Genome-wide bioinformatics analysis of human protease capacity for proteolytic cleavage of the SARS-CoV-2 spike glycoprotein

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) primarily enters the cell by binding the virus's spike (S) glycoprotein to the angiotensin-converting enzyme 2 receptor on the cell surface, followed by proteolytic cleavage by host proteases. Studies have identified furin and transmembrane protease serine 2 proteases in priming and triggering cleavages of the S glycoprotein, converting it into a fusion-competent form and initiating membrane fusion, respectively. Alternatively, SARS-CoV-2 can enter the cell through the endocytic pathway, where activation is triggered by lysosomal cathepsin L. However, other proteases are also suspected to be involved in both entry routes. In this study, we conducted a genome-wide bioinformatics analysis to explore the capacity of human proteases in hydrolyzing peptide bonds of the S glycoprotein. Predictive models of sequence specificity for 169 human proteases were constructed and applied to the S glycoprotein together with the method for predicting structural susceptibility to proteolysis of protein regions. After validating our approach on extensively studied S2' and S1/S2 cleavage sites, we applied our method to each peptide bond of the S glycoprotein across all 169 proteases. Our results indicate that various members of the proprotein convertase subtilisin/kexin type, type II transmembrane family serine protease, and kallikrein families, as well as specific coagulation factors, are capable of cleaving S2' or S1/S2 sites. We have also identified a potential cleavage site of cathepsin L at the K790 position within the S2' loop. Structural analysis suggests that cleavage of this site induces conformational changes similar to the cleavage at the R815 (S2') position, leading to the exposure of the fusion peptide and subsequent fusion with the membrane. Other potential cleavage sites and the influence of mutations in common SARS-CoV-2 variants on proteolytic efficiency are discussed.IMPORTANCEThe entry of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) into the cell, activated by host proteases, is considerably more complex in coronaviruses than in most other viruses and is not fully understood. There is evidence that other proteases beyond the known furin and transmembrane protease serine 2 can activate the spike protein. Another example of uncertainty is the cleavage site for the alternative endocytic route of SARS-CoV-2 entrance, which is still unknown. Bioinformatics methods, modeling protease specificity and estimating the structural susceptibility of protein regions to proteolysis, can aid in studying this topic by predicting the involved proteases and their cleavage sites, thereby substantially reducing the amount of experimental work. Elucidating the mechanisms of spike protein activation is crucial for preventing possible future coronavirus pandemics and developing antiviral drugs.

Predicting Structural Susceptibility of Proteins to Proteolytic Processing

The importance of 3D protein structure in proteolytic processing is well known. However, despite the plethora of existing methods for predicting proteolytic sites, only a few of them utilize the structural features of potential substrates as predictors. Moreover, to our knowledge, there is currently no method available for predicting the structural susceptibility of protein regions to proteolysis. We developed such a method using data from CutDB, a database that contains experimentally verified proteolytic events. For prediction, we utilized structural features that have been shown to influence proteolysis in earlier studies, such as solvent accessibility, secondary structure, and temperature factor. Additionally, we introduced new structural features, including length of protruded loops and flexibility of protein termini. To maximize the prediction quality of the method, we carefully curated the training set, selected an appropriate machine learning method, and sampled negative examples to determine the optimal positive-to-negative class size ratio. We demonstrated that combining our method with models of protease primary specificity can outperform existing bioinformatics methods for the prediction of proteolytic sites. We also discussed the possibility of utilizing this method for bioinformatics prediction of other post-translational modifications.

