Tumor imaging of [¹¹C]DAC. Decline of peripheral-type benzodiazepine receptor (PBR) expression in tumor-bearing mice with the carbon-ion irradiation

We used [¹¹C]DAC, a novel PBR positron emission tomography (PET) ligand, to evaluate its uptake in fibrosarcoma (NFSa)-bearing mice after the carbon-ion irradiation. After evaluating the tumor growth sizes in NFSa-bearing mice with a dose from 0 to 30 Gy of the carbon-ion irradiation, we selected the 20 Gy irradiated mice as an experimental group. In vitro binding assay was performed for the NFSa single cells removed from NFSa-bearing mice with or without the carbon-ion irradiation. The uptake of [¹¹C]DAC into the cells from irradiated mice were lower than that in the cells from non-irradiated mice. Biodistribution of [¹¹C]DAC was determined by a small animal PET scanner. The uptake of [¹¹C]DAC in tumor was decreased by the carbon-ion irradiation. However, decline of [¹¹C]DAC uptake was determined not only in tumor, but also in other organs. To confirm the change of PBR expression in the tumor, in vitro autoradiography was performed. Binding of [¹¹C]DAC on the tumor sections made from NFSa-bearing mouse with the carbon-ion irradiation was decreased, compared with the control. In this study, we have determined the decreased uptake of [¹¹C]DAC after the carbon-ion irradiation. The [¹¹C]DAC uptake in the tumor may a promising biomarker for evaluation the carbon-ion radiotherapy. (author)