Clinical Application of CAIX-Targeted PET Imaging in Tumors

According to the 2020 global cancer statistics, renal carcinoma ranks as the fourteenth most common malignant tumor worldwide. In 2020, there were 431,288 new cases and 179,368 deaths from renal cancer, and both the incidence and mortality rates are projected to continue rising by 2025. Early non-invasive diagnosis of clear cell renal cell carcinoma (ccRCC) is crucial for improving prognosis. Nuclear medicine molecular imaging offers the advantages of real-time, dynamic, and non-invasive detection of lesions throughout the body. However, there is currently a lack of highly efficient and targeted molecular probes for early and accurate diagnosis of this tumor in clinical practice.

The high expression of CAIX plays a central role in the pathogenesis of renal cancer by altering cellular metabolism, inducing angiogenesis, promoting epithelial-mesenchymal transition (EMT), invasion, and metastatic spread. CAIX is highly expressed in 95% of ccRCC cases. In fact, CAIX expression levels have been reported as an independent predictor of survival in advanced ccRCC. Moreover, CAIX expression in normal tissues is limited, primarily restricted to the stomach, the basolateral aspects of proliferating small intestinal crypt epithelial cells, and the gallbladder. Therefore, the differential expression of CAIX between ccRCC tumors and normal tissues highlights its potential as a robust target for nuclear medicine molecular probe research and development in ccRCC.

This study utilized high-throughput screening to identify small molecules with high affinity for CAIX. These molecules were subsequently cyclized and modified to enhance their in vivo stability. A bifunctional chelator, H3RESCA, was introduced at the C-terminus to construct the small-molecule compound RESCA-CAIX-LT. PET probes were prepared by radiolabeling with 68Ga or 18F, and their diagnostic efficacy for renal cancer was investigated. Small-animal PET imaging initially demonstrated that the probe exhibits high affinity and excellent imaging performance. The modifications also altered the in vivo metabolic profile of the original design, reducing non-specific uptake in organs such as the stomach, small intestine, and gallbladder. Furthermore, toxicological experiments confirmed the probe's high safety profile and in vivo stability.