Synthesis of amphipathic porphyrins and their photoinduced electron transfer reactions at the lipid bilayer-water interface

A one flask synthesis of cis-substituted amphipathic porphyrins is reported. These porphyrins were used to study electrostatic effects on photoinduced electron transfer across the lipid bilayer-water interface. A neutral porphyrin undergoes only dynamic interfacial electron transfer reactions irrespective of charge of the acceptor, although ionic strength effects indicate a negative charge on the porphyrin donor species. A dianionic porphyrin forms an interfacial static complex with a dicationic electron acceptor, methyl viologen, at low ionic strength. The electron transfer rate within the complex is slow, 10(5) approximately 10(6) s-1, which is attributed to a near orthogonal orientation between the donor and the acceptor pi orbitals.

Interaction of cationic porphyrins with DNA

Utilizing linear dichroism (LD), circular dichroism (CD), and fluorescence energy transfer, the binding geometries of a series of Co(3+)-porphyrins and their free ligands were examined. The compounds studied were Co-meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (CoTMPyP) and its free ligand (H2-TMPyP), Co-meso-tetrakis(N-n-butylpyridinium-4-yl)porphyrin (CoTBPyP) and its free ligand (H2TBPyP), and Co-meso-tetrakis(N-n-octylpyridinium-4-yl)porphyrin (CoTOPyP). The two non-metalloporphyrins exhibit negative LD, having angles of roughly 75 degrees relative to the DNA helix axis. They also display negative CD and a significant contact energy transfer from the DNA bases. On the other hand, the three metalloporphyrins display orientation angles of roughly 45 degrees between the porphyrin plane and the helix axis of DNA. Furthermore, they exhibit positive CD and no contact energy transfer from DNA bases. These observations show that the metalloporphyrins are not intercalated whereas non-metalloporphyrins having four freely rotating meso-aryl groups intercalate between the base pairs of DNA. In the presence of KHSO5, the cobalt porphyrins cleave closed circular PM2 DNA in a single strand manner, i.e., a single activation event on the porphyrin leads to a break in one of the DNA strands. A kinetic analysis of the cleavage data revealed that cleavage rates are in the order CoTMPyP > CoTBPyP > CoTOPyP with the difference being due to different DNA affinities rather than differences in cleavage rate-constants. Based on these and earlier observations, the metalloporphyrins appear bound to a partially melted region of DNA.

The protein moiety modulates the redox potential in cytochromes c

Cytochrome c is one of the most thoroughly documented oxidoreduction proteins. Its electron transfer activity, which involves an association between the heme group and the polypeptidic chain, is correlated with the redox potential value of the heme group. The redox potential covers a wide range up to 0.8 V, an extreme case being observed in the low-potential cytochromes c from sulfate reducing bacteria. On of the main roles of the polypeptidic moiety consists of modulating the redox potential value of the heme group. In this paper, some structural factors that seem likely to be involved in maintaining the redox potential value are described.

Phototherapeutic potential of alternative photosensitizers to porphyrins

Because of promising clinical results obtained with photodynamic therapy, more and more photosensitizers continue to be isolated (from natural sources), synthesized and evaluated, the development of which is considered to be a key factor for the successful clinical application of photodynamic therapy. Porphyrins and their analogs (as classical types of phototherapeutic agents) have been extensively reviewed. In this review, we have attempted to summarize the phototherapeutic potential (in particular, anticancer and antiviral aspects) of nonporphyrin photosensitizers (as a new generation of phototherapeutic agents) in more detail, which have been relatively much less reviewed hitherto. They include anthraquinones, anthrapyrazoles, perylenequinones, xanthenes, cyanines, acridines, phenoxazines and phenothiazines. They have shown certain phototherapeutic advantages over the presently used porphyrins. Some anthraquinones, perylenequinones, cyanines, phenoxazines and phenothiazines exhibit strong light absorption in the 'phototherapeutic window' (600-1000 nm), high photosensitizing efficacy and low delayed skin photosensitivity. Some of the nonporphyrin photosensitizers (such as rhodamine 123, merocyanine 540 and some cyanine cationic dyes) demonstrate higher selectivity for tumor cells. They can also be explored in connection with selective carcinoma photolysis strategy based on mitochondrion-, lysosome- or DNA-directed localization mode.

Laser-induced fluorescence line narrowing of native porphyrins in animal tissue

Using monochromatic laser excitation, narrowing of the porphyrins 0-0 fluorescence line in rat muscle tissue to a width of 50-70 cm-1 at 4.2 K is observed. Fluorescence spectra at different excitation wavelengths and excitation spectra are measured. Fluorescence line peak follows the shift of the excitation frequency. Several of the most prominent vibrational frequencies of porphyrins in the excited electronic state are determined.

Metabolically convertible lipophilic derivatives of pH-sensitive amphipathic photosensitizers

We propose the use of acetoxymethyl esters of pH-sensitive amphipathic photosensitizers (PS) for photodynamic therapy (PDT). These compounds may be applicable for PDT involving endocytosis of lipophilic carriers leading to lysosomal uptake of the esterified PS by target cells. Partial and/or total enzymatic de-esterification may result in the extralysosomal distribution of the photoactive agents, possibly culminating in a multisite photochemical response. We report here the synthesis and properties of chlorin e6 triacetoxymethyl ester (CAME) and pheophorbide a acetoxymethyl ester (PAME). Chlorin e6 and pheophorbide a are photocytotoxic chlorins that possess free carboxylate groups and exhibit optimum wavelengths of excitation substantially red shifted relative to hematoporphyrin derivative. Acetoxymethyl esterification of chlorin e6 and pheophorbide a was accomplished with bromomethyl acetate. High-performance liquid chromatography allowed for the purification of PAME, in 87% purity, and CAME, in 63% yield and 94% purity, as well as the detection of the presumed mono- and diesters of chlorin e6 as transient intermediates in the synthesis of CAME. The ultraviolet-visible absorption, fluorescence excitation and emission, NMR and mass spectra of the chlorin e6 triester are consistent with those expected for CAME. The pH-sensitive amphipathicity of pheophorbide a and chlorin e6 but not CAME was demonstrated using a water/1-octanol partition assay. The production of pheophorbide a from PAME and the sequential formation of the di- and monoesters and free chlorin e6 from CAME, by the action of lysosomal esterases obtained from cancer cells, demonstrate the potential of cellular enzymes to convert the lipophilic esters to pH-sensitive amphipathic PS.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl) cyclohex-2-enone on hepatic haem biosynthesis: species differences in hepatic porphyria

