7-Methylguanine Inhibits Colon Cancer Growth in Vivo.

7-Methylguanine (7-MG) is a natural inhibitor of poly(ADP-ribose) polymerase 1 and tRNA-guanine transglycosylase, the enzymatic activity of which is central for the proliferation of cancer cells. Recently, a number of preclinical tests have demonstrated the safety of 7-MG and a regimen of intragastric administration was established in mice. In the present work, the pharmacological activity of 7-MG was studied in BALB/c and BALB/c nude mice with transplanted tumors. It was found that 7-MG effectively penetrates tumor tissue and suppresses colon adenocarcinoma growth in the Akatol model, as well as in a xenograft model with human HCT116 cells.

Modeling of the Enzyme-Substrate Complexes of Human Poly(ADP-Ribose) Polymerase 1.

Poly(ADP-ribose) polymerase 1 (PARP-1) is a key DNA repair enzyme and an important target in cancer treatment. Conventional methods of studying the reaction mechanism of PARP-1 have limitations because of the complex structure of PARP-1 substrates; however, the necessary data can be obtained by molecular modeling. In this work, a molecular dynamics model for the PARP-1 enzyme-substrate complex containing NAD+ molecule and the end of the poly(ADP-ribose) chain in the form of ADP molecule was obtained for the first time. Interactions with the active site residues have been characterized where Gly863, Lys903, Glu988 play a crucial role, and the SN1-like mechanism for the enzymatic ADP-ribosylation reaction has been proposed. Models of PARP-1 complexes with more sophisticated two-unit fragments of the growing polymer chain as well as competitive inhibitors 3-aminobenzamide and 7-methylguanine have been obtained by molecular docking.

Drug-Related Carcinogenesis: Risk Factors and Approaches for Its Prevention.

The review summarizes the data on the role of metabolic and repair systems in the mechanisms of therapy-related carcinogenesis and the effect of their polymorphism on the cancer development risk. The carcinogenic activity of different types of drugs, from the anticancer agents to analgesics, antipyretics, immunomodulators, hormones, natural remedies, and non-cancer drugs, is described. Possible approaches for the prevention of drug-related cancer induction at the initiation and promotion stages are discussed.

Re-Examination of the Esophageal Squamous Cell Carcinoma Model in Rats Induced by N-Nitrososarcosine Ethyl Ester Precursors.

Studies of the molecular mechanisms of esophageal cancer development have to be carried out on sufficient amount of tumor material, obtained under conditions of controlled exposure to carcinogenic factors. Esophageal cancer models on laboratory animals serve an indispensable source of this material. One of these models is esophageal cancer induction in rats by N-nitroso compound precursors. Despite adequate reproduction of human esophageal cancer, this model in fact has not been used since the 1990ies. Re-examination of esophageal cancer model, induced by N-nitrososarcosine ethyl ester precursors, is carried out and its efficiency in induction of squamous cell carcinoma is confirmed.

Alterations in WNT Signaling in Leukemias.

The WNT/ß-catenin signaling pathway plays an important role in the differentiation and proliferation of hematopoietic cells. In recent years, special attention has been paid to the role of impairments in the WNT signaling pathway in pathogenesis of malignant neoplasms of the hematopoietic system. Disorders in the WNT/ß-catenin signaling in leukemias identified to date include hypersensitivity to the WNT ligands, epigenetic repression of WNT antagonists, overexpression of WNT ligands, impaired ß-catenin degradation in the cytoplasm, and changes in the activity of the TCF/Lef transcription factors. At the molecular level, these impairments involve overexpression of the FZD protein, hypermethylation of the SFRP, DKK, WiF, Sox, and CXXC gene promoters, overexpression of Lef1 and plakoglobin, mutations in GSK3ß, and ß-catenin phosphorylation by the BCR-ABL kinase. This review is devoted to the systematization of these data.

Antitumor effect of non-steroid glucocorticoid receptor ligand CpdA on leukemia cell lines CEM and K562.

Glucocorticoids (GCs) are widely used in chemotherapy of hematological malignancies, particularly leukemia. Their effect is mediated by glucocorticoid receptor (GR), a well-known transcription factor. Besides their therapeutic impact, GCs may cause a number of side effects leading to various metabolic complications. The goal of immediate interest is testing glucocorticoid analogs capable of induction/enhancement of GR transrepression, but preventing GR dimerization and transactivation leading to side effects. In this work we have investigated effects of a promising new selective GR agonist, 2-(4-acetoxyphenyl)-2-chloro-N-methylethylammonium chloride (CpdA), on CEM and K562 leukemia cells. Both cell lines express functional GR. CpdA compared with the glucocorticoid fluocinolone acetonide (FA) exerted more prominent cytostatic and apoptotic effects on the cells. Both cell lines exhibited sensitivity to CpdA, demonstrating a good correlation with the effects of FA on cell growth and viability. In contrast to FA, CpdA did not induce GR transactivation evaluated by no obvious increase in expression of GR target (and dependent) gene FKBP51. At the same time, luciferase assay showed that CpdA efficiently activated transrepression of NF-κB and AP-1 factors. We also evaluated the effect of combined action of CpdA and the proteasome inhibitor Bortezomib. The latter induced a caspase-dependent apoptosis in both T-cell leukemia cell lines. By treatment of CEM cells with different CpdA/GC and Bortezomib doses, we have designed a protocol where CpdA shows potentiating effect on Bortezomib cytotoxic activity. Generally, the present work characterizes a novel non-steroid GR ligand, CpdA, as a promising compound for possible application in leukemia chemotherapy.

[Analysis of blastomogenic activity of mammal carcinogens in Drosophila using the wts(P4) allele and RNA interference-induced p53 silencing].

The test for somatic mutagenesis and recombination in Drosophila is one of the widely used approaches for determination of possible carcinogenic effects of chemical compounds. The use of heterozygotes for mutant tumor suppressor gene wts enables more direct evaluation of the blastomogenic effects of chemical compounds, by tumor formation in the adult flies. This study presents evaluation of the SMART effectiveness upon the use of Drosophila heterozygotes for the wts(P4) gene, first included into the test system. The increase of the test resolution capacity compared to the literature data for the wts(P2) allele was observed. Using wts(P4) heterozygotes, a total of 20 carcinogenic compounds, and their slightly carcinogenic and noncarcinogenic analogs were tested. Specificity of the method was about 100%, and sensitivity depended on the type of the agent tested. The latter was absolute for the direct action carcinogens, with respect to carcinogens, requiring the metabolic activation. The sensitivity was elective and was limited by the presence of the enzymes capable of activating of these compounds. To increase the test sensitivity, the RNA interference-mediated silencing of the Drosophila p53 functional activity was successfully applied. Moreover, the frequency of wts tumor induction considerably increased both in spontaneous and induced mutagenesis conditions.