Src Mediates Cigarette Smoke–Induced Resistance to Tyrosine Kinase Inhibitors in NSCLC Cells

Abstract

The EGF Receptor (EGFR) is a proto-oncogene commonly dysregulated in several cancers including non-small cell lung cancer (NSCLC) and, thus, is targeted for treatment using tyrosine kinase inhibitors (TKIs) such as Erlotinib. However, despite the efficacy observed in NSCLC patients harboring oncogenic variants of the EGFR, general ineffectiveness of TKIs in NSCLC patients who are current and former smokers necessitates identification of novel mechanisms to overcome this phenomenon. Previously, we showed that NSCLC cells harboring either wild-type (WT) EGFR or oncogenic mutant (MT) L858R EGFR become resistant to the effects of TKIs when exposed to cigarette smoke (CS), evidenced by their auto-phosphorylation and prolonged downstream signaling. Here, we present Src as a target mediating CS-induced resistance to TKIs in both WT EGFR and L858R MT EGFR expressing NSCLC cells. First, we show that CS exposure of A549 cells leads to time-dependent activation of Src which then abnormally binds to the WT EGFR causing TKI resistance, contrasting previous observations of constitutive binding between inactive Src and TKI-sensitive L858R MT EGFR. Next, we demonstrate that Src inhibition restores TKI sensitivity in CS-exposed NSCLC cells, preventing EGFR auto-phosphorylation in the presence of Erlotinib. Furthermore, we show that over-expression of a dominant-negative Src (Y527F/K295R) restores TKI sensitivity to A549 exposed to CS. Importantly, the TKI resistance that emerges even in CS-exposed L858R EGFR expressing NSCLC cells could be eliminated with Src inhibition. Together, these findings offer new rationale for using Src inhibitors for treating TKI-resistant NSCLC commonly observed in smokers.

Impact of Smoking Status on EGFR-TKI Efficacy for Advanced Non–Small-Cell Lung Cancer in EGFR Mutants: A Meta-analysis

“…31 Moreover, other research demonstrated that TKI resistance in exon 21 L858R mutant NSCLC cells after exposure to cigarette smokeeinduced oxidative stress was due to structural alteration of EGFR upon binding of active c-Src to the receptor. 32 Interestingly, this could be eliminated with Src inhibition in vitro, which offered a new rationale for using Src inhibitors to treat TKIresistant NSCLC patients with exon 21 L858R mutation in smokers. 32 It also explained the result from subgroup analysis that nonsmokers received a significant PFS benefit only in the active EGFR-mutant cohort with a larger proportion of exon 21 L858R, instead of the active and nonclassical EGFR-mutant cohort.…”

“…32 Interestingly, this could be eliminated with Src inhibition in vitro, which offered a new rationale for using Src inhibitors to treat TKIresistant NSCLC patients with exon 21 L858R mutation in smokers. 32 It also explained the result from subgroup analysis that nonsmokers received a significant PFS benefit only in the active EGFR-mutant cohort with a larger proportion of exon 21 L858R, instead of the active and nonclassical EGFR-mutant cohort.…”

Impact of Smoking History on the Efficacy of Gefitinib in Patients with Non-Small Cell Lung Cancer Harboring Activating Epidermal Growth Factor Receptor Mutations

“…One report suggested that activation of the nicotinic acetylcholine receptor by cigarette smoking induced EGFR-TKI resistance [14]. Another report suggested that smoking induced EGFR posttranslational changes [15] and that the Src oncogene may confer resistance to treatment [16]. Moreover, it was reported that many chemicals contained in cigarette smoke have a high mutagenic activity [17].…”

Smoking History as a Predictor of Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors in Patients with Non-Small Cell Lung Cancer Harboring <b><i>EGFR</i></b> Mutations

“…Another report proposed that the SRC oncogene may confer resistance to treatment [20]. Additionally, it has been reported that many chemicals contained in cigarette smoke have high mutagenic activity [21]. According to these findings, the rate of genetic alterations is considerably higher in smokers with NSCLC harboring activating EGFR mutations than in nonsmokers with NSCLC harboring EGFR activating mutations [22, 23].…”