Background: Many plant secondary metabolites (PSMs) were shown to intercalate into DNA helix or interact with DNA grooves. This may influence histone-DNA interactions changeing chromatin structure and genome functioning. Methods: Nucleosome stability and linker histone H1.2, H1.4 and H1.5 localizations were studied in HeLa cells after the treatment with 15 PSMs, which are DNA-binders and possess anticancer activity according to published data. Chromatin remodeler CBL0137 was used as a control. Effects of PSMs were studied using fluorescent microscopy, flowcytometry, quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR), western-blotting. Results: We showed that 1-hour treatment with CBL0137 strongly inhibited DNA synthesis and caused intensive linker histone depletion consistent with nucleosome destabilization. None of PSMs caused nucleosome destabilization, while most of them demonstrated significant influence on linker histone localizations. In particular, cell treatment with 11 PSMs at non-toxic concentrations induced significant translocation of the histone H1.5 to nucleoli and most of PSMs caused depletion of the histones H1.2 and H1.4 from chromatin fraction. Curcumin, resveratrol, berberine, naringenin, and quercetin caused significant redistribution of all three variants of the studied linker histones showing some overlap of PSM effects on linker histone DNA-binding. We demonstrated that PSMs, which induced the most significant redistribution of the histone H1.5 (berberine, curcumin and naringenin), influence the proportion of cells synthesizing DNA, expressing or non-expressing cyclin B and influence cell cycle distribution. Berberine induction of H1.5 translocations to nucleoli was shown to occur independently on the phases of cell cycle (metaphase was not analyzed). Conclusions: For the first time we revealed PSM influence on linker histone location in cell nuclei that opens a new direction of PSM research as anticancer agents.

Previously we discovered that among 15 DNA-binding plant secondary metabolites (PSMs) possessing anticancer activity, 11 compounds cause depletion of the chromatin-bound linker histones H1.2 and/or H1.4. Chromatin remodeling or multiH1 knocking-down is known to promote the upregulation of repetitive elements, ultimately triggering an interferon (IFN) response. Herein, using HeLa cells and applying fluorescent reporter assay with flow cytometry, immunofluorescence staining and quantitative RT-PCR, we studied effects of PSMs both evicting linker histones from chromatin and not influencing their location in nucleus. We found that (1) 8 PSMs, evicting linker histone H1.2 from chromatin, activated significantly the type I IFN signaling pathway and out of these compounds resveratrol, berberine, genistein, delphinidin, naringenin and curcumin also caused LINE1 expression. Fisetin and quercetin, which also induced linker histone H1.2 eviction from chromatin, significantly activated only type I IFN signaling, but not LINE1 expression; (2) curcumin, sanguinarine and kaempferol, causing significant depletion of the chromatin-bound linker histone H1.4 but not significantly influencing H1.2 presence in chromatin, activate type I IFN signaling less intensively without any changes in LINE1 expression; (3) four PSMs, which did not cause linker histone eviction, displayed neither IFN signaling activation nor enhancement of LINE1 expression. Thus, we have shown for the first time that chromatin destabilization observed by depletion of chromatin-bound linker histone H1.2 caused by anticancer DNA-binding PSMs is accompanied by enhancement of type I IFN signaling, and that LINE1 expression often impacts this activation.

In preparing the review, articles on the functioning of the reverse transcriptase enzyme of endogenous repeat sequences LINE1, the mechanisms of action and antitumor activity of viral reverse transcriptase inhibitors. Articles available in the biomedical literature information databases SciVerse Scopus, PubMed, Web of Science, Russian Science CitationIndex (RSCI) were analyzed. The review used information from 140 publications, of which 95 and 39 were published, respectively, over the last ten and three years, 2 articles present the results of clinical studies, and 45 articles refer to results demonstrating the anticancer properties of the studied compounds in various models in vitro and in vivo. Aim. Based on data on the functional properties of the reverse transcriptase enzyme of endogenous repeat sequences LINE1 (long interspersed nuclear elements 1), analyze the potential use of viral reverse transcriptase inhibitors in oncology, presenting their classification and main mechanisms of action. About 98 % of the human genome consists of repetitive sequences, most of which are represented by mobil genetic elements, the activation of which leads to increased genome instability. These include long (LINE) and short (SINE) interspersed nuclear element repeated DNA sequences interspersed nuclear elements, respectively, which occupy about 45 % of the human genome. Increased expression levels of these sequences in the genome have been identified in many forms of malignant neoplasms. Their transposition occurs due to the expression of LINE1-encoded reverse transcriptase, whichis homologous to viral reverse transcriptase. To date, reverse transcriptase inhibitors of viruses of nucleoside and non-nucleoside structure have been developed and are successfully used in the clinic. These drugs demonstrate an inhibitory effect on both LINE1 reverse transcriptase and telomerase, which provides the tumor cell with the ability to overcome replicative senescence. Due to these properties, these compounds are expected to exhibit both their own antitumor activity and increase the sensitivity of tumor cells to the therapy of malignant neoplasms, which is experimentally confirmed in models of malignant tumors in vitro and in vivo. Use of reverse transcriptase inhibitors in combination therapy seems advisable both to prevent further genome rearrangements caused by LINE1 and to suppress the survival of tumor cells by inhibiting telomerase activity.

