Donata Dei

Synthesis of a new water-soluble octa-cationic phthalocyanine derivative for PDT

The synthesis and characterization of a new octa-cationic Zn‐phthalocyanine is described. This compound is water-soluble, not aggregated under a wide range of solvent conditions and is a powerful photosensitizer for the inactivation of microorganisms by using a strategy based on photodynamic therapy.

Photophysical, photochemical and antibacterial photosensitizing properties of a novel octacationic Zn(II)-phthalocyanine

A novel Zn(II)-phthalocyanine (1). peripherally substituted with four bis(N,N,N-trimethyl)amino-2-propyloxy groups prepared by chemical synthesis is shown to be an efficient photodynamic sensitizer with a quantum yield of 0.6 for singlet oxygen generation in neat water, which is reduced to about 0.3 in phosphate-buffered saline. The physicochemical properties of 1 in both the ground and the electronically excited states strongly depend on the nature of the medium; in particular, aggregation of 1 was favoured by polar media of high ionic strength. Compound 1 exhibited an appreciable affinity for a typical Gram-positive bacterium (Staphylococcus aureus) and a typical Gram-negative bacterium (Escherichia coli). Both bacterial strains were extensively inactivated upon 5 min-irradiation with 675 nm light in the presence of 1 microM photosensitizer, even though the binding of 1 to the two bacterial cells appears to occur according to different pathways. In particular, E. coli cells underwent initial photodamage at the level of specific proteins in the outer wall, thus promoting the penetration of the photosensitizer to the cytoplasmic membrane where some enzymes critical for cell survival were inactivated.

Approaches to selectivity in the Zn(II)–phthalocyanine-photosensitized inactivation of wild-type and antibiotic-resistant Staphylococcus aureus

A number of Zn(II)- phthalocyanines bearing peripheral substituents of cationic nature due to the presence of quaternarized anilinium or ammonium groups were shown to be efficient photoantimicrobial agents: a 4-5 log decrease in the survival of both wild-type or methicillin-resistant Staphylococcus aureus was obtained upon short irradiation times in the presence of phthalocyanine concentrations as low as 0.1 microM. A careful selection of the experimental protocol, and in particular the use of short (5 min) incubation times and mild irradiation parameters, allowed one to achieve a high selectivity of S. aureus photoinactivation as compared with important constituents of potential host tissues, such as human fibroblasts and keratinocytes. The efficiency and selectivity of the photoprocess were not affected by the presence of 5% human serum.

A novel 10B-enriched carboranyl-containing phthalocyanine as a radio- and photo-sensitising agent for boron neutron capture therapy and photodynamic therapy of tumours: in vitro and in vivo studies

The synthesis of a Zn(ii)-phthalocyanine derivative bearing four 10B-enriched o-carboranyl units (10B-ZnB4Pc) and its natural isotopic abundance analogue (ZnB4Pc) in the peripheral positions of the tetraazaisoindole macrocycle is presented. The photophysical properties of ZnB4Pc, as tested against model biological systems, were found to be similar with those typical of other photodynamically active porphyrin-type photosensitisers, including a singlet oxygen quantum yield of 0.67. The carboranyl-carrying phthalocyanine was efficiently accumulated by B16F1 melanotic melanoma cells in vitro, appeared to be partitioned in at least some subcellular organelles and, upon red light irradiation, induced extensive cell mortality. Moreover, ZnB4Pc, once i.v.-injected to C57BL/6 mice bearing a subcutaneously transplanted pigmented melanoma, photosensitised an important tumour response, provided that the irradiation at 600-700 nm was performed 3 h after the phthalocyanine administration, when appreciable concentrations of ZnB4Pc were still present in the serum. Analogously, irradiation of the 10B-ZnB4Pc-loaded pigmented melanoma with thermal neutrons 24 h after injection led to a 4 day delay in tumour growth as compared with control untreated mice. These results open the possibility to use one chemical compound as both a photosensitising and a radiosensitising agent for the treatment of tumours by the combined application of photodynamic therapy and boron neutron capture therapy.

Phthalocyanines as photodynamic agents for the inactivation of microbial pathogens

A variety of 1,8(11),15(18),22(25)- and 2,9(10),16(17),23(24)-tetra-substituted and 2,3,9,10,16,17,23,24-octa-susbtituted Zn(II) phthalocyanines, bearing dialkylaminophenoxy and trialkylammoniumphenoxy groups, have been synthetized, characterized and tested as photosensitizers against S. aureus, E. coli and C. albicans. All phthalocyanines exhibited intense absorption bands in the phototherapeutically useful 670-700 nm region, with a molar extinction coefficient of the order of 105 M-1.cm-1. All derivatives bearing positive charges showed a good photosensitizing efficiency (causing a greater than 4 log reduction in cell survival), as well as a high quantum yield for generation of singlet oxygen. Variations of the chemical structure appeared to strongly affect both the physicochemical properties and the phototoxic activities against microorganisms.