2-[1-(Ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl) cyclohex-2-enone (ETC) is a novel alkyl ketone herbicide. Continuous administration of ETC to mice for 28 days resulted in marked liver enlargement and severe intrahepatic cholestasis. These effects have been shown to result directly from a rapid and marked accumulation of porphyrin in the liver. The porphyrin which accumulates in the liver has been identified as protoporphyrin IX and dose response and time course studies confirm prior inhibition of mitochondrial ferrochelatase as the causal lesion. ETC was a very potent porphyrinogenic compound in mice, with a no-effect level for a single oral dose of 1 mg/kg. Rats and hamsters were insensitive to this type of hepatotoxicity following single oral doses of up to 750 mg/kg or following repeated, and indeed prolonged administration. The sensitivity of different species to ETC-induced porphyria correlated with the effect of ETC on hepatic ferrochelatase activity. The inhibition of ferrochelatase activity and the hepatic porphyria in mice were both found to be readily reversible upon withdrawal of ETC.

Recent advances in elucidation of biological corrinoid functions

Eleven adenosylcorrinoid-dependent rearrangements and elimination reactions have been described during the last four decades of vitamin B12 research. In contrast, only the cobamide-dependent methionine synthase was well established as a corrinoid-dependent methyl transfer reaction. yet, investigations during the last few years revealed nine additional corrinoid-dependent methyltransferases. Many of these reactions are catalyzed by bacteria which possess a distinct C1 metabolism. Notably acetogenic and methanogenic bacteria carry out such methyl transfers in their anabolism and catabolism. Tetrahydrofolate or a similar pterine derivative is a key intermediate in these reactions. It functions as methyl acceptor and the methylated tetrahydrofolate serves as a methyl donor.

Interactions of dicarboxylic porphyrins with membranes in relation to their ionization state

The interactions of dicarboxylic porphyrins with membrane systems are discussed with particular emphasis on the effect of the charge of the porphyrin and the nature of the side-chains. The incorporation of hematoporphyrin or related dicarboxylic porphyrins within small unilamellar vesicles as membrane models is favored by a decrease of the pH in the range of physiological pH values. This effect might play an important role in the retention of porphyrins by tumors, which are more acidic than normal tissues. Kinetics studies also show that the partition of the porphyrin between the lipidic bilayer and the aqueous phase is governed by its release rate rather than by its incorporation rate.

Spectroscopic studies of tin ethyl etiopurpurin in homogeneous and heterogeneous systems

Tin ethyl etiopurpurin is a promising second generation photosensitizer for photodynamic treatment of cancer. This compound is only poorly soluble in aqueous media and, therefore, needs a delivery system for administration to animals. Successful tumor eradication has previously been reported, following light exposure of rats previously administered with the purpurin formulated as a Cremophor El emulsion, in dipalmitoyl-phosphatidyl-choline liposomes or with gamma cyclodextrins. In this paper, we describe some absorbance and fluorescence studies of tin ethyl etiopurpurin in homogeneous and heterogeneous systems. In general, absorption and emission maxima were found to be red shifted as the environment changed from polar to non-polar. The viscosity and dielectric constant of the medium affected the purpurin fluorescence intensity. The liposome preparations were characterized by particle size determination, differential scanning calorimetry and by sensitizer fluorescence quenching studies. Photobleaching studies also showed variation owing to changes in the environment in which the dye was located.

Theoretical design of a bis-orthopepetide derivative of a tetracationic porphyrin targeted toward a six-base pair sequence of DNA

Tetra-(4-N-methylpyridyl)-porphyrin, (T4MPyP), is a tetracationic porphyrin that binds to G-C sequences of DNA by means of an intercalative mode. In order to extend its selective sequence recognition capacity for bases beyond the intercalation site, and in the major groove, we have undertaken the theoretical design of bis-ortho peptide derivatives of T4MPyP. In these, two ortho N-methylpiperidinium nitrogens are linked to a cationic residue, L-Lys, L-Orn, or L-Arg. The binding energetics of these novel compounds were compared for six distinct double-stranded palindromic hexanucleotide sequences. Four distinct modes of binding were compared: a) major, b) minor groove binding of both peptidic arms; c) a straddling mode in which each arm is in a different groove of DNA; d) exclusive binding of the arms to the sugar-phosphate backbone. For our most promising compound, that with Lys side-chains, a distinctive energetical advantage was computed in favor of an all-major groove binding to sequence d(CCCGGG)2. The corresponding complex is separated by an energy gap of 12 kcal/mol, with respect to the second-best sequence bound in the major groove, d(GGCGCC)2, and of 20 kcal/mol with respect to minor groove binding to sequence d(TACGTA)2. The results obtained with such a prototypic compound indicate that it is fully possible to design sequence selective (> 6 base-pairs) photosensitizers as peptide derivatives of T4MPyP and prompt the engineering of further, more complex analogs thereof.

