In this study we examine the effect of the phytoestrogen genistein on DNA methylation. DNA methylation is thought to inhibit transcription of genes by regulating alterations in chromatin structure. Estrogenic compounds have been reported to regulate DNA methylation in a small number of studies. Additionally, phytoestrogens are believed to affect progression of some human diseases, such as estrogen-dependent cancers, osteoporosis and cardiovascular disease. Specifically, our working hypothesis is that certain soy phytoestrogens, such as genistein, may be involved in preventing the development of certain prostate and mammary cancers by maintaining a protective DNA methylation profile. The objective of the present study is to use mouse differential methylation hybridization (DMH) arrays to test for changes in the methylation status of the cytosine guanine dinucleotide (CpG) islands in the mouse genome by examining how these methylation patterns are affected by genistein. Male mice were fed a casein-based diet (control) or the same diet containing 300 mg genistein/kg according to one of four regimens: control diet for 4 wk, genistein diet for 4 wk, control diet for 2 wk followed by genistein diet for 2 wk and genistein diet for 2 wk followed by control diet for 2 wk. DNA from liver, brain and prostate were then screened with DMH arrays. Clones with methylation differences were sequenced and compared with known sequences. In conclusion, consumption of genistein diet was positively correlated with changes in prostate DNA methylation at CpG islands of specific mouse genes.

In previous studies we observed that some allyl sulfides can cause increased acetylation of histones and differentiation in DS19 mouse erythroleukemia cells. In the present work we observed increased acetylation of histones with allyl isothiocyanate and butanethiol but not with butyl sulfide or butyl disulfide. Increased acetylation of histones was established by change in electrophoretic mobility, incorporation of [ 3 H]acetate or immunoblotting. Histone deacetylase in nuclei of DS19 cells was inhibited 74% by 0.5 mM allyl mercaptan and 43% by 0.5 mM butanethiol but was not significantly affected by 0.5 mM allyl isothiocyanate. There was some degree of reversibility in the effect of allyl isothiocyanate when the cells were incubated for 15 hr in fresh medium. The data suggested that allyl isothiocyanate may stimulate histone acetylation rather than inhibit histone deacetylation. Addition of allyl isothiocyanate, however, had very little or no additional effect on the induction of histone acetylation caused by trichostatin A. Histone acetyltransferase activity determined in cell homogenates was not increased by preincubation of cells with allyl isothiocyanate or inclusion of allyl isothiocyanate in the assay medium. It was concluded that treatment of mouse erythroleukemia cells with allyl isothiocyanate can cause increased acetylation of histones but the mechanism for this effect requires further elucidation.

Growth-inhibitory effects on DS19 mouse erythroleukemia cells were seen in the micromolar concentration range with allicin and S-allylmercaptocysteine and in the millimolar range with allyl butyrate, allyl phenyl sulfone, and S-allyl cysteine. Increased acetylation of histones was induced by incubation of cells with the allyl compounds at concentrations similar to those that resulted in the inhibition of cell proliferation. The induction of histone acetylation by S-allylmercaptocysteine was also observed in Caco-2 human colon cancer cells and T47D human breast cancer cells. In contrast to the effect on histone acetylation, there was a decrease in the incorporation of phosphate into histones when DS19 cells were incubated with 25 microM S-allylmercaptocysteine. Histone deacetylase activity was inhibited by allyl butyrate, but there was little or no effect with the allyl sulfur compounds examined in this study. A similar degree of downregulation of histone deacetylase and histone acetyltransferase was observed when DS19 cells were incubated with S-allylmercaptocysteine or allyl isothiocyanate. The induction of histone acetylation by S-allylmercaptocysteine was not blocked by a proteasome inhibitor. The mechanism by which S-allylmercaptocysteine induces histone acetylation remains to be characterized. It may be related in part to metabolism to allyl mercaptan, which is a more effective inhibitor of histone deacetylase.

The tendency for enhanced glycolysis in cancer cells presents a target for chemotherapy. In previous studies we observed that proliferation of colon and bladder cancer cells can be inhibited by treatment with either phenformin or an inhibitor of PFKFB3 namely 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO). In the present work we have examined the action of two inhibitors that are effective at lower concentrations than 3PO, namely 1-(3-pyridinyl)-3-(2-quinolinyl)-2-propen-1-one (PQP) and 1-(4-pyridinyl)-3-(2-quinolinyl)-2-propen-1-one (PFK15). The LDHA inhibitors that we chose to study in increasing order of IC50s were methyl 1-hydroxy-6-phenyl-4-(trifluoromethyl)-1H-indole-2-carboxylate (NHI-2) < isosafrole < oxamate. A synergistic anti-cancer effect of phenformin and oxamate has been reported. In the present work with colon and bladder cancer cells, additive but not synergistic growth inhibitory effects were seen with the LDHA inhibitors of which NHI-2 was effective at the lowest concentrations. Growth inhibition with PQP and PFK15 was compared in colon (Caco-2 and HT29) and bladder cancer cells (5637, HT1376, RT4, SW780, T24, TCCSUP and UM-UC-3). Apart from RT4 cells where the effects were similar, the effects were somewhat greater with PFK15 than with PQP and for both compounds the actions were seen at lower concentrations than in previous studies with 3PO. Actions on medium acidification and glucose uptake are more readily observed in the most rapidly growing cell lines. Effects of phenformin on medium pH and glucose concentration were decreased by the PFKFB3 and LDHA inhibitors that were examined. In accord with our previous studies on inhibitors of glycolysis, the increased medium acidification and glucose uptake caused by phenformin could be blocked by combined treatment with PFKFB3 or LDHA inhibitors. At the same time additive growth inhibitory effects were observed. The results supported the concept that combined treatment with phenformin and inhibitors of glycolysis can cause additive inhibition of cell proliferation while mitigating the lactic acidosis caused by phenformin as a single agent. Citation Format: Michael A. Lea, Yolanda Guzman, Charles desBordes. Inhibition of cancer cell growth by combined treatment with lactate dehydrogenase (LDHA) inhibitors and either phenformin or inhibitors of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 32.