Strategies to compare clinical antitherapeutic antibody data when changing assay platforms: a case study.

Zhihua Julia Qiu has over 20 years post PhD experience in academic institutes, pharmaceutical industry and biotechnology startup settings; focused on novel therapeutics discovery and development and diagnostic tools. She is currently a Scientist in the Bioanalytical Sciences department at Genentech; responsible for developing, evaluating and implementing Bioanalytical strategy to support protein therapeutics development. That includes assay development and validation to evaluate PK, antitherapeutic antibodies as well as biomarkers in both nonclinical and clinical studies for Immunology and Oncology indications. In addition, she has led the evaluation of multiple novel technology platforms and transitioning assay platform to enable continuous support for the development of protein therapeutics and antibody-drug conjugates.

A novel immunoassay to measure total serum lymphotoxin-α levels in the presence of an anti-LTα therapeutic antibody.

During drug development, measurement of suitable pharmacodynamic biomarkers is key to establishing in vivo drug activity. Binding of monoclonal antibody (mAb) therapeutics to soluble target proteins often results in elevated serum levels of their target antigen, and measuring total (free and bound) concentration of the target antigen can be an important means of demonstrating that the mAb has reached its specific target. However, accurately measuring soluble circulating antigen in preclinical or clinical samples in the presence of a therapeutic mAb presents a bioanalytical challenge. Particularly in the case of low molecular weight and/or multimeric targets, epitopes for capture and detection of the target by reagent antibodies can be obscured by bound therapeutic mAb. Lymphotoxin-alpha (LTα) is a cytokine in the TNF superfamily that has been implicated in the pathophysiology of autoimmune disease, and is a therapeutic target for neutralizing mAb. During preclinical safety studies in cynomolgus macaques, we encountered difficulties in measuring total LTα in serum of dosed animals. When serum LTα trimer was saturated with the anti-LTα mAb, binding of two reagent antibodies, as required for a classic sandwich ELISA, was not feasible, and dissociation methods were also found to be unsuitable. We therefore developed an approach in which excess anti-LTα mAb was added to the in vitro assay system to fully saturate all binding sites, and an anti-idiotypic antibody was used to detect bound therapeutic antibody. Using this method, total LTα could be accurately measured in cynomolgus macaque serum, and was observed to increase with increasing anti-LTα therapeutic mAb dose. Additional in vitro studies demonstrated that the method worked equally well in human serum. This assay strategy will be useful for quantifying total concentrations of other small and/or multimeric target proteins in the presence of a therapeutic antibody.

Pharmacokinetics and pharmacodynamics of anti-BR3 monoclonal antibody in mice.

PURPOSE: To characterize the pharmacokinetic (PK) and pharmacodynamic (PD) properties of a monoclonal antibody directed against the B-cell activating factor (BAFF) receptor 3 (BR3), following intravenous (IV) and subcutaneous (SC) administration in mice. METHODS: Single IV doses of 0.2, 2.0 and 20 mg/kg and a single SC injection of 20 mg/kg of anti-BR3 antibody was administered to mice. Serum drug and BAFF concentrations and splenic B-cell concentrations were measured at various time points. Pooled PK profiles were described by a two-compartmental model with time-dependent nonlinear elimination, and BAFF profiles were defined by an indirect response model. Fractional receptor occupancy served as the driving function for a competitive reversible antagonism model to characterize B-cell dynamics. RESULTS: Noncompartmental analysis revealed a decrease in drug clearance (31.3 to 7.93 mL/day/kg) with increasing IV doses. The SC dose exhibited slow absorption (T(max) = 2 days) and complete bioavailability. All doses resulted in a dose-dependent increase in BAFF concentrations and decrease in B-cell counts. The proposed model reasonably captured complex PK/PD profiles of anti-BR3 antibody after IV and SC administration. CONCLUSIONS: A mechanistic model was developed that describes the reversible competition between anti-BR3 antibody and BAFF for BR3 receptors and its influence on B-cell pharmacodynamics.

Identification and characterization of buried unpaired cysteines in a recombinant monoclonal IgG1 antibody.

The heterogeneity in therapeutic antibodies arising from buried unpaired cysteines has not been well studied. This paper describes the characterization of two unpaired cysteines in a recombinant humanized IgG1 monoclonal antibody (referred to as mAb A). The reversed-phase high-performance liquid chromatography (RP-HPLC) analysis of mAb A samples showed three distinct peaks, indicating the presence of three species. The heterogeneities observed in the RP-HPLC have been determined to arise from unpaired cysteines (Cys-22 and Cys-96) that are buried in the V(H) domain. The Fab containing free thiols (referred to as "free-thiol Fab") and the Fab containing the disulfide (referred to as "intact Fab") of mAb A were generated through limited Lys-C digestion and purified with an ion exchange chromatography method. The binding of free-thiol Fab and intact Fab to its antigen was measured in a cell-based binding assay and an enzyme linked immunosorbent assay. The unpaired cysteines in the Fab of mAb A were found to have no significant impact on the binding to its target. Consistent with these Fab binding data, the enriched intact mAb A containing free thiols was determined to be fully active in a potency assay. The data reported here demonstrate that the redox status of cysteines is potentially a major source of heterogeneity for an antibody.