Preclinical Anti-Tumor Activity of Hexabody-CD38 in Patient-Derived B Cell Lymphoma and Acute Myeloid Leukemia Xenograft Models

HexaBody^®-CD38 (GEN3014) is a next-generation CD38-specific IgG1 molecule with a hexamerization-enhancing mutation that leads to highly efficient induction of complement-dependent cytotoxicity (CDC) upon binding to CD38 positive tumor cells. HexaBody-CD38 is designed to induce strong anti-tumor activity in patients with CD38-expressing hematological malignancies through CDC and other Fc-mediated effector functions.

Previously we have shown that HexaBody-CD38 induces highly potent CDC-mediated cell death in multiple myeloma (MM), acute myeloid leukemia (AML), and B-cell non-hodgkin lymphoma (B-NHL) cells, including tumor cells in bone marrow samples from MM patients. In addition, HexaBody-CD38 demonstrated efficient ADCC and ADCP and induction of direct cell kill after Fc-crosslinking. Moreover HexaBody-CD38 induced strong inhibition of CD38 cyclase activity, which may contribute to reduction of immune suppression in the tumor microenvironment.

In this study, we show that in a panel of 23 MM, AML and B-NHL cell lines HexaBody-CD38 induced CDC, with EC50 values on average 7-fold lower than those of the CD38-targeting mAb daratumumab, which is part of the standard of care for MM. Cytotoxic activity of HexaBody-CD38 showed a positive correlation with CD38 expression levels. HexaBody-CD38 was especially more potent than daratumumab in cell lines with lower CD38 expression. Sensitivity to HexaBody-CD38-induced CDC was correlated with lower expression levels of complement regulatory proteins, including CD46, CD55 and CD59.

To exclude that the enhanced potency of HexaBody-CD38 resulted in lysis of healthy cell subsets known to express low levels of CD38, CDC in healthy donor leukocytes was assessed in vitro. HexaBody-CD38 (20 μg/mL) did not induce lysis of monocytes, B cells, T cells, granulocytes or erythrocytes, and only minor cytotoxicity of NK cells (median 13% lysis, range 9.5-55.1%). NK-cell lysis by daratumumab, assessed in parallel, was in the same range (median 8%, range 4.5-21.2%). Thus, HexaBody-CD38 shows superior potency in CD38-positive tumor cells while sparing healthy donor leukocytes and erythrocytes in vitro.

The anti-tumor activity of HexaBody-CD38 in vivo was evaluated in patient-derived AML and B-NHL xenograft (PDX) models in nude mice. In a screen using 9 B-NHL PDX models in a 1‑3 mice-per-treatment-group design, administration of two weekly doses of 5 mg/kg HexaBody-CD38 induced a strong anti-tumor response (relative tumor growth ≤10%, i.e. tumor stasis or tumor regression) in 2 models. Two models were classified as non-responder (relative tumor growth >70%) and 5 models could not be classified as either responder or non-responder (intermediates, relative tumor growth between 10 and 70%). A dose-response experiment in one of the responding models (Ly12638, 9 mice per group), confirmed potent anti-tumor activity of HexaBody-CD38, inducing complete tumor regression at a dose of 10 mg/kg (Figure 1A). In a screen using 5 AML PDX models in a 1‑3 mouse-per-treatment-group design, HexaBody-CD38 (5 mg/kg) induced a strong anti-tumor response in one model. One model was classified as non-responder and the remaining 3 models could not be classified as either responder or non-responder (intermediates). A dose-response experiment in one of the intermediate models (AML11810), demonstrated statistically significant and dose-dependent anti-tumor activity of HexaBody-CD38 in an in vivo study using a classical 9 mice per treatment group design (Figure 1B).

In summary, HexaBody-CD38 induced potent CDC in MM, B-NHL and AML cell lines, with superior potency compared to benchmark antibody daratumumab. HexaBody-CD38 was able to induce CDC in tumor cell lines with lower levels of CD38 expression, while sparing healthy leukocyte subsets. HexaBody-CD38 showed potent anti-tumor activity in vivo both in B-NHL and AML PDX models in nude mice. In these models, the contribution of mouse complement to the anti-tumor activity is limited and therapeutic activity is thought to be driven mainly through FcγR-mediated effector functions. This indicates that besides highly potent CDC, FcɣR-mediated effector mechanisms contribute to the preclinical activity of HexaBody-CD38 in hematological tumor models.

These preclinical data support clinical investigation of HexaBody-CD38 in CD38 positive hematologic malignancies, including MM, AML, and B cell lymphomas.