Abstract A057: 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 rates of recurrence and acquired chemoresistance. Recurrent tumors are suggested to originate from cancer stem-like cells (CSCs) which have been shown to have high MEK1/2 activity signaling pathway to survive and proliferate. Present work investigates the potential of selective MEK1/2 inhibition as a CSC-targeting HGSOC therapy approach. Methods: MEK1/2 pathway activity was evaluated in clinical HGSOC tissue samples and ovarian cancer cell lines 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 in vitro. Mouse xenografts were used to investigate MEK1/2 inhibition effect on tumor growth in vivo. Drug washout experimental model was used to study the lasting effects of MEK1/2 inhibition therapy. Results: MEK1/2 signaling is active in majority of HGSOC tissue samples and cell lines and is further stimulated by cisplatin treatment. MEK1/2 inhibitor trametinib drastically inhibits activity of MEK1/2 downstream signaling, causes prominent cell cycle arrest in G1/0-phase in vitro and reduces tumor growth rate in vivo, but does not induce cell death. Cells treated with trametinib display high CD133+ fraction and increased expression of stemness-associated genes. Transient trametinib treatment causes long-term increase in high ALDH1 activity cells that possess capability of surviving and growing in non-adherent conditions. Conclusions: MEK1/2 inhibition in HGSOC cells efficiently inhibits cell proliferation and tumor growth and therefore may be promising approach to suppress ovarian cancer cell growth. As MEK1/2 inhibition promotes stem-like properties, including ALDH activity, it should be used in combination with CSC-targeting drugs, especially ALDH1 inhibitors. Citation Format: Mikhail Chesnokov, Abdelrahman Yousif, ilana Chefetz. The MEK1/2 pathway as a therapeutic target in high-grade serous ovarian carcinoma [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A057. doi:10.1158/1535-7163.TARG-19-A057