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The FDA-approved anti-androgen Enzalutamide (Enz) has been used successfully as the last line therapy to extend castration-resistant prostate cancer (CRPC) patients' survival by an extra 4.8 months. However, CRPC patients eventually develop Enz-resistance that may involve the induction of the androgen receptor (AR) splicing variant ARv7. Here we found that Cisplatin (Cis) or Carboplatin, currently used in chemotherapy/radiation therapy to suppress tumor progression, could restore the Enz sensitivity in multiple Enz-resistant (EnzR) CRPC cells via directly degrading/suppressing the ARv7. Combining Cis or Carboplatin with Enz therapy can also delay the development of Enz-resistance in CRPC C4-2 cells. Mechanism dissection found that Cis or Carboplatin might decrease the ARv7 expression via multiple mechanisms including targeting the lncRNA-Malat1/SF2 RNA splicing complex and increasing ARv7 degradation via altering ubiquitination. Preclinical studies using in vivo mouse model with implanted EnzR1-C4-2 cells also demonstrated that Cis plus Enz therapy resulted in better suppression of EnzR CRPC progression than Enz treatment alone. These results not only unveil the previously unrecognized Cis mechanism to degrade ARv7 via targeting the Malat1/SF2 complex and ubiquitination signals, it may also provide a novel and ready therapy to further suppress the EnzR CRPC progression in the near future.

Background: While androgen-deprivation-therapy with the recently developed antiandrogen enzalutamide (Enz) shows promising therapeutic benefits in men with metastatic castration-resistant prostate cancer (PCa), many patients develop resistance to Enz, which may involve the induction of the androgen receptor (AR) splicing variant 7 (AR-v7)., Objective: Our aim is to identify the mechanisms responsible for AR-v7 production and to develop novel preclinical approaches to suppress the Enz-resistant (EnzR) PCa., Design, Setting, and Participants: We established EnzR-PCa cell lines and examined the long noncoding RNA Malat1 (Malat1) function in conferring Enz resistance. We also examined the in vivo effects of Malat1 short interfering RNA and the AR-v7 degradation enhancer, ASC-J9 ® ., Outcome Measurements and Statistical Analysis: Enz resistance and expression of Malat1 and AR-v7. All statistical comparisons were analyzed with a t-test or one way analysis of variance followed by t-test., Results and Limitations: We demonstrated that Malat1 is indispensable for Enz-induced AR-v7 production in VCaP and EnzR-C4-2 cells. We observed increased AR-v7 and Malat1 expression in our established EnzR-PCa cell lines and in some PCa patients who received Enz treatment. Targeting the Malat1/AR-v7 axis resulted in altering the PCa resistance to androgen deprivation therapy with Enz. The limitation of this study includes the small sample size from the same human patients before and after receiving Enz treatment., Conclusions: Targeting the Malat1/AR-v7 axis via Malat1-short interfering RNA or AR-v7 degradation enhancer ASC-J9 ® in EnzR-PCa cell lines and mouse models suppressed EnzR-PCa progression., Patient Summary: Androgen deprivation therapy-enzalutamide treatment may not be the best choice for prostate cancer patients who have higher expression of the Malat1/androgen receptor splicing variant 7 axis, and new therapies using Malat1-short interfering RNA or ASC-J9 ® may be developed in the future to better suppress enzalutamide-resistant prostate cancer., (Copyright © 2017 European Association of Urology. Published by Elsevier B.V. All rights reserved.)

Androgen deprivation therapy (ADT) with the newly developed powerful anti-androgen enzalutamide (Enz, also known as MDV3100) has promising therapeutic effects to suppress castration resistant prostate cancer (CRPC) and extending patients' lives an extra 4.8 months. However, most Enz therapy eventually fails with the development of Enz resistance. The detailed mechanisms how CRPC develops Enz resistance remain unclear and may involve multiple mechanisms. Among them, the induction of the androgen receptor (AR) mutant AR-F876L in some CRPC patients may represent one driving force that confers Enz resistance. Here, we demonstrate that the AR degradation enhancer, ASC-J9(®), not only degrades wild-type AR, but also has the ability to target AR-F876L. The consequence of suppressing AR-F876L may then abrogate AR-F876L mediated CRPC cell proliferation and metastasis. Thus, developing ASC-J9(®) as a new therapeutic approach may represent a novel therapy to better suppress CRPC that has already developed Enz resistance., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)