Two new sterically hindered phthalocyanines: synthetic and photodynamic aspects

Phthalocyanines as Photosensitizers in the Photodynamic Therapy of Cancer

The application of phthalocyanine derivatives in medicine as photosensitizers for photodynamic therapy of cancer diseases is reviewed. The emphasis is on the work of Russian authors, which is less covered in the scientific literature.

Photodynamic Therapy:In VitroPhotosensitizing Efficacy of Bis(tri-n-hexylsiloxy)silicon Phthalocyanine against Achromic M6 Melanocytes. ESR Study of Active Oxygen Intermediates

The in vitro photodynamic effect of bis(tri-n-hexylsiloxy)silicon phthalocyanine has been evaluated against the melanotic M6 cell line. The results showed that at 10-5M dose, LD50is obtained for a 150 J cm-2light dose and LD90for 540 J cm-2. Electron spin resonance spectroscopy was used with spin traps to study the type I and type II photochemical pathways involved and to detect active oxygen intermediates such as singlet oxygen, oxygen superoxide and hydroxyl radical. The two mechanisms occurred simultaneously and no change was observed when the phthalocyanine was entrapped in liposomes.

Laser-flash photolysis of dialkylbenzodipyridoporphyrazines

In the course of a fundamental study of photosensitizers for photodynamic therapy of cancer, a non-peripheral substituted phthalocyanine analogue, zinc bis(1,4-didecylbenzo)bis(3,4-pyrido)porphyrazine and its position isomers were examined to measure their photoexcited triplet state lifetimes in poly(methyl methacrylate) film using laser-flash photolysis. The isomer mixture of zinc bis(1,4-didecylbenzo)bis(3,4-pyrido)porphyrazine showed the most intense absorption in the 660-710 nm region, and the longer triplet state lifetime. The lowest symmetry isomer of zinc bis(1,4-didecylbenzo)bis(3,4-pyrido)porphyrazine was found to have the longest triplet state lifetime when all isomers were separated. The compound is proposed to be suitable for use as a photosensitizer for photodynamic therapy of cancer.

Syntheses and Functional Properties of Phthalocyanines

Metal phthalocyanine tetrasulfonic acids, metal phthalocyanine octacarboxylic acids, metal octakis(hexyloxymethyl)phthalocyanines, and metal anthraquinocyanines have been synthesized. Then, zinc bis(1,4-didecylbenzo)-bis(3,4-pyrido)porphyrazines, the cyclotetramerization products of a 1:1 mixture of 3,6-didecylphthalonitrile and 3,4-dicyanopyridine, were synthesized. Futher, subphthalocyanine and its derivatives, with substituents such as thiobutyl and thiophenyl moieties were synthesized. Electrochemical measurements were performed on the abovementioned phthalocyanine derivatives and analogues in order to examine their electron transfer abilities and electrochemical reaction mechanisms in an organic solvent. Moreover, 1,4,8,11,15,18,22,25-octakis(thio-phenylmethyl)phthalocyanes were synthesized. The Q-bands of the latter compounds appeared in the near-infrared region. Furthermore, non-colored transparent films in the visible region can be produced.

Synthesis and properties of trifluoroethoxy-coated binuclear phthalocyanine

A genuine example of non-aggregated highly fluorescent binuclear phthalocyanines is reported; spectroscopic studies and computations revealed that the two halves of trifluoroethoxy-coated binuclear phthalocyanine are rotated in the same directions so as to contact each other as much as possible.

Killing efficacy of a new silicon phthalocyanine in human melanoma cells treated with photodynamic therapy by early activation of mitochondrion-mediated apoptosis