Analysis of gene expression and mutation data points on contribution of transcription to the mutagenesis by APOBEC enzymes

Since the discovery of the role of the APOBEC enzymes in human cancers, the mechanisms of this type of mutagenesis remain little understood. Theoretically, targeting of single-stranded DNA by the APOBEC enzymes could occur during cellular processes leading to the unwinding of DNA double-stranded structure. Some evidence points to the importance of replication in the APOBEC mutagenesis, while the role of transcription is still underexplored. Here, we analyzed gene expression and whole genome sequencing data from five types of human cancers with substantial APOBEC activity to estimate the involvement of transcription in the APOBEC mutagenesis and compare its impact with that of replication. Using the TCN motif as the mutation signature of the APOBEC enzymes, we observed a correlation of active APOBEC mutagenesis with gene expression, confirmed the increase of APOBEC-induced mutations in early-replicating regions and estimated the relative impact of transcription and replication on the APOBEC mutagenesis. We also found that the known effect of higher density of APOBEC-induced mutations on the lagging strand was highest in middle-replicating regions and observed higher APOBEC mutation density on the sense strand, the latter bias positively correlated with the gene expression level.

Predictive models of protease specificity based on quantitative protease-activity profiling data

Bioinformatics-based prediction of protease substrates can help to elucidate regulatory proteolytic pathways that control a broad range of biological processes such as apoptosis and blood coagulation. The majority of published predictive models are position weight matrices (PWM) reflecting specificity of proteases toward target sequence. These models are typically derived from experimental data on positions of hydrolyzed peptide bonds and show a reasonable predictive power. New emerging techniques that not only register the cleavage position but also measure catalytic efficiency of proteolysis are expected to improve the quality of predictions or at least substantially reduce the number of tested substrates required for confident predictions. The main goal of this study was to develop new prediction models based on such data and to estimate the performance of the constructed models. We used data on catalytic efficiency of proteolysis measured for eight major human matrix metalloproteinases to construct predictive models of protease specificity using a variety of regression analysis techniques. The obtained results suggest that efficiency-based (quantitative) models show a comparable performance with conventional PWM-based algorithms, while less training data are required. The derived list of candidate cleavage sites in human secreted proteins may serve as a starting point for experimental analysis.

[The administration of neurocytoprotectors in a rat model of experimental spinal cord ischemia]

AIM

To study an effect of cortexin on functional recovery and morphology of the spinal cord of rats with spinal cord ischemia.

MATERIAL AND METHODS

Spinal cord ischemia was achieved by ligation of the infrarenal abdominal aorta in 16 rats stratified into two equal groups: the ligation of infrarenal aorta was performed in the control group, aorta ligation was performed also in the experimental group with preliminary intraperitoneally administration of cortexin in a dose of 0.15 mg/kg 30 min before procedure. Evaluation of neurologic deficit was performed by the Tarlov's scale. Morphological evaluation was made by analyzing the histological sections of the lumbar and sacral cord using the Nissl's method of coloring. Statistical analysis was performed as well.

RESULTS AND CONCLUSION

A pronounced and significant effect of cortexin, which was clinically expressed in a decrease in neurological deficit (p=0.0095), morphologically in an increase in the number of normochromic neurons (р=0.01), and a decrease in shrunken neurons (р=0.0001) and shadow cells (р=0.0003), was noted. The results suggest a potential myeloprotective effect of cortexin. The drug can be considered in the context of treatment of vascular myelopathy.

[The biomarkers of cerebral ischemia as a new method for the validation of the efficacy of cytoprotective therapy]

AIM

To study blood plasma concentrations of NR2-peptide in patients with ischemic stroke (IS) to assess its diagnostic value as a biomarker of cerebral ischemia and determine the dynamics of the biomarker during treatment with cortexin.

MATERIAL AND METHODS

One hundred and twenty patients, aged from 18 to 70 years, including 36 with transient ischemic attack (TIA) and 84 with IS in the carotid territory (n=70) and vertebral/basilar territory with the Wallenberg-Zakharchenko syndrome (n=14), were enrolled. The National Institute of Health Stroke scale (NIHSS) was used to assess neurological status. Blood plasma concentration of NR2-peptide was measured in all patients at admission and after treatment. All laboratory results were compared with neuroimaging (MRI, CT) data.

RESULTS

Concentrations of NR2-peptide detected in all patients were higher than in controls (>1.5 ng/ml), p<0.0001. The direct correlation between NR2-peptide (from 3.38 ng/ml to 15.6 ng/ml) and ischemic lesion (from few to 80 mm) was observed. A decrease in NR2-peptide concentration (from 8.5 to 5,.9 ng/ml, p<0.0001) was noted in patients treated with cortexin after 10-day treatment course.