Biochemistry of porphyria

1. The porphyrias are a group of metabolic disorders arising from defects in the haem biosynthetic pathway. Most forms are inherited as Mendelian autosomal dominants, but some types are recessive and others acquired through exposure to porphyrinogenic drugs and chemicals. There is a linked group of diseases, which are not porphyrias, but have in common alterations of haem biosynthesis. 2. The processes of haem biosynthesis are now well understood and the molecular biology of the functions and dysfunctions in the porphyrias are currently an area of intensive investigation. 3. The acute porphyrias, Acute Intermittent Porphyria, Variegate Porphyria and Hereditary Coproporphyria are of most importance since attacks of these may be life-threatening. 4. These diseases that usually present with a neurovisceral attack are characterized by excess production of the porphyrin precursors, 5-aminolaevulinate and porphobilinogen because of lowered activity of Porphobilinogen deaminase. 5. A variety of factors may precipitate these attacks including various drugs, alcohol, smoking, dieting or fasting and variations in steroid hormone levels. 6. The non-acute porphyrias are largely dermatological conditions, which present clinically as cutaneous photosensitivity. The dermatological changes are caused by the photosensitizing properties of circulating porphyrins and are accompanied by systemic effects of these porphyrins.

Photobleaching of mono-L-aspartyl chlorin e6 (NPe6): a candidate sensitizer for the photodynamic therapy of tumors

Most sensitizers used for the photodynamic therapy (PDT) of tumors photobleach on illumination. Thus, it is of interest to examine the photobleaching behavior of new sensitizers proposed for use in PDT. This report surveys the quantum yields and kinetics of the photobleaching of mono-L-aspartyl chlorin e6(NPe6), a hydrophilic chlorin that has many of the photoproperties desirable in a sensitizer for clinical PDT. It is a very effective sensitizer for the PDT of several types of model tumors in animals and is now in Phase I clinical trials. The quantum yield of NPe6 photobleaching in pH 7.4 phosphate buffer in air was 8.2 x 10(-4); this is greater than the yields for typical porphyrin photosensitizers. For example, the yields for hematoporphyrin and uroporphyrin are 4.7 x 10(-5) and 2.8 x 10(-5), respectively. The yield decreased significantly in organic solvents of low dielectric constant. The Sn derivative of NPe6 was more light stable than NPe6 (yield = 5.7 x 10(-6), while the Zn derivative was more sensitive (yield = 1.9 x 10(-2). Oxygen appeared to be necessary for the photobleaching of NPe6; however, bleaching was not inhibited by 100 mM azide, an efficient quencher of singlet oxygen. The photooxidizable substrates cysteine, dithiothreitol and furfuryl alcohol increased the quantum yield of photobleaching two- to four-fold, while the electron acceptor, metronidazole, increased it almost six-fold. Photobleaching yields for several other chlorins were also measured.

Preparation and characterization of covalently bound tetraphenylporphyrin-silica gel stationary phases for reversed-phase and anion-exchange chromatography

A tetraphenylporphyrin-based stationary phase for high-performance liquid chromatography is prepared by attaching a p-carboxyphenyl derivative of the porphyrin to aminopropyl silica gel through an amide bond. This stationary-phase support is used for the reversed-phase separation of several polycyclic aromatic hydrocarbons and is shown to exhibit novel shape selectivity toward planar aromatic solutes. Subsequent metalation of the immobilized tetraphenylporphyrin with either tin(IV) or indium(III) results in a stationary phase with anion-exchange characteristics. Both the tin(IV) and indium(III) metalloporphyrin-based stationary phases exhibit useful selectivity for the separation of aromatic sulfonates and aromatic carboxylates.

[The effect of various substituents, joined through the 5'- and 3'-ends of the primer, initiating properties during the polymerization reaction, catalyzed by AMV-revertase]

We investigated the interaction of AMV reverse transcriptase and Klenow fragment with oligonucleotide derivatives carrying different 3'- or 5'-terminal reactive groups. It was shown that the attachment of phenazinium, ethidium, and daunomycin residues to the 5'-terminal phosphate stabilized the enzyme template primer complexes, while cholesterol and hemin residues generally decreased their stability. The increased stability in solution correlated to a certain extent with the increase in affinity of the modified primers to the enzyme template complex. Coupling of bulky R residues to the primers had a weak effect on the maximal rate of primer conversion, which is likely to be a result of the lack of strong contacts between the substituents and the enzyme, and steric obstacles hindering translocation of the primer enzyme complex. We analyzed the inhibitory effect of 23 oligonucleotide derivatives (both complementary and noncomplementary to the template) with modified 3'- and 5'-ends, and revealed several analogs inhibiting polymerization catalyzed by AMV reverse transcriptase by 70-100% at 0.1-1 microM concentrations of the reagents.

Polyunsaturated fatty acid alkoxyl radicals exist as carbon-centered epoxyallylic radicals: a key step in hydroperoxide-amplified lipid peroxidation

13-Hydroperoxyoctadeca-9,11,15-trienoic acid was reacted with a catalytic amount of 5,10,15,20-tetraphenyl-21H,23H-porphyrin iron(III) chloride in dichloromethane containing 2,4,6-tri-tert-butylphenol. The principal products were identified as 13-oxooctadeca-9,11,15-trienoic acid, 13-oxotrideca-9,11-dienoic acid, and a series of isomeric epoxyaryl ethers [9-(2,4,6-tri-tert-butylphenoxy)-12,13-epoxyoctadec-10-enoic acids and 11-(2,4,6-tri-tert-butylphenoxy)-12,13-epoxyoctadec-9-enoic acids]. The epoxyaryl ethers are coupling products of 2,4,6-tri-tert-butylphenoxyl radical and an epoxyallylic radical formed by cyclization of an intermediate alkoxyl radical. The high yield of epoxyaryl ethers relative to 13-oxotrideca-9,11-dienoic acid suggests the equilibrium between alkoxyl radical and epoxyallylic radical lies predominantly toward epoxyallylic radical. This cyclization appears to be a key step in the amplification of lipid peroxidation by polyunsaturated fatty acid hydroperoxides.

