Antimitogenic and chemosensitizing effects of the methylation inhibitor zebularine in ovarian cancer

Abstract

Deoxycytosine methylation within CpG islands of tumor suppressor genes plays a prominent role in the development and progression of drug-resistant ovarian cancer. Consequently, epigenetic therapies directed toward tumor suppressor demethylation/reexpression could potentially reverse malignant phenotypes and chemosensitize recalcitrant tumors. In this report, we examined the demethylating agent zebularine [1-(B-D-ribofuranosyl)-1,2-dihydropyrimidin-2-one], in comparison with the well-known methylation inhibitor 5-aza-2V -deoxycytidine (5-aza-dC), for its ability to inhibit ovarian cancer cell proliferation and to demethylate and induce tumor suppressor genes. Zebularine exerted significant (>5-aza-dC) antiproliferative effects against the ovarian cancer cell lines Hey, A2780, and the cisplatin-resistant A2780/CP in a dose-dependent manner (65% versus 35% inhibition at 48 hours, zebularine versus 5-aza-dC). Moreover, 48-hour treatment with 0.2 mmol/L zebularine significantly induced demethylation of the tumor suppressors ras-associated domain family 1A and human MutL homologue-1. RASSF1A gene reexpression was also observed, as was reexpression of two other tumor suppressors, ARHI and BLU, although levels differed from those induced by 5-aza-dC. Global analyses of DNA methylation revealed similar overall demethylation (2.5-to 3-fold) by 5-aza-dC and zebularine as determined by methyl acceptance assay. However, differences in demethylation of individual loci were observed as determined by differential methylation hybridization. Finally, we found that zebularine could resensitize the drugresistant cell line A2780/CP to cisplatin, with a 16-fold reduction in the IC 50 of that conventional agent. In summary, zebularine seems to be a promising clinical candidate, singly or combined with conventional regimens, for the therapy of drug-resistant ovarian cancer.

Inhibition of Breast Cancer Cell Growth In vitro and In vivo: Effect of Restoration of Wwox Expression

“…Previous studies showed that the fragile WWOX gene is inactivated in a significant fraction of breast cancers (8,9), mainly due to DNA hypermethylation (13). DNA hypermethylation can be reversed by DNA methyltransferase inhibitors, such as DAC (24) or zebularine (25), agents that have therapeutic potential for cancers. Thus, we determined if restoration of Wwox expression in breast cancer cells lacking expression of endogenous Wwox would reverse cancer cell growth despite the numerous genetic alterations that have accumulated in breast cancer cells.…”

DNA Demethylating Antineoplastic Strategies: A Comparative Point of View

“…In addition, exposure to dZTP leads to reexpression of the cell cycle and apoptosis modulator RASSF1A after demethylation of its promoter in ovarian cancer cells and in a lymphoma mouse model. [62][63][64] However, higher doses of dZTP are required to obtain demethylation and gene reexpression levels comparable to those induced by azanucleosides. This may be because of its lower binding affinity for uridine/cytidine kinase, the enzyme responsible for nucleoside analog activation, or its sequestration by cytidine deaminase.…”

Epigenetic Therapies for Cancer

“…Although this drug works in a manner similar to 5-Aza-CR and 5-Aza-CdR, it is more stable and less toxic than 5-Aza-CR and 5-Aza-CdR DNMTis (Zhou et al, 2002;Cheng et al, 2003). In line with these findings, zebularine has been shown to reactivate tumor suppressor genes (Flotho et al, 2009;Billam et al, 2010), enhance tumor cells' chemotherapy and radiation sensitivity (Dote et al, 2005), exert angiostatic and antimitogenic activities (Balch et al, 2005;Hellebrekers et al, 2006) and to be stable enough for oral administration (Zhou et al, 2002;Cheng et al, 2003). In addition, at low doses, zebularine can be given to patients continuously without the overt cytoxicity associated with 5-Aza-CR and 5-Aza-CdR.…”