Androgens, through their actions on the androgen receptor (AR), are required for the development of the prostate and contribute to the pathologic growth dysregulation observed in prostate cancers. Consequently, androgen ablation has become an essential component of the pharmacotherapy of prostate cancer. In this study, we explored the utility of targeting processes downstream of AR as an alternate approach for therapy. Specifically, we show that the serum and glucocorticoid-regulated kinase 1 (SGK1) gene is an androgenregulated target gene in cellular models of prostate cancer. Furthermore, functional serum-and glucocorticoid-regulated kinase 1 (SGK1) protein, as determined by the phosphorylation of its target Nedd4-2, was also increased with androgen treatment. Importantly, we determined that RNA interference-mediated knockdown of SGK1 expression attenuates the androgen-mediated growth of the prostate cancer cell line LNCaP. Given these findings, we explored the utility of SGK1 as a therapeutic target in prostate cancer by developing and evaluating a small-molecule inhibitor of this enzyme. From these studies emerged GSK650394, a competitive inhibitor that quantitatively blocks the effect of androgens on LNCaP cell growth. Thus, in addition to androgen ablation, inhibition of pathways downstream of AR is likely to have therapeutic utility in prostate cancer. [Cancer Res 2008;68(18):7475-83]

One subclass of antiestrogens, the selective estrogen receptor down-regulators (SERDs), have received considerable attention of late as they competitively inhibit estrogen binding and induce a rapid, proteasome-dependent degradation of the receptor. Contained within this class of molecules is the steroidal antiestrogen ICI182,780 (faslodex), recently approved for the treatment of metastatic cancer, and GW5638/DPC974, a SERD that is currently being evaluated in the clinic. Given that mechanistic differences between different selective estrogen receptor modulators have been translated into important clinical profiles, it was of interest to determine if the SERD subclass of ligands were likewise functionally or mechanistically distinguishable. In this study, we show that although the steroidal and nonsteroidal SERDs target ERA for degradation, the underlying mechanism(s) are different. Of note was the identification of a specific protein-protein interaction surface presented on ERA in the presence of the ICI182,780-activated receptor which is required for degradation. Interestingly, this surface is also presented on ERA in the presence of RU58,668, a SERD that is chemically distinct from ICI182,780. This surface is not required for GW5638-mediated degradation, and thus, this SERD seems to affect ERA downregulation by a different mechanism. These data suggest that sequencing of therapies using drugs of this class is likely to be possible. Finally, because of the unmet need for orally active SERDS that function similarly to ICI182,780, we have used the insights from these mechanistic studies to develop and validate a high-throughput screen for compounds of this class with improved pharmaceutical properties. [Cancer Res 2007;67(19):9549-60]

Advanced prostate cancers preferentially metastasize to bone, suggesting that this tissue produces factors that provide a suitable microenvironment for prostate cancer cells. Recently, it has become clear that even in antiandrogen-resistant cancers, the androgen receptor (AR)-signaling axis is required for prostate cancer progression. Therefore, we hypothesized that AR may be involved in the regulation of pathways that are responsible for the homing of prostate cancer cells to select microenvironments. In support of this hypothesis, we have determined that chemokine (C-X-C motif) receptor 4 (CXCR4), the receptor for the chemokine CXCL12, is up-regulated in prostate cancer cells in response to androgens. Given that the levels of CXCL12 are elevated at sites of known prostate cancer metastases such as bone, these results suggest that androgens may influence prostate cancer metastasis. Specifically, we demonstrate that androgens increase the levels of both CXCR4 mRNA and functional protein in LNCaP prostate cancer cells. Importantly, androgens enhanced the migration of LNCaP cells toward a CXCL12 gradient, an effect that could be blocked by the specific CXCR4 antagonist AMD3100. Interestingly, CXCR4 is not directly regulated by androgens but rather is positively up-regulated by Krüppel-like factor 5 (KLF5), a transcription factor that we have shown to be an early, direct target of AR. Further, KLF5 is both required and sufficient for androgen-mediated CXCR4 expression and migration toward CXCL12. Taken together, these findings demonstrate that AR can utilize the CXCL12/CXCR4 axis through induction of KLF5 expression to promote prostate cancer progression and highlight the potential utility of CXCR4 antagonists as prostate cancer therapeutics.