Department of Chemistry & Biochemistry , University of the Sciences , Philadelphia , Pennsylvania 19104 , United States.
ACS Chem Biol. 2019 Jul 19;14(7):1471-1480. doi: 10.1021/acschembio.9b00191. Epub 2019 Jun 17.
BRAF is the most frequently mutated kinase in human cancers and is one of the major effectors of oncogenic RAS, making BRAF a target of considerable interest for anticancer drug development. Wild-type BRAF and a variety of oncogenic BRAF mutants are dependent on dimerization of the kinase domain, which also emerges as a culprit of drug resistance and side effects of current BRAF therapies. Thus, allosteric BRAF inhibitors capable of disrupting BRAF dimers could abrogate hyperactivated MAPK (mitogen-activated protein kinase) signaling driven by oncogenic BRAF or RAS and overcome the major limitations of current BRAF inhibitors. To establish this, we applied an approach to design a series of peptide inhibitors targeting the dimer interface of BRAF. One resulting inhibitor was found to potently inhibit the kinase activity of BRAF homo- and heterodimers, including oncogenic BRAF mutant. Moreover, this inhibitor synergizes with FDA-approved, ATP-competitive BRAF inhibitors against dimeric BRAF, suggesting that allosteric BRAF inhibitors have great potential to extend the application of current BRAF therapies. Additionally, targeting the dimer interface of BRAF kinase leads to protein degradation of both RAF and MEK, uncovering a novel scaffolding function of RAF in protecting large MAPK complexes from protein degradation. In conclusion, we have developed a potent lead peptide inhibitor for targeting the dimer interface of BRAF in cancer cells. The dual function of this peptide inhibitor validates the strategy for developing allosteric BRAF inhibitors that specifically dissociate RAF dimers and destabilize the MAPK signaling complex.
BRAF 是人类癌症中最常发生突变的激酶，也是致癌 RAS 的主要效应物之一，这使得 BRAF 成为抗癌药物开发的重要目标。野生型 BRAF 和多种致癌 BRAF 突变体依赖于激酶结构域的二聚化，这也成为耐药性和当前 BRAF 治疗副作用的罪魁祸首。因此，能够破坏 BRAF 二聚体的别构 BRAF 抑制剂可以阻断致癌 BRAF 或 RAS 驱动的过度激活的 MAPK（丝裂原激活蛋白激酶）信号，并克服当前 BRAF 抑制剂的主要局限性。为此，我们应用一种方法来设计一系列针对 BRAF 二聚体界面的肽抑制剂。发现一种结果抑制剂能够强烈抑制 BRAF 同型和异型二聚体的激酶活性，包括致癌 BRAF 突变体。此外，该抑制剂与 FDA 批准的、与 ATP 竞争的 BRAF 抑制剂协同作用于二聚体 BRAF，表明别构 BRAF 抑制剂具有很大的潜力来扩展当前 BRAF 治疗的应用。此外，靶向 BRAF 激酶的二聚体界面会导致 RAF 和 MEK 的蛋白降解，揭示 RAF 在保护大 MAPK 复合物免受蛋白降解方面的一种新的支架功能。总之，我们已经开发出一种针对癌细胞中 BRAF 二聚体界面的有效先导肽抑制剂。这种肽抑制剂的双重功能验证了开发特异性解离 RAF 二聚体并使 MAPK 信号复合物不稳定的别构 BRAF 抑制剂的策略。
