Background: Subsets of triple negative breast cancer (TNBC) such basal have activated signaling through the MAPK-ERK kinase (MEK) pathway. Use of MEK inhibitors in preclinical TNBC models demonstrates some cytostatic activity, but compensatory signaling through the PI3K/AKT pathway diminishes the antitumor effect of MEK inhibitor monotherapy in some TNBC cell lines. Combining a MEK inhibitor with an AKT inhibitor (horizontal blockade) may show increased antitumor activity. We sought to characterize the in vitro effects of the MEK inhibitor AZD6224 combined with the AKT inhibitor MK2206 in three different breast cancer cell lines.

Methods: Cell Titer-Blue cell viability experiments were performed to test dilutions of AZD-6244 or MK-2206 alone or in combination at various molar ratios over a 72 hour time period in MCF-7 (ER+), SKBR3 (HER2+), and MBA-231 (TNBC) cell lines. Synergy was evaluated using Chou and Talalay combination index (CI) analyses (effective dose levels of 0.75, 0.9 and 0.95). Evaluation of MEK and AKT activity in the untreated, AZD6224, MK2206, and AZD+MK treated cells was performed using a BioRad (Hercules, CA) Bio-plex p-ERK1/2 (Thr202/Tyr204, Thr185/Tyr187) + pAKT (Ser473) phosphoprotein assay on a Luminex100.

Results: Synergy was seen only in MDA-231 cells with a mean CI of .492 at a fixed dose ratio of 1:8. The mean fluorescence levels with standard errors of pERK1/2 and pAKT from duplicate experiments are shown in Table 1 in the four treatment groups. The greatest level of baseline MEK activation was seen in the MBA-231 cell line. A significant compensatory increase in p-AKT levels in the MBA-231 cells treated with AZD6224 alone was not observed, but this was seen in the SKBR3 cells.

Conclusions: The combination of AZD6224+MK2206 demonstrates enhanced antitumor activity in the TNBC MBA-231 cell line over AZD6224 monotherapy. The strategy of combining a MEK inhibitor with an AKT inhibitor should be further explored in the treatment of TNBC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C203.