LAUSR

The Notch signaling pathway, particularly endothelial Notch signaling, plays a key role in tumor formation and angiogenesis. Inhibiting Notch1 or its ligand, Delta-like ligand 4 (Dll4), can induce hypersprouting of the tumor vasculature and thus can reduce tumor perfusion and progression. However, due to the expression of Notch1 in multiple healthy cell types, pharmacologic blockade poses the challenge of inducing tissue hypoxia, vascular neoplasms, and toxicity in non-target tissues. Unlike Notch1, Notch4 expression is largely restricted to endothelium and is upregulated in models of triple negative breast cancer (TNBC). Loss of Notch4 in mice results in delayed developmental angiogenesis and reduced mammary tumor angiogenesis and perfusion. Therefore, Notch4 is an attractive potential pharmacologic target to interfere with tumorigenesis and minimize nonspecific toxicity. We determined that Notch4 is expressed primarily in tumor endothelium in both human and mouse mammary tumors, including murine syngeneic Py8119 tumors, as well as a selection of other human and syngeneic mouse tumor types such as B16F10 melanoma tumors. We explored the effects of Notch4 inhibition on the progression of murine mammary epithelial carcinoma using newly developed anti-Notch4 antibodies, 6-3-A6 and its humanized derivative E7011. Administration of E7011 or 6-3-A6 to orthotopically implanted Py8119 murine breast carcinoma and B16F10 melanoma significantly reduced tumor size in comparison to IgG-treated controls. We performed single cell RNA sequencing of Py8119 tumors treated with E7011 and found that although Notch4 transcripts were found specifically in the endothelium, the most notable effect of E7011 was a dramatic increase in the number of macrophages and cancer-associated fibroblasts, suggesting a non-cell autonomous effect. To examine the potential role of these immune cell population changes in facilitating E7011’s anti-tumor activity, we investigated treatment of Py8119 murine mammary carcinomas in the absence of macrophages. Administration of clodronate liposomes to eliminate macrophages blocked the anti-tumor effects of E7011 treatment. Taken together, our data suggests that tumor endothelial Notch4 promotes TNBC growth by altering the immune landscape and increasing anti-tumor macrophage recruitment, and that blockade via the novel anti-Notch4 E7011 antibody has potential therapeutic efficacy. Citation Format: Jason W. Eng, L.A. Naiche, Bhairavi Swaminathan, Yu Kato, Krishna Thakkar, Katherine Ann Alexander, Rahul Vadakath, James H. Herts, Rajyasree Emmadi, Junji Matsui, Jan K. Kitajewski. Notch4 inhibition by a novel neutralizing antibody reduces tumor progression and increases macrophage recruitment within the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB009.