Drug discovery is a complex and lengthy process. At its core lies assay development, the methodical creation of specialized tests designed to precisely identify and evaluate potential new medicines. Assay development is foundational for advancing drug candidates through the pipeline.
What Are Assays in Drug Discovery?
In drug discovery, an “assay” refers to a laboratory test or measurement designed to assess a specific biological or biochemical activity. The primary purpose of these tests is to quantify how a potential drug molecule interacts with a particular biological target, often implicated in a disease. For example, an assay might measure how strongly a compound binds to a specific protein or how it influences the growth of cancer cells.
Assays provide quantifiable data on a compound’s effect. Without them, researchers would lack the precise tools to determine if a substance has the desired therapeutic action or could cause unwanted side effects. Biochemical assays focus on molecular interactions, while cell-based assays examine how compounds affect living cells, offering insights into a drug’s efficacy and potential toxicity.
Developing a Drug Discovery Assay
Creating a new drug discovery assay begins with identifying a specific biological target, such as a particular protein, enzyme, or DNA sequence known to be involved in a disease. This target must be validated to confirm its role in the disease pathway before proceeding with assay design. Once a target is selected, researchers choose an appropriate measurement technique to observe the interaction between the compound and the target. Common detection methods include fluorescence, luminescence, or radioactivity, which generate a measurable signal.
Optimizing the assay conditions follows, ensuring accuracy and reliability. This involves adjusting factors like temperature, pH, reagent concentrations, and incubation times to achieve a clear and consistent signal. Finally, the assay is adapted for high-throughput testing, designed to be run efficiently on automated systems, often in miniaturized formats like 96, 384, or 1536-well microtiter plates. This adaptation allows for the rapid testing of a large number of compounds, accelerating the initial screening phase of drug discovery.
How Assays Find New Drugs
Developed assays are applied in the drug discovery pipeline, primarily through high-throughput screening (HTS). HTS utilizes automated robotic systems to rapidly test millions of compounds against a biological target. This rapid testing identifies “hits,” which are compounds showing initial desired biological activity, such as inhibiting an enzyme or activating a receptor.
After initial hits are identified, they undergo further evaluation through secondary and tertiary screens to confirm their specificity. These subsequent tests often use more complex, physiologically relevant models, like cell-based assays, to gain deeper insights into how the compounds affect biological systems. The most promising hits are then refined and optimized through “hit-to-lead” optimization, where their chemical structures are modified to improve properties like potency, selectivity, and safety, transforming them into “lead” compounds for further drug development.
Confirming Assay Accuracy
Assay validation is a process to ensure that an assay provides reliable, consistent, and accurate results. This is a necessary step before an assay can be confidently used to make decisions about potential drug candidates. Reproducibility is assessed by demonstrating that the assay yields similar results when performed multiple times under the same conditions or by different operators and equipment.
Sensitivity is another factor, indicating the assay’s ability to detect small changes or low concentrations of the target molecule. Specificity confirms that the assay measures only the intended biological activity and does not react with unrelated substances. Robustness evaluates how well the assay performs under minor variations in conditions, such as slight changes in temperature or reagent batches. These validation steps ensure the assay’s performance is suitable for its intended purpose throughout the drug discovery program.