in vitro assays used in preclinical safety

Genotoxicity refers to the tendency of a compound to cause damage to genetic material, typically DNA, which can lead to genetic mutations and increased cancer risks. So, in vitro assays for genotoxicity are used to identify compounds that are potentially carcinogenic. There are many assays that test for genotoxicity. Perhaps the most common is the Ames test. The Ames test monitors the tendency of bacteria to undergo mutations in order to survive in a nutrient-poor medium. If the test compound is mutagenic, more bacterial colonies will survive and be observed at the end of the assay. Another in vitro assay is the micronucleus test, which observes the formation of small membrane-bound DNA fragments in a cell culture. The DNA fragments are an indication of possible genotoxicity.
Phototoxicity is another safety risk. It is observed when a compound causes increased photosensitivity in an organism. Phototoxicity often arises when a compound distributes into the skin, breaks down upon exposure to light (UV light) within the skin, and then the breakdown products cause irritation. Phototoxicity can be screened preliminarily with an in vitro assay. During phototoxicity testing, cells are exposed to the test compound with and without light to determine whether the test compound with light decreases cell viability.
Safety pharmacology involves the screening of the activity of a compound against a broad panel of targets to check for off-target activity of a compound that may lead to undesirable activity and safety liabilities. The assay often includes dozens of different targets, which may be enzymes, receptors, or transporters associated with drug toxicity. Examples of targets in a safety panel include tyrosine kinases, dopamine transporters, ion channels, and adrenergic receptors. The assay normally measures target binding or percent inhibition of the test compound at a single concentration (that is often 10 μM). Compounds with 50% or higher binding or inhibition are considered significant concerns. Researchers often report panel results generally, such as compound X showed activity on two of 44 targets in a panel. Compounds with activity on more targets in the panel represent a higher collective risk. Panel activity can be used to prioritize or deprioritize compounds for advancement in a discovery program. All the in vitro assays discussed in this presentation are preliminary measures of safety liabilities. Compounds that advance and undergo optimization will continue to be tested through in vitro assays as well as in vivo studies in order to support clinical trials.