Abstract B66: Targeting bone remodeling by isoflavone and 3,3′-diindolylmethane in the context of prostate cancer bone metastasis

Prostate cancer (PCa) commonly progress from androgen dependence to castrate resistance and subsequent metastasis, especially bone metastasis. PCa bone metastases have long been believed to be osteoblastic because of extensive new bone formation in human PCa. However, recent studies have shown that there is an increased osteolytic activity in the early phases of PCa bone metastases, suggesting that targeting both osteolytic and osteoblastic molecules would be important for inhibiting bone remodeling, which could become a newer therapeutic strategy for inhibiting PCa bone metastasis. We have previously shown that dietary genistein could inhibit PCa growth in experimental bone metastasis in a SCID-human model. In the current study, we investigated whether Isoflavone mixture G2535 containing 70.5% genistein, and B-DIM (BioResponse formulated diindolylmethane) could regulate differentiation of osteoclasts and osteoblasts mediated through regulation of cellular signaling pathways that are involved in bone remodeling and PCa bone metastasis. Using cell co-culture and molecular experimental approaches, we found that PCa cells could interact with both pre-osteoclasts and pre-osteoblasts and stimulated the differentiation of osteoclasts and osteoblasts through up-regulation of RANKL, RUNX2 and osteopontin, suggesting that PCa cells could promote bone remodeling which would, in turn, favor PCa cells grown in the bone environment. We also observed that TGF-β could induce osteoclast differentiation and stimulate the expression of RANKL and CXCR-4 in PCa cells, suggesting that the increased level of TGF-β by tumor or stromal cells could promote bone remodeling and PCa metatstasis through RANKL and CXCR-4 signaling. Importantly, we found that Isoflavone and B-DIM could inhibit the differentiation of osteoclasts and osteoblasts through the inhibition of cell signal transduction in RANKL signaling pathway. We also found that RANKL up-regulated the expression of miR-92a, which is critically related to RANKL signaling, EMT and cancer progression. Isoflavone and B-DIM inhibited the expression of miR-92a, leading to the up-regulation of E-cadherin and down-regulation of vimentin. Moreover, Isoflavone and B-DIM also inhibited the expression of periostin, one of the osteoblast markers. By Ingenuity Pathway and Network Analysis, we also observed the regulatory effects of Isoflavone and B-DIM on multiple signaling pathways such as AR/PSA, NKX3-1/Akt/p27, LEF1/cyclin D1, MITF/NR3C1, etc. Real-time PCR and western Blot analysis confirmed the results from microarray showing increased level of p27 and decreased levels of MITF, PSA, and cyclin D by Isoflavone and B-DIM treatment. Therefore, Isoflavone and B-DIM with their multi-targeting effects could be useful for the prevention of PCa progression by inhibiting bone metastasis, and thus these agents could also be useful for the management of bone metastatic disease in combination with conventional therapeutics. These results warrant further in-depth mechanistic studies and in vivo animal experiments to appreciate the value of isoflavone and B-DIM in the prevention of PCa progression. Citation Format: Yiwei Li, Dejuan Kong, Aamir Ahmad, Bin Bao, Fazlul H. Sarkar. Targeting bone remodeling by isoflavone and 3,3′-diindolylmethane in the context of prostate cancer bone metastasis [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr B66.