Mechanism of p300 specific histone acetyltransferase inhibition by small molecules

Investigation of intermolecular interactions and binding mechanism of PU139 and PU141 molecules with p300 HAT enzyme via molecular docking, molecular dynamics simulations and binding free energy analysis

The p300 histone acetyltransferase (HAT) enzyme acetylates the lysine residue of histone promotes the transcription reaction. The abnormal function of p300 HAT enzyme causes various diseases such as Cancer, Asthma, Alzheimer, Diabetics, and AIDS. In the recent years, several studies have been conducted to design potential drug to inhibit this enzyme. Recently, an in vitro study has been performed on the synthetic molecules PU139 and PU141 to inhibit the p300 HAT enzyme. The present study aims to understand the binding affinity, intermolecular interactions, conformational stability and binding energy of PU139 and PU141 molecules in the active site of p300 HAT enzyme from the in silico studies. The molecular docking and molecular dynamics (MD) simulations were carried out for both ligands with the p300 HAT enzyme. The molecular docking and MD simulations reveals that both molecules forms expected interactions with the catalytic site key residues of p300 enzyme. The MD simulation shows the maximum RMSD value for the PU141 is 2.3 Å, whereas for PU139 is 3.3 Å; these low RMSD values indicate that both molecules are highly stable in the active site of p300. The calculated binding free energy of PU141 (-20.62 kcal/mol) is higher than the molecule PU139 (-17.67 kcal/mol). Among the results, PU141 shows the high binding affinity with p300 while comparing with PU139. The results of this in-silico study coupled with the findings reported in the in vitro study confirm that PU141 may be suitable for clinical study.Communicated by Ramaswamy H. Sarma.

KATs off: Biomedical insights from lysine acetyltransferase inhibitors

Lysine acetyltransferase (KAT) enzymes including the p300, MYST, and GCN5 families play major roles in modulating the structure of chromatin and regulating transcription. Because of their dysregulation in various disease states including cancer, efforts to develop inhibitors of KATs have steadily gained momentum. Here we provide an overview of recent progress on the development of high quality chemical probes of the p300 and MYST family of KATs and how they are emerging as useful tools for basic and translational investigation.

Discovery of a new class of triazole based inhibitors of acetyl transferase KAT2A

We have recently developed a new synthetic methodology that provided both N-aryl-5-hydroxytriazoles and N-pyridine-4-alkyl triazoles. A selection of these products was carried through virtual screening towards targets that are contemporary and validated for drug discovery and development. This study determined a number of potential structure target dyads of which N-pyridinium-4-carboxylic-5-alkyl triazole displayed the highest score specificity towards KAT2A. Binding affinity tests of abovementioned triazole and related analogs towards KAT2A confirmed the predictions of the in-silico assay. Finally, we have run in vitro inhibition assays of selected triazoles towards KAT2A; the ensemble of binding and inhibition assays delivered pyridyl-triazoles carboxylates as the prototype of a new class of inhibitors of KAT2A.

Histone modification and histone modification-targeted anti-cancer drugs in breast cancer: Fundamentals and beyond

Dysregulated epigenetic enzymes and resultant abnormal epigenetic modifications (EMs) have been suggested to be closely related to tumor occurrence and progression. Histone modifications (HMs) can assist in maintaining genome stability, DNA repair, transcription, and chromatin modulation within breast cancer (BC) cells. In addition, HMs are reversible, dynamic processes involving the associations of different enzymes with molecular compounds. Abnormal HMs (e.g. histone methylation and histone acetylation) have been identified to be tightly related to BC occurrence and development, even though their underlying mechanisms remain largely unclear. EMs are reversible, and as a result, epigenetic enzymes have aroused wide attention as anti-tumor therapeutic targets. At present, treatments to restore aberrant EMs within BC cells have entered preclinical or clinical trials. In addition, no existing studies have comprehensively analyzed aberrant HMs within BC cells; in addition, HM-targeting BC treatments remain to be further investigated. Histone and non-histone protein methylation is becoming an attractive anti-tumor epigenetic therapeutic target; such methylation-related enzyme inhibitors are under development at present. Consequently, the present work focuses on summarizing relevant studies on HMs related to BC and the possible mechanisms associated with abnormal HMs. Additionally, we also aim to analyze existing therapeutic agents together with those drugs approved and tested through pre-clinical and clinical trials, to assess their roles in HMs. Moreover, epi-drugs that target HMT inhibitors and HDAC inhibitors should be tested in preclinical and clinical studies for the treatment of BC. Epi-drugs that target histone methylation (HMT inhibitors) and histone acetylation (HDAC inhibitors) have now entered clinical trials or are approved by the US Food and Drug Administration (FDA). Therefore, the review covers the difficulties in applying HM-targeting treatments in clinics and proposes feasible approaches for overcoming such difficulties and promoting their use in treating BC cases.

Butyrylation Meets Adipogenesis-Probed by a p300-Catalyzed Acylation-Specific Small Molecule Inhibitor: Implication in Anti-obesity Therapy

The enzyme p300, besides having acetyltransferase activity, can also catalyze other acylation modifications, whose physiological implications are still being investigated. Here, we report that the level of histone butyrylation increases globally as well as locally in the promoters of pro-adipogenic genes during adipogenesis. To delineate the role of p300-catalyzed butyrylation from acetylation in adipogenesis, we identified a semisynthetic derivative (LTK-14A) of garcinol, which specifically inhibited histone butyrylation without affecting acetylation. Treatment of 3T3L1 cells with LTK-14A abolished adipogenesis with downregulation of pro-adipogenic genes along with inhibition of H4K5 butyrylation. Administering LTK-14A to high-fat diet-fed and genetically obese db/db mice led to attenuation/decrease in their weight gain. The reduced obesity could be partially attributed to the inhibition of H4K5 butyrylation in adipocytes and liver. This report therefore not only, for the first time, causally links histone butyrylation with adipogenesis but also presents a probable candidate for anti-obesity therapeutics.

An insight into therapeutic efficacy of heterocycles as histone modifying enzyme inhibitors that targets cancer epigenetic pathways

Histone modifying enzymes are the key regulators involved in the post-translational modification of histone and non-histone. These enzymes are responsible for the epigenetic control of cellular functions. However, deregulation of the activity of these enzymes results in uncontrolled disorders such as cancer and inflammatory and neurological diseases. The study includes histone acetyltransferases, deacetylases, methyl transferases, demethylases, DNA methyl transferases, and their potent inhibitors which are in a clinical trial and used as medicinal drugs. The present review covers the heterocycles as target-specific inhibitors of histone-modifying enzyme, more specifically histone acetyltransferases. This review also confers more recent reports on heterocycles as potential HAT inhibitors covered from 2016-2022 and future perspectives of these heterocycles in epigenetic therapy.

