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 anti-cancer drug development. A variety of oncogenic BRAF mutants and wild-type BRAF 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 <i>in silico </i>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. Interesting, the biological function of BRAF is not only dependent on its catalysis activity but also the scaffolding role independent of kinase activity, supported by the occurrence of kinase-dead mutations in BRAF. We applied biochemical, biophysical, and computational approaches to investigate the role of the scaffolding function and found that the peptide inhibitor potently eliminates the scaffolding function of BRAF by disrupting  BRAF dimers. As expected, the peptide inhibitor diminishes MAPK signaling driven by kinase-dead BRAF mutants, which occur frequently in lung carcinomas. 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. <br/>

Novel approach to inhibit both the catalytic and non-catalytic functions of RAF kinases

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.