Simultaneous Inhibition of the HGF/MET and Erk1/2 Pathways Affect Uveal Melanoma Cell Growth and Migration

Purpose
Nearly all primary uveal melanoma (UM) that metastasize involve the liver. Hepatocyte growth factor (HGF) is proposed to be an important microenvironmental element in attracting/supporting UM metastasis through activation of MET. The majority (>85%) of UM express mutations in the G-alpha proteins, that drive the MEK-ERK1/2 pathway. Thus, we proposed that the combination of MET and MEK inhibition would inhibit the growth and migration of G-alpha protein mutant versus non-mutant UM cells.
Methods
Western-blots demonstrated the relative protein levels of ERK1/2 and MET in UM cells. Cells were treated with the small molecule inhibitors AZD6244 (MEKi) and/or MK-8033 (METi) and downstream markers evaluated. Further studies determined the effect of combination MEKi and METi treatment on cell growth, apoptosis and migration.
Results
All G-alpha protein mutant UM cell lines express MET mRNA and protein. The level of mRNA expression correlates with protein expression. MEKi, but not METi treatment results in markedly reduced ERK1/2 phosphorylation. Either MEKi or METi treatment alone results in reduced cell proliferation, but only modest induction of apoptosis. The combination MEKi+METi results in significant reduction of proliferation in G-alpha protein mutant cells. UM cell migration was blocked by METi, but not MEKi treatment.
Conclusions
MET protein expression showed no correlation with G-alpha protein mutation status. Combining MEKi with METi treatment has added benefit to either treatment alone in reducing G-alpha protein mutant UM cell growth. Combining METi with MEKi treatment adds the effect of limiting uveal melanoma cell migration.