Gallium-68 Labeling of the Cyclin-Dependent Kinase 4/6 Inhibitors as Positron Emission Tomography Radiotracers for Tumor Imaging

Cheng Liu; Ziyi Yang; Mingyu Liu; Xiangwei Wang; Shaoli Song; Xiaoping Xu; Zhongyi Yang

doi:10.1021/acsomega.1c05073

Gallium-68 Labeling of the Cyclin-Dependent Kinase 4/6 Inhibitors as Positron Emission Tomography Radiotracers for Tumor Imaging

ACS Omega. 2021 Nov 18;6(47):32253-32261. doi: 10.1021/acsomega.1c05073. eCollection 2021 Nov 30.

Authors

Cheng Liu^{1

2

3

4

5}, Ziyi Yang^{1

2

4}, Mingyu Liu^{1

2

4

5}, Xiangwei Wang^{1

2

4}, Shaoli Song^{1

2

3

4

5}, Xiaoping Xu^{1

2

4}, Zhongyi Yang^{1

2

4}

Affiliations

¹ Department of Nuclear Medicine, Fudan University Shanghai Cancer Center, Shanghai 200032, China.
² Department of Oncology, Shanghai Medical College, Fudan University, Shanghai 200032, China.
³ Shanghai Institute of Medical Imaging, Fudan University, Shanghai 200032, China.
⁴ Shanghai Engineering Research Center of Molecular Imaging Probes, Shanghai 200032, China.
⁵ Department of Nuclear Medicine, Shanghai Proton and Heavy Ion Center, Fudan University Cancer Hospital, Shanghai 201315, China.

Abstract

Cyclin-dependent kinase 4 and 6 (CDK4/6) have emerged as interesting therapeutic drug targets with many potential applications in anti-tumors, especially in breast cancer. A novel CDK4/6 kinase-derived positron emission tomography (PET) imaging agent was designed based on palbociclib modified with a chelator DOTA. This new compound with a chelator DOTA-palbociclib was radiolabeled with gallium 68 (⁶⁸Ga). After labeling, the purity and stability were evaluated, and the blood pharmacokinetics were carried out in normal healthy mice. Human breast cancer MCF-7 (ER+/HER2-) cells were used for in vitro cell uptake tests. PET imaging and ex vivo biodistribution were conducted in MCF-7 tumor-bearing mice. Specific binding of tumors was evaluated by the blocking assay. Furthermore, the uptake of ⁶⁸Ga-DOTA-palbociclib in tumors was studied by autoradiography of tissue sections followed by immunofluorescence evaluation of CDK4 and CDK6. ⁶⁸Ga-DOTA-palbociclib was synthesized very simply in a high labeling rate and radiochemical purity in 10 min. The labeling compound showed excellent stability both in vitro and in vivo and exhibited good pharmacokinetics, making it suitable for in vivo imaging. Cell uptake studies display that co-incubation with palbociclib can inhibit cellular uptake of ⁶⁸Ga-DOTA-palbociclib. In vivo imaging and ex vivo biodistribution in mice bearing MCF-7 tumors both showed obvious radioactive uptake in the tumor and higher tumor-to-muscle ratios, while the tumor radioactivity accumulation was significantly decreased when prior administered with an excess of cold palbociclib, confirming CDK4/6 specific binding of ⁶⁸Ga-DOTA-palbociclib in vivo. Autoradiography of the avid tumor section showed a high correlation between immunofluorescence with the CDK4/6 positive areas of the tumor, further demonstrating that ⁶⁸Ga-DOTA-palbociclib specifically targeted CDK4/6 positive tumors. We synthesized ⁶⁸Ga-DOTA-palbociclib, a new CDK4/6 kinase PET imaging agent, and validated its excellent stability, pharmacokinetics, and specific tumor binding. Based on our primary results, ⁶⁸Ga-DOTA-palbociclib is a promising imaging agent with the potential to tailor a precise treatment program for CDK4/6 inhibitors.