Design, synthesis and characterisation of a novel type II B-RAF paradox breaker inhibitor

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• The B-Raf V600E mutation drives cancer by activating the mitogen-activated protein kinase (MAPK) pathway.
• Type I B-Raf inhibitors cause paradoxical MAPK pathway hyperactivation in wild-type B-Raf through kinase domain conformational changes and heterodimerization.
• Type II inhibitors bind B-Raf in a DFG-out conformation, preventing heterodimerization and hyperactivation.

Purpose of the Study:

• To design and characterize a novel B-Raf kinase domain inhibitor with a phenyl(1H-pyrrolo [2,3-b]pyridin-3-yl)methanone template.
• To create a hybrid inhibitor combining hinge-binding features of Type I inhibitors and back pocket binding of Type II inhibitors.
• To evaluate the inhibitor's binding mode, activity, selectivity, and conformational effects on wild-type and mutant B-Raf.

Main Methods:

• Synthesis of a novel hybrid B-Raf inhibitor.
• Determination of the inhibitor's binding mode through structural studies.
• In vitro activity and selectivity assays against B-Raf variants.
• Molecular dynamics simulations to assess conformational changes in B-Raf kinase domains.

Main Results:

• The novel inhibitor is active and selective for B-Raf.
• It binds to B-Raf in a DFG-out/αC-helix-in conformation.
• Crucially, the inhibitor does not induce paradoxical MAPK pathway hyperactivation in wild-type B-Raf.
• Molecular dynamics simulations confirmed the inhibitor's distinct conformational effects compared to Type I inhibitors.

Conclusions:

• A novel hybrid B-Raf inhibitor effectively targets the MAPK pathway without paradoxical activation.
• The inhibitor's design merges beneficial features of Type I and Type II inhibitors.
• This merging strategy presents a promising approach for developing a new class of B-Raf inhibitors for cancer therapy.
• The findings support further translational studies for clinical applications.