Whether creating animal models or cellular assays, it is important to have the correct research tool. Below is an overview of some of the types of Precision Toxicology™ models one can make and when these models are typically used.
Reporter cell lines – contain reporter genes (e.g. luciferase) that are attached to a regulatory sequence (promoter) or targeted within the endogenous gene of interest in cell culture or animals. Different regulatory sequences or targeted genes are chosen to detect genetic expression involved in the process or pathway of interest (i.e. toxicity). For example, reporter cell lines can be used to screen for toxicity by “tagging” a gene, such as p53, that is known to be activated during a toxicity event with a reporter gene such as luciferase.
Disease or patient specific models – these cells can be derived from patient populations, in which case correcting the mutation associated with the disease or phenotype via gene editing is required to confirm the mutation being studied is responsible for the phenotype, and not a background mutation. On the other hand, one could use a well characterized cell line and create the mutation associated with the disease in this cell line. Either way the research model and its isogenic companion are required for accurate discovery and toxicology assays. Cellular assays using patient specific cells can be used for toxicity and efficacy screens, and can even help screen patients for enriched clinical trials.
Humanized rodents – There are two ways an animal model can be ‘humanized’ 1- by replacing the endogenous rodent gene with a human gene and 2 – ablating endogenous cells or tissues (i.e. hepatocytes) and replacing them with engrafted human counterparts. In the later an immunocompromised rodent, often referred to as SCID, background is required so that the animal will not reject the exogenous human cells. By creating the humanized rodent, the physiology becomes more relevant to human studies; examples include how the animal responds to drug toxicity and metabolism. Humanized liver mice have demonstrated proper human specific hepatotoxicity when traditional animal models did not (1).
Knockout models – contain mutations that make one or more genes inoperative or null. Knockout rodents and in vitro assays are sometimes used for drug target identification as well as synthetic lethality screening. Synthetic lethality is when a combination of mutations in two or more genes leads to cell death, whereas a mutation in only one of these genes does not, and by itself is said to be viable. In a synthetic lethal genetic screen, it is necessary to begin with a mutation that does not kill the cell, although may confer a phenotype (for example, slow growth), and then systematically test other mutations at additional loci to determine which confer lethality. Synthetic lethality indicates functional relationships between genes (2).
- Xu et al. (2014) Fialuridine Induces Acute Liver Failure in Chimeric TKNOG Mice: A Model for Detecting Hepatic Drug Toxicity Prior to Human Testing. Plos Med.
- Tucker et al. (Nov 2003). Lethal combinations. Nat Genet.