Vaginal epithelial DNA damage and expression of preneoplastic markers in mice during chronic dosing with tumorigenic levels of 3'-azido-2',3'-dideoxythymidine.

3'-Azido-2',3'-dideoxythymidine (AZT, Retrovir, zidovudine), a nucleoside analogue currently used in the therapy of acquired immunodeficiency syndrome, induces papillomas and carcinomas in vaginal epithelium of mice as a result of lifetime drug administration. In this study, female CD-1 mice were administered AZT at doses of 180, 360, and 720 micrograms/ml of drinking water for 28 days to determine whether AZT became incorporated into vaginal DNA and whether this was associated with preneoplastic changes within the target tissue. In addition, bone marrow, a target for AZT-induced cytotoxicity in mice and humans, was examined for chromosomal aberrations. A positive correlation was observed between dose level of AZT, proliferation of cells in the basal layer of vaginal epithelium, and incorporation of AZT into vaginal DNA. Incorporation of AZT into vaginal DNA was originally detected by radioimmunoassay and confirmed by immunohistochemistry. An aberrant pattern for alpha 6 integrin distribution, similar to the pattern described in skin papillomas with high risk for malignant conversion, also increased with dose in mice given AZT. Chromosomal aberrations in bone marrow increased more than 4-fold in AZT-exposed animals. The genotoxicity demonstrated by incorporation of AZT into vaginal DNA and proliferation of vaginal epithelium may play an essential part in the ability of AZT to induce abnormal differentiation in vaginal epithelium and vaginal tumorigenesis in mice.