Synthesis and Preclinical Evaluation of Novel 68Ga-DOTA-RBB as Potential PET Radiotracer for Imaging CDK4/6 in Tumors

Many malignant tumors, including breast cancer, exhibit amplification and overexpression of cyclin-dependent kinase 4 and 6 (CDK4/6). Ribociclib, approved and used in clinical treatment, acts as a highly selective CDK4/6 inhibitor for ER+/HER2- breast cancer. By modifying ribociclib with the chelator DOTA, we designed and synthesized a novel CDK4/6-positive PET imaging agent, which was radiolabeled by ⁶⁸Ga for radioactive tagging. The radiotracer demonstrates high radiochemical purity, excellent stability in vitro and in vivo, and favorable pharmacokinetic characteristics. Cell uptake experiments using MCF-7 cells indicate that an excess of ribociclib (RBB) can inhibit cellular uptake of ⁶⁸Ga-DOTA-RBB. Imaging and biodistribution experiments in MCF-7 tumor-bearing nude mice show significant radioactive accumulation in the tumor. However, preadministration of excess ribociclib results in a substantial reduction in radioactive accumulation within the tumor. On the basis of our explorations, ⁶⁸Ga-DOTA-RBB, as a targeted imaging agent for CDK4/6-positive tumors, holds significant potential application values.