The induction of aneuploidy by alkylated purines: effects on early and late cell cycle events.

It has been shown that alkylated bases induce aneuploidy in mammalian cells in culture. The mechanism of action is not clear, however, data with 6-dimethyl amino purine (6DMAP) suggest that this analogue might act by affecting the cytoskeleton and protein kinases involved in cell cycle regulation (cdc2/p34). The aim of this work was to study the effect of O6methylguanine (O6meG), O6ethylguanine (O6etG) and 6DMAP on DNA synthesis induced by growth factors in two cell lines, 3T3 and CHEF/18 fibroblasts, which respond in opposite ways to substances affecting the cytoskeleton, colchicine and cholera toxin: DNA synthesis initiation is stimulated in 3T3 cells and inhibited in CHEF/18 cells by such compounds. Our results indicate that O6meG and O6etG behave like cholera toxin, in as much as they inhibit DNA synthesis induced by epidermal growth factor plus insulin in CHEF/18 cells, and stimulate it in 3T3 cells. 6DMAP behaves differently and inhibits DNA synthesis in both cell lines. The inhibition (or stimulation) was greater when alkylated bases were added before S phase started, suggesting that these compounds might affect early events of the cell cycle. In CHEF/18 cells the three alkylated bases were able to induce aberrant metaphases and ana-telophases with different efficiency (70-100%). The effect was not dependent on the G1-S block and it was reversible even after cell commitment to DNA synthesis.