5-AZACYTIDINE (aza-CR)—a s-triazine nucleoside analogue of cytidine—has strong inhibitory effects in various biological systems including neoplasms: it is a powerful bacteriostatic, antitumour and mutagenic agent1. Aza-CR also exhibits immunosuppressive, antimitotic, radioprotective and virostatic effects1. The cytostatic effect of aza-CR has primarily been directed against leukaemia2 and it has been used to treat human solid tumours3. During a study on the morphological transformation of C3H 10T½ C18 cells by cancer chemotherapeutic agents, it was noted that elongated multinucleated cells arose in cultures exposed to aza-CR4. The C3H 10T½ C18 line is a clonal line of mouse embryo cells developed at the McArdle Laboratory for Cancer Research for use in studies on chemical oncogenesis in vitro5–10. The cells are highly sensitive to post-confluence inhibition of cell division, show a remarkably low rate of spontaneous transformation and grow with a fibroblast-like morphology with long cytoplasmic processes in sparse cultures. When confluent, they form flat even monolayers and appear epithelioid. Scanning electron microscopy has shown the confluent cells to be extremely thin and polygonal with smooth surfaces resembling epithelial cells11. Here we describe experiments showing that the multinucleated tubular cells which arise in C3H 10T½ C18 cells treated with aza-CR are in fact functional myotubes.

Functional striated muscle cells from non-myoblast precursors following 5-azacytidine treatment

Passage of foot-and-mouth disease virus (FMDV) in cell culture in the presence of the mutagenic base analog 5-fluorouracil or 5-azacytidine resulted in decreases of infectivity and occasional extinction of the virus. Low viral loads and low viral fitness enhanced the frequency of extinction events; this finding was shown with a number of closely related FMDV clones and populations differing by up to 10(6)-fold in relative fitness in infections involving either single or multiple passages in the absence or presence of the chemical mutagens. The mutagenic treatments resulted in increases of 2- to 6.4-fold in mutation frequency and up to 3-fold in mutant spectrum complexity. The largest increase observed corresponded to the 3D (polymerase)-coding region, which is highly conserved in nonmutagenized FMDV populations. As a result, nucleotide sequence heterogeneity for the 3D-coding region became very similar to that for the variable VP1-coding region in FMDVs multiply passaged in the presence of chemical mutagens. The results suggest that strategies to combine reductions of viral load and viral fitness could be effectively associated with extinction mutagenesis as a potential new antiviral strategy.

Response of Foot-and-Mouth Disease Virus to Increased Mutagenesis: Influence of Viral Load and Fitness in Loss of Infectivity

One of the most readily quantitated indices of myeloid maturation in HL-60 cells is their ability to respond to the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate with increased respiratory burst activity. HL-60 cells exposed to the antileukemic drug, 5-azacytidine (3 to 5 microM) for 24 hr and subsequently cultured in its absence for 2 to 3 days develop an enhanced ability to respond to 12-O-tetradecanoylphorbol-13-acetate with increased respiratory burst activity detectable as an increase both in hexose monophosphate shunt activity and in the proportion of the population producing superoxide anion. 5-Azacytidine treatment also causes marked inhibition of DNA methyltransferase, and thus DNA synthesized by HL-60 cells during the 24-hr period of analogue treatment is essentially devoid of methylated cytosine residues. This suggests, as does our previous finding that a general inhibitor of transmethylation reactions, L-ethionine, can induce differentiation of HL-60 cells, that changes in gene expression triggered by these compounds may be linked to their ability to alter patterns of DNA methylation. Since at least 50% of HL-60 cells capable of forming colonies in soft agar after a 24-hr exposure to 5-azacytidine yield progeny that mature (i.e., produce superoxide anion in response to 12-O-tetradecanoylphorbol-13-acetate) 2 weeks after 5-azacytidine treatment, the results also indicate that the changes induced in HL-60 cells by limited exposure to 5-azacytidine are heritable and can influence gene expression many generations after treatment has been terminated.

https://cancerres.aacrjournals.org/content/canres/43/2/763.full.pdf

Effect of 5-azacytidine on differentiation and DNA methylation in human promyelocytic leukemia cells (HL-60).

Clinical studies involving 5-azacytidine, a ring analogue of cytidine, began in Europe in 1967 and the United States in 1970, and we review available preclinical and clinical studies here. The drug possesses cytotoxic, antimicrobial, antineoplastic, abortive, and mutagenic activity in various biological systems. 5-Azacytidine is thought to exert its antineoplastic effect through interference with nucleic acid metabolism. The dose-limiting toxicities are nausea, vomiting, and leukopenia, while the incidence of thrombocytopenia is low. Hepatic toxicity ranges from abnormal findings in liver function tests to hepatic coma. Clinical results in solid tumors are not encouraging, but 5-azacytidine shows consistent antitumor activity in patients with acute myelogenous leukemia resistant to previous treatment. An overall response rate of 36%, with 20% complete remissions, was achieved in 200 previously treated patients with acute myelogenous leukemia. Further studies must define the role of 5-azacytidine alone and in combination for the first-line treatment of acute myelogenous leukemia.

5-Azacytidine. A new anticancer drug with effectiveness in acute myelogenous leukemia.

Publisher Summary This chapter discusses some aspects of neuronal acetylcholine receptors (AChRs), reviews some of the recent studies of the mechanism by which chronic exposure to nicotine affects aα4β2 AChRs, and describes some of the pharmacological properties of neuronal AChRs, especially the differences between α7 and α8 AChRs and the usefulness of epibatidine (exo-2-(6-chloro-3-pyridyl)-7-azabicyclo-[2.2.l]-heptane) as a ligand for many types of neuronal AChRs. The basic homologies in structure of receptors in this superfamily have been illustrated in the chapter. Homologies in overall domain relationships are demonstrated by showing that functional mosaics could be made in which the large N-terminal extracellular domain of α7 AChRs could be grafted just before the first transmembrane domain to the C-terminal part of 5HT 3 receptors. This resulted in receptors with acetylcholine-gated cation channels having the ion selectivity of 5HT 3 receptors. Close similarities in the overall structures of the ion channels are demonstrated by showing that changing only three amino acids in the sequence lining the cation-specific channel of excitatory α7 neuronal AChRs to amino acids typical of the anion-specific channels of inhibitory glycine or GABA A receptors changed the ion selectivity of the mutated a7 AChR channels from cations to anions

Structure and function of neuronal nicotinic acetylcholine receptors.

Incorporation of 5-Azacytidine into nucleic acids of Escherichia coli

Inhibition of protein synthesis by 5-azacytidine in Escherichia coli

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2868%2980017-1

V. Pačes

Papers

Incorporation of 5-Azacytidine into nucleic acids of Escherichia coli

Inhibition of protein synthesis by 5-azacytidine in Escherichia coli

The effect of 5-azacytidine on the synthesis of ribosomes in escherichia coli.