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.

Previously we discovered that among 15 DNA-binding plant secondary metabolites (PSMs) possessing anticancer activity, 11 compounds cause depletion of the linker histones H1.2 and/or H1.4 from chromatin fraction. Chromatin remodeling or multiH1 knocking-down is known to promote the upregulation of repetitive elements, ultimately triggering an interferon response. Herein, using HeLa cells and applying fluorescent reporter assay with flow cytometry and quantitave RT-PCR, we found that among PSMs depleting linker histones, 8 compounds significantly activate type I interferon signaling pathway. Out of these compounds resveratrol, berberine, genistein, delphinidin, naringenin and curcumin also caused LINE1 expression detected by quantitate RT-PCR and by immunefluorescent staining analysis of ORF1 LINE1 and γ-H2AX. Fisetin and quercetin, which also induced linker histone depletion, significantly activated only type I interferon signaling, but not LINE1 expression. Curcumin, sanguinarine and kaempferol, causing depletion of the linker histone H1.4 more intensively respectively to H1.2, activate interferon signaling less intensively without any changes of LINE1 expression. For 4 PSMs, which did not cause linker histone depletion, we did not observe effects of interest. Thus, we have shown for the first time that activation of type I interferon signaling accompanies chromatin remodeling caused by PSMs, and LINE1 expression often impacts this activation.

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.