| Carcinogenicity testing is perhaps one of the most challenging aspects in drug development. Carcinogenicity tests not only provide the basis for human risk assessment and regulatory policy on synthetic drugs, but also for all compounds, including "natural" compounds, that are carcinogenic. Current assays, both in vitro and in vivo, rely on the induction of tumors or the detection of DNA-based mutational events (such as the Ames test) to indicate the potential for the studied agent to cause cancer. These studies are often used in conjunction with one another to assess carcinogenicity of a particular compound. While providing a certain level of support for the carcinogenic potential of compounds, these studies prove inadequate for the assessment of non-mutagenic carcinogens and provide little to no data as to a compounds mechanism(s) of action.;Regions of repetitive DNA sequence, known as microsatellites, and are particularly prone to genetic alteration, can serve as indicators of genomic instability, which has been implicated in the process of tumorigenesis. Recent studies of the sequenced genome have found many microsatellites in regions of DNA that do not directly code for proteins. Often they are found in untranslated regions (UTRs), namely the 5' and 3' UTRs, which surround protein-coding sequences and convey regulatory function, but microsatellites have also been found within introns. The presence of these repetitive sequences in non-coding DNA, has recently been supported by evidence indicating that a subset of noncoding regions are in fact transcribed, and that the resulting RNAs may function as "riboregulators", suggesting a functional importance of these regions. Assessment of the effects of compounds on these microsatellite regions may provide a better understanding about the underlying mechanistic process of carcinogenesis.;In this dissertation, I present the development of a novel dual-reporter model system aimed at detecting early genomic instability, using frameshift-prone microsatellites as indicators, to locate cells that are targets of non-mutagenic carcinogens. In addition, I focus this study on the liver, based on its recognition as the "first-pass" organ in the study of toxicology. |
