Src Inhibitors Act Through Different Mechanisms to Cooperate with Egfr or Mek Inhibitors in Nsclc Models Sensitive or Resistant to Erlotinib

Abstract

ABSTRACT Aim: The EGFR TKIs gefitinib and erlotinib are the first-line therapy for NSCLCs harboring EGFR-activating mutations. The intrinsic resistance to these agents and the onset of acquired resistance in the responders is a relevant clinical issue and the aim of this work is to test the efficacy of three different Src inhibitors in these models of resistance. Methods: We used a panel of human NSCLC cell lines with different EGFR/Ras mutational profile and erlotinib sensitivity: PC9 and HCC827 (EGFR-activating mutation, highly sensitive), Calu3 (EGFR/Ras wt; moderately sensitive), Calu3-ER (with acquired resistance), H1299 and A549 (Ras mutant; resistant), H1975 (EGFR T790M mutant; resistant). In these models, we tested three different Src inhibitors (saracatinib, dasatinib and bosutinib), both in vitro and in vivo Results: NSCLC cell lines showed different activation of EGFR- and Src-dependent pathways and variable sensitivity to Src inhibitors. A kinase assay demonstrated that all the compounds are able to directly inhibit not only Src, but also EGFR TK variants. However, in cell lysates only saracatinib and bosutinib efficiently reduced EGFR activation, while dasatinib was the more effective agent in inhibiting Src TK. In EGFR-activating mutant, erlotinib sensitive cells, saracatinib and bosutinib showed anti-proliferative effects related to simultaneous EGFR/Src inhibition. In EGFR wt/Ras mutant cells Src inhibition by dasatinib interfered with cell proliferation and signal transduction. Since Src inhibitors had only moderate effects as single agents, both in vitro and in vivo, we tested the combination of saracatinib with EGFR inhibitors (erlotinib or cetuximab) in EGFR-addicted cells, and of dasatanib with MEK inhibitors (selumetinib) in Ras mutant, erlotinib resistant models. These combinations were effective both in vitro and in vivo, inhibiting tumor growth, prolonging mice survival and interfering with signal transduction. Importantly, the combination of saracatanib and cetuximab was effective also in the erlotinib resistant, EGFR T790M mutant model. Conclusions: Src inhibitors may act with different mechanisms in NSCLC cell lines, depending on EGFR/Ras mutational profile. Integration of anti-Src agents with EGFR or MEK inhibitors could represent effective therapeutic options for different cohorts of NSCLC patients. Disclosure: All authors have declared no conflicts of interest.