Photodynamic therapy (PDT) is a promising therapeutic modality that utilizes a combination of a photosensitizer and visible light for the destruction of diseased tissues. Using human-pigmented melanoma cells, we examined the photokilling efficacy of new silicon-phthalocyanines (SiPc) that bore bulky axial substituents. The bis(cholesteryloxy) derivate (Chol-O-SiPc) displayed the best in vitro photokilling efficacy (LD(50) = 6-8 x 10(-9) M) and was seven to nine times more potent than chloro-aluminium Pc (ClAlPc), a known photosensitizer used as a reference. Although Chol-O-SiPc was half as potent as ClAlPc for promoting photo-oxidative membrane damage in a cell-free assay, early events of mitochondrion-mediated apoptosis upon PDT were triggered much faster, as demonstrated by kinetics studies examining cells with permeabilized mitochondrial membranes, cytochrome c release and caspase-9 activation. Inhibition of caspase-9 activity by a substrate analogue argued for its central role in the proapoptotic events leading to cell death by Chol-O-SiPc PDT. In addition, immunoblots showed that Bcl-2 antiapoptotic oncoprotein was not a primary target of Chol-O-SiPc in M3Dau cells treated with PDT. Conclusively, Chol-O-SiPc is a useful new photosensitizer with the property of triggering cell apoptosis mediated by mitochondria.

Porphyrazines with Annulated Diazepine Rings. 2. Alternative Synthetic Route to Tetrakis-2,3-(5,7-diphenyl-1,4-diazepino)porphyrazines: New Metal Complexes, General Physicochemical Data, Ultraviolet−Visible Linear and Optical Limiting Behavior, and Electrochemical and Spectroelectrochemical Properties

Following a previous report on the synthesis and physicochemical characterization of a novel class of porphyrazines carrying peripherally annulated seven-membered rings, i.e., tetrakis-2,3-(5,7-diphenyl-1,4-diazepino)porphyrazine [Ph(8)DzPzH(2)].4H(2)O and its metal derivatives [Ph(8)DzPzM].xH(2)O (x = 2-7, M = Mg(II)(H(2)O), Cu(II), and Zn(II)), a new more convenient procedure is reported here, allowing the preparation in high yields of the Li(I) and Na(I) derivatives of formulas [Ph(8)DzPzLi(2)].5H(2)O and [Ph(8)DzPzNa(2)].6H(2)O, which can be directly converted into other metal derivatives under mild conditions (room temperature) and in good yields. The series studied has been extended to include the Mn(II) and Co(II) complexes also reported here for the first time. Physicochemical characterization of the new "diazepinoporphyrazines" was based on fast atom bombardment (FAB) mass spectrometry and X-ray powder patterns, infrared (IR), electron paramagnetic resonance (EPR), and room-temperature magnetic susceptibility measurements. A detailed discussion of the UV-vis spectra emphasizes the role played by the external diazepine rings in electron delocalization through their tautomeric or protonated forms present in neutral, basic, and acidic media. The nonlinear optical effect of optical limiting for the different species [M = 2H, Mg(II)(H(2)O), Mn(II), Co(II), Cu(II), and Zn(II)] has also been measured. It has been observed that the extent of the optical limiting depends on the specific M center. The observed nonlinear optical features are analyzed and discussed in terms of the electronic and magnetic properties exhibited by some of the metal ions and taking into account the model of the excited-state absorption in which the nature of M determines the kinetics of formation of the highly absorbing state of the specific complex examined. As evidenced by the detailed electrochemical and spectroelectrochemical study carried out on this new class of macrocycles, one of the most important aspects is the facilitated electron delocalization for the oxidized and reduced species allowed by a 1H-6Htautomerism taking place on the peripheral diazepine rings.

Pharmacokinetic and phototherapeutic properties of axially substituted Si(IV)-tetradibenzobarreleno-octabutoxyphthalocyanines

Three Si(IV)-tetradibenzobarreleno-octabutoxyphthalocyanines (TDiBOPcs) bearing different axial ligands on the metal ion were studied for their tumour-localizing and-photosensitizing properties after i.v. injection via a Cremophor emulsion (0.35 mumol kg-1 b.w.) to Balb/c mice bearing an intramuscularly implanted MS-2 fibrosarcoma. In all cases, the maximum tumour accumulation of the photosensitizer (0.8-1.9 nmol g-1 of tissue) was found at 24 h after injection. The efficiency and selectivity of tumour targeting appeared to be dependent on the nature of the axial ligands; optimal values of these parameters were obtained in the case of the bis(trihexyl-siloxy)-substituted Si(IV)-TDiBOPc, which gave a 7-9 tumour/muscle ratio of phthalocyanine concentration at 24-48 h after injection. The extent of tumour response to PDT treatment was correlated with the concentration of the photosensitizer in the tumour tissue: upon 740 nm irradiation (180 mW cm-2, 200 J cm-2) at 48 h after injection of 0.35 mumol kg-1 of Si(IV)-TDiBOPc-C6H13, the tumour growth exhibited a delay of about 7 days.

