Abstract LB-97: Combination of a conformationally restricted polyamine analogue with DNA methyltransferase or histone deacetylase inhibition induces synergistic reexpression of aberrantly silenced tumor suppressor genes

Abstract

Abstract Aberrant epigenetic silencing of tumor suppressor genes is common in the initiation and progression of cancer. It involves abnormal DNA methylation patterns and alterations in covalent histone modifications, together resulting in a local chromatin architecture that is transcriptionally silent. Previously developed epigenetic-targeting drugs, such as DNA methyltransferase (DNMT) inhibitors and histone deacetylase (HDAC) inhibitors, have had limited success in the clinical setting, partially due to dose-limiting toxicities. Studies have shown, however, that low doses of the two classes of inhibitors (HDAC and DNMT) can be combined to produce a synergistic anti-tumor effect, and various combinations of these inhibitors are now in clinical trials. Polyamines are organic polycations that are abundant in the cell and have a natural affinity for DNA. The current studies examine the effects of combining a specific polyamine analogue, PG-11047, with established epigenetic-targeting drugs, including the DNMT inhibitor, 5-azacytidine, and the HDAC inhibitor, MS-275, in a human lung cancer cell line. PG-11047 ((2Z)-N1, N4-bis[3-(ethylamino)propyl]-2-butene-1,4-diamine) is a conformationally restricted polyamine analogue currently undergoing clinical evaluation. Unlike several related polyamine analogues, PG-11047 is not a potent inhibitor of purified lysine-specific demethylase-1 (LSD1) in vitro. However, we found that treatment of human lung cancer cells with PG-11047 alone is capable of globally increasing levels of histone marks associated with active chromatin, including dimethylated lysine 4 of histone H3, suggesting inhibition of LSD1. Combining PG-11047 with either 5-azacytidine or MS-275 resulted in synergistic increases in the expression of the CDH-13 (h-cadherin), GATA-4, p16, and sFRP2 tumor suppressor genes, all of which are expressed at extremely low levels in the cell line studied. The most dramatic responses were observed when combining PG-11047 with the inhibitor that produces the greatest individual effect: 5-azacytidine and PG-11047 for the CDH-13, sFRP2, and p16 genes, where repression appears to be a result of DNA hypermethylation, and MS-275 and PG-11047 for the GATA-4 gene, where repression can be relieved by treatment with the HDAC inhibitor alone, and is presumably dependent upon histone acetylation. These results, combining agents already under clinical investigation to enhance re-expression of silenced tumor suppressor genes, hold great promise for achieving an anti-tumor response while decreasing the toxic side effects associated with high doses of the individual epigenetic drugs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-97.