Abstract
The alkylating agent platinum is first-line chemotherapy treatment for high-grade serous carcinomas (HGSC) of tubal-ovarian origin. Platinum compounds cause DNA damage and induce apoptotic cell death in the bulk tumor population. However, subpopulations of tumor cells may exhibit diverging behaviors from the bulk tumor due to an alternate stress response that diverts tumor cells from apoptotic death. In this study, we identified a salvage survival pathway in which G2-arrested tumor cells bypassed apoptosis and progressed through aberrant mitotic events to then emerge as a distinct subpopulation of viable large hyperploid cells but with uncertain long-term propagation potential. Platinum-induced large hyperploid cells were flow sorted and showed rare regrowth capacity as compared to their more proficiently regenerating non-hyperploid counterparts. However, detailed time-lapse microscopy provided direct evidence that these hyperploid cells were mitotically active and could divide successfully to produce viable daughter cells. The hyperploid survival response was observed across different cell lines and utilization of this survival pathway was dependent on the strength of the G2-M checkpoint. Conceivably, this salvage survival strategy may contribute to increased genomic diversity of the regenerating tumor cell line through a coupled hyperploidization and de-polyploidization process that may be relevant for drug resistance.
Highlights
High grade serous carcinoma (HGSC) of tubalovarian origin is an aggressive epithelial tumor with poor survival outcomes [1]
The cell cycle and DNA ploidy status are correlated with markers of key cellular programs such as the DNA damage response and G2-M cell cycle checkpoint pathway via immunofluorescence staining. As this approach analyzes all tumor cells within a population at the single cell level, distinct subpopulational responses to treatment within the bulk tumor cell line can be revealed. Using this refined technical approach, here we demonstrate that platinum treatment induces nuclear enlargement in the surviving cell population of several HGSC cell line models, and this in-vitro observation resembles closely to the morphologic changes seen in-vivo in patient tumors after neoadjuvant chemotherapy treatment
We have utilized an in-vitro experimental model system, coupled with a robust quantitative image-based analysis approach, to systematically study the cellular dynamics of tumor cell survivors after platinum treatment. This was motivated by observations from patient tumors of high grade serous carcinoma after neo-adjuvant chemotherapy treatment where a distinct surviving subpopulation of large bizarre tumor cells were observed in addition to the residual tumor cells retaining the usual morphologic features [15,16,17]
Summary
High grade serous carcinoma (HGSC) of tubalovarian origin is an aggressive epithelial tumor with poor survival outcomes [1]. Platinum drugs are used as part of first-line therapy and exert genotoxic effects to tumor cells [2]. For tumor cells lacking a functional G1-S checkpoint such as in high grade serous carcinoma where the retinoblastoma (RB) and p53 pathways are perturbed, an arrest in cell cycle at the G2 phase is critical for DNA damage repair [4,5,6]. The serine/threonine kinase CHEK1 (CHK1) is an important regulator of the G2-M checkpoint downstream of the ataxia telangiectasia and Rad3-related protein (ATR) kinase, activated by DNA damage from genotoxic agents or replicative stresses [7, 8]. By stalling cells at the G2 phase, proper DNA damage repair can be performed to allow cell survival whereas irreparable double strand breaks would lead to apoptotic death [12]
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