The MEK1/2 pathway as a therapeutic target in high-grade serous ovarian carcinoma

Abstract

Rationale: High-grade serous ovarian carcinoma (HGSOC) is the deadliest of gynecological cancers due to high rate of recurrence and acquired chemoresistance. Mutation and activation of the RAS/MAPK pathway has been linked to cancer cell proliferation and therapeutic resistance in numerous cancers. While RAS mutations are not commonly observed in HGSOC, less is known about downstream pathway activation. We therefore sought to investigate the role of MEK1/2 signaling in ovarian cancer.Methods: MEK1/2 pathway activity was evaluated in clinical HGSOC tissue samples and ovarian cancer cell lines by using tissue microarray-based immunohistochemistry, immunoblotting, and RT-qPCR. OVCAR8 and PEO4 HGSOC cell lines were used to assess the effect of MEK1/2 inhibition on cell viability, proliferation rate, and stem-like characteristics. Xenografts were used in mice to investigate the effect of MEK1/2 inhibition on tumor growth in vivo. A drug washout experimental model was used to study the lasting effects of MEK1/2 inhibition therapy.Results: MEK1/2 signaling is active in a majority of HGSOC tissue samples and cell lines. MEK1/2 is further stimulated by cisplatin treatment, suggesting that MEK1/2 activation may play a role in chemotherapy resistance. The MEK1/2 inhibitor, trametinib, drastically inhibits MEK1/2 downstream signaling activity, causes prominent cell cycle arrest in the G1/0-phase in cell cultures, and reduces the rate of tumor growth in vivo, but does not induce cell death. Cells treated with trametinib display a high CD133 + fraction and increased expression of stemness-associated genes.Transient trametinib treatment causes long-term increases in a high ALDH1 activity subpopulation of cells that possess the capability of surviving and growing in non-adherent conditions. Conclusions: MEK1/2 inhibition in HGSOC cells efficiently inhibits proliferation and tumorgrowth and therefore may be a promising approach to suppress ovarian cancer cell growth. MEK1/2 inhibition promotes stem-like properties, thus suggesting a possible mechanism of resistance and that a combination with CSC-targeting drugs should be considered.

How to win the ovarian cancer stem cell battle: destroying the roots

“…Interestingly, in breast cancer, inhibition of AXL increased CSC chemosensitivity [ 106 ] , whereas histone deacetylase inhibitors manifested preferential targeting of breast CSCs, suggesting a potential therapeutic effect in ovarian CSCs as well [ 107 ] . In addition, a recent study of high-grade serous ovarian cancer revealed that an MEK1/2 inhibitor, trametinib, arrests cell proliferation but also enriches cancer stemness, suggesting a need for a combination regimen with CSC-targeted therapy [ 108 ] .…”