Inhibition of enhancer of zeste homolog 2 (EZH2) overcomes enzalutamide resistance in castration-resistant prostate cancer.

Enzalutamide, approved by the United States Food and Drug Administration in 2018 for the management of metastatic castration-resistant prostate cancer (CRPC), is an androgen receptor (AR) inhibitor. It blocks androgen binding to the AR, AR nuclear translocation, and AR-mediated DNA binding. Unfortunately, a considerable proportion of tumors eventually develop resistance during the treatment. The molecular mechanisms underlying enzalutamide resistance are not completely understood. Enhancer of zeste homolog 2 (EZH2), the catalytic subunit of polycomb repressor complex 2, has been proposed as a prognostic marker for prostate cancer (PCa). With the goal to test whether EZH2 also plays a critical role in acquisition of enzalutamide resistance in CRPC, here we examined whether EZH2 inhibition/depletion enhances the efficacy of enzalutamide in enzalutamide-resistant PCa cells. We show that combining the EZH2 inhibitor GSK126 with enzalutamide synergistically inhibits cell proliferation and colony formation and promotes apoptosis in enzalutamide-resistant PCa cells. EZH2 depletion also overcomes enzalutamide resistance in both cultured cells and xenograft tumors. Mechanistically, we found that EZH2 directly binds to the promoter of prostate-specific antigen and inhibits its expression in enzalutamide-resistant PCa cells. In agreement, bioinformatics analysis of clinical RNA sequencing data involving GSEA indicated a strong correlation between AR and EZH2 gene expression during PCa progression. Our study provides critical insights into the mechanisms underlying enzalutamide resistance, which may offer new approaches to enhance the efficacy of enzalutamide in CRPC.

Bai Y ，Zhang Z ，Cheng L ，Wang R ，Chen X ，Kong Y ，Feng F ，Ahmad N ，Li L ，Liu X ... -  《-》

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 ... -  《-》

Dual targeting of EZH2 and androgen receptor as a novel therapy for castration-resistant prostate cancer.

Castration-resistant prostate cancer (CRPC) emerges after androgen withdrawal therapy and remains incurable due to the lack of effective treatment protocols. Treatment with enzalutamide, a second generation androgen receptor (AR) antagonist, offers an initial response followed by drug resistance and tumor relapse. Enhancer of zeste homolog 2 (EZH2), a member of PRC2 complex, is an important target that acts as a coactivator of AR-mediated gene suppression whose oncogenic activity increases during castration. We hypothesize that dual targeting of EZH2 and AR could be highly effective in CRPC treatment. The present study aimed to examine the effectiveness of combination using EZH2 inhibitor GSK126 with antiandrogen enzalutamide in the treatment of CRPC cells. Treatment of 22Rv1 and C42B CRPC cells with a combination of GSK126 and enzalutamide led to synergistic inhibition of cell proliferation, cell cycle arrest and marked increase in cell death. Mechanistically, this combination treatment significantly reduced expression of AR and AR-v7, decrease in PSA and Akt activity, diminution of EZH2 and other members of PCR2 complex including SUZ12 and EED, with simultaneous loss of H3K27 trimethylation and dissociation between AR and PRC2 complex members compared to individual treatment. This study provides preclinical proof-of-concept that combined treatment of EZH2 inhibitor with AR antagonist results in synergistic anticancer effects opening new possibilities for treatment of CRPC tumors.

Shankar E ，Franco D ，Iqbal O ，Moreton S ，Kanwal R ，Gupta S ... -  《-》

Niclosamide inhibits androgen receptor variants expression and overcomes enzalutamide resistance in castration-resistant prostate cancer.

Enzalutamide, a second-generation antiandrogen, was recently approved for the treatment of castration-resistant prostate cancer (CRPC) in patients who no longer respond to docetaxel. Despite these advances that provide temporary respite, resistance to enzalutamide occurs frequently. Androgen receptor (AR) splice variants such as AR-V7 have recently been shown to drive castration-resistant growth and resistance to enzalutamide. This study was designed to identify inhibitors of AR variants and test its ability to overcome resistance to enzalutamide. The drug screening was conducted using luciferase activity assay to determine the activity of AR-V7 after treatment with the compounds in the Prestwick Chemical Library, which contains about 1,120 FDA-approved drugs. The effects of the identified inhibitors on AR-V7 activity and enzalutamide sensitivity were characterized in CRPC and enzalutamide-resistant prostate cancer cells in vitro and in vivo. Niclosamide, an FDA-approved antihelminthic drug, was identified as a potent AR-V7 inhibitor in prostate cancer cells. Niclosamide significantly downregulated AR-V7 protein expression by protein degradation through a proteasome-dependent pathway. Niclosamide also inhibited AR-V7 transcription activity and reduced the recruitment of AR-V7 to the PSA promoter. Niclosamide inhibited prostate cancer cell growth in vitro and tumor growth in vivo. Furthermore, the combination of niclosamide and enzalutamide resulted in significant inhibition of enzalutamide-resistant tumor growth, suggesting that niclosamide enhances enzalutamide therapy and overcomes enzalutamide resistance in CRPC cells. Niclosamide was identified as a novel inhibitor of AR variants. Our findings offer preclinical validation of niclosamide as a promising inhibitor of AR variants to treat, either alone or in combination with current antiandrogen therapies, patients with advanced prostate cancer, especially those resistant to enzalutamide.

Liu C ，Lou W ，Zhu Y ，Nadiminty N ，Schwartz CT ，Evans CP ，Gao AC ... -  《-》

Natural killer cells suppress enzalutamide resistance and cell invasion in the castration resistant prostate cancer via targeting the androgen receptor splicing variant 7 (ARv7).

Despite the success of androgen-deprivation therapy (ADT) with the newly developed anti-androgen enzalutamide (Enz, also known as MDV3100) to suppress castration resistant prostate cancer (CRPC) in extending patient survival by an extra 4.8 months, eventually patients die with the development of Enz resistance that may involve the induction of the androgen receptor (AR) splicing variant ARv7. Here we identify an unrecognized role of Natural Killer (NK) cells in the prostate tumor microenvironment that can be better recruited to the CRPC cells to suppress ARv7 expression resulting in suppressing the Enz resistant CRPC cell growth and invasion. Mechanism dissection revealed that CRPC cells, compared to normal prostate epithelial cells, could recruit more NK cells that might then lead to alterations of the microRNA-34 and microRNA-449 to suppress both ARv7 expression and ARv7-induced EZH2 expression to suppress CRPC cell invasion. Together, these results identify a new potential therapy using recruited NK cells to better suppress the Enz resistance and cell invasion in CRPC at the later enzalutamide resistant stage.

Lin SJ ，Chou FJ ，Li L ，Lin CY ，Yeh S ，Chang C ... -  《-》