Loss of Activating EGFR Mutant Gene Contributes to Acquired Resistance to EGFR Tyrosine Kinase Inhibitors in Lung Cancer Cells

Abstract

Non-small-cell lung cancer harboring epidermal growth factor receptor (EGFR) mutations attains a meaningful response to EGFR-tyrosine kinase inhibitors (TKIs). However, acquired resistance to EGFR-TKIs could affect long-term outcome in almost all patients. To identify the potential mechanisms of resistance, we established cell lines resistant to EGFR-TKIs from the human lung cancer cell lines PC9 and11–18, which harbored activating EGFR mutations. One erlotinib-resistant cell line from PC9 and two erlotinib-resistant cell lines and two gefitinib-resistant cell lines from 11–18 were independently established. Almost complete loss of mutant delE746-A750 EGFR gene was observed in the erlotinib-resistant cells isolated from PC9, and partial loss of the mutant L858R EGFR gene copy was specifically observed in the erlotinib- and gefitinib-resistant cells from 11–18. However, constitutive activation of EGFR downstream signaling, PI3K/Akt, was observed even after loss of the mutated EGFR gene in all resistant cell lines even in the presence of the drug. In the erlotinib-resistant cells from PC9, constitutive PI3K/Akt activation was effectively inhibited by lapatinib (a dual TKI of EGFR and HER2) or BIBW2992 (pan-TKI of EGFR family proteins). Furthermore, erlotinib with either HER2 or HER3 knockdown by their cognate siRNAs also inhibited PI3K/Akt activation. Transfection of activating mutant EGFR complementary DNA restored drug sensitivity in the erlotinib-resistant cell line. Our study indicates that loss of addiction to mutant EGFR resulted in gain of addiction to both HER2/HER3 and PI3K/Akt signaling to acquire EGFR-TKI resistance.

Antitumor Activity and Acquired Resistance Mechanism of Dovitinib (TKI258) in RET-Rearranged Lung Adenocarcinoma

“…5D and 6E). Similar to our findings, loss of addiction to mutant EGFR resulted in gain of addiction to both HER2/HER3 and PI3K/Akt signaling to acquire EGFR-TKI resistance (33).…”

Erlotinib Resistance in Lung Cancer Cells Mediated by Integrin β1/Src/Akt-Driven Bypass Signaling

“…Previously, we have reported the loss of PTEN expression with the loss of nuclear translocation of EGR-1, a transcription factor responsible for PTEN gene expression, in gefitinib-resistant clones (14)(15)(16). We also reported that either the complete or partial loss of the activated EGFR gene allele could also result in the acquisition of erlotinib resistance (17). In this present study, we further established erlotinib-resistant clones by step-wise selection following exposure to erlotinib and observed enhanced expression and activation of integrin b1 and Src.…”

“…After incubation for 72 hours, cytotoxicity was determined as described previously (17,18). Each value represents the average from triplicate wells AE SD.…”

In Vitro and In Vivo Characterization of Irreversible Mutant-Selective EGFR Inhibitors That Are Wild-Type Sparing

“…The most common form of lung cancer is non-small cell lung carcinoma (NSCLC), and, in a subset of these patients, tumor growth is driven by activating mutations in the epidermal growth factor receptor (EGFR). The most common activating mutations, accounting for 85% to 90% of all EGFR mutations, are the in-frame deletion in exon 19 (DelE746-A750) and the L858R point mutation in exon 21 (5,6). EGFR mutations occur in 10% to 15% of patients with NSCLC of Caucasian descent and 30% to 35% of patients with NSCLC of East Asian descent (5).…”