MEK inhibition is interesting but still has modest efficacy in KRASm LAC patients. STAT3 activation and AXL mediated epithelial-to-mesenchymal transition cause resistance to MEK inhibition. p21-activated kinase 1 (PAK1) regulates ERK activation and its role in KRASm LAC warrants further investigation. YAP1 suppression increases trametinib efficacy in KRASm LAC cells. We have explored the role of STAT3, AXL, PAK1 and YAP1 in KRASm LAC cells and developed a rationale for combinatorial strategies.
Quantitative real-time PCR gene expression analysis was performed in 4 KRASm LAC cell lines (H23, A549, H460 and Calu6). The MEK inhibitor (i) selumetinib was combined with evodiamine (STAT3i), R428 (AXLi) or ivermectin (dual YAP1-PAK1i). Cell viability was assessed by the thiazolyl blue assay and the combination index (CI) was calculated for the analysis of drug interactions.
We first evaluated the effect of selumetinib in the 4 KRASm LAC cell lines. H23 and H460 were less sensitive to selumetinib than A549 and Calu6. Among the cell lines examined, H23 cells had the highest STAT3 mRNA expression and the combination of selumetinib with evodiamine synergistically suppressed cell viability (CI = 0.8). The combination of R428 with selumetinib was also synergistic in H23 cells (CI = 0.58) that have moderate AXL mRNA expression. High PAK1 mRNA expression was detected in the A549 selumetinib-sensitive cell line, and the addition of the dual PAK1-YAP1i, ivermectin, to selumetinib increased the effect of MEK inhibition alone (CI = 0.17). To our surprise, the combination of ivermectin with selumetinib was not synergistic in the H23 cells that overexpress YAP1. H460 and Calu-6 cells have moderate or low STAT3, AXL, PAK1 and YAP1 expression. Further cell viability experiments as well as immunoblotting and biomarkers analysis in clinical tumor samples are ongoing.
The heterogeneous biology of KRASm LAC may partially explain the difficulties encountered in the development of efficient therapies. Our data, until now, identify STAT3, AXL and PAK1 as potential biomarkers and the targeting of them as a potential synergistic strategy to combine with MEK inhibition.
Clinical trial identification
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This work was supported by grants from the La Caixa Foundation and Red Tematica de Investigacion Cooperativa en Cancer (RTICC; grant RD12/0036/ 0072).
All authors have declared no conflicts of interest.