Coxsackievirus A7 and Enterovirus A71 Significantly Reduce SARS-CoV-2 Infection in Cell and Animal Models.

In this study, we investigated the features of co-infection with SARS-CoV-2 and the enterovirus vaccine strain LEV8 of coxsackievirus A7 or enterovirus A71 for Vero E6 cells and Syrian hamsters. The investigation of co-infection with SARS-CoV-2 and LEV-8 or EV-A71 in the cell model showed that a competitive inhibitory effect for these viruses was especially significant against SARS-CoV-2. Pre-infection with enteroviruses in the animals caused more than a 100-fold decrease in the levels of SARS-CoV-2 virus replication in the respiratory tract and more rapid clearance of infectious SARS-CoV-2 from the lower respiratory tract. Co-infection with SARS-CoV-2 and LEV-8 or EV-A71 also reduced the severity of clinical manifestations of the SARS-CoV-2 infection in the animals. Additionally, the histological data illustrated that co-infection with strain LEV8 of coxsackievirus A7 decreased the level of pathological changes induced by SARS-CoV-2 in the lungs. Research into the chemokine/cytokine profile demonstrated that the studied enteroviruses efficiently triggered this part of the antiviral immune response, which is associated with the significant inhibition of SARS-CoV-2 infection. These results demonstrate that there is significant viral interference between the studied strain LEV-8 of coxsackievirus A7 or enterovirus A71 and SARS-CoV-2 in vitro and in vivo.

Human Adenovirus and Influenza A Virus Exacerbate SARS-CoV-2 Infection in Animal Models.

In this study, we investigated the features of the infectious process by simulating co-infection with SARS-CoV-2 and human adenovirus type 5 (HAdV-5) or influenza A virus (IAV) in vitro and in vivo. The determination of infectious activity of viruses and digital PCR demonstrated that during simultaneous and sequential HAdV-5 followed by SARS-CoV-2 infection in vitro and in vivo, the HAdV-5 infection does not interfere with replication of SARS-CoV-2. The hamsters co-infected and mono-infected with SARS-CoV-2 exhibited nearly identical viral titers and viral loads of SARS-CoV-2 in the lungs. The hamsters and ferrets co-infected by SARS-CoV-2- and IAV demonstrated more pronounced clinical manifestations than mono-infected animals. Additionally, the lung histological data illustrate that HAdV-5 or IAV and SARS-CoV-2 co-infection induces more severe pathological changes in the lungs than mono-infection. The expression of several genes specific to interferon and cytokine signaling pathways in the lungs of co-infected hamsters was more upregulated compared to single infected with SARS-CoV-2 animals. Thus, co-infection with HAdV-5 or IAV and SARS-CoV-2 leads to more severe pulmonary disease in animals.

Oncolytic Effect of Adenoviruses Serotypes 5 and 6 Against U87 Glioblastoma Cancer Stem Cells.

BACKGROUND/AIM: Oncolytic adenoviruses are promising therapeutic agents against both the bulk of tumor cells and cancer stem cells. The present study intended to test the oncolytic capability of adenovirus serotype 6 (Ad6), which has a lower seroprevalence and hepatotoxicity relatively to adenovirus 5 (Ad5), against the glioblastoma and its cancer stem cells. MATERIALS AND METHODS: Oncolytic efficacy of Ad6 was compared to widespread Ad5 both in vitro and in vivo, using the U87 and U251 human glioblastoma cell lines and subcutaneously transplanted U87 cells in SCID mice, respectively. RESULTS: Ad6 had a dose-dependent cytotoxicity toward glioblastoma cells in vitro and its intratumoral injections lead to a significant (p<0.05) decrease in volume of U87 xenografts, similarly to Ad5. Based on the innate capability of glioblastoma cancer stem cells to internalize a fluorescent-labeled double-stranded DNA probe, the spatial localization of these cells was estimated and it was shown that the number of cancer stem cells tended to decrease under adenovirus therapy as compared to the control group. CONCLUSION: Ad6 was shown to be a promising agent for treating glioblastomas.

Ultrastructural analysis of the Krebs-2 ascites cancer cells treated with extracellular double-stranded DNA preparation.

Electron-microscopic analysis of the ultrastructure of the Krebs-2 carcinoma ascites cells in the first 90 min immediately after their exposure to fragmented double-stranded DNA has been performed. Morphological attributes of the treated cancer cells indicate the induction in these cells of destructive processes of presumably apoptotic type. The predominance of dystrophic-destructive changes in cells after the addition of DNA is supposed to be a consequence of the disturbance in metabolic processes caused by the experimental action.

A strategy to eradicate well-developed Krebs-2 ascites in mice.