Phthalocyanine-photosensitized inactivation of a pathogenic protozoan, Acanthamoeba palestinensis.

Incubation of Acanthamoeba palestinensis cells with a tetracationic phthalocyanine (RLP068) at concentrations ranging between 0.2 and 1.0 microM, caused a ready uptake of the photosensitizer with recoveries of the order of 0.5-2.5 nmol per mg of cell protein. The amount of cell-bound phthalocyanine did not appreciably change with incubation times ranging between 0.5 and 3 h. Fluorescence microscopic investigations showed an obvious accumulation of the phthalocyanine at the level of the vacuolar membranes. A nearly complete photoinduced cell death occurred upon irradiating A. palestinensis cells with 600-700 nm light with a total energy of 15-30 J cm(-2) using 1.0 microM RLP068 in the incubation medium. DAPI staining of the photosensitized cells indicates significant damage of the nucleus. On the other hand, photosensitization of the protozoan cells does not directly involve the mitochondria as shown by the lack of photoinduced decrease in the activity of typical mitochondrial enzymes, such as NADH dehydrogenase and citrate synthase.

Skin-photosensitizing properties of Zn(II)-2(3), 9(10), 16(17), 23(24)-tetrakis-(4-oxy-N-methylpiperidinyl) phthalocyanine topically administered to mice

A Zn-phthalocyanine derivative bearing four 4-oxy-N-methyl-piperidinyl peripheral substituents has been formulated in an azone-containing gel for topical administration and its potential as a photodynamic therapy agent has been investigated. The phthalocyanine displays an intense absorbance in the 680 nm range and shows a high photosensitizing activity toward a model biological substrate (N-acetyl-L-tryptophanamide). Upon administration of 20 microg cm(-2) onto the dorsal skin of Balb/c mice, maximal phthalocyanine concentrations (ca. 64.2 ng mg(-1) of skin) are reached at 1 h after the deposition. The photosensitizer appears to be localized in the epidermal layers, since (a) no detectable amounts of phthalocyanine are recovered from the mouse blood and liver; and (b) upon photoactivation with a diode laser at 675 nm, only the epidermis is heavily damaged, as shown by histological and ultrastructural analysis. The photodamage is largely of inflammatory nature and an essentially complete healing of the damaged skin is observed at 72 h after the end of the phototreatment. The minimal phototoxic dose for 20 microg cm(-2) photosensitizer and 675 nm irradiation is found to be (150 mW cm(-2)-120 J cm(-2)) or (180 mW cm(-2)-100 J cm(-2)).

Caracasandiamide, a truxinic hypotensive agent from Verbesina caracasana

Abstract A second hypotensive agent from Verbesina caracasana is shown to be the truxinic type dimer of the previously isolated 3,4-dimethoxycinnamoyl guanidinoamide. The new compound gave by alkaline hydrolysis a crystalline monoamide, which in turn by acid hydrolysis gave 3′,4′-dimethoxy-β-truxinic acid, identical with a synthetic specimen.

Synthesis of bicyclo[9.3.1]pentadecane derivatives, interesting intermediates for the preparation of taxuspine U and related diterpenoids☆

Abstract The synthesis of regioisomeric bicyclo[9.3.1]pentadecane-3-one derivatives 1 and 2, interesting synthons for the preparation of novel diterpenoids, has been accomplished through an approach that entails as a key step the formation of a twelve-membered ring by an unprecedented intramolecular Dieckmann cyclisation.

In vitro photosensitizing efficacy of cationic phthalocyanine derivatives against C.albicans: effect of serum albumins

The effect of serum albumins (as Fetal Calf Serum) on in vitro photosensing efficacy against C.albicans of three cationic Zn(II) phthalocyanine derivatives was evaluated. A clearly structure-dependent reduction in the antifungine activity was observed. For this reason the binding of the photosensitizers with albumins (as bovine serum albumin, BSA) at pH 7.4 was studied. Because of aggregation phenomena, the phthalocyanine derivatives showed little fluorescence in aqueous solutions and fluorescence intensity increased as a function of protein concentration. Titration plots were built and binding constant were determined. The obtained binding parameters and the hydrolipophilic properties of the studied molecules (octanol/water partition coefficient PO/W, number of cationic charges, amphipilicity) were correlated with the observed biological effect.