MODULATION OF NITROSOUREA TOXICITY IN RODENT EMBRYONIC-CELLS BY O-6-BENZYLGUANINE, A DEPLETOR OF O-6-METHYLGUANINE-DNA METHYLTRANSFERASE

Micromass culture systems of mesencephalon (CNS) and limb bud (LB) reg ions were used to evaluate the impact of the O-6-methylguanine-DNA met hyltransferase (MGMT) inhibitor, O-6-benzylguanine (BG), on ethylnitro sourea (ENU) and methylnitrosourea (MNU)-induced in vitro toxicity. Th ese primary rat embryo cells were preincubated with BG (2.5 mu M for C NS; 10 mu M for LB) for 24 hr and then ENU (0-1708 mu M) or MNU (0-160 0 mu M) was added, Five days after culture initiation, cell survival w as assessed using neutral red uptake and cell differentiation was asse ssed using selective staining (Alcian blue in LB cultures and hematoxy lin in CNS) and image analysis, In both LB and CNS cultures, preexposu re to BG resulted in a significant increase in inhibition of different iation following MNU exposure but no increase in cytotoxicity, There w ere no statistically significant changes in the toxicity induced by EN U in these differentiating cells consequent to BG preexposure. Our obs ervations lend support to the idea of a specific role for DNA adducts in defining MNU's toxic effects on cell viability and differentiation. (C) 1995 Academic Press, Inc.