1309P - Role of the Hedgehog Pathway in Mediating Resistance to Anti-Egfr Tyrosine Kinase Inhibitors in Non Small Cell Lung Cancer

Abstract

ABSTRACT In recent years, the management of non small lung cancer (NSCLC) has been moving towards molecular-guided treatment, and the best example of this new approach is the use of EGFR tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib. The clinical benefit observed with EGFR-TKIs in NSCLC is limited to a subset of patients, and the development of resistance, even in responders, is sooner or later observed. Several studies have provided new insights into the molecular basis of EGFR inhibitors resistance. Recently our group demonstrated the acquisition of a mesenchymal phenotype in an in vitro model of NSCLC cell lines with acquired resistance to anti-EGFR TKIs. Among the various molecular pathways, the Hedgehog (Hh) signaling pathway has emerged as an important mediator of carcinogenesis and cancer metastases. The objective of this research is to investigate the role of Hh signaling pathway in human NSCLC cell models of constitutive or acquired resistance to EGFR-TKIs. To investigate the expression profile of Hh signalling components in our panel of sensitive and resistant NSCLC cell lines, we performed analysis of mRNA and protein levels of Shh, Gli1 and Smo by using semiquantitative PCR and Western blot analysis. The experiment showed a strong expression of sonic Hh and Gli1 in NSCLC cell lines resistant to EGFR TKIs. In addition, PTCH mRNA levels resulted increased in TKI-resistant cell lines. This is of relevance, because PTCH gene itself is a target gene of Gli1 transcriptional activity and its levels indicates an activation of Hh signalling in such cells. Treatment with cyclopamine, a Smo inhibitor, strongly inhibited the proliferation of resistant NSCLC cell lines. Furthermore, treatment with cyclopamine blocked the invasive and migratory behavior of resistant cells. Of interest, the inhibition of Smo and Hh signaling pathway was accompanied by an inhibition of MET and MAPK phosphorylation. Our study should provide the opportunity to better understand the role of HH pathway in mediating resistance to anti-EGFR TKIs and to design new strategies to be easily transferred into clinical practice. Disclosure All authors have declared no conflicts of interest.