Search

The aim of the work was to study the features of the infectious process in the lungs of animals used as models for assessing SARS-CoV-2 pathogenicity.Materials and methods. The strain of SARS-CoV-2 alpha variant virus was used in the work. The experiments were carried out on linear and transgenic mice, Syrian hamsters, guinea pigs, ferrets and two types of primates: rhesus macaques and green monkey. The pathomorphological examination was performed by optical microscopy of histological lung preparations using a computerized microscope with digital microphotography.Results and discussion. A comparative histological analysis of the lungs in six different types of laboratory animals was carried out when modeling a new coronavirus infection; similar morphometric signs of the severity of the disease caused by the SARS-CoV-2 virus in sensitive animals were determined, and a dose-dependent correlation of pathological changes in lung tissues with intranasal administration of various infectious doses was revealed. The features of pathomorphological changes in six different animal species in the simulation of a new coronavirus infection have been characterized, and their dose-dependent nature determined. The presented research results can be used to select a model animal for the purpose of in-depth study of the pathogenesis of COVID-19 caused by newly isolated coronavirus variants, the dynamics of immune reactions of the body during the development of the disease, as well as in vivo studies of the protective effect of promising therapeutic drugs and vaccines.

Scientific relevance. The use of recombinant antigens in vaccine production is limited because vaccines based on such antigens tend to have low immunogenicity. However, a COVID-19 vaccine that combines recombinant SARS-CoV-2 spike glycoprotein as its antigen and virus-like immune-stimulating complexes (ISCOMs) as its adjuvant (Nuvaxovid) induces a protective virus-neutralising response. The State Research Center of Virology and Biotechnology “Vector” (hereinafter, Vector) has developed the ISCOM adjuvant Matrix-V, which plays a key role in inducing virus-neutralising antibodies. Studying Matrix-V will provide for the wide use of recombinant antigens combined with this adjuvant in the development and production of novel Russian vaccines.Aim. This study aimed to evaluate the humoral immune responses of experimental animals to intramuscular injections of a complex combining the recombinant Wuhan-type SARS-CoV-2 spike RBD antigen and the virus-like ISCOM adjuvant containing Quillaja saponaria saponins.Materials and methods. The Matrix-V ISCOM adjuvant was produced using Vector’s proprietary technology, which involves cross-flow filtration through Sartorius VivaFlow cassettes. To determine the saponin and residual detergent concentrations in Matrix-V, the authors conducted high-performance liquid chromatography. Having produced the recombinant SARS-CoV-2 RBD antigen, the authors used electron microscopy to analyse the ultrastructure of the ISCOM–antigen complex. In the study of the ISCOM–antigen complex, 25 female Balb/c mice (5 groups) and 15 male and female outbred guinea pigs (3 groups) received two intramuscular injections with a 14-day interval. Serum tests relied on virus neutralisation (VN) and enzyme-linked immunosorbent assay (ELISA) methods and used antigens of 8 SARS-CoV-2 variants (State Collection of Viruses and Rickettsia, Vector). The authors used Statistica 10 to analyse the results.Results. Two injections of the SARS-CoV-2 RBD antigen (mice: 7 μg, guinea pigs: 1 μg) alone did not induce statistically significant virus-neutralising antibody responses, as shown by the VN results. Two injections of the SARS-CoV-2 RBD antigen (mice: 7 μg, guinea pigs: 1 μg) adjuvanted with Matrix-V (25 μg) resulted in geometric mean antibody titres of 1:83–1:178 (mice) and 1:174–1:587 (guinea pigs) in the VN tests with the Wuhan variant. One injection of the antigen (1 μg or 7 μg) with Matrix-V (25 μg) induced antibodies only in individual cases, as demonstrated by the VN and/or ELISA results. The most intensive immune response was observed in ELISA tests with the Delta variant after two injections of the Ecto-S-Wuhan (1 μg) and Matrix-V (25 μg) complex. Immune responses did not differ between the group that received two injections of the Ecto-S-Wuhan antigen (1 μg) without the ISCOM adjuvant and the negative control group (titres below 1:100; p=0.95). Two injections of the SARS-CoV-2 RBD antigen (7 μg) without the ISCOM adjuvant induced antibodies in mice (titres between 1:248 and 1:1477).Conclusions. Two intramuscular injections of the complex containing the recombinant SARS-CoV-2 RBD antigen and the Matrix-V ISCOM adjuvant induce virus-neutralising antibodies. The approach proposed by the authors has the potential for use in the development of immunobiological medicinal products to prevent and treat a wide range of infectious diseases.

