Abstract B48: Intratumor ploidy heterogeneity as a chemoresistance mechanism in triple-negative breastcancer

Abstract

Abstract Background: Triple negative breast cancers (TNBC) are aggressive, heterogeneous tumors, and currently lack targeted therapies. Chemotherapy is the mainstay treatment, but tumor recurrence is a major cause of mortality and morbidity. Chemotherapy may select for resistant subclones that have a survival advantage over the bulk population of cancer cells and cause tumor relapse. DNA aneuploidy (abnormal number of chromosomes) is a common genetic feature in breast cancer and has been frequently associated with poor prognosis. Although, aneuploid or polyploid cancer cells can contribute to intratumor ploidy heterogeneity, their functional role in tumorigenesis and chemoresistance is largely undefined. Traditionally, polyploid cells were thought to arise due to defects in cell division and were considered to be senescent. However, recent reports have shown that polyploid cells represent a viable and proliferating subpopulation within a tumor and may have a direct role in regulating chemoresistance. Methods: In this study, we isolated and functionally characterized the diploid and polyploid sub-populations derived from TNBC cell lines. DNA ploidy was assessed in Hoechst 33342 stained cells using flow cytometry. Cells with greater than 4N DNA content were considered as polyploid. Next, we analyzed cell proliferation in HCC1937 cells using CFSE and DNA labeling. Live-cell imaging was performed on flow-sorted diploid and polyploid cells using IncuCyte Zoom to monitor cell proliferation in the absence and presence of mitotic inhibitor (docetaxel). Results: DNA ploidy analysis identified presence of polyploid cells in HCC1395 and HCC1937 cell lines at a frequency of 6.7% and 5.8% respectively. Polyploid cells have higher forward-scatter than diploid cells suggesting that they are larger in size. In addition, nuclear staining with Hoechst 33342 showed that giant polyploid cells contain enlarged and/or multiple nuclei. Time-lapse microscopy in polyploid cells revealed mitotic structures suggestive of multipolar cell division. Carboxyfluorescein diacetate, succinimidyl ester (CFSE) labeling showed that polyploid cycle slower than the predominant diploid population. Further, the IncuCyte cell proliferation assay also confirmed that sorted polyploid cells divide slower than the diploid cells and displayed resistance to docetaxel. Concusions: These findings indicate that there are functional differences between diploid and polyploid sub-populations. In our future studies, we will examine the isolated diploid and polyploid cells for differences in their tumorigenic potential and role in tumor recurrence. Citation Format: Rekha Gyanchandani, Adrian Lee. Intratumor ploidy heterogeneity as a chemoresistance mechanism in triple-negative breastcancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B48.