Study on liposomalization of zinc-coproporphyrin I as a novel drug in photodynamic therapy

Photodynamic therapy (PDT) with a photosensitizer and laser irradiation has been shown to have potential effects in cancer chemotherapy. However, the commercial drug clinically gave many problems due to the poor solubility of the photosensitizer in water and the photosensitivity as an adverse reaction of PDT. We have examined best condition on the liposomalization of Zn-complexed coproporphyrin I (ZnCPI) as novel photosensitizer.The difference of pH in buffer significantly changed the ZnCPI entrapped ratio. The entrapped ratio of ZnCPI in PBS(−) buffer was 10.8 ± 0.3%, whereas, these levels in some lactate buffer (below pH 5.0) increased. The change between the molecular form ⇔ ionic form of ZnCPI was occurred due to the change of the pH of buffer, and the amount of ZnCPI in the liposomal membrane changed. The difference of this level was considered to be contributed by the change of zeta potentials. Next, we examined the effect of the different pH of the buffer in liposomal preparation on the ZnCPI distribution in each tissue after each liposome administration. At 2 and 6 h post-injection of ZnCPI liposome (pH 4.6), the ZnCPI concentration in the plasma of Ehrlich ascites carcinoma bearing mice was shown to be higher compared to that in other groups. The ZnCPI concentrations in the tumor after 2 and 6 h of ZnCPI liposome (pH 4.6) treatment were shown to be higher than that in other groups. In conclusion, it is considered that the ZnCPI liposome (pH 4.6) had the effective antitumor activity with laser irradiation without the adverse reactions.