Interferon inducers are of interest as the first line of defense against viral infections, including influenza. Double-stranded ribonucleic acid (dsRNA) for intranasal administration has been developed, the excipients and drug components were selected at the Institute of Medical Biotechnology, a branch of the State Research Center of Virology and Biotechnology «Vector». This work presents the results of the study on antiviral activity and pharmacological safety of a new form of dsRNA. The antiviral activity of the preparation was studied in BALB/c mice infected with influenza A/Aichi/2/68 (H3N2) or Bishkek/01/2009 (H1N1pdm09) viruses. A safety study was performed with a single administration of intranasal dsRNA into white outbred ICR mice. The study showed that the administration of therapeutic and prophylactic regimen of intranasal dsRNA at a dose of 2.5 mg/kg increases the survival and average life expectancy of mice infected with the mentioned strains of influenza virus. The protective effect of the preparation in mice infected with a lethal dose of Bishkek/01/2009 virus was comparable to the effect of Tamiflu. The absence of toxic effects of intranasal dsRNA at a pharmacological dose in laboratory mice, the functional state of their physiological systems, as well as main types of metabolism, established in the experiments, lead to a conclusion concerning pharmacological safety of the preparation and the prospects for further work to complete pharmaceutical development of a new antiviral drug.

The aim of the work was to study the pathogenicity of newly emerging variants of SARS-CoV-2 on the model of the Syrian golden hamster.Materials and methods. We used the strains of SARS-CoV-2 virus related to the VOC circulating in the territory of the Russian Federation. The experiments were carried out on outbreed Syrian hamsters obtained from the nursery of the SSC VB “Vector”. The infectious titer of coronavirus in tissue samples collected from infected laboratory animals was determined on a Vero E6 cell culture. The Ct in RT-PCR was considered an additional parameter for monitoring the viral load in the samples. The severity of lung tissue damage in Syrian hamsters with COVID-19 was assessed by histological preparations.Results and discussion. 50 % infecting doses in case of the intranasal infection have been determined, histological analysis of lung tissues performed. The pathogenicity of various variants of the SARS-CoV-2 virus for the Syrian hamster has been evaluated, differences in infecting doses and pathological changes in the lungs have been revealed. SARS-CoV-2 viruses belonging to Beta genetic variant have the highest virulence, while Alpha variant has the lowest one when comparing the studied strains by the ID50 value. The Delta and Omicron variants have a matched ability to cause specific damage to the tissues of the respiratory tract, while being inferior only to the Beta variant. It has been demonstrated that Syrian hamsters are an adequate model for assessing the pathogenicity of the SARS-CoV-2 virus variants of concern. Variants of SARS-CoV-2 virus during intranasal infection has shown different degree of pathogenicity in the Syrian hamster model.

The COVID-19 pandemic has exacerbated the public’s need for effective vaccines. Consequently, significant financial support has been provided to developers of a number of innovative vaccines, including the vaccines with saponin-based adjuvants. In 2021, the World Health Organisation recommended Mosquirix, the first malaria vaccine, which contains a saponin adjuvant. An anti-covid vaccine by Novavax is in the approval phase. A promising approach to vaccine development is presented by the use of virus-like immune-stimulating complexes (ISCOMs) containing saponins and by the creation of combinations of ISCOMs with antigens. The aim of the study was to develop, produce and characterise virus-like immune-stimulating complexes based on saponins of Quillaja saponaria, as well as similar saponins of Russian-sourced Polemonium caeruleum. Materials and methods: The ISCOM adjuvants, Matrix-BQ and Matrix-BP, were produced using liquid chromatography and examined using electron microscopy. Balb/c mice were immunised intraperitoneally and intramuscularly with ISCOM-antigen preparations. Afterwards, the immunised animals were challenged with the influenza virus strain, A/California/4/2009(H1N1)pdm09, adapted and lethal to mice. The serum samples were examined using haemagglutination inhibition (HI) tests. Results: The authors produced the ISCOMs containing saponins of Quillaja saponaria and Polemonium caeruleum. After one intramuscular injection of either of the ISCOM-antigen preparations with 1 µg of each of A/Brisbane/02/2018 (H1N1) pdm09, A/Kansas/14/2017 (H3N2), and B/Phuket/3073/2013 haemagglutinin antigens (HAs), HI tests detected serum antibody titres to the corresponding antigens of ≥1:40. Two intramuscular injections of the ISCOM-antigen preparation containing 50 ng of each of the HAs and Matrix-BQ resulted in a protective response. In some animals, two intraperitoneal injections of ISCOM-antigen preparations resulted in the maximum antibody titre to the A/Kansas/14/2017 (H3N2) vaccine strain of 1:20,480. Two intramuscular injections of a test preparation containing 5 µg, 1 µg, 200 ng, or 50 ng of each of the HAs and Matrix-BQ or a control preparation containing 5 µg, 1 µg, or 200 ng of each of the HAs (commercially available vaccines) to the mice that were afterwards infected with the lethal influenza strain protected the experimental animals from death. Conclusions: The ISCOM-based preparations had high immunostimulatory activity in the mouse-model study. The presented results indicate the potential of further studies of ISCOM-based preparations in terms of both vaccine and immunotherapeutic development.

