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The purpose of the study was to analyze the existing methodological approaches to the experimental testing of resistance to chemotherapy and assess the prospects for their further application.Material and Methods. We analyzed publications regarding the experimental testing of tumor resistance to chemotherapy available in the databases, such as SciVerse Scopus (748), PubMed (1727), Web of Science (1025), RSCI (125). To obtain fulltext publications, the electronic resources of Research Gate, RSCI, CyberLenink were used. Forty-two modern publications (2012–19) including 18 articles of the founders of the methods analyzed in the review were cited.Results. The review discusses the characteristics of the main methods for assessing the resistance / sensitivity of tumor cells obtained from biopsy / surgical specimens to various chemotherapy drugs in vitro in monolayer and suspension cultures, in the form of spheroids, histo and organocultures, as well as in vivo xenografts of tumors in immunodeficient mice. During testing, the proliferative and metabolic activities as well as the level of cell death were considered as the main evaluated characteristics of tumor cells. The main indicators were the intensity of DNA synthesis, the level of protein or ATP in the cell, the activity of NADH-dehydrogenases, the level of apoptosis, and the integrity of cell structures. The advantages and disadvantages of the described methods, as well as the prospects for their further application were discussed.Conclusion. Over the past half century of using the experimental testing of tumor cell resistance in order to personalize chemotherapeutic treatment, the evolution of methodological approaches was based on the increase in their safety and sensitivity through the use of fluorescent compounds. The general vector for improving experiments on the personalization of tumor chemotherapy is aimed at approximating the experimental conditions to the processes occurring in the human body. Each of these methods has its own range of predictive power and, if used properly, can provide a useful guide for treatment.

Recently many new approaches for repurposing or repositioning of the clinically used drugs have been developed. Drug repurposing allows not only to use known schemes for the synthesis of biologically active compounds, but also to avoid multiple studies that are necessary for drug approval process – analysis of pharmacokinetics, carcinogenicity, acute and chronic toxicity, including cardiotoxicity, nephrotoxicity, allergenicity etc. It makes possible to reduce the number of experimental studies as well as costs of investigations. In cancer research drug repurposing includes screening for medicines used nowadays for the treatment of patients with non-cancer diseases which possess anticancer activity or able to enhance the effects of the standard anticancer chemotherapy, and search for new applications of known anticancer drugs for the treatment of different cancer types. Scientific rationale for the search of the compounds with potential anticancer properties among drugs with different applications is based on the multiple cross-talks of signaling pathways, which can inhibit cell proliferation. Modern advances in genomics, proteomics and bioinformatics, development of permanently improving databases of drug molecular effects and high throughput analytical systems allow researchers to analyze simultaneously a large bulk of existing drugs and specific molecular targets. This review describes the main approaches and resources currently used for the drug repurposing, as well as a number of examples.

Cytostatic drugs used in chemotherapy cause secondary tumors in some patients cured of the antecedent neoplasm. Thus the incidence of second neoplasia for cancer survivors compared with the general population represents a 4-fold to 6-fold increased risk.The review presents recent data on the mechanisms of malignant transformation of cells by cytostatics, on the characteristics of high- risk groups associated with congenital polymorphisms of xenobiotic metabolizing enzymes and DNA repair systems. Increased risk of drug-related cancer was observed in patients with high activity of P450 isoforms, transforming cytotoxic prodrugs into the active electrophilic metabolites and low level of detoxifying enzymes. All things being equal the risk of therapy related neoplasia is higher in patients with low activity of DNA repair enzymes. It is evaluated the possibility of experimental study of new targeted drugs carcinogenic potential in order to minimize the future risk of secondary malignancies.

Curaxins represent low molecular weight carbazole derivatives, which simultaneously activate p53-dependent apoptosis and inhibit NF-kBdependent signal transduction pathways. Antitumor activity of curaxin CBL0137 was demonstrated in vivo on the model of solid transplantable mouse colon adenocarcinoma Akatol. Significant tumor growth inhibition caused by CBL0137 treatment was observed. On the 37th day after tumor transplantation for CBL0137 oral doses 5, 10, 15 and 20 mg/kg the tumor growth inhibition indexes were 53, 50, 56 and 74 %, respectively. CBL0137 treatment extended life span of mice in all study groups receiving this test article. Maximum lifespan increase (81,7 %) was observed in the group of mice treated with 20 mg/kg dose of CBL0137. The cytotoxicity of CBL0137 was assessed on human colon cancer cells in vitro. We demonstrated that CBL0137 inhibits the expression COX2, which in its turn is known to exhibit antiapoptotic, pro-angiogenic and pro- metastatic properties. Thus, we demonstrated antitumor effect of CBL0137 against colon cancer in vitro and in vivo.