C646, a selective small molecule inhibitor of histone acetyltransferase p300, radiosensitizes lung cancer cells by enhancing mitotic catastrophe

P300 reduces TUBB4B expression to facilitate the biological process of migration and invasion of non-small cell lung cancer cells

This article explored the mechanism of E1A binding protein p300 (P300) and beta-tubulin 4B isotype-encoding gene (TUBB4B) in regulating the migration and invasion of non-small cell lung cancer (NSCLC) cells. TUBB4B and P300 expression in NSCLC tissues and cells was monitored by real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot. TUBB4B function on NSCLC cell migration, invasion and epithelial-mesenchymal transition (EMT) was monitored by wound healing assay, Transwell experiment and Western blot. The regulation of P300 on TUBB4B was monitored by qRT-PCR and Western blot. Mechanism of P300 and TUBB4B in regulating NSCLC cell migration and invasion was explored by rescue experiment. A xenograft tumor model was established by using nude mouse. As a result, low TUBB4B expression and high P300 expression was discovered in NSCLC tissues and cells. TUBB4B and P300 expression showed a negative correlation in NSCLC tissues. Lower TUBB4B but higher P300 was observed in tumor tissues of NSCLC patients with metastasis. TUBB4B overexpression suppressed NSCLC cell migration, invasion and EMT. TUBB4B silencing had opposite results. P300 overexpression inhibited TUBB4B expression, and P300 silencing facilitated TUBB4B overexpression in NSCLC cells. TUBB4B overexpression counteracted the promotion of P300 overexpression on NSCLC cell invasion and migration. TUBB4B silencing abrogated the inhibition of P300 knockdown on NSCLC cell invasion and migration. TUBB4B overexpression suppressed NSCLC cell in vivo growth. Thus, TUBB4B could be reduced by P300 in NSCLC. It exerted suppression role on NSCLC cell migration, invasion and EMT. TUBB4B may be a novel target for NSCLC treatment.

Discovery of novel nucleoside derivatives as selective lysine acetyltransferase p300 inhibitors for cancer therapy

P300 and CBP are two closely related histone acetyltransferases that are important transcriptional coactivators of many cellular processes. Inhibition of the transcriptional regulator p300/CBP is a promising therapeutic approach in oncology. However, there are no reported single selective p300 or CBP inhibitors to date. In this study, we designed and optimized a series of lysine acetyltransferase p300 selective inhibitors bearing a nucleoside scaffold. Most compounds showed excellent inhibitory activity against p300 with IC50 ranging from 0.18 to 9.90 μM, except for J16, J29, J40, and J48. None of the compounds showed inhibitory activity against CBP (inhibition rate < 50 % at 10 µM). Then the cytotoxicity of the compounds against a series of cancer cells were evaluated. Compounds J31 and J32 showed excellent proliferation inhibitory activity on cancer cells T47D and H520 with desirable selectivity profile of p300 over CBP. These compounds could be promising lead compounds for the development of novel epigenetic inhibitors as antitumor agents.

Transcriptional co-activators: emerging roles in signaling pathways and potential therapeutic targets for diseases

Specific cell states in metazoans are established by the symphony of gene expression programs that necessitate intricate synergic interactions between transcription factors and the co-activators. Deregulation of these regulatory molecules is associated with cell state transitions, which in turn is accountable for diverse maladies, including developmental disorders, metabolic disorders, and most significantly, cancer. A decade back most transcription factors, the key enablers of disease development, were historically viewed as 'undruggable'; however, in the intervening years, a wealth of literature validated that they can be targeted indirectly through transcriptional co-activators, their confederates in various physiological and molecular processes. These co-activators, along with transcription factors, have the ability to initiate and modulate transcription of diverse genes necessary for normal physiological functions, whereby, deregulation of such interactions may foster tissue-specific disease phenotype. Hence, it is essential to analyze how these co-activators modulate specific multilateral processes in coordination with other factors. The proposed review attempts to elaborate an in-depth account of the transcription co-activators, their involvement in transcription regulation, and context-specific contributions to pathophysiological conditions. This review also addresses an issue that has not been dealt with in a comprehensive manner and hopes to direct attention towards future research that will encompass patient-friendly therapeutic strategies, where drugs targeting co-activators will have enhanced benefits and reduced side effects. Additional insights into currently available therapeutic interventions and the associated constraints will eventually reveal multitudes of advanced therapeutic targets aiming for disease amelioration and good patient prognosis.

