title: Anti-tumor activity and toxicokinetics analysis of MGAH22, an anti-HER2 monoclonal antibody with enhanced Fcγ receptor binding properties.
abstract: BACKGROUND
  Response to trastuzumab in metastatic breast cancer correlates with expression of the high binding variant (158V) of the activating Fcγ receptor IIIA (CD16A). We engineered MGAH22, a chimeric anti-HER2 monoclonal antibody with specificity and affinity similar to trastuzumab, with an Fc domain engineered for increased binding to both alleles of human CD16A.
  
  
  METHODS
  MGAH22 was compared to an identical anti-HER2 mAb except for a wild type Fc domain. Antibody-dependent cell cytotoxicity (ADCC) assays were performed with HER2-expressing cancer cells as targets and human PBMC or purified NK cells as effectors. Xenograft studies were conducted in mice with wild type murine FcγRs; in mice lacking murine CD16; or in mice lacking murine CD16 but transgenic for human CD16A-158F, the low-binding variant. The latter model reproduces the differential binding between wild type and the Fc-optimized mAb for human CD16A. The JIMT-1 human breast tumor line, derived from a patient that progressed on trastuzumab therapy, was used in these studies. Single and repeat dose toxicology studies with MGAH22 administered intravenously at high dose were conducted in cynomolgus monkeys.
  
  
  RESULTS
  The optimized Fc domain confers enhanced ADCC against all HER2-positive tumor cells tested, including cells resistant to trastuzumab's anti-proliferative activity or expressing low HER2 levels. The greatest improvement occurs with effector cells isolated from donors homozygous or heterozygous for CD16A-158F, the low-binding allele. MGAH22 demonstrates increased activity against HER2-expressing tumors in mice transgenic for human CD16A-158F. In single and repeat-dose toxicology studies in cynomolgus monkeys, a species with a HER2 expression pattern comparable to that in humans and Fcγ receptors that exhibit enhanced binding to the optimized Fc domain, MGAH22 was well tolerated at all doses tested (15-150 mg/kg) and exhibited pharmacokinetic parameters similar to that of other anti-HER2 antibodies. Induction of cytokine release by MGAH22 in vivo or in vitro was similar to that induced by the corresponding wild type mAb or trastuzumab.
  
  
  CONCLUSIONS
  The data support the clinical development of MGAH22, which may have utility in patients with low HER2 expressing tumors or carrying the CD16A low-binding allele.
authors: MacroGenics, Inc., 9640 Medical Center Drive, Rockville, MD 20850, USA. nordstromj@macrogenics.com
authors: Jeffrey L
authors: JL
authors: Nordstrom
authors: Sergey
authors: S
authors: Gorlatov
authors: Wenjun
authors: W
authors: Zhang
authors: Yinhua
authors: Y
authors: Yang
authors: Ling
authors: L
authors: Huang
authors: Steve
authors: S
authors: Burke
authors: Hua
authors: H
authors: Li
authors: Valentina
authors: V
authors: Ciccarone
authors: Tengfei
authors: T
authors: Zhang
authors: Jeffrey
authors: J
authors: Stavenhagen
authors: Scott
authors: S
authors: Koenig
authors: Stanford J
authors: SJ
authors: Stewart
authors: Paul A
authors: PA
authors: Moore
authors: Syd
authors: S
authors: Johnson
authors: Ezio
authors: E
authors: Bonvini
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D061067:Antibodies, Monoclonal, Humanized / Q000494:pharmacology; D000920:Antibody-Dependent Cell Cytotoxicity; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005260:Female; D006801:Humans; D008252:Macaca fascicularis; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D009369:Neoplasms / Q000378:metabolism; D011485:Protein Binding; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000276:immunology / Q000378:metabolism; D017452:Receptors, IgG / Q000378:metabolism*; D000068878:Trastuzumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D018719:Erb-b2 Receptor Tyrosine Kinases; D017452:Receptors, IgG; D000068878:Trastuzumab; C496124:FCGR3A protein, human