CONCLUSION

NR2-peptide blood assay is a reliable hemotest of brain ischemia. Cortexin has a sufficient therapeutic efficacy.

EFFECT OF LOW-INTENSITY RED LASER ON GROWTH OF STAPHYLOCOCCUS AUREUSAND SENSITIZING EFFECT OF PHOTODITAZIN

AIM

Study the effect of laser emission in the red spectrum on growth of methicillin- sensitive. and methicillin-resistant strains of Staphylococcus aureus, as well as photodynamic effect of photosensitizer photoditazin.

MATERIALS AND METHODS

Effect of light of semiconduc- tor red laser (X 660 nm, 100 mW/cm2) at 30,'60, 90 and 180 J/cm2 on growth of S. aureus colonies was determined. Time of exposure 5; 10, 15 and 30 minutes. In certain series of experiments bacterial cells were sensitized in advance by a Water. solution of photoditazin at a concentration of5xl0-6 M.

RESULTS

Red laser emission was established to cause a pronounced suppression of bacterial growth. This effect on standard S. aureus strain only took place dur- ing use of relatively high exposure doses (180 J/cm2). Photosensitivity of methicillin-resistant strain turned out to be significantly higher: bacteriostatic effect of red light was noted already at the dose of 60 J/cm2. Treatment of bacterial cells with photoditazin in advance signifi- cantly enhanced growth-inhibiting effect of laser light.

[Perspectives of disodium salt 2.4-di(1-metoxyethyl)-deuteroporphyrin - IX ("Dimegin") application for photodynamic therapy in non-oncologic cases]

Effects of disodium salt 2,4-di(1-metoxyethyl)-deuteroporphyrine-IX (Dimegin) and the light from Soret band (»395-405 nm) at the viability of microbial cells and at their potential to form microbial biofilms have been compared with traditional antiseptics. Irradiation of microbial cells of S. aureus, E. coli, C. albicans and others with diode light (power density 0.05 Wt/cm2) caused a bactericidial effect similar to that obtained with standard anticeptics (chlorhexidine and dioxidine). A comparative study of the effectiveness of Dimegin and Photoditazine (a soluble salt of chlorine e6) as photosensitizers have been performed using the test system of erythrocyte hemolysis in vitro under irradiation with light from the Sore band. Results have shown insignificant difference in the photodynamic effect with similar doses of absorbed light and preparation concentration.

Evaluation and comparison of current fetal ultrasound image segmentation methods for biometric measurements: a grand challenge

This paper presents the evaluation results of the methods submitted to Challenge US: Biometric Measurements from Fetal Ultrasound Images, a segmentation challenge held at the IEEE International Symposium on Biomedical Imaging 2012. The challenge was set to compare and evaluate current fetal ultrasound image segmentation methods. It consisted of automatically segmenting fetal anatomical structures to measure standard obstetric biometric parameters, from 2D fetal ultrasound images taken on fetuses at different gestational ages (21 weeks, 28 weeks, and 33 weeks) and with varying image quality to reflect data encountered in real clinical environments. Four independent sub-challenges were proposed, according to the objects of interest measured in clinical practice: abdomen, head, femur, and whole fetus. Five teams participated in the head sub-challenge and two teams in the femur sub-challenge, including one team who tackled both. Nobody attempted the abdomen and whole fetus sub-challenges. The challenge goals were two-fold and the participants were asked to submit the segmentation results as well as the measurements derived from the segmented objects. Extensive quantitative (region-based, distance-based, and Bland-Altman measurements) and qualitative evaluation was performed to compare the results from a representative selection of current methods submitted to the challenge. Several experts (three for the head sub-challenge and two for the femur sub-challenge), with different degrees of expertise, manually delineated the objects of interest to define the ground truth used within the evaluation framework. For the head sub-challenge, several groups produced results that could be potentially used in clinical settings, with comparable performance to manual delineations. The femur sub-challenge had inferior performance to the head sub-challenge due to the fact that it is a harder segmentation problem and that the techniques presented relied more on the femur's appearance.

