Chemotherapy enriches for an invasive triple-negative breast tumor cell subpopulation expressing a precursor form of N-cadherin on the cell surface

// Erik R. Nelson 1,5 , Shenduo Li 4 , Margaret Kennedy 4 , Sturgis Payne 4 , Kelly Kilibarda 4 , Jeffrey Groth 4 , Michelle Bowie 4 , Edgardo Parilla-Castellar 4 , Gustaaf de Ridder 4 , Paul Kelly Marcom 4 , Matthew Lyes 4 , Bercedis L. Peterson 2 , Michael Cook 3 , Salvatore V. Pizzo 4 , Donald P. McDonnell 5 and Robin E. Bachelder 4 1 Department of Molecular and Integrative Physiology, University of Illinois at Urbana Champaign, Urbana and University of Illinois Cancer Center, University of Illinois at Chicago, Chicago, IL, USA 2 Department of Biostatistics and Bioinformatics, Duke University School of Medicine, Durham, NC, USA 3 Department of Immunology, Duke University School of Medicine, Durham, NC, USA 4 Department of Pathology, Duke University Medical Center, Durham, NC, USA 5 Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC, USA Correspondence to: Robin E. Bachelder, email: // Keywords : Precursor-N-cadherin, triple-negative breast cancer, invasion, metastasis, chemotherapy resistance Received : August 16, 2016 Accepted : October 07, 2016 Published : October 28, 2016 Abstract Background: Although most triple-negative breast cancer (TNBC) patients initially respond to chemotherapy, residual tumor cells frequently persist and drive recurrent tumor growth. Previous studies from our laboratory and others’ indicate that TNBC is heterogeneous, being composed of chemo-sensitive and chemo-resistant tumor cell subpopulations. In the current work, we studied the invasive behaviors of chemo-resistant TNBC, and sought to identify markers of invasion in chemo-residual TNBC. Methods: The invasive behavior of TNBC tumor cells surviving short-term chemotherapy treatment in vitro was studied using transwell invasion assays and an experimental metastasis model. mRNA expression levels of neural cadherin (N-cadherin), an adhesion molecule that promotes invasion, was assessed by PCR. Expression of N-cadherin and its precursor form (pro-N-cadherin) was assessed by immunoblotting and flow cytometry. Pro-N-cadherin immunohistochemistry was performed on tumors obtained from patients pre- and post- neoadjuvant chemotherapy treatment. Results: TNBC cells surviving short-term chemotherapy treatment exhibited increased invasive behavior and capacity to colonize metastatic sites compared to untreated tumor cells. The invasive behavior of chemo-resistant cells was associated with their increased cell surface expression of precursor N-cadherin (pro-N-cadherin). An antibody specific for the precursor domain of N-cadherin inhibited invasion of chemo-resistant TNBC cells. To begin to validate our findings in humans, we showed that the percent cell surface pro-N-cadherin (+) tumor cells increased in patients post- chemotherapy treatment. Conclusions: TNBC cells surviving short-term chemotherapy treatment are more invasive than bulk tumor cells. Cell surface pro-N-cadherin expression is associated with the invasive and chemo-resistant behaviors of this tumor cell subset. Our findings indicate the importance of future studies determining the value of cell surface pro-N-cadherin as: 1) a biomarker for TNBC recurrence and 2) a therapeutic target for eliminating chemo-residual disease.