Utility of Indian fruits in cancer prevention and treatment: Time to undertake translational and bedside studies

The World Health Organization predicts a 70% increase in cancer incidents in developing nations over the next decade, and it will be the second leading cause of death worldwide. Traditional plant-based medicine systems play an important role against various diseases and provide health care to a large section of the population in developing countries. Indigenous fruits and their bioactive compounds with beneficial effects like antioxidant, antiproliferative, and immunomodulatory are shown to be useful in preventing the incidence of cancer. India is one of the biodiversity regions and is native to numerous flora and fauna in the world. Of the many fruiting trees indigenous to India, Mango (Mangifera indica), Black plum (Eugenia jambolana or Syzygium jambolana), Indian gooseberry (Emblica officinalis or Phyllanthus emblica), kokum (Garcinia indica or Brindonia indica), stone apple or bael (Aegle marmelos), Jackfruit (Artocarpus heterophyllus), Karaunda (Carissa carandas) and Phalsa (Grewia asiatica), Monkey Jackfruit (Artocarpus lakoocha) and Elephant apple (Dillenia indica) have been shown to be beneficial in preventing cancer and in the treatment of cancer in validated preclinical models of study. In this review, efforts are also made to collate the fruits' anticancer effects and the important phytochemicals. Efforts are also made at emphasizing the underlying mechanism/s responsible for the beneficial effects in cancer prevention and treatment. These fruits have been a part of the diet, are non-toxic, and easily acceptable for human application. The plants and some of their phytochemicals possess diverse medicinal properties. The authors propose that future studies should be directed at detailed studies with various preclinical models of study with both composite fruit extract/juice and the individual phytochemicals. Additionally, translational studies should be planned with the highly beneficial, well-investigated and pharmacologically multifactorial amla to understand its usefulness as a cancer preventive in the high-risk population and as a supportive agent in cancer survivors. The outcome of both preclinical and clinical studies will be useful for patients, the healthcare fraternity, pharmaceutical, and agro-based sectors.

Diet-derived small molecules (nutraceuticals) inhibit cellular proliferation by interfering with key oncogenic pathways: an overview of experimental evidence in cancer chemoprevention

Discouraging statistics of cancer disease has projected an increase in the global cancer burden from 19.3 to 28.4 million incidences annually within the next two decades. Currently, there has been a revival of interest in nutraceuticals with evidence of pharmacological properties against human diseases including cancer. Diet is an integral part of lifestyle, and it has been proposed that an estimated one-third of human cancers can be prevented through appropriate lifestyle modification including dietary habits; hence, it is considered significant to explore the pharmacological benefits of these agents, which are easily accessible and have higher safety index. Accordingly, an impressive embodiment of evidence supports the concept that the dietary factors are critical modulators to prevent, retard, block, or reverse carcinogenesis. Such an action reflects the ability of these molecules to interfere with multitude of pathways to subdue and neutralize several oncogenic factors and thereby keep a restraint on neoplastic transformations. This review provides a series of experimental evidence based on the current literature to highlight the translational potential of nutraceuticals for the prevention of the disease through consumption of enriched diets and its efficacious management by means of novel interventions. Specifically, this review provides the current understanding of the chemopreventive pharmacology of nutraceuticals such as cucurbitacins, morin, fisetin, curcumin, luteolin and garcinol toward their potential as anticancer agents.

Synthesis and Biological Evaluation of Spirocyclic Chromane Derivatives as a Potential Treatment of Prostate Cancer

As a significant co-activator involved in cell cycle and cell growth, differentiation and development, p300/CBP has shown extraordinary potential target in cancer therapy. Herein we designed new compounds from the lead compound A-485 based on molecular dynamic simulations. A series of new spirocyclic chroman derivatives was prepared, characterized and proven to be a potential treatment of prostate cancer. The most potent compound B16 inhibited the proliferation of enzalutamide-resistant 22Rv1 cells with an IC₅₀ value of 96 nM. Furthermore, compounds B16–P2 displayed favorable overall pharmacokinetic profiles, and better tumor growth inhibition than A-485 in an in vivo xenograft model.

Stereodivergent Strategy in Structural Determination: Asymmetric Total Synthesis of Garcinol, Cambogin, and Related Analogues

The asymmetric total synthesis of five biologically significant polycyclic polyprenylated acylphloroglucinols (PPAPs), including garcinol and cambogin, was achieved through a highly diastereoselective and stereodivergent strategy. Along the way, an efficient cascade Dieckmann cyclization was employed to construct the bicyclo[3.3.1]nonane core in one step. The synthesis provided a general approach toward the chiral endo-type B PPAPs and their C-30 diastereomers in a single sequence, which resolved the challenges of the absolute configuration determination/structural revision of PPAPs bearing exocyclic stereocenters.

Histone Acetyltransferases and Stem Cell Identity

Acetylation of histones is a key epigenetic modification involved in transcriptional regulation. The addition of acetyl groups to histone tails generally reduces histone-DNA interactions in the nucleosome leading to increased accessibility for transcription factors and core transcriptional machinery to bind their target sequences. There are approximately 30 histone acetyltransferases and their corresponding complexes, each of which affect the expression of a subset of genes. Because cell identity is determined by gene expression profile, it is unsurprising that the HATs responsible for inducing expression of these genes play a crucial role in determining cell fate. Here, we explore the role of HATs in the maintenance and differentiation of various stem cell types. Several HAT complexes have been characterized to play an important role in activating genes that allow stem cells to self-renew. Knockdown or loss of their activity leads to reduced expression and or differentiation while particular HATs drive differentiation towards specific cell fates. In this study we review functions of the HAT complexes active in pluripotent stem cells, hematopoietic stem cells, muscle satellite cells, mesenchymal stem cells, neural stem cells, and cancer stem cells.

Epigenetics of addiction

Substance use disorders are complex biopsychosocial disorders that have substantial negative neurocognitive impact in various patient populations. These diseases involve the compulsive use of licit or illicit substances despite adverse medicolegal consequences and appear to be secondary to long-lasting epigenetic and transcriptional adaptations in brain reward and non-reward circuits. The accumulated evidence supports the notion that repeated drug use causes changes in post-translational histone modifications and in DNA methylation/hydroxymethylation processes in several brain regions. This review provides an overview of epigenetic changes reported in models of cocaine, methamphetamine, and opioid use disorders. The accumulated data suggest that future therapeutic interventions should focus on the development of epigenetic drugs against addictive diseases.

