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Updated: Aug 18, 2026
Analysis of Cell Cycle Position in Mammalian Cells
Published on: January 21, 2012
PD1 blockade alters cell-cycle distribution and affects 3'-deoxy-3'-[18F]fluorothymidine uptake in a mouse CT26 tumor
Motofumi Suzuki1, Takuma Matsuda1, Kohei Nakajima1
1Laboratory of Bioanalysis and Molecular Imaging, Graduate School of Pharmaceutical Sciences, Hokkaido University, North 12, West 6, Kita-ku, Sapporo, Hokkaido, 060-0812, Japan.
Objective:
We previously reported that alterations of the tumor microenvironment (TME) by programmed death receptor-1 (PD1) blockade affected tumor glucose metabolism and tumor 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) uptake. In cancer cells, high glycolysis allows cells to sustain rapid proliferation since glycolysis is closely related to the proliferation of cancer cells. Therefore, imaging of cellular proliferation may provide more detail of TME alterations. In this study, we investigated how TME alterations by PD1 blockade affects the uptake of 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT), which is a 18F-radiolabeled thymidine derivative and is taken up by proliferating cells.
Methods:
Mice inoculated with murine colon carcinoma CT26 cells were intraperitoneally administered an anti-PD1 antibody on Day 0, when the tumor volume exceeded 50 mm3, and Day 5. [18F]FLT-PET imaging was performed pre-treatment (Day 0) and post treatment (Day 7). Tumor infiltrating lymphocytes (TILs) were identified by flow cytometry. [18F]FLT accumulation and localization in tumor tissue was evaluated by autoradiography and immunohistochemistry. The cell-cycle distribution of tumors and CT26 cells exposed to cytokines (interleukin-2, interferon [INF]-γ, and tumor necrosis factor [TNF]-α) was analyzed by flow cytometry.
Results:
PD1 blockade increased CD8+ and CD4+ T cells in tumor tissue and significantly suppressed tumor proliferation; however, tumor [18F]FLT uptake remained unchanged. Autoradiography and immunohistochemistry showed that [18F]FLT was mainly taken up by cancer cells, but not TILs. Flow cytometric analysis demonstrated that the population of cells in G2/M phase increased after PD1 blockade. Moreover, INF-γ and TNF-α significantly increased cells in G2/M phase in vitro.
Conclusion:
PD1 blockade-induced alteration of the TME increased CT26 tumor cells in the G2/M phase, which have high thymidine kinase 1 activity. Therefore, [18F]FLT is taken up by tumor cells even if tumor proliferation is suppressed. This observation may be useful for evaluating the response to immunotherapy.
Insights
Programmed death receptor-1 (PD1) blockade alters the tumor microenvironment, increasing cancer cells in the G2/M phase. Despite suppressed proliferation, [18F]FLT uptake by tumor cells remains, aiding immunotherapy response evaluation.
Area of Science:
- Oncology
- Immunology
- Radiochemistry
Background:
- Programmed death receptor-1 (PD1) blockade modulates the tumor microenvironment (TME).
- Previous studies showed PD1 blockade affects tumor glucose metabolism and [18F]FDG uptake.
- Cellular proliferation is crucial for cancer growth and is closely linked to glycolysis.
Purpose of the Study:
- To investigate how PD1 blockade-induced TME alterations affect the uptake of 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT).
- [18F]FLT is a radiotracer used to image proliferating cells.
- To assess the utility of [18F]FLT for evaluating immunotherapy response.
Main Methods:
- Mice with CT26 colon carcinoma received anti-PD1 antibody treatment.
- [18F]FLT-PET imaging was performed before and after treatment.
- Tumor-infiltrating lymphocytes (TILs), [18F]FLT uptake, and cell-cycle distribution were analyzed.
Main Results:
- PD1 blockade increased T cells but did not change overall tumor proliferation or [18F]FLT uptake.
- [18F]FLT was primarily taken up by cancer cells, not TILs.
- PD1 blockade increased the proportion of tumor cells in the G2/M phase, a phase associated with high thymidine kinase 1 activity.
Conclusions:
- PD1 blockade increases CT26 tumor cells in the G2/M phase, which exhibit high thymidine kinase 1 activity.
- [18F]FLT is taken up by these tumor cells, even when overall proliferation is suppressed.
- This finding suggests [18F]FLT imaging may be valuable for assessing immunotherapy response.
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