The topic of porphyrin photosensitization was reviewed in this Journal three years ago (Amagasa, 1981) as part of a commentary on photodynamic dye action. During the intervening years, a substantial amount of new literature has appeared. This review will provide some background material and summarize reports on the topic published in 1982 and 1983. More detailed papers on the general topic of photosensitization have recently been published by Spikes (1982. 1983) and by Ito (1983).

HEMATOPORPHYRIN and HPD: PHOTOPHYSICS, PHOTOCHEMISTRY and PHOTOTHERAPY

Photodynamic therapy involves light-induced destruction of tumors containing a photosensitizer such as hematoporphyrin derivative. We conducted a collaborative study to evaluate the efficacy of this form of therapy in treating superficial transitional-cell carcinoma of the bladder. Thirty-seven patients were evaluated and 20 were selected for treatment. A total of 50 papillary tumors and 3 areas of carcinoma in situ were treated. All except two tumors were smaller than 2.5 cm. Assessments for treatment response and toxicity were carried out three months after treatment. The initial diagnosis of one patient was revised after the biopsy material was reviewed, and this patient was not included in the analysis. Complete eradication of all tumors was observed in 9 of 19 patients (47 percent), including those with carcinoma in situ. In the remaining 10 of these 19 patients, 13 tumors could not be eradicated (the overall eradication rate was 37 of 50 tumors [74 percent]), but 9 of the 10 patients had a ...

Photodynamic therapy with hematoporphyrin derivative in the treatment of superficial transitional-cell carcinoma of the bladder.

The incorporation of proto-, uro- and hematoporphyrin in low density lipoproteins (LDL) of human blood has been studied by equilibrium dialysis, fluorescence and absorption spectroscopy. The lipoproteins may efficiently compete with albumin in the binding of protoporphyrin to human blood proteins in patients suffering from protoporphyria. It can be concluded that hydrophobic porphyrins bind to blood proteins.



The complexation of hydrophobic porphyrins in LDL is responsible not only for efficient photodynamic effect at the lipoprotein level, but also for photoinduced lipid peroxidation and for consumption of β-carotene incorporated into LDL which are one of their natural carriers. The water-soluble uroporphyrin, although an efficient photosensitizer for the LDL apoprotein photoinactivation, is much less efficient for lipid peroxidation and β-carotene bleaching. The 353 nm laser flash photolysis shows that porphyrin triplet states are not affected by the physiological β-carotene content of LDL but are fully accessible to oxygen.

Interaction of human serum low density lipoproteins with porphyrins: a spectroscopic and photochemical study

(1986). The Photochemistry of Haematoporphyrin and Related Systems. International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine: Vol. 50, No. 3, pp. 421-452.

The photochemistry of haematoporphyrin and related systems.

The effects of various scavengers of reactive oxygen and/or radical species on cell survival in vitro of EMT6 and CHO cells following photodynamic therapy (PDT) or gamma irradiation were compared. None of the agents used exhibited major direct cytotoxicity. Likewise, none interfered with cellular porphyrin uptake, and none except tryptophan altered singlet oxygen production during porphyrin illumination. The radioprotector cysteamine (MEA) was equally effective in reducing cell damage in both modalities. In part, this protection seems to have been induced by oxygen consumption in the system due to MEA autoxidation under formation of H2O2. The addition of catalase, which prevents H2O2 buildup, reduced the effect of MEA to the same extent in both treatments. Whether the remaining protection was due to MEA's radical-reducing action or some remaining oxygen limitation is unclear. The protective action of MEA was not mediated by a doubling of cellular glutathione levels, since addition of buthionine sulfoximine, which prevented glutathione increase, did not diminish the observed MEA protection. The hydroxyl radical scavenger mannitol also afforded protection in both kinds of treatment, but it was approximately twice as effective in gamma irradiation as in PDT. This is consistent with the predominant role of OH radicals in ionizing radiation damage and their presumed minor involvement in PDT damage. Superoxide dismutase, a scavenger of O2, acted as a radiation protector but was not significantly effective in PDT. Catalase, which scavenges H2O2, was ineffective in both modalities. Tryptophan, an efficient singlet oxygen scavenger, reduced cell death through PDT by several orders of magnitude while being totally ineffective in gamma irradiation. These data reaffirm the predominant role of 1O2 in the photodynamic cell killing but also indicate some involvement of free radical species.

Effects of scavengers of reactive oxygen and radical species on cell survival following photodynamic treatment in vitro: comparison to ionizing radiation.

— Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin, and three 0-acyl compounds derived from it (the monoacetate, the diacetate and the disuccinate).



After 347 nm irradiation in water containing 2% Triton X-100, haematoporphyrin forms the triplet state (φT= 0.92) and photoionises monophotonically (φI= 0.03). For the O-acyl derivatives, φT approaches unity and photoionisation is reduced. In acetone the triplet yield of all four compounds are close to unity. The difference and corrected spectra for the triplet species are presented and decay rates (k1˜104s-1) and oxygen quenching constants (kQ˜1.5times109M-1s-1) for the triplet state have been measured. The difference and corrected spectra for the semi-reduced species in methanol and semi-oxidised species in aqueous Triton X-100 are presented.



The photophysical characteristics in fluid solution of haematoporphyrin and its 0-acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins.

P. A. Scourides

Papers

The triplet and radical species of haematoporphyrin and some of its derivatives.