The aim of the research was to study reproduction features of SARS-CoV-2 coronavirus strains of various genetic lines on Vero and Vero E6 cell culture.Materials and methods. The SARS-CoV-2 virus strains related to the variants of concern (VOC) circulating in the territory of the Russian Federation were used in the research. The strains of the SARS-CoV-2 virus were deposited in the State Collection of Pathogens of Viral Infections and Rickettsioses at the FBIS SSC VB “Vector” of the Rospotrebnadzor. The experiments were carried out on Vero and Vero E6 cell cultures. The dynamics of infectious virus accumulation was determined by titration of culture fluid samples 24, 48, 72, 96 hours after infection (MOI – from 1 to 0,00001 CPE50/cell). Plaque formation was studied on Vero E6 cell culture under 0.2 % agar coating. Image analysis and plaque size calculation were performed using GIMP (GNU Image Manipulation Program).Results and discussion. The study describes the dynamics of accumulation of infectious virus in the culture fluid depending upon multiplicity of infection for the strains of SARS-CoV-2 virus belonging to different genetic lines. Differences in the morphology of plaques on the monolayer of Vero E6 cell culture under agar coating are shown. SARS-CoV-2 virus strains related to Alfa and Delta VOC demonstrate maximum reproduction rate among the studied strains (infectious titer is higher than 7 lg TCID50/100µl). Omicron VOC forms small plaques under agar coating and at a low multiplicity of infection has a low reproduction rate. Thus, SARS-CoV-2 virus strains belonging to different genetic lines have significant differences in the rate of reproduction on Vero and Vero E6 cell culture.

The aim of the research was to assess the susceptibility of mice of different lines to newly emerging variants of SARS-CoV-2.Materials and methods. The SARS-CoV-2 virus strains belonging to variants of concern (VOC) circulating in the territory of the Russian Federation were used in the study. Experiments involved three inbred mouse lines (BALB/c, CBA and C57Bl/6z) and CD1 outbred mice taken from the nursery of the SSC VB “Vector” of the Rospotrebnadzor. The infectious titer of coronavirus in tissue samples obtained from the laboratory animals was determined on a Vero E6 cell culture. The (Ct) threshold value in RT-PCR was considered an additional parameter for monitoring the viral load in the samples. The severity of lung tissue damage was assessed using histological preparations.Results and discussion. The susceptibility of various mouse lines to the genetic variant Beta of the SARS-CoV-2 virus has been investigated. During intranasal infection of the inbred and outbred mice with strains of VOC at a dose of 2·103 TCID50, the virus replicated in the lungs with maximum concentrations 72 hours after infection. The pathogenicity of genetic variants of the SARS-CoV-2 virus for BALB/c mice has been assessed, a 50 % infectious dose for intranasal infection (ID50) determined. Histological analysis showed COVID-19-specific lung tissue lesions in infected animals. Our study proves that BALB/c mice can be used as a model animal in screening studies when evaluating the effectiveness of therapeutic, vaccine preparations and studying the pathogenesis caused by VOC of the SARS-CoV-2 virus: Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Omicron (B.1.1.529) and the like.

