(T1130-01-07) Current Strategies for Using Commercial Kit in Regulated Bioanalysis

Purpose: PK/TK bioanalysis of a biological compound by LBA typically requires a specific and tailor-made method. A complete method development requires drug specific critical reagents, such as capture and detection antibodies, that entail extensive generation time. Commercial kits are a potential solution that contain ready to use assay plates and critical reagents, typically with procedures available. While these kits are often used for biomarker assays, they can be applied for PK/TK bioanalysis depending on the unique characteristics of the administered drug. The currently issued ICH M10 provides some guidelines on using commercial kits for PK/TK bioanalysis. A successful feasibility assessment of the kit reduces development time of a new LBA assay. However, commercial kits must be adapted by bioanalytical laboratories in order to follow the ICH M10 guidelines. These kit adaptations may include all or some of these modifications to the procedure: changing the reference standard to better represent the drug product, changing the standard curve range to align with the study requirements, and to prepare all the standard curve and QCs in the same matrix as study samples. Furthermore, the limited quantity of kits from the same lot is a limitation for long-term planning as required by clinical studies, and therefore kit lot-to-lot qualification needs to be properly planned and executed. Herein, we provide examples of challenges and mitigation strategies to repurpose commercial kits for regulated PK bioanalysis.

Methods: Repurposing of commercial kits for PK bioanalysis was performed in two different studies. These two case studies utilized a sandwich ELISA kit to quantitate the recombinant drugs. The kit supplied reference standard was replaced with the sponsor’s reference standard to generate the standard curve and QCs in sample matrix instead of kit supplied calibrator diluent. In the third case study, commercially available kit was selected to support a PD study. Multiple kit lots were used during Method Development and validation which required cross-qualification and investigation due to lot-to-lot variability in performance.

Results: In the first case study, the kit instructions provided consistent variability issue throughout the standard curve during the method development. The variability issue was addressed by modifying the kit procedure. The sample loading volume was decreased, the stop solution volume and concentration were changed, the substrate incubation time was decreased, and additional shaking step was included after the stop solution addition. These changes enabled the %C.V. of all standard points to be within range. The second case study was to use a commercial kit in a pre-clinical study using rat serum. The suggested range of the kit was more than 5000-fold lower than the expected Cmax, thus requiring extending the curve range. However, the curve range extension resulted in selectivity and variability issues, where 7/10 rat serum lots evaluated had an unacceptable negative %bias or %C.V. The selectivity issue was addressed by optimizing the method through increasing the minimum required dilution, and raising the LLOQ, whereas the % C.V. issue was addressed by filtering the kit supplied blocking buffer solution. These changes resulted in 6/6 remaining lots to meet acceptance criteria for selectivity and no C.V. issues were observed. The third case study focuses on the importance of establishing robust kit qualification procedure. For this clinical study, MD was successfully completed with a kit lot and no issues were observed. Additionally, different lots were tested and consistency among lots was confirmed. Method validation was initiated afterwards with a new lot, and the initial kit qualification met acceptance qualification. However, a failure trend was observed during method validation where runs were failing due to standards not meeting acceptance criteria. A preliminary investigation exploring the assay procedure was conducted but failed to identify the root cause of the issue. A retrospective review of the data demonstrated the that 75% of the failed runs using the new kit lot failed whereas only 2 runs failed with the other lots. The kit supplier was communicated to perform a kit lot test. The supplier confirmed an inconsistency in the new lot while performing inter-precision run.

Conclusion: ICH M10 provides guidelines on the use of commercial kits for regulated PK bioanalysis. In order to comply with these guidelines, the assay procedure would require changes to the kit supplied procedure. Commercial kits can be helpful when repurposed to support early stage drug development programs to reduce timelines and provide quick decision making results. As the test cases demonstrated, these changes come with potential challenges and risks requiring careful planning and execution during method development. Early feasibility assessment can provide insight on the cost effectiveness of a kit. It is important to weigh the cost to benefit early on as kits are not optimal for regulated bioanalysis and further cost/time is expected on the back end to bridge into a specific PK assay.