Preclinical Characterization of AMG 424, a Novel Humanized T Cell-Recruiting Bispecific Anti-CD3/CD38 Antibody

Introduction: Multiple myeloma (MM) is a highly prevalent hematological malignancy, with a worldwide incidence of over 62,000 patients in 2012. Despite significant progress in the development of MM treatments in the last decade, there is a great unmet medical need for MM patients who relapse on existing therapies. Given the greater time needed for relapses to manifest when minimal residual disease (MRD) is reduced, new therapies should be aimed at eliminating MRD. Bispecific T cell engager (BiTE^®) molecules recruit T cells to cancer cells and trigger T cell-dependent cellular cytotoxicity (TDCC). BiTEs are clinically validated for the treatment of hematological malignancies and have the potential to greatly reduce MRD. CD38 is a membrane protein normally expressed by plasma cells, lymphocytes, and other immune cells and is a clinically validated tumor-associated antigen expressed at high levels on MM cells. Herein, we describe for the first time AMG 424, a novel, humanized T cell-recruiting bispecific anti-CD3/CD38 antibody containing an XmAb^® Fc domain that cross-reacts with nonhuman primate (NHP) CD3 and CD38. AMG 424 was selected for its affinity for CD3 and CD38 in an effort to overcome the challenges associated with CD38 and CD3 binding.

Methods: A panel of eight novel bispecific molecules that bind with various affinities to CD3 and CD38 were tested in a series of in vitro assays, including TDCC against cancer cell lines, autologous B cell depletion, cytokine release, and soluble CD38 interference assays. AMG 424 was selected from this panel and evaluated in vivo for its ability to induce tumor growth inhibition and prolong survival in an orthotopic MOLM-13-luc xenograft model in NOD/SCID gamma mice co-implanted with human T cells. AMG 424 was also tested in a repeat dose study in NHPs in which depletion of peripheral CD38-expressing target cells was monitored as a pharmacodynamic endpoint. Finally, the potential of AMG 424 to be combined with relevant standard-of-care therapies was evaluated in vitro.

Results: In vitro, AMG 424 demonstrated complete redirected lysis activity against cancer cells with CD38 surface density as low as ~2,000 copies per cell. Compared with molecules with greater CD3 affinity, AMG 424 triggered the release of less IFN-γ and TNF-α in the presence of target cells. Moreover, in the presence of soluble CD38 (200 ng/mL), the in vitro potency of AMG 424 was decreased less than two-fold, whereas molecules with greater affinity for CD38 were decreased nearly ten-fold. Thus, the reduced affinity of AMG 424 for CD3 and CD38 versus other molecules may improve tolerability and pharmacokinetic variability. In tumor-bearing mice with pre-activated human T cells, AMG 424 induced 98% tumor growth inhibition and prolonged survival by more than 70%. In NHPs, AMG 424 depleted peripheral CD38-expressing target cells. In vitro, AMG 424 activity was minimally affected when combined with existing standard-of-care therapies.

Conclusions: AMG 424 is a novel, humanized, bispecific T cell-recruiting anti-CD3/CD38 antibody that targets MM cancer cells through T-cell dependent redirected lysis, an approach with the potential to eliminate MRD. AMG 424 completely cleared target cells in TDCC assays and triggered depletion of target cells in vivo. These results support further investigation of AMG 424 as a single agent or combined with existing standard-of-care therapies.