Abstract B36: The response of colorectal cancer cells to 5-FU and oxaliplatin mimicking the clinical schedule involves the interplay between of apoptosis, senescence, and cytoprotective autophagy
Authors: Zanon Andréa Baldasso , Franco Nayara , Lopez Patrícia Luciana da Costa , Lenz Guido , Filippi-Chiela Eduardo C. 
Published: May 2019

Abstract
Colorectal cancer (CRC) is among the most common and aggressive cancers worldwide. Primary therapy to CRC includes 5-fluoruracil (5-FU) and oxaliplatin (Oxa). Here, we aim to investigate the cellular mechanisms that mediate the response of CRC to the cotreatment with 5-FU and OXA, in a schedule that mimics the clinics, i.e., 48 h of exposure to the drugs followed by two weeks before the second treatment. We repeated this cycle twice. Our main objective was to understand the outcome of CRC cells after the period of exposure to the drugs, in order to understand the mechanisms of response and resistance to the treatment. To do this, we used the CRC human cell lines HCT116 and HT29. We found that acutely (48 h), drugs did not show additive toxicity. However, chronically the combination had a strong additive effect, reducing both the growth of the population of cells and the growth of single cells in a clonogenic assay. 5-FU induced apoptosis, peaking 3d after treatment, while Oxa induced senescence 7 days after treatment, both in higher extent in HCT116 than in HT29 cells. The cotreatment induced an intense, transitory autophagy in both cell lines, reaching a peak 5 to 7 days after the treatment. Pharmacologic suppression of autophagy during its peak of activation but not together with the chemotherapeutics strongly reduced cell growth. In summary, in the first cycle of treatment we found that the combination of 5-FU and OXA for 48 h had additive toxicity along two weeks by the combination of apoptosis (induced by 5-FU) and senescence (induced by Oxa). However, both cell lines displayed regrowth from day 7 after treatment onwards. In addition, suppression of autophagy strongly decreased cancer cells' growth and clonogenicity. Then, we performed a second cycle of 5-FU and Oxa in the cells. Interestingly, cells were more sensitive to the second cycle of treatment, suggesting that resistance was not established. However, along the second cycle of treatment we found that (i) senescent cells (induced in the first cycle of treatment) survived to the second cycle of treatment, while nonsenescent cells were sensitive, and (ii) that cells acquired a phenotype that resembles the epithelial to mesenchymal transition, which is a hallmark of cancer progression. The next step, which is ongoing, is the evaluation of autophagy in the second cycle of treatment, as well as the long-term analysis of those cells that were suppressed to autophagy in the first cycle of treatment. Translationally, our data suggest that the rational modulation of autophagy may increase the toxicity of 5-FU plus Oxa cotreatment. Furthermore, we found that senescent cells, which can have a protumor role due to their secretome, resisted to the second cycle of treatment, so that the elimination of these cells could improve the efficacy of the combined therapy with 5-FU and Oxa in CRC.
Citation Format: Andréa Baldasso Zanon, Nayara Franco, Patrícia Luciana da Costa Lopez, Guido Lenz, Eduardo C. Filippi-Chiela. The response of colorectal cancer cells to 5-FU and oxaliplatin mimicking the clinical schedule involves the interplay between of apoptosis, senescence, and cytoprotective autophagy [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr B36.