Novel isoelectric target depletion (ITaD) protocol reduces the need for specific reagents for immunogenicity testing.

Background: The development of immunogenicity assays for clinical drug candidates targeting soluble proteins is challenging when the soluble target might produce either false-positive or false-negative signals in bridging anti-drug antibody screening assays. A generic soluble target removal protocol that uses a pH-dependent depletion was evaluated. Results: An anti-drug antibody bridging assay with a pH-dependent soluble target depletion step was successfully developed. Endogenous target levels of ∼600 nM could be depleted below 8 pM. The assay was highly drug tolerant and met regulatory requirements. Conclusion: A reagent-independent target depletion protocol can be used for immunogenicity testing in the presence of a soluble target. The generic protocol circumvents common depletion or masking protocols.

Validation of a ligand-binding assay for active protein drug quantification following the 'free analyte QC concept'.

AIM: Active drug assays are becoming increasingly important in protein drug development. We describe the validation of a ligand-binding assay for active protein drug quantification and address practical challenges as well as regulatory implications. RESULTS: A bioanalytical method for active protein drug quantification was successfully validated. Validation data prove that this method can be routinely used applying the commonly accepted acceptance criteria for ligand-binding assays. CONCLUSION: Active drug assays are a powerful tool to elucidate the pharmacokinetic/pharmacodynamic relationship as they take into consideration the influence of various matrix components, such as soluble ligand and anti-drug antibodies. However, not all aspects of the validation concept described in the guidelines for pharmacokinetic assays can be applied to active drug assays and thus regulatory guidelines should be adapted in consequence.

Free analyte QC concept: a novel approach to prove correct quantification of free therapeutic protein drug/biomarker concentrations.

Quantification of free drug concentrations is highly challenging due to the dynamic drug-ligand equilibrium, which may result in incorrect results. Current QC concepts do not adequately cover all of the important influencing factors: the assay itself (format and procedure); the calibration concept; the sample preparation; and the sample storage. Here, we propose a 'free analyte QC concept' that enables quantitative testing of these four factors and, thus, provides best possible proof of correct free drug quantification. The principle of the free analyte QC concept and an example of its application for a free drug assay is described. A comparison of this novel approach with current approaches and how the new concept fits (or does not fit) with current regulatory guidelines is discussed.