5-Azacytidine induces micronuclei in and morphological transformation of Syrian hamster embryo fibroblasts in the absence of unscheduled DNA synthesis

Abstract

Summary lt is known that 5-azacytidine (5-AC) induces tumors in several organs of rats and mice. The mechanisms of these effects are still poorly understood although it is known that 5-AC can be incorporated into DNA. Furthermore, it can inhibit DNA methylation. The known data on its clastogenic andjor gene mutation-inducing potential are still controversial. Therefore, we have investigated the kinds of genotoxic effects caused by 5-AC in Syrian hamster embryo (SHE) fibroblasts. Three different endp6ints (micronucleus formation, unscheduled DNA synthesis (UDS) and cell transforrnation) were assayed under similar conditions of metabolism and dose at target in this cell system. 5-AC induces morphological transformation of SHE cells, but not UDS. Therefore, 5-AC does not seem to cause repairable DNA lesions. Furthermore, our studies revealed that 5-AC is a potent inducer of mkronuclei in the SHE system. Immunocytochemical analysis revealed that a certain percentage of these contain kinetochores indicating that 5-AC may induce both clastogenic events and numerical chromosome changes.5-Azacytidine (5-AC) is an effective antineoplastic compound which has been used in the treatment of leukemia (Saiki et al., 1978). lt induces tumors in several organs of rats (Carr et al., 1984) and mice in utero (Schmahl et al., 1985). 5-AC is a cytidine analog containing a nitrogen atom at the 5 position instead of a carbon. Incor-

Cell-cycle dependent micronucleus formation and mitotic disturbances induced by 5-azacytidine in mammalian cells

“…Our results are consistent with other reports of the compound's clastogenicity (Call et al, 1986;Shelby, 1992;Stopper et al, 1992;Fucik, 1970;Walker et al, 1987). However, Van Hummelen and coworkers (Van Hummelen et al, 1992) asserted that 5-azacytidine is an aneugen.…”

“…The decondensation or out of cycle condensation effects may be responsible for the formation of the chromatid bridges (incomplete untangling of the chromatids) before separation in anaphase. These chromatid .bridges may be caused by the same mechanism that results in the endomitosis that we and others have observed (Fucik et al, 1970;Hori, 1983;Stopper et al, 1992). As an example, DNA topoisemerase II, an enzyme with an essential role in chromatid separation, may be impaired in its function when interacting with hemi-or hypo-methylated or undercondensed DNA.…”

Effects of 5-azacytidine on the centromeric region of human fibroblasts studied by CREST staining and in situ hybridization on cytokinesis-blocked cells

“…In the control slides, approximately half of the observed micronuclei were CREST* MN and FISH* MN. whereas in the 5-azaCtreated cells the frequencies of CREST* MN were reduced to about 25% of the total micronuclei at both treatment times, in accordance with data obtained in Syrian hamster cells (Stopper et al, 1992). Similarly, only 17% to 25% of micronuclei were found to be positive after in situ hybridization for the centro meric DNA probe, irrespective of the 5-azaC dose.…”

Preferential induction of chromosome 1 multibranched figures and whole-arm deletions in a human pro-B cell line treated with 5-azacytidine or 5-azadeoxycytidine

“…The frequency of multibranched chromosome 1 figures was lower than at 3 d after treatment (2% vs. 10-20%). This decrease might be due to selective loss of these abnormal structures, e.g., in micronuclei (Stopper et al, 1992).…”