BRAF-inhibitor Associated MEK Mutations Increase RAF-Dependent and -Independent Enzymatic Activity

Area of Science:

• Oncology
• Molecular Biology
• Cancer Genetics

Background:

• Alterations in MEK1/2 are observed in various cancers, affecting response to targeted therapies like BRAF and MEK inhibitors.
• MEK1/2 mutations can arise in both treatment-naïve cancers and following therapy, particularly in BRAF-V600E-mutant melanoma and colorectal cancer.

Purpose of the Study:

• To investigate the functional consequences of MEK1/2 alterations based on their structural location (allosteric pocket vs. helix-A).
• To determine the impact of these MEK1/2 mutations on sensitivity to BRAF and MEK inhibitors and downstream signaling.
• To identify potential alternative therapeutic strategies for tumors with MEK1/2-resistant mutations.

Main Methods:

• Categorization of MEK1/2 alterations into those affecting the allosteric pocket versus helix-A.
• Assessment of inhibitor sensitivity (BRAF and MEK inhibitors) for different mutation categories.
• Analysis of phospho-ERK1/2 levels and MEK1/2 catalytic activity using biochemical assays for representative variants like MEK1-Q56P.

Main Results:

• MEK1/2 alterations in the allosteric pocket confer resistance to MEK inhibitors but retain sensitivity to BRAF inhibitors.
• Mutations in helix-A reduce sensitivity to both BRAF and MEK inhibitors, leading to elevated phospho-ERK1/2 levels independently of MEK phosphorylation.
• A representative helix-A variant (MEK1-Q56P) exhibited increased catalytic efficiency and phosphorylation-independent activity.

Conclusions:

• Classifying MEK1/2 mutations by structural location and functional consequences is essential for predicting treatment response.
• Helix-A MEK1/2 mutations confer resistance to current BRAF and MEK inhibitors.
• Targeting downstream effectors like ERK may be necessary to overcome resistance mediated by helix-A MEK1/2 alterations.