Triple negative breast cancer initiating cell subsets differ in functional and molecular characteristics and in γ‐secretase inhibitor drug responses

Diana J Azzam,Jun Sun,Dorraya El‐Ashry,Andy J Minn,Joyce M Slingerland,Xiaoqing Han,Seth A Wander,Anthony J Capobianco,Prathibha Ranganathan,Dekuang Zhao,Katherine Drews‐Elger,Candace A Gilbert,Manuel Picon‐Ruiz

doi:10.1002/emmm.201302558

Abstract

Increasing evidence suggests that stem-like cells mediate cancer therapy resistance and metastasis. Breast tumour-initiating stem cells (T-ISC) are known to be enriched in CD44+CD24neg/low cells. Here, we identify two T-ISC subsets within this population in triple negative breast cancer (TNBC) lines and dissociated primary breast cancer cultures: CD44+CD24low+ subpopulation generates CD44+CD24neg progeny with reduced sphere formation and tumourigenicity. CD44+CD24low+ populations contain subsets of ALDH1+ and ESA+ cells, yield more frequent spheres and/or T-ISC in limiting dilution assays, preferentially express metastatic gene signatures and show greater motility, invasion and, in the MDA-MB-231 model, metastatic potential. CD44+CD24low+ but not CD44+CD24neg express activated Notch1 intracellular domain (N1-ICD) and Notch target genes. We show N1-ICD transactivates SOX2 to increase sphere formation, ALDH1+ and CD44+CD24low+cells. Gamma secretase inhibitors (GSI) reduced sphere formation and xenograft growth from CD44+CD24low+ cells, but CD44+CD24neg were resistant. While GSI hold promise for targeting T-ISC, stem cell heterogeneity as observed herein, could limit GSI efficacy. These data suggest a breast T-ISC hierarchy in which distinct pathways drive developmentally related subpopulations with different anti-cancer drug responsiveness.

Highlights

Many cancers appear to be driven by stem‐like cells that self‐ renew, differentiate to yield heterogeneous progeny and survive (1) Braman Family Breast Cancer Institute, Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, FL, USA (2) Department of Biochemistry and Molecular Biology, University of Miami Miller School of Medicine, Miami, FL, USA (3) Sheila and David Fuente Cancer Biology Program, Miami, FL, USA (4) Department of Radiation Oncology, Abramson Family Cancer ResearchInstitute, University of Pennsylvania, Philadelphia, PA, USA (5) Molecular Oncology, Department of Surgery, Sylvester ComprehensiveCancer Center, Miami, FL, USA (6) Department of Medicine, University of Miami Miller School of Medicine,ß 2013 The Authors
Surface CD44 and CD24 expression were assayed in established breast cancer lines and in seven patient‐ derived triple negative breast cancer (TNBC) dissociated tumour cultures (DTs)
Earlier work showed primary human CD44þCD24neg/lowESAþ breast cancer cells were enriched for Tumour‐initiating stem cell (T‐ISC), with

Summary

Introduction

While surface CD24 is observed in subsets of T‐ISC from liver (Lee et al, 2011), colon (Yeung et al, 2010) and pancreas (Li et al, 2007), the T‐ISC phenotype described for primary breast cancers show negative or low level surface CD24 (CD44þCD24neg/low; Al Hajj et al, 2003). This contrasts with normal mammary progenitors cells, which express CD24 (Pece et al, 2010; Spike et al, 2012). It is noteworthy that CD24þ cells are increased in metastatic compared to primary breast cancers (Shipitsin et al, 2007)

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