately fails due to development of drug resistance. Identification of chemotherapy-induced changes in tumor biology may provide insight into drug resistance mechanisms. Experimental Design: We studied gene expression differences between groups of liver metastases that were exposed to preoperative chemotherapy or not. Multiple patient-derived colonosphere cultures were used to assess how chemotherapy alters energy metabolism by measuring mitochondrial biomass, oxygen consumption, and lactate production. Genetically manipulated colonosphere-initiated tumors were used to assess how altered energy metabolism affects chemotherapy efficacy. Results: Gene ontology and pathway enrichment analysis revealed significant upregulation of genes involved in oxidative phosphorylation (OXPHOS) and mitochondrial biogenesis in metastases that were exposed to chemotherapy. This suggested chemotherapy induces a shift in tumor metabolism from glycolysis towards OXPHOS. Indeed, chemotreatment of patientderived colonosphere cultures resulted in an increase of mitochondrial biomass, increased expression of respiratory chain enzymes, and higher rates of oxygen consumption. This was mediated by the histone deacetylase sirtuin-1 (SIRT1) and its substrate, the transcriptional coactivator PGC1a. Knockdown of SIRT1 or PGC1aprevented chemotherapy-inducedOXPHOS and significantly sensitized patient-derived colonospheres as well as tumor xenografts to chemotherapy. Conclusion: Chemotherapy of colorectal tumors induces a SIRT1/PGC1a-dependent increase in OXPHOS that promotes tumor survival during treatment. This phenomenon is also observed in chemotherapy-exposed resected liver metastases, strongly suggesting that chemotherapy induces long-lasting changes in tumor metabolism that potentially interfere with drug efficacy. In conclusion, we propose a novel mechanism of chemotherapy resistance that may be clinically relevant and therapeutically exploitable. Clin Cancer Res; 1–10. 2015 AACR.