26P - Role of the Hedgehog pathway in preventing occurrence of resistance to first, second, third generation EGFR-TKIs in first line therapy of NSCLC models with EGFR activating mutations

Abstract

NSCLC patients with EGFR activating mutations can be treated with different lines of EGFR tyrosine kinase inhibitors (EGFR-TKIs), and it is still unknown which is the best EGFR-TKIs in first line. This work investigates the best choice of treatment in the first line setting in EGFR mutant NSCLC models. The in vivo model of sensitivity is represented by nude mice xenografted with human cancer NSCLC cell lines harboring the EGFR activating mutation (del ex19) HCC827, which is known to not develop T790M. Mice have been randomized to receive first line therapy with a first generation EGFR-TKIs (gefitinib), second generation EGFR-TKIs (afatinib) or third generation EGFR-TKIs (osimertinib). Additionally treatments were continued until occurrence of resistance in order to obtain new in vivo models of resistance to each generation of TKIs. Each resistant tumor has been collected and analyzed for gtene and protein expression. According to RECIST criteria, a dose-dependent decrease in tumor volume of almost all mice treated with each inhibitor was evident after 14 weeks of treatment. Response rates were similar among inhibitors. Western blot analysis on protein extract from tumors resistant to afatinib and to osimertinib showed increased levels of Hedgehog related proteins as compared to untreated controls. Preliminary results from gene analysis revealed appearance of SMO mutation (V404M) in one tumor resistant to osimertinib, with an allelic frequency of 50%, comparing to baseline. These data demonstrate that, in cell models not developing T790M-mediated resistance, first, second and third generation EGFR-TKIs are equivalent in terms of tumor response. In such models, Hedgehog pathway activation plays an important role as mediator of first line EGFR-TKIs treatment suggesting new strategy of combination of Hedgehog inhibitors with EGFR-TKIs in first line to prevent the occurrence of resistance.