[Effective photosensibilizator selection for E.N.T.-organ diseases treatment, based on their accumulation in pathologically changed tissues]

Accumulation of photosensibilisators - derivatives of E6 chlorines ("Radachlorine", "Photoditazine", "Zelevsky's balsam") in the mucous membrane and selection of most effective sources of emission have been investigated in 30 patients with rhinosinusitis and 10 with tonsillitis. As a source of emission we used light emitting diode (LED) matrix device "ACT" (wavelength approximately 405 nm (Sore band)) and a laser device LAHTA-"MILON"-ML500-SP (wavelength 662 nm). Drug accumulation in the mucous membrane and changes of their concentrations after emission were evaluated by changes of fluorescence, measured with a LESA-01-BIOSPEC spectrometer. The percent of fluorescence decrease ranged from 50% to 92.7%. This suggests intensive disintegration of photosensibilisators, and consequently, high therapeutic activity of this method. Effectiveness of this method is also confirmed by clinical results.

[Inhibition of no-dependent soluble human platelet guanylate cyclase by isatin]

Isatin (indole-dione-2,3) is an endogenous indole that exhibits a wide spectrum of biological and pharmacological activities. Physiologically relevant concentrations of isatin (ranged from 1 nM to 10 M) did not influence basal activity of soluble human platelet guanylate cyclase (sGC), but caused a bell-shaped inhibition of the NO-activated enzyme. Inhibition of the NO-dependent activation by isatin did not depend on a chemical nature of the NO donors. The inhibitory effects of ODC (a heme-dependent inhibitor of sGC) and isatin were non-additive suggesting that the inhibitory effect of isatin may involve the heme binding domain (possibly heme iron) and experiments with hemin revealed some isatin-dependent changes in its spectrum. Isatin also inhibited sGC activation by the allosteric activator YC-1. It is suggested that the bell shaped inhibition of the NO-dependent activation of sGC by isatin may be attributed to complex interaction of isatin with the heme binding domain and the allosteric YC-1-binding site of sGC.

[Long-term prognosis in patients with acute non-ST-segment elevation myocardial infarction depending on dynamics of tissue myocardial dopplerography]

AIM

To study long-term prognosis in patients with non-ST elevation acute myocardial infarction (AMI) with reference to changes in myocardial tissue dopplerography (MTD) in the course of treatment.

MATERIAL AND METHODS

MTD echocardiography was conducted in 88 non-ST elevation AMI (mean age 58.0-9.8 years) and 34 healthy volunteers (mean age 58.0 +/- 9.8 years). Measurements were made of the velocity of systolic, early and late diastolic peaks at 4 levels of interventricular septum, anterior, lateral and inferior walls of the left ventricle (LV). MTD was repeated before the discharge from hospital. The patients were followed up for 10-18 months after the discharge.

RESULTS

By MTD results the patients were divided into 3 subgroups: 1--an asymmetric decrease of MTD values--17(19.3%) patients who had a 20% reduction of the systolic and early diastolic peak velocity compared to healthy controls on one or two adjacent LV walls; subgroup 2--a diffuse decline of MTD values--61 (69.3%) patients. Their velocity of systolic and early diastolic peaks was subnormal on all the walls, all levels of estimation; subgroup 3--10 (11.4%) patients without MTD changes. These proportions changed in the course of treatment: the number of patients with a diffuse decrease of MTD values reduced to 31 (35.3%), the number of patients with an asymmetric MTD decrease rose to 37 (42%), and with unchanged MTD rose to 20 (22.7%) patients. The rate of development of congestive cardiac failure (CCF) and asymptomatic LV dysfunction in the long-term period was significantly higher in the subgroup with retained diffuse decrease of MTD values.

CONCLUSION

The treatment of non-ST elevation AMI reduces the number of patients with a diffuse decrease of MTD values and elevates the number of patients with asymmetric decrease of MTD and unchanged MTD. Persistence of MTD diffuse changes is an unfavourable prognostic factor in relation to CCF and LV silent dysfunction.

