Comparison of conventional and novel PET tracers for imaging mesothelioma in nude mice with subcutaneous and intrapleural xenografts.

摘要

INTRODUCTION: Malignant mesothelioma is a highly aggressive tumor originating in the pleura, peritoneum and pericardium, and the prognosis of patients undergoing current treatment remains poor. To develop new therapies, it is important to have a noninvasive imaging system for evaluating the efficacy of such prospective treatments. We have established clinically relevant mouse models and evaluated conventional and novel positron emission tomography (PET) tracers. METHODS: Epithelioid and sarcomatoid mesothelioma cells were inoculated subcutaneously and intrapleurally into nude mice. Biodistribution and PET imaging studies were conducted by injecting [(18)F]fluoro-2-deoxy-D-glucose (FDG), 3'-[(18)F]fluoro-3'-doxythymidine (FLT) or 4'-methyl-[(11)C]thiothymidine (S-dThd) into the mouse models. In vitro cellular uptake of [(14)C]FDG and [(3)H]FLT and thymidine kinase 1 (TK(1)) activity in both cell lines were measured. Expression of glucose transporter 1 (GLUT-1) and Ki-67 in xenografted tumors was evaluated by immunohistochemical staining. RESULTS: In epithelioid mesothelioma models, biodistribution experiments showed that tumor uptake of [(11)C]S-dThd was significantly higher than that of [(18)F]FDG. On the other hand, in sarcomatoid models, [(18)F]FDG showed significantly higher accumulation than the other two tracers. These differential uptakes of the three tracers were confirmed by PET imaging. The cellular uptake of [(14)C]FDG and [(3)H]FLT and TK(1) activity in sarcomatoid cells were higher than those of epithelioid cells. GLUT-1 protein was strongly expressed in sarcomatoid but not in epithelioid tumor. We observed a high percentage of Ki-67-positive cells in both epithelioid and sarcomatoid tumors. CONCLUSIONS: We established nude mouse models of epithelioid and sarcomatoid subtypes of mesothelioma. PET tracers applicable for the evaluation of epithelioid and sarcomatoid mesothelioma would vary: [(18)F]FLT and [(11)C]S-dThd seemed suitable for the epithelioid subtype and [(18)F]FDG seemed suitable for the sarcomatoid subtype in our mouse models. Our results indicated that cellular uptake and TK(1) activity in vitro are not always consistent with tracer uptake of [(18)F]FLT and [(11)C]S-dThd in vivo. These mouse models and PET imaging might be useful tools for evaluating new and effective treatments in mesothelioma.