We describe the strategy, which allows curing experimental mice engrafted with Krebs-2 ascites. The strategy is based on the facts that i) Krebs-2 tumor-initiating stem cells (TISCs) are naturally capable of internalizing fragments of extracellular double-stranded DNA (dsDNA); ii) upon delivery into TISCs, these dsDNA fragments interfere with the on-going DNA repair process so that TISCs either die or lose their tumorigenic potential. The following 3-step regimen of therapeutic procedures leading to eradication of Krebs-2 ascites is considered. Firstly, three timed injections of cyclophosphamide (CP) exactly matching the interstrand cross-link (ICL) repair phases that lead to synchronization of ascites cells in late S/G2/M. Secondly, additional treatment of ascites 18 hours post each CP injection (at NER/HR transition timepoint) with a composite dsDNA-based preparation interfering with the NER and HR repair pathways, so that tumorigenic properties of ascites cells are compromised. Thirdly, final treatment of mice with a combination of CP and dsDNA injections as ascites cells undergo apoptotic destruction, and the surviving TAMRA+ TISCs arrested in late S/G2/M phases massively enter into G1/S, when they regain sensitivity to CP+dsDNA treatment. Thus, this regimen assures that no viable cells, particularly Krebs-2 TISCs, remain.

Comparative analysis of pathologic processes developing in mice housed in SPF vs non-SPF conditions and treated with cyclophosphamide and dsDNA preparation.

In our earlier studies, we observed that when mice are treated with cyclophosphamide and fragmented exogenous dsDNA (18-30 h post cytostatic treatment), they develop a very characteristic set of symptoms and 80-90% of such animals succumb within 6-25 days. This was called "delayed death" phenomenon, and the gap between cyclophosphamide and DNA injections required for such phenotype to develop was termed "death window". We established that mice succumbed to multi-organ failure, which was caused by systemic inflammation and sepsis. These processes unfolded along with accidental involution of lymphoid organs, which resulted from the failure of CD34(+) hematopoietic stem cells to differentiate into lymphoid lineage progenitors. Here we compare SPF and non-SPF animals, and demonstrate that the major cause of systemic inflammation and sepsis observed upon such treatments is activation of an opportunistic infection. Mice of the same strain (CBA) housed under SPF conditions do not develop the characteristic symptoms, nor do they become moribund. Yet, regardless of the breeding conditions, upon synergistic action of cyclophosphamide and dsDNA, CD34(+) hematopoietic stem cells consistently fail to give rise to lymphoid lineage progenitors. We demonstrate that this differentiation defect is reversible and that population of lymphoid progenitors is restored by day 29 after cyclophosphamide injection.

Using ICR and SCID mice as animal models for smallpox to assess antiviral drug efficacy.

The possibility of using immunocompetent ICR mice and immunodeficient SCID mice as model animals for smallpox to assess antiviral drug efficacy was investigated. Clinical signs of the disease did not appear following intranasal (i.n.) challenge of mice with strain Ind-3a of variola virus (VARV), even when using the highest possible dose of the virus (5.2 log10 p.f.u.). The 50 % infective doses (ID50) of VARV, estimated by the virus presence or absence in the lungs 3 and 4 days post-infection, were 2.7 ± 0.4 log10 p.f.u. for ICR mice and 3.5 ± 0.7 log10 p.f.u. for SCID mice. After i.n. challenge of ICR and SCID mice with VARV 30 and 50 ID50, respectively, steady reproduction of the virus occurred only in the respiratory tract (lungs and nose). Pathological inflammatory destructive changes were revealed in the respiratory tract and the primary target cells for VARV (macrophages and epithelial cells) in mice, similar to those in humans and cynomolgus macaques. The use of mice to assess antiviral efficacies of NIOCH-14 and ST-246 demonstrated the compliance of results with those described in scientific literature, which opens up the prospect of their use as an animal model for smallpox to develop anti-smallpox drugs intended for humans.

Combination of cyclophosphamide and double-stranded DNA demonstrates synergistic toxicity against established xenografts.

BACKGROUND: Extracellular double-stranded DNA participates in various processes in an organism. Here we report the suppressive effects of fragmented human double-stranded DNA along or in combination with cyclophosphamide on solid and ascites grafts of mouse Krebs-2 tumor cells and DNA preparation on human breast adenocarcinoma cell line MCF-7. METHODS: Apoptosis and necrosis were assayed by electrophoretic analysis (DNA nucleosomal fragmentation) and by measurements of LDH levels in ascitic fluid, respectively. DNA internalization into MCF-7 was analyzed by flow cytometry and fluorescence microscopy. RESULTS: Direct cytotoxic activity of double-stranded DNA (along or in combination with cyclophosphamide) on a solid transplant was demonstrated. This resulted in delayed solid tumor proliferation and partial tumor lysis due to necrosis of the tumor and adjacent tissues. In the case of ascites form of tumor, extensive apoptosis and secondary necrosis were observed. Similarly, MCF-7 cells showed induction of massive apoptosis (up to 45%) as a result of treatments with double-stranded DNA preparation. CONCLUSIONS: Double-stranded DNA (along or in combination with cyclophosphamide) induces massive apoptosis of Krebs-2 ascite cells and MCF-7 cell line (DNA only). In treated mice it reduces the integrity of gut wall cells and contributes to the development of systemic inflammatory reaction.

