Insufficient drug tolerance presents a major challenge in the development of neutralizing antibody (NAb) assays for biotherapeutics. Sample pre-treatment using solid-phase extraction with acid dissociation (SPEAD) is widely reported to improve drug tolerance. In this paper, a case study is presented in which SPEAD was used in conjunction with a competitive ligand binding NAb assay format. A significant degree of biotin-drug conjugate leaching was observed resulting in the reporting of both false positive and false negative results in NAb assay. Mitigation steps have been evaluated to address drug/biotin-drug conjugate leaching. These steps included assessment of the streptavidin-coated plate in conjunction with biotin-drug conjugates at various biotin molar challenge ratios (MCR). In addition, an alternative method based on covalent capture of the drug on an aldehyde-activated plate was assessed. Both approaches were compared for the degree of drug/biotin-drug conjugate leaching during the second elution step of the SPEAD procedure. Moreover, the impact of various conditions on the assay performance was assessed, including elution pH, sample incubation time, and biotin MCR. For the covalent drug capture method, capture conditions were evaluated. Optimized conditions in both streptavidin capture and covalent capture methods enabled a significant reduction of drug/biotin-drug conjugate leaching. A streptavidin high binding capacity approach using biotin-drug conjugate with a MCR of 50:1 was chosen as the optimal method yielding a NAb assay with a fit for purpose sensitivity (153 ng/mL) and a drug tolerance of up to 50 μg/mL with 500 ng/mL PC.
Keywords: ACE; SPEAD; anti-drug antibody; biotin-drug conjugate/drug leaching; drug tolerance; immunogenicity; neutralizing antibody; sample pre-treatment.