Targeting the MIF/CXCR7/AKT Signaling Pathway in Castration-Resistant Prostate Cancer.

Although androgen deprivation therapy (ADT) is an effective treatment for metastatic prostate cancer, incurable castration-resistant prostate cancer (CRPC) inevitably develops. Importantly, androgen receptor (AR) continues to be critical for prostate cancer growth and progression after ADT. One of the underlying molecular mechanisms is derepression of AR-repressed genes involved in cell cycle and proliferation after ADT. Here, the data demonstrate that C-X-C chemokine receptor type 7 (CXCR7), a seven-transmembrane G-protein-coupled chemokine receptor, is an AR-repressed gene and is upregulated after ADT. AR directly regulates CXCR7 using clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) gene editing. Macrophage migration inhibitory factor (MIF) was identified as a ligand for CXCR7, which induces expression of cell-cycle genes through activating AKT signaling pathway. Previous studies have been focused on chemokine CXCL12 and its receptor CXCR4 in mediating metastasis of various cancer types, including prostate cancer. The critical roles of CXCL12/CXCR4 axis in the interaction between cancer cells and their microenvironment render it a promising therapeutic target in cancer treatment. The data suggest that the MIF/CXCR7/AKT pathway drives CRPC growth and metastasis independent of the CXCL12/CXCR4 axis. Furthermore, CXCR7 blockade in combination with anti-androgen enzalutamide inhibits CRPC tumor growth and potentially prevents metastasis. Notably, both MIF and CXCR7 are overexpressed in CRPC patient specimens and therefore are attractive therapeutic targets for these patients. IMPLICATIONS: This work suggests that CXCR7 plays more important roles than CXCR4 in CRPC progression; thus, targeting CXCR7 in combination with anti-androgen is a promising therapeutic approach for metastatic CRPC.

Rafiei S ，Gui B ，Wu J ，Liu XS ，Kibel AS ，Jia L ... -  《-》

Activation of MAPK Signaling by CXCR7 Leads to Enzalutamide Resistance in Prostate Cancer.

Castration-resistant prostate cancer (CRPC) that has developed resistance to the new-generation androgen receptor (AR) antagonist enzalutamide is a lethal disease. Transcriptome analysis of multiple prostate cancer models identified CXCR7, an atypical chemokine receptor, as one of the most upregulated genes in enzalutamide-resistant cells. AR directly repressed CXCR7 by binding to an enhancer 110 kb downstream of the gene and expression was restored upon androgen deprivation. We demonstrate that CXCR7 is a critical regulator of prostate cancer sensitivity to enzalutamide and is required for CRPC growth in vitro and in vivo. Elevated CXCR7 activated MAPK/ERK signaling through ligand-independent, but β-arrestin 2-dependent mechanisms. Examination of patient specimens showed that CXCR7 and pERK levels increased significantly from localized prostate cancer to CRPC and further upon enzalutamide resistance. Preclinical studies revealed remarkable efficacies of MAPK/ERK inhibitors in suppressing enzalutamide-resistant prostate cancer. Overall, these results indicate that CXCR7 may serve as a biomarker of resistant disease in patients with prostate cancer and that disruption of CXCR7 signaling may be an effective strategy to overcome resistance. SIGNIFICANCE: These findings identify CXCR7-mediated MAPK activation as a mechanism of resistance to second-generation antiandrogen therapy, highlighting the therapeutic potential of MAPK/ERK inhibitors in CRPC.

Li S ，Fong KW ，Gritsina G ，Zhang A ，Zhao JC ，Kim J ，Sharp A ，Yuan W ，Aversa C ，Yang XJ ，Nelson PS ，Feng FY ，Chinnaiyan AM ，de Bono JS ，Morrissey C ，Rettig MB ，Yu J ... -  《-》

Combination of carmustine and selenite effectively inhibits tumor growth by targeting androgen receptor, androgen receptor-variants, and Akt in preclinical models: New hope for patients with castration resistant prostate cancer.

Despite established androgen receptor (AR) antagonists, AR/AR-variants signaling remain a major obstacle for the successful treatment of castration resistant prostate cancer (CRPC). In addition, CRPC cells adapt to survive via AR-independent pathways to escape next generation therapies. Therefore, there is an urgent need for drugs that can target these signaling pathways in CRPC. In this study, we sought to determine whether carmustine and selenite in combination could induce apoptosis and inhibit growth of CRPC in-vitro and in-vivo. CRPC (22Rv1, VCaP, and PC-3) cell lines in culture and xenograft mouse were used. Combination of carmustine and selenite treatment significantly increased reactive oxygen species, apoptosis and growth inhibition in CRPC cells with down regulation of anti-apoptotic (Bcl-2 and Mcl-1) and proliferative proteins (c-Myc and cyclin-D1). This effect was associated with complete reduction of AR/AR-variants, AR-V7, PSA and significant induction of p27Kip1. Combination treatment substantially abolished phospho-Akt, phospho-GSK-3β, and anchorage-independent growth in AR-positive and AR-negative cells. Consistent with in-vitro results, combination treatment effectively induced apoptosis and completely inhibited xenograft tumor growth and markedly reduced AR/AR-variants, AR-V7, PSA, and Bcl-2 in xenograft tumors without causing genotoxicity in host mice. Individual agent treatment showed only partial effect. The combination treatment showed a significant synergistic effect. The present study is the first to demonstrate that the combination of carmustine and selenite treatment completely suppressed CRPC tumor growth by reducing AR/AR-variants and Akt signaling. Our findings suggest that the combination of carmustine and selenite could constitute a promising next-generation therapy for successful treatment of patients with CRPC.

