Chlorin-type photosensitizers photochemically derived from vinyl porphyrins

The reaction of singlet oxygen with four vinyl-substituted dicarboxylic porphyrins, vinyldeuteroporphyrin (VD), ethylvinyldeuteroporphyrin (EVD), hydroxyethylvinyldeuteroporphyrin (HVD) and protoporphyrin (PP) in organic solutions is investigated. The main products, the "hydroxyaldehyde" chlorin-type derivatives, are formed with a concentration-dependent photochemical quantum yield that reaches a maximum of 7.4 +/- 1.6 x 10(-3). However, owing to the high turnover of singlet-oxygen production, these chlorin-type compounds are easily prepared photochemically with a chemical yield of 70% and little side product formation. In chemical ionization mass spectrometry, these compounds display an unusual fragmentation with a loss of 16 mass units. This is attributed to the loss of the oxygen bound to the saturated carbon of the modified pyrrole unit. All these compounds sensitize the formation of singlet oxygen with a yield around 0.8. They interact with singlet oxygen with rate constants of 5 x 10(6)-9 x 10(6) M-1 s-1, lower than those measured for vinyl porphyrins. These data are likely to help in the characterization of photoproducts of vinyl porphyrins relevant to photodynamic therapy (PP, HVD). As exemplified with VD and EVD, they also point out the reaction of singlet oxygen as an efficient route to chlorin-type photosensitizers.

Enhancement of meta-tetrahydroxyphenylchlorin-sensitized photodynamic treatment on human tumor xenografts using a water-soluble vitamin E analogue, Trolox

Photodynamic therapy (PDT) using meta-tetrahydroxyphenylchlorin (mTHPC) performed on HT29 human colon adenocarcinoma xenografts in nude mice was shown to be enhanced by Trolox, a water-soluble vitamin E analogue. Trolox, injected i.p. at 250 mg/kg body weight 90 min before PDT, delayed tumor doubling time from 13 (PDT only) to 19 days. Enhancement of the tumoricidal effect of PDT by Trolox required the presence of the drug at the photochemical stage since its injection after irradiation is ineffective. HPLC measurements indicated that 1 hr after injection the Trolox concentration in plasma was as high as 0.8 mM. In vivo measurements of mTHPC fluorescence in mice treated by PDT with or without Trolox injection showed that Trolox did not protect mTHPC from photodegradation. Laser flash photolysis studies performed in solution demonstrated that Trolox reduces triplet mTHPC efficiently (reaction rate constant 2 x 10(7) M(-1) * sec(-1)) leading to the formation of radical products. Kinetic considerations suggest that the Trolox-mediated radical pathway can work in relay with singlet oxygen in hypoxic conditions, providing a possible explanation for the observed enhancement of mTHPC-sensitized PDT by Trolox.

Kinetics of DNA adduct formation and removal in mouse hepatocytes following in vivo exposure to 5,9-dimethyldibenzo[c,g]carbazole

5,9-Dimethyldibenzo[c,g]carbazole (DMDBC), a potent mouse hepatocarcinogen, has been shown to induce a non-linear increase in mutant frequency in the liver of the transgenic MutaMouse. To gain insight into the mechanisms underlying the mutagenicity of DMDBC in vivo, DNA damage formation and removal were monitored in mouse hepatocytes over 4-144 h after a single skin application of 10 or 90 mg/kg DMDBC. DNA adducts were measured by (32)P-post-labeling. DNA repair was assessed by: (i) the unscheduled DNA synthesis (UDS) assay, which measures [(3)H]thymidine incorporation into hepatocyte DNA undergoing excision repair; (ii) the Comet assay, which detects DNA strand breaks transiently produced between the incision and rejoining steps of the excision repair process. A plateau of approximately 400 DNA adducts/10(8) nucleotides was reached 24 h after treatment with 10 mg/kg and remained unchanged until 144 h. UDS activity was significantly induced at 15 and 24 h, while no DNA strand breaks were observed at any sampling time. These results suggest that DNA repair mechanisms were efficiently induced and the formation of a high degree of DNA damage was avoided at this dose level. Following exposure to 90 mg/kg DMDBC, the number of DNA adducts increased sharply to a maximum at 24 h ( approximately 8000/10(8) nucleotides) and then declined to approximately 500/10(8) nucleotides at 144 h. UDS activity was markedly induced from 15 to 72 h. Low levels of DNA strand breaks were observed at 24 and 48 h. The formation of large numbers of DNA adducts and the emergence of DNA strand breaks despite a strong initial induction of UDS activity suggested that DNA repair mechanisms were saturated at this dose level. This phenomenon could partly account for the non-linear induction of gene mutations previously reported in the liver of the transgenic MutaMouse.

