Spindle disturbances induced by benzo[a]pyrene and 7, 12-dimethylbenz[a]anthracene in a Chinese hamster cell line (V79-MZ) and the stability of the numerical chromosome aberrations that follow.

We previously reported that benzo[a]pyrene (BP) and 7, 12-dimethylbenz[a]anthracene (DMBA) induce aneuploidy and polyploidy, respectively, in the Chinese hamster cell line V79-MZ in the absence of S9 mix. In the present study we investigated the effect of BP and DMBA on the mitotic spindle. BP caused incomplete spindle formation and DMBA inhibited spindle formation completely. The combined results indicate that incomplete spindles caused by BP resulted in aneuploidy, and the absence of spindle formation caused by DMBA resulted in polyploidy. The induced polyploidy was stable for several serial passages in fresh medium. BP and DMBA induced different chromosome number distributions. After BP treatment, the normal distribution of chromosome number was restored in 4 days. After DMBA treatment, on the other hand, a tetraploid peak was maintained for 2 months following an initial transient broad distribution of chromosome number after 1 day. The results suggest that different mechanisms were involved in the induction of numerical aberrations by BP and DMBA. Furthermore the induction of numerical aberrations by BP and DMBA was reproducible over 5 months of passages. In four clones tested, the frequency of cells with the modal chromosome number in control cultures gradually decreased from 82% on the average just after cloning to 62% 5 months later. BP and DMBA induced characteristic ploidy changes following succeeding cell passages for up to 5 months, indicating that the ability to respond to BP and DMBA was stable for that period of time. Because these findings were specific to V79-MZ cells, this cell line might be a good tool for studying chemicals that induce numerical chromosome aberrations.