Ionel Rosenthal

The Phthalocyanines: A New Class of Mammalian Cells Photosensitizers with a Potential for Cancer Phototherapy

Phthalocyanines, porphyrin-like compounds with maximum absorption in the red, which were previously reported to localize selectively in tumours, have been shown to be efficient photosensitizers of mammalian cells in culture, thus making them possible candidates to replace haematoporphyrin derivatives in cancer phototherapy.

Photodynamic Treatment of Transplantable Bladder Tumors in Rodents After Pretreatment with Chloroaluminum Tetrasulfophthalocyanine

Chloroaluminum tetrasulfophthalocyanine (AlPCS) was used as a photosensitizer for the photodynamic treatment of transplantable N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide (FANFT) induced urothelial tumors. Two groups of six rats each were injected with AlPCS (three micrograms./gm. body weight) and 24 hours after injection underwent photodynamic treatment with red light (greater than 590 nm., 360 joules/cm.2). Tumors examined four hours (Group I) and 24 hours (Group II) after the completion of phototreatment showed extensive hemorrhagic necrosis. Tumors treated with AlPCS alone showed no changes. In two other groups of six rats each, blood flow to tumors treated with AlPCS alone (Group III) and AlPCS plus light (Group IV) was measured using the radioactive microsphere technique. AlPCS plus light resulted in a significant decrease (p less than .05) in tumor blood flow within 10 minutes of completion of phototreatment while AlPCS alone had no effect on tumor blood flow. These findings are similar to those observed when higher doses (10 micrograms./gm. to 20 micrograms./gm. body weight) of hematophorphyrin derivative (HpD) and light were used for phototreatment of FANFT induced tumors. AlPCS is a stable sulfonated derivative of tetraazotetrabenzoporphyrin which absorbs maximally in the red portion of the visible spectrum, a region with good tissue penetration properties. These studies suggest the AlPCS may be a useful new agent for photodynamic therapy of cancer.

Sonolysis of perhalomethane as studied by EPR and spin trapping

Intense ultrasonic waves have been reported to produce chemical changes by the phenomenon of cavitation (1-3). Although some sonochemically induced reactions proceed undoubtedly by an ionic mechanism (4-7), others most probably involve free radical intermediates (8, 9) although no direct evidence has been provided. We report our attempts to generate free radicals at room temperature in fluid solutions by ultrasonic exposure and their detection by EPR. We found that sonolysis of pure carbon tetrachloride or trichlorobromomethane generates free radicals which could be spin-trapped by 2-methyl-2nitrosopropane and identified. A Bransonic 12 ultrasonic cleaner (frequency, 50 kHz) was used as a generator of ultrasonic waves. The reaction mixture (3 ml) contained in a Pyrex test tube was held in the middle of the bath, and the vertical position of the tube was adjusted to maintain the same level of liquid inside the tube as outside. Particular care was taken to insure the reproducibility, by positioning the tube in the same place, keeping the water level and the temperature in the bath constant (23”C), etc. (10). The intensity of ultrasonic irradiation under these experimental conditions was monitored before each experiment by a calorimetric procedure which measures the amount of chlorine released in CC&-saturated water by ortho-tolidine reagent (II). Thus, a mixture of 3 ml water saturated with CCL, and 0.15 ml o&o-tolidine reagent (0.1% solution, Fisher Scientific Co.) was sonicated for 30 sec. The intensity of the yellow color was measured in a l-cm cell at 436 nm to be 0.8 IC_ 0.1 under our experimental conditions. When CCL or CCl,Br containing 2-methyl-2-nitrosopropane (1.5 mg/ml) was sonicated and subsequently analyzed by EPR, a spectrum composed of a triplet of ON = 6.7 G could be recorded (Fig. 1). This splitting characteristic of an acyl spin adduct (12) is attributed to the nitroxone I

Photosensitized formation of ascorbate radicals by chloroaluminum phthalocyanine tetrasulfonate: An electron spin resonance study

The chloroaluminum phthalocyanine tetrasulfonate sensitized photooxidation of ascorbic acid to ascorbate radical (A.-) was followed by electron spin resonance (ESR) spectroscopy. In air saturated aqueous media, steady-state amounts of A.- are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished--more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN3 and tryptophan) was studied, as was replacement of water by D2O and saturation with O2. The results are indicative of free radical production by direct reaction between ascorbate ion and sensitized phthalocyanine (a Type I mechanism) in competition with the (Type II) reaction of HA- with singlet oxygen, a reaction which does not produce ascorbate radical intermediates.