Targeting of HIV gp120 by oligonucleotide-photosensitizer conjugates. Light-induced damages

Some guanine-rich oligonucleotides inhibit HIV infectivity through interaction with the gp120 glycoprotein. Besides, photoinactivation of viruses attracts attention for blood decontamination. The feasibility of targeting a red light-absorbing chlorin-type photosensitizer to gp120 through covalent coupling with 8-mer phosphodiester oligodeoxynucleotides is investigated. Some conjugates inhibit binding of antibodies directed to gp120. Inhibition is significantly increased upon red light activation. The activity of the conjugates correlates with their ability to self-associate, a process strongly favored by the propensity of the hydrophobic chlorin moiety to dimerize. Thus, the photosensitizer moiety both promotes structures with a higher affinity for gp120 and, upon light activation, can induce site-directed damages to the protein.

Kinetic and equilibrium studies of incorporation of di-sulfonated aluminum phthalocyanine into unilamellar vesicles

The interactions of cis-di-sulfonated aluminum phthalocyanine (PcS(2)Al) with dimyristoylphosphatidylcholine (DMPC) unilamellar vesicles have been investigated by fluorescence spectroscopy. At pH 7.0, PcS(2)Al incorporates into the vesicles with a high affinity constant (2.7x10(6) M(-1), in terms of phospholipid concentration). The fluorescence changes following rapid mixing of PcS(2)Al with vesicles are biphasic. The first phase is attributed to the entry of PcS(2)Al into the vesicles, as deduced from the linear dependence of the rate upon lipid concentration. More surprisingly, this rate is strongly pH dependent with a marked maximum around pH 7.3, a result interpreted in terms of the coordination state of the aluminum ion in aqueous solutions. At this pH, a hydroxide ion neutralizes the residual positive charge of the metal ion that remains unbalanced after coordination by the phthalocyanine cycle. A water molecule is likely to complete the metal coordination sphere. Only this form, PcAl(+)(OH(-))(OH(2)), with an uncharged core is quickly incorporated into the vesicles. The protonation of OH(-) or the deprotonation of the coordinated H(2)O leading to a positively or negatively charged core, respectively, account for the observed pH effect. Studies on the effect of cholesterol addition and exchange of PcS(2)Al between vesicles and albumin all indicate the absence of transfer of the phthalocyanine between the vesicle hemileaflets, a result expected from the presence of the two negatively charged sulfonated groups at the ring periphery. Instead, the slower kinetic phase is likely due to the movement of the phthalocyanine becoming more buried within the outer leaflet upon the loss of the water molecule coordinated to the aluminum ion.

Effect of mitogenic or regenerative cell proliferation on lacz mutant frequency in the liver of MutaTMMice treated with 5, 9-dimethyldibenzo[c,g]carbazole

The purpose of this work was to investigate the impact of cell proliferation on liver mutagenesis. The genotoxic hepatocarcinogen 5, 9-dimethyldibenzo[c,g]carbazole (DMDBC) was administered to lacZ transgenic MutaTMMice at a non-hepatotoxic dose of 10 mg/kg, which induces only a slight increase in the liver lacZ mutant frequency (MF). To determine if cell proliferation stimuli enhanced DMDBC mutagenicity, MF was analyzed in mice first receiving DMDBC 10 mg/kg, then approximately 2 weeks later, either carbon tetrachloride (CCl4, a cytotoxic agent inducing regenerative cell proliferation) or phenobarbital (PB, a mitogenic agent inducing direct hyperplasia). In preliminary studies, the extent of cell proliferation induced by CCl4, PB and DMDBC was determined in non-transgenic CD2F1 mice by means of 5-bromodeoxyuridine labeling. The labeling index was significantly increased after CCl4 and PB, while no change was detected with DMDBC. MF was then determined in MutaTMMice 28 days after initial DMDBC treatment. No increase in MF was detected in mice receiving CCl4 or PB alone. A 2- to 3-fold increase in MF was detected in mice treated with 10 mg/kg DMDBC alone. In contrast, MF was markedly increased in mice receiving DMDBC followed by proliferative treatment (15-fold with CCl4 and 25-fold with PB). These results demonstrate that expression of DMDBC-induced mutations in mouse liver largely depends on the induction of cell proliferation (by a cytotoxic or mitogenic stimulus) and illustrate that MutaTMMouse is a valuable tool to investigate the early events of liver carcinogenesis.

