Abstract C037: Chemotherapy causes de novo induction of invasive breast cancer cells
Authors: Friedman-DeLuca Madeline , Karagiannis George S. , Duran Camille L. , Sanchez Luis Rivera , Patel Prachiben P. , Shukla Suryansh , Barth Nicole D. , Sharma Ved P. , Papanicolaou Michael , Condeelis John S. , Oktay Maja H. , Entenberg David 
Published: November 2024

Abstract
Metastasis is the leading cause of breast cancer (BC) death, and tumor cells must migrate and invade to metastasize. BC cells that express the actin regulatory protein MenaINV have an enhanced ability to migrate and intravasate within the primary tumor, and extravasate at secondary sites. Though chemotherapy improves patient survival, treatment with paclitaxel, a chemotherapy used for BC, leads to upregulation of MenaINV and an increase in metastasis in mice. MenaINV expression can be induced in BC cells through Notch1 signaling with macrophages, which are often recruited to tumors in response to chemotherapy. MenaINV-expressing cells are also resistant to paclitaxel, begging the question of whether paclitaxel increases MenaINV by de novo induction or by selectively killing non-MenaINV-expressing cells. We hypothesized that paclitaxel causes de novo MenaINV induction by increasing macrophage-tumor cell Notch signaling. Understanding this pro-metastatic effect of chemotherapy is crucial to refining treatment strategies. MMTV-PyMT mice bearing spontaneous mammary tumors were used as a model of BC. Mice were treated with paclitaxel or vehicle every 5 days for a total of 3 treatments. To study the role of macrophages in the paclitaxel-mediated MenaINV increase, in addition to paclitaxel, one cohort of mice was co-administered the macrophage-depleting agent clodronate or vehicle. To study the role of Notch signaling, a second cohort of mice was co-administered the Notch inhibitor DAPT or vehicle. Immunofluorescence staining was used to evaluate tumors for: %MenaINV+ area, proportion of apoptotic cells, macrophage density, and macrophage expression of Notch ligands Jag1 and Jag2. Paclitaxel-treated tumors expressed significantly more MenaINV even when tumor cell death did not increase, indicating that chemotherapy increases MenaINV expression by induction. Both macrophages and Notch signaling were needed for this effect to occur. Interestingly, paclitaxel did not increase macrophage infiltration or macrophage expression of Notch ligands, suggesting that paclitaxel may increase MenaINV by acting on tumor cells to promote Notch signaling. Paclitaxel causes de novo MenaINV induction that is macrophage- and Notch-dependent. Studies aiming to further elucidate the mechanism behind paclitaxel-mediated MenaINV induction are ongoing. These results lay the groundwork for novel microenvironment-based therapies to alleviate the pro-metastatic effects of chemotherapy in BC.
Citation Format: Madeline Friedman-DeLuca, George S. Karagiannis, Camille L. Duran, Luis Rivera Sanchez, Prachiben P. Patel, Suryansh Shukla, Nicole D. Barth, Ved P. Sharma, Michael Papanicolaou, John S. Condeelis, Maja H. Oktay, David Entenberg. Chemotherapy causes de novo induction of invasive breast cancer cells [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr C037.