RAF inhibitors promote RAS-RAF interaction by allosterically disrupting RAF autoinhibition

Area of Science:

• Molecular biology
• Cell signaling
• Drug discovery

Background:

• First-generation RAF inhibitors paradoxically activate ERK signaling in RAS-active cells.
• RAF dimerization and enhanced RAS-RAF association are key factors in this paradoxical activation.
• The precise mechanism underlying RAS-RAF association enhancement by RAF inhibitors remained unclear.

Purpose of the Study:

• To elucidate the molecular mechanism by which RAF inhibitors enhance RAS-RAF association.
• To identify key properties of ideal RAF inhibitors for improved therapeutic outcomes.

Main Methods:

• Investigated the effect of RAF inhibitors on intramolecular interactions within RAF proteins.
• Utilized biochemical assays to study RAS-RAF association and RAF dimerization.
• Profiled second-generation RAF inhibitors to assess their mode of action and identify liabilities.

Main Results:

• RAF inhibitors disrupt intramolecular interactions between the RAF kinase domain and its N-terminal regulatory region, independent of RAS activity.
• This disruption provides a molecular basis for enhanced RAS-RAF association and co-operativity between RAS activity and RAF inhibitors in driving RAF activation.
• Second-generation RAF inhibitors show improved action but possess liabilities, highlighting the need for specific inhibitor properties.

Conclusions:

• RAF inhibitors' paradoxical ERK signaling activation is due to disrupted intramolecular RAF interactions.
• An ideal RAF inhibitor should possess high binding affinity across all RAF paralogs and maintain the enzyme's autoinhibited state.
• Understanding these mechanisms is crucial for developing more effective RAF-targeted therapies.