Hunting for electrophiles that harm human DNA: Frits Sobels Award Lecture.

This lecture is dedicated to Frits Sobels and his farsighted vision on research directions in genetic toxicology. Some accomplishments by the author's research group in the area of cancer etiology research and pre-clinical drug safety evaluation are presented. Praziquantel, an antischistosomal drug, was found to be devoid of any genetic effects which determined the drug companies to proceed with further safety evaluation and marketing. This highly efficient life-saving drug is now in use world wide. Biomonitoring methods have been developed to quantitate carcinogens, their metabolites or DNA adducts in humans exposed environmentally and endogenously to genotoxic agents. The methods were applied in ecological and case-control studies aimed at establishing causal relationships between exposure and disease. Results from both field studies in Iran and laboratory investigations supported the hypothesis that opium use, in particular ingestion of its pyrolysates, may be a risk factor for esophageal cancer in this region, probably acting together with nutritional deficiencies and thermal injury. By applying the nitrosoproline (NPRO) test in ecological studies on esophageal cancer causation in China some support was obtained for the involvement of N-nitroso compounds. In inhabitants of high risk areas endogenous nitrosamine synthesis could be markedly reduced by ingestion of vitamin C. Ultrasensitive detection methods for etheno-DNA adducts, which are formed by lipid peroxidation products resulting from increased oxidative stress, have been developed. Known cancer risk factors such as metal storage, chronic inflammatory processes and a high omega-6 PUFA fat diet increased the background level of these miscoding DNA adducts many times. They were found to increase progressively in premalignant lesions of cancer-prone tissues of humans and rodents, probably contributing to the genetic instability that drives cells to malignancy. Etheno-DNA adducts are thus promising markers to verify the efficiency of chemopreventive measures in humans.