Discovery of Cyclic Peptides Targeting the BRAF Dimer Interface as Dual Inhibitors

RAF dimerization is crucial for oncogenic signaling in RAS mutant tumors, contributing to resistance to mitogen-activated protein kinase pathway inhibitors by promoting dysregulated BRAF dimerization. This makes it a promising target for overcoming resistance caused by paradoxical extracellular signal-regulated kinase (ERK) signaling activation resulting from BRAF mutations (e.g., BRAF^V600E) and inhibitors like vemurafenib and dabrafenib. Peptide inhibitors such as Braftide (TRHVNILLFM) block BRAF dimerization but lack cell permeability and biological activity within cells. A promising solution is conjugating cell-penetrating peptides (CPPs). However, this approach involves a trade-off: it produces a larger molecule and increases the level of off-target cytotoxicity. On the basis of the crystal structure of the BRAF homodimer, we developed a series of linear and cyclic peptides derived from Braftide. Among these peptides, CBF-2-2 crosses the cell membrane without the aid of CPPs and significantly inhibits tumor cell growth, exhibiting greater serum stability than Braftide. Moreover, the composite peptide SCBF-2-2, which contains an anti-invasion sequence, disrupts BRAF dimers, effectively inhibits cancer cell proliferation and invasion, reduces ERK phosphorylation, and suppresses tumor growth in the A549 mouse xenograft model. SCBF-2-2 offers a new starting point for developing dual-function antitumor peptides that target the BRAF dimer.