Cycle arrest and aneuploidy induced by zidovudine in murine embryonic stem cells

Zidovudine (3'-azido-3'-deoxythymidine; AZT) is a nucleoside analogue widely used for the treatment of acquired immune deficiency syndrome (AIDS). Medical guidelines recommend the use of AZT by pregnant women in order to reduce risk of HIV vertical transmission. Although it is efficacious, little is known about the side effects of AZT on embryonic development. In this sense, we used murine embryonic stem (mES) cells as a model to investigate the consequences of AZT exposure for embryogenesis. Firstly, mES colonies were incubated with AZT (50 or 100 mu M) and cell cycle profile was evaluated. While 27.7 +/- 5.43% of untreated mES cells were in G2/M phase, this percentage raised to 45.96 +/- 4.18% after AZT exposure (100 mu M). To identify whether accumulation of cells in G2/M phase could be related to chromosome missegregation with consequent cell cycle arrest, aneuploidy rate was evaluated after AZT treatment. Untreated colonies presented 39.6 +/- 8.4% of cells aneuploid, while after AZT 100 mu M treatment, the proportion of aneuploid cells raised to 67.8 +/- 3.4% with prevalence of chromosome loss. This event was accompanied by micronuclei formation as AZT 100 mu M treated mES cells presented a 2-fold increase compared to untreated ones. These data suggest that AZT exerts genotoxic effects and increases chromosome instability at early stages of embryonic development.