Abstract C128: Development of therapeutic anti-Jagged1 monoclonal antibodies

Background: The Notch pathway is an evolutionarily conserved cell-signaling system that plays an important role in both physiologic and pathologic conditions such as embryonic development and cancer. In the latter, Notch signaling has been reported to promote tumor growth by regulating different aspects of tumor biology such as cell survival, proliferation, angiogenesis, and stemness. Because of its importance, targeting of this pathway has been attempted via both small molecules (γ-secretase inhibitors; GSIs) and neutralizing antibodies (against individual Notch receptors or DLL4 ligand) but limitations still hamper the clinical use of such therapeutics, generally due to pathway complexity and toxicities caused by complete pathway inhibition (GSIs). Targeting Notch ligands such as Jagged1 (JAG1), offers the opportunity to selectively block specific elements of the pathway important in tumor biology thus avoiding normal tissue toxicities. Methods : Structural studies defined a region of JAG1 (DSL + EGF1-3) that bound Notch1, which was used as an immunogen. Using classical hybridoma technology we have generated and subsequently characterised a panel of monoclonal antibodies (mAbs) against the JAG1 ligand, both in vitro (cell signaling and cell biology assays) and in vivo (tumor xenografts in both mice and rats). Results : Four functional blocking mAbs recognised a unique JAG1 epitope within its DSL domain binding interface with Notch1, effectively blocking ligand-receptor interaction in vitro . Importantly, our mAbs were cross-reactive with rat Jag1 but not the murine orthologue. These were able to inhibit endogenous JAG1-induced signaling in tumor and stromal cells (eg. vascular smooth muscle cells). JAG1 mAb treatment reduced in vitro breast cancer 3D growth, exhibiting reduced expression of important genes such as HES1 , IL6 and decreased numbers of cancer stem cells. Treatment did not affect JAG2-induced growth, or signaling mediated by other Notch ligands (eg. DLL4), confirming mAb specificity. Importantly, JAG1 mAb treatment in vivo inhibited Notch signaling and tumor growth in cancer xenograft models in two different host animals. Host body weight, blood tests and histological analysis detected no toxicity. Conclusions : We generated neutralizing mAbs able to inhibit JAG1-induced signaling both in vitro and in vivo . The ability of JAG1 blockade to impair tumor growth without toxicity indicates it has the potential to make a contribution to the current arsenal of cancer therapeutics. This mAb treatment will be subjected to further in vivo testing, both alone and in combination with other therapeutic approaches, to further expand our knowledge of its clinical potential and mechanism of action. Funding and conflicts of interest This work is supported by Cancer Research UK and the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre Programme. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health. We have filed a patent application, WO/2014/111704, claiming therapeutic use of the JAG1 antibodies. Citation Format: Massimo Masiero, Demin Li, Pat Whiteman, Carol Bentley, Jenny Greig, Tasneem Hassanali, Sarah Watts, Stephen Stribbling, Jenna Yates, Ji-Liang Li, Susan Mary Lea, Penny Ann Handford, Adrian Llewellyn Harris, Alison Hilary Banham. Development of therapeutic anti-Jagged1 monoclonal antibodies. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C128.