MEK inhibitor resistance mechanisms and recent developments in combination trials.

The mitogen-activated protein kinase (MAPK) pathway plays a vital role in cellular processes such as gene expression, cell proliferation, cell survival, and apoptosis. Also known as the RAS-RAF-MEK-ERK pathway, the MAPK pathway has been implicated in approximately one-third of all cancers. Mutations in RAS or RAF genes such as KRAS and BRAF are common, and these mutations typically promote malignancies by over-activating MEK and ERK downstream, which drives sustained cell proliferation and uninhibited cell growth. Development of drugs targeting this pathway has been a research area of great interest, especially drugs targeting the inhibition of MEK. In vitro and clinical studies have shown promise for certain MEK inhibitors (MEKi) , and MEKi have become the first treatment option for certain cancers. Despite promising results, not all patients have a response to MEKi, and mechanisms of resistance typically arise in patients who do have a positive initial response. This paper summarizes recent developments regarding MEKi, the mechanisms of adaptive resistance to MEKi, and the potential solutions to the issue of adaptive MEKi resistance.