Structure and RAF family kinase isoform selectivity of type II RAF inhibitors tovorafenib and naporafenib

Upon activation by RAS, RAF family kinases initiate signaling through the MAP kinase cascade to control cell growth, proliferation, and differentiation. Among RAF isoforms (ARAF, BRAF, and CRAF), oncogenic mutations are by far most frequent in BRAF. The BRAFV600E mutation drives more than half of all malignant melanoma and is also found in many other cancers. Selective inhibitors of BRAFV600E (vemurafenib, dabrafenib, encorafenib) are used clinically for these indications, but they are not effective inhibitors in the context of oncogenic RAS, which drives dimerization and activation of RAF, nor for malignancies driven by aberrantly dimerized truncation/fusion variants of BRAF. By contrast, a number of "type II" RAF inhibitors have been developed as potent inhibitors of RAF dimers. Here, we compare potency of type II inhibitors tovorafenib (TAK-580) and naporafenib (LHX254) in biochemical assays against the three RAF isoforms and describe crystal structures of both compounds in complex with BRAF. We find that tovorafenib and naporafenib are most potent against CRAF but markedly less potent against ARAF. Crystal structures of both compounds with BRAFV600E or WT BRAF reveal the details of their molecular interactions, including the expected type II-binding mode, with full occupancy of both subunits of the BRAF dimer. Our findings have important clinical ramifications. Type II RAF inhibitors are generally regarded as pan-RAF inhibitors, but our studies of these two agents, together with recent work with type II inhibitors belvarafenib and naporafenib, indicate that relative sparing of ARAF may be a property of multiple drugs of this class.

 

Comments：

The passage discusses the role of RAF family kinases in signaling through the MAP kinase cascade to regulate cell growth, proliferation, and differentiation. It notes that oncogenic mutations are most frequently found in BRAF, and that selective inhibitors of the BRAFV600E mutation are used clinically for various cancers. However, these inhibitors are not effective against oncogenic RAS or truncation/fusion variants of BRAF. The passage then describes the development of type II RAF inhibitors, which are potent inhibitors of RAF dimers. It compares the potency of two such inhibitors, tovorafenib and naporafenib, in biochemical assays against the three RAF isoforms and notes that they are most potent against CRAF but less potent against ARAF. Crystal structures of both compounds with BRAFV600E or WT BRAF are also described. The passage concludes that relative sparing of ARAF may be a property of multiple drugs of this class, which has important clinical implications.

Related Products

Cat.No.	Product Name	Information
S7121	Tovorafenib (MLN2480)	Tovorafenib (MLN2480, BIIB-024, TAK580, AMG-2112819, BSK1369, DAY-101) is an oral, selective pan-Raf kinase inhibitor in chinical trials.

Related Targets

Raf