Dieter Woehrle

NAPHTHALOCYANINE COMPLEXES AS POTENTIAL PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY OF TUMORS

In the present paper information about the synthesis and results on the pharmacokinetic and experimental photodynamic therapy (PDT) of naphthalocyanines are given. The photodynamic activity of differently substituted zinc(II)- and silicon(IV)-naphthalocyanines using liposomes or Cremophor EL as drug-delivery systems is shown on different tumor models. For the evaluation of the phototherapeutic effect different assessment criteria were used, including light and electron microscopy observations. The main conclusions which can be arrived at on the basis of our findings are the following: silicon(IV)-naphthalocyanine seems to be not a very effective tumor sensitizer, especially in the treatment of pigmented melanoma, while zinc(II)-naphthalocyanines appear to be very promising for PDT of tumors. Their selective targeting and slow clearance from tumor tissue, fast clearance from skin and pronounced phototherapeutic effect on different tumor models and especially at melanotic tumors, even after application of low drug doses, make this group of photosensitizers very attractive for successful PDT of cancer.

Electron transfer reaction between metalloporphyrins covalently bound to polystyrene in N,N-dimethylformamide

Abstract Iron(III) chloro- and manganese(III) chloro-complexes of 5,10,15,20-tetrakis-(4-aminophenyl)-21 H ,23 H -porphin were covalently bound to a polymer of ethenylbenzene with (4-chloromethyl)ethenylbenzene. Electron transfer from the polymer-bound manganese(II) complex to the polymer-bound iron(III) complex was investigated by stopped-flow visible spectrometry under pseudo-first-order conditions in N , N -dimethylformamide. The observed data for the electron transfer were compared with those for electron transfer between the corresponding low molecular weight metallo-porphyrins. It was found that the pseudo-first-order rate constants for the reaction between the low molecular weight metallo-porphyrins were higher than those for the same process between the polymer complexes. On the other hand, the activation energy for electron transfer between the polymer-bound metallo-porphyrins (9.2 kJ mol −1 ) was considerably lower than that corresponding to the reaction between the low molecular weight metallo-porphyrins (16.8 kJ mol −1 ). These effects are discussed with reference to the role of polymer chains.

Imaging of tumors by time-delayed laser-induced fluorescence

A technique to improve signal-to-background ratio in fluorescence images of superficially growing tumors marked with photosensitizers is described. Time-delayed detection of fluorescence following pulsed-laser excitation allows suppression of the autofluorescence background falling into the fluorescence band of the photosensitizer. This technique exploits the longer fluorescence-decay times of porphyrin-based photosensitizers compared to average decay times of tissue autofluorescence. The feasibility of time-delayed fluorescence imaging of tumors has been demonstrated in vitro. From time-delayed fluorescence spectra the authors infer that the ratio between photosensitizer signal and autofluorescence background can be improved by about one order of magnitude.

Incorporation of organic dye molecules in nanoporous crystals for the development of hexagonal solid state microlasers

Molecular sieves, such as nanoporous AlPO4-5, can host a wide variety of laser-active dyes. Slim dyes like Coumarin40 or Oxazine 1, fitting into the channel pores, as well as bulky dyes like rhodamines and Oxazine 750, being located in defect sites of the molecular sieve structure, are embedded during microwave-assisted crystallization. The fast microwave-assisted crystallization offers a new procedure for the stable and monomeric encapsulation of organic dyes into molecular sieves without any degradation of the chromophores and enables the control of the morphology of the host material. Based on this class of materials a new form of microlasers has been created. Their properties depend on size and shape of the molecular sieve crystals. The microcrystals act as hexagonal ring resonators (whispering gallery mode). In dependence on the morphology of the crystals different laser properties have been observed in agreement with theoretical predictions. Large hexagonal crystals (diameter of the hexagonal plane > 7 micrometers ) revealed multiline laser emission, while smaller crystals (diameter about 5 micrometers ) oscillate on one single line. The laser threshold power density decreases with decreasing diameter of the crystals. In terms of pumping needed to reach lasing molecular sieve microlasers are comparable to quantum dot semiconductor lasers.

New biotinylated phthalocyanines for the photodynamic therapy of cancer

Suitable substituted phthalocyanines are promising and widely investigated photosensitizers (PS) for the photodynamic therapy of cancer (PDT). However, selective accumulation of the PSs in tumor tissues, avoiding contamination of healthy tissues, is still an unsolved central problem. We present first results on the synthesis of new biotinylated phthalocyanines as potentially selective photosensitizers when applied in a polyphasic tumor targeting (tumor cell plus first step: biotinylated/monoclonal antibody, second step: streptavidin, and third step: biotinylated PS). The binding and the photodynamic activity of biotinylated PS in this three step model is shown in tumor cell lines.

Spectroscopic studies on Si-phthalocyanines and Si-naphthalocyanines

Some photophysical properties (steady-state absorption, fluorescence and phosphorescence, fluorescence decay times and singlet oxygen quantum yields) of silicon phthalocyanines with methoxypolyethylene glycol (MPEG)-substituents of various chain length at the silicon atom [SiPc(OCH2CH2)n-OCH3; n equals 1,2,3,12], silicon phthalocyanine covalently bound to the water soluble polymer methoxypolyethylene glycol [SiPc(-O-MPEG 5000)2] and silicon naphthalocyanine [SiNc(CH2CH2OCH3)2] have been studied. The aim of these investigations was to get information about the influence of methoxypolyethylene-glycol-coupling on photophysical sensitizer parameters.