[Study of photodynamic treatment for P-388 lympho-leukemia in mice]

Data are presented on the results of photodynamic treatment (PDT) of mice DBA2 with transplantable lympho-leukemia P-388. Different regimens of photosensitizer Dimegin and emission were used. Both intravenous PDT and in combination with local PDT should be recommended.

Analysis of close proximity quenching of phosphorescent metalloporphyrin labels in oligonucleotide structures

Quenching of phosphorescent platinum(II) and palladium(II) coproporphyrin (MeCP) labelled oligonucleotides was investigated. Strong hybridization-specific quenching was observed in duplex DNA structures with a variety of quenchers and with two identical porphyrin labels when in close proximity. Classical resonance energy transfer mechanism was ruled out, since quenching did not correlate with spectral overlaps and lifetime changes were insignificant. Quenching of MeCP by the free quenchers in solution revealed that porphyrin-porphyrin quenching is predominantly static while other dyes quench dynamically. The results suggest that the quenching in DNA duplex proceeds via direct contact.

YC-1-like potentiation of NO-dependent activation of soluble guanylate cyclase by derivatives of protoporphyrin IX

The influence of protoporphyrin IX derivatives--2,4-di(1-methoxyethyl)-deuteroporphyrin IX disodium salt (dimegin) and hematoporphyrin IX (HP)--on the activation of human platelet soluble guanylate cyclase by sodium nitroprusside was investigated. Dimegin and HP, like 1-benzyl-3-(hydroxymethyl-2-furyl)indazole (YC-1), produce synergistic effects on the activation of soluble guanylate cyclase by sodium nitroprusside. The synergistic activation of the enzyme by the combination of 10 microM sodium nitroprusside and 5 microM dimegin (or 5 microM HP) was 190 +/- 19 and 134 +/- 10%, respectively. The synergistic activation of guanylate cyclase by 3 microM YC-1 and 10 microM sodium nitroprusside was 255 +/- 19%. Dimegin and HP had no effect on the activation of guanylate cyclase by YC-1; they did not change the synergistic effect of YC-1 (3 microM) and sodium nitroprusside (10 microM) on guanylate cyclase activity. The synergistic activation of NO-stimulated guanylate cyclase activity by dimegin and HP represents a new biochemical effect of these compounds that may have important pharmacotherapeutic and physiological significance.

Photodynamic effect of novel chlorin e6 derivatives on a single nerve cell

Chlorin e(6) and its derivatives are promising sensitizers for photodynamic therapy (PDT). In order to compare the photodynamic effects of 8 novel derivatives of chlorin e(6) and to explore some mechanisms of their effects at the cellular level, we studied PDT-induced changes in bioelectric activity of crayfish mechanoreceptor neuron that was used as a sensitive experimental model. Neurons were insensitive to red laser irradiation (632.8 nm; 0.3 W/cm(2)) or to photosensitizers alone, but changed firing rate and died under the photodynamic effect of nanomolar concentrations of sensitizers. The dynamics of neuron responses depended on photosensitizer type and concentration. The dependence of neuron lifetime on photosensitizer concentration allowed comparing efficiencies of different photosensitizers. Radachlorin was the most potent photosensitizer comparable with mTHPC. High photodynamic efficiency of some chlorin e(6) derivatives was related to weak dependence of neuron lifetime on sensitizer concentration, indicating to the initiation of 2-3 secondary processes such as free radical membrane damage by one absorbed photon. Photodynamic efficiency of sensitizers depended on amphiphilicity influencing their intracellular localization.

[Photohemolysis sensitized by deuteroporphyrin-IX derivatives: determination of binding strength of dyes to erythrocytes]

A comparative analysis of the ability of 4-(1-methyl-3-hydroxybutyl)-deuteroporphyrin-IX (I) and 2,4-di-(1-methyl-3-hydroxybutyl)-deuteroporphyrin-IX (II) to photosensitize hemolysis of human erythrocytes was performed. The photohemolytic efficiency of dye I was shown to be about 60 times higher than that of dye II. It was found that a part of each dye tightly binds to erythrocyte membranes and is not removed by washing. A method for estimating the share of the dye tightly bound to the membrane (beta) was proposed, which takes into account the shielding effect produced by the free dye and the photohemolytic efficiency of the bound dye. It was shown that the beta values for dyes I and II are 86 and 61% and correlate with the coefficients of distribution of the dyes in the octanol/water system (20.7 and 17.0, respectively).