Photochemistry of Pyrimidine Bases as Studied by E.S.R. and Spin-trapping

The direct photoexcitation of pyrimidine bases in D2O solutions yields free radicals which could be conveniently identified by spin-trapping with 2-methyl-2-nitrosopropane. Most of the radicals formed were attributed to D-addition to one end of the 5,6 double bond. However, orotic acid and iso-orotic acid yielded N(3) centred free radicals, formed by homolytic cleavage of the N-H bond. No indication could be found for a free radical involvement in the photocleavage of cyclobutane-type pyrimidine dimers.

Electron spin resonance and spin-trapping studies of radiation damage in biologically significant molecules

Abstract Recent electron spin resonance (ESR) and spin trapping studies of γ-radiation induced radicals in protein and nucleic acid constituents in the polycrystalline state and in aqueous solutions are reviewed. When complex mixtures of spin-adducts are generated, the identification of radicals is facilitated by combining spin trapping with high pressure liquid chromatography, using ESR as an in-line detector. For high molecular weight polypeptides and polynucleotides, enzymatic hydrolysis of the spin trapped macromolecular radicals appears to be a promising approach. Attempts to spin trap radicals inside γ-irradiated cells and whole animals are discussed.

Photoinduced reactions of dibenzoyl peroxide as studied by EPR and spin-trapping

Abstract The photochemical reactions of dibenzoyl peroxide with some organic compounds were found by EPR and spin-trapping to generate free radicals in dimethyl sulfoxide solutions at room temperature. Two reaction mechanisms occur which determine the structures of the radicals generated. The first involves a one-electron oxidation and the second a hydrogen atom transfer. The prevailing mechanism is primarily dependent on the structure of the substrate. With carboxylic acids the one-electron oxidation occurs exclusively, leading to the loss of the carboxyl group and to formation of the alkyl radical. For alcohols both alkoxy radicals and hydrogen-abstraction α-carbon radicals were spin trapped. The alkoxy radicals were generated by the electron transfer mechanism. Finally pyrimidine bases such as thymine and cytosine yielded C(5)-centered radicals which could also be explained by an electron transfer mechanism. These observations are of interest because of the recently observed skin tumor-promoting activity of dibenzoyl peroxide.

E.S.R. and Spin-trapping Studies of Dihydropyrimidines. γ-Radiolysis in the Polycrystalline State and U.V. Photolysis in Aqueous Solution

gamma-Radiolysis in the polycrystalline state and U.V. photolysis in aqueous solution at 220 nm of several dihydropyrimidines and their derivatives have been investigated by spin-trapping and electron spin resonance. 2-Methyl-2-nitrosopropane was used as the spin-trap. The spin-adducts of the 6-yl radicals obtained fall into two categories. Those from dihydro-1-methyluracil, dihydro-6-methyluracil, dihydro-1-ethyluracil and dihydro-1-methylcytosine exhibit a beta-nitrogen hyperfine coupling constant (alpha beta N) equal to or less than 2.0 G while the ones fom dihydro-orotic acid, dihydrouracil and dihydrothymine showed much larger alpha beta N values (greater than 3.3 G). Dihydrouridine gives radicals characteristic of both the dihydropyrimidine ring and the sugar moiety. The same radicals were obtained by gamma-radiolysis or U.V. photolysis. For all the 5-yl radicals obtained by U.V. photolysis, a direct photoexcitation mechanism is proposed.

Effect of antiooxidants on phthalocyanine photosensitization of human erythrocytes

Photohemolysis of human erythrocytes sensitized by sulfonated aluminum phthalocyanine was used as an endpoint to study possible chemical modifications of photodynamic therapy. Ascorbate, in concentrations up to 0.1 mM, had a small protective effect. In larger amounts it stimulated the rate of photohemolysis in a concentration dependent manner up to 1mM, by a factor of 2. Azide and D20 tests indicated some participation of singlet oxygen, although to a lesser extent than in the absence of ascorbate. Kinetic considerations augur for a reaction path initiated by an interaction of excited sensitizer-ascorbate, parallel to the singlet oxygen-mediated process. Because of the ubiquitous presence of ascorbate in human tissues in concentrations comparable to those of dissolved oxygen, it is a reasonable estimation that in photodynamic therapy, a fraction of the photodynamic damage proceeds via a Type I, ascorbate-assisted, mechanism. Tocopherol had an effect opposite to that of ascorbate, namely it inhibited the photohemolysis. Likewise, quercetin, a plant flavonoid, was protective against phthalocyanine-induced photohemolysis.

Photosensitization by Phthalocyanines. Chemical Structure - Photodynamic Activity Relationship

The very intense light absorption of phthalocyanine (PC) dyes in the spectral region of effective tissue penetration, combined with a substantial chemical stability, insignificant systemic toxicity, preferential retention in malignant tumors and, last but not least, outstanding photodynamic activity, propelled this class of dyes from photobiological obscurity to the highlights of photodynamic therapy.