Abstract 3332: Targeting cancer stem cells in ovarian cancer

Abstract

Abstract Ovarian cancer is a disease commonly complicated by the presence of ascites in the abdominal cavity which represents a major clinical problem. Currently, the treatment for ovarian cancer entails cytoreductive surgery followed by chemotherapy, mainly cisplatin or carboplatin combined with paclitaxel. Although this regimen is initially effective in a high percentage of cases, unfortunately within few months of initial treatment, tumor relapse occurs because of platinum-resistance. This is attributed mainly due to the presence of cancer stem cells (CSCs) present in ascites which are chemo-resistant and responsible for recurrence of cancer. In our preliminary studies, we show for the first time that withaferin A (WFA), a bioactive compound isolated from the plant Withania somnifera targets putative CSCs. Treatment of nude mice bearing orthotopic ovarian tumors with WFA resulted in a 70% to 80% reduction in tumor growth, complete inhibition of metastasis, and a significant elimination of the cells expressing CSCs markers - CD44, CD24, CD34, CD117, ALDH1 and Oct4 and down regulation of Notch1 and its downstream signaling genes (Hes1 and Hey1) reported to play crucial role for self-renewal and maintenance of CSCs. In addition, WFA also resulted in a significant inhibition of securin expression an “oncogene” important in ovarian tumorigenesis. In contrast, treatment of mice with CIS alone had the opposite effects, causing an increase in cells expressing CSC markers and Notch1 signaling pathway. However, combining of WFA with CIS showed enhanced effects on suppression of securin as well as elimination of CSCs. This may explain the development of platinum-resistance and recurrence of cancer in patients treated with first line chemotherapy. Based on this information, we hypothesize that a combination of WFA with CIS should target ovarian cancer cells as well as cancer stem cells by reducing securin and CSCs thereby reducing CIS resistance and recurrence of ovarian cancer. In our study, we used cells from ascites from patients with recurrent ovarian cancer and determine the effect of WFA alone and in combination with CIS on tumorigenic functions of ascites cells and CSCs from ascites in vitro and in vivo, and defined the molecular mechanisms associated with self-renewal, maintenance and recurrence of cancer in relation to expression of securin. Because the two agents act synergistically, this combination may minimize side effects as well as induction of cisplatin resistance and recurrence of cancer. In addition, this study will justify the initiation of phase I/phase II clinical trials to assess potential toxicity and efficacy of WFA/CIS combination in advanced/recurrent ovarian cancer patients. Citation Format: Sham S. Kakar, Mariusz Z. Ratajczak. Targeting cancer stem cells in ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3332.