Distribution of endogenous and injected porphyrins at the subcellular level in rat hepatocytes and in ascites hepatoma

Intracellular localization of photosensitizers

The intracellular localization of photosensitizers can be studied by different methods. One method involves homogenization of the cells followed by differential ultracentrifugation which leads to fractions enriched in nuclear, mitochondrial, and microsomal material as well as a supernatant fraction. More detailed information can be obtained by electron microscopy of cells exposed to light in the presence of photosensitizers. This method is based on the assumption that damage is primarily induced at intracellular sites where the concentration of photosensitizer is high. By irradiating the cells at 6 degrees C, where biochemical reactions are slow, and then incubating them for different times at 37 degrees C, it is possible to follow the development of damage. The amount of photosensitized damage to enzymes or cell functions whose localization in the cells is known gives information about the intracellular localization of the sensitizer. Fluorescence microscopy is the most direct method and is widely applicable because most photosensitizers fluoresce. Lipophilic dyes generally localize in membrane structures. In future more attention should be paid to the localization of dyes in lysosomes, as suggested by early reports. Mitochondria, the endoplasmic reticulum and nuclear membrane are other important loci for intracellular localization of sensitizers.

Targeted intracellular delivery of photosensitizers to enhance photodynamic efficiency

Photodynamic therapy (PDT) is a novel treatment, used mainly for anticancer therapy, that depends on the retention of photosensitizers (PS) in tumour cells and irradiation of the tumour with appropriate wavelength light. Photosensitizers are molecules such as porphyrins and chlorins that, on photoactivation, effect strongly localized oxidative damage within target cells. The PS used for PDT localize in various cytoplasmic membranous structures, but are not found in the most vulnerable intracellular sites for reactive oxygen species, such as the cell nucleus. The experimental approaches discussed in the present paper indicate that it is possible to design highly efficient molecular constructs, PS carriers, with specific modules conferring cell-specific targeting, internalization, escape from intracellular vesicles and targeting to the most vulnerable intracellular compartments, such as the nucleus. Nuclear targeting of these PS-carrying constructs results in enhanced photodynamic activity, maximally about 2500-fold that of free PS. Future work is intended to optimize this approach to the point at which tumour cells can be killed rapidly and efficiently, while minimizing normal cell and tissue damage.

Measurement of the rate of uptake and subcellular localization of porphyrins in cells using fluorescence digital imaging microscopy

A fluorescence imaging system incorporating a cooled slow-scan charge-coupled device camera was used to study the rate of uptake and subcellular localization of prophyrins in living cells. Measurements were carried out on human dermal fibroblasts (D532) using two different prophyrins meso-tetra(4-N-methylpyridyl)porphine (TMPP) and meso-tetra(4-N-hexylpyridyl)porphine (THPP). It was observed that TMPP was rapidly taken up by cells and principally located in the nucleus. The THPP, on the other hand, internalized more slowly and exhibited a particulate distribution in the cytoplasm.

Cellular responses to hematoporphyrin-induced photooxidative damage in Fanconi anemia, xeroderma pigmentosum and normal human fibroblasts

Several observations reported in the literature suggest that singlet oxygen (1O2) might play a role in the clastogenic process in Fanconi anemia (FA) cells, and that the antioxidant status of xeroderma pigmentosum (XP) may also be altered. In order to test the ability of FA and XP cells, relative to normal cells, to cope with 1O2 damage, the effects of photosensitization by hematoporphyrin (HP) have been determined (i) on host cell reactivation (HCR) of damaged infecting herpes simplex virus (HSV) or transfecting SV40 DNA, and (ii) on DNA template capability and clonogenicity of treated cells. Results showed no significant difference among the three types of cells, either for the survival of HP-photosensitized HSV, or for the yields of SV40 virus following transfection of cultures with damaged viral DNA. The treatment of cells with HP plus 365-nm light leads to a dose-dependent, homothetic reduction of 18S and 28S ribosomal RNA (rRNA) synthesis, presumably through a mechanism other than the formation of transcription termination sites. After a 24-h post-exposure incubation, the rate of rRNA synthesis was restored to higher than normal levels in all cell lines. Finally, two FA cell lines showed a higher survival to HP photosensitization than two normal cell lines. Another FA cell line and XP-A and XP-C cells were in the range of sensitivity of the two normal strains for this treatment. These results indicate that FA cells possess an antioxidant defense system at least as efficient as that of normal cells for processing 1O2-induced damage.

