CCKBR (Gastrin Receptor) as a Theranostic Target in Oncology: Biological Rationale, Diagnostic Imaging, and Next-Generation Peptide-Based Drug Development

Cholecystokinin B receptor (CCKBR) is a promising theranostic target because of its overexpression in several malignancies, including medullary thyroid carcinoma, small-cell lung cancer, gastric cancer, and pancreatic cancer. Its high-affinity ligand binding and efficient receptor-mediated internalization provide a strong biological basis for molecular imaging and peptide receptor radionuclide therapy (PRRT). Recent advances in radiolabeled gastrin and mini-gastrin analogues have improved tumor targeting, metabolic stability, and pharmacokinetic profiles, supporting their application in both diagnostic imaging and radionuclide therapy. This review summarizes the molecular biology and tumor expression of CCKBR, recent progress in SPECT/PET imaging and targeted radionuclide therapy, and advances in ligand and pharmacokinetic engineering. Despite substantial progress, CCKBR-targeted theranostics remain less clinically established than SSTR- or PSMA-based platforms. Major challenges include heterogeneous receptor expression, renal and gastric uptake, limited prospective clinical evidence, and the lack of standardized imaging, dosimetry, and treatment protocols. Addressing these limitations will be essential for the broader clinical translation of CCKBR-targeted theranostics.