Purpose: The cancer/germline antigen NY-ESO-1 is variably expressed in epithelial ovarian cancer (EOC), with most tumors showing low or heterogeneous expression, which limits patient responses to NY-ESO-1 vaccine therapy. We tested the hypothesis that promoter and global genomic DNA methylation status correlates with intertumor and intratumor NY-ESO-1 expression status in EOC.

Experimental Design: We utilized 78 EOC tumors and 10 normal ovary controls for quantitative DNA methylation analyses and NY-ESO-1 expression analysis by immunohistochemistry (IHC) and quantitative reverse transcriptase PCR. A subset of EOC tumors were used to perform microdissections of NY-ESO-1 IHC-positive and NY-ESO-1 IHC-negative tissue regions, followed by DNA methylation analyses. EOC cell lines were treated in vitro with decitabine to determine the functional contribution of DNA methylation to NY-ESO-1 gene regulation in EOC.

Results: Compared with normal ovary, bulk EOC tissues display increased NY-ESO-1 expression, reduced NY-ESO-1 promoter methylation, and reduced LINE-1 DNA methylation. However, NY-ESO-1 expression is not significantly associated with NY-ESO-1 promoter methylation status in bulk tumors. We hypothesized that this resulted from heterogeneous intratumor NY-ESO-1 expression. Supporting this idea, experiments using microdissected material revealed that intertumor and intratumor NY-ESO-1 expression heterogeneity is significantly correlated with promoter and global DNA methylation status in EOC. Moreover, decitabine treatment functionally restored NY-ESO-1 expression in nonexpressing EOC cell lines.

Conclusion: DNA methylation status is associated with both intertumor and intratumor NY-ESO-1 expression status in EOC. These findings support a novel chemoimmunotherapy approach using decitabine to augment NY-ESO-1 vaccine therapy for treatment of recurrent EOC.