Abstract 795: Epigenetics, cell cycle and drug-resistant ovarian cancer

Epithelial ovarian cancer (EOC) is the most lethal of the gynaecological malignancies and currently stage III/IV disease is associated with a 25% 5 year survival rate. A major factor associated with advanced EOC is the development of drug resistant disease, characterised by a lack of response to platinum and taxane based agents. In an effort to clarify mechanisms underlying chemorefractory EOC we have developed a number of drug resistant cancer cell lines. DNA microarray screening of drug resistant versus drug sensitive cell lines (combining a methylation reversal step using demethylating agents) indicated down-regulation of a number of genes with evidence of epigenetic silencing by promoter methylation in many cases. We have identified P57kip2 a cyclin dependent kinase inhibitor (CDKi) as a gene that is subjected to methylation in carboplatin-resistance, as shown in the PEO1CarbR line. Using a siRNA approach, silencing of the p57kip2 gene in drug sensitive parental PEO1 or SKOV-3 cells gave rise to a reduced sensitivity to platinum agents i.e. cisplatin or carboplatin as assessed using apoptosis with the annexinV assay and flow cytometry. Using chemosensitivity testing (MTT) of PEO1 parental and PEO1CarbR lines versus seliciclib (a CDK2 inhibitory drug) we saw an association with sensitivity to this agent with down-regulation of p57kip2. The IC50 values obtained for the human ovarian cancer cell line PEO1 and PEO1CarboR were 27.4 and 19.2μM, respectively (p =