Kinetics of induction of DNA damage and lacZ gene mutations in stomach mucosa of mice treated with beta-propiolactone and N-methyl-N'-nitro-N-nitrosoguanidine, using single-cell gel electrophoresis and MutaMouse models

beta-Propiolactone (BPL) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) are two direct alkylating agents that induce multiple genetic lesions and tumors in the rodent stomach. We measured the kinetics of the induction of DNA damage by using the single-cell gel electrophoresis assay (SCGE) and the induction of gene mutations by using the MutaMouse model in the glandular stomach mucosa of mice exposed to a single oral administration of BPL or MNNG. The aims were to determine the optimal sampling time and to investigate the cause-effect relationship between DNA damage and gene mutations. The induction of comets, evaluated in individual cells with the tail moment, was analyzed 1, 2, 4, 24, and 72 hr after a single oral administration of 25 mg/kg BPL or 20 mg/kg MNNG. The effects of both compounds were most intense at the earlier sampling times (1-2 hr), tailing off 4 hr after treatment and becoming undetectable at 72 hr. The lacZ mutant frequency (MF) was measured 3, 7, 14, 28, and 50 days after a single oral administration of 150 mg/kg BPL or 100 mg/kg MNNG, and 3 and 14 days after a single administration of 25 mg/kg BPL or 20 mg/kg MNNG. The MF was strongly enhanced at the highest doses and all sampling times, the most marked effects being observed 14 days (11.1-fold) and 28 days (19.0-fold) after BPL and MNNG administration, respectively. At the lowest doses, only a small increase in MF ( approximately 2.5- to 3.5-fold) was found at both sampling times. Primary DNA damage detected with SCGE shortly after treatment (1-2 hr) was rapidly (3 days) transformed into stable gene mutations that remained detectable for 50 days. These results illustrate the ability and complementarity of the SCGE and MutaMouse models to assess the genotoxicity of direct alkylating agents in the mouse gastric mucosa in vivo.

Kinetics of induction of DNA adducts, cell proliferation and gene mutations in the liver of MutaMice treated with 5,9-dimethyldibenzo[c,g]carbazole

5,9-Dimethyldibenzo[c,g]carbazole (DMDBC) is a synthetic derivative of the environmental pollutant 7H-dibenzo[c,g]carbazole. DMDBC is a potent genotoxic carcinogen specific for mouse liver. Using the MutaMouse lacZ transgenic mouse model and a positive selection assay, we measured lacZ mutant frequency (MF) in the liver 28 days after a single s.c. administration of DMDBC at 3, 10, 30, 90 or 180 mg/kg. MF remained low at 3 and 10 mg/kg, but increased markedly from 30 mg/kg onwards. To investigate the reason for this non-linear response, we examined mechanisms potentially involved in mutation induction in the liver. Genotoxic effects such as DNA adduct formation were detected in 32P-post-labelling studies. Liver sections were examined for microscopic changes and cell proliferation. These parameters, and MF, were studied 2, 4, 7, 14, 21 and 28 days after a single s.c. administration of 10 or 90 mg/kg DMDBC. At 10 mg/kg, a dose found to double the MF on day 28, DNA adducts reached a level of 200-600 adducts per 10(8) nucleotides from day 4 to day 28. No changes in histology or cell proliferation were detected at this low dose. At 90 mg/kg, MF increased gradually from day 7 to day 28 (maximum 44-fold). The DNA adduct level ranged from 400 to 4500 adducts per 10(8) nucleotides on day 2, then stabilized at approximately 400 adducts per 10(8) nucleotides on day 4. An early cytotoxic effect was detected microscopically in centrilobular hepatocytes, and was followed by liver cell proliferation. These data suggest that the marked increase in MF in MutaMouse liver after treatment in vivo with DMDBC at 90 mg/kg may be explained by the induction of replicative DNA synthesis due to a cytotoxic effect, allowing the fixation of persistent DNA adducts into mutations.