Metabolic Reprogramming by Reduced Calorie Intake or Pharmacological Caloric Restriction Mimetics for Improved Cancer Immunotherapy

Caloric restriction and fasting have been known for a long time for their health- and life-span promoting effects, with coherent observations in multiple model organisms as well as epidemiological and clinical studies. This holds particularly true for cancer. The health-promoting effects of caloric restriction and fasting are mediated at least partly through their cellular effects-chiefly autophagy induction-rather than reduced calorie intake per se. Interestingly, caloric restriction has a differential impact on cancer and healthy cells, due to the atypical metabolic profile of malignant tumors. Caloric restriction mimetics are non-toxic compounds able to mimic the biochemical and physiological effects of caloric restriction including autophagy induction. Caloric restriction and its mimetics induce autophagy to improve the efficacy of some cancer treatments that induce immunogenic cell death (ICD), a type of cellular demise that eventually elicits adaptive antitumor immunity. Caloric restriction and its mimetics also enhance the therapeutic efficacy of chemo-immunotherapies combining ICD-inducing agents with immune checkpoint inhibitors targeting PD-1. Collectively, preclinical data encourage the application of caloric restriction and its mimetics as an adjuvant to immunotherapies. This recommendation is subject to confirmation in additional experimental settings and in clinical trials. In this work, we review the preclinical and clinical evidence in favor of such therapeutic interventions before listing ongoing clinical trials that will shed some light on this subject.

Synthesis and Multiplexed Activity Profiling of Synthetic Acylphloroglucinol Scaffolds

Reported here are novel formic-acid-mediated rearrangements of dearomatized acylphloroglucinols to access a structurally diverse group of synthetic acylphloroglucinol scaffolds (SASs). Density-functional theory (DFT) optimized orbital and stereochemical analyses shed light on the mechanism of these rearrangements. Products were evaluated by multiplexed activity profiling (MAP), an unbiased platform which assays multiple biological readouts simultaneously at single-cell resolution for markers of cell signaling, and can aid in distinguishing genuine activity from assay interference. MAP identified a number of SASs that suppressed pS6 (Ser235/236), a marker for activation of the mTOR and ERK signaling pathways. These results illustrate how biomimetic synthesis and multiplexed activity profiling can reveal the pharmacological potential of novel chemotypes by diversity-oriented synthesis.

Dietary molecules and experimental evidence of epigenetic influence in cancer chemoprevention: An insight

The world-wide rate of incidence of cancer disease has been only modestly contested by the past and current preventive and interventional strategies. Hence, the global effort towards novel ideas to contain the disease still continues. Constituents of human diets have in recent years emerged as key regulators of carcinogenesis, with studies reporting their inhibitory potential against all the three stages vis-a-vis initiation, promotion and progression. Unlike drugs which usually act on single targets, these dietary factors have an advantage of multi-targeted effects and pleiotropic action mechanisms, which are effective against cancer that manifest as a micro-evolutionary and multi-factorial disease. Since most of the cellular targets have been identified and their consumption considered relatively safe, these diet-derived agents often appear as molecules of interest in repurposing strategies. Currently, many of these molecules are being investigated for their ability to influence the aberrant alterations in cell's epigenome for epigenetic therapy against cancer. Targeting the epigenetic regulators is a new paradigm in cancer chemoprevention which acts to reverse the warped-up epigenetic alterations in a cancer cell, thereby directing it towards a normal phenotype. In this review, we discuss the significance of dietary factors and natural products as chemopreventive agents. Further, we corroborate the experimental evidence from existing literature, reflecting the ability of a series of such molecules to act as epigenetic modifiers in cancer cells, by interfering with molecular events that map the epigenetic imprints such as DNA methylation, histone acetylation and non-coding RNA mediated gene regulation.

Chromatin-modifying drugs and metabolites in cell fate control

For multicellular organisms, it is essential to produce a variety of specialized cells to perform a dazzling panoply of functions. Chromatin plays a vital role in determining cellular identities, and it dynamically regulates gene expression in response to changing nutrient metabolism and environmental conditions. Intermediates produced by cellular metabolic pathways are used as cofactors or substrates for chromatin modification. Drug analogues of metabolites that regulate chromatin-modifying enzyme reactions can also regulate cell fate by adjusting chromatin organization. In recent years, there have been many studies about how chromatin-modifying drug molecules or metabolites can interact with chromatin to regulate cell fate. In this review, we systematically discuss how DNA and histone-modifying molecules alter cell fate by regulating chromatin conformation and propose a mechanistic model that explains the process of cell fate transitions in a concise and qualitative manner.

Role of histone acetyltransferase inhibitors in cancer therapy

The development of cancer is a complex phenomenon driven by various extrinsic as well as intrinsic risk factors including epigenetic modifications. These post-translational modifications are encountered in diverse cancer cells and appear for a relatively short span of time. These changes can significantly affect various oncogenic genes and proteins involved in cancer initiation and progression. Histone lysine acetylation and deacetylation processes are controlled by two opposing classes of enzymes that modulate gene regulation either by adding an acetyl moiety on a histone lysine residue by histone lysine acetyltransferases (KATs) or via removing it by histone deacetylases (KDACs). Deregulated KAT activity has been implicated in the development of several diseases including cancer and can be targeted for the development of anti-neoplastic drugs. Here, we describe the predominant epigenetic changes that can affect key KAT superfamily members during carcinogenesis and briefly highlight the pharmacological potential of employing lysine acetyltransferase inhibitors (KATi) for cancer therapy.

Bicyclic polyprenylated acylphloroglucinols and their derivatives: structural modification, structure-activity relationship, biological activity and mechanism of action

Bicyclic polyprenylated acylphloroglucinols (BPAPs), the principal bioactive benzophenone products isolated from plants of genera Garcinia and Hypericum, have attracted noticeable attention from the synthetic and biological communities due to their fascinating chemical structures and promising biological activities. However, the potential drug interaction, undesired physiochemical properties and toxicity have limited their potential use and development. In the last decade, pharmaceutical research on the structural modifications, structure-activity relationships (SARs) and mechanisms of action of BPAPs has been greatly developed to overcome the challenges. A comprehensive review of these scientific literature is extremely needed to give an overview of the rapidly emerging area and facilitate research related to BPAPs. This review, containing over 226 references, covers the progress made in the chemical synthesis-based structure modifications, SARs and the mechanism of action of BPAPs in vivo and vitro. The most relevant articles will focus on the discovery of lead compounds via synthetic modifications and the important BPAPs for which the direct targets have been deciphered. From this review, several key points of the SARs and mode of actions of this novel class of compounds have been summarized. The perspective and future direction of the research on BPAPs are concluded. This review would be helpful to get a better grasp of medicinal research of BPAPs and become a compelling guide for chemists dedicated to the synthesis of these compounds.

Discovery of Highly Potent, Selective, and Orally Efficacious p300/CBP Histone Acetyltransferases Inhibitors

p300 and CREB-binding protein (CBP) are ubiquitously expressed pleiotropic lysine acetyltransferases and play a key role as transcriptional co-activators that are essential for a multitude of cellular processes. Despite great importance, there is a lack of highly selective, potent, druglike p300/CBP inhibitors. Through the artificial-intelligence-assisted drug discovery pipeline and further optimization, we reported the discovery of novel, highly selective, potent small-molecule inhibitors of p300/CBP histone acetyltransferases (HAT) with desired druglike properties, exemplified by B026. Our data demonstrated that B026, with half maximal inhibitory concentration (IC₅₀) values of 1.8 nM to p300 and 9.5 nM to CBP enzyme inhibitory activity, is the most potent, selective p300/CBP HAT inhibitor. Moreover, B026 achieves significant and dose-dependent tumor growth inhibition in an animal model of human cancer, suggesting that B026 is a highly promising p300/CBP HAT inhibitor and warrants extensive preclinical investigation as a potential clinical development candidate.

