Toxicity screening using biosensors that measure DNA damage.

Toxicity continues to be a major cause of drug development failures. An assessment of drug toxicity as early in the discovery/development cycle as possible is important to minimize the economic impact of discontinuing a drug late in development. Currently, batteries of biological testing protocols provide good assessment and predictions of toxicity in the general population; however, new cost-effective procedures based on simpler biochemical systems that are arranged in biosensor formats are emerging that may be very useful for early toxicity screening. In particular, biosensors employing thin films of DNA and pure metabolic enzymes show promise in predicting genotoxicity. In such biosensor systems, the enzyme/drug reaction is run in a DNA/enzyme film, which acts as a nanoreactor to produce metabolites in close proximity to high concentrations of DNA. The rate of damage to the DNA is then taken as the genotoxicity endpoint. Formation of nucleobase-drug adducts is detected by catalytic voltammetry capillary LC-MS after hydrolysis of the DNA, or optically by incorporating an electrochemiluminescent polymer into the biosensor films. Similar sensors using a redox polymer specific for 8-oxoguanine in DNA can be used to monitor oxidative stress. The most advanced genotoxicity biosensors feature arrays that can contain many metabolic enzymes, such as cytochrome P450s. Arrays based on electrochemiluminescence can be read using a simple apparatus featuring a charge-coupled device camera. These arrays can obtain relative genotoxicity data for a series of enzymes simultaneously. This new biosensor technology is compared to other emerging methods for toxicity screening.