Recent development of molecular and genetic technologies has demonstrated at the molecular level the co-evolutionary principles of interaction between microbiota, virome and the host organism, as well as the role of microorganisms and viruses both in maintaining physiological homeostasis and in the development of various diseases, including malignant neoplasms. The presented review is devoted to the analysis and generalization of modern data on microorganisms and viruses inhabiting the human body, their role in the processes of initiation, promotion and progression of carcinogenesis. The review provides information on known oncogenic viruses and microorganisms according to the modern classification of carcinogenic agents of the International Agency for Research on Cancer. Mechanistic data on the procarcinogenic effect of microbiota and virome are considered in accordance with the modern concept of key characteristics of a carcinogenic agent. Particular attention is paid to the analysis of data on the influence of microbiota and virome on the immunity of the host organism, including both the first results of immunotherapy with Coley toxin of soft tissue sarcomas and osteosarcomas, and data on the influence of individual types of microorganisms on the formation of the immunocompetent cell profile of the host organism. In addition, the influence of intratumor and intracellular microbiota, respectively, on the microenvironment of tumor cells and cellular signaling, including in solid tumors that have no contact with the external environment are also discussed. The data presented are important in terms of the holobiota concept, showing the interdependent existence of the human body, microorganisms and viruses, to improve the prevention and therapy of malignant neoplasms.

Background. An in-depth study of the participation of the microbiota in the pathogenesis of tumors has opened up new opportunities for the development of alternative approaches to the diagnosis, therapy and prevention of malignant neoplasms.Aim. To summarize the data on the practical use of microbiota profile features as a marker of carcinogenesis and diagnosis, as well as to consider its participation in the combined treatment and prevention of cancer.Materials and methods. A literature search was carried out in the databases NCBI MedLine (PubMed), Scopus, web of Science using keywords that determine the purpose of the study. Results from original studies, meta-analyses, randomized controlled clinical trials, and traditional, systematic, and umbrella reviews published in recent years were analysed.Results. Qualitative and quantitative changes in the composition of the microbiota associated with the pathogenesis of oncological diseases make it possible to use them as markers for determining the risk of developing malignant neoplasms and predicting a wide range of tumors. The mechanisms that determine the use of the microbiota in anticancer therapy are diverse. The effect on the immune system is the most significant. Of great interest are artificially created hybrid nanoparticles covered with a membrane of bacterial vesicles and tumor cells to activate specific antitumor immunity. In terms of cancer prevention, the use of probiotics, prebiotics and synbiotics discovered by I.I. Mechnikov was fundamentally substantiated.Conclusion. The complex of scientific genomic and epigenetic data obtained in mechanistic and epidemiological studies on the role of the microbiota in the pathogenesis of tumors is currently evaluated as the most significant result justifying its practical application as a component of cancer diagnosis, therapy and prevention.

Introduction. The use of hypomethylating agents in the treatment of acute myeloid leukemia has increased overall patient survival by 12 %. However, alongside their potent antitumor effect, hypomethylating agents negatively impact genome stability due to the transposition of activated LINE1 elements, which contributes to the short duration of remission. Since LINE1 retrotransposition requires the ORF2-encoded reverse transcriptase, homologous to the retroviral enzyme, we proposed combining hypomethylating agents with a non-nucleoside inhibitor of this enzyme to reduce the genotoxic effects of 5-azacytidine.Aim. To evaluate the effect of efavirenz on 5-azacytidine in cultured acute myeloid leukemia cells regarding: сytotoxic activity, expression of long interspersed nuclear elements (LINE1), the level of genetic instability.Materials and methods. The study was conducted on THP-1 and KG-1 acute myeloid leukemia cell lines. 5-Azacytidine (hypomethylating agents) and efavirenz (reverse transcriptase inhibitor) were used. Cytotoxicity was assessed via the resazurin assay, apoptosis and necrosis rates were measured by flow cytometry, LINE1 expression was quantified using real-time polymerase chain reaction, and DNA damage was evaluated via the comet assay.Results. Efavirenz did not affect the cytotoxicity of 5-azacytidine. Immunofluorescence staining of LINE1-encoded ORF1 protein and flow cytometry confirmed that efavirenz did not alter LINE1 expression levels. However, comet assay data indicated that combining 5-azacytidine with efavirenz reduced its genotoxic effects.Conclusion. Our findings demonstrate, for the first time, the potential of a novel acute myeloid leukemia treatment strategy combining hypomethylating agents with reverse transcriptase inhibitors.