Preclinical Mechanistic Studies Investigating Neutrophil and Lymphoid Cell Depletion By IMGN529, a CD37-Targeting Antibody-Drug Conjugate (ADC)

• Published in: Blood 2014-12, Vol.124 (21), p.3119-3119
• Main Authors: Deckert, Jutta, Ponte, Jose F., Coccia, Jennifer A., Lanieri, Leanne, Chicklas, Sharon, Yi, Yong, Watkins, Krystal, Ruiz-Soto, Rodrigo, Romanelli, Angela, Lutz, Robert J.
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V124.21.3119.3119

CD37 is a surface antigen widely expressed on malignant B cells in non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL). In normal tissues, CD37 expression is restricted to lymphoid tissues and blood cells, with high levels of expression on B lymphocytes and low levels on non-B lymphoid and myeloid cells. IMGN529 is a CD37-targeting ADC currently in a Phase I clinical study in adult patients with relapsed or refractory NHL (NCT01534715). This ADC uniquely combines the intrinsic pro-apoptotic and immune effector activities of its anti-CD37 antibody component with the potent cytotoxic mechanism provided by targeted delivery of its maytansinoid payload, DM1. In the Phase I study, IMGN529 has demonstrated early evidence of clinical activity. A reduction in lymphocyte counts was also observed in the majority of patients after dosing, consistent with the proposed mechanism of action of a CD37-targeted therapy. However, in the initial dose-escalation phase, some patients experienced transient, early-onset neutropenia. To investigate the potential mechanisms of this transient neutropenia observed in patients, different pre-clinical models were considered and utilized to recapitulate clinical findings. In vitro studies with peripheral blood cells from normal human donors demonstrated that incubation with IMGN529 for 1 hour or 24 hours resulted in significant B-cell depletion with no apparent neutrophil depletion detected, similar to observations after rituximab treatment. In contrast, alemtuzumab treatment in vitro resulted in both B-cell and neutrophil depletion. This is consistent with the high level of CD37 expression on target B cells and the relatively low CD37 expression level on other blood cells. Analysis of cytokine release by normal human donor peripheral blood cells incubated with IMGN529 revealed increased levels of IL-8, CCL2 (MCP-1) and CCL4 (MIP-1β), but not IL-6 or TNF, to a similar extent as rituximab but less pronounced than alemtuzumab. An anti-murine CD37 antibody was identified to enable in vivo studies in a murine model and characterize CD37 expression on murine blood cells. Similar to the expression profile of CD37 in human peripheral blood cells, CD37 expression on murine peripheral blood cells was highest in B cells, with much lower expression seen on T cells and granulocytes. In vivo activity of the anti-muCD37 antibody and the corresponding ADC, with the same SMCC-DM1 linker-payload combination as IMGN529, was evaluated to di