Preclinical Evaluation of 44Sc-Labeled Anti-EGFR Fab

PET and PET/CT scans at various time points p.i., image reconstruction, and region-of-interest (ROI) analyses were performed using a microPET/microCT Inveon rodent model scanner (Siemens Medical Solutions USA, Inc.) and Inveon Research Workplace [IRW] vendor software, respectively, as described previously. ^{30 (link)} Each tumor-bearing mouse was injected with 1.85-3.7 MBq of ⁴⁴Sc-CHX-A″-DTPA-Cetuximab-Fab via the tail vein and static PET scans were performed. In order to improve the detection statistics and minimize inter-scan variability due to radioactive decay, 20 million coincidence events per mouse were acquired for every static PET emission scan (energy window: 350-650 keV; time window 3.432 ns; resolution 1.5 mm). Quantitative data is presented as percentage injected dose per gram (%ID/g) of tissue. Blocking studies were carried out to evaluate EGFR specificity of ⁴⁴Sc-CHX-A″-DTPA-Cetuximab-Fab in vivo, in which a group of three mice bearing U87MG tumors were each injected with 2 mg of Cetuximab, 24 h before ⁴⁴Sc-CHX-A″-DTPA-Cetuximab-Fab administration. Biodistribution studies were carried out after the last PET scans to validate the PET results. The radioactivity in the tissue was measured using a gamma-counter (Perkin Elmer) and presented as %ID/g.