The tumor microenvironment is now established as an integral and essential component of carcinogenesis playing a critical role in early tumor development. Therefore, targeting the interaction between a growing cancerous lesion and its microenvironment is considered an important translational cancer preventive strategy. Fibroblasts are a key cellular component of the prostate cancer (PCA) microenvironment as they have the capacity to remodel that microenvironment, promoting tumor growth, angiogenesis, invasiveness, and metastasis. Earlier studies have shown that the cancer preventive agent silibinin has broad spectrum efficacy against PCA but its effect on the PCA-fibroblast interaction remains unknown. In the present study we developed cell culture models to study the molecular interaction between PCA and fibroblasts and the effect of silibinin therein. We treated human PCA PC3 cells with DMSO or silibinin (30-60 μM dose) and collected conditioned media labeled as CCM (control conditioned media) or SBCM (silibinin treated conditioned media) respectively. Human prostate fibroblasts (PrSC) were exposed to CCM or SBCM (volume normalized with respective cell number) and we analyzed cell growth, morphology, invasiveness and molecular alterations. It was revealed that CCM exposure resulted in PrSC attaining an elongated morphology, increased invasiveness, and enhanced α-SMA (alpha-smooth muscle actin) and vimentin expression, overall transforming into a ‘myofibroblast’ phenotype permissive to prostate cancer growth and progression. In contrast, PrSC exposed to SBCM failed to manifest a myofibroblast phenotype lacking an elongated morphology, exhibiting decreased invasiveness and reduced α-SMA and vimentin expression. Analyses of CCM and SBCM revealed that the inhibitory effect of silibinin could be the result of decreasing levels of TGFβ1 secreted by PCA cells. These results are currently being validated in other PCA cells (Du145, C4-2B). To investigate the effect of silibinin directly on the fibroblasts component of PCA, we employed both PrSC treated with CCM as well as cancer-associated fibroblasts (CAFs) obtained from PCA patients. Silibinin (30-90 μM dose) exposure inhibited the invasiveness of and α-SMA expression in both CCM-treated PrSC as well as CAFs. Ongoing studies also suggest that silibinin targets CAF-induced EMT (epithelial-to-mesenchymal transition) and invasiveness of human PCA LNCaP cells. These results collectively show that silibinin could target PCA, PrSC, and CAFs as well as their cancer promoting interactions and suggest a role for silibinin in PCA prevention and intervention.

Citation Format: Harold J. Ting, Gagan Deep, Chapla Agarwal, Scott D. Cramer, Lina M. Romero, Rajesh Agarwal. Silibinin inhibits prostate cancer and stromal cells interaction through targeting TGFβ and α-smooth muscle actin. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A86.