Many compounds that cause DNA damage and related perturbations share common features in their structure and biochemical effects, and these parameters can be used to help categorize agents by mechanisms of action. From the view of bond force and structure, interactions between a compound and DNA can be either covalent or non-covalent. A covalent interaction is irreversible, although there are some exceptions. In addition, covalent bulky adducts can cause
DNA backbone distortion, which in turn can affect both transcription and replication, such as by disrupting protein complex recruitment. Interactions between DNA and non-covalent agents are through van der Waals forces, hydrogen bonding, hydrophobic, and/or charge transfer forces and as such are reversible. Noncovalent agents can be classified into groove binding agents and DNA intercalators. Both general types of interactions lead to genetic changes such as stalled replication, cell cycle delays, cytotoxicity, mutations, and consequent genomic instability that can contribute to cancer development. Thus, genotoxicity testing has become a crucial component of safety evaluation for new drugs and chemicals. Compared to 2-year animal carcinogenicity trials, the genotoxicity testing battery provides sensitive, relatively simple, fast and economical tools for detection of genetic damage. Since its conception in 1970s, the genotoxicity battery has effectively assured genetic safety of consumer chemicals and/or drugs. However, it has been pointed out that the current testing paradigm features relatively low specificity for predicting carcinogenicity, particularly in case of in vitro mammalian mutation and/or chromosome damage assays. Thus, the interpretation and risk assessment of positive findings in the in vitro mammalian mutation and/or chromosome damage assays is a major challenge to both industry and regulatory agencies.
Historically, transcriptional activation has been utilized in the development of a variety of molecular toxicology assays. For instance, transcriptional activation of the SOS pathway in bacteria and RAD54 pathway in yeast has been used to monitor for genotoxicity using single-gene promoter–reporter assay systems. In mammalian cells, discovery of the gadd and other stress-genes, and an appreciation of the central role for p53 in many DNA damage response pathways and cancer development provided the foundation for development of pre-genomic approaches for detection of genotoxicity in mammalian cells. Therefore, application of broad mechanisms-based scientific approaches such as “–omic” methodology might be advantageous for providing insights into the multifaceted nature of toxic mechanisms of new drugs and chemicals.
Agilent Certified Service Provider Program
Our toxicogenomics facility has extensive experience in stress signaling, injury responses, and development of biomarkers based on gene expression. A major focus is delineation of transcriptomic responses to genotoxic stress as well as to a variety of other classes of toxic agents with environmental and/or pharmacologic importance. We also have advanced data analysis and bioinformatic capabilities for integrating omics results into systems biology and systems medicine.
We are certified in Agilent single color expression microarray analysis and also have in-depth experience with 2-color microarrays. Our staff has had rigorous training and expertise in transcriptomics, and all assays are carried out under strict quality control. Contract service is available for wide-ranging applications in molecular toxicology and cancer research.
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