Abstract 4095: c-Met activation mediates resistance to polo-like kinase 1 inhibitor-induced apoptosis in non-small cell lung cancer
Authors: Singh Ratnakar , Shen Li , Tong Pan , Wang Jing , Johnson Faye M. 
Published: July 2017

Abstract
Background: Inhibiting polo-like kinase 1 PLK1 may be an effective treatment for non-small cell lung cancer (NSCLC). PLK1 is a key regulator of mitosis and DNA damage checkpoints. PLK1 inhibitors are well tolerated, but only a few unselected patients with NSCLC respond to single-agent therapy. However, predictive biomarkers have not been used to select patients who are likely to experience a response to PLK1 inhibitors, and the mechanisms of resistance to PLK1 inhibitors have not been elucidated, making these unknowns a major gap in knowledge. To address this gap, we compared basal gene and protein expression in 63 NSCLC cell lines and discovered that mesenchymal NSCLC cell lines were more sensitive to PLK1 inhibitors than epithelial cell lines in vitro and in vivo. The induction of apoptosis in some NSCLC cell lines at very low drug concentrations and the need to find better therapy for mesenchymal NSCLC motivated us to further study PLK1 inhibition.
Methods: To identify the pathways involved in PLK1 inhibitor-induced apoptosis, we used 3 pairs of isogenic NSCLC cell lines in which we had induced a mesenchymal phenotype using TGF-β. These isogenic lines were treated with the PLK1 inhibitor (volasertib) for 24 hours and levels of 301 proteins and phosphoproteins were simultaneously measured before and after treatment with volasertib using reverse phase protein array (RPPA).
Results: The induction of a mesenchymal phenotype using TGF-β increased PLK1 inhibition-induced DNA damage and apoptosis in 3 NSCLC cell lines. To further elucidate mechanisms of resistance to PLK1 inhibition, we compared gene and protein expression in these isogenic cell lines, before and after PLK1 inhibition. There were 35, 12 and 43 proteins differentially regulated following PLK1 inhibition in epithelial vs. mesenchymal lines in HCC366, H1975, and HCC4006 cell lines, respectively at False Discovery rate 0.1. Phosphorylated FAK (Y397) and c-Met (Y1234/1235) were consistently inhibited following PLK1 inhibition in the mesenchymal lines but activated in the epithelial lines. These changes were confirmed by Western blotting. Total FAK and c-Met protein and mRNA levels were not affected, demonstrating post-translational changes. The inhibition of c-Met using EMD 1214063 led to FAK inhibition but FAK inhibition did not affect c-Met activation. The combination of c-Met inhibitor and volasertib increases sensitivity in NSCLC cell lines tested. The combinations led to more apoptosis than the single-agent inhibitors.
Conclusions: NSCLC cell lines have diverse sensitivities to PLK1 inhibition, which is consistent with the results of clinical trials of PLK1 inhibitors in solid tumors, but no studies to date explain these diverse responses to PLK1 inhibition. We have identified c-Met activation as a previously unknown pathway of resistance to PLK1 inhibition in epithelial NSCLC.
Citation Format: Ratnakar Singh, Li Shen, Pan Tong, Jing Wang, Faye M. Johnson. c-Met activation mediates resistance to polo-like kinase 1 inhibitor-induced apoptosis in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4095. doi:10.1158/1538-7445.AM2017-4095