Subcellular localization of hematoporphyrin derivative in bladder tumor cells in culture

Mitochondria have been implicated as a primary subcellular site of porphyrin localization and photodestruction. However, other organelles including the cell membrane, lysosomes and nucleus have been shown to be damaged by hematoporphyrin derivative (HpD) photosensitized destruction as well. In this study we attempted to follow the translocation of the fluorescent components of HpD in human bladder tumor cells (MGH-U1) in culture to determine whether specific subcellular localization occurs over time. Following a 30 min exposure to HpD the cellular fluorescence was examined immediately and 1, 2, 4, and 24 h after HpD removal using fluorescence microscopy and an interactive laser cytometer. The in vitro translocation of dye appeared to be fairly rapid with fluorescence present at the cell membrane and later (1-2 h) within a perinuclear area of the cytoplasm. To determine whether HpD had become concentrated into a specific subcellular organelle, these fluorescence distribution patterns were compared with fluorescent marker dyes specific for mitochondria, endoplasmic reticulum and other membranous organelles. The HpD fluorescence did not appear to be as discrete as the dyes specific for mitochondria or endoplasmic reticulum but appeared similar to the diffuse cytomembrane stain. Finally, the interaction between the fluorescent components of HpD and the cellular constituents was evaluated using a "fluorescence redistribution after photobleaching" technique. The results indicated that the mean lateral diffusion for HpD in MGH-U1 cells was 1.05 x 10(-8) cm2/s, a rate closer to that of lipid diffusion (10(-8)) than that of protein diffusion (10(-10)).(ABSTRACT TRUNCATED AT 250 WORDS)

Cytotoxic effects and physicochemical properties of marycin: a new hematoporphyrin derivative

This paper reports some physico-chemical properties and cytotoxic activity of marycin, a new hematoporphyrin derivative. The data show that marycin is a new compound, different from the other porphyrins tested. This product appears to be pure by adsorption or reversed phase thin-layer chromatography and high performance liquid chromatography and has chromatographic behavior different from those of other porphyrins tested. It does not appear to link to some tested metals and has a UV-visible absorbance spectrum different from that of a hematoporphyrin methylester. Furthermore, marycin has cytotoxic activity against K-562, ZR-75, MCF-7, HT-29, LOVO, human tumor cell lines and the MRC-9 human lung embryonic cell line. The new radiometric assay was used for all cell lines. Marycin decreases the growth index, measured by the radiometric assay as 14CO2 production. The cytotoxic activity is dose-dependent. Marycin is active at low doses but the activity varies with the cell line studied. The compound has low toxicity on the normal cell line MRC-9. Marycin is very liposoluble and would be expected to have high affinity and toxicity for tumors. The compound is active without light activation. How marcyin acts is still a matter for speculation.

Photosensitization of mammalian cells by psoralens and porphyrins

Because of the ability of photosensitizers to induce specific photochemical reactions in vivo, leading to cell injury and death, many such molecules have been considered as therapeutic agents. Among them two classes of sensitizers, i.e. furocoumarins (psoralens) and porphyrins, are currently used for the photochemotherapy of various skin diseases and malignant lesions. Different types of cell responses can result according to the intracellular localization of the photosensitizer and to the nature of the photochemistry induced by the chromophore which absorbs photons. In this review, the cytological aspects of photosensitization by psoralens and porphyrins will be discussed.

