Drugging the Undruggable Coactivators using Small Molecule Inhibitors

蛋白质-蛋白质相互作用（PPI）在大多数生物过程中起着核心作用，因此代表了 治疗发展的一类重要靶点。基于生物制品的治疗剂，如抗体， 在PPI监管方面取得了巨大成功。然而，抗体只能应用于细胞表面的蛋白质靶点 这是由于它们对质膜的不渗透性。虽然小分子药物可以很容易地穿过细胞膜， 应用小分子抑制剂（SMI）破坏PPI是一项具有挑战性的任务，因为大约750- 1，500 PPIs的界面处涉及蛋白质表面积的0.02，这对于SMI来说太大而无法覆盖。此外，本发明还提供了一种方法， 这些相互作用的蛋白质表面不具有口袋状小分子结合位点。这些PPI 研究中心被认为是SMI的“不可治疗”目标。药物开发的圣杯就是 生物制剂调节PPI的能力。我们最近开发了一种基于细胞的功能测定，用于高水平的 通量筛选（HTS），以确定类固醇受体共激活因子-3（SRC-3）的SMI，SRC-3是一个大的，大多数是非类固醇的。 核结构蛋白在没有任何SRC-3结构信息的情况下，我们确定并改进了一系列SMI 可以靶向SRC-3-第一代SMI棉酚、第二代SMI蟾蜍灵和第三代SMI蟾蜍灵， SMI SI-2是一种非常有前途的候选药物。在我们最近的报告（PNAS 2016）中，我们证明了SI-2可以 选择性地降低转录活性和SRC-3的蛋白质浓度在细胞中通过直接 与SRC-3的物理相互作用，并选择性诱导乳腺癌细胞死亡，IC 50值为低nM 范围（3-20 nM），同时不影响正常细胞活力。此外，体内研究表明，SI-2 可以显著抑制乳腺癌小鼠模型中的原发性肿瘤生长并降低SRC-3蛋白水平。 尽管SI-2具有令人鼓舞的抗肿瘤活性，但其血浆半衰期相对较短（1 h）。在 初步研究，我们已经确定SI-12具有与SI-2相似的生物活性，但大大改善了 血浆半衰期（6 h）。在目标1中，我们将进一步优化SI-2 SRC-3 SMI“独特的”衍生物，其具有改进的药物活性。 比如财产在目标2和3中，我们将利用新型SRC-3 SMI解决两个主要问题， 当前乳腺癌治疗的挑战--雌激素受体阳性患者对内分泌治疗的抵抗 (ER+）乳腺癌和三阴性乳腺癌（TNBC）中的肿瘤转移。成功完成 该项目不仅将通过开发“一流”的治疗方案， 一种靶向致癌共激活因子的药物，但也鼓励其他研究人员开发靶向 蛋白质-蛋白质相互作用，被指定为“重要但不可治疗”的目标。

Protein–protein interactions (PPIs) play a central role in most biological processes, and therefore represent an important class of targets for therapeutic development. Biologics based therapeutics, such as antibodies, exemplify success in PPI regulation. However, antibodies can only be applied to protein targets on cell surface due to their impermeability to plasma membranes. Although small molecule drugs can readily cross membranes, applying small molecule inhibitors (SMIs) to disrupt PPIs is a challenging task because approximately 750–1,500 Å2 of protein surface area is involved at the interface of PPIs, which is too large for SMIs to cover. In addition, these interacting protein surfaces do not have pocket-like small molecule binding sites. Therefore, these PPI sites are deemed as “undruggable” targets for SMIs. The Holy Grail of drug development is to render small molecules the power of biologics to regulate PPIs. We recently developed a cell-based functional assay for high throughput screening (HTS) to identify SMIs for steroid receptor coactivator-3 (SRC-3), a large and mostly non- structured nuclear protein. Without any SRC-3 structural information, we identified and improved a series of SMIs that can target SRC-3—the 1st generation SMI gossypol, the 2nd generation SMI bufalin, and the 3rd generation SMI SI-2, a highly promising drug candidate. In our recent report (PNAS 2016), we demonstrated that SI-2 can selectively reduce the transcriptional activities and the protein concentrations of SRC-3 in cells through direct physical interactions with SRC-3, and selectively induce breast cancer cell death with IC50 values in the low nM range (3-20 nM) while not affecting normal cell viability. Furthermore, the in vivo study demonstrated that SI-2 can significantly inhibit primary tumor growth and reduce SRC-3 protein levels in a breast cancer mouse model. Despite of the encouraging antitumor activities of SI-2, it has a relatively short plasma half-life (1 h). In the preliminary study, we have identified SI-12 that has similar biological activities to SI-2 but a much improved plasma half-life (6 h). In Aim 1, we will further optimize SI-2 SRC-3 SMI `unique' derivatives with improved drug- like properties. In Aims 2 and 3, we will take advantage of the novel SRC-3 SMI to address the two major challenges for current breast cancer treatment—resistance to endocrine therapy in estrogen receptor positive (ER+) breast cancer and tumor metastasis in triple negative breast cancer (TNBC). Successful completion of this project will not only significantly improve breast cancer treatment through the development of a `first-in-class' drug that targets oncogenic coactivators, but also encourage other researchers to develop strategies to target protein-protein interactions that are designated as `important but undruggable' targets in the future.