BI 836909, a Novel Bispecific T Cell Engager for the Treatment of Multiple Myeloma Induces Highly Specific and Efficacious Lysis of Multiple Myeloma Cells in Vitro and Shows Anti-Tumor Activity in Vivo

BI 836909 is a Bispecific T cell Engager (BiTE^®), designed to redirect the body's endogenous T cells towards cells expressing B cell maturation antigen (BCMA) on the cell surface.

BCMA is a highly plasma cell specific antigen and shows homogeneous expression on the cell surface of multiple myeloma, plasma cell leukemia and plasmacytoma cells. In normal tissues, BCMA expression is restricted to plasma cells, while other normal tissues do not express BCMA. This highly selective expression pattern makes BCMA an ideal target for T cell redirecting therapy.

The pharmacological effect of BI 836909 depends on its simultaneous binding to both the CD3 epsilon subunit of the T cell receptor complex on T cells as well as to BCMA on multiple myeloma cells, resulting in the lysis of the BCMA-expressing cells.

In vitro, unstimulated peripheral blood mononuclear cells (PBMCs) were co-cultured with several multiple myeloma cell lines and increasing concentrations of BI 836909, and tumor cell lysis, T cell activation, and induction of cytokine release were assessed. BI 836909 induced dose-dependent redirected lysis of human multiple myeloma cell lines with EC₉₀ values ranging from 16 to 810 pg/mL. Viability of BCMA-negative cells was not affected, demonstrating the specificity of BI 836909 for BCMA. The expression of the activation markers CD69 and CD25 on T cells and the release of cytokines by T cells were target-dependent and occurred only in the presence of BCMA-positive cells.

In vivo anti-tumor activity of BI 836909 was assessed in NOD/SCID mice reconstituted with human T cells and bearing subcutaneous or orthotopic xenografts derived from human multiple myeloma cell lines.

In the subcutaneous NCI-H929 xenograft model, animals were treated with BI 836909 by daily intravenous or subcutaneous bolus injections. Statistically significant dose-dependent anti-tumor activity was observed at doses of 50 µg/kg/day and higher. The efficacy of BI 836909 was comparable after intravenous and subcutaneous administration, when the difference in bioavailability of the different routes was considered.

In an orthotopic L-363 xenograft model, treatment with BI 836909 resulted in a statistically significant prolonged survival at doses of 5 µg/kg/day and higher.

BI 836909 shows comparable cross-reactive binding to both BCMA and CD3 epsilon of human and macaque origin at picomolar and low nanomolar affinities respectively, thus allowing the assessment of pharmacodynamics, pharmacokinetics, and safety in non-human primates. In toxicity studies, cynomolgus monkeys were administered doses of up to 135 µg/kg/day of BI 836909 via continuous intravenous infusion, and up to 405 µg/kg/day via daily subcutaneous injection for up to 28 days. A dose- dependent decrease in plasma cells was observed in the bone marrow of treated animals compared to the vehicle control group, consistent with BCMA expression on cynomolgus monkey plasma cells, this demonstrated the pharmacological activity of BI 836909.

These pre-clinical data demonstrate that BI 836909 is a highly potent, efficacious and BCMA-selective T cell redirecting agent and support clinical testing of BI 836909 in multiple myeloma patients.