Suppression of STAT3 Phosphorylation and RelA/p65 Acetylation Mediated by MicroRNA134 Plays a Pivotal Role in the Apoptotic Effect of Lambertianic Acid

As p300-mediated RelA/p65 hyperacetylation by signal transducers and activators of transcription 3 (STAT3) is critical for NF-κB activation, in the current study, the apoptotic mechanism of lambertianic acid (LA) was explored in relation to STAT3 phosphorylation and RelA/p65 acetylation in MCF-7, DU145, PC-3, and MDA-MB-453 cells. LA significantly increased the cytotoxicity, sub G 1 population, and the cleavage of poly (ADP-ribose) polymerase (PARP) in MDA-MB-453 or PC-3 cells (STAT3 mutant), more than in the MCF-7 or DU145 cells (STAT3 wild). Consistently, LA inhibited the phosphorylation of STAT3 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and disrupted the interaction between p-STAT3, p300, NF-κB, and RelA/p65 acetylation (Ac-RelA/p65) in the MCF-7 and DU145 cells. Also, LA reduced the nuclear translocation of STAT3 and NF-κB via their colocalization, and also suppressed the protein expression of XIAP, survivin, Bcl-2, Bcl-xL, vascular endothelial growth factor (VEGF), Cox-2, c-Myc and mRNA expression of interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α) in MCF-7 cells. Conversely, IL-6 blocked the ability of LA to suppress the cytotoxicity and PARP cleavage, while the depletion of STAT3 or p300 enhanced the PARP cleavage of LA in the MCF-7 cells. Notably, LA upregulated the level of miRNA134 and so miRNA134 mimic attenuated the expression of pro-PARP, p-STAT3, and Ac-RelA, while the miRNA134 inhibitor reversed the ability of LA to reduce the expression of Ac-RelA and pro-PARP in MCF-7 cells. Overall, these findings suggest that LA induced apoptosis via the miRNA-134 mediated inhibition of STAT3 and RelA/p65 acetylation.

Histone acetyltransferase inhibitors: An overview in synthesis, structure-activity relationship and molecular mechanism

Acetylation, a key component in post-translational modification regulated by HATs and HDACs, is relevant to many crucial cellular contexts in organisms. Based on crucial pharmacophore patterns and the structure of targeted proteins, HAT inhibitors are designed and modified for higher affinity and better bioactivity. However, there are still some challenges, such as cell permeability, selectivity, toxicity and synthetic availability, which limit the improvement of HAT inhibitors. So far, only few HAT inhibitors have been approved for commercialization, indicating the urgent need for more successful and effective structure-based drug design and synthetic strategies. Here, we summarized three classes of HAT inhibitors based on their sources and structural scaffolds, emphasizing on their synthetic methods and structure-activity relationships and molecular mechanisms, hoping to facilitate the development and further application of HAT inhibitors.

Role of histone acetylation in gastric cancer: implications of dietetic compounds and clinical perspectives

Histone modifications regulate the structural status of chromatin and thereby influence the transcriptional status of genes. These processes are controlled by the recruitment of different enzymes to a specific genomic site. Furthermore, obtaining an understanding of these mechanisms could help delineate alternative treatment and preventive strategies for cancer. For example, in gastric cancer, cholecalciferol, curcumin, resveratrol, quercetin, garcinol and sodium butyrate are natural regulators of acetylation and deacetylation enzyme activity that exert chemopreventive and anticancer effects. Here, we review the recent findings on histone acetylation in gastric cancer and discuss the effects of nutrients and bioactive compounds on histone acetylation and their potential role in the prevention and treatment of this type of cancer.

Inhibitor of CBP Histone Acetyltransferase Downregulates p53 Activation and Facilitates Methylation at Lysine 27 on Histone H3

Tumor suppressor p53-directed apoptosis triggers loss of normal cells, which contributes to the side-effects from anticancer therapies. Thus, small molecules with potential to downregulate the activation of p53 could minimize pathology emerging from anticancer therapies. Acetylation of p53 by the histone acetyltransferase (HAT) domain is the hallmark of coactivator CREB-binding protein (CBP) epigenetic function. During genotoxic stress, CBP HAT-mediated acetylation is essential for the activation of p53 to transcriptionally govern target genes, which control cellular responses. Here, we present a small molecule, NiCur, which blocks CBP HAT activity and downregulates p53 activation upon genotoxic stress. Computational modeling reveals that NiCur docks into the active site of CBP HAT. On CDKN1A promoter, the recruitment of p53 as well as RNA Polymerase II and levels of acetylation on histone H3 were diminished by NiCur. Specifically, NiCur reduces the levels of acetylation at lysine 27 on histone H3, which concomitantly increases the levels of trimethylation at lysine 27. Finally, NiCur attenuates p53-directed apoptosis by inhibiting the Caspase 3 activity and cleavage of Poly (ADP-ribose) polymerase (PARP) in normal gastrointestinal epithelial cells. Collectively, NiCur demonstrates the potential to reprogram the chromatin landscape and modulate biological outcomes of CBP-mediated acetylation under normal and disease conditions.

Lysine acetyltransferase inhibitors: structure-activity relationships and potential therapeutic implications

Lysine acetylation is a post-translational modification of both histone and nonhistone proteins that is catalyzed by lysine acetyltransferases and plays a key role in numerous biological contexts. The dysregulation of this enzyme activity is implicated in many human pathologies such as cancer, neurological and inflammatory disorders. Many lysine acetyltransferase inhibitors (KATi) have been developed so far, but there is still the need for new, more potent, metabolically stable and selective KATi as chemical tools for studying KAT biology and/or as potential therapeutic agents. This review will examine the features of KAT enzymes and related diseases, with particular emphasis on KATi (bisubstrate analogs, natural compounds and synthetic derivatives), analyzing their mechanism of action, structure-activity relationships, pharmacokinetic/pharmacodynamic properties and potential future applications.

