Design, Synthesis, and Preclinical Evaluation of Inhibitor-Based Radiotracers for Potential Application in Monitoring CDK4/6 Expression

Cyclin-dependent kinases 4 and 6 (CDK4/6) are essential
drivers
of cell cycle progression and have been validated as important therapeutic
targets in oncology. In this study, we report the design, synthesis,
and preclinical validation of a series of novel radiotracers ([68Ga]Ga-PY01–[68Ga]Ga-PY08) based on the
pharmacophore of CDK4/6 inhibitor ribociclib. Flexible linkers and
functionalized amino acids were incorporated to optimize pharmacokinetic
and targeting properties. Among eight radiotracers, [68Ga]Ga-PY03 showed superior pharmacological and pharmacokinetic properties,
including high stability, strong CDK4/6 binding affinity and low nonspecific
uptake. Micro-PET/CT imaging demonstrated its capability to detect
CDK4/6-overexpressed tumors and dynamically monitor CDK4/6 expression
post-therapeutic. Importantly, [68Ga]Ga-PY03 also enabled
quantitative assessment of CDK4/6 target occupancy, providing a potential
tool for therapy response evaluation. In summary, these findings demonstrate
the potential of [68Ga]Ga-PY03 as a PET radiotracer to
monitor the CDK4/6 expression in tumors.

细胞周期蛋白依赖性激酶4和6（Cyclin-dependent kinases 4 and 6, CDK4/6）是细胞周期进程的关键驱动因子，已被验证为肿瘤学领域的重要治疗靶点。本研究报道了一系列基于CDK4/6抑制剂瑞博西尼（ribociclib）药效团的新型放射性示踪剂（[68Ga]Ga-PY01至[68Ga]Ga-PY08）的设计、合成及临床前验证工作。研究引入柔性连接子与功能化氨基酸，以优化其药代动力学与靶向特性。在8种放射性示踪剂中，[68Ga]Ga-PY03展现出更优异的药理学与药代动力学特性，包括高稳定性、强CDK4/6结合亲和力以及低非特异性摄取。微型PET/CT成像结果证实，该示踪剂可用于检测CDK4/6过表达肿瘤，并动态监测治疗后CDK4/6的表达水平。尤为重要的是，[68Ga]Ga-PY03还可实现CDK4/6靶点占有率的定量评估，为治疗响应评估提供了潜在的检测工具。综上，本研究结果证实[68Ga]Ga-PY03作为PET放射性示踪剂，在肿瘤CDK4/6表达监测领域具有良好的应用潜力。