Post-translational modifications of histones: Mechanisms, biological functions, and therapeutic targets

Histones are DNA-binding basic proteins found in chromosomes. After the histone translation, its amino tail undergoes various modifications, such as methylation, acetylation, phosphorylation, ubiquitination, malonylation, propionylation, butyrylation, crotonylation, and lactylation, which together constitute the "histone code." The relationship between their combination and biological function can be used as an important epigenetic marker. Methylation and demethylation of the same histone residue, acetylation and deacetylation, phosphorylation and dephosphorylation, and even methylation and acetylation between different histone residues cooperate or antagonize with each other, forming a complex network. Histone-modifying enzymes, which cause numerous histone codes, have become a hot topic in the research on cancer therapeutic targets. Therefore, a thorough understanding of the role of histone post-translational modifications (PTMs) in cell life activities is very important for preventing and treating human diseases. In this review, several most thoroughly studied and newly discovered histone PTMs are introduced. Furthermore, we focus on the histone-modifying enzymes with carcinogenic potential, their abnormal modification sites in various tumors, and multiple essential molecular regulation mechanism. Finally, we summarize the missing areas of the current research and point out the direction of future research. We hope to provide a comprehensive understanding and promote further research in this field.

The pattern of histone H3 epigenetic posttranslational modifications is regulated by the VRK1 chromatin kinase

BACKGROUND

Dynamic chromatin remodeling is associated with changes in the epigenetic pattern of histone acetylations and methylations required for processes based on dynamic chromatin remodeling and implicated in different nuclear functions. These histone epigenetic modifications need to be coordinated, a role that may be mediated by chromatin kinases such as VRK1, which phosphorylates histones H3 and H2A.

METHODS

The effect of VRK1 depletion and VRK1 inhibitor, VRK-IN-1, on the acetylation and methylation of histone H3 in K4, K9 and K27 was determined under different conditions, arrested or proliferating cells, in A549 lung adenocarcinoma and U2OS osteosarcoma cells.

RESULTS

Chromatin organization is determined by the phosphorylation pattern of histones mediated by different types of enzymes. We have studied how the VRK1 chromatin kinase can alter the epigenetic posttranslational modifications of histones by using siRNA, a specific inhibitor of this kinase (VRK-IN-1), and of histone acetyl and methyl transferases, as well as histone deacetylase and demethylase. Loss of VRK1 implicated a switch in the state of H3K9 posttranslational modifications. VRK1 depletion/inhibition causes a loss of H3K9 acetylation and facilitates its methylation. This effect is similar to that of the KAT inhibitor C646, and to KDM inhibitors as iadademstat (ORY-1001) or JMJD2 inhibitor. Alternatively, HDAC inhibitors (selisistat, panobinostat, vorinostat) and KMT inhibitors (tazemetostat, chaetocin) have the opposite effect of VRK1 depletion or inhibition, and cause increase of H3K9ac and a decrease of H3K9me3. VRK1 stably interacts with members of these four enzyme families. However, VRK1 can only play a role on these epigenetic modifications by indirect mechanisms in which these epigenetic enzymes are likely targets to be regulated and coordinated by VRK1.

CONCLUSIONS

The chromatin kinase VRK1 regulates the epigenetic patterns of histone H3 acetylation and methylation in lysines 4, 9 and 27. VRK1 is a master regulator of chromatin organization associated with its specific functions, such as transcription or DNA repair.

Pharmacological targeting of CBP/p300 drives a redox/autophagy axis leading to senescence-induced growth arrest in non-small cell lung cancer cells

p300/CBP histone acetyltransferases (HAT) are critical transcription coactivators involved in multiple cellular activities. They act at multiple levels in non-small cell lung carcinoma (NSCLC) and appear, therefore, as promising druggable targets. Herein, we investigated the biological effects of A-485, the first selective (potent) drug-like HAT catalytic inhibitor of p300/CBP, in human NSCLC cell lines. A-485 treatment specifically reduced p300/CBP-mediated histone acetylation marks and caused growth arrest of lung cancer cells via activation of the autophagic pathway. Indeed, A-485 growth-arrested cells displayed phenotypic markers of cell senescence and failed to form colonies. Notably, disruption of autophagy by genetic and pharmacological approaches triggered apoptotic cell death. Mechanistically, A-485-induced senescence occurred through the accumulation of reactive oxygen species (ROS), which in turn resulted in DNA damage and activation of the autophagic pathway. Interestingly, ROS scavengers were able to revert senescence phenotype and restore cell viability, suggesting that ROS production had a key role in upstream events leading to growth arrest commitment. Altogether, our data provide new insights into the biological effects of the A-485 and uncover the importance of the autophagic/apoptotic response to design a new combinatorial anticancer strategy.