The aim of the study was to create a highly immunogenic vaccine construct based on a recombinant variant of a replication-defective MVA strain of vaccinia virus, expressing virus-like particles that mimic natural infection with Marburg virus. Materials and methods. The recombinant virus was obtained through recombination between homologous viral DNA sequences and the insertion plasmid pDel2-GP-VP-Pat which carries transgenes of the structural proteins GP and VP40 of Marburg virus, flanked by fragments of MVA strain genome. Structure of the recombinant virus was confirmed in PCR and using sequencing, transgenes expression was analyzed by Western blotting, viruslike particles formation was recorded using electron microscopy. Evaluation of immunogenicity and protectivity was carried out using a guinea pig model. The antibody titer was determined in enzyme-linked immunosorbent assay. To assess T-cell response, the intracellular staining of cytokines was used, followed by analysis of samples on a flow cytometer. Results and discussion. On the basis of highly attenuated MVA strain of vaccinia virus a recombinant variant MVA-GP-VP40-MARV has been constructed, carrying a cassette of transgenes, GP and VP40, of Marburg virus in the region of deletion II of the genome. The expression of transgenes in MVA-permissive CER cells infected with recombinant MVA-GP-VP40-MARV strain and secretion of GP and VP40 proteins into culture medium have been demonstrated. Electron microscopy analysis has revealed the presence of Marburg virus-like particles in the culture medium of cells 12 hours after infection. Double vaccination of guinea pigs with MVA-GP-VP40-MARV strain at a dose of 108 PFU/animal induced the formation of antibodies to Marburg and vaccinia viruses, as well as 100 % protection against lethal Marburg virus infection (50 LD50). Using original TEpredict software, the structure of T-helper epitopes of GP protein has been predicted. Using the ICS method, the biological activity of these epitopes has been experimentally confirmed and it was shown that they provide the induction of a T-cell immune response as part of the MVA-GP-VP40-MARV vaccine construct.

The paper describes some biological features of the radioprotective effect of double-stranded RNA preparation. It was found that yeast RNA preparation has a prolonged radioprotective effect after irradiation by a lethal dose of 9.4 Gy. 100 % of animals survive on the 70th day of observation when irradiated 1 hour or 4 days after 7 mg RNA preparation injection, 60 % animals survive when irradiated on day 8 or 12. Time parameters of repair of double-stranded breaks induced by gamma rays were estimated. It was found that the injection of the RNA preparation at the time of maximum number of double-stranded breaks, 1 hour after irradiation, reduces the efficacy of radioprotective action compared with the injection 1 hour before irradiation and 4 hours after irradiation. A comparison of the radioprotective effect of the standard radioprotector B-190 and the RNA preparation was made in one experiment. It has been established that the total RNA preparation is more efficacious than B-190. Survival on the 40th day after irradiation was 78 % for the group of mice treated with the RNA preparation and 67 % for those treated with B-190. In the course of analytical studies of the total yeast RNA preparation, it was found that the preparation is a mixture of single-stranded and double-stranded RNA. It was shown that only double-stranded RNA has radioprotective properties. Injection of 160 μg double-stranded RNA protects 100 % of the experimental animals from an absolutely lethal dose of gamma radiation, 9.4 Gy. It was established that the radioprotective effect of double-stranded RNA does not depend on sequence, but depends on its double-stranded form and the presence of “open” ends of the molecule. It is supposed that the radioprotective effect of double-stranded RNA is associated with the participation of RNA molecules in the correct repair of radiation-damaged chromatin in blood stem cells. The hematopoietic pluripotent cells that have survived migrate to the periphery, reach the spleen and actively proliferate. The newly formed cell population restores the hematopoietic and immune systems, which determines the survival of lethally irradiated animals.

Nearly all lethal viral outbreaks in the past two decades were caused by newly emerging viruses. Viruses are often studied by electron microscopy (EM), which provides new high-resolution data on the structure of viral particles relevant to both fundamental virology and practical pharmaceutical nanobiotechnology. Electron microscopy is also applied to ecological studies to detect viruses in the environment, to analysis of technological processes in the production of vaccines and other biotechnological components, and to diagnostics. Despite the advances in more sensitive methods, electron microscopy is still in active use for diagnostics. The main advantage of EM is the lack of specificity to any group of viruses, which allows working with unknown materials. However, the main limitation of the method is the relatively high detection limit (107 particles/mL), requiring viral material to be concentrated. There is no most effective universal method to concentrate viruses. Various combinations of methods and approaches are used depending on the virus and the goal. A modern virus concentration protocol involves precipitation, centrifugation, filtration, and chromatography. Here we describe the main concentrating techniques exemplified for different viruses. Effective elution techniques are required to disrupt the bonds between filter media and viruses in order to increase recovery. The paper reviews studies on unique traps, magnetic beads, and composite polyaniline and carbon nanotubes, including those of changeable size to concentrate viral particles. It also describes centrifugal concentrators to concentrate viruses on a polyethersulfone membrane. Our review suggests that the method to concentrate viruses and other nanoparticles should be chosen with regard to objectives of the study and the equipment status of the laboratory.

