Accounting for Variability
Biomarker analysis is a common practice in pharmacokinetic/pharmacodynamics (PK/PD) modeling to learn about a drug’s mechanism of action.
Biomarker assays and kits can be 510(k)-approved, lab-developed, or RUO kits. Several venders produce RUO kits. Multiple lots are generated yearly, with a shelf life less than a year. Since clinical trials can extend for years, a system is needed to link data generated from one kit lot to another.
Each kit may contain several key components, and testing each individual reagent would be unfeasible. To address RUO kit variability, BioAgilytix Labs has implemented the concept of lot bridging.
To quantify the kit as a unit to assure performance consistency, a series of stability QCs and fresh samples are tested over multiple days, both on the previous and new lots. A correction factor—a numerical multiplier—is generated and used to normalize the new lot with the validation, or a previous lot. Lot bridging reduces noise in the resulting data, making it more meaningful for statisticians and clinicians to interpret.
“Even if you have a beautifully validated assay, lot-to-kit-lot variability influences results and has to be accounted for. Kit variability has nothing to do with the drug effectiveness and may point you in the wrong direction if quality data is not generated,” says Afshin Safavi, Ph.D., svp, bioanalytical operations, BioAgilytix Labs. “When you are supporting PK studies conducted under GLP, with specific regulatory requirements and guidelines, typically the drug acts as the calibrator or standard. The assays can be set up in a way that removes, or minimizes, the critical reagents lot-to-lot variability.”
“Much biomarker work is secondary, to learn about drug mechanism of action. Calibrators and controls may, or may not, be available commercially, and may come in a variety of forms. For most biomarkers, there is no universal standard available,” Safavi adds. “Therefore, the concept of ‘fit for purpose’ is used for biomarker assay validation and analysis support.”
“At BioAgilytix Labs, we validate the assays, treating them as if they were almost a regulated study with the proper documentation. This is how we discovered the extent of biomarker kit lot variability in the market today,” he explains. “Lot bridging becomes especially important if you want to compare studies, perform multiyear studies or add more cohorts to ongoing studies, which requires the purchase of additional kits from a different lot.”