ERCC1, KRAS mutation, redox status, and oxaliplatin sensitivity in colorectal cancer: “Radical” change in an old model.

Abstract

e14156 Background: Oxaliplatin (Oxa) is widely used in metastatic colorectal cancer, but currently there are not valid predictors of response to this drug. In our recent retrospective clinical study we have shown a greater efficacy of Oxa in patients with metastatic colorectal cancer with mutated (mt) K-RAS. We hypothesized that the mutational status of K-RAS could influence the expression of ERCC1 and cellular Redox status. Methods: We used four cell lines of colorectal cancer: two K-RAS wild type (wt) (HCT-8, HT-29) and two K-RAS mt (SW620, SW480). We evaluated the sensitivity of these cell lines to Oxa by MTT-test and the ERCC1 levels before and after 24h exposure to Oxa by RT-PCR. We silenced K-RAS in a K-RAS mt cell lines to evaluate the impact on Oxa sensitivity and ERCC1 levels. We also silenced ERCC1 in order to confirm the importance of this protein as a Oxa resistance factor. Cellular oxidative stress was determined by DCFDA. Results: The K-RAS mt cell lines were more sensitive to Oxa (p<0.001). The basal levels of ERCC1 did not show significant differences between K-RAS mt and wt cell line, however, after 24h exposure to Oxa, only the K-RAS wt lines showed the ability to induce ERCC1, with a statistically significant difference (p<0.005). The silencing of K-RAS in K-RAS mt cell lines (SW620s) demonstrated to reduce sensitivity to Oxa associated with the acquisition of the ability to induce ERCC1. The silencing of ERCC1 in K-RAS wt cell lines enhance the sensibility to Oxa. The levels of reactive oxygen species were higher in K-RAS mt cell lines. The Pearson correlation test showed a statistically significant relationship between basal levels of ROS and sensitivity to Oxa ("r" -0,988, p<0.01). The baseline levels of ROS were higher SW620 than the line SW620s. The administration of Oxa in these cell lines resulted in a statistically higher fluorescence index in SW620 versus SW620s (p<0.003). Conclusions: The K-RAS mutated cell lines were more sensitive to Oxa. This feature seems to be secondary to the inability of these cells to induce ERCC1 after exposure to Oxa and to the synergism between K-RAS mutation and Oxa in increasing oxidative stress. K-RAS can thus be a predictor of response to Oxa in colorectal cancer.