Introduction. The abolition of smallpox vaccination has led to the disappearance of population immunity to pox viruses. However, the threat of infection by pathogenic orthopoxviruses persists and determines the need to develop sensitive and operational methods for indicating pathogens. Objectives and purposes. Development of a sensitive, fast and easy-to-use immunochemical test for the detection of orthopoxviruses in the «point of care» format. Material and methods. We used preparations of cultural vaccinia virus (VV) with varying degrees of purification, polyclonal antibodies from hyperimmune rabbit serum, and equipment from a previously developed autonomous kit for dot-immunoassay on flat protein arrays. Results and discussion. It has been established that rabbit polyclonal antibodies can be used in a single-stage dotanalysis, both as a capture agent immobilized on a substrate and as a detection reagent bound with colloidal gold particles. It is shown that the effectiveness of the detection of VV is inversely related to the degree of purification of viruses from sub-viral structures. The sensitivity of the rapid detection of viruses in a crude preparation was about 30 times higher than in pure viral material. The increase in sensitivity, presumably, occurs due to binding to the capture antibodies of subviral structures, which form large aggregates of sensitized gold particles. The test does not detect cross-reactions with heterogeneous viruses (measles, rubella and chickenpox) that cause exantematous diseases. Conclusion. The one-stage variant of the dot-immunoassay reduces the analysis time to 40 minutes and improves the detection sensitivity of orthopoxviruses in crude viral preparations to the range of 105-104 PFU / ml. Full makeup, ease of analysis and the ability to visually accounting for results allow the test to be used outside of laboratories.

Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. When studying samples containing viruses, one confronts an unavoidable question of the quantitative determination of viral particles in the sample. One of the simplest and efficient approaches to quantitative determination of viral particles in preparation includes the use of electron microscopy; however, a high detection threshold is a significant limitation of this method (107 particles per ml). Usually, such sensitivity is insufficient and can result in error diagnosis. This study aims to develop a method making it possible to detect the number of viral particles more precisely and work with samples in which the concentration of particles is lower than 107/ml. The method includes a concentration of viral particles on the polyethersulfone membrane applied in centrifugal concentrators and subsequent calculation using an electron microscope. We selected env-pseudoviruses using a lentiviral system making it possible to obtain standardized samples of virus-like particles that are safer than a live virus. Suspension of viral particles (a volume of 20 ml) was placed into the centrifugal concentrator and centrifuged. After that, we took a membrane out of the centrifugal concentrator and evaluated the number of particles on the ultrathin section using an electron microscope. The number of viral particles on the whole surface of the filter (a square of 4 сm2) was 4×107 virions, the initial concentration of pseudoviruses in the sample was 2×106 per 1 ml (4×107 particles per 20 ml). As a result, the developed method enables one to evade the major disadvantage of quantitative determination of viruses using electron microscopy regarding a high detection threshold (concentration of particles 107/ml). Furthermore, the centrifugal concentrator makes it possible to sequentially drift a considerable volume of the suspension through the filter resulting in enhancement of test sensitivity. The developed approach results in increased sensitivity, accuracy, and reproducibility of quantitative analysis of various samples containing animal, plant or human viruses using electron microscopy.

Primary cultures of human glioblastoma were obtained from the surgical material of patients K. (female, 61 years, Ds: relapse of glioblastoma) and Zh. (female, 60 years, Ds: relapse of glioblastoma). The effectiveness of a new therapeutic approach aimed at destroying the cancer cell community was evaluated on the primary cell lines of human glioblastoma culture by employing a new strategy of tumor-initiating stem cell synchronization and a domestic strategy of their eradication "3+1". The key elements of the strategy were the following indicator results: (1) evaluation of the presence of tumor-initiating stem cells in a population of cells from analyzed cultures by their ability to internalize double-stranded labeled DNA (TAMRA+ cells); (2) determination of the reference time points of the repair cycle of DNA interstrand cross-links induced by cross-linking cytostatic mitomycin C; (3) evaluation of cell cycle synchronization; (4) determination of the time (day after therapy initiation) when TAMRA+ cells were synchronously present in phase G1/S of the cell cycle, sensitive to the therapy; and (5) establishment of the TAMRA+ (tumor-initiating stem cells) eradication schedule. The cultures were treated with cross-linking cytostatic mitomycin C and a compositional DNA preparation. After the treatments, cell division slows down, and the cultures degrade. The K cell line completely degraded within 30 days of observation. The cell number of the Zh culture fell to nearly one-third of the starting value by day 15 of observation. On day 15, this indicator constituted 1/7.45 for mitomycin C and 1/10.28 for mitomycin C + DNA with reference to the control. The main target of the mitomycin C + DNA regimen was TAMRA+ tumor-initiating stem cells of the glioblastoma cell populations. The action of mitomycin C alone or in the combination with DNA demonstrated effective elimination of TAMRA+ tumor-initiating stem cells and the whole primary cultures of human glioblastomas.

