Photochemical OFF/ON Cytotoxicity Switching by Using a Photochromic Surfactant with Visible Light Irradiation

Photochemical switching of cytotoxicity by using spiropyran compounds with pyridinium and alkyl groups was investigated. The spiropyran compound, SP6, with a hexyl group as the alkyl group displayed negative photochromism, in which the hydrophilic open merocyanine form (MC form) was stable and isomerized to the hydrophobic closed spiro form (SP form) by visible light irradiation. Both MC and SP forms exhibited amphiphilicity because of the hydrophobic hexyl and hydrophilic pyridinium groups introduced. Cytotoxicity toward HeLa cells was observed for both MC and SP forms of SP6 at concentrations higher than the critical aggregation concentration of the isomers CACMC and CACSP (CACMC > CACSP), respectively. In contrast, cytotoxicity by SP6 was activated by visible light irradiation at concentrations between CACMC and CACSP; thus, photochemical switching of cytotoxicity from the OFF to ON state was achieved. Cytotoxicity was revealed to be caused by disruption of the cell membrane. The results provide an important step in developing novel nextgeneration photochemotherapy drugs.

Automated summary

This study investigated the photochemical switching of cytotoxicity by using spiropyran compounds with pyridinium and alkyl groups. The results showed that the two isomers of SP6 (MC and SP) displayed different cytotoxicity under visible light irradiation at different concentrations, achieving the photochemical switching of cytotoxicity. These findings are important for the development of novel photochemotherapy drugs.