Research Progress of Polycyclic Polyprenylated Acylphloroglucinols

Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a class of hybrid natural products sharing the mevalonate/methylerythritol phosphate and polyketide biosynthetic pathways and showing considerable structure and bioactivity diversity. This review discusses the progress of research into the chemistry and biological activity of 421 natural PPAPs in the past 11 years as well as in-depth studies of biological activities and total synthesis of some PPAPs isolated before 2006. We created an online database of all PPAPs known to date at http://www.chem.uky.edu/research/grossman/PPAPs . Two subclasses of biosynthetically related metabolites, spirocyclic PPAPs with octahydrospiro[cyclohexan-1,5'-indene]-2,4,6-trione core and complicated PPAPs produced by intramolecular [4 + 2] cycloadditions of MPAPs, are brought into the PPAP family. Some PPAPs' relative or absolute configurations are reassigned or critically discussed, and the confusing trivial names in PPAPs investigations are clarified. Pharmacologic studies have revealed a new molecular mechanism whereby hyperforin and its derivatives regulate neurotransmitter levels by activating TRPC6 as well as the antitumor mechanism of garcinol and its analogues. The antineoplastic potential of some type B PPAPs such as oblongifolin C and guttiferone K has increased significantly. As a result of the recent appearances of innovative synthetic methods and strategies, the total syntheses of 22 natural PPAPs including hyperforin, garcinol, and plukenetione A have been accomplished.

Lysine Acetylation Goes Global: From Epigenetics to Metabolism and Therapeutics

Post-translational acetylation of lysine residues has emerged as a key regulatory mechanism in all eukaryotic organisms. Originally discovered in 1963 as a unique modification of histones, acetylation marks are now found on thousands of nonhistone proteins located in virtually every cellular compartment. Here we summarize key findings in the field of protein acetylation over the past 20 years with a focus on recent discoveries in nuclear, cytoplasmic, and mitochondrial compartments. Collectively, these findings have elevated protein acetylation as a major post-translational modification, underscoring its physiological relevance in gene regulation, cell signaling, metabolism, and disease.

The epigenetic factor PCAF regulates vascular inflammation and is essential for intimal hyperplasia development

Objective

Genetic P300/CBP-associated factor (PCAF) variation affects restenosis-risk in patients. PCAF has lysine acetyltransferase activity and promotes nuclear factor kappa-beta (NFκB)-mediated inflammation, which drives post-interventional intimal hyperplasia development. We studied the contributing role of PCAF in post-interventional intimal hyperplasia.

Methods and results

PCAF contribution to inflammation and intimal hyperplasia was assessed in leukocytes, macrophages and vascular smooth muscle cells (vSMCs) in vitro and in a mouse model for intimal hyperplasia, in which a cuff is placed around the femoral artery. PCAF deficiency downregulate CCL2, IL-6 and TNF-alpha expression, as demonstrated on cultured vSMCs, leukocytes and macrophages. PCAF KO mice showed a 71.8% reduction of vSMC-rich intimal hyperplasia, a 73.4% reduction of intima/media ratio and a 63.7% reduction of luminal stenosis after femoral artery cuff placement compared to wild type (WT) mice. The association of PCAF and vascular inflammation was further investigated using the potent natural PCAF inhibitor garcinol. Garcinol treatment reduced CCL2 and TNF-alpha expression, as demonstrated on cultured vSMCs and leukocytes.

To assess the effect of garcinol treatment on vascular inflammation we used hypercholesterolemic ApoE*3-Leiden mice. After cuff placement, garcinol treatment resulted in reduced arterial leukocyte and macrophage adherence and infiltration after three days compared to untreated animals.

Conclusions

These results identify a vital role for the lysine acetyltransferase PCAF in the regulation of local inflammation after arterial injury and likely the subsequent vSMC proliferation, responsible for intimal hyperplasia.

Targeting cancer using KAT inhibitors to mimic lethal knockouts

Two opposing enzyme classes regulate fundamental elements of genome maintenance, gene regulation and metabolism, either through addition of an acetyl moiety by histone acetyltransferases (HATs) or its removal by histone de-acetyltransferases (HDAC), and are exciting targets for drug development. Importantly, dysfunctional acetylation has been implicated in numerous diseases, including cancer. Within the HAT superfamily the MYST family holds particular interest, as its members are directly involved in the DNA damage response and repair pathways and crucially, several members have been shown to be down-regulated in common cancers (such as breast and prostate). In the present study we focus on the development of lysine (K) acetyltransferase inhibitors (KATi) targeting the MYST family member Tip60 (Kat5), an essential protein, designed or discovered through screening libraries. Importantly, Tip60 has been demonstrated to be significantly down-regulated in many cancers which urgently require new treatment options. We highlight current and future efforts employing these KATi as cancer treatments and their ability to synergize and enhance current cancer treatments. We investigate the different methods of KATi production or discovery, their mechanisms and their validation models. Importantly, the utility of KATi is based on a key concept: using KATi to abrogate the activity of an already down-regulated essential protein (effectively creating a lethal knockout) provides another innovative mechanism for targeting cancer cells, while significantly minimizing any off-target effects to normal cells. This approach, combined with the rapidly developing interest in KATi, suggests that KATi have a bright future for providing truly personalized therapies.

Bromodomain inhibitors and cancer therapy: From structures to applications

Aberrations in the epigenetic landscape are a hallmark of cancer. Alterations in enzymes that are “writers,” “erasers,” or “readers” of histone modification marks are common. Bromodomains are “readers” that bind acetylated lysines in histone tails. Their most important function is the regulation of gene transcription by the recruitment of different molecular partners. Moreover, proteins containing bromodomains are also epigenetic regulators, although little is known about the specific function of these domains. In recent years, there has been increasing interest in developing small molecules that can target specific bromodomains. First, this has helped clarify biological functions of bromodomain-containing proteins. Secondly, it opens a new front for combatting cancer. In this review we will describe the structures and mechanisms associated with Bromodomain and Extra-Terminal motif (BET) inhibitors and non-BET inhibitors, their current status of development, and their promising role as anti-cancer agents.

Syntheses of (+)-30-epi-, (-)-6-epi-, (±)-6,30-epi-13,14-Didehydroxyisogarcinol and (±)-6,30-epi-Garcimultiflorone A Utilizing Highly Diastereoselective, Lewis Acid-Controlled Cyclizations

The first syntheses of 13,14-didehydroxyisogarcinol (6) and garcimultiflorone A (5) stereoisomers are reported in six steps from a commercially available phloroglucinol. Lewis acid-controlled, diastereoselective cationic oxycyclizations enabled asymmetric syntheses of (-)-6-epi-6 and (+)-30-epi-6. A similar strategy enabled production of the meso-dervied isomers (±)-6,30-epi-6 and (±)-6,30-epi-5. Finally, a convenient strategy for gram scale synthesis was developed utilizing diastereomer separation at a later stage in the synthesis that minimized the number of necessary synthetic operations to access all possible stereoisomers.

