Abstract 1073: Increased internalization and processing of the CD37-targeting antibody-drug conjugate, naratuximab emtansine (IMGN529), in the presence of rituximab leads to enhanced potency in diffuse large B-cell lymphoma models
Authors: Hicks Stuart W. , Lai Katharine C. , Yi Yong , Shah Prerak , Gavrilescu Cristina L. , Ponte Joe , Sloss Callum M. , Romanelli Angela 
Published: July 2017

Abstract
Naratuximab emtansine (IMGN529) is an investigational CD37-targeting antibody-drug conjugate (ADC) that has shown both preclinical and clinical activity in DLBCL . We have shown that rituximab, an anti-CD20 monoclonal antibody, enhances the preclinical activity of IMGN529. The combination of IMGN529 and rituximab is more active than either agent alone, and this benefit is associated with an increase in apoptosis and cell death, resulting in enhanced potency in DLBCL models. Efficacy of ADCs, such as IMGN529, relies on the internalization, intracellular trafficking and degradation of the ADC leading to the release of the cytotoxic catabolite. To explore the mechanism underlying the enhanced activity of the combination, we investigated the effect of rituximab treatment on the binding, internalization and processing of IMGN529 in vitro. To evaluate the effect on the internalization of IMGN529, DLBCL cell lines were incubated with fluorescently-labeled K7153A antibody (the CD37 targeting moiety of IMGN529) alone or in combination with rituximab or a non-targeting control antibody. K7153A internalization was similar whether incubated alone or with the non-targeting control. However, when cells were co-incubated with K7153A and rituximab, the internalization of K7153A significantly increased. This increase was also observed with other anti-CD20 antibodies suggesting an anti-CD20 class effect.
Radiolabeled processing studies were performed to determine if the observed increase in internalization led to a corresponding increase in antibody degradation, which is required for the release of the cytotoxic agent in IMGN529. By trace-labeling the K7153A antibody with tritiated propionate (3H-K7153A), we were able to follow binding, uptake, and degradation of the antibody component of IMGN529 in DLBCL cell lines. Following pulse exposure, the amount of 3H-K7153A degraded after 24 hours remained the same whether treated alone or in combination with other B-cell targeting antibodies. However, when combined with rituximab the percentage of degraded 3H-K7153A increased as much as 3-fold and a similar increase of 3H catabolite was generated. When compared, the combination of K7153A and rituximab produced considerably more catabolite (~6-fold, p-value &lt;0.0001) than the combination of rituximab and a CD19-targeting antibody.
These findings suggest a novel mechanism where the increased potency of IMGN529 and rituximab can be explained by CD20 binding resulting in an increase in internalization and degradation of IMGN529, leading to generation of greater amounts of cytotoxic agent. Overall, these data provide a biological rationale for the enhanced activity of the rituximab plus IMGN529 combination, further supporting the clinical development strategy of this combination in DLBCL.
Citation Format: Stuart W. Hicks, Katharine C. Lai, Yong Yi, Prerak Shah, Cristina L. Gavrilescu, Joe Ponte, Callum M. Sloss, Angela Romanelli. Increased internalization and processing of the CD37-targeting antibody-drug conjugate, naratuximab emtansine (IMGN529), in the presence of rituximab leads to enhanced potency in diffuse large B-cell lymphoma models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1073. doi:10.1158/1538-7445.AM2017-1073