Overexpression and amplification of cyclin-dependent kinase 4/6 (CDK4/6) occur in many cancers and may be the cause of resistance to CDK4/6 inhibitors in preclinical models. However, there are few investigations on the assessment of CDK4/6 expression in tumors or other tissues. Palbociclib, which was approved in 2015 to treat ER+/HER2-breast cancer in combination with letrozole, is a selective CDK4/6 inhibitor. In this study, an intermediate (compound 3), which could be hydrolyzed into the ligand (compound L) consisting of palbociclib as the bioactive molecule and 6-hydrazino nicotinamide (HYNIC) as the bifunctional chelator, was synthesized. Compound L was radiolabeled with 99mTc using tricine/TPPTS or tricine/TPPMS as co-ligands. 99mTc-tricine-TPPTS-L and 99mTc-tricine-TPPMS-L were prepared with high radiochemical purity without postlabeling purification. They had great in vitro stability. Both radiotracers were hydrophilic, but 99mTc-tricine-TPPTS-L had a lower log P value. In vitro cell uptake studies in MCF-7 cells showed that cellular uptake was blocked by preincubation with palbociclib, suggesting a CDK4/6-mediated uptake mechanism. Biodistribution in mice bearing MCF-7 tumors showed that 99mTc-tricine-TPPTS-L had higher tumor uptake than 99mTc-tricine-TPPMS-L, while they had comparable tumor-to-muscle and tumor-to-blood ratios. Radioactivity accumulation in tumors was obvious in micro-SPECT/CT images with 99mTc-tricine-TPPTS-L. When mice were preinjected with palbociclib, tumor uptake of 99mTc-tricine-TPPTS-L significantly decreased and the tumor accumulation was clearly lost, confirming CDK4/6 specificity. All results in this work indicated that 99mTc-tricine-TPPTS-L is a promising tumor imaging agent that targets CDK4/6.

中文翻译：

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用于细胞周期蛋白依赖性激酶4/6阳性肿瘤成像的99mTc标记的HYNIC-palbociclib类似物的制备和评估。

细胞周期蛋白依赖性激酶4/6（CDK4 / 6）的过度表达和扩增发生在许多癌症中，并且可能是在临床前模型中对CDK4 / 6抑制剂产生耐药性的原因。但是，关于评估肿瘤或其他组织中CDK4 / 6表达的研究很少。Palbociclib是一种选择性CDK4 / 6抑制剂，于2015年获准与来曲唑联合治疗ER + / HER2乳腺癌。在这项研究中，合成了一种中间体（化合物3），它可以水解成由palbociclib作为生物活性分子和6-肼基烟酰胺（HYNIC）作为双功能螯合剂组成的配体（化合物L）。使用tricine / TPPTS或tricine / TPPMS作为共配体，用99mTc对化合物L进行放射性标记。制备的99mTc-三嗪-TPPTS-L和99mTc-三嗪-TPPMS-L具有高放射化学纯度，无需后期标记纯化。它们具有出色的体外稳定性。两种放射性示踪剂都是亲水性的，但99mTc-三氢甲基-TPPTS-L的log P值较低。在MCF-7细胞中进行的体外细胞摄取研究表明，与palbociclib一起预孵育会阻止细胞摄取，这表明CDK4 / 6介导的摄取机制。在患有MCF-7肿瘤的小鼠中的生物分布表明，99mTc-三嗪-TPPTS-L比99mTc-三嗪-TPPMS-L具有更高的肿瘤摄取，而它们的肿瘤与肌肉和肿瘤与血液的比率相当。在99mTc-tricine-TPPTS-L的micro-SPECT / CT图像中，肿瘤中的放射性蓄积非常明显。当给小鼠预先注射palbociclib时，肿瘤对99mTc-tricine-TPPTS-L的摄取显着降低，并且肿瘤的积累明显消失，从而证实了CDK4 / 6的特异性。这项工作的所有结果都表明99mTc-tricine-TPPTS-L是靶向CDK4 / 6的有前途的肿瘤成像剂。