Histone acetyltransferases: challenges in targeting bi-substrate enzymes

Histone acetyltransferases (HATs) are epigenetic enzymes that install acetyl groups onto lysine residues of cellular proteins such as histones, transcription factors, nuclear receptors, and enzymes. HATs have been shown to play a role in diseases ranging from cancer and inflammatory diseases to neurological disorders, both through acetylations of histone proteins and non-histone proteins. Several HAT inhibitors, like bi-substrate inhibitors, natural product derivatives, small molecules, and protein–protein interaction inhibitors, have been developed. Despite their potential, a large gap remains between the biological activity of inhibitors in in vitro studies and their potential use as therapeutic agents. To bridge this gap, new potent HAT inhibitors with improved properties need to be developed. However, several challenges have been encountered in the investigation of HATs and HAT inhibitors that hinder the development of new HAT inhibitors. HATs have been shown to function in complexes consisting of many proteins. These complexes play a role in the activity and target specificity of HATs, which limits the translation of in vitro to in vivo experiments. The current HAT inhibitors suffer from undesired properties like anti-oxidant activity, reactivity, instability, low potency, or lack of selectivity between HAT subtypes and other enzymes. A characteristic feature of HATs is that they are bi-substrate enzymes that catalyze reactions between two substrates: the cofactor acetyl coenzyme A (Ac-CoA) and a lysine-containing substrate. This has important—but frequently overlooked—consequences for the determination of the inhibitory potency of small molecule HAT inhibitors and the reproducibility of enzyme inhibition experiments. We envision that a careful characterization of molecular aspects of HATs and HAT inhibitors, such as the HAT catalytic mechanism and the enzyme kinetics of small molecule HAT inhibitors, will greatly improve the development of potent and selective HAT inhibitors and provide validated starting points for further development towards therapeutic agents.

Inhibitors of enzymes catalyzing modifications to histone lysine residues: structure, function and activity

Gene expression is partly controlled by epigenetic mechanisms including histone-modifying enzymes. Some diseases are caused by changes in gene expression that can be mitigated by inhibiting histone-modifying enzymes. This review covers the enzyme inhibitors targeting histone lysine modifications. We summarize the enzymatic mechanisms of histone lysine acetylation, deacetylation, methylation and demethylation and discuss the biochemical roles of these modifications in gene expression and in disease. We discuss inhibitors of lysine acetylation, deacetylation, methylation and demethylation defining their structure-activity relationships and their potential mechanisms. We show that there are potentially indiscriminant off-target effects on gene expression even with the use of selective epigenetic enzyme inhibitors.

KATching-Up on Small Molecule Modulators of Lysine Acetyltransferases

The reversible acetylation of lysines is one of the best characterized epigenetic modifications. Its involvement in many key physiological and pathological processes has been documented in numerous studies. Lysine deacetylases (KDACs) and acetyltransferases (KATs) maintain the acetylation equilibrium at histones but also many other proteins. Besides acetylation, also other acyl groups are reversibly installed at the side chain of lysines in proteins. Because of their involvement in disease, KDACs and KATs were proposed to be promising drug targets, and for KDACs, indeed, five inhibitors are now approved for human use. While there is a similar level of evidence for the potential of KATs as drug targets, no inhibitor is in clinical trials. Here, we review the evidence for the diverse roles of KATs in disease pathology, provide an overview of structural features and the available modulators, including those targeting the bromodomains of KATs, and present an outlook.

Generation of a Selective Small Molecule Inhibitor of the CBP/p300 Bromodomain for Leukemia Therapy

The histone acetyltransferases CBP/p300 are involved in recurrent leukemia-associated chromosomal translocations and are key regulators of cell growth. Therefore, efforts to generate inhibitors of CBP/p300 are of clinical value. We developed a specific and potent acetyl-lysine competitive protein-protein interaction inhibitor, I-CBP112, that targets the CBP/p300 bromodomains. Exposure of human and mouse leukemic cell lines to I-CBP112 resulted in substantially impaired colony formation and induced cellular differentiation without significant cytotoxicity. I-CBP112 significantly reduced the leukemia-initiating potential of MLL-AF9(+) acute myeloid leukemia cells in a dose-dependent manner in vitro and in vivo. Interestingly, I-CBP112 increased the cytotoxic activity of BET bromodomain inhibitor JQ1 as well as doxorubicin. Collectively, we report the development and preclinical evaluation of a novel, potent inhibitor targeting CBP/p300 bromodomains that impairs aberrant self-renewal of leukemic cells. The synergistic effects of I-CBP112 and current standard therapy (doxorubicin) as well as emerging treatment strategies (BET inhibition) provide new opportunities for combinatorial treatment of leukemia and potentially other cancers.

CBP30, a selective CBP/p300 bromodomain inhibitor, suppresses human Th17 responses

Th17 responses are critical to a variety of human autoimmune diseases, and therapeutic targeting with monoclonal antibodies against IL-17 and IL-23 has shown considerable promise. Here, we report data to support selective bromodomain blockade of the transcriptional coactivators CBP (CREB binding protein) and p300 as an alternative approach to inhibit human Th17 responses. We show that CBP30 has marked molecular specificity for the bromodomains of CBP and p300, compared with 43 other bromodomains. In unbiased cellular testing on a diverse panel of cultured primary human cells, CBP30 reduced immune cell production of IL-17A and other proinflammatory cytokines. CBP30 also inhibited IL-17A secretion by Th17 cells from healthy donors and patients with ankylosing spondylitis and psoriatic arthritis. Transcriptional profiling of human T cells after CBP30 treatment showed a much more restricted effect on gene expression than that observed with the pan-BET (bromo and extraterminal domain protein family) bromodomain inhibitor JQ1. This selective targeting of the CBP/p300 bromodomain by CBP30 will potentially lead to fewer side effects than with the broadly acting epigenetic inhibitors currently in clinical trials.

A novel cell-permeable, selective, and noncompetitive inhibitor of KAT3 histone acetyltransferases from a combined molecular pruning/classical isosterism approach

Selective inhibitors of the two paralogue KAT3 acetyltransferases (CBP and p300) may serve not only as precious chemical tools to investigate the role of these enzymes in physiopathological mechanisms but also as lead structures for the development of further antitumor agents. After the application of a molecular pruning approach to the hardly optimizable and not very cell-permeable garcinol core structure, we prepared many analogues that were screened for their inhibitory effects using biochemical and biophysical (SPR) assays. Further optimization led to the discovery of the benzylidenebarbituric acid derivative 7h (EML425) as a potent and selective reversible inhibitor of CBP/p300, noncompetitive versus both acetyl-CoA and a histone H3 peptide, and endowed with good cell permeability. Furthermore, in human leukemia U937 cells, it induced a marked and time-dependent reduction in the acetylation of lysine H4K5 and H3K9, a marked arrest in the G0/G1 phase and a significant increase in the hypodiploid nuclei percentage.

