Synthesis and preclinical investigation of 99mTc-p-SCN-Bzl-DTPA-cetuximab for targeting EGFR using head and neck squamous cell carcinoma (HNSCC) xenografts
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To assess the preclinical potential of technetium-99m labelled conjugated para-isothiocyanato-benzyl diethylene triamine penta-acetic acid cetuximab (99mTc-p-SCN-Bzl-DTPA cetuximab) for imaging EGFR in HNSCC mice and rabbits xenografts. Cetuximab, a chimeric monoclonal antibody targeting EGFR, was conjugated with p-SCN-Bzl-DTPA followed by labelling with 99mTc. The labelled conjugate was evaluated for in vitro stability in L−cysteine at 37 °C. The 99mTc-p-SCN-Bzl-DTPA cetuximab was also investigated for immunoreactivity, internationalization kinetics, dose escalation (up to 300 µg) and biodistribution in HNSCC mice xenograft. The suitability of labelled moiety as a specific EGFR radio-tracer was assessed in HNSCC rabbit xenograft. 99mTc-p-SCN-Bzl-DTPA cetuximab exhibited more than 98% radiochemical purity at room temperature. In excess L−cysteine, it showed a stable behaviour at 37 °C up to 4 h p.l. The labelled conjugate was internalized in vitro in FaDu tumor cells up to 19.55%. Significantly higher uptake in tumor (at 10 µg; 34.75 ± 0.38% ID/g: pi) was seen in HNSCC mice xenograft with dose escalation assay from 1 to 300 µg/mouse. Blocking of EGFR with excess cetuximab consequently decreased the uptake of tumor up to 6.80 ± 1.25%. SPECT images of rabbit xenograft confirmed increase in tumor to background ratio after 4 h pi and validated its potential in preclinical trial as a specific FaDu tumor tracer. Our in vitro and in vivo preclinical findings indicate that the 99mTc-p-SCN-Bzl-DTPA cetuximab prepared at optimal dose of cetuximab could become a useful tool for EGFR imaging in HNSCC using SPECT.
Keywords99mTc-p-SCN-Bzl-DTPA-cetuximab EGFR HNSCC xenograft
We thank the Higher Education Commission (HEC), Islamabad, Pakistan for providing all sorts of financial assistance under National Research Program for Universities. The instant study is part of the HEC funded research grant No. 3122.
GR performed conjugation of cetuximab with p-SCN-Bzl-DTPA, labeling with radionuclide, in vitro studies and biodistribution in animal model mice. SQS performed the imaging studies using rabbit xenograft. All authors read and approved the final manuscript.
Compliance with ethical standards
Conflict of interest
No conflict of interests.
Ethics approval and consent to participate
No human was involved in this study. Experiments on mice and rabbits models were executed in compliance with Nuclear Medicine Research Laboratory (NMRL) and approval of ethics committee at Institute of Chemical Sciences (ICS), University of Peshawar.