Cancer-prone hereditary diseases associated with abnormalities of DNA repair

Comparative analyses of relative ERCC3 and ERCC6 mRNA levels in gliomas and adjacent non-neoplastic brain

Nucleotide excision repair (NER) is an ordered process in nonmalignant cells, in both human and nonhuman systems. We previously reported that in human brain there is discordant mRNA expression of excision repair cross-complementing (ERCC) 1 and ERCC2 in malignant tissues, concurrent with excellent concordance of these genes in nonmalignant tissues from the same patients. Here we have extended these studies to compare low-grade tumors to high-grade tumors and to include ERCC3 (which links DNA repair with DNA transcription) and ERCC6 (which is essential for gene-specific repair). Glial tumor and adjacent normal brain specimens from 19 individuals were studied. Paired malignant and nonmalignant tissues were obtained from 12 of these patients. For ERCC3, there was excellent concordance of mRNA expression between malignant and nonmalignant tissues from the same individuals (P = 0.003). For ERCC6, no concordance was observed (P = 0.314). Tumor tissue from patients with high-grade gliomas exhibited marked discordance of mRNA expression patterns in situations in which good concordance was observed in tumor tissue from low-grade gliomas. We previously established that malignant brain tumors show increased disorder of genes in the NER process, as compared with nonmalignant tissues. These data suggest that increasing disorder in the NER process may occur as cells move from low-grade to high-grade malignancy.

Future research directions for evaluating human genetic and cancer risk from environmental exposures

The utility of biomarkers for evaluating the genotoxicity of environmental exposures is well documented. Biomarkers of both exposure and effect provide bases for assessing human-genotoxicant interactions and may be indicative of future disease risk. At present, there is little information on the predictive value of these assays for either a population or the individuals tested. This paper describes some aspects of biomarker assays, the possible use of susceptibility measures in biomonitoring protocols, and the need for evaluation of disease relevance. A population study involving epidemiologists, geneticists, toxicologists, statisticians, and physicians is proposed to determine the disease relevance of these biomarkers.

Biochemical toxicology of chemical teratogenesis

Although exposure during pregnancy to many drugs and environmental chemicals is known to cause in utero death of the embryo of fetus, or initiate birth defects (teratogenesis) in the surviving offspring, surprisingly, little is known about the underlying biochemical and molecular mechanisms, or the determinants of teratological susceptibility, particularly in humans. In vitro and in vivo studies based primarily on rodent models suggest that many potential embryotoxic xenobiotics are actually proteratogens that must be bioactivated by enzymes such as the cytochromes P450 and peroxidases such as prostaglandin H synthase to teratogenic reactive intermediary metabolites. These reactive intermediates generally are electrophiles or free radicals that bind covalently (irreversibly) to, or directly of indirectly oxidize, embryonic cellular macromolecules such as DNA, protein, and lipid, irreversibly altering cellular function. Target oxidation, known as oxidase stress, often appears to be mediated by reactive oxygen species (ROS) such as hydroxyl radicals. The precise nature of the teratologically relevant molecular targets remains to be established, as do the relative conditions of the various types of macromolecular lesions. Teratological suseptibility appears to be determined in part by a balance among pathways of maternal xenobiotic elimination, embryonic xenobiotic bioactivation and detoxification of the xenobiotic reactive intermediate, direct and indirect pathways for the detoxification of ROS (cytoprotection), and repair of macromolecular lesions. Due largely to immature or otherwise compromised embryonic pathways for detoxification, Cytoprotection, and repair, the embryo is relatively susceptible to reactive intermediates, and teratogenesis via this mechanism can occur from exposure to therapeutic concentrations of drugs, or supposedly safe concentrations of environmental chemicals. Greater insight into the mechanisms involved in human reactive intermediate-mediated teratogenicity, and the determinants of individual teratological susceptibility, will be necessary to reduce the unwarranted embryonic attrition from xenobiotic exposure.