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

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. An anti-drug antibody bridging assay with a pH-dependent soluble target depletion step was successfully developed.

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.

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.