Excellent antitumor effects for gastrointestinal cancers using photodynamic therapy with a novel glucose conjugated chlorin e6

Abstract

BackgroundPhotodynamic therapy (PDT) exploits the reaction between photosensitizer and irradiated light to generate potentially therapeutic reactive oxygen species such as singlet oxygen in cancer cells. We have reported several sugar-conjugated chlorins that express stronger antitumor effects in PDT than talaporfin sodium (TS), a second-generation photosensitizer clinically used in Japan. In this study, we developed a novel glucose-conjugated chlorin e6 (G-chlorin e6) and evaluated its antitumor effects. MethodsG-chlorin e6 was synthesized with a core photosensitizer chlorin e6 conjugated to glucose. We measured the half maximal inhibitory concentration (IC50) to compare the PDT effects of G-chlorin e6 and TS, and flow cytometry was performed to examine the accumulation of G-chlorin e6 in cancer cells. We also compared the accumulation of G-chlorin e6 between normal immortalized esophageal epithelial cells and esophageal cancer cells. Antitumor effects of G-chlorin e6 PDT were finally analyzed in allograft tumor mouse models. ResultsPDT in vitro using G-chlorin e6 elicited 9, 000–34,000 times stronger antitumor effects than TS, and there was 70–190 times more G-chlorin e6 accumulated than TS by flow cytometry. G-chlorin e6 accumulated more selectively in esophageal cancer cells than in esophageal immortalized epithelial cells, and in an allograft model, PDT with G-chlorin e6 showed very strong antitumor effects and a 40% complete response (CR) rate. ConclusionsG-chlorin e6 showed excellent tumor selectivity, and PDT using G-chlorin e6 revealed the strongest anti-tumor effects among all sugar-conjugated chlorins that we have studied. G-chlorin e6 is considered to be the best photosensitizer for next-generation PDT.