Enhancement of Hematoporphyrin Derivative Uptake in Vitro and in Vivo by Tumor Cells in the Presence of Lanthanum

Hematoporphyrin derivative is currently used as a photochemotherapeutic agent in the treatment of neoplasms. The uptake of hematoporphyrin derivative was determined in vitro and as a function of time with Ehrlich ascites cells in the presence of lanthanum and in vivo with VFM1 tumor-bearing mice pretreated by intratumoral injection of LaCl3. Our results indicate that the treatment with lanthanum increases the uptake of hematoporphyrin derivative by tumor cells.

Differential interaction of porphyrins used in photoradiation therapy with ferrochelatase

The mechanism of porphyrin accumulation by tumours is not yet established. If metabolism aids porphyrin elimination, tumours, unlike normal tissues, may not metabolize porphyrins used clinically, such as proto-, haemato-, OO'-diacetyl-haemato- and monohydroxyethyl-monovinyl-deutero-porphyrin. Proto-, haemato- and monohydroxyethyl-monovinyl-deutero-porphyrin are substrates for the mitochondrial enzyme ferrochelatase (EC 4.99.1.1), which can form haem analogues from exogenous porphyrins. The Km values for proto-, haemato- and monohydroxyethyl-monovinyl-deutero-porphyrin are 11, 22 and 23 microM respectively. However, OO'-diacetyl-haematoporphyrin is an effective competitive inhibitor with Ki of 11 microM. Hepatic ferrochelatase specific activity is 5.9 and 5.5 nmol of haem/h per mg of protein respectively in normal Buffalo rat and in those bearing the extrahepatic Morris 7288C hepatoma, and is only 0.13 nmol/h per mg in the hepatomas. Therefore low ferrochelatase activity in cancerous cells may provide one means whereby some porphyrins accumulate in tumours, and the ability of certain porphyrins to act as ferrochelatase inhibitors may provide another.

Cell biology of hematoporphyrin derivative (HPD)

Tissue culture cells were treated with hematoporphyrin derivative (HPD) and analyzed for (1) HPD uptake, (2) HPD washout, and (3) fluorescence changes. The absorption peaks were the same for HPD in solution and HPD bound to cells. HPD was taken up by all cell types rapidly within the first 10 hours of exposure, and leveled off by 20 hours of exposure. HPD came out of all cell types to control levels by 72 hours after removal of the HPD bathing solution. The HPD appeared to come out of the malignant 3-T-12 cells more slowly than from the parental (non-malignant) 3-T-3 cells. The fluorescence spectrum of HPD-treated cells changed markedly from the time that the bathing HPD solution was removed from the cells. As time progressed the weakly fluorescent 590-nm peak increased greatly and the 615-nm and 630-nm peaks decreased significantly.

Effect of hematoporphyrin and red light on AH-130 solid tumors in rats

Thirty Wistar albino rats with a subcutaneous Yoshida hepatoma AH-130 were exposed to 590 to 690 nm light from a high pressure Xenon arc-lamp 24 h after intraperitoneal injection of hematoporphyrin, 5 to 10 mg/kg. In all cases, the tumor decreased rapidly in size, due to necrosis caused both by direct action of the photoactivated porphyrin on the tumor cells and by secondary effects on blood vessels. No injury of normal tissues was detected. At 2 months after phototreatment, no recurrence had occurred and the skin over the tumor area was healed. Favourable therapeutic response was obtained in preliminary experiments by irradiating the Hp-injected tumor-bearing rats with 632.8 nm-light from an He/Ne laser source.

Time-resolved fluorescence microscopy of hematoporphyrin-derivative in cells

This work presents measurements of time-resolved fluorescence microscopy of hematoporphyrin-derivative (HpD) in single cells of mice tissue (both tumor and normal cells), in HeLa Cells, and in solution. The measurements were performed using a pulsed-laser microfluorometer with high spatial and temporal resolution. In agreement with the results obtained with other techniques, it has been found that the tumor cells examined present an HpD uptake about five times higher than that of the normal cells of the corresponding tissue and that, within a cell, HpD become localized mainly in the cytoplasm. It has also been found that the fluorescence decay time is different in cells as compared with solution, and that the presence of HpD stabilizes cell auto-fluorescence. These results are discussed.