Preclinical Potency, Affinity, and Pharmacokinetics of APG990, a Half-Life Extended Antibody Against OX40L

Background: Signaling through the OX40-OX40L pathway has been implicated in the pathogenesis of many inflammatory conditions, including atopic dermatitis. APG990 is a fully human monoclonal antibody (mAb) designed to bind to OX40L and block inflammatory signaling mediated by the interaction between OX40 and OX40L. APG990 contains YTE amino acid modifications in the Fc region to extend its half-life and a LALA modification to ablate Fc-mediated function. Methods: Multiple preclinical assays were used to assess the ability of APG990 to bind OX40L, as well as the impact of APG990 on downstream OX40/OX40L binding and signaling. An antibody based on the published sequence of amlitelimab was used as a positive control. The affinity of APG990 for OX40L was measured by surface plasmon resonance (SPR). To investigate the ability of APG990 to inhibit human OX40L binding, an ELISA assay was used to assess APG990 and human OX40 competitive binding to immobilized human OX40L. To investigate the ability of APG990 to inhibit human OX40L-induced signaling, the effects of increasing concentrations of APG990 were assessed on a human OX40 reporter cell line. Activated human primary CD4+ T cells were used to evaluate the concentration-dependent blocking ability of OX40L. Activated human primary CD4+ T cells were used to assess the APG990 concentration-dependent blockage of OX40L-induced IL-2 release. The pharmacokinetics of APG990 were evaluated following a single bolus (SC or IV) of APG990 in cynomolgus monkeys. Results: APG990 bound OX40L from humans with a KD of 106.38 pM (vs 70.91 for amlitelimab). APG990 inhibited human OX40L binding to OX40 in a concentration-dependent manner, with an IC90 of 6.5 nM (vs 4.7 nM for amlitelimab), and blocked OX40L-induced IL-2 release (IC90 of 2.9 nM for APG990 vs 2.3 nM for amlitelimab). APG990 blocked human OX40L-induced activation of OX40 reporter cells with an IC90 of 4.5 nM (vs 7.8 nM in amlitelimab). In NHPs, APG990 exhibited a mean serum half-life of 26.9 (IV) and 25.5 (SC) days, versus 19.8 (IV) and 22.2 (SC) for amlitelimab APG990 was well-absorbed, with an average bioavailability of 96%. Conclusions: APG990 demonstrated strong binding affinity for OX40L and effectively blocked inflammatory signaling mediated by the interaction between OX40L and OX40. APG990 has a longer half-life than amlitelimab but similar binding affinity and potency. These results support clinical investigations with APG990 for the treatment of inflammatory conditions, such as atopic dermatitis.