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 治疗发展的一类重要靶点。以生物制剂为基础的疗法，如抗体， PPI监管的成功例证。然而，抗体只能应用于细胞表面的蛋白质靶标。 由于它们对质膜的不透过性。尽管小分子药物可以很容易地跨膜， 应用小分子抑制剂(SMI)来干扰PPI是一项具有挑战性的任务，因为大约有750-1500 PPI的界面处有2/2的蛋白质表面积，太大，SMI无法覆盖。此外, 这些相互作用的蛋白质表面没有口袋状的小分子结合位点。因此，这些PPI 这些网站被认为是中小企业“无法下药”的目标。药物开发的圣杯是把小的 分子是生物制品调节PPI的力量。我们最近开发了一种基于细胞的高密度脂蛋白功能检测方法。 用于鉴定类固醇受体辅活化子-3(SRC-3)的SMI的吞吐量筛查(HTS)，SRC-3是一种大的且主要是非 结构核蛋白。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 它可以靶向SRC-3-第一代SMI棉酚，第二代SMI蟾酥，以及第三代 SMI SI-2，一种非常有希望的候选药物。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SRC-3在细胞中的转录活性和蛋白浓度 与SRC-3的物理相互作用，并在低NM选择性地诱导IC50值为的乳腺癌细胞死亡 范围(3-20 nm)，不影响正常细胞活力。此外，体内研究表明，SI-2 能显著抑制乳腺癌小鼠模型的原发肿瘤生长，降低SRC-3蛋白水平。 尽管SI-2具有良好的抗肿瘤活性，但其血浆半衰期较短(1h)。在 初步研究发现，SI-12具有与SI-2相似的生物活性，但比SI-2有很大改善 血浆半衰期(6h)。在目标1中，我们将用改进的药物进一步优化SI-2 SRC-3 SMI“独特”的衍生物- 就像房产一样。在目标2和目标3中，我们将利用新的SRC-3 SMI来解决两个主要问题 当前乳腺癌治疗面临的挑战--雌激素受体阳性者对内分泌治疗的抵抗 (ER+)乳腺癌与三阴性乳腺癌(TNBC)肿瘤转移成功完成 该项目不仅将显著改善乳腺癌的治疗，还将通过开发一流的 靶向致癌辅活化子的药物，但也鼓励其他研究人员制定针对 未来被指定为“重要但不能用药”的目标的蛋白质-蛋白质相互作用。

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.