Changes in DNA methylation are associated with changes in somatic cell fate without the alteration of coding sequences. In addition to its use as a traceable biomarker, reversible DNA methylation could also serve as a therapeutic target. In particular, if the development of drug resistance is associated with changes in DNA methylation, then demethylation might reverse the resistance phenotype. The reversion of the drug-resistance might then be feasible if the association between abnormal DNA methylation and the development of drug-resistance could be identified. Methylation differences between the drug-resistance cervical cancer cell, SiHa, and its derived oxaliplatin-resistant S3 cells were detected by methylation specific microarray. The drug-resistance cells were treated with demethylation agent to see if the resistance phenotype were reversed. Targeted methylation of one of the identified locus in normal cell is expected to recapitulate the development of resistance and a two-component reporter system is adopted to monitor the increase of DNA methylation in live cells. In this report, we identified methylation changes, both genome-wide and within individual loci, in the oxaliplatin-resistant cervical cancer cell S3 compared with its parental cell line SiHa. Treatment of S3 with a demethylation agent reversed increases in methylation and allowed the expression of methylation-silenced genes. Treatment with the demethylation agent also restored the sensitivity of S3 to cisplatin, taxol, and oxaliplatin to the same level as that of SiHa. Finally, we found that methylation of the target gene Casp8AP2 is sufficient to increase drug resistance in different cells. These results suggest that global methylation is associated with the development of drug resistance and could serve as a biomarker and therapeutic target for drug resistance in cervical cancer.

Background: The Cdc42-interacting protein-4, Trip10 (also known as CIP4), is a multi-domain adaptor protein involved in diverse cellular processes, which functions in a tissue-specific and cell lineage-specific manner. We previously found that Trip10 is highly expressed in estrogen receptor-expressing (ER⁺) breast cancer cells. Estrogen receptor depletion reduced Trip10 expression by progressively increasing DNA methylation. We hypothesized that Trip10 functions as a tumor suppressor and may be involved in the malignancy of ER-negative (ER^-) breast cancer. To test this hypothesis and evaluate whether Trip10 is epigenetically regulated by DNA methylation in other cancers, we evaluated DNA methylation of Trip10 in liver cancer, brain tumor, ovarian cancer, and breast cancer. Methods: We applied methylation-specific polymerase chain reaction and bisulfite sequencing to determine the DNA methylation of Trip10 in various cancer cell lines and tumor specimens. We also overexpressed Trip10 to observe its effect on colony formation and in vivo tumorigenesis. Results: We found that Trip10 is hypermethylated in brain tumor and breast cancer, but hypomethylated in liver cancer. Overexpressed Trip10 was associated with endogenous Cdc42 and huntingtin in IMR-32 brain tumor cells and CP70 ovarian cancer cells. However, overexpression of Trip10 promoted colony formation in IMR-32 cells and tumorigenesis in mice inoculated with IMR-32 cells, whereas overexpressed Trip10 substantially suppressed colony formation in CP70 cells and tumorigenesis in mice inoculated with CP70 cells. Conclusions: Trip10 regulates cancer cell growth and death in a cancer type-specific manner. Differential DNA methylation of Trip10 can either promote cell survival or cell death in a cell type-dependent manner.

Targeting abnormal DNA methylation represents a therapeutically relevant strategy for cancer treatment as demonstrated by the US Food and Drug Administration approval of the DNA methyltransferase inhibitors azacytidine and 5-aza-2'-deoxycytidine for the treatment of myelodysplastic syndromes. But their use is associated with increased incidences of bone marrow suppression. Alternatively, procainamide has emerged as a potential DNA demethylating agent for clinical translation. While procainamide is much safer than 5-aza-2'-deoxycytidine, it requires high concentrations to be effective in DNA demethylation in suppressing cancer cell growth. Thus, our laboratories have embarked on the pharmacological exploitation of procainamide to develop potent DNA methylation inhibitors through lead optimization. We report the use of a DNA methylation two-component enhanced green fluorescent protein reporter system as a screening platform to identify novel DNA methylation inhibitors from a compound library containing procainamide derivatives. A lead agent IM25, which exhibits substantially higher potency in GSTp1 DNA demethylation with lower cytotoxicity in MCF7 cells relative to procainamide and 5-aza-2'-deoxycytidine, was identified by the screening platform. Our data provide a proof-of-concept that procainamide could be pharmacologically exploited to develop novel DNA methylation inhibitors, of which the translational potential in cancer therapy/prevention is currently under investigation.