Abstract 113: A comparative preclinical PET imaging study between [11C]erlotinib and [18F]afatinib
Authors: Slobbe Paul , Windhorst Albert , Walsum Marijke Stigter-van , Schuit Robert , Smit Egbert , Niessen Heiko , Dongen Guus van , Poot Alex 
Published: May 2015

Abstract
Background: The epidermal growth factor receptor (EGFR) is an established target for the treatment of advanced non-small cell lung cancer (NSCLC). EGFR tyrosine kinase inhibitors (TKIs) gefitinib, erlotinib and afatinib have been approved for treatment of NSCLC. The Efficacy of those TKIs depends on the presence of activating mutations of EGFR (exon 19 del. or L858R point mutation). Therefore, the EGFR mutational status needs to be ascertained by an invasive biopsy before treatment; however this is often compromised by sampling errors due to tumor heterogeneity or by lack of access to the tumor tissue. We hypothesize that PET-imaging with radiolabeled TKIs (TKI-PET) can provide a tool to determine and predict responsiveness to EGFR TKIs in vivo. Previously, this was demonstrated with the reversible EGFR inhibitor [11C]erlotinib that showed higher uptake in patients harboring exon 19 deletions of EGFR. Therefore, to validate the application of TKI-PET imaging, we developed irreversible second generation TKI afatinib as a PET tracer and extensively evaluated both [18F]afatinib and [11C]erlotinib in a comparative preclinical imaging study to determine the feasibility of TKI-PET as a potential personalized medicine tool.
Methods: The synthesis of [11C]erlotinib was already established in our center. The synthesis of [18F]afatinib was developed using an innovative three step radiosynthesis. Both tracers were thoroughly evaluated in a PET imaging study in mice bearing a panel of three clinically relevant EGFR expressing human NSCLC xenografts. The three selected cell lines are: A549 with wild-type EGFR, H1975 with the sensitizing mutation L858R and the acquired resistance related mutation T790M and HCC827 cell line with the sensitizing exon 19 deletion. Other factors influencing uptake were also investigated, such as tracer metabolism and effects of drug efflux transporters.
Results: [18F]afatinib was successfully synthesized in an overall decay corrected yield of 17 ± 2.3% with a radiochemical purity of &gt;97% and a specific activity of &gt;200 GBq/µmole at end of synthesis. In a panel of lung cancer xenograft models, [11C]erlotinib and [18F]afatinib both showed an increased uptake in the treatment sensitive cell line, while showing low to no uptake in wild type or acquired resistance cell lines. [18F]afatinib showed a higher tumor-to-background ratio than [11C]erlotinib in the sensitive cell line. In vivo blocking of the P-gp drug efflux transporter with tariquidar revealed an increased uptake of both tracers indicating that they are substrates for efflux pumps.
Conclusions: The new TKI-PET tracer [18F]afatinib has been synthesized successfully. [11C]erlotinib and [18F]afatinib show similar uptake patterns across EGFR mutations, while uptake appears to correspond with treatment sensitivity. A treatment study in mice will be performed to directly correlate uptake to sensitivity.
Citation Format: Paul Slobbe, Albert Windhorst, Marijke Stigter-van Walsum, Robert Schuit, Egbert Smit, Heiko Niessen, Guus van Dongen, Alex Poot. A comparative preclinical PET imaging study between [11C]erlotinib and [18F]afatinib. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 113. doi:10.1158/1538-7445.AM2014-113