TGF-β is an important paracrine factor in tumorigenesis. Ligand binding of the type I and II TGF-β receptors initiate downstream signaling. The role of stromal TGF-β signaling in prostate cancer progression is unknown. In mice the conditional stromal knockout of the TGF-β receptor type II expression (Tgfbr2fspKO) resulted in the development of prostatic intraepithelial neoplasia and progression to adenocarcinoma within seven months. Clinically, we observed a loss of TGF-β receptor type II expression in 69% of human prostate cancer-associated stroma compared to 15% of stroma associated with benign tissues (n =140, p value < 0.0001). To investigate the mechanism of paracrine TGF-β signaling in prostate cancer progression, we compared the effect of the prostatic stromal cells from Tgfbr2fspKO and Tgfbr2floxE2/floxE2 mice on LNCaP human prostate cancer cells in vitro and tissue recombination xenografts. Induction of LNCaP cell proliferation and tumorigenesis was observed by Tgfbr2fspKO prostate stroma as a result of elevated Wnt3a expression. Neutralizing antibodies to Wnt3a reversed LNCaP tumorigenesis. The TGF-β inhibition of Wnt3a expression was in part through the suppression of Stat3 activity on the Wnt3a promoter. In conclusion, the frequent loss of stromal TβRII expression in human prostate cancer can relieve the paracrine suppression of Wnt3a expression.

Despite its function as an inhibitor of urokinase and tissue-type plasminogen activator (PA), PA inhibitor-1 (PAI-1) has a paradoxical pro-tumorigenic role in cancer promoting angiogenesis and tumor cell survival. In this review we summarize pre-clinical evidence in support of the pro-tumorigenic function of PAI-1 that has led to the testing of small molecule PAI-1 inhibitors, initially developed as anti-thrombotic agents, in animal models of cancer. The review discusses the challenges and the opportunities that lay ahead to the development of efficacious and non-toxic PAI-1 inhibitors as anti-cancer agents.

Mechanisms of androgen dependence of the prostate are critical to understanding prostate cancer progression to androgen independence associated with disease mortality. Transient elevation of transforming growth factor-B (TGF-B) occurs after androgen ablation. To determine the role of TGF-B on prostate response to androgen ablation, conditional TGF-B type II receptor knockout mouse models of the epithelia (Tgfbr2 NKX3.1KO ) and stromal fibroblasts (Tgfbr2 fspKO ) were used. After castration, the prostates of Tgfbr2 NKX3.1KO mice had apoptosis levels similar to those expected for control Tgfbr2 floxE2/floxE2 mice. Prostates of Tgfbr2 fspKO mice, however, had reduced regression and high levels of proliferation associated with canonical Wnt activity throughout the glandular epithelia regardless of androgen status. In contrast, Tgfbr2 floxE2/floxE2 prostates had epithelial canonical Wnt activity only in the surviving proximal ducts after castration. In vitro studies showed that androgen antagonist, bicalutamide, transiently elevated both Tgfbr2 floxE2/floxE2 and Tgfbr2 fspKO stromal expression of Wnt-2, Wnt-3a, and Wnt-5a. The neutralization of Wnt signaling by the expression of secreted frizzled related protein-2 (SFRP-2) resulted in decreased LNCaP prostate epithelial cell proliferation in stromal conditioned media transfer experiments. In vivo tissue recombination studies using Tgfbr2 fspKO prostatic stromal cells in combination with wild-type or SV40 large T antigen expressing epithelia resulted in prostates that were refractile to androgen ablation. The expression of SFRP-2 restored the Tgfbr2 fspKO -associated prostate responsiveness to androgen ablation. These studies reveal a novel TGF-B, androgen, and Wnt paracrine signaling axis that enables prostatic regression of the distal ducts after androgen ablation while supporting proximal duct survival.

Prostate cancer is an androgen-dependent disease subject to interactions between the tumor epithelium and its microenvironment. Here, we found that epigenetic changes in prostatic cancer-associated fibroblasts (CAF) initiated a cascade of stromal-epithelial interactions. This facilitated lethal prostate cancer growth and development of resistance to androgen signaling deprivation therapy (ADT). We identified a Ras inhibitor, RASAL3, as epigenetically silenced in human prostatic CAF, leading to oncogenic Ras activity driving macropinocytosis-mediated glutamine synthesis. Interestingly, ADT further promoted RASAL3 epigenetic silencing and glutamine secretion by prostatic fibroblasts. In an orthotopic xenograft model, subsequent inhibition of macropinocytosis and glutamine transport resulted in antitumor effects. Stromal glutamine served as a source of energy through anaplerosis and as a mediator of neuroendocrine differentiation for prostate adenocarcinoma. Antagonizing the uptake of glutamine restored sensitivity to ADT in a castration-resistant xenograft model. In validating these findings, we found that prostate cancer patients on ADT with therapeutic resistance had elevated blood glutamine levels compared with those with therapeutically responsive disease (odds ratio = 7.451, P = 0.02). Identification of epigenetic regulation of Ras activity in prostatic CAF revealed RASAL3 as a sensor for metabolic and neuroendocrine reprogramming in prostate cancer patients failing ADT.