Abstract 3493: New, highly potent antibodies to death receptors having Fc mutations to increase antitumor activity

Abstract

Abstract Death receptors DR4 (TRAIL-R1) and DR5 (TRAIL-R2 or Apo2) are TNF receptor superfamily members that are receptors for TRAIL (Apo2 ligand), an immunomodulatory cytokine. Binding of TRAIL to DR4 or DR5 can activate the extrinsic apoptotic pathway selectively in tumor cells. Agonist antibodies to death receptors DR4 and DR5 thus have potential for treatment of cancer and may be better than derivatives of TRAIL itself because of their superior pharmacokinetics and receptor selectivity. However, despite dramatic effects in vitro and in preclinical xenograft models, several agonist antibodies to DR4 and especially DR5 have not provided significant therapeutic benefit in clinical trials. While resistance mechanisms in cancer cells are undoubtedly one reason, another factor may be inadequate potency of the antibodies tested. We therefore used intense immunization and screening protocols to develop very potent anti-DR4 and anti-DR5 monoclonal antibodies (mAbs), which were humanized to make the mAbs denoted HuD114 and HuG4.2 respectively. These mAbs were substantially more effective at killing tumor cells in vitro than the mAbs that have been tested in clinical trials. In addition, we introduced one or two mutations into the Fc (constant) regions of these and other potent anti-DR4 and anti-DR5 mAbs in order to increase affinity for the Fc gamma receptor IIb. Cross-linking, as provided by binding of anti-DR4 and anti-DR5 mAbs to Fc gamma receptors on immune cells, is required for effective transmission of an apoptotic signal through the death receptors. Accordingly, introduction of these mutations greatly increased the ability of the mAbs to kill tumor cells in vitro in the presence of human peripheral blood mononuclear cells, and to inhibit the growth of tumor xenografts in mouse models, with two mutations generally more effective than a single mutation. As a complementary approach to increase cross-linking, we also developed bispecific antibodies containing two binding domains from an anti-DR4 mAb and two binding domains from an anti-DR5 mAb. These bispecific mAbs were made in the IgG-like Bs(scFv)4-IgG format consisting of a homodimer of two monomers, each monomer having a single chain Fv from an anti-DR4 mAb linked to a heavy chain constant region, and a single chain Fv from an anti-DR5 mAb linked to a light chain constant region. Such a bispecific mAb was more effective at killing tumor cells than an anti-DR4 or anti-DR5 mAb alone, or even a mixture of anti-DR4 and anti-DR5 mAbs. Based on their potency in vitro and in animal models, we believe that HuD114 and HuG4.2, enhanced by the Fc mutations and/or in bispecific form, have the potential for greater clinical efficacy than previously tested anti-DR4 and anti-DR5 mAbs and thus merit further investigation. Citation Format: Lihong Wang, Yi Ding, Hangil Park, April Zhang, Zhengran Wang, Maximiliano Vasquez, Cary Queen, Jin Kim. New, highly potent antibodies to death receptors having Fc mutations to increase antitumor activity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3493.