ALBERT

Description: Abstract 1543 BMS-936564/MDX-1338 is a fully human monoclonal antibody that specifically recognizes human CXCR4 and is currently in phase 1 studies in patients with relapsed/refractory acute myeloid leukemia (AML) and multiple myeloma (MM). CXCR4 has been identified as a prognostic indicator for AML and other malignancies, in which greater expression of CXCR4 correlates with disease severity. CXCR4 is a seven-transmembrane, G-protein-coupled receptor in the CXC chemokine receptor family. In response to stimulation by its ligand, the chemokine CXCL12, CXCR4 activates calcium flux, chemotaxis and mediates directional migration of hematopoietic cells. In healthy adults, the receptor is predominantly expressed on B and T cells, monocytes, macrophages, NK and dendritic cells, as well as lymphoid and myeloid precursor cells. Expression of CXCR4 is elevated in a variety of cancers and the interaction of CXCR4 on tumor cells with CXCL12 in the bone marrow promotes tumor cell survival and growth. An antagonist of this pathway is predicted to be efficacious in a variety of hematologic malignancies. In vitro studies demonstrate that BMS-936564/MDX-1338 binds to CXCR4expressing cells with low nanomolar affinity. The antibody blocks CXCL12 binding to CXCR4 expressing cells and inhibits CXCL12 induced migration and calcium flux with low nanomolar EC50 values. When given as monotherapy on established tumors, the antibody exhibits anti-tumor activity in multiple AML, NHL and MM xenograft models. BMS-936564/MDX-1338 is an IgG4 and thus does not elicit complement dependent cytotoxicity (CDC) or antibody dependent cell mediated cytotoxicity (ADCC). In vitro and in vivo studies suggest that BMS-936564/MDX-1338 induces apoptosis as one mechanism of tumor growth inhibition. Here we describe the in vitro and in vivo characterization and activities of BMS-936564/MDX-1338. Disclosures: Kuhne: Bristol-Myers Squibb: Employment. Mulvey:Bristol-Myers Squibb: Employment. Chen:Bristol-Myers Squibb: Employment. Pan:Bristol-Myers Squibb: Employment. Chong:Bristol-Myers Squibb: Employment. Niekro:Bristol-Myers Squibb: Employment. Kempe:Bristol-Myers Squibb: Employment. Henning:Bristol-Myers Squibb: Employment. Cohen:Bristol-Myers Squibb: Employment. Korman:Bristol-Myers Squibb: Employment. Cardarelli:Bristol-Myers Squibb: Employment.

Description: Therapeutic monoclonal antibodies kill target cells by multiple mechanisms including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent phagocytosis (ADP), complement-dependent cytotoxicity (CDC), and direct induction of apoptosis. Antibody binding to FcgRIIIA (CD16), which is expressed on NK cells, macrophages, and CD8+ cells, is essential for ADCC. MDX-1401 is a fully human monoclonal antibody of IgG1 (kappa) isotype that binds to human CD30. This second generation anti-CD30 antibody was derived from parental antibody MDX-060 but differs in that the oligosaccharides of the IgG1 lack fucose, a property that conveys increased antibody affinity for Fc receptor CD16 (FcgRIIIa) and thus stimulates both more potent and efficacious ADCC than a fucosylated IgG1. The KD of the parental antibody for CD30 expressed on L540 Hodgkin’s lymphoma cells is approximately 1.4 nM while the KD of MDX-1401 is 1.9 nM, demonstrating that binding affinity for antigen are nearly identical. However, the EC50 for MDX-1401 binding to CD16-transfected cells is approximately 3 nM compared to barely detectable binding by parental antibody, confirming that the absence of fucose conveys increased affinity for FcgRIIIa. Data is presented that demonstrates MDX-1401 has significantly improved potency and efficacy in an ADCC assay as evidenced by a decrease in EC50 as well as an increase in maximum specific lysis. Importantly, the enhanced ADCC activity is observed among a large panel of cell lines with varying numbers of CD30 receptors per cell, including one cell line with low antigen expression in which parental antibody failed to induce ADCC. MDX-1401 enhances ADCC activity with all polymorphic variants including lower affinity FcgRIIIa Phe/Phe158 and FcgRIIIa Phe/Val158 effector cells. Furthermore, MDX-1401 is efficacious in inhibiting growth of CD30+ tumor xenografts in mice. The low doses of antibody required for ADCC activity irrespective of donor genotype, the capacity to mediate ADCC of target cells expressing low levels of CD30, and increased in vivo efficacy support the development of MDX-1401 for treatment of malignant lymphoma. Phase 1 studies in subjects with Hodgkin’s lymphoma are currently underway.

