Genetic effects of 2-aminopurine in mammalian cells.

The effects of 2-aminopurine (APur) on mutations, sister-chromatid exchanges (SCEs) and proliferation were investigated in V79 cells by means of cytogenetic and flowcytometric experiments. APur did not induce SCEs after a 3-h treatment before the addition of BrdUrd but SCE frequencies were increased after treatment for two cell cycles in the presence of BrdUrd. SCEs were mainly produced during the second cell cycle of the SCE experiment when BrdUrd substituted DNA is replicated. APur also caused a high percentage of polyploid cells. Compared on the basis of DNA content, SCE induction was the same in diploid and tetraploid metaphases. APur-induced SCEs are strongly influenced by nucleosides. The presence of deoxycytidine (dCyd) caused a reduction of AP-induced SCEs to about control level while addition of deoxythymidine (dThd) enhanced SCE induction. Flow cytometric measurements revealed a small increase in S-Phase cells and a strong accumulation in G2/M after APur treatment in the presence of BrdUrd. S-phase delay was strongly enhanced when BrdUrd substituted DNA is replicated. Addition of dCyd removed the APur-induced inhibition of S-phase in both protocols. Using the same treatment protocol, APur also induced mutations at the HPRT locus. In contrast to their effects on SCEs and proliferation neither BrdUrd nor dCyd had an effect on APur-induced mutations, and dThd reduced the mutation frequency. The results demonstrate that APur-induced SCEs and mutations occur independently from each other. APur-induced mutations obviously occur by a mispairing mechanism while SCEs are a consequence of pool imbalances during replication.