Potential of [(11)C](R)-PK11195 PET Imaging for Evaluating Tumor Inflammation: A Murine Mammary Tumor Model

Background: Breast tumor inflammation is an immunological process that occurs mainly by mediation of Tumor-Associated Macrophages (TAM). Aiming for a specific measurement of tumor inflammation, the current study evaluated the potential of Positron Emission Tomography (PET) imaging with [(11)C](R)-PK11195 to evaluate tumor inflammation in a mammary tumor animal model. Methods: Female Balb/C mice were inoculated with 4T1 cells. The PET imaging with [(11)C](R)-PK11195 and [(18)F]FDG was acquired 3 days, 1 week, and 2 weeks after cell inoculation. Results: The [(11)C](R)-PK11195 tumor uptake increased from 3 days to 1 week, and decreased at 2 weeks after cell inoculation, as opposed to the [(18)F]FDG uptake, which showed a slight decrease in uptake at 1 week and increased uptake at 2 weeks. In the control group, no significant differences occurred in tracer uptake over time. Tumor uptake of both radiopharmaceuticals is more expressed in tumor edge regions, with greater intensity at 2 weeks, as demonstrated by [(11)C](R)-PK11195 autoradiography and immunofluorescence with TSPO antibodies and CD86 pro-inflammatory phenotype. Conclusion: The [(11)C](R)-PK11195 was able to identify heterogeneous tumor inflammation in a murine model of breast cancer and the uptake varied according to tumor size. Together with the glycolytic marker [(18)F]FDG, molecular imaging with [(11)C](R)-PK11195 may provide a better characterization of inflammatory responses in cancer.