APPLICATION OF LONG-CIRCULATING LIPOSOMES TO CANCER PHOTODYNAMIC THERAPY

Photodynamic therapy (PDT) as a cancer treatment is notable for its qu ite low side effects in comparison with those of chemotherapy and radi otherapy. However, the accumulation of porphyrin derivatives used in P DT into tumor tissues is rather low. Since long-circulating liposomes are known to accumulate passively into tumor tissues, we liposomalized a porphyrin derivative, benzoporphyrin derivative monoacid ring A (BP D-MA), and used these liposomes to investigate the usefulness of PDT f or tumor-bearing mice. BPD-MA was liposomalized into glucuronate-modif ied liposomes, which are known to be long-circulating. These liposomes were injected i.v. into Balb/c mice bearing Meth A sarcoma, and tumor regression and survival time were monitored after irradiation with la ser light. Tumor regression and complete curing of tumor (80% cure rat e by the treatment with 6 mg/kg BPD-R?IA) were observed when long circ ulating liposomalized BPD-MA was injected and laser-irradiated. In con trast, only a 20% cure rate was obtained when the animals were treated with BPD-MA solution or BPD-MA entrapped in conventional liposomes. T hese results suggest that a long-circulating liposomal formulation of photo-sensitive agents is useful for PDT.