Rheumatoid arthritis (RA) is a serious systemic disease of connective tissue, mainly affecting joints but also with different extra-articular manifestations. In the course of RA the degenerative changes occur in cartilage surfaces of affected joints and also in subchondral bone tissue, joints get deformed and lose their mobility. RA affects about 1 % of the global human population. Biological therapy with recombinant protein inhibitors of inflammatory cytokines is an effective and well-accepted treatment of RA. TNF inhibitors such as recombinant receptors or monoclonal antibodies are the most widely used biotherapeutics in clinical practice. However, this treatment has some serious side effects. The patients treated with TNF inhibitors are more susceptible to infection diseases, they are also at higher risk of developing neoplastic or autoimmune disorders. Biotherapeutics become less effective or even lose their efficiency with evoking specific antidrug antibodies. These drawbacks are in general associated with repeated systemic injections of large amounts of recombinant protein required to achieve the therapeutic efficacy. Genetic therapy might provide a good and effective solution. Viral genes coding for immunomodulatory factors could be used to create new gene therapy products to treat RA and other human disease. Poxviruses, as compared to other viral families, have an unprecedentedly rich set of such immunomodulatory genes. In particular, they have genes encoding TNF-binding proteins. Previously in a variety of laboratory models we have shown that recombinant TNF-binding protein CrmB can effectively block TNF. In this work we demonstrated that candidate antirheumatic genotherapeutic plasmid constructions encoding poxviral TNF-binding proteins have low immunogenicity.

Previously, we reported on the development of a therapeutic regimen allowing eradication of primary murine Krebs-2 ascites transplants. This protocol involved multiple injections of dsDNA preparations administered during the NER and HR phases of repair of interstrand DNA cross-links induced by prior cyclophosphamide treatments. Mice treated under this protocol frequently developed secondary ascites, which indicated that some tumor-inducing cancer stem cells could survive the treatment and caused relapse. Further, we observed that animals receiving multiple dsDNA injections developed pronounced systemic inflammatory response. This prompted us to develop a more straightforward treatment regimen based on the synergistic activity of cyclophosphamide and dsDNA preparations, which would allow complete eradication of established primary Krebs-2 ascites and also be less toxic for the treated animals. This protocol relies on a precisely timed single injection of dsDNA during the NER/HR transition period of each repair cycle. Under this protocol, 8-day remission of Krebs-2 engrafted mice was achieved, which was similar to the results of the multiple-injection treatment schedule. We observed an increase in the average life span of Krebs-2- transplanted mice on a single-injection regimen, which was consistent with reduced toxicity of such treatment.

Cumulative evidence obtained in this series of studies has guided the logic behind the development of a novel composite dsDNA-based preparation whose therapeutic application according to the specific regimen completely cures the mice engrafted with otherwise lethal Krebs-2 ascites. The likely mechanism involves elimination of TAMRA+ tumor-inducing stem cells (TISCs) from Krebs-2 tumors. We performed quantitative analysis of TISC dynamics in Krebs-2 ascites following treatment with the cytostatic drug cyclophosphamide (CP) and untreated control cells. In intact ascites, TISC percentage oscillates around a certain value. Following CP treatment and massive apoptosis of committed cancer cell subpopulation, we observed relative increase in TISC percentage, which is consistent with reduced susceptibility of TISCs to CP. Nonetheless, this treatment apparently synchronizes TISCs in a cell cycle phase when they become sensitive to further drug treatments. We describe the regimen of synergistic DNA + CP activity against Krebs-2 ascites. This protocol results in a complete cure of 50 % of Krebs-2 engrafted mice and involves three metronomic injections of CP exactly at the timepoints when repair cycles are about to finish combined with dsDNA injections 18 hours following each CP injection. The “final shot” uses CP + DNA treatment, which targets the surviving yet highly synchronized and therefore treatmentsensitive cells. The first three CP/DNA injections appear to arrest Krebs-2 cells in late S-G2-M phase and result in their simultaneous progression into G1-S phase. The timing of the “final shot” is crucial for the successful treatment, which eradicates tumorigenic cell subpopulation from Krebs-2 ascites. Additionally, we quantified the changes in several biochemical, cellular and morphopathological parameters in mice throughout different treatment stages.

