Antitumor activity of a combination of dual PI3K/mTOR inhibitor SAR245409 and selective MEK1/2 inhibitor pimasertib in endometrial carcinomas.

OBJECTIVE: We aimed to clarify whether dual inhibition of PI3K/MAPK and MAPK pathways synergistically suppresses cell growth in endometrial cancer cells.

METHODS: We exposed a panel of 12 endometrial cancer cell lines to a PI3K/mTOR inhibitor (voxtalisib, SAR245409) and/or a MEK inhibitor (pimasertib). The effect of each drug singly or in combination was evaluated by MTT assay, flow cytometry, and immunoblotting. Combination indexes (CIs) were calculated using the Chou-Talalay method to evaluate the synergy.

RESULTS: The IC50 values for SAR245409 and pimasertib varied from 0.5 μM to 7 μM and from 0.1 μM to >20 μM, respectively. A combination of both compounds (1 μM SAR245409 and 30 nM pimasertib) caused a synergistic antitumor effect in 6 out of 12 endometrial cell lines (CI, 0.07-0.46). The synergistic effect was exclusively observed in 6 pimasertib-sensitive cell lines (IC50 of pimasertib, ≤5 μM). We found that 30 nM pimasertib, a concentration much lower than the IC50 for each cell line, was sufficient to cause a synergistic effect with SAR245409. Flow cytometric analysis showed that this combination significantly increased the population of G1 cells. However, a combination of rapamycin (an mTOR inhibitor) and pimasertib did not induce a synergistic effect in endometrial cancer cells, except for HEC-1B cells.

CONCLUSIONS: The combination of a PI3K/mTOR inhibitor and a MEK inhibitor induced a synergistic antitumor effect in certain endometrial cancer cells. This study underscores the importance of using optimized doses of antitumor agents, singly or in combination, in treating endometrial cancer.