Pitfalls in Assay Development

Developing an assay for a product line or as a laboratory developed test (LDT) can create a number of challenges for product development teams, resulting in lost time and money and having a negative impact on the product’s Return On Investment (ROI). This article will not focus on the technical challenges resulting from teams failing to grasp the science behind the intended use nor the commercial challenges due to lack of clinical utility. Assuming a team manages to get these right, what separates the most effective development teams from the rest is their focus on de-risking three aspects of product development early in feasibility. These are stability strategy for the assay, platform or system integration, and scale up during transfer from R&D to manufacturing or production. By identifying these as risks early in the product development process, teams can significantly improve their odds of delivering an assay on time and budget.

It is a common misconception to think that stability of an assay is simply the product’s shelf life during storage. The stability strategy also encompasses raw material stability, assay in-use stability (number of uses from a single vial, open pack conditions, freeze-thaws allowed, and on-board storage), and transport stability, which incorporates environmental and mechanical stress an assay is exposed to upon shipment from a manufacturing to a production or customer facility. Teams do not build these risks into the stability strategy till the product fails stability verification or worse fails in the customer’s lab. It is discovered too late that the product shipped under ambient condition is unstable upon exposure to 60°C in summers or 0°C in winters. The development team finds during verification that the second use out of a double use vial fails because additional dead volume was not considered. The manufacturing team decides to use a raw material close to the end of its shelf life because the raw material had not expired, only to find the development team performed raw material evaluation at the beginning of the material’s shelf life. These scenarios are very real and become presented as stability issues identified late in development, leading to reformulation of the assay followed by retesting. Since stability testing is time dependent, issues with assay stability can result in extensive time delays to the product development schedule and at worst case the assay being pulled off the market due to failure to meet label claims.

As automation continues to become mainstream, assays run on an instrument require that the biochemistry solution is compatible with the hardware and software components of the system. Alcohol based formulations on an electrical system can increase fire hazard and fail to meet regulations. Detergent containing formulations produce foaming that can impact how the system pipettes the liquid; whereas lack of a surfactant in a liquid that adheres to the surface of the pipette tips could lead to cross contamination if the same pipette tip is used at multiple steps. Or perhaps, the script executing the instructions on the system times out because it ran out of time to complete the step. By not identifying integration risks early in the product development process, these risks turn into issues during system integration and end up costing time and money due to chemistry reformulation and platform changes.

Manufacturing or running assays as LDTs requires that the assay is mass produced to reduce the cost of goods sold to increase gross profits. If scale up was overlooked by the product development team, then increasing the volume of a reagent from 10 milliliters in R&D to 1 to 10 liters in manufacturing may result in loss of homogeneity in a formulation. There may be a requirement that the formulation needs to be stored under frozen conditions and used after thawing to a homogeneous mixture. A 10 mL solution will thaw differently from a 1 L solution. It is possible that some of these risks may not be identified till the process validation phase or much worse if the right quality control criteria is not in place, risks may go unidentified till presented as issues by the customer, leading to product recalls.

Product development teams are encouraged to focus on the stability, system integration, and scale up strategies for their assay development needs during the feasibility phase. By identifying these as risks early in the development process, the teams will be able to establish an exit quality control criteria that needs to be met at each technical or design review stage. Design reviewers would be well advised to ask questions that challenge the design from a stability, system integration, and scale up perspective. By doing this right, development teams can significantly increase the odds of successfully launching their products on time and on budget.