Tumour photosensitizers: approaches to enhance the selectivity and efficiency of photodynamic therapy

While Photofrin, the photosensitizer currently in clinical use for photodynamic therapy (PDT) of tumours, has been shown to be both efficacious and safe in the treatment of a variety of human cancers, its chemical heterogeneity and low absorbance in the phototherapeutically useful wavelength range (600-850 nm) make the development of new photosensitizers with improved characteristics desirable. A suitable manipulation of the molecular structure of porphyrins offers several interesting possibilities for controlling the optical and photophysical properties of the photosensitizer, as well as its biodistribution between tumour and peritumoural tissues or at the subtissular and subcellular level. The achievement of these goals may also be facilitated by the association of the photosensitizer with selected delivery systems, opening the way to a qualitative and quantitative improvement of PDT.

Octa-alkyl zinc phthalocyanines: potential photosensitizers for use in the photodynamic therapy of cancer

The synthesis, characterization and electronic spectra of a series of nine 1,4,8,11,15,18,22,25-octa-alkyl zinc phthalocyanines (ZnPc), potential photosensitizers for the photodynamic therapy of cancer, are described. The substituents on the phthalocyanine (Pc) macrocycle "red-shift" the absorbance maximum, in cyclohexane, of all nine members of this series to a value of 703 +/- 2 nm, with a corrected fluorescence emission maximum for the octadecyl derivative of 715 nm. The solubilities and degree of aggregation of six examples in cyclohexane have been measured. The highest homologue, the octadecyl derivative, remains essentially unaggregated to a concentration of 1.5 x 10(-4) mol dm-3. the photostability of this Pc has been examined and the compound shown to be sensitive to photooxidation processes which lead to its decomposition to 3,6-bis-decylphthalimide. Known singlet oxygen quenchers inhibit the photodecomposition. In a comparative study, the octadecyl ZnPc underwent a more rapid photodecomposition than the corresponding metal-free derivative.

Unusually high affinity of Zn(II)-tetradibenzobarrelenooctabutoxy-phthalocyanine for low-density lipoproteins in a tumor-bearing mouse

An important factor in determining the efficacy of photosensitizing compounds in photodynamic therapy of tumors is the level to which tumors take up the photosensitizers after systemic injection. This parameter seems to be related to the transport modalities of the photosensitizer in the bloodstream. In this work the photosensitizer Zn(II)-tetradibenzobarrelenooctabutoxyphthalocyanine was shown to have an unprecedentedly high association with low-density lipoproteins (71% of the phthalocyanine in the plasma) when delivered in Cremophor micelles to tumor-bearing mice. This was accompanied by a particularly high tumor uptake at 24 h post-injection.

Role of oxygen in the phototoxicity of phthalocyanines

The presence of molecular oxygen is a determinant in the phototoxicity of phthalocyanines, and photosensitized oxidation is the accepted chemical mechanism for photo-dynamic action. However, it is difficult to establish whether the process is initiated by a type I electron transfer, or by a type II energy transfer reaction to form singlet oxygen. Usually, the involvement of singlet oxygen in photodamage has been indicated by the inhibition of the biological effect by a competitive physical or chemical singlet oxygen quencher, or by a rate increase in D2O, in which singlet oxygen has a longer lifetime than in H2O. Unfortunately, these techniques are not completely specific for singlet oxygen. Moreover, thermodynamic considerations suggest that photoinduced electron abstraction from appropriate biomaterials could compete with singlet oxygen production under in vivo conditions. This likely source of one electron-oxidized primary radicals, which can provide the precursors of the oxidative damage in phthalocyanine photosensitization, suggests the possibility of modulated toxicity by interaction with chemical additives. Examples of such additives recently studied are ascorbate, tocopherol and quercetin, all of which are natural antioxidants.