Ligand-binding assays (LBA) are widely used to quantify biotherapeutics to support clinical development. Anti-drug antibodies (ADA), which are commonly observed with biotherapeutic administration, can interfere with drug quantitation. Characterizing and addressing ADA interference is critical from both bioanalytical and clinical perspectives, as this could impact exposure-response relationship analysis and dose selection in clinical trials. Here, we report a holistic approach to assess the ADA interference for a drug concentration assay for a monoclonal drug candidate Biologic-x. Biologic-X is in clinical development for the treatment of immunological indications. An LBA using the target as a capture reagent was implemented for drug concentration determination. Theoretically, this assay is subject to free target and ADA interference. The ADA interference was particularly a concern for Biologic-X as the ADA incidence and titer for this drug candidate were considerably high, and the neutralizing ADA was prevalent. The initial assessment with a surrogate positive control sample confirmed that ADA was indeed interfering with the drug quantitation. This raised concerns about whether the reported drug concentrations were accurate and whether detection was consistent across samples with different ADAs. We selected study samples with various ADA statuses and titers and tested them under various dilution factors. The result demonstrated that the ADA was not expected to alter the drug concentrations under conditions applied for study sample analysis. This LBA was deemed as a functional total drug assay at the conditions specified even though using a target as capture reagent. The approach can be applied to other biotherapeutic programs.
Learning Objectives:
Assess drug concentration assay suitability.
Regulatory expectations and requirements for clinical drug concentration assay.
Assess and mitigate potential assay interfering factors for drug concentration assays.