Kinetics of the interactions of a dicarboxylic porphyrin with unilamellar lipidic vesicles: interplay between bilayer thickness and pH in rate control

The transfer of a dicarboxylic porphyrin from phosphatidylcholine fluid-phase unilamellar vesicles towards albumin is studied focusing on bilayer thickness and pH effects. The kinetics of this process yield the rate constants for the porphyrin flip-flop from the inner to the outer hemileaflet and its exit towards aqueous medium. Phospholipids with monounsaturated 14-22 carbon chains are used. Interplay between bilayer thickness and pH for the control of the rate constants is observed. This results in the amplification, at physiological pH, of the effect of membrane thickness on the flip-flop and exit rates as compared to pH 8.5 and 6.5. These data are explained by the degree of porphyrin burying within the bilayer resulting from a compromise between favorable hydrophobic interactions with the hydrocarbon phase and unfavorable penetration of the polar carboxylic chains. The balance between the two effects depends particularly on the neutralization of one carboxylic chain. Considering the bilayer hydrophobicity profile and the porphyrin size, the optimization of hydrophobic interactions appears dependent on the bilayer thickness. The flip-flop and the exit are governed by neutralization and deprotonation of the carboxylic chains, respectively, the rate of these proton exchanges being dependent on the porphyrin location within the bilayer.

Comparative mutagenicity of 7H-dibenzo[c,g]carbazole and two derivatives in MutaMouse liver and skin

7H-Dibenzo[c,g]carbazole (DBC) is an environmental pollutant that produces DNA adducts and tumors in mouse liver and skin following subcutaneous injection and topical application. The two synthetic derivatives 5,9-dimethyl-DBC (DMDBC) and N7-methyl-DBC (NMDBC) induce tissue-specific lesions. DNA adducts and tumors are observed only in liver following exposure to DMDBC and only in skin following exposure to NMDBC. We used the positive selection MutaMouse model to measure the induction of mutations in the two target organs, 28 days after a single subcutaneous injection or topical application of DBC, DMDBC and NMDBC. In liver, DBC and DMDBC induced 30- to 50-fold increases in mutant frequency (MF), while NMDBC had only a weak effect, regardless of the route of administration. After topical application, DBC and NMDBC produced 3.4- to 7.9-fold increases in MF in skin, while DMDBC had a weak effect. After subcutaneous injection, the three compounds had no or weak effect in skin. This study shows gene mutations arise in the respective target organs in which primary DNA damage and tumors are observed. These results illustrate the relevance of the MutaMouse model for testing organ-specific mutagens.

Cloning, sequencing and structural analysis of 976 base pairs of the promoter sequence for the rat lipoprotein lipase gene. Comparison with the mouse and human sequences

We cloned and sequenced the -976bp promoter of the rat lipoprotein lipase LPL gene. The sequence was compared with the mouse and human sequences. The homology between the rat and mouse LPL nucleotide sequences was not quite as strong in the promoter sequence as in the coding sequence. Among the 976nt promoter there were 118 divergences, i.e. 11.8%, compared to only 5.6% for the LPL coding region. However, within the 200nt immediately 5' to the transcriptional start site (proximal promoter), the divergence was only 4%. New potential cis-elements (such as CACCC, GATA, GC and GA boxes, IRS, Krox, MEF 2, E-box, CCArGG and 1/2 VDRE) were identified in the rat, mouse or human LPL gene.

The intrinsic factor-vitamin B12 receptor and target of teratogenic antibodies is a megalin-binding peripheral membrane protein with homology to developmental proteins

The present report shows the molecular characterization of the rat 460-kDa epithelial glycoprotein that functions as the receptor facilitating uptake of intrinsic factor-vitamin B12 complexes in the intestine and kidney. The same receptor represents also the yolk sac target for teratogenic antibodies causing fetal malformations in rats. Determination of its primary structure by cDNA cloning identified a novel type of peripheral membrane receptor characterized by a cluster of eight epidermal growth factor type domains followed by a cluster of 27 CUB domains. In accordance with the absence of a hydrophobic segment, the receptor could be released from renal cortex membranes by nonenzymatic and nonsolubilizing procedures. The primary structure has no similarity to known endocytic receptors but displays homology to epidermal growth factor and CUB domain proteins involved in fetal development, e.g. the bone morphogenic proteins. Electron microscopic immunogold double labeling of rat yolk sac and renal proximal tubules demonstrated subcellular colocalization with the endocytic receptor megalin, which is expressed in the same epithelia as the 460-kDa receptor. Furthermore, megalin affinity chromatography and surface plasmon resonance analysis revealed a calcium-dependent high affinity binding of the 460-kDa receptor to megalin, which thereby may mediate its vesicular trafficking. Due to the high number of CUB domains, accounting for 88% of the protein mass, we propose the name cubilin for the novel receptor.

