Localizing and photosensitizing mechanism by tetra(3-hydroxyphenyl)porphin in vivo on human malignant melanoma xenografts in athymic nude mice

Temoporfin (Foscan®, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin)--a second-generation photosensitizer

This review traces the development and study of the second-generation photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin through to its acceptance and clinical use in modern photodynamic (cancer) therapy. The literature has been covered up to early 2011.

Correlation of subcellular and intratumoral photosensitizer localization with ultrastructural features after photodynamic therapy

Photodynamic therapy (PDT) of cancer typically involves systemic administration of tumor-localizing photosensitizers followed 48-72 h later by exposure to light of appropriate wavelengths. Knowledge about the distribution of photosensitizers in tissues is still fragmentary. In particular, little is known as to the detailed localization patterns of photosensitizers in neoplastic and normal tissues as well as the relationship between such patterns and the actual targets for the photosensitizing effect. This review focuses on ultrastructural features seen in treated cells and tumors. An attempt is made to correlate these findings with the subcellular/intratumoral localization pattern of the photosensitizers in tumor cell lines in vitro and in tumor models in vivo. Several subcellular sites are main targets of PDT with different sulfonated aluminum phthalocyanines (AIPcSn) in the human tumor cell line LOX. Nuclei are not among the primary targets. Overall, the ultrastructural changes correlate well with the data about the subcellular localization patterns for each analogue of AIPcSn in the same cell line. Similar findings are also obtained for the family of sulfonated mesotetraphenylporphines (TPPSn) in the NHIK 3025 cell line. The mechanisms involved in the killing of tumors by PDT seem to be a complex interplay between direct and indirect (via vascular damage) effects on neoplastic cells according to the intratumoral localization pattern of the applied dye. Several factors can affect the localization pattern of a drug, such as its chemical character, the mode of drug delivery, the time interval between drug administration and light exposure, and tumor type. Furthermore, whether local immune reactions (such as macrophages) and apoptosis (programmed cell death) are involved in the destruction of neoplastic cells by PDT in vivo is still an enigma. A general model for PDT-induced tumor destruction is suggested.

Structure-activity relationship of porphines for photoinactivation of bacteria

The antibacterial photodynamic effects of uncharged (o-tetrahydroxyphenyl porphine [THPP], m-THPP and p-THPP), cationic (5,10,15,20-tetra[4-N-methylpyridyl]porphine [TMPyP]) and anionic (5,10,15,20-tetra[4-sulfonatophenyl porphine] [TPPS4]) porphines on Staphylococcus aureus and Escherichia coli bacteria inactivation were examined. The results show that uncharged porphines provoked antibacterial photodynamic activity on S. aureus, and also on E. coli in the presence of the membrane-disorganizing peptide polymixin B nonapeptide (PMNP). The TMPyP compound was highly photoactive toward gram-positive bacteria but only marginally effective on gram-negative cells, whereas TPPS4 showed no activity on either gram-positive or gram-negative bacteria. The photoactivity of TMPyP is due to the electrostatic attraction between the positively charged sensitizer molecule and the negatively charged membrane of the gram-positive target cells. For TPPS4, the inactivity toward gram-positive bacteria is due to electrostatic repulsion between the charged sensitizer molecule and the cell membrane. For gram-negative bacteria, the inactivity is conceivably due to preferential (electrostatic) binding to the positively charged PMNP, which is an adjuvant for membrane disorganization, but has no effect on cell viability. For hydrophobic sensitizers, the photoactivity depends on the state of aggregation. The extent of deaggregation of the different THPP isomers was determined by fluorescence measurements of bound sensitizers and could be positively correlated with their photoinactivation capacity. We conclude that the structure-activity relationships of these porphines are affected by their net charge and by aggregation.

Evaluation of a new photosensitizer, meso-tetra-hydroxyphenyl-chlorin, for use in photodynamic therapy: a comparison of its photobiological properties with those of two other photosensitizers

The properties of a new photosensitizer, meso-tetra-hydroxyphenyl-chlorin (mTHPC), were studied using V79 cells (Chinese-hamster lung fibroblasts). Comparisons were made with 2 other photosensitizers: photofrin II (PII) and meso-tetra-hydroxyphenyl-porphyrin (mTHPP). A main advantage of mTHPC is that it has a strong absorption at 652 nm. Maximal cellular uptake of the dye was observed after 24 hr incubation of the cells with the drug. Using a confocal laser-scanning fluorescence microscope, we observed a diffuse distribution of mTHPC in the cytoplasm. Furthermore, the lipophilicity of mTHPC was compared with that of the components of PII by means of high-pressure liquid chromatography (HPLC). Absorption and fluorescence spectroscopy indicated that aggregated as well as monomeric mTHPC was bound to the cells. The action spectrum for photo-inactivation of the cells showed that aggregated mTHPC did not contribute significantly to its photosensitizing effects. In the present cellular system, the efficiency of photodynamic therapy (PDT) with mTHPC (cells were irradiated at a wavelength of 652 nm) was higher than with PII (irradiation at 630 nm) or with mTHPP (648 nm). The quantum yield for photo-inactivation of cells was smaller for mTHPC than for mTHPP and PII. The addition of 1,3-diphenylisobenzofuran (DPBF) reduced cell inactivation during PDT. Thus, PDT with mTHPC seems to act at least partly via a type-II process.

Stereochemical factors in the transport and binding of photosensitizers in biological systems and in photodynamic therapy

The uptake and biological activity of porphyrins and phthalocyanines in tumours were correlated with the geometrical features of the photosensitizer molecules. The data suggest that a critical distance of approximately 1.2 nm between oxygen atoms (originating in SO3-, COO- or OH substituents) characterizes a biologically active photosensitizer for photodynamic therapy. We propose that tubulin, which is available in large amounts during mitosis, is the main receptor molecule which binds these photosensitizers. Basic amino acid residues or tightly bound cations in tubulin or homologous proteins may act as binding sites on the receptor molecule.

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

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.