• Selective myeloma cell killing and enhanced effector function of a novel anti-BCMA antibody conjugated with MMAF via noncleavable linker.• Specific multiple myeloma antigen for monoclonal antibody-based immunotherapy.B-cell maturation antigen (BCMA), highly expressed on malignant plasma cells in human multiple myeloma (MM), has not been effectively targeted with therapeutic monoclonal antibodies. We here show that BCMA is universally expressed on the MM cell surface and determine specific anti-MM activity of J6M0-mcMMAF (GSK2857916), a novel humanized and afucosylated antagonistic anti-BCMA antibody-drug conjugate via a noncleavable linker. J6M0-mcMMAF specifically blocks cell growth via G 2 /M arrest and induces caspase 3-dependent apoptosis in MM cells, alone and in coculture with bone marrow stromal cells or various effector cells. It strongly inhibits colony formation by MM cells while sparing surrounding BCMA-negative normal cells. J6M0-mcMMAF significantly induces effector cell-mediated lysis against allogeneic or autologous patient MM cells, with increased potency and efficacy compared with the wild-type J6M0 without Fc enhancement. The antibody-dependent cell-mediated cytotoxicity and apoptotic activity of J6M0-mcMMAF is further enhanced by lenalidomide. Importantly, J6M0-mcMMAF rapidly eliminates myeloma cells in subcutaneous and disseminated mouse models, and mice remain tumor-free up to 3.5 months. Furthermore, J6M0-mcMMAF recruits macrophages and mediates antibody-dependent cellular phagocytosis of MM cells. Together, these results demonstrate that GSK2857916 has potent and selective anti-MM activities via multiple cytotoxic mechanisms, providing a promising next-generation immunotherapeutic in this cancer. (Blood. 2014;123(20):3128-3138) IntroductionAlthough there is no monoclonal antibody (mAb)-based targeted therapy approved to treat patients with multiple myeloma (MM), many mAbs targeting different antigens have been preclinically and clinically evaluated. ) were either moved toward or remain in clinical development based on encouraging results from preclinical studies. However, these antigens still lack specificity and are also expressed in other normal tissues including natural killer (NK) or other effectors, which could limit their clinical utility. Therefore, novel therapeutic mAbs to achieve improved MM selectivity, simultaneously targeting cytotoxic drugs to MM cells, are urgently needed.B-cell maturation antigen (BCMA), a member of the tumor necrosis factor receptor superfamily (TNFRSF17), is selectively induced during plasma cell differentiation and is nearly absent on naive and memory B cells. 13,14 Upon binding to its ligands B-cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL), the survival of bone marrow (BM) plasma cells and plasmablasts is promoted.15,16 BCMA does not maintain normal B-cell homeostasis, but is required for the survival of long-lived plasma cells. 17 In MM, BCMA messenger RNA (mRNA) is commonly expressed at high levels in malignant plasma...

B-cell maturation antigen (BCMA, also termed TNFRSF17) is an attractive therapeutic target due to its restricted expression on normal and malignant plasma cells (PC). GSK2857916 (or J6M0-MMAF) is a BCMA-specific antibody conjugated to the microtubule-disrupting agent monomethyl auristatin F (MMAF) via a protease-resistant linker. To evaluate the clinical potential of this agent, tumour cells from seventy multiple myeloma (MM) patients were assessed for BCMA expression by immunohistochemistry and flow cytometry. All patients tested expressed BCMA, at varying levels, and both surface and intracellular expression were observed. BCMA expression is maintained through relapse, extramedullary spread and in residual disease post therapy. BCMA levels may also be prognostically useful as higher levels of BCMA were associated with poorer outcomes, even taking into account genetic risk. We observed rapid internalization of surface BCMA and newly expressed protein by 1 h, suggesting a mechanism for J6M0-MMAF activity even with low surface antigen. J6M0-MMAF mediated cytotoxicity of MM cells varied with dose and antigen levels, with clonogenic progenitors killed at lower doses than mature cells. In comparison, J6M0-MMAF killing of primary CD138(+) myeloma cells occurred with slower kinetics. Our observations support BCMA to be a promising therapeutic target in MM for novel therapies such as J6M0-MMAF.

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