Prostate cancer is the most commonly diagnosed cancer and increasing with the expanding aging Veteran population. Transforming growth factor-beta (TGF-ss) plays a central role in prostate cancer, initiation and progression to castrate resistance. We specifically demonstrated through transgenic mouse models that the conditional knockout of the TGF-ss receptor type II (Tgfbr2) in prostate epithelia has little effect on tumorigenesis or castrate responsiveness. In contrast, the stromal fibroblastic Tgfbr2 knockout resulted in the development of adenocarcinoma and castrate-resistant growth. Strikingly, castrate resistance in these models was not dependent on cancer progression. We found that even tissue recombinants of Tgfbr2-KO prostate stromal cells with androgen dependent wild type prostate epithelia became castrate resistant. Thus, the castrate resistance and tumorigenesis are biochemically separable events. Our preliminary data indicate that the co-evolution of the human prostate stroma and metastatic tumor-associated bone microenvironment involves epigenetic changes associated with emergence of heterogeneity in TGF-ss receptor type II expression. We will test the central hypothesis that, TGF-ss signaling plays an important role in stromal-epithelial interactions responsible for castrate resistant prostate cancer (CRPC). We found that the loss of TGF-ss responsiveness in prostate fibroblastic cells results in elevated epigenetic silencing of Wnt ligand antagonists and CXCL12. However, there was cooperative induction of CXCL12 expression by TGF-ss signaling competent stromal cells when they were co-cultured with those having a knockout of Tgfbr2. The interaction of the heterotypic stromal fibroblastic cells in affecting the epithelial castrate responsiveness is the focus of Aim 1. It is still poorly understood how in prostate cancer androgen receptor function is abnormally switched from a pro- differentiation role in development and normal adult prostate homeostasis, to one pro-proliferation in cancer. Since prostate epithelial androgen responsiveness is mediated through prostate stromal androgen signaling, the role of stromal epigenetic signaling will be the focus of Aim 2. The knockout of Tgfbr2 up regulates Stat3 signaling. The role of Stat3 in prostate stromal androgen signaling will be determined in terms of its role on androgen receptor activity and paracrine role on the associated epithelia. CRPC can develop in the prostates of patients with local metastasis. However, for the many patients that develop distant metastasis, the role of the prostate microenvironment on castrate resistance is less relevant. Instead, the osteoblasts and bone marrow fibroblastic cells are primary cellular components that interact with the metastasized prostate cancer. The actions of TGF-ss on osteoblasts and bone marrow fibroblastic cells, that make up the metastatic prostate cancer microenvironment, is the focus of Aim 3. We are uniquely positioned to address the role of cancer associated stromal changes that occur in castrate resistant growth. Based on TGF-ss's role in tumor suppressor silencing and defining stromal heterogeneity, we will use novel cell culture, tissue recombination xenografting, and transgenic mouse models to address the primary cause for death due to prostate cancer. !
NARATIVE Prostate cancer is the second leading cause of cancer-related death in men. The male Veteran population, often associated with elevated tobacco use, has a greater rate of mortality of the disease than the general population. Further, exposure to herbicides like Agent Orange by Vietnam Veterans is a proven risk factor for prostate cancer. Mortality from prostate caner results from those cancers that become resistant to therapeutics that generally block androgen signaling. Stromal-epithelial interactions can mediate prostate cancer initiation and resistance to androgen deprivation therapy. Mechanisms of how the prostate microenvironment and that of the primary metastatic site, bone, can regulate hormone therapy response are addressed in this proposal. The approaches include how the epigenetic changes regulate heterotypic cooperation in tumor-associated stromal cells. It is encouraging that such epigenetic changes are reversible and mechanisms tractable. These studies will direct future therapeutics targeting the stromal compartment in human prostate cancer.
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