Spectral-luminescent study of the porphyrin-diketones and their complexes

Syntheses of octaethylporphine-diketone (OEPDK) and its platinum(II) and palladium(II) complexes (PtOEPDK, PdOEPDK) were optimized, and the dyes were isolated in a pure form in preparative quantities. They were characterized by the NMR, UV-VIS absorption and emission spectroscopy. Electronic spectra of these dyes (absorption and luminescence) were investigated in detail, and compared to corresponding porphyrins and porphyrin-monoketones. OEPDK showed a strong fluorescence at about 700 nm, while PtOEPDK and PdOEPDK showed very weak room-temperature phosphorescence in the region of 850-1100 nm and practically no fluorescence. Protonation mechanisms were studied for these dyes. Protonation at sites other than pyrrole nitrogen atoms was shown to occur, corresponding protomeric spectral forms are presented. The possibilities of the use of porphyrin-diketones as longwave fluorescent and phosphorescent probes are discussed.

Photodynamic effect of deuteroporphyrin IX and hematoporphyrin derivatives on single neuron

The photodynamic effects of 6 new deuteroporphyrin IX derivatives with different amphiphilicity and lipophilicity, as well as effects of known hematoporphyrin derivatives Photofrin II and Photoheme on isolated crayfish mechanoreceptor neurons were studied. After 30 min photosensitization, neurons were irradiated with He-Ne laser (632.8 nm, 0.3 W/cm(2)), and changes in their firing frequency were recorded. Neuron firing was shown to be very sensitive to photodynamic effect of the studied deuteroporphyrin IX derivatives causing irreversible firing abolition at pikomolar concentrations while Photoheme and Photofrin II were effective in the nanomolar range. The most effective sensitizers were 4-(1-methyl-3-hydroxybutyl)- and 4-(1-methyl-2-acetyl-3-oxobutyl)-deuteroporphyrins. Extinction and amphiphilicity were shown to be the most important properties determining photodynamic efficiency of the studied photosensitizers.

[Preparation and certain properties of the liposomal substance 2,4-di(1-methyl-3-hydroxybutyl)deuteroporphyrin-IX]

A liposome preparation of a porphyrin photosensitizer for photodynamic therapy of tumors (PDT) was obtained. The in vitro efficiency of the photosensitizer was enhanced 2.5-fold through the liposome formulation. The composition and some properties of the new preparation were studied. An algorithm for a complex approach to the prediction of photosensitizer efficiencies by model experiments in vitro was developed. This approach is based on the use of two models: the determination of coefficient of distribution between n-octanol and a phosphate buffer, pH 7.4, and the determination of the cytotoxic effect on the culture of CaOv ovarian adenocarcinoma cells.

Photosensitization of skin-derived cell lines by Dimegin [2,4-di-(alpha-methoxyethyl)-deuteroporphyrin IX] in vitro

The deuteroporphyrin-IX derivative Dimegin [2,4-di-(alpha-methoxyethyl)-deuteroporphyrin IX] was investigated with respect to cellular uptake, intracellular localization and cell survival following photodynamic treatment in human cell lines derived from the skin (SCL1 and SCL2, squamous cell carcinoma; HaCaT keratinocytes; N1 fibroblasts). Using flow cytometry, we determined the cellular fluorescence as a marker of the uptake of Dimegin after incubation for 24 h. The intracellular localization of Dimegin was analysed using fluorescence microscopy and co-staining with fluorescent dyes specific for cell organelles. Following irradiation with an incoherent light source (580-740 nm) using a light dose of 24 J/cm2, phototoxicity was determined by means of trypan blue dye exclusion, MTT assays and growth curves. The relative Dimegin fluorescence of the different cell lines declined as follows: SCL1 > HaCaT > N1 > SCL2. Intracellular localization of Dimegin was found in the mitochondria. For all cell lines Dimegin concentrations above 15 microM yielded a significant phototoxic effect. The EC50 for SCL1 cells was 8.9 +/- 2.0 microM Dimegin. The EC50 for the cell lines increased as follows: SCL1 < HaCaT < N1 < SCL2, thus correlating with the cellular fluorescence of Dimegin. The results of the MTT assay were confirmed by trypan blue dye exclusion assay and growth curves. In conclusion, the study shows that Dimegin is an effective photosensitizer with a rapid mechanism of action in vitro, resulting in an immediate loss of plasma membrane integrity following irradiation.

