Singlet oxygen-producing activity and photodynamic biological effects of acridine compounds.

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Abstract
The singlet oxygen-producing activities and photodynamic biological activities of acridine compounds were compared. Singlet oxygen was trapped by 2,2,6,6-tetramethyl-4-piperidone (TEMP), and 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (TEMPO) produced was detected by electron spin resonance (ESR) spectrometry. TEMPO production was inhibited by NaN3 and enhanced in D2O, confirming it to be an adequate ESR spectroscopic indicator for singlet oxygen. Comparison of TEMPO-producing activities revealed that acriflavine and proflavine, which are the most potent photosensitizers both in cell inactivation and petite induction of yeast [Saccharomyces cerevisiae], produced the most intense and long-lived ESR signals. However there was no clear difference of TEMPO-producing activity between biologically ineffective acridines such as acridine and quinacrine and effective ones such as acridine yellow and 6,9-diamino-2-ethoxyacridine. These results suggested that the differences observed in the photodynamic biological effects among the acridine compounds depend mainly on the differences of drug distribution and only partly on the differences of singlet oxygen-producing activity of the dye molecule itself.