Photodynamic action of hypocrellin dyes: structure¯activity relationships

Hypocrellin and its derivatives were compared for their photodynamic effects on human oral cavity epithelial carcinoma KB cell line. The amphiphilicity as well as the singlet oxygen generating quantum yield of the hypocrellin dyes affected their photodynamic activity. The most hydrophilic dyes exhibited the lowest phototoxic activity, whereas the hydrophobic and amphiphilic dyes with higher singlet oxygen-generating quantum yield, exhibited high photodynamic activity. Cysteamine mono- and di-substituted hypocrellin B and cysteine mono-substituted hypocrellin B, demonstrating strong red absorption in the domain of phototherapeutic window (600¯900 nm), proper hydrophobic and amphiphilic properties and high photocytotoxicity to KB cells, might prove to be potential phototherapeutic agents.