Mechanisms in photodynamic therapy: part one—-photosensitizers, photochemistry and cellular localization

Cremophor EL: the drawbacks and advantages of vehicle selection for drug formulation.

Basic principles of photodynamic therapy

The tissue photosensitizer protoporphyrin IX (PpIX) is an immediate precursor of heme in the biosynthetic pathway for heme. In certain types of cells and tissues, the rate of synthesis of PpIX is determined by the rate of synthesis of 5-aminolevulinic acid (ALA), which in turn is regulated via a feedback control mechanism governed by the concentration of free heme. The presence of exogenous ALA bypasses the feedback control, and thus may induce the intracellular accumulation of photosensitizing concentrations of PpIX. However, this occurs only in certain types of cells and tissues. The resulting tissue-specific photosensitization provides a basis for using ALA-induced PpIX for photodynamic therapy. The topical application of ALA to certain malignant and non-malignant lesions of the skin can induce a clinically useful degree of lesion-specific photosensitization. Superficial basal cell carcinomas showed a complete response rate of approximately 79% following a single exposure to light. Recent preclinical studies in experimental animals and human volunteers indicate that ALA can induce a localized tissue-specific photosensitization if administered by intradermal injection. A generalized but still quite tissue-specific photosensitization may be induced if ALA is administered by either subcutaneous or intraperitoneal injection or by mouth. This opens the possibility of using ALA-induced PpIX to treat tumors that are too thick or that lie too deep to be accessible to either topical or locally injected ALA.

Endogenous protoporphyrin IX, a clinically useful photosensitizer for photodynamic therapy.

Paclitaxel and its formulations.

By means of a chemical extraction procedure and confocal laser scanning microscopy, we investigated the kinetic patterns of uptake and biolocalization of 5-aminolevulinic acid (ALA)-induced porphyrins in s.c. transplanted tumors, adjacent normal skin and muscle, and liver of mice bearing mammary carcinoma, after i.p. injection of 250 mg/kg ALA or topical application of ALA (20% in an oil-in-water emulsion). Furthermore, we evaluated the tumor responses after either i.p. injection or topical application of 5-ALA followed by laser irradiation (632 nm, 150 mW/cm2, 25 min) by measuring the treated tumor regression/regrowth time and by light and electron microscopy. Strong fluorescence of ALA-induced porphyrins was detected in the tumor, skin and liver tissues, while little fluorescence was seen in the adjacent muscle tissue. Moreover, the highest amounts of ALA-induced porphyrins in the tumor and skin tissues were found 1 hr after i.p. injection, whereas the amounts of the porphyrins in both tissues increased with increasing time after topical application of ALA. The fluorescence of the porphyrins was localized in several components of the skin tissue (epidermis, hair follicles and their associated sebaceous glands). Furthermore, the fluorescence was diffusely distributed in the s.c. transplanted tumor tissue. Little could be observed under a confocal laser scan microscope (CLSM) in the muscle tissue. The uptake and biolocalization data correlate well with the results of PCT efficiency of the same tumor model with ALA-induced porphyrins. Light and electron microscopy showed that the mitochondria of the tumor cells and of the endothelial cells and the basal lamina of vascular walls beneath the endothelium in the tumor tissue were initially extensively destroyed after PCT with ALA-induced porphyrins. Thereafter, diffuse degeneration followed by local and/or diffuse severe necrosis of the tumor cells was found. This may be due mainly to the initial damage to mitochondria in the cancerous and endothelial cells and also to the destruction of the vascular wall in the tumor tissue. © 1992 Wiley-Liss, Inc.

Distribution and photosensitizing efficiency of porphyrins induced by application of exogenous 5-aminolevulinic acid in mice bearing mammary carcinoma.

The History, Classification, and Incidence of the Porphyrias.- Porphyrins and Enzymes of the Heme Biosynthetic Pathway.- The Acute Porphyrias.- Pathogenesis of the Neuropathy of Acute Porphyria.- Drugs, Chemicals, and Porphyria.- The Photochemistry, Photobiology, and Phototherapeutic Use of Porphyrins.- Cutaneous Hepatic Porphyria.- Erythropoietic Protoporphyria.- Congenital Porphyria.- Porphyrins in Diseases Other than the Porphyrias.- Porphyria in Animals.- Perspective.- References.

Disorders of Porphyrin Metabolism

Diseases of porphyrin metabolism

A comparison of different photosensitizing dyes with respect to uptake C3H-tumors and tissues of mice.

1. Coproporphyrinogenase has been prepared from rat-liver mitochondria and its properties have been studied. The isoelectric point was found to be around pH5·0 and the molecular weight to be 80000±8000. The pH optimum of the enzymic reaction was 7·4 and the apparent Km was of the order 0·03mm. The enzyme was destroyed by boiling and irreversible inactivation occurred below pH3·5. It could be stored at −10° without loss of activity. The enzyme acts specifically on coproporphyrinogen III and does not form protoporphyrinogen from trans-2,4-diacrylicdeuteroporphyrin or its porphyrinogen. It was unaffected by prolonged dialysis and no cofactor requirement could be demonstrated. 2. Column chromatography of a partially purified enzyme preparation on Sephadex G-200 was found to be an improved method of purification, which gave a coproporphyrinogenase 58-fold purified. The purified enzyme was studied electrophoretically but no evidence was obtained to suggest that more than one enzyme was involved in the reaction. 3. The action was studied of various compounds added to the system. The presence of monothiol groups in the enzyme system was indicated, whereas vicinal dithiol groups were not involved in the reaction. Metal-chelating agents did not inhibit the reaction and no requirement for the presence of any essential metal has been found. All attempts to demonstrate the presence of a prosthetic group, in particular flavines, failed. Neither pyridoxal phosphate nor ATP was involved in the reaction, nor was a mitochondrial electron-transport chain required for the activity of the enzyme. Some circumstantial evidence was obtained to suggest that cis-2,4-diacrylicdeuteroporphyrin is an intermediate in the reaction.

/pdf/purification-and-properties-of-coproporphyrinogenase-4eijspzt31.pdf

Claude Rimington

Papers

Distribution and photosensitizing efficiency of porphyrins induced by application of exogenous 5-aminolevulinic acid in mice bearing mammary carcinoma.

Disorders of Porphyrin Metabolism

Diseases of porphyrin metabolism

A comparison of different photosensitizing dyes with respect to uptake C3H-tumors and tissues of mice.

Purification and properties of coproporphyrinogenase.