[Current aspects of the evaluation of ERBB2 activation in breast cancer. Therapeutic perspectives]

The ERBB2 (HER-2/neu) protooncogene encodes a transmembrane protein with an intracellular tyrosine kinase activity. It is principally activated by gene amplification and its product, the erbB2 protein, becomes oncogenic when overexpressed. Quantitative PCR is both a simple and reliable method for the evaluation of ERBB2 activation, whereas immunoenzymatic methods allow quantitative determination of erbB2 protein in tissue and sera. ERBB2 amplification and/or surexpression is actually recognized as a prognostic factor in breast cancer and would be predictive in the therapeutic response. It might lead also to new therapeutic modalities using specific targeted drugs.

Effect of ethylnitrosourea and methyl methanesulfonate on mutation frequency in Muta Mouse germ cells (seminiferous tubule cells and epididymis spermatozoa)

As part of the Germ Cell Collaborative Study, we used the positive-selection Muta Mouse model to evaluate the effects of two direct alkylating agents, ethylnitrosourea (ENU) and methyl methanesulfonate (MMS), on male germ cells. The LacZ mutation frequency in seminiferous tubule cells and epididymis spermatozoa was measured 3, 14, 25 and 50 days after a single intraperitoneal (i.p.) administration of 150 mg/kg ENU and 3 and 14 days after a single i.p. administration of 40 mg/kg MMS. Three and 14 days after ENU treatment, the mutation frequency was slightly but significantly increased in seminiferous tubule cells (3.5- and 3.6-fold, respectively), while it remained unchanged in epididymis spermatozoa. After 25 and 50 days, time-dependent increase in the mutation frequency was observed in seminiferous tubule cells (8.9- and 14.3-fold, respectively) and epididymis spermatozoa (3.4- and 7.9-fold, respectively), confirming the sensitivity of premeiotic cells to the mutagenic activity of ENU. Three and 14 days after MMS administration, the mutation frequency remained unchanged in seminiferous tubule cells and epididymis spermatozoa. The inability of Muta Mouse model to reveal the mutagenic activity of MMS was confirmed in bone marrow cells, 14 days after treatment. These data indicate that the Muta Mouse model can be used to detect the induction of gene mutations but not chromosome damage in germ cells.

Human lipoprotein lipase last exon is not translated, in contrast to lower vertebrates

We have sequenced the first fish (zebrafish, Brachydanio rerio) lipoprotein lipase (LPL) cDNA clone. Similarities were found in mammalian LPL cDNA, but the codon spanning the last two exons (which is thus split by the last intron) is AGA (Arg) as opposed to TGA in mammals. Exon 10 is thus partially translated. These results were confirmed with rainbow trout (Oncorhynchus mykiss). We also investigated whether mammal TGA coded for selenocystein (SeCys), the 21st amino acid, but found that this was not the case: TGA does not encode SeCys but is a stop codon. It thus appears that the sense codon AGA (fish) has been transformed into a stop codon TGA (human) during the course of evolution. It remains to be determined if the "loss" of the C-terminal end of mammalian LPL protein has conferred an advantage in terms of LPL activity or, on the contrary, a disadvantage (e.g., susceptibility to diabetes or atherosclerosis).

Determination of plasma protein-bound malondialdehyde by derivative spectrophotometry

We describe a method for the measurement of protein-bound malondialdehyde with the thiobarbituric acid reaction in human plasma using second-derivative spectrophotometry. Calibration was done by spectrum height measurement from the baseline at 532 nm. The data were compared with those obtained by using conventional absorbance and fluorimetric measurements. The results were linear from 0.2 to 80 mumol/l and the detection limit was 0.19 mumol/l. Within-run and between-run precision, evaluated by analysing pooled normal plasma, were 8 and 14% respectively. The method was tested for the influence of bilirubin, haemoglobin, glucose, urea, uric acid, sucrose and N-acetyl-neuraminic acid which interfered in the colorimetric method but not in the technique proposed here. The mean (+/-SD) malondialdehyde concentration determined in 59 healthy blood donors with the new assay was 0.34 (+/-0.14) mumol/l. This assay procedure could represent an alternative to high-performance liquid chromatography for the measurement of malondialdehyde in biological media.