Rationale and Strategies for In Vitro Screening Assays
Early identification of potential genotoxic issues with candidate compounds is an essential part of a product development process. BioReliance offers a variety of rapid, low-cost genetic toxicology assays that can be performed with milligram quantities of test article. These non-GLP assays are utilized early in the development process for various reasons, including: lead optimization, prediction of the results of GLP regulatory-compliant assays and to investigate mechanism of action and relative potency.
Selection of Assays
Selection of the appropriate assay or group of assays is critical to the success of a screening program. Many screening assays are available to investigate different mechanisms of DNA damage, each with different strengths and weaknesses. Some assays use the same cells and endpoints as used in core GLP regulatory assays that eventually will be run on the final drug or chemical. Other assays use different cells, endpoints or biomarkers of DNA damage.
When designing a screening program, various factors need to considered including: the purpose of the testing (e.g. prediction of GLP assays or investigation of mechanism of action), how the data will be used, the quantity of test article available, cost and timeline.
BioReliance scientists are available to work with you to design the most appropriate screening approach to meet your needs. With our scientists, you gain the advantage of decades of experience from globally recognized experts who have worked with most every category of drugs and chemicals.
There are three areas of screening that can be performed: Structure-Activity Relationship (SAR), high throughput screening, and predictive screening.
Structure Activity Relationship
Quantitative Structure Activity Relationship (qSAR) involves in silico methods designed to find relationships between chemical structure and biological activity of compounds. This technique is a primary step in lead candidate selection and is useful in pharmaceutical development, agricultural and industrial chemical assessment, and impurity analysis. Since in silico analyses do not require synthesis of the chemical of interest, they provide a cost and time effective approach to early screening. BioReliance collaborates with the Gad Consulting group and with one submission to BioReliance a report from multiple systems and independent recommendations on further testing are provided.
High Throughput (HTP) Screening Assays
As the development of a product is advanced, prioritization of which ingredients to proceed with is often made by conducting testing on small scale synthesis batches. At this stage of pharmaceutical lead optimization, high throughput screening methods that utilize small amounts of test article and can be performed on high numbers of chemicals at the same time with a short turnaround time are useful. HTP assays can also be used to prioritize industrial and agriculture chemicals and make decisions which chemicals are continued in development and/or marketed.
Both the GreenScreen® HC assay and Ames II™ assay are performed in 96-well plates and provide general information on the genotoxicity of chemicals. The Ames II™ Assay measures bacterial mutagenicity thereby predicting results of the GLP Ames assay. The GreenScreen® HC assay measures induction of p53 as a way of assessing general DNA damage.
Most recently BioReliance has launched the CAN FlowScreen™ assay which can determine mode of action and genotoxicity. Whereas the Ames II™ and GreenScreen® either provide specific predictivity for one assay or are general predictors, the CAN FlowScreen (as described in the above article) can provide information on which MOA is present therefore providing definitive information on whether or not a substance is genotoxic and whether or not it should be continued.
Predictive Screening Assays
Before chemicals go through the regulatory required GLP assays, they can be evaluated in predictive screening assays, which are smaller versions of the GLP assays, therefore require much smaller amounts of test article and can be performed in less time and for less money. These assays provide the greatest prediction for how a chemical compound will perform in the GLP assay. In this category are Ames Assays (Mini, Micro, and Abbreviated), screening versions of in vitro mammalian mutation assays (Mouse Lymphoma Assay), and screening versions of in vitro mammalian cytogenetics assays (Chromosome Aberration and Micronucleus Assays).
Overview of BioReliance Screening Assays
The table below lists out the types of assays and their classifications. BioReliance’s globally recognized scientists are available to work with you to design the most appropriate screening approach to meet your needs. For questions, please consult a BioReliance Technical Representative.
Non-GLP Assays for Discovery, Early Development and Screening
Purpose of Testing/Detection
Structure-Activity Relationship (SAR)
in silico Testing
Linking chemical structure to a chemical property
High Throughput Screening Assays
Mode of Action Determination
Predictive Screening Assays
Mini Ames, Micro Ames,
In Vitro Mammalian Mutation
In Vitro Mammalian Cytogenetics
Chromosome Aberration Micronucleus
Morphological Transforming Activity
Neutral Red Uptake (NRU)
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