Synthesis and preclinical investigation of 99m Tc-p-SCN-Bzl-DTPA-cetuximab for targeting EGFR using head and neck squamous cell carcinoma (HNSCC) xenografts.

To assess the preclinical potential of technetium-99m labelled conjugated para-isothiocyanato-benzyl diethylene triamine penta-acetic acid cetuximab ( ^99m Tc-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 ^99m Tc. The labelled conjugate was evaluated for in vitro stability in _L- cysteine at 37 °C. The ^99m Tc-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. ^99m Tc-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 ^99m Tc-p-SCN-Bzl-DTPA cetuximab prepared at optimal dose of cetuximab could become a useful tool for EGFR imaging in HNSCC using SPECT.