SUMMARY Castration-resistant prostate cancer (CRPC) requires tumors to engage metabolic mechanisms that allow sustained testosterone and/or dihydrotestosterone to stimulate progression. 17β-Hydroxyste-roid dehydrogenase type 4 (17βHSD4), encoded by HSD17B4, is thought to inactivate testosterone and dihydrotestosterone by converting them to their respective inert 17-keto steroids. Counterintuitively, HSD17B4 expression increases in CRPC and predicts poor prognosis. Here, we show that, of five alternative splice forms, only isoform 2 encodes an enzyme capable of testosterone and dihydrotestosterone inactivation. In contrast with other transcripts, functional expression of isoform 2 is specifically suppressed in development of CRPC in patients. Genetically silencing isoform 2 shifts the metabolic balance toward 17β-OH androgens (testosterone and dihydrotestosterone), stimulating androgen receptor (AR) and CRPC development. Our studies specifically implicate HSD17B4 isoform 2 loss in lethal prostate cancer.

Prostate cancer cells move from their primary site of origin, interact with a distant microenvironment, grow, and thereby cause death. It had heretofore not been possible to selectively inhibit cancer cell motility. Our group has recently shown that inhibition of intracellular activation of Raf1 with the smallmolecule therapeutic KBU2046 permits, for the first time, selective inhibition of cell motility. We hypothesized that simultaneous disruption of multiple distinct functions that drive progression of prostate cancer to induce death would result in advanced disease control. Using a murine orthotopic implantation model of human prostate cancer metastasis, we demonstrate that combined treatment with KBU2046 and docetaxel retains docetaxel's antitumor action, but provides improved inhibition of metastasis, compared with monotherapy. KBU2046 does not interfere with hormone therapy, inclusive of enzalutamide-mediated inhibition of androgen receptor (AR) function and cell growth inhibition, and inclusive of the ability of castration to inhibit LNCaP-AR cell outgrowth in mice. Cell movement is necessary for osteoclast-mediated bone degradation. KBU2046 inhibits Raf1 and its downstream activation of MEK1/2 and ERK1/2 in osteoclasts, inhibiting cytoskeleton rearrangement, resorptive cavity formation, and bone destruction in vitro, with improved effects observed when the bone microenvironment is chemically modified by pretreatment with zoledronic acid. Using a murine cardiac injection model of human prostate cancer bone destruction quantified by CT, KBU2046 plus zoledronic exhibit improved inhibitory efficacy, compared with monotherapy. The combined disruption of pathways that drive cell movement, interaction with bone, and growth constitutes a multifunctional targeting strategy that provides advanced disease control.

AKAP12/SSeCKS/Gravin (AKAP12) is thought to act as a metastasis suppressor through its direct scaffolding of major signaling proteins such as PKC, PKA and Src, in a spatiotemporal manner (1). For example, AKAP12 inhibition of Src-mediated oncogenic signaling, including induction of VEGF secretion by tumor cells, correlates with inhibition of neovascularization at metastatic sites (2). We have established AKAP12-null (KO) mice and demonstrated that they are cancer-prone in regards to the formation of spontaneous prostatic dysplasia and to carcinogen-induced skin cancer formation (3, 4). However, the role of AKAP12 in host microenvironment in regards to tumor or metastasis control has yet to be elucidated. In this study, we utilized an orthotropic, subcutaneous injection model of B16F10 melanoma to address whether the loss of AKAP12 in the host facilitates metastasis. Although the size of the primary tumors was similar in WT vs. KO mice, KO mice exhibited increased rates of peritoneal metastasis. The peritoneal fluid (PF) of KO mice was more potent than WT-PF in inducing in vitro chemotaxis. Comparison of the cytokines/chemokines using antibody arrays showed a severe upregulation of multiple potential chemoattractants in the KO-PF, including CXCL9/10/11, known ligands for CXCR3, a chemokine receptor upregulated 12-fold in B16F10 versus the low-metastatic B16F0 variant. Pre-injection of KO-PF, but not WT-PF, into WT mice was sufficient to induce high levels of peritoneal metastasis from subcutaneous sites. Taken together, our study suggests that AKAP12 controls metastasis by regulating the production of chemoattractants in the peritoneum, produced either by local microenvironmental cells or by recruited inflammatory cells. References: (1) Gelman, I. H. (2002) Front Biosci 7, 1782-1797. (2) Su, B., Zheng, Q., Vaughan, M.M., Bu, Y., and Gelman, I.H. (2006) Cancer Res. 66, 5599-5607 (3) Akakura, S., Huang, C., Nelson, P. J., Foster, B., and Gelman, I. H. (2008) Cancer Res. 68, 5096-5103. (4) Akakura, S., Bouchard, R., Bshara, W., Morrison, C., and Gelman, I. H. (2011) Int. J. Can. 129, 2025-2031. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3429. doi:1538-7445.AM2012-3429