Improvement of Photodynamic Activity by a Stable System Consisting of a C₆₀ Derivative and Photoantenna in Liposomes

Abstract

A dyad system comprising a lipid membrane-incorporated fullerene derivative with an <i>N</i>,<i>N</i>-dimethylpyrrodinium group (C₆₀-<b>1</b>) and a photoantenna molecule (DiD) did not exhibit the high photodynamic activity expected based on its singlet oxygen generation ability. Comparison with a fullerene derivative with an amide substituent (C₆₀-<b>2</b>) suggested the cause to be that some of the fullerene derivative had been released from the liposomes, partly disrupting the dyad system. The dyad system of C₆₀-<b>2</b> and DiD exhibited about twice the photodynamic activity toward HeLa cells as that of C₆₀-<b>1</b> and DiD, due to the suppression of the release of the fullerene derivative from the liposomes. The hydrophobicity/hydrophilicity balance of the substituent in fullerene derivatives was shown to be very important to obtain a dyad system in liposomes characterized by high photodynamic activity.