Identification of cancer stem cells and a strategy for their elimination.

It has been established previously that up to 40% of mouse CD34(+) hematopoietic stem cells are capable of internalizing exogenous dsDNA fragments both in vivo and ex vivo. Importantly, when mice are treated with a combination of cyclophosphamide and dsDNA, the repair of interstrand crosslinks in hematopoietic progenitors is attenuated, and their pluripotency is altered. Here we show for the first time that among various actively proliferating mammalian cell populations there are subpopulations capable of internalizing dsDNA fragments. In the context of cancer, such dsDNA-internalizing cell subpopulations display cancer stem cell-like phenotype. Furthermore, using Krebs-2 ascites cells as a model, we found that upon combined treatment with cyclophosphamide and dsDNA, engrafted material loses its tumor-initiating properties which we attribute to the elimination of tumor-initiating stem cell subpopulation or loss of its tumorigenic potential.

Delivery and processing of exogenous double-stranded DNA in mouse CD34+ hematopoietic progenitor cells and their cell cycle changes upon combined treatment with cyclophosphamide and double-stranded DNA.

We previously reported that fragments of exogenous double-stranded DNA can be internalized by mouse bone marrow cells without any transfection. Our present analysis shows that only 2% of bone marrow cells take up the fragments of extracellular exogenous DNA. Of these, ~45% of the cells correspond to CD34+ hematopoietic stem cells. Taking into account that CD34+ stem cells constituted 2.5% of the total cell population in the bone marrow samples analyzed, these data indicate that as much as 40% of CD34+ cells readily internalize fragments of extracellular exogenous DNA. This suggests that internalization of fragmented dsDNA is a general feature of poorly differentiated cells, in particular CD34+ bone marrow cells. When linearized plasmid DNA was used as a source of exogenous DNA, we observed that exonucleolytic processing and ligation of double-stranded DNA termini occurred in the bone marrow cells that had this DNA internalized. We also recovered "hybrid" plasmids that encompass kanamycin-resistance gene from the exogenous plasmid DNA and the fragments of plasmids from host enterobacteria, which is suggestive of recombination events taking place upon DNA internalization. CD34+ cells make up the distinctive bone marrow cell population that internalizes extracellular DNA. Cell cycle analysis of CD34+ cells treated with cyclophosphamide only or in combination with dsDNA, suggests that these cells have distinct biologic responses to these treatments. Namely, whereas upon cyclophosphamide treatment bone marrow stem cells become arrested at S-G2 phases, combined cyclophosphamide+dsDNA treatment leads to cell cycle progression without any delay. This indicates that when the genome is undergoing repair of interstrand crosslinks, injection of fragmented exogenous dsDNA results in immediate reconstitution of genome integrity. We observe that cyclophosphamide-only or a combined cyclophosphamide+dsDNA treatment of cells lead to two distinct waves of apoptosis in CD34+ progenitors. We also show that cyclophosphamide and cyclophosphamide+dsDNA injections promote division of CD34+ cells at distinct time periods.

"Delayed death" phenomenon: a synergistic action of cyclophosphamide and exogenous DNA.

Morbidity and mortality in mice were observed upon administration of exogenous DNA following their pre-treatment with a cytostatic agent cyclophosphamide. Upon intraperitoneal injections, the fragments of exogenous DNA reached bone marrow cells. These cells were also found to internalize up to 1800 kb of exogenous DNA ex vivo. The 18-24 h time frame represents a final stage in the repair of DNA double-strand breaks, so when exogenous DNA was administered within this critical period of time, pathological changes were observed in many target organs. Namely, bone marrow cells underwent a sustained increase in apoptosis. Copy number of B1 and B2 DNA repeats in bone marrow cells remained unchanged, whereas in the control group of animals their levels were significantly decreased. Finally, the bone marrow cells of moribund animals completely lacked lymphoid progenitors, yet the CD34+ hematopoietic stem cell counts were normal. Histopathology analysis suggested that mice died due to accidental involution of lymphoid organs combined with a systemic inflammatory process induced by massive administration of exogenous DNA and depletion of lymphoid lineage.