ASSESSMENT OF GENOTOXICITY AND MUTAGENICITY OF 1,2-DIOXETANES IN HUMAN-CELLS USING A PLASMID SHUTTLE VECTOR

1,2-Dioxetanes are efficient sources of triplet excited carbonyl compo unds on thermal decomposition. They cause photochemical and photobiolo gical transformations in the dark. In order to study the genotoxicity and mutagenicity of 1,2-dioxetanes, the replicating shuttle vector pZ1 89 was damaged with 3,3,4-trimethyl-1,2-dioxetane (TrMD) or 3-hydroxym ethyl-3,4,4-trimethyl-1,2-dioxetane (HTMD) in vitro and subsequently t ransfected into normal human lymphoblasts. We found a dose-dependent i ncrease of genotoxicity (decrease of plasmid survival) and increase of mutation frequency with both dioxetanes. However, TrMD was less mutag enic than HTMD at similar genotoxicity. Sequence analysis of the supF gene revealed more point mutations than deletions. Single base substit utions occurred exclusively at G:C sites: 94.6% of point mutations wit h TrMD and 100% with HTMD were G:C to T:A and G:C to C:G transversions . These are the typical mutations following 7,8-dihydro-8-oxoguanine ( 8-oxo-G) formation, the main DNA lesion induced by TrMD and HTMD. Only with TrMD we found 5.4% G:C to A:T transitions, probably reflecting t he more pronounced ability of TrMD to form some pyrimidine dimers. Our results indicate that 8-oxo-G is also the most relevant modification in in vivo mutagenesis.