Hematoporphyrin ethers--I. Generalized synthesis and chemical properties

A Convenient Synthesis of Haematoporphyrin Ester-Ethers under Ultrasound Irradiation

A convenient approach to the synthesis of haematoporphyrin ester-ethers from haemin under ultrasound irradiation has been developed. This method provides several advantages such as shorter reaction time, high yields and environmental friendliness.

The history of PDT in Norway Part one: Identification of basic mechanisms of general PDT

Photodynamic therapy (PDT) is now an established treatment of malignant and premalignant dysplasias. A number of first and second generation photosensitizers have been studied in Norway. The aim has been to improve PDT efficiency and applicability. Many critical details regarding the mechanisms of PDT were elucidated by researchers in Norway. In this review we focus on the most important findings related to these basic mechanisms, such as generation of singlet oxygen, estimations of its lifetime, the oxygen effect itself, the subcellular localization of photosensitizers with different properties, their photodegradation during PDT and their tumour selectivity.

Magnetically responsive photosensitizing reagents for possible use in photoradiation therapy

The ability of a magnetically responsive material to function as a carrier for photosensitizing agents for use in photoradiation therapy (PRT) has been examined in vitro. The photosensitizer has been attached to the magnetically responsive matrix (Dynabeads) by non-specific adsorption, Intralipid-mediated adsorption and poly-L-lysine mediated adsorption. In these studies, it has been demonstrated that conditions of attachment of photosensitizer to the matrix may be adapted in order to facilitate a diffuse or highly localized photo-toxic effect on target cells in vitro. The authors believe that this system may represent a novel approach to targeting photosensitizing agents to specific areas, thereby circumventing some of the problems associated with conventional photoradiation therapy (PRT), particularly in hollow organs.

Photobiological properties of hematoporphyrin diesters: evaluation for possible application in photochemotherapy of cancer

The dimethyl, diethyl, dipropyl, dibutyl, diamyl, dihexyl and diheptyl esters of hematoporphyrin (Hp) were synthesized and shown to be more strongly retained on a reverse phase (C18) high performance liquid chromatography column than most components of Photofrin II (PII) - the sensitizer used for photochemical treatment of cancer in the clinic. The Hp diesters were found to be less efficient than PII in sensitizing cells to photoinactivation. This was partly due to de-esterification of the Hp diesters by esterase activity in the serum. The de-esterification of the Hp diesters was highly dependent on the ester group, with Hp dimethyl ester (t1/2 for conversion to Hp monomethyl ester was 6 min) being de-esterified with a rate 500 times faster than that for Hp diheptyl ester. Incubation of NHIK 3025 cells with these dyes showed that the Hp diesters were all partly located in extranuclear spots and partly diffusely distributed in the cytoplasm. The fluorescing spots may be due to lysosomally located Hp diesters, since the lysosomal marker enzyme beta-Nacetyl-D-glucosaminidase was partly inactivated by Hp diesters and light.

Mitotic inhibition by phenylporphines and tetrasulfonated aluminium phthalocyanine in combination with light

This work relates to studies on modes of phototoxicity by tetrasulfonated aluminium phthalocyanine (AlPcS4), tetrahydroxy- and monosulfonated meso-tetraphenylporphines (3-THPP and TPPS1) on culture cells. Toxicity at moderate light exposures appears to be related to inhibition of microtubule function. Treatment of human cervix carcinoma cells of the line NHIK 3025 incubated for 18 h with the sensitizers and exposed to light inhibits multiplication for the first hours after light exposure, a significant fraction of the cells accumulating in mitosis. For the first hours after treatment, the mitotic cells were always mainly found in metaphase; generally seen as c-metaphases and three-group metaphases. During this time, anaphase and telophase cells were absent or greatly reduced in number. Indirect immunofluorescence staining of beta-tubulin showed that the spindle apparatus of mitotic cells was perturbed in all cases. The accumulation in mitosis was more extensive after treatment with AlPcS4 and light than after treatment with 3-THPP or TPPS1 and light. This may be related to the great difference in the lipophilic properties of these sensitizers; i.e. AlPcS4 being highly water soluble while TPPS1 and 3-THPP are lipophilic sensitizers. The lipophilicity of several sensitizers has been measured by two different methods, the partition between an aqueous and a lipophilic phase (Triton X-114) and the binding strength to a reverse phase column. The results show that the measured relative lipophilicity of the sensitizers may be influenced by the method of analysis.

