RG 108

RG108 is a DNA methyltransferase (DMNT) inhibitor that enhanced reprogramming of OK-transduced MEFs in the presence of BIX. It is a small molecule that effectively blocked DNA methyltransferases in vitro and did not cause covalent enzyme trapping in human cell lines. DNA methylation regulates gene expression in normal and malignant cells. DNA methyltransferase inhibitors are able to reactivate epigenetically silenced genes. RG108 caused demethylation and reactivation of tumor suppressor genes, but it did not affect the methylation of centromeric satellite sequences. These results establish RG108 as a DNA methyltransferase inhibitor with fundamentally novel characteristics that will be particularly useful for the experimental modulation of epigenetic gene regulation.

References

Yan Shi, Caroline Desponts, Jeong Tae Do, Heung Sik Hahm, Hans R. Schöler, Sheng Ding. Induction of Pluripotent Stem Cells from Mouse Embryonic Fibroblasts by Oct4 and Klf4 with Small-Molecule Compounds. Cell Stem Cell. 2008; 3(5): 568 – 574.

Bodo Brueckner, Regine Garcia Boy, Pawel Siedlecki. Epigenetic Reactivation of Tumor Suppressor Genes by a Novel Small-Molecule Inhibitor of Human DNA Methyltransferases. Cancer Research. 2005; 65(14): 6305 – 11.

Pharmacokinetics of the Experimental Non-Nucleosidic DNA Methyl Transferase Inhibitor N-Phthalyl-L-Tryptophan (RG 108) in Rats.[Pubmed:26525153]

Basic Clin Pharmacol Toxicol. 2016 May;118(5):327-32.

DNA methyl transferase (DNMT) inhibitors can re-establish the expression of tumour suppressor genes in malignant diseases, but might also be useful in other diseases. Inhibitors in clinical use are nucleosidic cytotoxic agents that need to be integrated into the DNA of dividing cells. Here, we assessed the in vivo kinetics of a non-nucleosidic inhibitor that is potentially free of cytotoxic effects and does not require cell division. The non-specific DNMT inhibitor N-phthalyl-L-tryptophan (RG 108) was injected subcutaneously in rats. Blood was drawn 0, 0.5, 1, 2, 4, 6, 8 and 24 hr after injection and RG 108 in plasma was measured by high-performance liquid chromatography coupled to mass spectrometry. Trough levels and area under the curve (AUC) were significantly higher with multiple-dose administration and cytochrome inhibition. In this group, time to maximal plasma concentration (tmax , mean +/- S.D.) was 37.5 +/- 15 min., terminal plasma half-life was approximately 3.7 h (60% CI: 2.1-15.6 h), maximal plasma concentration (Cmax) was 61.3 +/- 7.6 muM, and AUC was 200 +/- 54 mumol.h/l. RG 108 peak levels were not influenced by cytochrome inhibition or multiple-dose administration regimens. Maximal tissue levels (Cmax in mumol/kg) were 6.9 +/- 6.7, 1.6 +/- 0.4 and 3.4 +/- 1.1 in liver, skeletal and heart muscle, respectively. We conclude that despite its high lipophilicity, RG 108 can be used for in vivo experiments, appears safe and yields plasma and tissue levels in the range of the described 50% inhibitory concentration of around 1 to 5 muM. RG 108 can therefore be a useful tool for in vivo DNMT inhibition.

Comparing The Effects of Small Molecules BIX-01294, Bay K8644, RG-108 and Valproic Acid, and Their Different Combinations on Induction of Pluripotency Marker-Genes by Oct4 in The Mouse Brain.[Pubmed:25685732]

Cell J. 2015 Winter;16(4):416-25. Epub 2015 Jan 13.

OBJECTIVE: Every cell type is characterized by a specific transcriptional profile together with a unique epigenetic landscape. Reprogramming factors such as Oct4, Klf4, Sox2 and c-Myc enable somatic cells to change their transcriptional profile and convert them to pluripotent cells. Small molecules such as BIX-01294, Bay K8644, RG-108 and valproic acid (VPA) are reported as effective molecules for enhancing induction of pluripotency in vitro, however, their effects during in vivo reprogramming are addressed in this experimental study. MATERIALS AND METHODS: In this experimental study, Oct4 expressing lentiviral particles and small molecules BIX-01294, Bay K8644 and RG-108 were injected into the right ventricle of mice brain and VPA was systematically administered as oral gavages. Animals treated with different combinations of small molecules for 7 or 14 days in concomitant with Oct4 exogenous expression were compared for expression of pluripotency markers. Total RNA was isolated from the rims of the injected ventricle and quantitative polymerase chain reaction (PCR) was performed to evaluate the expression of endogenous Oct4, Nanog, c-Myc, klf4 and Sox2 as pluripotency markers, and Pax6 and Sox1 as neural stem cell (NSC) markers. RESULTS: Results showed that Oct4 exogenous expression for 7 days induced pluripoten- cy slightly as it was detected by significant enhancement in expression of Nanog (p<0.05). Combinatorial administration of Oct4 expressing vector and BIX-01294, Bay K8644 and RG-108 did not affect the expression of pluripotency and NSC markers, but VPA treatment along with Oct4 exogenous expression induced Nanog, Klf4 and c-Myc (p<0.001). VPA treatment before the induction of exogenous Oct4 was more effective and significantly increased the expression of endogenous Oct4, Nanog, Klf4, c-Myc (p<0.01), Pax6 and Sox1 (p<0.001). CONCLUSION: These results suggest VPA as the best enhancer of pluripotency among the chemicals tested, especially when applied prior to pluripotency induction by Oct4.

