The rational modulation of autophagy sensitizes colorectal cancer cells to 5-fluouracil and Oxaliplatin

Abstract

AbstractColorectal cancer (CRC) is the third most common and deadliest cancers globally. The primary chemotherapy used for treating CRC is a co-treatment of 5-fluoruracil (5FU) and Oxaliplatin (OXA). In this study, we investigated the cellular mechanisms that contribute to the response and resistance of CRC cells to these drugs using an experimental design mimicking the clinical schedule. To this, we treated and analyzed CRC human cell lines HCT116 and HT29 with the drugs for 48h, followed by analysis for two additional weeks. We found that although the drugs did not show additive toxicity at 48 hours, they had a strong additive effect in the weeks post-treatment, reducing both the regrowth of cell population and the proliferative capacity of single cells. Co-treatment induced apoptosis and senescence, peaking at 3 days and 7 days after treatment, respectively. However, despite this, cells from all conditions resumed population proliferation and acquired a viable phenotype. We then search for cellular mechanisms involved in the tolerance and recurrence of CRC cells. In the weeks post-treatment, the co-treatment showed the greatest toxicity and, in contrast to single treatments, blocked the enrichment of CD133-positive cells. Furthermore, our findings indicated that cells that resisted 5FU and/or OXA triggered high levels of autophagy. Autophagy levels reached a peak 5 to 7 days after the treatment. Pharmacologic suppression of autophagy during its activation, but not together with the chemotherapeutics, strongly reduced cell regrowth and clonogenicity. Overall, our preclinical model provides new insights into the cellular mechanisms that underlie the response and resistance of CRC cells to 5FU and OXA, suggesting optimized, time-specific autophagy inhibition as a new avenue for improving the efficacy of current treatments.