Abstract 1513: Analysis of spatiotemporal phenotypic heterogeneity in chemoresistant triple negative breast cancer using imaging mass cytometry
Authors: Rinkenbaugh Amanda L. , Sinha Vidya C. , Echeverria Gloria V. , Zhang Xiaomei , Shao Jiansu , Symmans W. Fraser , Moulder Stacy L. , Piwnica-Worms Helen 
Published: September 2020

Abstract
Tumors are increasingly appreciated as complex ecosystems, wherein functional interactions between tumor subclones, as well as components of the microenvironment, contribute to progression and drug resistance. While some studies have focused on soluble factors that mediate these interactions, little is known about the communication between physically neighboring tumor subclones (and their microenvironment). To investigate the nature and impact of such localized interactions, we are assessing the activation status of key cancer signaling pathways in neighboring tumor cells; importantly, we are characterizing these features at the single cell level within physically intact tumors. Triple negative breast cancer (TNBC) exhibits a high degree of intratumor heterogeneity, which has contributed to a lack of effective targeted therapy options. Chemotherapy remains the standard of care; however approximately half of patients have substantial residual disease following chemotherapy, which is associated with a high risk of recurrence. Our objective is to spatially define signaling heterogeneity using patient-derived xenograft (PDX) models before and after chemotherapy treatment, to determine if spatially-defined signaling niches drive chemoresistance in TNBC. We hypothesize that neighborhoods of cells possess specialized phenotypes that mediate chemoresistance, and when disrupted, will inhibit the growth of chemoresistant tumors. We are employing imaging mass cytometry (IMC),a next-generation immunostaining approach that allows for simultaneous measurement of 30-40 biomarkers while retaining the spatial organization of the sample.Wehave constructed an IMC panel of antibodies that combines markers for tissue architecture, tumor and immune cell phenotyping, and signaling pathway activation. Our PDX collection features sequential pairs derived from biopsies taken before and after chemotherapy treatment. IMC of the pre-/post-chemotherapy pairs revealed spatial patterns of pathway activation that emerged following treatment, including increases in PI3K/mTOR and localized MAPK signaling. To complement these studies, we treated PDX models with chemotherapy and analyzed tumors via IMC throughout the course of treatment. Again, we observed the emergence of increased MAPK signaling, localized to discrete neighborhoods within the tumor. Taken together, our findings suggest that unique signaling niches arise following treatment. Our goal is to now determine whether these signaling niches functionally contribute to chemoresistance and if disruption of these niches can inhibit the growth of chemoresistant disease.
Citation Format: Amanda L. Rinkenbaugh, Vidya C. Sinha, Gloria V. Echeverria, Xiaomei Zhang, Jiansu Shao, W. Fraser Symmans, Stacy L. Moulder, Helen Piwnica-Worms. Analysis of spatiotemporal phenotypic heterogeneity in chemoresistant triple negative breast cancer using imaging mass cytometry [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1513.