A multi-stage process including transient polyploidization and EMT precedes the emergence of chemoresistent ovarian carcinoma cells with a dedifferentiated and pro-inflammatory secretory phenotype.

Verena Rohnalter,Rolf Müller,Florian Finkernagel,Till Adhikary,Katrin Roth,Maike Bensberg,Kristina Dorzweiler,Julia Obert,Sabine Müller-Brüsselbach

doi:10.18632/oncotarget.5552

Abstract

DNA-damaging drugs induce a plethora of molecular and cellular alterations in tumor cells, but their interrelationship is largely obscure. Here, we show that carboplatin treatment of human ovarian carcinoma SKOV3 cells triggers an ordered sequence of events, which precedes the emergence of mitotic chemoresistant cells. The initial phase of cell death after initiation of carboplatin treatment is followed around day 14 by the emergence of a mixed cell population consisting of cycling, cell cycle-arrested and senescent cells. At this stage, giant cells make up >80% of the cell population, p21 (CDKN1A) in strongly induced, and cell numbers remain nearly static. Subsequently, cell death decreases, p21 expression drops to a low level and cell divisions increase, including regular mitoses of giant cells and depolyploidization by multi-daughter divisions. These events are accompanied by the upregulation of stemness markers and a pro-inflammatory secretory phenotype, peaking after approximately 14 days of treatment. At the same time the cells initiate epithelial to mesenchymal transition, which over the subsequent weeks continuously increases, concomitantly with the emergence of highly proliferative, migratory, dedifferentiated, pro-inflammatory and chemoresistant cells (SKOV3-R). These cells are anchorage-independent and grow in a 3D collagen matrix, while cells on day 14 do not survive under these conditions, indicating that SKOV3-R cells were generated thereafter by the multi-stage process described above. This process was essentially recapitulated with the ovarian carcinoma cell line IGROV-1. Our observations suggest that transitory cells characterized by polyploidy, features of stemness and a pro-inflammatory secretory phenotype contribute to the acquisition of chemoresistance.

Highlights

Ovarian cancer ranks fifth as the cause of death from cancer in women with >20,000 new cases annually in the United States, >40,000 in the European Union and >50% of new cases diagnosed worldwide in developing countries [1]
SKOV3 cells are moderately sensitive to CPT, but highly resistant cells can be selected for after drug exposure. Using this experimental system we found an ordered sequence of events that preceded the emergence of chemoresistance, which could essentially be recapitulated with TP53mutated IGROV-1 cells, an ovarian cancer cell line most likely of low-grade serous adenocarcinoma origin [53, 56]
After an initial phase of cell death mainly resulting from mitotic catastrophe, as indicated by the interphase cells with multiple micronuclei, CPT-treated SKOV3 cells showed typical temporal alterations of cell morphology associated with profound changes in size, resulting in highly resistant cells after 21 weeks (Figure 1A, 1B; subsequently referred to as SKOV3-R cells)

Summary

Introduction

Ovarian cancer ranks fifth as the cause of death from cancer in women with >20,000 new cases annually in the United States, >40,000 in the European Union and >50% of new cases diagnosed worldwide in developing countries [1]. Ovarian cancer has a dire prognosis with an overall 5-year survival rate of

Methods

Results

Conclusion