Drug Development of Skp2 PROTACs in Cancer

摘要 Skp2是一种F-box蛋白，构成SCF泛素E3连接酶复合体的四个亚基之一，调节 通过靶向泛素化和降解其底物，如细胞周期抑制物，实现细胞周期进展 第27页。Skp2 E3连接酶在癌症中有广泛的意义，特别是在雄激素非依赖性的人类转移中。 前列腺癌。我们发现Skp2在转移性前列腺癌组织中表达上调。 和抗去势前列腺癌(CRPC)，并与Myc表达相关。我们进一步展示了 Skp2是Akt的一种新的E3连接酶，它触发非蛋白水解性K63连接的Akt泛素化，促进 生长因子介导的Akt膜募集和激活。所有这些都表明，Skp2同时 调节Akt信号和p27降解，以及twist介导的EMT促进CRPC进展和 对雄激素剥夺疗法(ABT)的抵抗。尽管Skp2 SCF复合体E3连接酶是高度有效的 针对癌症的药物靶点，由于缺乏有效的蛋白质-蛋白质相互作用抑制剂，Skp2 SCF复合体 E3连接酶仍被认为是不可用药。蛋白水解靶向嵌合体(PROTAC)方法可以 由于其催化降解，提高了非药物抑制剂的效力。在这项提案中，我们发现 一种有效的Skp2 PRO-1，在体外治疗窗口比小分子抑制剂提高100倍以上。 Skp2-Pro-1能在100 nM的浓度下完全降解癌细胞中的Skp2，并证明 在具有挑战性和晚期的CRPC肿瘤中，Skp2的体内完全降解和强大的抗肿瘤疗效 模型包括具有完整免疫力的遗传CRPC小鼠模型。为了获得两名临床候选人，我们 将评估基于Cereblon的PROTAC Skp2-PRO-1的PK性能，并改进其PK和药物 作为第一临床候选对象的财产。我们将进一步开发基于VHL/或MDM2的Skp2 PROTAC作为 后备候选人。最后，我们将在先进的CRPC活体模型中验证临床候选对象 不同的异种移植模式、癌症有机物、患者来源的异种移植(PDX)和遗传小鼠模型。这个 由此产生的临床候选人将进入IND使能研究，以进行第一阶段临床试验 癌症的治疗。

Abstract Skp2, an F-box protein that constitutes one of the four subunits of the SCF ubiquitin E3 ligase complex, regulates cell-cycle progression by targeting ubiquitination and degradation of its substrates, such as the cell-cycle inhibitor p27. Skp2 E3 ligase has a broad implication in cancer, especially for androgen-independent human metastatic prostate cancer. We showed that Skp2 expression was upregulated in metastatic prostate cancer specimens and castration-resistant prostate cancer (CRPC) and correlated with Myc expression. We further demonstrated that Skp2 is a novel E3 ligase for Akt that triggers nonproteolytic K63-linked ubiquitination of Akt, facilitating growth factor-mediated Akt membrane recruitment and activation. All together suggest that Skp2 simultaneously regulates Akt signaling and p27 degradation, and TWIST-mediated EMT to promote CRPC progression and resistance to androgen deprivation therapy (ABT). Although Skp2 SCF complex E3 ligase is a highly validated drug target for cancer, due to the lack of an effective protein-protein interaction inhibitors, Skp2 SCF complex E3 ligase is still considered as non-drugable. The proteolysis targeting chimera (PROTAC) approach could increase potency of non-drugable inhibitors due to its catalytic degradation. In this proposal, we have discovered a potent Skp2 PRO-1 by improving therapeutic window more than 100 fold in vitro over small molecule inhibitors. Skp2-PRO-1 can completely degrade Skp2 with 100 nM concentration in cancer cells and demonstrate the complete in vivo Skp2 degradation and robust antitumor efficacy in challenging and advanced CRPC tumor models including the genetic CRPC mouse model with intact immunity. To obtain two clinical candidates, we will evaluate the PK properties of Skp2-PRO-1, a Cereblon based PROTAC and improve its PK and drug properties as the first clincial candidate. We will further develop a VHL/or MDM2 based Skp2 PROTAC as the back-up candidate. Finally we will validate the clinical candidates in advanced CRPC in vivo models using diverse xenograft modes, cancer organoids, patient-derived xenografts (PDXs) and genetic mouse models. The resulted clinical candidates will be advanced into the IND enabling studies for the phase I clinical trials for the treatment of cancer.