Abstract 2480: Chemotherapy increases invasive cancer stem cells in breast cancer
Authors: Friedman Madeline , Duran Camille L. , Sharma Ved P. , Condeelis John S. , Oktay Maja H. , Karagiannis George S. , Entenberg David 
Published: April 2023

Abstract
Background: Metastasis is the leading cause of breast cancer (BC) death. To successfully metastasize, tumor cells must have both invasive and stem-like phenotypes. BC cells that express MenaINV, an invasive isoform of the actin regulatory protein Mena, have an enhanced ability to migrate and intravasate within the primary tumor, and extravasate at secondary sites. BC cells with a stem-like phenotype can withstand anoikis during hematogenous dissemination and initiate metastatic growth. Therefore, MenaINVHigh cancer stem cells (CSCs) have high metastatic potential and can be considered the most dangerous cells in the tumor. We recently showed that MenaINV and the CSC program can be induced independently in BC cells via direct contact with tumor associated macrophages (TAMs). Though chemotherapy improves survival, recent evidence shows that for some BC patients, chemotherapy may increase metastatic dissemination, though the reasons for this are unclear. Chemotherapy causes extensive cell death and a proinflammatory cytokine surge that recruits macrophages to the primary tumor and enhances the assembly of the tumor cell dissemination portals TMEM doorways. Given that TAM-tumor cell contact induces MenaINV and the CSC program in BC cells, we hypothesized that chemotherapy promotes dissemination by increasing TAM-tumor cell contact, leading to the induction of MenaINVHigh cells, CSCs, and “double positive” MenaINVHigh CSCs.
Methods: We used two models of BC (MMTV-PyMT mice bearing spontaneous mammary tumors, and HT17 patient-derived xenografts) which recapitulate metastatic triple-negative BC in mice. Mice were treated with paclitaxel (10 mg/kg, IV) every 5 days for a total of 3 treatments. Mouse subgroups received an additional treatment of liposomes with the macrophage-depleting agent clodronate (200 µL, 18.4 µM concentration, IP), or PBS control liposomes, every 2 days. Mammary tumors were evaluated for: (1) TAM density, (2) number of “single positive” cells - defined as those expressing high levels of Sox9 (CSC marker) or MenaINV (invasion marker) - and (3) the number of “double positive” MenaINVHigh CSCs (Sox9HighMenaINVHigh).
Results: We found that chemotherapy increased TAM density, and this corresponded with an increase in “double positive” MenaINVHigh CSCs. Upon macrophage depletion, MenaINVHigh CSCs fell to below baseline levels regardless of chemotherapy treatment. Chemotherapy did not increase “single positive” cells.
Conclusion: The induction of prometastatic MenaINVHigh CSCs during chemotherapy is macrophage dependent. The finding that chemotherapy only affected double positive cells suggests that MenaINV and the CSC program are induced together, rather than independently, by TAMs. Further work is required to determine the mechanism of this co-induction. These results lay the groundwork for novel microenvironment-based therapies to alleviate the prometastatic effects of chemotherapy in BC.
Citation Format: Madeline Friedman, Camille L. Duran, Ved P. Sharma, John S. Condeelis, Maja H. Oktay, George S. Karagiannis, David Entenberg. Chemotherapy increases invasive cancer stem cells in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2480.