HDAC modulation and cell death in the clinic.

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are two opposing classes of enzymes, which finely regulate the balance of histone acetylation affecting chromatin packaging and gene expression. Imbalanced acetylation has been associated with carcinogenesis and cancer progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. This implies that epigenetic alterations are amenable to pharmacological interventions. Accordingly, some epigenetic-based drugs (epidrugs) have been approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment. Here, we focus on the biological features of HDAC inhibitors (HDACis), analyzing the mechanism(s) of action and their current use in clinical practice.

Total synthesis of the proposed structures of the DNA methyl transferase inhibitors peyssonenynes, and structural revision of peyssonenyne B.

The purported structures of the peyssonenynes A and B isolated from Peyssonnelia caulifera, and considered to be geometric isomers at the acetoxyenediyne moiety, have been synthesized. The E and Z geometries of the synthetic compounds were secured by the magnitude of the (3)J(H9-C7) values measured using the EXSIDE band-variant of the gradient HSQC pulse sequence and by the chemical shifts of C(6). Comparison of the NMR data of the synthetic and natural products revealed that only those of the Z isomers matched, which correspond to peyssonenyne A. Using HPLC analysis it was found that peyssonenyne B must correspond to the sn-2 positional isomer of the Z sn-1/3 counterpart. The four synthetic sn-1/3 diastereomers are roughly equipotent as DNMT1 inhibitors when evaluated on a radioactive methyl transfer enzymatic assay after immunoprecipitation from K562 human leukemia cells with anti-DNMT1 antibody.

Molecular analysis of the apoptotic effects of BPA in acute myeloid leukemia cells.

BACKGROUND: BPA (bisphenol A or 2,2-bis(4-hydroxy-phenol)propane) is present in the manufacture of polycarbonate plastic and epoxy resins, which can be used in impact-resistant safety equipment and baby bottles, as protective coatings inside metal food containers, and as composites and sealants in dentistry. Recently, attention has focused on the estrogen-like and carcinogenic adverse effects of BPA. Thus, it is necessary to investigate the cytotoxicity and apoptosis-inducing activity of this compound. METHODS: Cell cycle, apoptosis and differentiation analyses; western blots. RESULTS: BPA is able to induce cell cycle arrest and apoptosis in three different acute myeloid leukemias. Although some granulocytic differentiation concomitantly occurred in NB4 cells upon BPA treatment, the major action was the induction of apoptosis. BPA mediated apoptosis was caspase dependent and occurred by activation of extrinsic and intrinsic cell death pathways modulating both FAS and TRAIL and by inducing BAD phosphorylation in NB4 cells. Finally, also non genomic actions such as the early decrease of both ERK and AKT phosphorylation were induced by BPA thus indicating that a complex intersection of regulations occur for the apoptotic action of BPA. CONCLUSION: BPA is able to induce apoptosis in leukemia cells via caspase activation and involvement of both intrinsic and extrinsic pathways of apoptosis.

HDAC inhibitors repress BARD1 isoform expression in acute myeloid leukemia cells via activation of miR-19a and/or b.

Over the past years BARD1 (BRCA1-associated RING domain 1) has been considered as both a BRCA1 (BReast Cancer susceptibility gene 1, early onset) interactor and tumor suppressor gene mutated in breast and ovarian cancers. Despite its role as a stable heterodimer with BRCA1, increasing evidence indicates that BARD1 also has BRCA1-independent oncogenic functions. Here, we investigate BARD1 expression and function in human acute myeloid leukemias and its modulation by epigenetic mechanism(s) and microRNAs. We show that the HDACi (histone deacetylase inhibitor) Vorinostat reduces BARD1 mRNA levels by increasing miR-19a and miR-19b expression levels. Moreover, we identify a specific BARD1 isoform, which might act as tumor diagnostic and prognostic markers.

A DNA methyltransferase modulator inspired by peyssonenyne natural product structures.

A novel epigenetic modulator that displays a DNMT1 inhibition and DNMT3A activation profile was characterized (compound 8). This compound is a derivative of palmitic acid that incorporates the putative reactive functional group (diynone) of the peyssonenyne natural products. Other analogues containing the diynone or an acetoxyenediyne did not show the same biological profile. In U937 human leukemia cells, diynone 8 induced cell differentiation and apoptosis, which correlated with the expression of Fas protein. Very surprisingly, diynone 8 was toxic to normal human fibroblasts (BJ) and mouse embryo fibroblasts (MEF), but not to immortalized human fibroblasts (BJEL); this unique effect was not observed with the classical DNMT inhibitor 5-azacytidine. Therefore, compound 8 interferes in a very specific manner with signaling pathways, the activities of which differ between normal and immortalized cell types. This toxicity is reminiscent of the effects of Dnmt1 ablation on mouse fibroblasts. In fact, some of the genes deregulated by the loss of Dnmt1 are similarly deregulated by 8, but not by the DNMT inhibitor SGI-1027.

Identification of PR-SET7 and EZH2 selective inhibitors inducing cell death in human leukemia U937 cells.

Chemical manipulations undertaken on some bis(bromo- and dibromo-phenol) compounds previously reported by us as wide-spectrum epigenetic inhibitors let us to identify bis (bromo- and dibromo-methoxyphenyl) derivatives highly selective for PR-SET7 and EZH2 (compounds 4, 5, 9, and 10). Western blot analyses were carried out in U937 cells to determine the effects of such compounds on the methyl marks related to the tested enzymes (H3K4me1, H3K9me2, H4H20me1, and H3K27me3). The 1,5-bis(3-bromo-4-methoxyphenyl)penta-1,4-dien-3-one 4 (EC(50) vs EZH2 = 74.9 µM), tested in U937 cells at 50 µM, induced massive cell death and 28% of granulocytic differentiation, highlighting the potential use of EZH2 inhibitors in cancer.

Synthesis and biological characterization of the histone deacetylase inhibitor largazole and C7- modified analogues.

Largazole 4a and analogues with modifications at the C7 position, as well as 2,4'-bithiazole 5a, have been synthesized using an acyclic cross-metathesis of the corresponding depsipeptide structures assembled by N-C6(O) or C15(O)-N lactam formation. Similar to the parent system 4a, the series of largazole depsipeptides 4b-d, but not 2,4'-bithiazole 5a, showed a marked inhibition of recombinant HDAC1 and selectivity over HDAC4, as well as strong pro-apoptotic effects on the NB4 leukemia cell line, but they failed to induce differentiation to mature granulocytes. Functional assays of the analogues correlated with the in vitro activities, as shown by increased H3 and alpha-tubulin acetylation levels and p21(WAF1/CIP1) up-regulation in NB4 cells. The activity of the natural product HDACi largazole 4a is not significantly altered by the presence of groups of different size (H, Et, Ph) at C7 on the dihydrothiazole ring.