Anaerobic breakdown of uroporphyrins I and III to bile pigments by extracts of Clostridium tetanomorphum

Two blue bile pigments were formed under anaerobic conditions from the tetrapyrrole precursor delta-aminolevulinate by cells and cell extracts of Clostridium tetanomorphum. These compounds were also formed by cell extracts from the octacarboxylic tetrapyrrole, uroporphyrin III. Bactobilin, the first bacterial bile pigment to be discovered, is related to uroporphyrin I. The present results hence increase the number of bile pigments related to bactobilin. Bactobilin and its isomers differ markedly from the eukaryotic bile pigments which are all related to the dicarboxylic compound, protoporphyrin IX. The enzyme participating in the formation of the bacterial bile pigments was obligatorily anaerobic, in decided contrast to the only other known bile pigment-forming enzyme, the eukaryotic oxygen-requiring heme oxygenase.

Free radicals in melanin-cationic porphyrin complexes in the dark and under light irradiation

Electron Paramagnetic Resonance (EPR) spectroscopy was employed in the study of the interaction between L-3,4-dihydroxyphenylalanine (L-Dopa) melanin and the cationic porphyrins meso-tetrakis(1-methylpyridinium-4yl)-porphyrin (TMPyP), meso-tetrakis-(1-benzylpyridinium-4-yl)-porphyrin (TBzPyP), and their respectives complexes ZnTMPyP and ZnTBzPyP. By monitoring signal intensities and progressive microwave power saturation it was shown that the interaction increases the equilibrium concentration of free radicals in L-Dopa melanin in the dark. The extent of increase is dependent on the presence of molecular oxygen and on the type of porphyrin. Not all interacting sites available for complexation in L-Dopa melanin are involved in the formation of free radicals. It was also observed that the interaction with porphyrins promotes an increase in the number of photoinduced free radicals in L-Dopa melanin during illumination with visible light.

Pharmaceutics and drug delivery aspects of heme and porphyrin therapy

The importance of porphyrins and metalloporphyrins as therapeutic drugs has increased significantly over the last decade. This review highlights some of the challenges faced by pharmaceutical scientists in formulating these drugs into stable, effective, and safe dosage forms. Most activity in the clinic has focused on three areas: photodynamic therapy of cancer (e.g., hematoporphyrin derivatives), porphyrias and hematological diseases (e.g., heme), and various forms of jaundice (e.g., tin porphyrins). The biodistribution, stability, aggregation, toxicology, and analytical methodology of porphyrin drugs are all important considerations in the pharmaceutical development of porphyrin drugs. The utility of delivery systems such as liposomes hold promise of increasing the therapeutic potential of these drugs. Future prospects for therapeutic applications of porphyrin drugs are also discussed.

Phototransformations of porphyrins in aqueous and micellar media

Porphyrin photoproducts with absorption maxima at 640 and 660 nm are formed in aqueous and micellar solutions during light exposure. Changes in the dimethoxyhaematoporphyrin (DMHp) Soret band on irradiation suggest that the photoproduct (640 nm) formation is conditioned by the "sandwich"-type self-associates. The formation of the photoproduct (660 nm) in micellar haematoporphyrin (Hp) and photosan-3 (PS) solutions and its formation in small amounts in phosphate-buffered solution (PBS), is related to the presence of covalently linked porphyrin structures and/or interaction with surfactant molecules. PS is the most photostable of the three investigated porphyrins. Its photostability is probably due to the presence of covalently linked "sandwich"-type aggregates.

Stereochemical factors in the transport and binding of photosensitizers in biological systems and in photodynamic therapy

The uptake and biological activity of porphyrins and phthalocyanines in tumours were correlated with the geometrical features of the photosensitizer molecules. The data suggest that a critical distance of approximately 1.2 nm between oxygen atoms (originating in SO3-, COO- or OH substituents) characterizes a biologically active photosensitizer for photodynamic therapy. We propose that tubulin, which is available in large amounts during mitosis, is the main receptor molecule which binds these photosensitizers. Basic amino acid residues or tightly bound cations in tubulin or homologous proteins may act as binding sites on the receptor molecule.

[Porphyrin derivatives of oligonucleotides. I. Synthesis of oligonucleotide derivatives bearing 2,4-di(alpha-(2-hydroxyethoxy)ethyl)- deuteroporphyrin IX or a metal complex of it and study of the oxidative modification of DNA by these derivatives]

A method for coupling 2,4-di[alpha-(2-hydroxyethoxy)ethyl] deuteroporphyrin dimethyl ether (IX), DDPOH and its complexes with metals to the 5'- or 3'-end of oligonucleotides was elaborated. In the presence of an oxidizing agent (H2O2), Fe(III)DDP-derivatives of oligonucleotides modified single-stranded DNA. The reaction was strictly site-specific and occurred at two neighbouring guanosine residues. A few types of modification were observed: cross-linking, modification leading to DNA cleavage upon piperidine treatment, and direct chain scission. The total modification yield reached 90%. Covalent attachment of Fe(III)DDP-group to oligonucleotides increased the efficiency of their uptake and the melting temperature of their complementary complexes.

Induction of circular dichroism of symmetrical porphyrins bound to random coil polypeptides in aqueous solutions

Absorption spectra and c.d. spectra have been measured in the region of Soret transition for aqueous solutions of porphine-meso-tetra(4-N-methylpyridinium) (TMpyP) tosylate in the presence of poly-L-glutamic acid, and of sodium porphine-meso-tetra(4-benzenesulphonate) (TPPS) or sodium porphine-meso-tetra(4-benzoate) (TPPC) in the presence of poly-L-lysine, all at high [P]/[D] ratios at neutral pH. The TmpyP-poly-L-glutamic acid system shows essentially no hypochromism and negligibly weak induced c.d., while the TPPS-poly-L-lysine or TPPC-poly-L-lysine system exhibits strong hypochromism and strong induced c.d. The former absorption band slightly shifts to red, but the latter shows a large blue shift. The primary interaction of the porphyrin with the polypeptide is their electrostatic binding. The difference in their interaction must arise from different degrees of hydrophobic interaction, and stronger interaction of TPPS or TPPC with poly-L-lysine would cause most of TPPS ions or all of TPPC ions bound on poly-L-lysine to dimerize, fix rigidly and couple together electronically on fully charged poly-L-lysine.

