Abstract 122: The subclonal dynamics of gross ploidy alterations in TNBC cells under chemotherapeutic pressure

Abstract

Abstract Solid tumors such as triple-negative breast cancer (TNBC) have characteristically high rates of aneuploidy and polyploidy. Chromosome-level aneuploidies are known to arise through errors in cytokinesis, but many of the mechanisms which drive large-scale ploidy alterations such as whole genome doubling (WGD) are still under investigation. WGD and subsequent ploidy reduction has been implicated as a key event in cancer evolution across patient samples. Further, in vitro studies have suggested that cells may undergo polyploidization to survive certain chemotherapies. Here, we apply lineage tracing technologies to test the hypotheses that some cells are primed to undergo WGD through endocycling or cell-cell fusion and that active polyploidization is a mechanism to resist chemotherapy. To deconvolve WGD by endocycling from WGD by cell-cell fusion, we transduced the TNBC cell line HCC1806 to create parallel populations with transcribed DNA barcodes on H2B-GFP or H2B-mCherry. All experiments were performed with homotypic cocultures containing equal proportion of cells from each fluorescent barcode population. With this method, ploidy alterations due to endoreplication were identifiable as monofluorescent single-barcoded cells with increased ploidy, while ploidy changes due to fusion were identifiable as double positive (GFP+mCherry+) double-barcoded cells with increased ploidy. The cell population was treated with an LD75 dose of doxorubicin and parallel plates were monitored by live-cell imaging. At each timepoint (pre-treatment, then 3, 5, and 14 days post-treatment), triplicate plates were stained with Hoechst and sorted into two fractions for lysis and DNA extraction: Near diploid (~2N) and ii) Hyperploid (> 4N). Barcode composition of cells from each fraction and each timepoint was determined through Illumina sequencing of barcode amplicons. Here, we will present preliminary results revealing the subclonal dynamics of gross ploidy alterations through normal culture conditions and chemotherapeutic perturbation. This study will elucidate whether pre-existing or de novo polyploidy promotes cell survival during chemotherapy, and determine if gross ploidy alterations occur randomly or through deterministic selection. Citation Format: Andrea L. Gardner, Lan Zheng, Patrik Parker, Kennedy Howland, Daylin Morgan, Amy Brock. The subclonal dynamics of gross ploidy alterations in TNBC cells under chemotherapeutic pressure [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 122.