Skin Tumorigenesis and Ki-Ras and Ha-Ras Mutations in Tumors From Adult Mice Exposed in Utero to 3'-Azido-2',3'-Dideoxythymidine

This study was designed to evaluate the potential initiating effects of transplacental 3'-azido-2',3'-dideoxythymine (AZT) and the role of ras mutational activation in skin tumors induced in a two-stage mouse skin model. In addition, mouse liver and lung tumors from a transplacental AZT tumorigenicity study reported elsewhere (Olivero et al., J Natl Cancer Inst 89:1602-1608, 1997) were examined for evidence of ras activation. For both tumor studies, pregnant CD-1 mice were given either vehicle or 25 mg of AZT daily on days 12-18 of gestation. In the 1997 study, the offspring were given no further exposure and were killed at 1 yr of age. For the skin tumor study, all mice received twice-weekly topical 1 2-O-tetradecanoyl-phorbol-13-acetate (TPA) treatment from weeks 5-35; half of the mice had been exposed to AZT in utero. At weeks 16-18, 30, 31, and 34-41, the skin tumor incidences in mice given AZT and TPA were significantly higher than in mice given TPA alone (P less than or equal to 0.05). At week 41, the average numbers of tumors per mouse were 1.44 +/- 0.36 (mean +/- standard error of the mean) and 0.57 +/- 0.13 for mice given AZT plus TPA and TPA alone, respectively (P = 0.006). Mutagenesis in ras exons I and II was determined by polymerase chain reaction (PCR) and dye-terminator cycling sequencing of PCR products. Ha-ras exon I codons 12 and 13 were mutated in 1 1 of 19 tumors (58%) from mice given AZT and TPA and in one of 15 tumors (7%) from mice given PPA alone (P = 0.004). The only mutation in Ha-ras codon 12 (four in four tumors examined) was a G-->A transition in the second base, and the major mutation in codon 13 (six in seven tumors examined) was a G-->T transversion in the second base. In skin tumors, AZT exposure did not increase the number of Ha-ras codon 61 mutations, and no Ki-ras mutations were observed. Analysis of ras mutations in liver and lung tumors from mice exposed to AZT in utero (Olivero et al., J Natl Cancer Inst 89:1602-1608, 1997) with no TPA promotion showed ro significant AZT-related increases. (C) 1998 Wiley-Liss, Inc.(dagger). [References: 38]

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