Use of a reversion assay HGPRT- to HGPRT+ to demonstrate mutagenic adaptation in V79 Chinese hamster cells.

A reverse mutation assay HGPRT- to HGPRT+ has been used to demonstrate adaptation to the mutagenic effects of monofunctional alkylating agents. HGPRT- cells exposed to single doses of methylating or ethylating agents show maximum revertant frequencies immediately after treatment and these subsequently decline exponentially. Cells pre-treated with MNNG (1.0 microM) or MMS (0.27 mM) then challenged 6-168 h later with MNNG or EMS showed a consistent reduction in revertant frequencies. Pretreatment with EMS did not result in any reduction in EMS-induced reversion frequency. In parallel experiments no modifications in survival kinetics were observed. V79 cells do not remove O6-methylguanine and totally lack O6-methylguanine transferase activity, therefore other lesions and repair enzymes must be involved in the mutagenic adaptation observed.