In breast cancer, the primary tumor is usually not lethal, while metastatic spread to other organs is a frequent cause of death. Up to 20% of breast cancer diagnoses are triple negative breast cancer (TNBC) makes and late stage metastatic TNBC can have a 5-year survival as low as 11%. TNBC is unresponsive to hormonal and targeted therapies of other types of breast cancer. Surgery and adjuvant chemotherapy are effective treatment options for early stage disease, but there are very few therapeutic options for advanced metastatic TNBC spread. For metastasis to occur, circulating tumor cells (CTCs) must cross the endothelial barrier twice: first to migrate away from the primary tumor and enter systemic circulation (intravasation), and then to exit circulation to colonize other tissues (extravasation).

We are currently exploring the role of Jagged-1 (Jag1), a Serrate class Notch ligand, in the metastatic process. Jag1 is expressed in many human TNBC cell lines and its expression is associated with a worse prognosis in the clinic. Our data suggest that Jag1 presented on tumor cells promotes extravasation behavior, particularly TNBC binding to endothelium and subsequent transendothelial migration (TEM).

Our preliminary studies have blocked Jag1 function with the Notch decoy N110-24, which utilizes EGF-like repeats of the Notch1 receptor that unproductively bind Jag1. Treatment with N110-24 reduces the ability of D3H2LN cells, a Jag1high derivative of the MDA-MB-231, to attach endothelial cells in vitro. Treatment with N110-24 also impedes the ability of these highly metastatic human TNBC cells to migrate across a monolayer of human primary endothelial cells. We therefore conclude that Jag1-Notch signaling inhibition via N110-24 suppresses activities required for TEM of TNBC cells.

However, the mechanistic role of Jag1, however, is not understood in TEM. Both TNBC and endothelial cells express Jag1, and the aforementioned secreted decoys may target Jag1 signaling either within TNBC cells, within endothelial cells, or between cell types. We hypothesize that tumor expression of Jag1 is critical for metastasis. In order to explore the effects of tumor-derived Jag1 on tumor-intrinsic signaling, we have knocked out Jag1 in D3H2LN cells and generated multiple Jag1KO clonal lines, which have been interrogated for downstream transcriptional changes related to TEM. To explore the effects of tumor-derived Jag1 on neighboring endothelium, we are studying the extravasation capabilities of Jag1KO clonal lines using dynamic systems that will track TNBC adhesion, rolling, and TEM under dynamic flow in vitro as well as characterizing their metastatic potential in vivo. Our studies are elucidating a mechanism of Jag1-mediated metastasis via endothelial interactions.

Citation Format: Benjamin Gordon, Reyhaan A Chaudhri, Tim Sargis, LA Naiche, Jan K Kitajewski. The study of jag1-notch in the extravasation of triple negative breast cancer cells in metastasis [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS19-12.