P2.03-45 PKCι-PAK1 Pathway Modulates Sensitivity to Therapy in EGFR, KRAS Mutant Adenocarcinoma and Squamous Cell Carcinoma

p21-activated kinase 1 (PAK1) stimulates growth and metastasis in several types of tumors, including non-small cell lung cancer (NSCLC). Protein kinase C iota (PKCi) is an enzyme highly expressed in NSCLC that regulates PAK1 signaling. To understand intrinsic and acquired resistance to different MAPK signaling inhibitors, we explored PKCι-PAK1 signaling in EGFR/KRAS mutant adenocarcinoma or squamous cell carcinoma (SCC) cell lines by combination therapy using PAK1 inhibitor and PKCι inhibitor. Three lung cancer cell lines were used: HCC827 and H23 lung adenocarcinoma cells that carries EGFR and KRAS mutations, respectively, and H520 (PAK1 amplified squamous cell carcinoma). Cell viability assays and western blotting were applied to evaluate the effect of IPA-3 (PAK1 inhibitor) plus auranofin (PKCι inhibitor). Since IPA-3 is only for laboratory use, we explored alternative PAK-1 inhibitor and tested combination effect with auranofin. IPA-3 plus auranofin was highly synergistic (Combination index was less than 0.4) in EGFR mutant adenocarcinoma (HCC827), KRAS mutant adenocarcinoma (H23) and SCC with PAK1 amplification (H520) cell lines in MTT assay and colony forming assay. We revealed OTSSP167 (a MELK inhibitor in phase I/II trials) inhibits phosphorylated PAK1 and combination of OTSSP167 plus auranofin showed similar synergism in the 3 cell lines. The combination of auranofin with either IPA-3 or OTSSP167 ablated EGFR phosphorylation and downstream signaling pathways: ERK, AKT, STAT3, YAP1 and inhibited the expression of RTKs: AXL, MET, and CDCP1. The combination of IPA-3 plus auranofin is promising treatment in different subclasses NSCLC with driver EGFR or KRAS mutations, as well as SCC with PAK1 amplification. OTSSP167 also works as PAK1 inhibitor. The therapeutic effect of PAK-1 inhibitor and PKCι inhibitor was validated using OTSSP167 plus auranofin.