Evaluation of porphyrin characteristics required for photodynamic therapy

The cytotoxicity (in the dark), phototoxicity (red light) and subcellular localization (using confocal laser scanning microscopy) were determined for 15 porphyrins (1-15) in C6 glioma cells. The partition coefficient in 2-octanol was also determined for each porphyrin at pH 7.4. The cytotoxicity increased with pi (log of partition coefficient) up to pi values of +2. The 7 porphyrins with cationic side chains exhibited a classical parabolic correlation between phototoxicity and pi, with maximal activity at a pi value of approximately 1.0. There was also a significant correlation between subcellular localization and degree of phototoxicity, with the three most photosensitive porphyrins all possessing cationic side chains, and all three localizing in mitochondria.

Evaluation of tumour and tissue distribution of porphyrins for use in photodynamic therapy

A range of pure, monomeric porphyrins were synthesised and their localising capacities compared to HpD and Hp at 6 h and 24 h post injection in the mouse C6 intracerebral glioma model as well as in normal brain, skin, muscle, kidney, spleen, liver, lung and whole blood. The partition coefficients were examined between PBS and 2-octanol over the pH range 7.4-6.6 and pH profiles were established. A parabolic relationship was observed between log (porphyrin tumour concentration) at pH 7.4, with maximal tumour localisation at log (partition coefficient), pi, of approximately zero. Porphyrins with side chains with nett cationic character also exhibited up upward (parabolic) dependence on pi for most tissues studied, with maximal porphyrin localisation at pi of 0-0.5. In contrast, those porphyrins with nett anionic character exhibited a downward (negative) parabolic trend for all eight tissues studied, with minimal porphyrin localisation at pi of approximately zero. Four porphyrins (4, 11, 12, 13) exhibited similar or better tumour localisation than HpD, and two (11 and 12) offer promise as lead compounds for the design of improved porphyrins for use in PDT.

Subcellular localization of porphyrins using confocal laser scanning microscopy

The in vitro subcellular distribution patterns of 10 porphyrins, varying in hydrophobicity and charge, were studied using confocal laser scanning microscopy on two cell lines (V79 and C6 glioma cells) for incubation times up to 24 h. All of the porphyrins were taken up rapidly by both cell lines and distinct classes of subcellular distribution patterns were observed: general cytoplasmic staining; localization in lysosomes (usually associated with general cytoplasmic staining); localization in mitochondria (and general cytoplasmic staining); localization in mitochondria with subsequent uptake into lysosomes. Structure-localization relationships which have emerged are that porphyrins with dominantly cationic side chains localize in mitochondria, whereas those with a more anionic character tend to localize in lysosomes.

Localization of fluorescent Photofrin II and aluminum phthalocyanine tetrasulfonate in transplanted human malignant tumor LOX and normal tissues of nude mice using highly light-sensitive video intensification microscopy

