68Ga Small Peptide Imaging: Comparison of NOTA and PCTA

In this study, a bifunctional version of the chelate PCTA was compared to the analogous NOTA derivative for peptide conjugation, 68Ga radiolabeling, and small peptide imaging. Both p-SCN-Bn-PCTA and p-SCN-Bn-NOTA were conjugated to cyclo-RGDyK. The resulting conjugates, PCTA-RGD and NOTA-RGD, retained their affinity for the peptide target, the αvβ3 receptor. Both PCTA-RGD and NOTA-RGD could be radiolabeled with 68Ga in >95% radiochemical yield (RCY) at room temperature within 5 min. For PCTA-RGD, higher effective specific activities, up to 55 MBq/nmol, could be achieved in 95% RCY with gentle heating at 40 °C. The 68Ga-radiolabeled conjugates were >90% stable in serum and in the presence of excess apo-transferrin over 4 h; 68Ga-PCTA-RGD did have slightly lower stability than 68Ga-NOTA-RGD, 93 ± 2% compared to 98 ± 1%, at the 4 h time point. Finally, the tumor and nontarget organ uptake and clearance of 68Ga-radiolabeled PCTA-RGD and NOTA-RGD was compared in mice bearing HT-29 colorectal tumor xenografts. ...