Abstract
BackgroundThe two main mechanisms of resistance to EGFR tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) are the occurrence of T790M secondary mutation in the kinase domain of EGFR and MET amplification. The aim of the present study was to test whether early changes of 18F-fluorodeoxyglucose (18F-FDG) uptake in animal models bearing erlotinib-resistant NSCLC may have different imaging patterns of response to erlotinib depending on the molecular mechanisms underlying resistance.Animal tumor models were developed using NSCLC H1975 cells bearing the T790M mutation and H1993 cells with MET amplification. Nude mice bearing erlotinib-resistant H1975 and H1993 xenografts (four animals for each cell line and for each treatment) were subjected to 18F-FDG PET/CT scan before and immediately after treatment (50 mg/kg p.o. for 3 days) with erlotinib, WZ4002, crizotinib, or vehicle. A three-dimensional region of interest analysis was performed to determine the percent change of 18F-FDG uptake in response to treatment. At the end of the imaging studies, tumors were removed and analyzed for glycolytic and mitochondrial proteins as well as levels of cyclin D1.ResultsImaging studies with 18F-FDG PET/CT in H1975 tumor-bearing mice showed a reduction of 18F-FDG uptake of 25.87 % ± 8.93 % after treatment with WZ4002 whereas an increase of 18F-FDG uptake up to 23.51 % ± 9.72 % was observed after treatment with erlotinib or vehicle. Conversely, H1993 tumors showed a reduction of 18F-FDG uptake after treatment with both crizotinib (14.70 % ± 1.30 %) and erlotinib (18.40 % ± 9.19 %) and an increase of tracer uptake in vehicle-treated (56.65 % ± 5.65 %) animals. The in vivo reduction of 18F-FDG uptake was always associated with downregulation of HKII and p-PKM2 Tyr105 glycolytic proteins and upregulation of mitochondrial complexes (subunits I–IV) in excised tumors.Conclusions 18F-FDG uptake is a reliable imaging biomarker of T790M-mediated resistance and its reversal in NSCLC whereas it may not be accurate in the detection of MET-mediated resistance.
Highlights
The two main mechanisms of resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) are the occurrence of T790M secondary mutation in the kinase domain of EGFR and MET amplification
We showed that the inhibition of EGFR signaling in NSCLC cells inhibits aerobic glycolysis and restores oxidative phosphorylation through the concerted downregulation of hexokinase II (HKII) and pyruvate kinase M2 phosphorylated at Tyr105 (p-Pyruvate kinase M2 (PKM2) Tyr105) and upregulation of mitochondrial complexes (OXPHOS) [16]
Since in a previous study [16] we showed that inhibition of EGFR signaling in NSCLC cells reduces aerobic glycolysis and restores oxidative phosphorylation through the concerted downregulation of HKII and p-PKM2 Tyr105 and upregulation of mitochondrial complexes (OXPHOS), we tested the levels of these selected markers of energy metabolism in tumors from untreated and treated animals
Summary
The two main mechanisms of resistance to EGFR tyrosine kinase inhibitors (TKIs) in non-small cell lung cancer (NSCLC) are the occurrence of T790M secondary mutation in the kinase domain of EGFR and MET amplification. Advanced NSCLC patients are candidates to first-line therapy with EGFR TKIs such as gefitinib and erlotinib if their tumors bear activating mutations of EGFR that have been recognized as the major determinant of effective tumor response to these targeted agents [2]. About half of resistant tumors develop T790M secondary mutations in EGFR which prevent an effective inhibition by EGFR TKIs [6, 7] whereas an additional 15–20 % of tumors undergoes amplification of MET receptor tyrosine kinase [8] which causes a lateral activation of EGFR signaling cascade despite receptor inhibition
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