Inhibition Of Notch Signaling By A Notchl Monoclonal Antibody Induces Robust Anti-Tumor Efficacy In T-Cell Acute Lymphoblastic Leukemia And Breast Cancer

Notch signaling is deregulated in T-cell acute lymphoblastic leukemia (T-ALL) and advanced solid tumors, making it an attractive target for oncology drug development. In this present report, we describe a novel mouse monoclonal antibody, Notch1 mAb, that specifically binds to the negative regulatory region (NRR) of human Notch1 receptor. Using a T-ALL cell line, HPB-ALL, that harbors mutations in Notch1 heterodimerization and PEST domains, we demonstrated that Notch1 mAb blocked Notch signaling by reduction of Notch1 intracellular domain (NICD) and down-regulation of Notch target genes, Hes-1 and cMyc. Notch1 mAb caused cell growth inhibition of HPB-ALL and several other T-ALL cell lines, via induction of cell cycle arrest and apoptosis. Notch1 mAb treatment resulted in robust NICD reduction and marked antitumor efficacy in HBP-ALL xenograft model. Additional mechanism-of-action studies revealed inhibition of tumor cell proliferation and induction of apoptosis in HPB-ALL tumors, suggesting that the anti-tumor activity of Notch1 mAb may be mediated by its direct effects on tumor cell growth or survival. Furthermore, this antibody led to a significant reduction in leukemia progenitor cells (LPCs) baring NOTCH1 mutation in bioluminescent humanized T-ALL LPC mouse models. In addition to its inhibitory effect on mutant Notch1, Notch1 mAb also displayed robust neutralization activity on wild type Notch1 and caused tumor growth inhibition in breast cancer models MDA-MB-231 and MX-1 by targeting the wild type receptor in these tumor types. Interestingly, using a gamma secretase inhibitor PF-03084014, we showed that Notch1 mAb and PF-03084014 elicited similar degree of biology responses in HPB-ALL cells. Our results indicate that antibodies that bind to NRR can act as potent inhibitors of Notch1 signaling and provide opportunities for development of novel cancer therapeutics for T-ALL and solid tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1765. doi:10.1158/1538-7445.AM2011-1765