Curcumin action in prostate cancer cells and fibroblasts.

Abstract

Curcumin is a component of the Indian spice turmeric that has shown anti-cancer activity across a range of models. This includes prostate cancer, the most commonly diagnosed cancer in Australia. While much of the current literature relates to epithelial cells, there is no information regarding curcumin activity or resistance in prostate fibroblasts. With curcumin recently entering clinical trials for prostate cancer and being increasingly used as a dietary supplement, it is critical to gain an understanding of curcumin action and potential resistance in these cells, given their reported contribution to cancer progression. Furthermore, with drug resistance being a major setback to cancer therapy, it is also important to investigate curcumin-based combination strategies to enhance efficacy and avoid the development of resistance. The aims of this thesis were therefore to comparatively investigate mechanisms of curcumin action in prostate cancer cells and fibroblasts, to explore the potential for curcumin resistance to occur in prostate fibroblasts and to examine the ability of curcumin to re-sensitise prostate cancers resistant to drozitumab, a monoclonal antibody against death receptor 5 (DR5). Curcumin inhibited prostate cancer cell and fibroblast viability, androgen receptor (AR) activity and androgen-regulated gene expression; effects potentially caused by a decrease in AR residence on DNA. While microarray analysis of curcumin-treated fibroblasts crossed with publically available data from curcumin-treated prostate cancer cells revealed little overlap in genes, both cell lineages underwent cell cycle arrest in response to treatment. However, cell cycle arrest occurred via divergent mechanisms in different prostate cell lines. Long-term culture of prostate fibroblasts in curcumin resulted in curcumin tolerance rather than resistance, characterised by increased cell survival and decreased cell cycle arrest in response to treatment. Curcumin-tolerant fibroblasts were differentiated from sensitive fibroblasts based on a subset of differentially expressed genes, some of which had previously been associated with resistance to cancer therapies, and some of which had lost curcumin-responsiveness in tolerant fibroblasts. Many of the latter genes were androgen-regulated, and tolerant fibroblasts subsequently demonstrated reduced AR function and androgen regulation of genes, concomitant with a decrease in AR residence on DNA. The culture of tolerant fibroblasts in curcumin-free media restored curcumin sensitivity, and partially restored AR function and the ability of androgens to regulate gene expression. Tolerant fibroblasts demonstrated changes in genes responsible for extracellular matrix composition and secretion of growth factors, and when co-cultured with prostate cancer cells, a decrease in cancer cell adhesion and increase in proliferation was observed. Finally, cell line studies confirmed that curcumin re-sensitised drozitumab-resistant prostate cancer cells to drozitumab-induced apoptosis via up-regulation of the drug target DR5. While the same effect was not observed in vivo, drozitumab treatment alone demonstrated surprising anti-cancer activity. This thesis provides a greater understanding of curcumin action across multiple prostate cell lines and explores, for the first time, the development and potential implications of curcumin tolerance in prostate fibroblasts. This data provides new insights into how curcumin-based therapies or prevention strategies may affect the whole prostate, and offers considerations for curcumin use in future preclinical and clinical studies.