A comparative kinetic observation of the in vivo biolocalization of Photofrin II (P-II) and aluminum phthalocyanine tetrasulfonate (AIPCS4) in a transplanted human malignant tumor LOX and in normal tissues of nude mice has been made by means of highly light-sensitive video intensification microscopy at various intervals after i.p. administration. In the human tumor LOX, transplanted to athymic nude mice, fluorescence of P-II was observed on the membrane and in the cytoplasm of tumor cells, and in the stroma 4-48 hr post-injection. From 72 hr post-injection almost all fluorescing P-II had disappeared from the membrane of the tumor cells while strong fluorescence was still found in the stroma. AIPCS4 fluorescence was seen mainly in tumorous stroma with none detected in the tumor cells. Almost no fluorescence was found in the tumorous stroma 24 hr after injection. In most normal tissues observed, P-II was eliminated at a much slower rate than AIPCS4, but the in vivo biolocalization of the 2 drugs was similar. They were observed primarily where collagenous proteins are normally found, i.e. basal lamina, collagenous connective tissue, and in keratinized epithelium, renal epithelium, mononuclear phagocyte system and on the membrane of muscular cells. In addition, AIPCS4 had a strong affinity for the bronchiogenic epithelium. In the skin, P-II was distributed in keratinized epithelium, hair, hair follicles and their accessory, collagenous connective tissue of dermis, whereas AIPCS4 was present only in hair and collagenous connective tissue of dermis. No fluorescence of P-II or of AIPCS4 was found in the skin epidermis, nor in the transitional epithelium of the bladder mucosa.

Hematoporphyrin diethers--V. Plasma protein binding and photosensitizing efficiency

1. Binding of added hematoporphyrin (HP) ethers to human plasma proteins and lipoproteins has been investigated by ultracentrifugation. 2. The binding to low density lipoproteins (LDL) has been discussed in terms of photosensitized tumor growth delay of tumors and HPLC-retention time, i.e. degree of polarity. 3. The LDL-binding data show a uniform relationship to sensitizing efficiency and degree of polarity, the only exception being HP-diamyl ether. No such uniform relationship exists for less related dyes, such as HP, tetraphenylporphyrin tetrasulfonate and HP-dimethyl ether.

Preparation and photosensitizing properties of hematoporphyrin ethers

Hematoporphyrin ethers having acyl or aryl substituents in the 2 and 4 positions of the porphyrin ring have been synthesized, starting from protoporphyrin HBr adduct, and tested for photosensitizing efficiency on cells in vitro and transplanted tumors in mice. In general, they resemble the tumor localizing fraction of hematoporphyrin derivative (Hpd). Cellular uptake and retention runs parallel with the degree of their non-polarity and in vitro sensitizing efficiencies are up to ten times that of Hpd or Photofrin II (P II). They have high quantum yields for inactivation of cells and also relatively low in vivo skin/tumor concentration ratios.

Interactions between porphyrins and mitochondrial benzodiazepine receptors

Dicarboxylic porphyrins were reported to be potent inhibitors of the binding of benzodiazepines to peripheral drug receptors in mitochondria, but the reverse does not appear to be true. Moreover, the photosensitization of mitochondria by the tumor-localizing porphyrin dimer/oligomer fraction of 'HPD' was not inhibited by benzodiazepines in cell culture.

Hematoporphyrin ethers--III. Cellular uptake and photosensitizing properties

1. The cellular uptake and the efficiency in sensitizing cells to photoinactivation were determined for hematoporphyrin (Hp) diphenyl ether, Hp dicyclohexyl ether and Hp dihexyl ether. 2. The phenyl diether was taken up by the cells to the same degree as was the clinically used porphyrin preparation photofrin II, while the dihexyl and notably the dicyclohexyl ether were taken up 3-4 times better. 3. Furthermore, the quantum yields for photoinactivation of cells were similar for the three diethers and twice as large as that for photofrin II. 4. Fluorescence- and absorption spectroscopy indicate that these findings are related to the fact that photofrin II is much more aggregated in the cells than are the three Hp diethers. 5. When cells loaded with the porphyrins are incubated with porphyrin-free medium containing serum a certain percentage of the cell-bound drug is removed: 14% for photofrin II, 28% for Hp diphenyl ether, 50% for Hp dicyclohexyl ether and 20% for Hp dihexyl ether. 6. With respect to cell uptake and retention of the dyes, the data did not show any uniform relationship to the polarity of the drugs, in contrast to what has been found earlier for Hp diethers of linear hydrocarbons.

