Abstract 212: Withaferin A in combination with cisplatin targets CD44 and Oct4 positive cancer stem cells in ovarian cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Currently, the treatment for ovarian cancer entails cytoreductive surgery followed by chemotherapy, mainly, carboplatin coupled with paclitaxel. Although this treatment regimen is initially effective in a high percentage of cases, it is associated with severe side effects and within 6 to 24 months of initial treatment, tumor relapse occurs, which is attributed to the carcinomas having become platinum-resistant. Due to the poor survival of women with platinum-resistant carcinomas, and the severe side effects an alternative treatment strategy is warranted. We developed a novel strategy that combines cisplatin with withaferin A (WFA). WFA, a bioactive compound isolated from the plant Withania somnifera, is used in the US as an over-the-counter dietary supplement. More recently, it has been shown to prevent tumor growth, angiogenesis, and metastasis. In addition, WFA has been reported to inhibit Notch 1 signaling an important signaling pathway for the self-renewal and maintenance of cancer stem cell population. Based on this information, we hypothesize that a novel combination of withaferin A and cisplatin can target ovarian cancer cells and also ovarian cancer stem cells, which can reduce the cisplatin side effects and recurrence of ovarian cancer. Our hypothesis is supported by our preliminary studies in which epithelial ovarian cancer cell lines (A2780 and CaOV3 and A2780/CP70) when co-treated with low doses of the WFA (1.5 µM) and cisplatin (20 µM), resulted in inhibiting 80 to 90% cell proliferation within 48 h of treatment. In contrast, same concentration of each drug when used alone exhibited only 15% to 20% inhibition, respectively. In addition, treatment of nude mice bearing orthotopic ovarian tumors with WFA/cisplatin combination resulted in 80 to 90% reduction in tumor growth and complete inhibition of metastasis to other organs. In addition, treatment of mice bearing ovarian tumors with WFA/cisplatin combination showed a significant reduction in CD44 positive cancer stem cells analyzed by immuno-staining and western blot analysis of the CD44 protein. Tumors collected from mice treated with cisplatin alone revealed enrichment of CD44 positive cancer stem cells and expression of CD44 protein. Analysis of Notch1 signaling gene and its downstream signaling gene Hes1 showed a significant down regulation of expression. Notch1 plays an important role in renewal and maintenance of cancer stem cells which are reported to be chemo-resistance and play critical role in recurrence of cancer. Based on our results, we conclude that WFA/cisplatin combination therapy not only suppresses ovarian tumor growth but minimizes/eliminates cancer stem cell population, hence reduces the drug resistance and recurrence of cancer. This work was support by funds from James Graham Brown Cancer Center. Presenting author is a post-doctoral fellow. Citation Format: Sanjay K. Singh, J C. States, Sham S. Kakar. Withaferin A in combination with cisplatin targets CD44 and Oct4 positive cancer stem cells in ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 212. doi:10.1158/1538-7445.AM2014-212