S-adenosylmethionine metabolism in HL-60 cells: effect of cell cycle and differentiation

Enzymatic Fluoromethylation Enabled by the S-Adenosylmethionine Analog Te-Adenosyl-L-(fluoromethyl)homotellurocysteine

Fluoromethyl, difluoromethyl, and trifluoromethyl groups are present in numerous pharmaceuticals and agrochemicals, where they play critical roles in the efficacy and metabolic stability of these molecules. Strategies for late-stage incorporation of fluorine-containing atoms in molecules have become an important area of organic and medicinal chemistry as well as synthetic biology. Herein, we describe the synthesis and use of Te-adenosyl-L-(fluoromethyl)homotellurocysteine (FMeTeSAM), a novel and biologically relevant fluoromethylating agent. FMeTeSAM is structurally and chemically related to the universal cellular methyl donor S-adenosyl-L-methionine (SAM) and supports the robust transfer of fluoromethyl groups to oxygen, nitrogen, sulfur, and some carbon nucleophiles. FMeTeSAM is also used to fluoromethylate precursors to oxaline and daunorubicin, two complex natural products that exhibit antitumor properties.

Effects of DMSO on the Pluripotency of Cultured Mouse Embryonic Stem Cells (mESCs)

DMSO is a commonly used solvent in biological studies, as it is an amphipathic molecule soluble in both aqueous and organic media. For that reason, it is the vehicle of choice for several water-insoluble substances used in research. At the molecular and cellular level, DMSO is a hydrogen-bound disrupter, an intercellular electrical uncoupler, and a cryoprotectant, among other properties. Importantly, DMSO often has overlooked side effects. In stem cell research, the literature is scarce, but there are reports on the effect of DMSO in human embryoid body differentiation and on human pluripotent stem cell priming towards differentiation, via modulation of cell cycle. However, in mouse embryonic stem cell (mESC) culture, there is almost no available information. Taking into consideration the almost ubiquitous use of DMSO in experiments involving mESCs, we aimed to understand the effect of very low doses of DMSO (0.0001%-0.2%), usually used to introduce pharmacological inhibitors/modulators, in mESCs cultured in two different media (2i and FBS-based media). Our results show that in the E14Tg2a mESC line used in this study, even the smallest concentration of DMSO had minor effects on the total number of cells in serum-cultured mESCs. However, these effects could not be explained by alterations in cell cycle or apoptosis. Furthermore, DMSO did not affect pluripotency or differentiation potential. All things considered, and although control experiments should be carried out in each cell line that is used, it is reasonable to conclude that DMSO at the concentrations used here has a minimal effect on this particular mESC line.

Inhibition of histone H3K79 methylation selectively inhibits proliferation, self-renewal and metastatic potential of breast cancer

Histone lysine methylation regulates gene expression and cancer initiation. Bioinformatics analysis suggested that DOT1L, a histone H3-lysine79 (H3K79) methyltransferase, plays a potentially important role in breast cancer. DOT1L inhibition selectively inhibited proliferation, self-renewal, metastatic potential of breast cancer cells and induced cell differentiation. In addition, inhibitors of S-adenosylhomocysteine hydrolase (SAHH), such as neplanocin and 3-deazaneplanocin, also inhibited both H3K79 methylation and proliferation of breast cancer cells in vitro and in vivo. The activity of SAHH inhibitors was previously attributed to inhibition of H3K27 methyltransferase EZH2. However, inhibition of EZH2 by a specific inhibitor did not contribute to cell death. SAHH inhibitors had only weak activity against H3K27 methylation and their activity is therefore mainly due to DOT1L/H3K79 methylation inhibition. Overall, we showed that DOT1L is a potential drug target for breast cancer.

A medicinal chemistry perspective for targeting histone H3 lysine-79 methyltransferase DOT1L

Histone H3 lysine79 (H3K79) methyltransferase DOT1L plays an important role in the activation and maintenance of gene transcription. It is essential for embryonic development as well as normal functions of the hematopoietic system, heart, and kidney in adults. DOT1L has been found to be a drug target for acute leukemia with mixed lineage leukemia (MLL) gene translocations. The rearranged onco-MLL can recruit DOT1L, causing aberrant H3K79 methylation, overexpression of leukemia relevant genes, and eventually leukemogenesis. Potent DOT1L inhibitors possess selective activity against this type of leukemia in cell-based and animal studies, with the most advanced compound being in clinical trials. In the medicinal chemistry point of view, we review the biochemistry, cancer biology, and current inhibitors of DOT1L, as well as biophysical (including X-ray crystallographic) investigation of DOT1L-inhibitor interactions. Potential future directions in the context of drug discovery and development targeting DOT1L are discussed.