Garcinol, an acetyltransferase inhibitor, suppresses proliferation of breast cancer cell line MCF-7 promoted by 17β-estradiol

The acetyltransferase inhibitor garcinol, a polyisoprenylated benzophenone, is extracted from the rind of the fruit of Garcinia indica, a plant found extensively in tropical regions. Anti-cancer activity has been suggested but there is no report on its action via inhibiting acetylation against cell proliferation, cell cycle progression, and apoptosis-inhibtion induced by estradiol (E2) in human breast cancer MCF-7 cells. The main purposes of this study were to investigate the effects of the acetyltransferase inhibitor garcinol on cell proliferation, cell cycle progression and apoptosis inhibition in human breast cancer MCF-7 cells treated with estrogen, and to explore the significance of changes in acetylation levels in this process. We used a variety of techniques such as CCK-8 analysis of cell proliferation, FCM analysis of cell cycling and apoptosis, immunofluorescence analysis of NF-κB/ p65 localization, and RT-PCR and Western blotting analysis of ac-H3, ac-H4, ac-p65, cyclin D1, Bcl-2 and Bcl- xl. We found that on treatment with garcinol in MCF-7 cells, E2-induced proliferation was inhibited, cell cycle progression was arrested at G0/G1 phase, and the cell apoptosis rate was increased. Expression of ac-H3, ac-H4 and NF-κB/ac-p65 proteins in E2-treated MCF-7 cells was increased, this being inhibited by garcinol but not ac- H4.The nuclear translocation of NF-κB/p65 in E2-treated MCF-7 cells was also inhibited, along with cyclin D1, Bcl-2 and Bcl-xl in mRNA and protein expression levels. These results suggest that the effect of E2 on promoting proliferation and inhibiting apoptosis is linked to hyperacetylation levels of histones and nonhistone NF-κB/ p65 in MCF-7 cells. The acetyltransferase inhibitor garcinol plays an inhibitive role in MCF-7 cell proliferation promoted by E2. Mechanisms are probably associated with decreasing ac-p65 protein expression level in the NF-κB pathway, thus down-regulating the expression of cyclin D1, Bcl-2 and Bcl-xl.

KATs in cancer: functions and therapies

Post-translational acetylation of lysines is most extensively studied in histones, but this modification is also found in many other proteins and is implicated in a wide range of biological processes in both the cell nucleus and the cytoplasm. Like phosphorylation, acetylation patterns and levels are often altered in cancer, therefore small molecule inhibition of enzymes that regulate acetylation and deacetylation offers much potential for inhibiting cancer cell growth, as does disruption of interactions between acetylated residues and ‘reader’ proteins. For more than a decade now, histone deacetylase (HDAC) inhibitors have been investigated for their ability to increase acetylation and promote expression of tumor suppressor genes. However, emerging evidence suggests that acetylation can also promote cancer, in part by enhancing the functions of oncogenic transcription factors. In this review we focus on how acetylation of both histone and non-histone proteins may drive cancer, and we will discuss the implications of such changes on how patients are assigned to therapeutic agents. Finally, we will explore what the future holds in the design of small molecule inhibitors for modulation of levels or functions of acetylation states.

Polyphenols and the modulation of gene expression pathways: can we eat our way out of the danger of chronic disease?

Plant-derived dietary polyphenols may improve some disease states and promote health. Experimental evidence suggests that this is partially attributable to changes in gene expression. The rational use of bioactive food components may therefore present an opportunity to activate or repress selected gene expression pathways and, consequently, to manage or prevent disease. It remains to be determined whether this use of bioactive food components can be done safely. This article reviews the associated controversies and limitations of polyphenol therapy. There is a paucity of clinical data on the rational use of polyphenols, including a lack of knowledge on effective dosage, actual chemical formulations, bioavailability, distribution in tissues, the effect of genetic variations, differences in gut microflora, the synergistic (or antagonistic) effects observed in extracts, and the possible interaction between polyphenols and lipid domains of cell membranes that may alter the function of relevant receptors. The seminal question of why plants make substances that benefit humans remains unanswered, and there is still much to learn in terms of correlative versus causal effects of human exposure to various nutrients. The available data strongly suggest significant effects at the molecular level that represent interactions with the epigenome. The advent of relatively simple technologies is helping the field of epigenetics progress and facilitating the acquisition of multiple types of data that were previously difficult to obtain. In this review, we summarize the molecular basis of the epigenetic regulation of gene expression and the epigenetic changes associated with the consumption of polyphenols that illustrate how modifications in human nutrition may become relevant to health and disease.

Caloric restriction mimetics: towards a molecular definition

Caloric restriction, be it constant or intermittent, is reputed to have health-promoting and lifespan-extending effects. Caloric restriction mimetics (CRMs) are compounds that mimic the biochemical and functional effects of caloric restriction. In this Opinion article, we propose a unifying definition of CRMs as compounds that stimulate autophagy by favouring the deacetylation of cellular proteins. This deacetylation process can be achieved by three classes of compounds that deplete acetyl coenzyme A (AcCoA; the sole donor of acetyl groups), that inhibit acetyl transferases (a group of enzymes that acetylate lysine residues in an array of proteins) or that stimulate the activity of deacetylases and hence reverse the action of acetyl transferases. A unifying definition of CRMs will be important for the continued development of this class of therapeutic agents.

Isolation and biological activity of compounds from Garcinia preussii

CONTEXT

Plants of the genus Garcinia (Clusiaceae) are traditionally used to relieve stomachaches, toothaches, and as a chew stick.

OBJECTIVE

In order to determine which compounds were responsible for these activities, a phytochemical investigation of the fruits and leaves of Garcinia preussii Engl. was pursued.

MATERIALS AND METHODS

Plants were extracted by solvents of various polarities. Compounds isolation was then carried out using chromatography methods (medium- and high-pressure liquid chromatography, open column and thin-layer chromatography). The isolated compounds were identified and characterized by using 1D and 2D NMR spectroscopies. The antioxidant activity was evaluated using DPPH(•), ABTS(•-), ALP, and ORAC assays. The antimicrobial activity was assayed against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis by determining the minimum inhibitory concentration (MIC) value. The cytotoxic activity of most of the isolated compounds was evaluated on a small panel of human cancer cell lines (DU145, HeLa, HT-29, and A431) using the XTT method.

RESULTS

The phytochemical investigation of G. preussii led to the isolation of eight known compounds, six benzophenones and two flavonoids. These compounds were tested for their biological activities. 1, 2, 3, 4, 7 and 8 demonstrated a high free radical scavenging activity with ER50 ranging from 0.1 to 0.7. The antimicrobial activity was shown only against Gram-positive bacteria for 1, 4, and 5. A moderate cytotoxic activity with IC50 ranging from 7 to 50 µM was observed, except for 6 which was not active.

CONCLUSION

These results appear to support some of the properties reported for Garcinia species.

