Abstract 1538: Margetuximab mediates greater Fc-dependent anti-tumor activities than trastuzumab or pertuzumab in vitro
Authors: Liu Liqin , Yang Yinhua , Burns Robert , Li Jonathan , Li Haiquan , Gorlatov Sergey , Moore Paul , Nordstrom Jeffrey 
Published: August 2019

Abstract
Margetuximab (M) is an investigational Fc-engineered anti-HER2 monoclonal antibody (mAb) with potential for greater immune-mediated anti-tumor activity than trastuzumab (T). M and T bind the same subdomain IV epitope, but M binds with higher affinity to activating Fc receptor, CD16A (FcγRIIIA), and lower affinity to inhibitory Fc receptor, CD32B (FcγRIIB). Pertuzumab (P) binds to a subdomain II epitope and has the same wild type Fc domain as T. We compared in vitro properties of M, T and P and combinations of M+P and T+P to evaluate Fc domain contributions to anti-HER2 mAb mediated activities. By surface plasmon resonance, M, T and P bound to the HER2 extracellular domain with similar high affinity. Binding affinities of M and T were unchanged if P was pre-bound, indicating lack of interaction. M, T and P exhibited comparable binding to HER2-expressing cell lines. Anti-proliferative activities of M and T toward HER23+ cells (N87, SKBR3 or BT474) in the absence or presence of ligands (EGF or HRG1β) were similar, whereas P exhibited weaker activity. In the absence of ligands, M+P or T+P were comparably as active as M or T alone. In presence of ligands, M+P and T+P were generally more active than M or T alone. Antibody-dependent cell-mediated cytotoxicity (ADCC) was evaluated with N87 and SKBR3 target cells (HER23+, expressing a reporter gene to measure viability) and NK effector cells from donors with differing CD16A158 genotypes. M was 7- to 84-fold more potent than T, as well as 69- to 744-fold more potent than P. Greater differences generally were seen with effector NK cells bearing the more common CD16A158 FF and VF genotypes than with the less common, high affinity CD16A158 VV genotype. While addition of P enhanced mean potency of T by 2- to 3-fold, no such effect was seen with M; however, M or M+P was 7- to 25-fold more potent than T+P. Results with JIMT-1 cells (HER22+) were similar, albeit with lower differential than with HER23+ target cells. NK cells were monitored by flow cytometry following incubation of peripheral blood mononuclear cells with HER2+ target cells and mAbs. M induced greater expression of markers of activation (CD137), cytolytic capability (granzyme B, perforin) and proliferation (Ki67) than T. An anti-HER2 mAb with an inactivated Fc domain was ineffective, indicating that induced changes in NK cells were Fc-dependent. In conclusion, M and T bind HER2 with similar affinity and exhibit comparable anti-proliferative activity that is enhanced by addition of P if ligands (EGF or HRG1β) are present. Relative to T, M mediates superior ADCC with effector cells of all CD16A genotypes and promotes greater NK cell activation and expansion. The M+P combination maintains superior ADCC compared to the T+P combination.
Citation Format: Liqin Liu, Yinhua Yang, Robert Burns, Jonathan Li, Haiquan Li, Sergey Gorlatov, Paul Moore, Jeffrey Nordstrom. Margetuximab mediates greater Fc-dependent anti-tumor activities than trastuzumab or pertuzumab in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1538.