Abstract 3050: Multimeric IgM antibodies targeting DR5 are potent and rapid inducers of tumor cell apoptosis and cell death in vitro and in vivo
Authors: Wang Beatrice , Kothambawala Tasnim , Wang Ling , Saini Avneesh , Baliga Ramesh , Sinclair Angus , Keyt Bruce 
Published: August 2019

Abstract
The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its functional receptors, death receptor 4 (DR4) and death receptor 5 (DR5) are attractive anti-tumor targets because of their ability to directly induce apoptosis in cancer cells. Though several agonistic IgG antibodies targeting DR5 have demonstrated evidence of preclinical efficacy, little evidence of clinical efficacy was observed likely due to insufficient receptor crosslinking in the tumor microenvironment. We have developed a novel multivalent IgM antibody targeting DR5 that effectively clusters the receptor and rapidly induces apoptosis and tumor cell cytotoxicity. In Colo205 colorectal tumor cells, anti-DR5 IgM induced caspase activation was detected within 30 minutes and by 2 hours nearly all cells had undergone apoptosis, demonstrating a more rapid and greater magnitude of apoptotic induction than anti-DR5 IgG. In an in vitro cytotoxicity screen of solid and hematologic tumor cell lines, an IgM antibody targeting DR5 ranged from 100-fold to greater than 10,000-fold more potent compared to IgG targeting DR5, and IgM was potent on cell lines resistant to IgG crosslinking mediated cell death. In vivo, anti-DR5 IgM induced tumor eradication in the Colo205 model, tumor regression in the IgG-resistant colorectal HCT15 model, and significantly extended overall survival in the B-cell leukemia model Nalm-6 even though dosing was only within the first week of study. In all in vivo studies the IgM was significantly more efficacious than IgG targeting DR5. The DR5 targeting IgM antibody was also efficacious in large established Colo205 tumors up to 600 mm3 in volume and in colorectal patient-derived xenograft (PDX) models as well. When administered in conjunction with standard of care chemotherapy Irinotecan, anti-DR5 IgM induced durable tumor regression in the HCT15 colorectal carcinoma model with 14 out of 30 animals from 2 separate studies tumor free at the end of study (day 71); no animals dosed with IgG were tumor free. In a less sensitive pancreatic model BxPC3, combination of standard of care Gemcitabine with anti-DR5 IgM resulted in an additive effect, while the IgG plus Gemcitabine efficacy was more modest and not statistically significant compared to Gemcitabine alone. Taken together, these results demonstrate that efficient IgM clustering of DR5 is significantly more potent in vitro and in vivo than IgGs and support the development of a human IgM antibody therapeutic targeting DR5 with the potential to treat both solid and hematologic tumors.
Citation Format: Beatrice Wang, Tasnim Kothambawala, Ling Wang, Avneesh Saini, Ramesh Baliga, Angus Sinclair, Bruce Keyt. Multimeric IgM antibodies targeting DR5 are potent and rapid inducers of tumor cell apoptosis and cell death in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3050.