Developmentof a Novel 68Ga-Labeled RadiotracerTargeting Carbonic Anhydrase IX for the Diagnosis of Clear Cell RenalCell Carcinoma

Carbonic anhydrase IX (CAIX) is highly expressed in most clear cell renal cell carcinomas (ccRCCs), making it an attractive candidate for the development of a molecular imaging target. This study investigated the preclinical performance and clinical feasibility of 68Ga-C1, a novel developed CAIX-targeted bicyclic peptide PET tracer. The binding characteristics and biological properties of 68Ga-C1 were first assessed through in vitro experiments. Subsequently, their imaging performance was evaluated in CAIX-expressing ccRCC cell lines and xenograft mouse models. A pilot translational study was then conducted in individuals suspected of renal cell carcinoma (RCC) and in ccRCC patients undergoing evaluation for disease recurrence or metastatic progression. In preclinical investigations, 68Ga-C1 demonstrated strong affinity for CAIX, selective accumulation in CAIX-positive tumor cells and xenografts, favorable pharmacokinetic behavior, and an acceptable safety profile. Clinically, five patients presenting with newly detected renal masses and seven ccRCC patients after nephrectomy who were suspected of recurrence or metastasis underwent 68Ga-C1 PET imaging. High uptake of 68Ga-C1 was detected in nine ccRCC patients and in one angiosarcoma patient with positive CAIX expression, whereas a pathologically confirmed non-ccRCC lesion showed negligible tracer accumulation. These findings support its potential as a noninvasive PET tracer for the detection, characterization, and restaging of CAIX-positive renal malignancies.