Isolation of an epigenetically defined cisplatin tolerant proliferative population from a chemosensitive ovarian cancer cell line


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Alun Passey1,Bob Brown1
1Imperial College London

Abstract

Background

Epithelial ovarian cancer (EOC) has a poor prognosis in part due to recurrence of chemoresistant disease after treatment with platinum based therapy. Little is known about how populations of ovarian cancer cells are initially able to tolerate cytotoxic drugs before evolution of chemoresistant disease. Previous studies have demonstrated the presence of “drug tolerant persistent populations” within chemosensitive cancer cell lines are defined by expression of chromatin regulating enzymes.

Method

A2780 cells were treated with a regimen of four days IC50 dose of cisplatin followed by colony formation after 10 days, cells were then harvested for analysis. IC50 for cisplatin was determined by MTS assay. SAHA, GSK343 and JQ1 were used for the inhibition of HDACs, EZH2 and BRD4 respectively. Cancer stem cell content was assessed by ALDEFLOURTM assay.

Results

A2780 cells when cultured for four days in IC50 dose of cisplatin and allowed to recover and form colonies over 10 days showed a 3-fold increase in resistance to cisplatin in contrast to untreated cells or cells treated for only 2 days. These were termed cisplatin tolerant proliferative populations which showed loss of resistance after 5 passages indicating a temporary drug tolerant phenotype. The tolerant population did not show evidence of an enriched cancer stem cell population. These tolerant populations were resensitised to cisplatin by inhibition of histone deacetylases, EZH2 and BRD4.

Conclusion

We identified a population of cells derived from a chemosensitive ovarian cancer cell line which continue to proliferate after cisplatin treatment and shows reversible increased resistant to cisplatin, which are sensitised by inhibition of enzymes which modulate the chromatin state.  These data indicate that treatment of chemosensitive cancer cells with short, relatively low doses of cisplatin select for a proliferative cell population with a differentially regulated chromatin state which is better able to tolerate cisplatin. 

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