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.

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.

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BackgroundExtracellular 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.MethodsApoptosis 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.ResultsDirect 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.ConclusionsDouble-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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12935-015-0180-6) contains supplementary material, which is available to authorized users.

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Background: In 2020, the pandemic caused by novel coronavirus infection has become one of the most critical global health challenges during the past century. The lack of a vaccine, as the most effective way to control the novel infection, has prompted the development of a large number of preventive products by the scientific community. We have developed a candidate vaccine (EpiVacCorona) against novel coronavirus infection caused by SARS-CoV-2 that is based on chemically synthesized peptides conjugated to a carrier protein and adsorbed on aluminum hydroxide and studied the specific activity of the developed vaccine. Aims: Study of the immunogenicity and protectivity of the peptide candidate vaccine EpiVacCorona. Materials and methods: the work was performed using standard molecular biological, virological and histological methods. Results: It was demonstrated that EpiVacCorona, when administered twice, spaced 14 days apart, to hamsters, ferrets, and non-human primates (African green monkeys, rhesus macaques) at a dose of 260 g, which is equal to one inoculation dose for humans, induces virus-specific antibodies in 100% of the animals. Experiments in hamsters showed this vaccine to be associated with the dose-dependent immunogenicity. The vaccine was shown to accelerate the elimination of the virus from the upper respiratory tract in ferrets and prevent the development of pneumonia in hamsters and non-human primates following a respiratory challenge with novel coronavirus. Conclusions: The results of a preclinical specific activity study indicate that the use of EpiVacCorona has the potential for human vaccination.

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Krebs-2 solid carcinoma was cured using a new “3+1” strategy for eradication of Krebs-2 tumor-initiating stem cells. This strategy was based on synchronization of these cells in a treatment-sensitive phase of the cell cycle. The synchronization mechanism, subsequent destruction of Krebs-2 tumor-initiating stem cells, and cure of mice from a solid graft were found to depend on the temporal profile of the interstrand cross-link repair cycle. Also, the temporal profile of the Krebs-2 interstrand repair cycle was found to have a pronounced seasonal cyclicity at the place of experiments (Novosibirsk, Russia). As a result, the therapeutic effect that is based on application of the described strategy, originally developed for the “winter repair cycle” (November−April), is completely eliminated in the summer period (June−September). We conclude that оne of the possible and the likeliest reasons for our failure to observe the therapeutic effects was the seasonal cyclicity in the duration of the interstrand repair cycle, the parameter that is central to our strategy.