Thamilselvan V ，Menon M ，Thamilselvan S 《-》

Cotargeting Androgen Receptor Splice Variants and mTOR Signaling Pathway for the Treatment of Castration-Resistant Prostate Cancer.

The PI3K/Akt/mTOR pathway is activated in most castration-resistant prostate cancers (CRPC). Transcriptionally active androgen receptor (AR) plays a role in the majority of CRPCs. Therefore, cotargeting full-length (FL) AR and PI3K/Akt/mTOR signaling has been proposed as a possible, more effective therapeutic approach for CRPC. However, truncated AR-splice variants (AR-V) that are constitutively active and dominant over FL-AR are associated with tumor progression and resistance mechanisms in CRPC. It is currently unknown how blocking the PI3K/Akt/mTOR pathway impacts prostate cancer driven by AR-Vs. Here, we evaluated the efficacy and mechanism of combination therapy to block mTOR activity together with EPI-002, an AR N-terminal domain (NTD) antagonist that blocks the transcriptional activities of FL-AR and AR-Vs in models of CRPC. To determine the functional roles of FL-AR, AR-Vs, and PI3K/Akt/mTOR pathways, we employed EPI-002 or enzalutamide and BEZ235 (low dose) or everolimus in human prostate cancer cells that express FL-AR or FL-AR and AR-Vs (LNCaP95). Gene expression and efficacy were examined in vitro and in vivo EPI-002 had antitumor activity in enzalutamide-resistant LNCaP95 cells that was associated with decreased expression of AR-V target genes (e.g., UBE2C). Inhibition of mTOR provided additional blockade of UBE2C expression. A combination of EPI-002 and BEZ235 decreased the growth of LNCaP95 cells in vitro and in vivo Cotargeting mTOR and AR-NTD to block transcriptional activities of FL-AR and AR-Vs provided maximum antitumor efficacy in PTEN-null, enzalutamide-resistant CRPC. Clin Cancer Res; 22(11); 2744-54. ©2015 AACR.

Kato M ，Banuelos CA ，Imamura Y ，Leung JK ，Caley DP ，Wang J ，Mawji NR ，Sadar MD ... -  《-》

Inhibition of noncanonical Wnt pathway overcomes enzalutamide resistance in castration-resistant prostate cancer.

Because androgen receptor (AR) signaling is essential for prostate cancer (PCa) initiation and progression, castration is the main approach for treatment. Unfortunately, patients tend to enter a stage called castration-resistant prostate cancer (CRPC) despite the initial response to castration. For various reasons, AR signaling is reactivated in CRPC. As such, AR signaling inhibitors, such as enzalutamide, has been approved by the Food and Drug Administration to treat CRPC in the clinic. However, the limited success of these new drugs suggests an immediate unmet need to understand the underlying mechanisms for resistance so novel targets can be identified to enhance their efficacy. An unbiased bioinformatics analysis was performed with the existing human patient dataset and RNA-seq results of in-house PCa cell lines to identify new targets to overcome enzalutamide resistance. Cell viability and growth were detected by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and colony formation assay. Cell invasion and migration were detected by transwell assay. Protein levels were detected by Western blot or immunofluorescence. We found that the noncanonical Wnt signaling was activated in enzalutamide-resistant PCa cells and that the activation of noncanonical Wnt signaling was correlated with AR expression and disease progression. This was validated by the elevated expression of noncanonical Wnt pathway members such as Wnt5a, RhoA, and ROCK in enzalutamide-resistant PCa cells in comparison to their enzalutamide-sensitive counterparts. And, both Y27632, an inhibitor of ROCK, and depletion of ROCK enhanced the efficacy of enzalutamide in enzalutamide-resistant PCa cells. Of significance, a combination of Y27632 and enzalutamide inhibited 22RV1-derived xenograft tumor growth synergistically. Finally, ROCK depletion plus enzalutamide treatment inhibited invasion and migration of enzalutamide-resistant PCa cells via inhibition of epithelial-mesenchymal transition. The noncanonical Wnt pathway is activated in enzalutamide-resistant PCa and inhibition of noncanonical Wnt pathway overcomes enzalutamide resistance and enhances its efficacy in CRPC.

Chen X ，Liu J ，Cheng L ，Li C ，Zhang Z ，Bai Y ，Wang R ，Han T ，Huang C ，Kong Y ，Feng F ，Liu X ... -  《-》