Biparatopic antibodies (BpAbs) are an attractive format of engineered therapeutic antibodies that bind to two distinct epitopes of a single antigen. Accelerated cell internalization is anticipated in many developmental campaigns, and both bivalent and tetravalent forms have been developed for this purpose. However, their pharmacokinetic properties have not been understood systematically; thus, optimization approaches for BpAbs have been limited. In this study, we conducted a comparative biodistribution analysis of bivalent and tetravalent BpAbs using the same variable fragments. Two different pairs of epitopes of human epidermal growth factor receptor 2 (HER2) were targeted, and their distribution was evaluated in a tumor xenograft model by 111In-labeling. Bivalent BpAbs showed higher accumulation in tumors than tetravalent BpAbs in both cases. However, epitope-dependent differences in biodistribution did not correlate with those of the original monoclonal antibodies. In addition, cell internalization during the early stages of incubation was higher for tetravalent BpAbs. These results suggest the advantage of bivalent BpAbs over tetravalent BpAbs in pharmacokinetics; however, the design may require optimization depending on the mechanism of action of the BpAb of interest.
Akiba et al. (2026) studied this question.