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Micronuclei induced by modulators of methylation: analogs of 5-azacytidine
1Institute of Pharmacology and Toxicology, University of Würzburg, Germany.
Abstract:
Jones and coworkers demonstrated a qualitative correlation between 5-azacytidine and some of its analogs in inducing changes in cell morphology and their ability in preventing DNA methylation. Previously, we evaluated the same compounds to determine their ability to induce trifluorothymidine (TFT) resistance in L5178Y mouse cells and found that their mutagenic potency also correlated with their reported ability to induce morphological changes in C3H10T1/2 cells. Here, we examine four of the same analogs, 5-fluoro-2'-deoxycytidine, 5-azacytidine, 5,6-dihydro-5-azacytidine and 6-azacytidine, to find out if micronuclei induced by these compounds correlated with these effects. The most cytotoxic analog was 5-fluoro-2'-deoxycytidine, followed by 5-azacytidine. 5,6-Dihydro-5-azacytidine and 6-azacytidine were substantially less cytotoxic. All four compounds induced micronuclei. The lowest dose ranges at which responses were observed for micronucleus induction were -0.04 microM for 5-fluoro-2'-deoxycytidine, 0.2 microM for 5-azacytidine and 10-20 microM for 5,6-dihydro-5-azacytidine and 6-azacytidine. Lack of kinetochore staining in most of the micronuclei indicated that all four compounds were clastogenic. We note a general trend in the biological activity of these analogs: compounds that are specifically blocked at the 5 position such as 5-azacytidine and 5-fluoro-2'-deoxycytidine effect changes in cell morphology, cytotoxicity, TFT resistance and the induction of micronuclei at very low doses. 5-Azacytidine analogs that possess more chemically accessible 5 positions such as 5,6-dihydro-5-azacytidine and 6-azacytidine either require doses that are orders of magnitude greater to induce these effects or are unable to induce changes in cell morphology and TFT resistance at doses below which the compound is lethal to the cells.
Insights
This study investigated four 5-azacytidine analogs for their ability to induce micronuclei, correlating this with cytotoxicity and mutagenicity. Analogs with a blocked 5-position showed potent effects at lower doses, unlike those with accessible 5-positions.
Area of Science:
- * Biochemistry
- * Genetics
- * Toxicology
Background:
- * Previous research established a correlation between 5-azacytidine analogs, cell morphology changes, and DNA methylation inhibition.
- * Prior studies indicated a link between mutagenic potency (trifluorothymidine resistance) and morphological changes induced by these compounds.
Purpose of the Study:
- * To investigate the correlation between micronuclei induction by four 5-azacytidine analogs and their known biological effects.
- * To compare the clastogenic potential of 5-fluoro-2'-deoxycytidine, 5-azacytidine, 5,6-dihydro-5-azacytidine, and 6-azacytidine.
Main Methods:
- * Evaluation of cytotoxicity and micronuclei induction across a range of doses for four 5-azacytidine analogs.
- * Assessment of kinetochore staining in induced micronuclei to determine clastogenicity.
Main Results:
- * 5-Fluoro-2'-deoxycytidine and 5-azacytidine were the most cytotoxic and induced micronuclei at the lowest doses.
- * 5,6-Dihydro-5-azacytidine and 6-azacytidine exhibited lower cytotoxicity and required significantly higher doses for micronuclei induction.
- * All four compounds were found to be clastogenic, as indicated by the lack of kinetochore staining in most micronuclei.
Conclusions:
- * A trend exists where 5-azacytidine analogs with a blocked 5-position (e.g., 5-azacytidine, 5-fluoro-2'-deoxycytidine) exhibit potent biological activity at low doses.
- * Analogs with accessible 5-positions (e.g., 5,6-dihydro-5-azacytidine, 6-azacytidine) require much higher doses for similar effects or fail to induce them before becoming lethal.