Michigan Center for Translational Pathology, University of Michigan, Ann Arbor, MI 48109, USA; Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA; Rogel Cancer Center, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Departments of Internal Medicine, Pharmacology, and Medicinal Chemistry, University of Michigan, Ann Arbor, MI 48109, USA.
Neoplasia. 2020 Feb;22(2):111-119. doi: 10.1016/j.neo.2019.12.003. Epub 2020 Jan 10.
Androgen receptor (AR) antagonists, such as enzalutamide, have had a major impact on the treatment of metastatic castration-resistant prostate cancer (CRPC). However, even with the advent of AR antagonist therapies, patients continue to develop resistance, and new strategies to combat continued AR signalling are needed. Here, we develop AR degraders using PROteolysis TArgeting Chimeric (PROTAC) technology in order to determine whether depletion of AR protein can overcome mechanisms of resistance commonly associated with current AR-targeting therapies. ARD-61 is the most potent of the AR degraders and effectively induces on-target AR degradation with a mechanism consistent with the PROTAC design. Compared to clinically-approved AR antagonists, administration of ARD-61 in vitro and in vivo results in more potent anti-proliferative, pro-apoptotic effects and attenuation of downstream AR target gene expression in prostate cancer cells. Importantly, we demonstrate that ARD-61 functions in enzalutamide-resistant model systems, characterized by diverse proposed mechanisms of resistance that include AR amplification/overexpression, AR mutation, and expression of AR splice variants, such as AR-V7. While AR degraders are unable to bind and degrade AR-V7, they continue to inhibit tumor cell growth in models overexpressing AR-V7. To further explore this, we developed several isogenic prostate cell line models in which AR-V7 is highly expressed, which also failed to influence the cell inhibitory effects of AR degraders, suggesting that AR-V7 is not a functional resistance mechanism for AR antagonism. These data provide compelling evidence that full-length AR remains a prominent oncogenic driver of prostate cancers which have developed resistance to AR antagonists and highlight the clinical potential of AR degraders for treatment of CRPC.
雄激素受体(AR)拮抗剂,如恩扎鲁胺,对转移性去势抵抗性前列腺癌(CRPC)的治疗产生了重大影响。然而,即使出现了 AR 拮抗剂治疗,患者仍会产生耐药性,需要新的策略来对抗持续的 AR 信号。在这里,我们使用 PROteolysis TArgeting Chimeric(PROTAC)技术开发 AR 降解剂,以确定 AR 蛋白的耗竭是否可以克服与当前 AR 靶向治疗相关的常见耐药机制。ARD-61 是最有效的 AR 降解剂之一,能够有效地诱导 AR 蛋白的靶标降解,其机制与 PROTAC 的设计一致。与临床批准的 AR 拮抗剂相比,ARD-61 在体外和体内给药可导致更有效的抗增殖、促凋亡作用,并减弱前列腺癌细胞中 AR 下游靶基因的表达。重要的是,我们证明 ARD-61 在恩扎鲁胺耐药模型系统中发挥作用,这些模型系统具有多种不同的耐药机制,包括 AR 扩增/过表达、AR 突变和 AR 剪接变体(如 AR-V7)的表达。虽然 AR 降解剂无法结合和降解 AR-V7,但它们在过表达 AR-V7 的模型中仍能抑制肿瘤细胞生长。为了进一步探索这一点,我们开发了几种同源前列腺细胞系模型,其中 AR-V7 高表达,这也不会影响 AR 降解剂的细胞抑制作用,这表明 AR-V7 不是 AR 拮抗作用的功能性耐药机制。这些数据提供了令人信服的证据,证明全长 AR 仍然是对 AR 拮抗剂产生耐药性的前列腺癌的主要致癌驱动因素,并强调了 AR 降解剂治疗 CRPC 的临床潜力。
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