Existence of a small subset of cancer cells referred to as tumor initiating stem cells (TISCs) largely responsible for tumor progression and resistance to chemotherapeutic cytostatic drugs reperesent an important recent paradigm shift. The present work is the first report in the series of papers from our group where we describe the development of anticancer therapy based on the selective targeting of TISCs. Here were characterize a cytoreductive activity of cyclophosphamide (CP), double-stranded DNA (dsDNA) and combinations thereof against the TISC population present in mouse Krebs-2 ascites. We evaluated engraftment potential of Krebs-2 cancer cells treated in ascites-bearing mice in vivo, followed by re-engraftment to congenic recipient mice in a form of a solid graft. These data indicate that with our approach TISCs can be completely eliminated even from a well-established ascites. We demonstrate that dsDNA-internalizing and CD34-positive cells are more sensitive to the synergistic effects of CP and dsDNA. When Krebs-2 ascites are treated with human DNA 1-12 hours post CP injection, this results in either elimination of cells that internalize TAMRA-labeled DNA (TISCs) or alters their phenotype, which is accompanied with the loss of surface expression of CD34. Next, we show that the timepoint 18 hrs post CP treatment is critical to the ongoing repair process in that it divides the repair into two phases: nucleotide excision repair + dsDNA break repair and homologous recombination. Importantly, both of these phases can be conveniently used for targeting the tumorigenic potential of the graft. In the context of monotherapy, CP is most effective against ascites grafts when administered as serial injections. To achieve maximum efficiency, the timing of consecutive injections must match the time when cancer cells found at G2/M during the first injection enter G1/S and/or the time of active repair via homologous recombination.

In the present paper, we report on the series of experiments where multiple regimens of CP and dsDNA injections were tested for targeting the ascites form of murine Krebs-2 cancer in situ. We show that combining CP with cross-linked human and salmon dsDNA results in a synergistic toxicity for ascites-bearing mice, an observation supported by the histopathology analysis of organs and tissues of experimental animals. In contrast, using a composite mixture of native and cross-linked human and salmon DNA after CP injections leads to a significant increase in average lifespan of the treated mice. Further, we demonstrate that repeated rounds of CP+dsDNA injections result in dramatic anticancer effect. The timing of injections is chosen so that they target the cells that were insensitive to the previous treatments as they were in the G2/M phase. 3-4 rounds of injections are needed to eliminate the subpopulation of tumor-initiating cancer stem cells. Our experiments identified the regimen when complete resorption of the primary Krebs-2 ascites occurs in all of the treated animals, followed by a remarkable remission period lasting 7-9 days. Yet, this regimen does not prevent secondary site metastases (either solid or ascites form) from developing, which is likely caused by the migration of ascites cells into adjacent tissues or by incomplete eradication of cancer stem cells. To address these and other questions, we expanded the study and performed histopathology analysis, which indicated that secondary metastases is not the only cause of death. In fact, many animals displayed unfolding systemic inflammatory reaction which was culminated by multiple organ failure. Thus, we developed the concept for treating ascites form of Krebs-2 cancer, which allows elimination of the primary ascites.

At present, there is no animal model for smallpox that reflects the weakened immune system in people and can therefore help assess the prophylactic (highly preventive) efficiency of antiviral drugs. To fill in the gap, we have explored the possibility of using outbred immunodeficient SCID mice as a model animal for smallpox with the aid of virolo­gical, histological and electron microscopic and sta­tistical methods. There was no clinical evidence of disease by intranasal infection of mice at a dose of 5.2 log10 PFU (plaque forming units). At the same time, the 50 % infective dose (ID50) of VARV estimated for animals by registering the presence of the virus in their lungs after 4 days post i.n. infection was 3.5 log10 PFU and was relatively similar to that in humans, theoretically determined by identification of the clinical picture of the disease. Virus replication was detected only in the respiratory organs of mice challenged i.n. with VARV at a dose of 5.2 log10 PFU (50 ID50). The values for its concentrations in the lungs and nose resembled those for affected people and well-known animal models (Macaca cynomolgus and ICR mice), respiratorily infected with VARV at similar doses. The existing model animals were not significantly different from SCID mice in the duration of viral presence in the lungs. Moreover, in SCID mice, as in humans and other animal models, similar pathomor- phological changes of inflammatory necrotic nature in the respiratory organs have been reported. Using SCID mice in assessing the prophylactic efficacy of the antiviral drugs NIOCH-14 and ST-246 demonstrated the adequacy of the results obtained to those described in the literature. This opens up the prospect of using SCID mice as an animal model for smallpox to develop antiviral drugs intended for people with severe immuno­suppressive states.