Description: Background Hematopoietic stem cell (HSC) transplantation (HSCT) is a well-established procedure that, with or without gene therapy, is curative for numerous severe life-threatening diseases including genetic blood disorders and blood cancers. While advances have been made, there are still substantial concerns since these chemo- and radiation therapy based procedures cause long-term toxicities such as infertility and secondary malignancies or even result in high mortality. We have previously established in a series of preclinical studies a novel chemo- and radiation-free non-toxic monoclonal antibody (Ab) -based conditioning regimen for autologous and allogeneic HSCT (Czechowicz et al., Akanksha et al. and George et al.). This cKIT-CD47 Ab-based regimen selectively depletes host HSCs for HSCT while sparing off-target toxicities caused by chemotherapy/radiation. By significantly decreasing morbidity/mortality associated with traditional conditioning regimens, antibody-mediated conditioning could expand the patient population eligible to receive HSCT for a variety of disorders. We developed a novel cKIT Ab (FSI-174), with an active Fc, and in combination with our CD47 magrolimab (previously 5F9, blocks the don't eat me pathway) could be utilized to translate the promising preclinical findings into clinical studies for safe and less toxic bone marrow conditioning for HSCT. Here we present the functional characterization of FSI-174 as single Ab and in combination with magrolimab in vitro and in non-human primate (NHP) studies. Methods We tested if FSI-174 could block stem cell factor signaling and we explored if FSI-174 alone or in combination with magrolimab could promote phagocytosis of cKIT positive cells (Kasumi-1). In addition, we determined if FSI-174 could cause mast cell degranulation. Subsequently, we explored the potential of FSI-174 alone (Phase A) or in combination with magrolimab (Phase B) to deplete HSCs in NHPs (rhesus macaques)in vivo. In Phase A, single doses of FSI-174 (0.3, 1, or 3 mg/kg) were administered alone. In Phase B, FSI-174 (0.3 or 3 mg/kg) was administered in combination with magrolimab (5mg/kg priming and 20 mg/kg maintenance dose). Bone marrow aspirates and core biopsies and peripheral blood were sampled before the study start and throughout the study. Frequency of bone marrow HSCs and cKIT receptor occupancy (RO) was determined by flow cytometry. In addition, the PK profile of FSI-174 was determined. Results In-vitro analysis demonstrated that FSI-174 decreases proliferation of HSPCs and enhances phagocytosis of cKIT positive cells, and the addition of magrolimab synergistically enhances the phagocytosis. Strikingly, FSI-174 did not cause mast cell degranulation in vitro. In the NHPs, complete (100%) cKIT receptor occupancy was achieved at all FSI-174 dose levels and was maintained for 1 to 9 days correlating with increasing doses and pharmacokinetics. The FSI-174 Cmax was found to be proportional to dose and mean Cmax increased from 6.25 ug/mL to 49.2 ug/mL. In Phase A, FSI-174 alone did not decrease the frequency of bone marrow HSCs compared to PBS control and had no effect on the peripheral blood cell counts. However, in Phase B, when FSI-174 was combined with magrolimab it significantly decreased the frequency of bone marrow HSCs with the nadir at day 9 and no recovery over 85 days compared to PBS control. Notably, there were no changes in peripheral blood cell counts over the course of the studies with no cytopenias in combination treatment. Conclusions We have developed a novel cKIT Ab (FSI-174) that meets the desired profile of stem cell factor block, promotion of phagocytosis, but without promoting mast cell degranulation. Furthermore, in the NHPs studies we have confirmed our chemo- and radiation-free cKIT-CD47 Ab -based conditioning approach with FSI-174 and magrolimab. As anticipated by our previous preclinical studies, monotherapy with FSI-174 does not deplete bone marrow HSCs in NHPs. Notably, no cytopenias are observed with either monotherapy or combination therapy. These data demonstrate the specificity, efficacy and safety of FSI-174/ magrolimab combination have great potential for conditioning regimen for HSCT in a chemotherapy and radiation free manner. Given the favorable safety profile of magrolimab across several clinical studies, these results are paving the way to the first-in-human trials for this novel conditioning for HSCT. Disclosures Marjon: Forty Seven Inc: Employment, Equity Ownership. Chen:Forty Seven Inc.: Consultancy, Equity Ownership. Duan:Forty Seven Inc.: Employment, Equity Ownership. Choi:Forty Seven inc: Employment, Equity Ownership. Sompalli:Forty Seven Inc: Employment, Equity Ownership. Feng:Forty Seven Inc: Employment, Equity Ownership. Mata:Forty Seven inc: Employment, Equity Ownership. Chen:Forty Seven Inc: Employment, Equity Ownership. Kean:HiFiBio: Consultancy; BlueBirdBio: Research Funding; Gilead: Research Funding; Regeneron: Research Funding; EMDSerono: Consultancy; FortySeven: Consultancy; Magenta: Research Funding; Bristol Meyers Squibb: Patents & Royalties, Research Funding; Kymab: Consultancy; Jazz: Research Funding. Chao:Forty Seven Inc: Employment, Equity Ownership. Chao:Forty Seven, Inc.: Employment, Equity Ownership, Patents & Royalties. Takimoto:Forty Seven, Inc.: Employment, Equity Ownership, Patents & Royalties. Agoram:Forty Seven Inc.: Employment, Equity Ownership. Majeti:FortySeven: Consultancy, Equity Ownership, Other: Board of Director; BioMarin: Consultancy. Weissman:Forty Seven Inc.: Consultancy, Equity Ownership, Patents & Royalties. Liu:Forty Seven Inc: Employment, Equity Ownership, Patents & Royalties. Volkmer:Forty Seven, Inc.: Employment, Equity Ownership, Patents & Royalties.