Charge variants in IgG1: Isolation, characterization, in vitro binding properties and pharmacokinetics in rats

Abstract

Antibody charge variants have gained considerable attention in the biotechnology industry due to their potential influence on stability and biological activity. Subtle differences in the relative proportions of charge variants are often observed during routine biomanufacture or process changes and pose a challenge to demonstrating product comparability. To gain further insights into the impact on biological activity and pharmacokinetics (PK) of monoclonal antibody (mAb) charge heterogeneity, we isolated the major charge forms of a recombinant humanized IgG1 and compared their in vitro properties and in vivo PK. The mAb starting material had a pI range of 8.7-9.1 and was composed of about 20% acidic variants, 12% basic variants, and 68% main peak. Cation exchange displacement chromatography was used to isolate the acidic, basic, and main peak fractions for animal studies. Detailed analyses were performed on the isolated fractions to identify specific chemical modification contributing to the charge differences, and were also characterized for purity and in vitro potency prior to being administered either subcutaneously (SC) or intravenously (IV) in rats. All isolated materials had similar potency and rat FcRn binding relative to the starting material. Following IV or SC administration (10 mg/kg) in rats, no difference in serum PK was observed, indicating that physiochemical modifications and pI differences among charge variants were not sufficient to result in PK changes. Thus, these results provided meaningful information for the comparative evaluation of charge-related heterogeneity of mAbs, and suggested that charge variants of IgGs do not affect the in vitro potency, FcRn binding affinity, or the PK properties in rats.

Figure 1

Chromatographic profiles obtained from a (A) IEC shown in full scale and (B) SEC shown in expanded scale for all charge variant fractions, starting material and buffer blanks. See Table 2 for numerical values obtained from these analyses.

Figure 2

Representative sensorgrams of fitted data from the kinetic analysis of all charge variant fractions (A) acidic, (B) main, (C) basic and (D) starting material to immobilized rat FcRn. Black lines are fitted curves using a bivalent binding model. All sample concentrations (from bottom to top) are 62.5, 125, 250, 500, 1,000, 2,000 and 4,000 nM. Residual plot shows the difference between experimental and fitted data for every point in the sensorgram. Also see Table 4 for clarity.

Figure 3

Linear changes in serum concentrations versus time for all charge variant fractions following single (A) intraveneous or (B) subcutaneous administration of 10 mg/kg in normal rats. The assay minimum quantifiable concentration was 0.4 µg/mL in rat serum. Results are mean ± SD (n = 12 rats/time point).