Radiolabeled EGFR TKI as predictive imaging biomarkers in NSCLC patients – an overview

18F-Labeled brain-penetrant EGFR tyrosine kinase inhibitors for PET imaging of glioblastoma

Significant evidence suggests that the failure of clinically tested epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (e.g. erlotinib, lapatinib, gefitinib) in glioblastoma (GBM) patients is primarily attributed to insufficient brain penetration, resulting in inadequate exposure to the targeted cells. Molecular imaging tools can facilitate GBM drug development by visualizing drug biodistribution and confirming target expression and localization. To assess brain exposure via PET molecular imaging, we synthesized fluorine-18 isotopologues of two brain-penetrant EGFR tyrosine kinase inhibitors developed specifically for GBM. Adapting our recently reported radiofluorination of N-arylsydnones, we constructed an ortho-disubstituted [18F]fluoroarene as the key intermediate. The radiotracers were produced on an automated synthesis module in 7-8% activity yield with high molar activity. In vivo PET imaging revealed rapid brain uptake in rodents and tumor accumulation in an EGFR-driven orthotopic GBM xenograft model.

Pharmacokinetic analysis of 6-O-[18F]FEE for PET imaging of EGFR mutation

6-O-[¹⁸F]Fluoroethylerlotinib (6-O-[¹⁸F]FEE), with a suitable half-life for commercial distribution, may be a good replacement for [¹¹C]erlotinib to identify epidermal growth factor receptor (EGFR) positive tumors with activating mutations to tyrosine kinase inhibitors therapy. In this study, we explored the fully automated synthesis of 6-O-[¹⁸F]FEE and investigated its pharmacokinetics in tumor-bearing mice. 6-O-[¹⁸F]FEE with high specific activity (28-100 GBq/μmol) and radiochemistry purity (over 99 %) was obtained by two-step reaction and Radio-HPLC separation in PET-MF-2 V-IT-1 automated synthesizer. PET imaging of 6-O-[¹⁸F]FEE in HCC827, A431, and U87 tumor-bearing mice with different EGFR expression and mutation was performed. Uptake and blocking of PET imaging indicated that the probe specifically targeted exon 19 deleted EGFR (the quantitative analysis of tumor-to-mouse ratio for HCC827, HCC827 blocking, U87, A431 was 2.58 ± 0.24, 1.20 ± 0.15, 1.18 ± 0.19, and 1.05 ± 0.13 respectively). Dynamic imaging was used to study the pharmacokinetics of the probe in tumor-bearing mice. Logan plot graphical analysis demonstrated late linearity and a high fitting correlation coefficient (0.998), supporting reversible kinetics. According to the Akaike Information Criterion (AIC) rule, the 2-compartment reversible model was more consistent with the metabolic properties of 6-O-[¹⁸F]FEE. The automated radiosynthesis and pharmacokinetic analysis will promote clinically transformation of 6-O-[¹⁸F]FEE.