Microscale determination of the spectral characteristics and carbon-isotopic compositions of porphyrins

Molar extinction coefficients for band III of Ni porphyrins are calculated from results of spectrophotometric and manometric analyses of individual etioporphyrins, DPEP, cyclic, and diDPEP porphyrins known to initially be pure from mass spectrometry, 1H NMR, and analytical HPLC studies. A method for determining carbon-isotopic compositions and purity of micromolar quantities of individual porphyrins using combined spectrophotometric and manometric techniques is presented.

Photosensitizing properties of mono-L-aspartyl chlorin e6 (NPe6): a candidate sensitizer for the photodynamic therapy of tumors

There is a large amount of interest in chlorins as photosensitizers for the photodynamic therapy of tumors because of their strong absorption in the red, where light penetration into mammalian tissues is efficient. Mono-L-aspartyl chlorin e6 (NPe6), in phosphate buffer of pH 7.4, had absorption peaks at 400 and 654 nm with molar absorption coefficients of 180,000 and 40,000 M-1 cm-1 respectively. In buffer, the NPe6 triplet had a peak at 440 nm and a lifetime under argon of approximately 300 microseconds. The triplet was efficiently quenched by ground state oxygen (kQ = 1.9 x 10(9) M-1 s-1) with the formation of singlet oxygen, as identified by its near infrared luminescence. The quantum yield of singlet oxygen production was 0.77. A number of substrates were efficiently photo-oxidized by NPe6, including furfuryl alcohol, cysteine, histidine, tryptophan and human serum albumin. These reactions were efficiently inhibited by azide (which did not quench NPe6 triplets), indicating that they are probably mediated by singlet oxygen. Thus, NPe6 has a desirable array of photoproperties for a sensitizer to be used in the clinical photodynamic therapy of tumors.

Solid-phase introduction and intracellular photoinduced reaction of a water-soluble meso-tetracarboxyporphine conjugated to an antisense oligodeoxyribonucleotide

Oligonucleotide conjugated with water-soluble meso-tetra(4-carboxyphenyl) porphine (TPPC4) has been prepared by a supporting synthesis and novel solid-phase conjugation strategy. The conjugates could be used in dual fashion: i) on formation of iron complex, target DNA could be site-specifically cleaved on incubation with dithiothreitol; ii) on incubation of RR 1022 rat epithelial cell culture with non-metalized oligonucleotide TPPC4 conjugate, cytotoxic effect was detected after irradiation with laser light at 635 nm.

Carbon and nitrogen isotopic compositions of alkyl porphyrins from the Triassic Serpiano oil shale

The carbon and nitrogen isotopic compositions of seven of the most abundant alkylporphyrins from the Serpiano oil shale (marine, Triassic) were determined. For the C31 and C32 butanoporphyrins, values of delta 13CPDB and delta 15NAIR averaged -24.0% and -3.1%. In contrast, the C31 and C32 methylpropanoporphyrins, DPEP, and a C30 13-nor etioporphyrin had delta 13C and delta 15N values averaging -27.5 and -3.3%, respectively. Carbon and nitrogen isotopic values for kerogen averaged -30.8 and -0.9, whereas those for total extract averaged -31.6, and -4.0%. The butanoporphyrins apparently derive from a biological source different from that giving rise to the other porphyrins, their 13C enrichment not being related to carbon isotopic fractionation accompanying diagenetic reactions. The delta 15N values for all the porphyrins indicate that the depletion of 15N observed in the kerogen is of primary origin. Consistent with the very high abundance of hopanoids and methyl hopanoids in the aliphatic hydrocarbon fraction, it is suggested that cyanobacterial fixation of N2 may have been the main cause of 15N depletion.

Sn-chlorin e6 antibacterial immunoconjugates. An in vitro and in vivo analysis

Monoclonal antibody-Sn-chlorin e6 immunoconjugates were prepared by the site-selective covalent modification of the monoclonal oligosaccharide moiety. By carefully controlling the reaction conditions and introducing triethanolamine groups as axial ligands of the Sn moiety, conjugates with in vivo biodistribution properties similar to underivatized IgG were prepared. By varying the reaction conditions, conjugates were reproducibly prepared with a range of photosensitizer to mAb molar ratios from 1.6 to 10. Based on a competitive inhibition radioimmunoassay, conjugates prepared by this method showed selectivity and binding affinity comparable to the unmodified antibody. The immunoconjugates had only slightly lower singlet oxygen yields than that observed with the Sn-chlorin e6 precursor indicating that negligible aggregation or structural modification of the chromophores occurred during the synthesis process. In vitro cell killing experiments demonstrated that all conjugates possessed significant cytotoxic activity. Biodistribution studies in mice showed that conjugates prepared with axial ligands had significant serum retention 24 h after injection while conjugates prepared without the triethanolamine ligand were much more rapidly cleared. In vivo specificity was demonstrated using rats infected with Fisher immunotype I P. aeruginosa at a site in the left posterior thigh muscle. Target to background ratios exceeded 60 at 120 h after conjugate injection of the specific immunoconjugate, compared to a ratio of only 6 for a non-specific mouse IgG conjugate. Biodistribution patterns at 120 h post injection indicate that the conjugates were both biologically active and structurally intact.