Modification of monoclonal and polyclonal IgG with palladium (II) coproporphyrin I: stimulatory and inhibitory functional effects induced by two different methods

Antibodies conjugated with porphyrins and metalloporphyrins have a great potential for applications in fluorescence or phosphorescence immunoassays as well as in photodynamic therapy, radioimaging and internal radiation therapy of cancer. Here we describe how the new preactivated metalloporphyrin, palladium (II) coproporphyrin I-tetra-N-hydroxysuccinimide ester, can be covalently attached to mouse monoclonal and rabbit anti-human ferritin antibodies. The advantages of the proposed reagent over the previously reported carboxylic porphyrins coupled through carbodiimide activation are indicated. Conformational changes in antibodies caused by each of the two methods were assessed from their binding to the antigen (a probe for the antibody Fv domain) and anti-IgG antibodies probing the global conformation of the CH2 domain in the Fc fragment. Porphyrin coupling through carbodiimide activation resulted in a decrease in both functional activities of modified antibodies even at low levels of modification. In contrast, when the N-hydroxysuccinimide (NHS) derivative of porphyrin was used, enhancement of the antigen-binding affinity of porphyrin-antibody conjugates occurred due to an increase in the conformational mobility (flexibility) of the modified antibodies. The stimulatory effect of conjugation was maximal when one porphyrin molecule was coupled to an antibody molecule. Coupling of NHS-activated porphyrin at pH 7.4, 7.8 and pH 8.5 suggested that the high efficiency of the reaction at pH 8.5 could be attributed predominantly to the formation of antibody aggregates, only 50% of which were covalently cross-linked. The lowest percentage of aggregates in porphyrin-antibody conjugates was found at pH 7.4 and a molar reagent-to-protein ratio in the 10:1-40:1 range. Thus, the use of the NHS-activated carboxylic porphyrin provides a mild, simple and convenient procedure for preparing antibody conjugates with enhanced antigen-binding affinity.

Monoclonal antibodies against metalloporphyrins. Specificity of interaction with structurally different metalloporphyrins

Monoclonal antibodies against Pd-coproporphyrin I have been obtained. The antibody specificity for free as well as for conjugated Pd-coproporphyrin I is characterized. Affinity constants are estimated for 3 monoclonal antibodies effectively interacting with free Pd-coproporphyrin I. A comparative study on the binding of monoclonal antibodies with analogues and derivatives of Pd-coproporphyrin I has revealed that the antigen is mainly located inside the antibody paratope. The protein adjoins complementary to the metalloporphyrin in such a manner that antibodies obtained discern only isomer I, and to some degree, isomer III of coproporphyrin.

Kinetics of oxidation of o-dianisidine by hydrogen peroxide in the presence of antibody complexes of iron(III) coproporphyrin

The complex of iron(III) coproporphyrinI (FeCPI) with antibody D5E3 was studied as an artificial peroxidase, using o-dianisidine as a substrate. At saturation with respect to antibody, the initial rates of o-dianisidine oxidation are practically the same for free and bound FeCPI at a concentration 5 x 10(-9)M, but the catalytic rate constant (kc) for bound FeCPI exceed (kc) for free FeCPI by two- to three-fold. This difference can be explained by a real enhancement of (kc) at the antibody-active site. The dependence of initial rates of the reaction on substrate concentrations obeyed Michaelis-Menten kinetics and revealed substrate activation at high concentrations of o-dianisidine. A comparison of the Stern-Volmer constants for o-dianisidine-induced quenching of the porphyrin fluorescence proves that antibody-bound coproporphyrin is equivalently accessible to the substrate as protoporphyrin bound to apoperoxidase from horseradish peroxidase (HRP). Based on analysis of the (kc) dependence on H2O2 concentrations in the FeCPI-antibody system, we suggest that interaction with hydrogen peroxide is the rate-limiting step for the oxidation reaction.

