Abstract 1639: Targeting the p38 MAPK pathway inhibits irinotecan resistance in colon adenocarcinoma

Abstract

Abstract Despite recent advances in the treatment of colon cancer, tumor resistance is a frequent cause of chemotherapy failure. To better elucidate the molecular mechanisms involved in resistance to irinotecan (and its active metabolite SN38), we established SN38-resistant clones derived from the colon adenocarcinoma HCT-116 and SW48 cell lines. These clones show various levels (6 to 60 fold) of resistance to SN-38 and display enhanced levels of activated MAPK p38 as compared to the corresponding parental cells. Because four different isoforms of p38 have been described, we then studied the effect of p38 overexpression or downregulation of each isoform on cell sensivity to SN38 and found that both alpha and beta isoforms are involved in the development of resistance to SN38. In this line, we show that cell treatment with SB202190, which specifically inhibits p38 alpha and beta, enhanced the cytotoxic activity of SN38, but not of 5-FU or oxaliplatin. Moreover, p38 inhibition sensitized tumor cells derived from both SN38-sensitive and -resistant HCT116 cells to irinotecan treatment in xenograft models. Finally, we detected less phosphorylated p38 in primary colon cancer of patients sensitive to irinotecan-based treatment, compared to non-responder patients. This indicates that enhanced level of expression of phosphorylated p38 could predict the absence of clinical response to irinotecan. Altogether, our results show for the first time that the p38 MAPK pathway is involved in irinotecan sensitivity and suggest that phosphorylated p38 expression level could be used as a marker of clinical resistance to irinotecan. They further suggest that targeting the p38 pathway may be a potential strategy to overcome resistance to irinotecan-based chemotherapies in colorectal cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1639. doi:10.1158/1538-7445.AM2011-1639