Effect of eribulin on cell growth and PI3K pathway activity with and without RAD001 in triple-negative and HER2-expressing breast cancer.

Abstract

173 Background: Patients with triple-negative breast cancer have high levels of Akt expression and activation of the PI3K-mTOR pathway. Eribulin is a microtubule-targeting agent with benefits in treating refractory triple negative disease. Our objective was to evaluate its efficacy in inhibiting PI3K pathway activity and cell growth both alone and in combination with the mTOR inhibitor RAD001. Methods: MDA468, BT549 and SKBR3 breast cancer cell lines were used for this study. MTT assays were used to assess growth inhibition after 72 hour treatment with eribulin alone and in combination with RAD001. Combination indices (CI) generated by Chou-Talalay plots were used to quantify synergy. Western blots were used to evaluate the expression of phosphorylated Akt-Ser473 (pAkt) and S6K1 after 24 hours of treatment with both agents. Results: Both MDA468 and SKBR3 cells treated with eribulin in varying concentrations showed inhibition of pAkt expression. Standard dilutions of eribulin in combination with log dilutions of RAD001 resulted in marked synergistic growth inhibition (CI<<1) in both MDA468 and BT549 cells. Western blot analysis for MDA468 cells treated with the combination erubulin and RAD001 showed a dose related suppression of pAkt along with complete inhibition of pS6K1, while RAD001 alone increased pAkt. Conclusions: Our study shows dose related inhibition of Akt activation as well as inhibition of cell growth in triple negative breast cancer and HER2 cell lines treated with eribulin alone or combined with RAD001. We also show reversal of the pAkt feedback response seen with mTOR inactivation, and a significant synergistic growth inhibition with combination treatment. These findings point to a potential role for eribulin and RAD001 in the treatment of refractory triple-negative breast cancer. [Table: see text]