Development of Highly Potent Clinical Candidates for Theranostic Applications against Cholecystokinin-2 Receptor Positive Cancers.

Peptide receptor radionuclide therapy (PRRT) is a promising form of systemic radiation therapy designed to eradicate cancer. Cholecystokinin-2 receptor (CCKR) is an important molecular target that is highly expressed in a range of cancers. This study describes the synthesis and characterization of a novel series of Lu-labeled peptides ([Lu]Lu--) in comparison with the reference CCKR-targeting peptide CP04 ([Lu]Lu-). [Lu]Lu- showed high chemical purity (HPLC ≥ 94%), low Log  (-4.09 to -4.55) with strong binding affinity to CCKR ( 0.097-1.61 nM), and relatively high protein binding (55.6-80.2%) and internalization (40-67%). Biodistribution studies of the novel Lu-labeled peptides in tumors (AR42J and A431-CCKR) showed uptake one- to eight-fold greater than the reference compound CP04 at 1, 24, and 48 h. Rapid clearance and high tumor uptake and retention were established for [Lu]Lu--, making these compounds excellent candidates for theranostic applications against CCKR-expressing tumors.