Abstract 2496: Epothilones synergistically induce CRC cell death in combination with standard chemotherapy in part through a p53-dependent pathway
2010-04-01

Abstract Epothilones are a novel class of microtubule stabilizing agents with known antitumor activity. However, clinical response rates to epothilones vary widely, and the underlying molecular mechanisms that predict response to therapy remain to be clarified. Loss of p53 tumor suppressor pathway function is a common event in many cancers, including colorectal cancer (CRC). However, it is yet unknown how p53 status affects the response to epothilones in CRC. To explore the role of the p53 pathway in epothilone antitumor activity, we quantified the antitumor efficacy of Patupilone (Pp) and Ixabepilone (Ix) in combination with standard CRC chemotherapy agents in isogenic HCT116 p53+/+ and p53-/- as well as in isogenic RKO and SW48 p53+/+ and -/- cell lines. Cells were treated with oxaliplatin (Ox), 5-flourouracil (5FU), irinotecan (Ir) as well as Pp and Ix in different doses and combinations, and cell cycle perturbations and apoptosis induction were determined. We found that all the tested agents induced cell death in a dose- and p53 status-dependent manner. Both epothilones displayed enhanced antitumor activity in p53+/+ cells compared to p53-/- cells, suggesting a p53 dependent mechanism; however, Pp induced apoptosis more efficiently than Ix as single agent (IC50s for Pp in p53+/+ cells 15nm and in p53-/- cells 50nm; IC50s for Ix 50nm and &amp;gt;100nm respectively). Intriguingly, Pb and Ix induced a G2/M checkpoint arrest in p53+/+, but not p53-/- cells. Addition of Ix or Pb to either Ox, 5FU or Ir dramatically enhanced apoptosis in p53+/+ and -/- cells at doses that normally did not demonstrate any antitumor activity when administered as single agents. In p53 +/+ cells oxaliplatin alone induced 50% apoptosis at a concentration of 50 μM; Pp alone at 2 nM induced 25% apoptosis. However when IC50 of Ox was combined with 2nM Pp, we found a dramatic apoptosis-induction of &amp;gt;95%. This synergistic effect was less pronounced in p53-/- cells, however in p53-/- cells, addition of epothilones to standard chemotherapy also increased response rates efficiently compared to standard chemotherapy alone with 50μM Ox alone inducing &amp;lt;20% apoptosis, Pp alone at 5nM inducing 20% apoptosis - but combination of 50μM Ox with 5 nM Pp inducing more than 50% apoptosis, and combination of 10nm Pp and IC50 of Ox resulting in &amp;gt;80% apoptosis in p53-/- cells. Similar intriguing results were seen for combinations of 5FU or Ir with Pb, as well as for combinations of standard chemotherapy with Ix. Thus, epothilones dramatically potentiate the efficacy of standard CRC chemotherapy (Ox, 5FU, Ir), and apoptosis induction is largely dependent on p53 status. These findings suggest that epothilones in combination with current standard chemotherapeutics in CRC may be clinically useful, and that evaluation of p53 status should be taken into consideration during the design of future clinical trials using these classes of agents. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2496.