Metabolic aspects of epigenome: coupling of S-adenosylmethionine synthesis and gene regulation on chromatin by SAMIT module

Histone and DNA methyltransferases utilize S-adenosyl-L-methionine (SAM), a key intermediate of sulfur amino acid metabolism, as a donor of methyl group. SAM is biosynthesized by methionine adenosyltransferase (MAT) using two substrates, methionine and ATP. Three distinct forms of MAT (MATI, MATII and MATIII), encoded by two distinct genes (MAT1A and MAT2A), have been identified in mammals. MATII consists of α2 catalytic subunit encoded by MAT2A and β regulatory subunit encoded by MAT2B, but the physiological function of the β subunit is not clear. MafK is a member of Maf oncoproteins and functions as both transcription activator and repressor by forming diverse heterodimers to bind to DNA elements termed Maf recognition elements. Proteomics analysis of MafK-interactome revealed its interaction with both MATIIα and MATIIβ. They are recruited specifically to MafK target genes and are required for their repression by MafK and its partner Bach1. Because the catalytic activity of MATIIα is required for the MafK target gene repression, MATIIα is suggested to provide SAM locally on chromatin where it is recruited. One of the unexpected features of MATII is that MATIIα interacts with many chromatin-related proteins of diverse functions such as histone modification, chromatin remodeling, transcription regulation, and nucleo-cytoplasmic transport. MATIIα appears to generate multiple, heterogenous regulatory complexes where it provides SAM. Considering their function, the heterooligomer of MATIIα and β is named SAMIT (SAM-integrating transcription) module within their interactome where it serves SAM for nuclear methyltransferases.

Synthesis, Activity and Metabolic Stability of Non-Ribose Containing Inhibitors of Histone Methyltransferase DOT1L

Histone methyltransferase DOT1L is a drug target for MLL leukemia. We report an efficient synthesis of a cyclopentane-containing compound that potently and selectively inhibits DOT1L (K_i = 1.1 nM) as well as H3K79 methylation (IC₅₀ ~ 200 nM). Importantly, this compound exhibits a high stability in plasma and liver microsomes, suggesting it is a better drug candidate.

Selective inhibitors of histone methyltransferase DOT1L: design, synthesis, and crystallographic studies

Histone H3-lysine79 (H3K79) methyltransferase DOT1L plays critical roles in normal cell differentiation as well as initiation of acute leukemia. We used structure- and mechanism-based design to discover several potent inhibitors of DOT1L with IC(50) values as low as 38 nM. These inhibitors exhibit only weak or no activities against four other representative histone lysine and arginine methyltransferases, G9a, SUV39H1, PRMT1 and CARM1. The X-ray crystal structure of a DOT1L-inhibitor complex reveals that the N6-methyl group of the inhibitor, located favorably in a predominantly hydrophobic cavity of DOT1L, provides the observed high selectivity. Structural analysis shows that it will disrupt at least one H-bond and/or have steric repulsion for other histone methyltransferases. These compounds represent novel chemical probes for biological function studies of DOT1L in health and disease.

Differential cell cycle perturbation by transmethylation inhibitors

Cell cycle distribution of HL-60 cells was studied by flow cytometry after incubation with the transmethylation inhibitors 3-deaza-(+/-)-aristeromycin (c3 Ari) and 3-deazaadenosine (c3 Ado). Cells were incubated with the drugs (25 microM) for two cell doublings in control cells (36 hr). The presence of c3 Ari caused a dose-dependent, reversible G2 + M arrest, whereas c3 Ado-treated cells accumulated in G0/G1. The G2 + M arrest was also found in NIH/3T3 cells incubated for 36 hr with 25 microM c3 Ari, but not in U937 and K562 cells. Possible mechanisms for the described effects of c3 Ari are discussed from the perspective that inhibition of S-adenosyl homocysteine hydrolase, and subsequent inhibition of transmethylation reactions, at present is the only known site of action of c3 Ari.