Abstract
Plasmid DNA has been efficiently photocleaved by pheophorbides (Phdes) a and b. Phde b has photocleaved DNA more effectively than Phde a either in the presence or the absence of oxygen.
Photocleavage efficiency of Phde b in the presence of oxygen is higher than in the absence of oxygen, 100% and 40%, respectively. In contrast, the efficiency of Phde a in the presence of oxygen is lower than in the absence of oxygen, 15% and 25%.
Singlet oxygen production by Phdes a and b can not be observed in the aqueous medium used here (1mM Tris-HCl, 0.1 mM EDTA, pH8), although Phde a has shown the high quantum yields for singlet oxygen production in methanol (0.61) and toluene (0.85). Thus the increase of photocleavage by Phde b in the presence of oxygen is not due to the formation of singlet oxygen.
Fluorescence microscopic observation has demonstrated a rapid incorporation of pheophorbide a into nuclei, mitochondria and lysosome of human oral mucosa cells.
These results strongly indicate the possibility of DNA scission by Phde in photodynamic therapy, and higher therapeutic effect can be expected by use of Phde b in place of Phde a.