Photo-oxidative stability of various tetra-azaporphyrin derivatives in solution and correlation with semiempirical MO calculations

For the application of photosensitizers in PDT attention must be given to the stability of these compounds. For various substituted and annelated tetraazaporphyrins zinc complexes the experimentally determined first order rate constant of the photo-oxidative decomposition in DMF were compared with the calculated values of the HOMO energy level. The method described allows one to predict the photo-oxidative stability by calculating their HOMO levels which is important for the use of macrocyclic metal complexes in the photodynamic therapy of cancer. To high photo-oxidative stability leads to risks in healthy tissues and reduces photodynamic effects in tumor tissues. To low photo-oxidative stability cause problems in preparation, purification and in vivo persistency of photosensitizers for tumor treatment.

Independent pathway for inclusion complexes of porphyrinoid drugs in tumors: the separation from the lipoprotein pathway in plasma

Phthalocyanines and m-TPPs were substituted with two or three t-butyl phenyl anchor groups to build up inclusion complexes with dimeric (beta) -cyclodextrins. These complexes proved to be stable enough to hinder complexation of the porphyrinoids with plasma lipoproteins and, so, offer an independent pathway to transfer porphyrinoids to photosensitize tumor tissue.

Time-resolved photoelectrochemical measurements and photovoltaic efficiency of electrochemically self-assembled ZnO-dye electrodes

Dye-modified ZnO thin films were prepared by electrochemically induced crystallization from aqueous mixtures of zinc nitrate and water-soluble dyes. A direct crystallization of semiconductor/ dye composites without heat treatment is seen as a significant advantage of this method. Moreover, characterization of these materials has revealed ordered growth of ZnO crystallites as well as formation of ordered dye assemblies, thus characterizing this method as electrochemical self-assembly. The photoelectrochemical properties of these unique ZnO-dye thin film electrodes were investigated in photocurrent transient measurements in the ms-regime and by steady- state voltammetric measurements. Two sets of electrodes are discussed, employing either metal complexes of tetrasulfophthalocyanines (TSPcMt; Mt = Zn, Al, Si) or the xanthene dye Eosin Y. For aggregates of TSPcMt on ZnO, efficient charge-transfer to the electrolyte is found, leading to low surface charging and low surface recombination of photogenerated holes with electrons from the ZnO, at however, rather low injection efficiencies of electrons into the conduction band of ZnO. This efficiency was higher for adsorbed monomers of TSPcMt leading to a considerably higher quantum efficiency of the photocurrent in spite of increased surface charging and recombination of holes. Higher photocurrents were observed for ZnO sensitized with monomers of Eosin Y caused by both, efficient electron transfer from the dye to ZnO as well as hole transfer from the dye to the electrolyte. Not only dye molecules which were directly accessible from the electrolyte, but also those which were enclosed within matrix cavities proved to be photoelectrochemically active.

Experimental PDT: studies on new Si-phthalocyanines and Si-naphthalocyanines in Cremophor emulsions

In the present work the following silicon (IV) - phthalocyanines and -naphthalocyanines bearing methoxyethylene glycol or methoxypolyethylene glycol covalently bound at the silicon are investigated: SiPc[OCH2CH2OCH3]2 (SiPc1), SiNc[OCH2CH2OCH3]2 (SiNc), SiPc[(OCH2CH2)nOCH3] with n approximately 115 (SiPc2). The phototherapeutic effect was shown at Lewis lung carcinoma implanted in mice. SiPc2 is monomeric soluble in water whereas the other two compounds aggregated in this solvent. Therefore these compounds were dissolved monomer in in aqueous Cremophor solution before in vivo administration. Laser irradiation was applied 7 days after implantation and 24 h after drug administration at the following wavelength (eta) ext: 672 nm for SiPc1 and SiPc2, 782 nm for SiNc. In all cases a fluence rate of 370 mW/cm2 at fluence of 360 J/cm2 was used. The assessment criteria for the tumor response were the changes in the mean tumor diameter with time, regrowth delay and average survival time (AST). According to the first parameter the most promising result was obtained after treatment with SiPc1. For example the mean tumor diameter increases as follows: SiPc1 less than SiPc2 less than SiNc very much less than control group without photosensitizer. The regrowth delay showed the same trend. however, for AST another dependence was observed. AST was the longest for SiPc2 (26 days) and shortest for SiNc (22 days). Compared to the control group (without sensitizer and irradiation) the AST was 9 days longer after SiPc2 treatment. Comparing SiPc1 and SiPc2 the chain length of the substituents does not influence the phototherapeutic properties. The detected therapeutic results probably are connected with the long wavelength absorption of the photosensitizers. The relatively lower affectivity of SiNc may be due to a lower degree of tumor accumulation as it was observed in our preliminary pharmacokinetic studies. It is also possible that the shorter AST after treatment with SiNc is connected with a greater dark toxicity.