Hematoporphyrin ethers--II. Improvements in method, synthesis of the dihexyl, dicyclohexanyl and diphenyl ethers and their preliminary biological evaluation

1. Hematoporphyrin 2.4-dihexyl, -dicyclohexanyl and -diphenyl ethers have been synthesized. 2. Their chemical and physical properties are recorded. The possibility of isomerism is discussed. 3. Preliminary tests have indicated that they possess high photosensitizing efficiency on human cancer cells.

Porphyrin derivatives having physical and chemical characteristics similar to those of the active components of hematoporphyrin derivative and with very strong photosensitizing effects

The tumour-localizing fraction of hematoporphyrin derivative (Hpd) is thought to possess an essentially diporphyrin ether structure or, alternatively, a diporphyrin ester structure, the properties of which facilitate its retention in malignant cells and its biological activity on irradiation. To elucidate this problem further, we have synthesized the dimethyl, diethyl, dipropyl, di-n-butyl and di-iso-butyl ethers of hematoporphyrin. These ethers show chromatographic properties very similar to those of the active components of Hpd. Furthermore, they are much better photosensitizers in a cellular system than are crude Hpd or Photofrin II, and, like the components of Hpd, they are taken up and retained by cells according to their degree of non-polarity.

Destruction of erythroleukaemic cells by photoactivation of endogenous porphyrins

Selective destruction of Friend erythroleukaemic cells (FELC) was potentiated by stimulation of endogenous porphyrin synthesis followed by light sensitization. Endogenous porphyrin biosynthesis in FELC was induced by supplementation of 5-amino levulinic acid (5-ALA) at a concentration of 5 X 10(-4) M. The main accumulated product, after 4 days culture, was uroporphyrin, while after 8 days culture the cells were loaded with protoporphyrin, up to 1.5 micrograms 10(-7) cells. Photoirradiation of the cells for 2 min, accumulating endogenous porphyrins, induced cardinal deformations and cell disintegration in greater than 95% of the cells, as examined by scanning electron microscopy (SEM). The photodynamic destruction effects were dependent on cultivation time with 5-ALA. Flow cytometry analysis showed an immediate expansion of cell volume subsequent to irradiation, presumably a consequence of water influx. Transmission electron microscopy (TEM) of photosensitized cells after different time intervals of culture in 5-ALA medium, revealed initial damage to mitochondria and water influx into the nuclear envelope, after 2 days. After 3-4 days in culture the water influx phenomenon was pronounced, chromatin condensation took place and slight rupture of the outer membrane was detected. Cells photosensitized after 5-6 days of culture were completely disintegrated leaving a nuclear remnant and an enormously swollen nuclear envelope. The culture time dependence of the process, showed an interrelationship between the photodynamic effect and porphyrin accumulation sites in cellular compartments. The study presents a specific method for erythroleukaemic cell inactivation.

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

Nine dyes, all potential sensitizers for photodynamic cancer therapy (PDT), were injected in mice with C3H mammary carcinomas. Twenty-four hours later the animals were sacrificed and the dye concentrations in tumors and 9 other tissues were measured by means of spectrofluorimetry. The 9 dyes were: Photofrin II (PII), hematoporphyrin (HP)-di-hexyl-ether, PSD-007 (a sensitizer used in clinical trials in China), tetraphenyl porphine tetrasulfonate (TPPS4), tetra(3-hydroxy phenyl)porphyrin (3THPP), aluminium phthalocyanine tetrasulfonate (AlPCTS), aluminium phthalocyanine (AlPC), chlorin e6 (Chl e6) and merocyanine 540 (MC 540). The porphyrin precursor delta-aminolevulinic acid was also tested and found to induce porphyrin fluorescence in tumors and some other tissues. The best tumorlocalizer of those tested was 3THPP. This drug also showed a favorable tissue distribution. The following dyes showed lower skin/tumor concentration ratios than PII (the most widely used dye for PDT): Chl e6, PSD-007, HP-di-hexyl-ether and 3THPP. Low brain/tumor ratios were found for: PSD-007, HP-di-hexyl-ether, 3THPP, TPPS4 and AlPCTS.