The temporal dynamics of chromosome instability in ovarian cancer cell lines and primary patient samples

Abstract

Epithelial ovarian cancer (EOC) is the most prevalent form of ovarian cancer and has the highest mortality rate. Novel insight into EOC is required to minimize the morbidity and mortality rates caused by recurrent, drug resistant disease. Although numerous studies have evaluated genome instability in EOC, none have addressed the putative role chromosome instability (CIN) has in disease progression and drug resistance. CIN is defined as an increase in the rate at which whole chromosomes or large parts thereof are gained or lost, and can only be evaluated using approaches capable of characterizing genetic or chromosomal heterogeneity within populations of cells. Although CIN is associated with numerous cancer types, its prevalence and dynamics in EOC is unknown. In this study, we assessed CIN within serial samples collected from the ascites of five EOC patients, and in two well-established ovarian cancer cell models of drug resistance (PEO1/4 and A2780s/cp). We quantified and compared CIN (as measured by nuclear areas and CIN Score (CS) values) within and between serial samples to glean insight into the association and dynamics of CIN within EOC, with a particular focus on resistant and recurrent disease. Using quantitative, single cell analyses we determined that CIN is associated with every sample evaluated and further show that many EOC samples exhibit a large degree of nuclear size and CS value heterogeneity. We also show that CIN is dynamic and generally increases within resistant disease. Finally, we show that both drug resistance models (PEO1/4 and A2780s/cp) exhibit heterogeneity, albeit to a much lesser extent. Surprisingly, the two cell line models exhibit remarkably similar levels of CIN, as the nuclear areas and CS values are largely overlapping between the corresponding paired lines. Accordingly, these data suggest CIN may represent a novel biomarker capable of monitoring changes in EOC progression associated with drug resistance.

Role of chromosomal instability in cancer progression

“…Moreover, since recent work has highlighted potential differences between some commonly used cancer cell lines and their intended tumour model, particularly in ovarian cancer (Anglesio et al 2013, Domcke et al 2013, it is critical to assess CIN mechanisms in cell line panels that represent the genetic features of their intended represented cancer type as closely as possible. In addition to carefully selecting cell lines to analyse, it may be advisable, where feasible, to move towards the classification of CIN mechanisms from tumour samples directly isolated from patients, such as circulating tumour cells (CTCs) or other forms of liquid biopsy such as ascites-derived tumour cells (Penner-Goeke et al 2017). Such efforts would not only alleviate concerns about applicability of tumourderived cell lines but also allow the assessment of CIN in a temporal manner (Penner-Goeke et al 2017).…”

“…In addition to carefully selecting cell lines to analyse, it may be advisable, where feasible, to move towards the classification of CIN mechanisms from tumour samples directly isolated from patients, such as circulating tumour cells (CTCs) or other forms of liquid biopsy such as ascites-derived tumour cells (Penner-Goeke et al 2017). Such efforts would not only alleviate concerns about applicability of tumourderived cell lines but also allow the assessment of CIN in a temporal manner (Penner-Goeke et al 2017). This would provide an important advancement of our understanding of the dynamics of CIN during tumour evolution.…”

Chromosome Instability; Implications in Cancer Development, Progression, and Clinical Outcomes

“…Alternatively, minimally invasive approaches including the isolation and analysis of circulating tumor cells (CTCs) or tumor cells isolated from serial ascites samples (fluid accumulation within the peritoneal cavity containing tumor cells) could be employed; however, ascites is only associated with certain tumor types and in only a small subset of individuals. In fact, Penner-Goeke and colleagues [22] recently identified unique temporal dynamics for CIN in drug-resistant and recurrent high-grade serous ovarian cancer. Furthermore, while the temporal approach allows for the calculation of an exact 'rate' of change, it is limited in that CIN is a highly heterogeneous phenotype that is not expected to be associated with a single 'rate'-rather, a spectrum of rates within a given population.…”

“…For example, solid tumors are comprised of neoplastic cells constituting the tumor parenchyma and reactive stroma, as well as the structural component comprised of connective tissues, the extracellular matrix, blood vessels, and cells of the adaptive and innate immune systems [96]. Analyses of biopsied materials collected from distinct tumor regions [97,98] along with repeated sampling over time [22,99] have identified significant cell-to-cell heterogeneity and ongoing genetic changes, respectively. Furthermore, patient-specific sequencing has also identified genetic heterogeneity as existing between primary and metastatic lesions (see Section 4) within the same patient and that is indicative of CIN and tumor evolution [100,101].…”

Mechanisms of Chromosomal Instability in High-grade Serous Ovarian Carcinoma

“…High-grade serous ovarian carcinoma (HGSC) represents an important clinical challenge; despite initial positive responses to first-line platinum therapy, most patients unfortunately relapse, leading to a poor overall survival for this disease 13 . HGSC genomes bear the scars of chromosomal instability as evidenced by highly aberrant genomic landscapes 4,14,15 and evidence of ongoing CIN has been demonstrated in ascites-derived HGSC cells 16 . There has been extensive interest in interpreting the mutational signatures encoded within tumour and cancer cell line genomes over recent years 17,18 .…”