Synthesis and in vitro evaluation of biotinylated RG108: a high affinity compound for studying binding interactions with human DNA methyltransferases.[Pubmed:16536454]

Bioconjug Chem. 2006 Mar-Apr;17(2):261-6.

Small-molecule inhibitors of DNA methyltransferases such as RG108 represent promising candidates for cancer drug development. We report the synthesis and in vitro analysis of a biotinylated RG108 conjugate, 2-(1,3-dioxo-1,3-dihydro-isoindol-2-yl)-3-(5-[3-[5-(2-oxo-hexahydro-thieno[3,4-d] imidazol-4-yl)pentanoylamino]propoxy]-1H-indol-3-yl)propionic acid (bio-RG108), for the evaluation of interactions with DNA methyltransferase enzymes. The structural design of the chemically modified inhibitor was aided by molecular modeling, which suggested the possibility for extensive chemical modifications at the 5-position of the tryptophan moiety in RG108. The inhibitory activity of the corresponding derivative was confirmed in a cell-free biochemical assay, where bio-RG108 showed an undiminished inhibition of DNA methyltransferase activity (IC50 = 40 nM). Bio-RG108 therefore represents a suitable bioconjugate for the elucidation of inhibitory mechanisms and for the affinity purification of RG108-associated proteins.

Functional diversity of DNA methyltransferase inhibitors in human cancer cell lines.[Pubmed:16510601]

Cancer Res. 2006 Mar 1;66(5):2794-800.

DNA methyltransferase inhibitors represent promising new drugs for cancer therapies. The first of these compounds (5-azacytidine, Vidaza) has recently been approved as an antitumor agent, and others are presently in various stages of their preclinical or clinical development. Most of the archetypal inhibitors have been established and characterized in different experimental systems, which has thus far precluded their direct comparison. We have now established defined experimental conditions that allowed a comparative analysis of the six most widely known DNA methyltransferase inhibitors: 5-azacytidine (5-aza-CR), 5-aza-2'-deoxycytidine (5-aza-CdR), zebularine, procaine, (-)-epigallocatechin-3-gallate (EGCG), and RG108. Of these, 5-aza-CR, 5-aza-CdR, zebularine, and EGCG were found to exhibit significant cytotoxicity in human cancer cell lines. 5-aza-CdR and EGCG were also found to be genotoxic, as evidenced by the induction of micronuclei. In addition, 5-aza-CR, 5-aza-CdR, zebularine, and RG108 caused concentration-dependent demethylation of genomic DNA, whereas procaine and EGCG failed to induce significant effects. Finally, the experiments in cancer cell lines were complemented by a cell-free in vitro assay with purified recombinant DNA methyltransferase, which indicated that RG108 is the only drug capable of direct enzyme inhibition. These results show a substantial diversity in the molecular activities of DNA methyltransferase inhibitors and provide valuable insights into the developmental potential of individual drugs.

Epigenetic reactivation of tumor suppressor genes by a novel small-molecule inhibitor of human DNA methyltransferases.[Pubmed:16024632]

Cancer Res. 2005 Jul 15;65(14):6305-11.

DNA methylation regulates gene expression in normal and malignant cells. The possibility to reactivate epigenetically silenced genes has generated considerable interest in the development of DNA methyltransferase inhibitors. Here, we provide a detailed characterization of RG108, a novel small molecule that effectively blocked DNA methyltransferases in vitro and did not cause covalent enzyme trapping in human cell lines. Incubation of cells with low micromolar concentrations of the compound resulted in significant demethylation of genomic DNA without any detectable toxicity. Intriguingly, RG108 caused demethylation and reactivation of tumor suppressor genes, but it did not affect the methylation of centromeric satellite sequences. These results establish RG108 as a DNA methyltransferase inhibitor with fundamentally novel characteristics that will be particularly useful for the experimental modulation of epigenetic gene regulation.

RG108 (N-Phthalyl-L-tryptophan) is a non-nucleoside DNA methyltransferases (DNMTs) inhibitor (IC50=115 nM) that blocks the DNMTs active site. RG108 (N-Phthalyl-L-tryptophan) causes demethylation and reactivation of tumor suppressor genes, but it does not affect the methylation of centromeric satellite sequences.

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