Injections ofexogenous DNAin combination witha cytostatic agent cyclophosphamide (CP) cause illness anddeathofexperimental mice. This phenomenon is referredto this as delayeddeath. It has been foundthat upon intraperitoneal injections fragments ofexogenous DNAreachthe bone marrowniche andenter the nuclei ofbone marrowcells (BMCs). Also, fragments ofexogenous DNAare capturedfrom culture medium byBMCs generatedex vivo. Upon suchtreatment, the fragments are incorporatedinto cells in a non-degradedform. We estimate that under suchconditions upto 1800 kb ofexogenous DNAcan be present in BMCs as fragments. After ex vivo incubation withBMCs, fragments ofexogenous DNAinternalizedin cells ofbothintact andCP pre-treatedmice become circularized. It has been shown that fragments ofexogenous DNAcan form high-molecular weight structures in vivo. Moreover, fragments localizedin BMCnuclei are suggestedto integrate into chromosome(s) ofrecipient mouse genomes when treatedwithCP andexogenous DNA.

Mice were observed to get sick and die upon administration of exogenous DNA in a specific period of time following their pretreatment with the cytostatic cyclophosphamide (CP) (Dolgova et al., 2011). It was established that exogenous DNA reaches internal compartments of bone marrow cells (BMCs) where it is processed (Dolgova et al., 2012a). Thus, BMCs appear to be the primary targets for the synergic action of these preparations (Dolgova et al., 2012b).In the present study, we show that the copy number for mouse interspersed genomic repeats decreases in the genome of mouse mononuclear cells as a result of interstrand cross-link (ICL) repair after pre-treatment with cytostatic CP. This phenomenon occurs within the time span from 18 to 24 h following CP injection, which corresponds to the final step in the repair of the majority of double-strand breaks (DSBs), as predominant intermediates in ICL repair. Injections of exogenous DNA in CP-pretreated mice preserve the copy number of interspersed repeats at the original level. Our results suggest that the fragments of exogenous DNA participate in ICL-induced DSB repair, thereby compromising the repair process.

The synergic action of the cytostatic drug cyclophosphamide (CP) and fragmented exogenous DNA causes illness and death in mice (Dolgova et al., 2011–2013). The observed «delayed death» effect was most clearly pronounced when the DNA preparation was administered 18 to 30 hours after CP treatment. This time span is designated as «death window».It was found that injections of exogenous DNA result in sustained increase in bone marrow cell (BMC) apoptosis, which occurs throughout the time of DNA administration (18–30 hours). Exogenous DNA, both allogeneic and belonging to various taxa induces BMCs apoptosis. Plasmid DNA has the greatest effect on apoptosis induction.The analysis of reduction and restoration of BMC subpopulations as the mice progressed to death revealed a virtually complete loss of the 12–20-mkm fraction of the cell population (about 3–4 % vs. 35–40 % in the control), which corresponds to the maximum leukopenia on day 3 after CP treatment. However, the relative amount of CD34+ hematopoietic stem cells (HSCs) from day 15 and till the end of the observation constituted 1,2–1,4 %, which corresponds to the wild-type range. Comparison of BMC smears from the sternal bone marrow of the CP and CP+DNA groups of mice indicates that the BMC populations isolated from CP+DNA animals lack young committed lymphopoiesis progenitor cells. Moreover, the affected mice had immature blast cell types in their blood, which was never observed in healthy or CP-treated mice. Pathological and morphological analyses show that starting from posttreatment day 9, mice that received CP+DNA preparations displayed pronounced morphological changes in their lungs, liver, pancreas, central and peripheral immune system organs, and brain. Most of the pathological changes observed are consistent with severe inflammatory response. This suggestion is proven by structural equivalents of functional involution of lymphoid organs, such as thymus, spleen, and lymph nodes.We speculate that the death of treated animals resulted from multiple organ dysfunctions caused by accidental involution of lymphoid organs and the systemic inflammatory response syndrome, both associated with injections of fragmented exogenous DNA into experimental animals within the «death window», which corresponds to the final step in the repair of the majority of CP-induced double-strand breaks.

of MPV after 7 days postinfection, applying peroral administration once within 24 hours (24 hours before infection and 7 days after infection of mouse with 60 µg/g of a preparation). Displayed is the feasibility of using 8–15-days-old ICR mice (body weight 9–11 g) as an animal model for evaluation of therapeutic efficacy of the preparations under development against Monkeypox and smallpox.