Combinatorial ERK Inhibition Enhances MAPK Pathway Suppression in BRAF-Mutant Melanoma

Small molecule inhibitors targeting BRAF mutations at V600 and downstream MEK represent a significant advancement in treating BRAF-mutant melanoma. However, resistance mechanisms, often involving reactivation of the MAPK pathway via ERK1/2, limit their efficacy. The ERK1/2 inhibitor ravoxertinib (GDC0994) was tested on melanoma cell lines with and without resistance to BRAFi or BRAFi + MEKi. Short-term assays evaluated cell viability, apoptosis induction, and pathway modulation via Western Blot, while long-term effects were assessed using a colony formation assay. Resistant and parental melanoma cells responded to long-term ERKi treatment with reduced growth, independent of sensitivity to BRAF or MEK inhibitors. Adding ERKi to BRAFi/MEKi significantly enhanced apoptosis and growth inhibition, particularly in resistant lines. Although ravoxertinib alone showed limited antitumor activity, its combination with BRAFi/MEKi yielded substantial benefits, especially in chronic settings. These findings suggest that combinatorial regimens incorporating ERK inhibitors represent a promising therapeutic strategy for BRAF-mutant melanoma.