Abstract A252: KRAS mutant lung cancer cells are differentially responsive to MEK inhibition due to AKT or STAT3 activation: Implication for combinatorial approach

Abstract

Abstract KRAS is frequently mutated in non-small cell lung cancer (NSCLC), resulting in the activation of the MEK/ERK pathway. High-throughput mutation profile has shown that lung cancer frequently harbors co-mutation of cancer related genes. Therefore, given that cancer cells have multiple genetic alterations, combinatorial therapeutic strategy is demanded for effective cancer therapy. To address this, we first characterized MEK dependence in four NSCLC cells. Two cells (H358, A549) carried KRAS mutation only, and the other two (H23, H157) harbored co-mutation of KRAS/PTEN. H358 cells with KRAS mutation only were sensitive to MEK inhibition. However, the other KRAS mutant A549 cells were resistant to MEK inhibition. Previously, we have shown that dual inhibition of EGFR and MEK signaling shows a synergistic effect on KRAS mutant gastric cancer cells by suppressing compensatory activation of AKT. Here we also observed that this combination was effective in KRAS mutant A549 cells. However, the combination was ineffective in H23 and 157 cells with co-mutation of KRAS/PTEN. Compared to KRAS mutant/PTEN wild-type cells, STAT3 was significantly activated following MEK inhibition in KRAS/PTEN co-mutant cells. Combined STAT3 inhibition by a JAK2 inhibitor or gene knockdown with MEK inhibition blocked STAT3 activation, synergistically suppressed cell growth, and induced apoptosis in co-mutant cells. Taken together, our study provides molecular insights that help explain the heterogeneous response to MEK inhibition in KRAS mutant lung cancers, and presents a rationale for the clinical investigation of combination of MEK and EGFR inhibitor or MEK and STAT3 inhibitor depending on PTEN status. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A252.