Optical absorption and fluorescence spectroscopy studies of ground state melanin-cationic porphyrins complexes

Optical absorption and fluorescence spectroscopies were employed in the study of the interaction between synthetic L-dopa (dihydroxyphenylalanine) melanin and the cationic porphyrins tetrakis(4-N-methylpyridyl) porphyrin (TMPyP), tetrakis(4-N-benzylpyridyl)porphyrin (TBzPyP), zinc tetrakis(4-N-methylpyridyl)porphyrin (ZnTMPyP) and zinc tetrakis (4-N-benzylpyridyl)porphyrin (ZnTBzPyP). Optical absorption and fluorescence properties of the porphyrins were dependent on the symmetry of the central ring. No evidence was found for dimerization of the porphyrins in phosphate buffer, pH 7, in the concentration range between 4 x 10(-8) to 5 x 10(-5) M. Addition of L-dopa melanin red shifted the optical absorption spectra of porphyrins, concomitant to broadening and reduction in intensity of the bands. L-Dopa melanin also strongly quenched the fluorescence of the porphyrins. Time resolution of the fluorescence decay of porphyrins showed at least two lifetimes that were only slightly modified in the presence of melanin. The interaction between melanin and porphyrin resulted in the formation of non-fluorescent ground state complexes. It was found that there are two different classes of binding sites in melanin for complexation with cationic porphyrins and the values of dissociation constants are of the order of 10(-8) M. These values and the number of binding sites are dependent on the nature of the porphyrins. It was shown that the binding has electrostatic origin, but it is also affected by metal coordination and hydrophobic interaction.

Identification of heme macrocycle type by near-infrared magnetic circular dichroism spectroscopy at cryogenic temperatures

The electron paramagnetic resonance (EPR) and near-infrared magnetic circular dichroism (MCD) spectra of the azide and cyanide adducts of nitrimyoglobin and hydroperoxidase II from Escherichia coli have been measured at cryogenic temperatures. For the first time, ligand-to-metal charge-transfer transitions in the near-infrared have been observed for an Fe(III)-chlorine system. It is shown that near-ultraviolet-to-visible region electronic spectra of 'green' hemes such as these are an unreliable indicator of macrocycle type. However, the combined application of EPR and near-infrared MCD spectroscopies clearly distinguishes between the porphyrin-containing nitrimyoglobin and the chlorine-containing hydroperoxidase II.

1H-NMR comparative study of the active site in shark (Galeorhinus japonicus), horse, and sperm whale deoxy myoglobins

1H-NMR spectra of deoxy myoglobins (Mbs) from shark (Galeorhinus japonicus), horse, and sperm whale have been studied to gain insights into their active site structure. It has been demonstrated for the first time that nuclear Overhauser effect (NOE) can be observed between heme peripheral side-chain proton resonances of these paramagnetic complexes. Val-E11 methyl and His-F8 C delta H proton resonances of these Mbs were also assigned from the characteristic shift and line width. The hyperfine shift of the former resonance was used to calculate the magnetic anisotropy of the protein. The shift analysis of the latter resonance, together with the previously assigned His-F8 N delta H proton resonance, revealed that the strain on the Fe-N epsilon bond is in the order horse Mb approximately whale Mb < shark Mb and that the hydrogen bond strength of the His-F8 N delta H proton to the main-chain carbonyl oxygen in the preceding turn of the F helix is in the order shark Mb < horse Mb < whale Mb. Weaker Feporphyrin interaction in shark Mb was manifested in a smaller shift of the heme methyl proton resonance and appears to result from distortion of the coordination geometry in this Mb. Larger strain on the Fe-N epsilon bond in shark Mb should be to some extent attributed to its lowered O2 affinity (P50 = 1.1 mmHg at 20 degrees C), compared to whale and horse Mbs.

Photosensitizing efficiency of two regioisomers of the benzoporphyrin derivative monoacid ring A (BPD-MA)

Benzoporphyrin derivative, monoacid ring A (BPD-MA), currently in clinical trials as a photosensitizer for photodynamic therapy for cancer, consists of two regioisomers (A1 and A2) present in equal proportions. The contribution of the regioisomers to the overall photosensitizing potency of BPD-MA was tested in vitro and in vivo. The in vitro photosensitizing potencies of BPD-MA-A1 and -A2 were tested in a standard cytotoxicity assay using M1 (rhabdomyosarcoma of DBA/2 mice) tumor cells and were found to be equivalent. The in vivo photosensitizing efficacies of the regioisomers were tested in the M1 tumor model in DBA/2 mice and were also found to be equivalent. Biodistribution of the regioisomers in mouse plasma, tumor and liver was studied in M1 tumor-bearing DBA/2 mice at 15 min and 3 hr post intravenous injection of [14C]BPD-MA-A1/A2 at 4 mg/kg body weight. Plasma and extracts from tumor and liver were analysed by HPLC and tested for radioactivity. The two regioisomers were eliminated from plasma and liver at different rates, which resulted in A1:A2 ratios of 1:0.28 in plasma and 1:0.75 in liver at 3 hr post injection. The differential elimination was not observed to any significant degree in the tumor, where even at 3 hr post injection the A1:A2 ratio was 1:1.15. Therefore, we concluded that in tumor tissue, at 3 hr post injection, the time at which laser photodynamic therapy is carried out, both regioisomers were present in about equal proportions. Further, both regioisomers were fully active as determined by an in vitro cytotoxicity assay following extraction.

Quantum yields and kinetics of the photobleaching of hematoporphyrin, Photofrin II, tetra(4-sulfonatophenyl)-porphine and uroporphyrin

Porphyrins used as sensitizers for the photodynamic therapy (PDT) of tumors are progressively destroyed (photobleached) during illumination. If the porphyrin bleaches too rapidly, tumor destruction will not be complete. However, with appropriate sensitizer dosages and bleaching rates, irreversible photodynamic injury to the normal tissues surrounding the tumor, which retain less sensitizer, may be significantly decreased. This paper surveys the quantum yields and kinetics of the photobleaching of four porphyrins: hematoporphyrin (HP), Photofrin II (PF II), tetra(4-sulfonatophenyl)porphine (TSPP) and uroporphyrin I (URO). The initial quantum yields of photobleaching, as measured in pH 7.4 phosphate buffer in air, were: 4.7 x 10(-5), 5.4 x 10(-5), 9.8 x 10(-6), and 2.8 x 10(-5) for HP, PF II, TSPP and URO respectively; thus, the rates of photobleaching are rather slow. Low oxygen concentration (2 microM) significantly reduced the photobleaching yields. However, D2O increased the yields only slightly, and the singlet oxygen quencher, azide, had no effect, even at 0.1 M. Photosensitizing porphyrins in body fluids, cells and tissues may be closely associated with various photooxidizable molecules and electron acceptors and donors. Therefore, selected model compounds in these categories were examined for their effects on porphyrin photobleaching. A number inhibited and/or accelerated photobleaching, depending on the compound, the porphyrin and the reaction conditions. For example, 1.0 mM furfuryl alcohol increased the photobleaching yields of HP and URO more than 5-fold, with little effect on PF II or TSPP. In contrast, the electron acceptor, methyl viologen, increased the photobleaching yield of TSPP more than 10-fold, with little accelerating effect on the other porphyrins. These results suggest that the mechanism(s) of the photobleaching of porphyrin photosensitizers in cells and tissues during PDT may be complex.

