Methods of DNA adduct determination and their application to testing compounds for genotoxicity

At the International Workshop on Genotoxicity Test Procedures (IWGTP) held in Washington, DC (March 25-26, 1999), a working group considered the uses of DNA adduct determination methods For testing compounds for genotoxicity. When a drug or chemical displays an unusual or inconsistent combination of positive and negative results in in vitro and in vivo genotoxicity assays and/or in carcinogenicity experiments, investigations into whether or not D NA adducts are formed may be helpful in assessing whether or not the test c ompound is a genotoxin. DNA adduct determinations can be carried out using radiolabeled compounds and measuring radioactive decay (scintillation count ing) or isotope ratios (accelerator mass spectrometry) in the isolated DNA. With unlabeled compounds adducts may be measured by (32)p-post-labeling an alysis of the DNA, or by physicochemical methods including moss spectrometr y, fluorescence spectroscopy, or electrochemical detection, or by immunoche mical methods. Each of these approaches has different strengths and limitat ions, influenced by sensitivity, cost, time, and interpretation of results. The design of DNA binding studies needs to be on a case-by-case basis, dep ending on the compound's profile of activity. DNA purity becomes increasing ly important the more sensitive, and less chemically specific, the assay. W hile there may be adduct levels at which there is no observable biological effect, there are at present insufficient data on which to set a threshold level For biological significance. (C) 2000 Wiley-Liss, Inc.