Poster Presentation 25th Lorne Cancer Conference 2013

Combination therapy with raloxifene and a novel curcumin analog for the treatment of hormone refractory prostate cancer: in vitro mechanisms for synergistic cytotoxicity (#334)

Aloran Mazumder 1 , Maree Gould 2 , Sebastien Taurin 1 , Helen D Nicholson 2 , Rhonda J Rosengren 1
  1. Department of Pharmacology and Toxicology, University of Otago, Dunedin, New Zealand
  2. Department of Anatomy, University of Otago, Dunedin, New Zealand

The survival rate for men with hormone refractory prostate cancer has not changed significantly in the last 30 years. Thus there is a need for new drug treatments for this aggressive cancer.  Our lab has had success with second generation curcumin derivatives as novel therapies for ER negative breast cancer. In this study we examined the combination of raloxifene and 2,6-bis(pyridin-4-ylmethylene)-cyclohexanone (RL91), a potent 2nd generation curcumin derivative as a novel treatment for hormone refractory prostate cancer. The combination treatment showed highly potent cytotoxicity toward PC3 prostate cancer cells compared to individual treatments. Specifically, EC50 values of 2 µM and 10 µM were produced by RL91 and raloxifene, respectively. Moreover, this combination decreased cell number by 85% compared to control after 96 h of treatment, as determined by the sulforhodamine B assay. Raloxifene is known to modulate the activity of estrogen receptor alpha (ERα) and beta (ERβ).  The activation of ERα, ERβ as well as the epidermal growth factor receptor (EGFR), is crucial for the proliferation of hormone refractory prostate cancer (HRPC). To determine how raloxifene potentiates the cytotoxic effect of RL91, the localization of these receptors was examined by fluorescent microscopy. The results showed that ERα, ERβ, the androgen receptor (AR) and EGFR were expressed in PC3 cells. Furthermore, raloxifene treatment (10 µM) promoted EGFR internalization in the cytoplasm, resulting in a decreased expression of active EGFR. A similar effect was also seen for ERβ where translocation from the nucleus to the cytoplasm occurred as early as 6 h following raloxifene treatment. These results suggest that raloxifene-mediated changes in the localization of ERβ and the EGFR provide a mechanism by which raloxifene enhances the cytotoxicity of RL91 in PC3 cells. This novel mechanism should be explored further in order to develop new therapies for HRPC.