Abstract 3350: Inhibition of breast cancer and cancer stem cells via a novel micheliolide analogue CY-9

Abstract

Abstract Natural products that target cancer stem cells (CSCs) have the potential to treat cancers and reduce the occurrence of relapse. The sesquiterpene lactone parthenolide has received much attention for its ability to preferentially target CSCs over their normal equivalents. However, poor pharmacokinetics have severely limited the clinical use of parthenolide, and prompted synthesis of a water soluble analogue, LC-1. Although currently in Phase I trials for disseminated cancers, LC-1 suffers from a short half-life, which could potentially limit its efficacy. In order to identify new sesquiterpene lactones which function similarly to parthenolide and LC-1 but with improved pharmacokinetics, we tested a new micheliolide analogue CY-9 for activity against both breast cancer and CSCs. Using the MTS assay, SUM159 breast cancer cells displayed sensitivity to CY-9 with an IC50 of 5 μM, which is similar to reported inhibitory concentrations of parthenolide. SUM159 cells assayed for Aldefluor expression after a three day treatment with CY-9 (1, 2.5, 5 μM) showed a 27%, 64%, and 83% reduction in their CSC populations, respectively. This CSC depletion was largely reversed in SUM159 cells that were pre-treated with the antioxidant N-Acetyl-Cysteine (NAC) before exposure to CY-9. Inhibition of SUM159 CSC self-renewal after CY-9 treatment was assayed using tumorsphere formation of single SUM159 Aldefluor-positive cells. A seven day treatment of 5 μM CY-9 reduced SUM159 Aldefluor-positive cell tumorsphere formation by 74%. Under drug-free conditions, tumorsphere formation was reduced by 26% in the second passage, but returned to control levels by the third passage. Western blotting also showed that 5 μM CY-9 reduced the levels of nuclear NF-κB. These results demonstrate the effectiveness of our new micheliolide analogue CY-9 at targeting populations of both bulk breast tumor cells and CSCs. The slight reduction in tumorsphere formation under drug-free conditions suggests that inhibition of self-renewal plays a minor role in CY-9's activity against CSCs. Loss of CY-9 activity with cells pre-treated with NAC suggests that the inhibitory effect of CY-9 is partially mediated by its interaction with biologically relevant cysteines and/or ROS generation. Additionally, as NF-κB is vital for defense against cellular stressors such as ROS, depletion of nuclear NF-κB might also explain the observed inhibition with CY-9. Together, these results warrant further study of CY-9 as a potential therapy for breast cancer and CSCs. 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 3350. doi:10.1158/1538-7445.AM2011-3350