(W0930-09-53) Preclinical Evaluation of Pharmacokinetic, Receptor Occupancy, and Immunogenicity Profiles of a Bispecific Antibody Construct in a Monkey Study

Purpose: HLX301 is a novel bispecific antibody construct targeting at human PD-L1 and TIGIT. Preclinical pharmacokinetic (PK), anti-drug antibodies (ADA), and receptor occupancy (RO) profiles were investigated in cynomolgus monkeys.

Methods: A multi-dose toxicology study was conducted, where cynomolgus monkeys received once-weekly intravenous administration of HLX301 for 3 weeks at doses of 20, 60, and 120 mg/kg HLX301 concentrations in monkey serum were measured with two assays, including an ELISA intended to measure total concentration and a target-binding assay intended to measure serum concentrations of intact molecule (Figure 1). ADA were analyzed with a bridging immunoassay, and RO in CD3+ cells evaluated with a competitive-binding flowcytometry assay.

Results: PK and RO profiles are shown in Figure 2. The concentrations of total versus intact HLX301 were fairly consistent and there was no obvious difference between two sets of PK data, indicating in vivo stability of the molecule. RO results of three dose levels were all above 80% on the first day after administration, and receptor occupancy was maintained in a saturated level from D1 to D15. A dose-dependent drop in receptor occupancy was observed on Day 22. Inter-individual differences in drug concentrations and RO were largely observed on Day 22 onward when certain animals appeared to develop ADA responses. The RO results and concentrations of HLX301 in 60 mg/kg dose group were used in the modeling, and a PK-PD model with E₀ of 68.0, Emax of 29.9, and EC50 of 0.365 was obtained. According to the equation, when more than 80% of RO is desired, the concentration of HLX301 should be higher than 0.245 μg/mL.

Conclusion: HLX301 is stable following administration into monkeys. Dose-dependent and saturated receptor occupancy illustrated that HLX301 obtain a well target-bound capability.


Figure 1. PK assay design