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.

Clearance times of porphyrin derivatives from mice as measured by in vivo fluorescence spectroscopy

The clearance times of 17 different porphyrin derivatives from SKH:HR-1 mice have been measured using the technique of in vivo fluorescence spectroscopy. This technique monitors the in vivo porphyrin fluorescence observed from the external skin surface. Most hydrophilic porphyrin derivatives show relatively short clearance times, in the order of 2.5-6 h. The dicarboxylic acid porphyrins, proto-, hydroxyethylvinyldeutero- and hematoporphyrin IX have clearance times of 7.8, 12.2 and 14.7 h respectively. The mixture hematoporphyrin derivative has an intermediate clearance time of 12.6 h. N-methylated porphyrins show clearance times in the vicinity of 15-22 h. Monoaspartyl chlorin e6 shows the longest clearance time of all porphyrin derivatives measured (30.3 h).

Configuration of triporphyrin ethers probed by fluorescence measurements

The fluorescence spectra and lifetimes of triporphyrin ethers derived from hematoporphyrin, mesoporphyrin and protoporphyrin were examined, together with relative hydrophobicities estimated from reverse-phase high performance liquid chromatography (HPLC) elution times. The following data suggest a molecular arrangement with two of the three rings in a "folded configuration". The trimers display a greater fluorescence yield (phi f) than the corresponding diporphyrin ethers which contain only the two folded rings. The fluorescence lifetime data for the trimers are consistent with signals from both a folded ring pair (7-8 ns) and a free ring (14 ns). Reverse-phase HPLC studies indicate that the trimers are intermediate in hydrophobicity between the monomers and dimers. Preliminary data suggest that, for certain peripheral substitutions, the trimer configuration is superior to the dimer for photodynamic therapy.

Photochemical release of bases from nucleosides and their derivatives by water-soluble iron(III) porphyrins

The compounds [meso-tetrakis(1-methyl-4-pyridiniumyl)porphyrinato]iron(III ) (FeIIITMPyP) and [meso-tetrakis(3,5-dichloro-1-methyl-4-pyridiniumyl)porphyrinat o]iron(III) (FeIIITCl2MPyP) photocatalysed the release of bases from nucleosides and their derivatives. The ribonucleosides, of which cytidine (C) gave the highest yield, produced much higher yields of free base than the corresponding deoxyribonucleosides. Under an argon atmosphere, virtually quantitative reduction of FeIIITMPyP into FeIITMPyP by C or 2'-deoxycytidine (dC) was observed and the reduction by C was much more effective than by dC. The increased reactivity of ribonucleosides relative to deoxyribonucleosides was ascribed to a difference in the binding properties of the porphyrin-nucleoside interactions and to base-releasing degradation of ribonucleosides from their C-2' carbon radical.

DNA intercalation and photosensitization by cationic meso substituted porphyrins

Several cationic porphyrins are known to bind to DNA by intercalative and outside binding modes. This study identifies the cis and trans isomers of bis(N-methyl-4-phridiniumyl)diphenyl porphyrin as DNA intercalators based on evidence from a DNA topoisomerase I assay. Moreover, both isomers are shown to be potent photosensitizers of DNA, inducing multiple S1 nuclease sensitive breaks in the phosphodiester backbone. Porphyrin-induced photodamage in DNA was also shown to be quantitatively dependent upon ionic strength and to inhibit the action of restriction endonucleases. The results indicate that these porphyrins can be useful probes of DNA structure and have potential as DNA-targeted photosensitizers.

Selective tumor uptake of a boronated porphyrin in an animal model of cerebral glioma

The prognosis for patients with high-grade cerebral glioma is poor. Most treatment failures are due to local recurrence of tumor, indicating that a more aggressive local therapy could be beneficial. Adjuvant treatments such as porphyrin-sensitized photodynamic therapy (PDT) or boron neutron capture therapy (BNCT) have the potential to control local recurrence. The selective tumor uptake of a boronated porphyrin was studied in CBA mice bearing an implanted intracerebral glioma. Biopsy samples of tumor, normal brain, and blood were analyzed by a fluorometric assay following intraperitoneal and intravenous administration of boronated protoporphyrin (BOPP). This compound was selectively localized to tumor at ratios as high as 400:1 relative to normal brain. Confocal laser scanning microscopy of glioma cells in vitro and in vivo showed that BOPP was localized within mitochondria and excluded from the nucleus of these cells. This discrete subcellular localization was confirmed by density gradient ultracentrifugation after homogenization of mouse tumor biopsies. The selective discrete localization of these compounds within the tumor suggests that this compound may be used as a dual PDT/BNCT sensitizer.

