EHPnet: Doing a World of Good

The uptake, retention and effects of aluminium chloro sulphonated phthalocyanine (AlSPc) were measured in two cell lines, UV-2237 a murine fibrosarcoma and the non-tumorigenic NIH/3T3 fibroblast line. The behaviour of cells treated with AlSPc was compared with that of those treated with haematoporphyrin derivative (HpD), a photosensitizer often used in photodynamic therapy (PDT) of cancer. AlSPc absorbs light strongly in the red region, is taken up by cells in a dose dependent fashion and is retained in vitro over a period of days (5 days after exposure >40% remains cell-associated versus <25% of HpD). Additionally AlSPc was less cytotoxic to cells, maintained in darkness or exposed to room light, compared to HpD (100% viability versus 0% viability 3 days after 60min exposure to room light). However red light (-600-700nm) caused greater toxicity in AlSPc-treated cells (100%) than in similarly exposed HpD-treated cells (<60%). No significant differences were detected between the responses of the fibrosarcoma and the fibroblast cell lines. These characteristics of AlSPc suggest that it may prove to be a useful photosensitizer for PDT of cancer and this possibility is discussed. Photodynamic therapy (PDT) of cancer is a relatively new technique that has been used clinically for the treatment of a variety of neoplasms. The basis of the technique is the systemic administration of photosensitizing dyes which localize to, or are retained preferentially by, the neoplastic lesion; the tumour is then exposed to light of the appropriate wavelength which photo-activates the dye leading to the generation of cyto-toxic products. Selectivity of effect is a consequence of both the preferential accumulation of the dye and the accuracy of light delivery. At the present time the photosensitizer of choice in PDT is haematoporphyrin derivative (HpD) which shows preferential tumour localizing ability in a wide variety of human tumours (Lipson et al. The tumoricidal effect of HpD following light exposure is generally attributed to the formation of singlet oxygen generated by the transfer of energy from the excited HpD to tissue oxygen (Weishaupt et al., 1976; Moan et al., 1979). While the reasons for the preferential accumulation of HpD in neoplastic tissue, and even the exact basis of its anti-tumour effects, remain to be elucidated it has been used in the treatment of has many characteristics which make it less than an ideal photosensitizer. HpD is formed by the treatment of haematoporphyrin with a mixture of acetic and sulphuric acid (Lipson et …