Photophysical properties of sinoporphyrin sodium and explanation of its high photo-activity

Sinoporphyrin sodium (DVDMS) is a novel photosensitizer with high photodynamic therapy (PDT) effect. Reasons for its high photo-activity were investigated according to the study of photophysical characteristics of DVDMS. Extinction coefficients (ϵ) of DVDMS at 405 nm and 630 nm are 4.36 × 10⁵ and 1.84 × 10⁴ M^-1.cm^-1; fluorescence quantum yield (Φ_F) is 0.026; quantum yield of lowest triplet state formation is 0.94 and singlet oxygen quantum yield (Φ_δ) is 0.92. Although Φ_δ of DVDMS is only 10% higher than that of Photofrin^® (0.83), the extinction coefficient of DVDMS at 630 nm is 10-fold greater than that of Photofrin^®. This leads to its higher singlet oxygen generation efficiency (μ Φ_δ). The higher μ Φ_δ of DVDMS can result in an effective reduction of dosage (1/10 of Photofrin^®) reaching the same cytotoxic effect as Photofrin^®. Even though Φ_F is approximately equal to that of Photofrin^®, brightness (μ Φ_F) of DVDMS is 10-fold greater than that of Photofrin^® because of the 10-fold greater extinction coefficient. Thus, fluorescence diagnosis ability of 0.2 mg/kg DVDMS is comparable to that of 2 mg/kg Photofrin^® used in PDT. Overall, the 10-fold greater extinction coefficients are responsible for the high brightness and singlet oxygen generation efficiency of DVDMS.