Investigation of heme distortions and heme-protein coupling in the isolated subunits of oxygenated human hemoglobin by resonance Raman dispersion spectroscopy

To probe the distortions of the heme groups resulting from heme-apoprotein interaction in the isolated subunits of oxygenated human hemoglobin (i.e., alpha SH-oxyHbA and beta SH-oxyHbA), the dispersion of the depolarization ratio of the Raman lines at 1375 cm-1 (nu 4) and 1638 cm-1 (nu 10) was measured at various pHs. The data were analyzed in terms of vibronic coupling parameters which depend on symmetry-classified normal distortions of the heme groups. In the alpha-chain the nu 10 mode is not affected by symmetry-lowering distortions. In the beta-chain, however, this mode is significantly influenced by asymmetric B1g and B2g distortions. This was interpreted in terms of different interactions between the peripheral substituents and the porphyrin macrocycle in the respective chains. The nu 4 mode of both chains is subject to B1g (B2g) and A2g distortions, which are more pronounced in beta SH-oxyHbA. This is most probably due to differences in the repulsive interactions between the proximal imidazole and the pyrrole. While the depolarization ratio of both lines investigated is pH-independent in alpha SH-oxyHbA, it exhibits a significant pH dependence in beta SH-oxyHbA. This parallels the finding that the isolated beta-chains exhibit a Bohr effect whereas the alpha-chains do not. Consequently, the pH dependence of the coupling parameters and the Bohr effect of beta SH-oxyHbA could be rationalized in terms of the very same proton binding processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Some aspects of the early evolution of photosynthesis

The early evolution of a photocatalytic system of the porphyrin type, able to efficiently collect and utilize solar energy for primary electron transfer is discussed. Experimental results concerning some spectral and photochemical properties of the porphyrins, biosynthetic precursors of chlorophyll and their complexes with polymeric templates are reviewed. Protoporphyrin IX associated with pigmented proteinoid is demonstrated to be a favourable candidate for a role of a photosensitizer of the first photosynthetic reaction centers. The origin and early evolution of the photosynthetic electron transfer chain and of the phosphorylating mechanism are discussed with emphasis on the energetic mechanisms of archaebacteria.

A review of in vivo studies of porphyrins and unexpected fluorescences. An interpretation of the results

Clinical applications of porphyrins lead research biologists to characterize these compounds according to their fluorescence. These measurements revealed unexpected fluorescence spectra in addition to those of the injected porphyrins. The general characteristics of the spectra of porphyrins are reviewed. The technique permitting studies on animals in a waking state and the advantages of this method are shown. The studies in this field are reviewed and spectra reproduced. Among the observed fluorescences, those which cannot be attributed to injected porphyrins are divided into two groups. The first group, above 580 nm, seems to result from molecular associations (polymers or micelles of injected porphyrins). The second group, from 560-575 nm, seems to belong to a natural compound. Some spectroscopic observations and some medical reports lead us to identify it as an unusual natural porphyrin and perhaps as metalloporphyrin. Some authors have mentioned a Zn porphyrin. Finally, the importance of continuing the study of this natural porphyrin is discussed.

Evidence that a formyl-substituted iron porphyrin is the prosthetic group of myeloperoxidase: magnetic circular dichroism similarity of the peroxidase to Spirographis heme-reconstituted myoglobin

To probe the identity of the active site heme-type prosthetic group of myeloperoxidase, whose structure has not been established unambiguously [proposed structures are (i) a chlorin (dihydroporphyrin) or (ii) a formyl-substituted porphyrin such as present in heme a], Spirographis heme (2-formyl-4-vinyldeuteroheme IX) has been incorporated into apo-myoglobin as a possible iron porphyrin model. Comparison of parallel derivatives of these two green proteins with magnetic circular dichroism spectroscopy reveals considerable similarities between several derivatives of these proteins, including the pyridine hemochromogen, the native ferric, ferrous-oxy, and ferrous-CO forms. In contrast, the magnetic circular dichroism spectra of available iron chlorin (octaethylchlorin) model complexes in analogous ligation and oxidation states do not show any significant spectral similarities to myeloperoxidase. This finding provides important evidence in favor of a formyl-substituted porphyrin as the structure of the prosthetic group macrocycle of myeloperoxidase.

Potential photosensitizers for photodynamic therapy. III. Photophysical properties of a lipophilic chlorin and its zinc and tin chelates

Photophysical properties of a lipophilic chlorin derivative and its zinc and tin chelates were investigated in chloroform. The quantum yields of the fluorescence phi F, of the S1----T1 intersystem crossing phi T and of singlet oxygen (1 delta g) formation phi delta, as well as the Stern-Volmer constants for the quenching of the S1 states by oxygen and the rate constants of quenching of O2(1 delta g) by the chlorins were measured. In comparison to the metal-free chlorin an increase of phi T and a decrease of phi F have been observed for the metal-containing derivatives, whereas the phi delta values remain constant.

Time-gated fluorescence spectroscopy of porphyrin derivatives and aluminium phthalocyanine incorporated in vivo in a murine ascitic tumour model

The effect of systemic administration on drug uptake at cellular level was evaluated using time-gated fluorescence spectroscopy performed on a murine ascitic tumour model. Mice bearing L1210 leukaemia were injected intraperitoneally or intravenously with 25 mg per kg body weight hematoporphyrin derivative (HpD), 12.5 mg per kg body weight photofrin II (PII), 25 or 5 mg per kg body weight disulphonated aluminium phthalocyanine (AlS2Pc). Every 2 h and for up to 22 or 30 h, mice were sacrificed, leukaemic cells extracted from the peritoneum, washed, and resuspended in buffer for fluorescence measurements. HpD and PII emission spectra were almost identical 12 h after intraperitoneal injection with main peaks at 630 nm and no appreciable changes afterwards. In the first 12 h, the PII fluorescence spectrum was constant, while in the case of HpD a shoulder at 615 nm was detectable. Similar fluorescence behaviour was observed after intravenous administration of porphyrin derivatives. These results seem to confirm that the tumour localizing fraction is the part actually retained by the cells. The AlS2Pc spectrum peaked at 685 nm and did not change in any of our experiments. AlS2Pc is incorporated more rapidly with respect to porphyrins, as was clearly observed in the case of intravenous administration, where the AlS2Pc fluorescence was readily detectable after 2 h, whereas the PII emission became apparent only after 4-6 h.