Abstract 204: Understanding breast cancer resistance to chemotherapy: Characterization of cancer cell sub-populations in residual and relapsed tumors
Authors: Aloia Andrea , Petrova Evgeniya , Deas Olivier , Banis Sophie , Ven Enora L. , Bosio Andreas , Hardt Olaf , Cairo Stefano , Judde Jean-Gabriel 
Published: May 2015

Abstract
Tumor recurrence fueled by residual tumor cells having survived chemotherapy represents the principal cause of breast cancer treatment failure. Triple-negative breast cancer (TNBC) is a heterogeneous disease at both molecular and cellular level, and the presence of different tumor cell sub-populations is likely the reason for this heterogeneity and for the incomplete response to neoadjuvant chemotherapy observed for most TNBC. To identify and isolate tumor cell sub-populations that resist to chemotherapy, we used a panel of 45 antibody fluorochrome conjugates in combination with multi-parameter flow cytometry to screen for the expression of a set of cell surface markers during the course of tumor chemotherapy. This set of markers represented both proteins involved in stem cell function and proteins known to be over-expressed in stem cells or cancer stem cell sub-populations. As a source of tumor samples, we used a panel of TNBC patient-derived xenografts (PDXs). These tumor models are known to preserve the morphology, molecular characteristics and drug response profile of the original patient tumors. We used TNBC PDX models to reproduce in vivo chemotherapy-induced tumor regression and relapse. Tumor dissociation, depletion of mouse cells and multi-parameter flow cytometry allowed us to measure the percentage of marker expression only in the fraction of human tumor cells.
We found that the expression of most of markers was very heterogeneous among the different TNBC models analyzed. In residual tumors, we observed enrichment or depletion of several cell populations expressing stem and cancer stem cell markers such as CD44+ and CD133/1+. Interestingly, in the majority of relapsed tumors, the percentage of these marker-positive cells shifted back to pre-treatment levels. Moreover, the percentage of certain tumor cell sub-populations was higher in untreated chemotherapy-resistant tumors compared to untreated chemotherapy-sensitive ones. To study the properties of enriched tumor cells sub-populations, we coupled cell separation of marker-positive tumor cells to large scale molecular analysis. Microarray-based gene expression analysis of sorted tumor cells revealed cell sub-populations with up-regulated signaling pathways related to stem cell function, cell migration or EMT. Further in vivo and in vitro assays with sorted sub-populations are currently being performed to search for possible functional role of selected markers during tumor resistance to chemotherapy and initiation of tumor relapse.
In summary, by coupling PDX and cell surface marker screening technologies, we have identified distinct tumor cell sub-populations which are associated with tumor resistance to chemotherapy. We believe that this approach will help gaining knowledge of tumor cell adaptation and selection in response to chemotherapy, which will ultimately lead to design tailored treatments for TNBCs.
Citation Format: Andrea Aloia, Evgeniya Petrova, Olivier Deas, Sophie Banis, Enora Le Ven, Andreas Bosio, Olaf Hardt, Stefano Cairo, Jean-Gabriel Judde. Understanding breast cancer resistance to chemotherapy: Characterization of cancer cell sub-populations in residual and relapsed tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 204. doi:10.1158/1538-7445.AM2014-204