Pneumocystis jirovecii Rtt109, a novel drug target for Pneumocystis pneumonia in immunosuppressed humans

Pneumocystis pneumonia (PcP) is a significant cause of morbidity and mortality in immunocompromised patients. In humans, PcP is caused by the opportunistic fungal species Pneumocystis jirovecii. Progress in Pneumocystis research has been hampered by a lack of viable in vitro culture methods, which limits laboratory access to human-derived organisms for drug testing. Consequently, most basic drug discovery research for P. jirovecii is performed using related surrogate organisms such as Pneumocystis carinii, which is derived from immunosuppressed rodents. While these studies provide useful insights, important questions arise about interspecies variations and the relative utility of identified anti-Pneumocystis agents against human P. jirovecii. Our recent work has identified the histone acetyltransferase (HAT) Rtt109 in P. carinii (i.e., PcRtt109) as a potential therapeutic target for PcP, since Rtt109 HATs are widely conserved in fungi but are absent in humans. To further address the potential utility of this target in human disease, we now demonstrate the presence of a functional Rtt109 orthologue in the clinically relevant fungal pathogen P. jirovecii (i.e., PjRtt109). In a fashion similar to that of Pcrtt109, Pjrtt109 restores H3K56 acetylation and genotoxic resistance in rtt109-null yeast. Recombinant PjRtt109 is an active HAT in vitro, with activity comparable to that of PcRtt109 and yeast Rtt109. PjRtt109 HAT activity is also enhanced by the histone chaperone Asf1 in vitro. PjRtt109 and PcRtt109 showed similar low micromolar sensitivities to two reported small-molecule HAT inhibitors in vitro. Together, these results demonstrate that PjRtt109 is a functional Rtt109 HAT, and they support the development of anti-Pneumocystis agents directed at Rtt109-catalyzed histone acetylation as a novel therapeutic target for human PcP.

Inhibition of STAT3 dimerization and acetylation by garcinol suppresses the growth of human hepatocellular carcinoma in vitro and in vivo

Background

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) has been linked with proliferation, survival, invasion and angiogenesis of a variety of human cancer cells, including hepatocellular carcinoma (HCC). Thus, novel agents that can suppress STAT3 activation have potential for both prevention and treatment of HCC. Here we report, garcinol, a polyisoprenylated benzophenone, could suppress STAT3 activation in HCC cell lines and in xenografted tumor of HCC in nude mice model.

Experimental design

Different HCC cell lines have been treated with garcinol and the inhibition of STAT3 activation, dimerization and acetylation have been checked by immunoblotting, immuno-fluorescence, and DNA binding assays. Xenografted tumor model has been generated in nude mice using HCC cell line and effect of garcinol in the inhibition of tumor growth has been investigated.

Results

Garcinol could inhibit both constitutive and interleukin (IL-6) inducible STAT3 activation in HCC cells. Computational modeling showed that garcinol could bind to the SH2 domain of STAT3 and suppress its dimerization in vitro. Being an acetyltransferase inhibitor, garcinol also inhibits STAT3 acetylation and thus impairs its DNA binding ability. The inhibition of STAT3 activation by garcinol led to the suppression of expression of various genes involved in proliferation, survival, and angiogenesis. It also suppressed proliferation and induced substantial apoptosis in HCC cells. Remarkably, garcinol inhibited the growth of human HCC xenograft tumors in athymic nu/nu mice, through the inhibition of STAT3 activation.

Conclusion

Overall, our results suggest that garcinol exerts its anti-proliferative and pro-apoptotic effects through suppression of STAT3 signaling in HCC both in vitro and in vivo.

Epigenetic changes in inflammatory and autoimmune diseases

In higher eukaryotic organisms epigenetic modifications are crucial for proper chromatin folding and thereby proper regulation of gene expression. In the last years the involvement of aberrant epigenetic modifications in inflammatory and autoimmune diseases has been recognized and attracted significant interest. However, the epigenetic mechanisms underlying the different disease phenotypes are still poorly understood. As autoimmune and inflammatory diseases are at least partly T cell mediated, we will provide in this chapter an introduction to the epigenetics of T cell differentiation followed by a summary of the current knowledge on aberrant epigenetic modifications that dysfunctional T cells display in various diseases such as type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, inflammatory bowel disease, and asthma.

Naphthoquinone-mediated inhibition of lysine acetyltransferase KAT3B/p300, basis for non-toxic inhibitor synthesis

Hydroxynaphthoquinone-based inhibitors of the lysine acetyltransferase KAT3B (p300), such as plumbagin, are relatively toxic. Here, we report that free thiol reactivity and redox cycling properties greatly contribute to the toxicity of plumbagin. A reactive 3rd position in the naphthoquinone derivatives is essential for thiol reactivity and enhances redox cycling. Using this clue, we synthesized PTK1, harboring a methyl substitution at the 3rd position of plumbagin. This molecule loses its thiol reactivity completely and its redox cycling ability to a lesser extent. Mechanistically, non-competitive, reversible binding of the inhibitor to the lysine acetyltransferase (KAT) domain of p300 is largely responsible for the acetyltransferase inhibition. Remarkably, the modified inhibitor PTK1 was a nearly non-toxic inhibitor of p300. The present report elucidates the mechanism of acetyltransferase activity inhibition by 1,4-naphthoquinones, which involves redox cycling and nucleophilic adduct formation, and it suggests possible routes of synthesis of the non-toxic inhibitor.

A cell-free fluorometric high-throughput screen for inhibitors of Rtt109-catalyzed histone acetylation

The lysine acetyltransferase (KAT) Rtt109 forms a complex with Vps75 and catalyzes the acetylation of histone H3 lysine 56 (H3K56ac) in the Asf1-H3-H4 complex. Rtt109 and H3K56ac are vital for replication-coupled nucleosome assembly and genotoxic resistance in yeast and pathogenic fungal species such as Candida albicans. Remarkably, sequence homologs of Rtt109 are absent in humans. Therefore, inhibitors of Rtt109 are hypothesized as potential and minimally toxic antifungal agents. Herein, we report the development and optimization of a cell-free fluorometric high-throughput screen (HTS) for small-molecule inhibitors of Rtt109-catalyzed histone acetylation. The KAT component of the assay consists of the yeast Rtt109-Vps75 complex, while the histone substrate complex consists of full-length Drosophila histone H3-H4 bound to yeast Asf1. Duplicated assay runs of the LOPAC demonstrated day-to-day and plate-to-plate reproducibility. Approximately 225,000 compounds were assayed in a 384-well plate format with an average Z' factor of 0.71. Based on a 3σ cut-off criterion, 1,587 actives (0.7%) were identified in the primary screen. The assay method is capable of identifying previously reported KAT inhibitors such as garcinol. We also observed several prominent active classes of pan-assay interference compounds such as Mannich bases, catechols and p-hydroxyarylsulfonamides. The majority of the primary active compounds showed assay signal interference, though most assay artifacts can be efficiently removed by a series of straightforward counter-screens and orthogonal assays. Post-HTS triage demonstrated a comparatively small number of confirmed actives with IC₅₀ values in the low micromolar range. This assay, which utilizes five label-free proteins involved in H3K56 acetylation in vivo, can in principle identify compounds that inhibit Rtt109-catalyzed H3K56 acetylation via different mechanisms. Compounds discovered via this assay or adaptations thereof could serve as chemical probes or leads for a new class of antifungals targeting an epigenetic enzyme.