Richard S. Murant

Increased efficacy of photodynamic therapy of R3230AC mammary adenocarcinoma by intratumoral injection of Photofrin II.

Photodynamic therapy consists of the systemic administration of a derivative of haematoporphyrin (Photofrin II) followed 24-72 h later by exposure of malignant lesions to photoradiation. We investigated the efficacy of this treatment after direct intratumoral injection of Photofrin II. This direct treatment regimen resulted in higher rates of inhibition of mitochondrial cytochrome c oxidase (5.13% J-1 cm-2 x 10(-1) and succinate dehydrogenase (3.14% J-1 cm-2 x 10(-1] in vitro at 2 h after intratumoral injection compared to rates of inhibition obtained after intraperitoneal drug administration: 0.51 and 0.42% J-1 cm-2 x 10(-1), respectively. A significant delay in tumour growth in vivo was observed in animals that received intratumoral injections 2 h before photoradiation compared to animals injected intraperitoneally at either 2 or 24 h before photoradiation. The treatment protocols were compared with control groups, consisting of Photofrin II administration intratumorally or intraperitoneally without photoradiation, or photoradiation in the absence of Photofrin II. These data indicate that the intratumoral injection regimen with Photofrin II enhanced the efficacy of photodynamic therapy. The greater delay in tumour growth observed after intratumoral administration of Photofrin II suggests a mechanism favouring direct cell damage.

PHOTOSENSITIZING EFFECTS OF HEMATOPORPHYRIN DERIVATIVE IMMOBILIZED ON SEPHAROSE

Abstract— The cytotoxicity that ensues following photosensitization by hematoporphyrin derivative (Hpd) is attributed to production of singlet oxygen. Many of the cellular end points reported to be affected are localized to membranes, hydrophobic environments conducive to partitioning of hydrophobic porphyrins in Hpd. In order to test the hypothesis that efficacy of Hpd‐induced photosensitization is enhanced by its ability to freely enter cells or subcellular organelles, we immobilized Hpd on a sepharose support. This immobilized reagent was found to produce 1O2 when photoradiated, in yields similar to those observed for Hpd in solution, as evidenced by the bleaching of p‐nitrosodimethylaniline in the presence of imidazole. The immobilized Hpd was capable of photosensitizing, i.e. inhibit, cytochrome c oxidase activity in intact mitochondrial membranes and in aqueous solution. However, enzymes located on the interior of mitochondrial membranes (F0F1 ATP synthase and succinate dehydrogenase), in the mitochondrial matrix (malate dehydrogenase), or on the inside of the plasma membrane, (Na++ K+)‐ ATPase, were unaffected by immobilized Hpd plus photoradiation compared to free Hpd. The results suggest that photosensitization by Hpd most likely arises from entry of the photosensitizer into the biological membrane, although proteins on the exterior membrane surface may be susceptible to damage by 1O2 produced in proximity to their location.

Mitochondria In Cancer Cells As Targets Of Photodynamic Therapy

Encouraging results are being reported in treatment of cancer by photodynamic therapy, consisting of the administration of hematoporphyrin photosensitizers and subsequent illumination of the neoplastic lesion with visible light. Studies in our laboratory have peen directed towards defining cellular sites of action of these photosensitizers. Results obtained using a rodent mammary carcinoma in vitro and in vivo indicate that an important target of tumor photosensitization is the mitochondrion, effects that are manifested by inhibition of enzymes involved in electron transport and oxidative phosphorylation. These events in turn lead to a significant reduction in cellular ATP, which we suggest represents an early and important mechanism that contributes to the ensuing tumor cytotoxicity. Optimization of this mechanism could provide improved efficacy of treatment.