[The effect of hematoporphyrin derivative on the postradiation recovery of hemopoiesis in mice]

In experiments with mice exposed to gamma quanta (6.0 Gy) it was shown that a single injection of disodium salt of 2,4-di(alpha-methoxyethyl)deuteroporphyrin IX (50 and 12 mg/kg) both 15 min before and 15 min after irradiation promoted postirradiation regeneration of all bone marrow haemopoiesis compartments. The agent produced a more pronounced stimulatory effect when administered after irradiation.

[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.

Photodestruction in vitro of tumour cells sensitized by porphyrins and their conjugates with specific antibodies

The photodynamic action of a number of carboxylic porphyrins and their covalent conjugates with specific monoclonal IgM antibodies on a human lung adenocarcinoma cell line was studied. All the conjugates showed strong phototoxicity which did not correspond with the phototoxicity of the free porphyrins. Absolute quantum yields of singlet oxygen photogeneration by the porphyrins and their conjugates were obtained and compared with the phototoxicity of the compounds.

[Photosensitized formation of singlet oxygen in water solutions of covalent porphyrin-antibody conjugates]

The effective photogeneration of singlet molecular oxygen (1O2) by porphyrins (coproporphyrin I; 2,4-bi (alpha-methoxyethyl) deuteroporphyrin IX and cyclopanten-coproporphyrin I) conjugated with antibodies (mouse monoclonal IgG and IgM and human gamma-globulin) have been observed with the direct luminescence method of 1O2 detection. Absolute quantum yields of 1O2 formation by the conjugates have been determined. The data suggest that porphyrin-antibody conjugates are promising for the use as drugs in photodynamic tumor treatment.

Palladium(II)-coproporphyrin I as a photoactivable group in sequence-specific modification of nucleic acids by oligonucleotide derivatives

The 34-mer oligodeoxynucleotide was shown to be selectively modified at the G17 position upon photoirradiation in the presence of complementary 17-mer oligodeoxynucleotide bearing Pd(II)-coproporphyrin I covalently linked to the 5'-end phosphate group.

[Fluorescent immunoanalysis. Synthesis, spectro-fluorescent and immunologic properties of conjugates of coproporphyrin I with antibodies]

The synthesis of protein conjugates with the new high-efficient fluorescent labile coproporphyrin-I was optimized. A number of conjugates of monoclonal antibodies with different coproporphyrin-I content were synthesized, and their spectral properties were studied in water and micellar solutions, i.e. adsorption, excitation and emission spectra, fluorescence quantum yields, fluorescence pH-dependences. The binding constants of coproporphyrin-I and its protein conjugates with serum albumin were determined. The antibodies labelled with coproporphyrin-I retain the functional activity and photochemically stable in water solutions. The sensitivity of fluorometric detection of coproporphyrin-I and its conjugates with proteins is more than 10 times greater than in case of FITC.

[Effect of aniline and hydrazine derivatives on reversible oxygen addition in model systems of cobalt complexes of etioporphyrin and alpha, beta, gamma, delta-tetraphenylporphine]

The influence of aniline and hydrazine derivatives on the reversible oxygenation of cobaltous complexes of etioporphyrin I and alpha,beta,gamma,delta-tetraphenylporphin has been studied by means of ESR and electronic spectra. The formation of stable six-coordinated complexes with the said reagents prevents the oxygenation. The excess of hydrazines cause the destruction of porphyrin nucleus. The formation of intermediate dihydroporphyrins (chlorins) has been noticed.