Protein acylation: mechanisms, biological functions and therapeutic targets

Metabolic reprogramming is involved in the pathogenesis of not only cancers but also neurodegenerative diseases, cardiovascular diseases, and infectious diseases. With the progress of metabonomics and proteomics, metabolites have been found to affect protein acylations through providing acyl groups or changing the activities of acyltransferases or deacylases. Reciprocally, protein acylation is involved in key cellular processes relevant to physiology and diseases, such as protein stability, protein subcellular localization, enzyme activity, transcriptional activity, protein-protein interactions and protein-DNA interactions. Herein, we summarize the functional diversity and mechanisms of eight kinds of nonhistone protein acylations in the physiological processes and progression of several diseases. We also highlight the recent progress in the development of inhibitors for acyltransferase, deacylase, and acylation reader proteins for their potential applications in drug discovery.

Epimutations and Their Effect on Chromatin Organization: Exciting Avenues for Cancer Treatment

The three-dimensional architecture of genomes is complex. It is organized as fibers, loops, and domains that form high-order structures. By using different chromosome conformation techniques, the complex relationship between transcription and genome organization in the three-dimensional organization of genomes has been deciphered. Epigenetic changes, such as DNA methylation and histone modification, are the hallmark of cancers. Tumor initiation, progression, and metastasis are linked to these epigenetic modifications. Epigenetic inhibitors can reverse these altered modifications. A number of epigenetic inhibitors have been approved by FDA that target DNA methylation and histone modification. This review discusses the techniques involved in studying the three-dimensional organization of genomes, DNA methylation and histone modification, epigenetic deregulation in cancer, and epigenetic therapies targeting the tumor.

The role of protein acetylation in carcinogenesis and targeted drug discovery

Protein acetylation is a reversible post-translational modification, and is involved in many biological processes in cells, such as transcriptional regulation, DNA damage repair, and energy metabolism, which is an important molecular event and is associated with a wide range of diseases such as cancers. Protein acetylation is dynamically regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs) in homeostasis. The abnormal acetylation level might lead to the occurrence and deterioration of a cancer, and is closely related to various pathophysiological characteristics of a cancer, such as malignant phenotypes, and promotes cancer cells to adapt to tumor microenvironment. Therapeutic modalities targeting protein acetylation are a potential therapeutic strategy. This article discussed the roles of protein acetylation in tumor pathology and therapeutic drugs targeting protein acetylation, which offers the contributions of protein acetylation in clarification of carcinogenesis, and discovery of therapeutic drugs for cancers, and lays the foundation for precision medicine in oncology.

N-1,2,3-Triazole-isatin derivatives: anti-proliferation effects and target identification in solid tumour cell lines

Molecular hybridization approaches have become an important strategy in medicinal chemistry, and to this end, we have developed a series of novel N-1,2,3-triazole-isatin hybrids that are promising as tumour anti-proliferative agents. Our isatin hybrids presented high cytotoxic activity against colon cancer cell line SW480, lung adenocarcinoma cell line A549, as well as breast cancer cell lines MCF7 and MDA-MB-231. All tested compounds demonstrated better anti-proliferation (to 1-order of magnitude) than the cis-platin (CDDP) benchmark. In order to explore potential biological targets for these compounds, we used information from previous screenings and identified as putative targets the histone acetyltransferase P-300 (EP300) and the acyl-protein thioesterase 2 (LYPLA2), both known to be involved in epigenetic regulation. Advantageous pharmacological properties were predicted for these compounds such as good total surface area of binding to aromatic and hydrophobic units in the enzyme active site. In addition, we found down-regulation of LYPLA2 and EP300 in both the MCF7 and MDA-MB-231 breast cancer cells treated with our inhibitors, but no significant effect was detected in normal breast cells MCF10A. We also observed upregulation of EP300 mRNA expression in the MCF10A cell line for some of these compounds and the same effect for LYPLA2 mRNA in MCF7 for one of our compounds. These results suggest an effect at the transcriptional regulation level and associated with oncological contexts.

Histone acetyltransferases CBP/p300 in tumorigenesis and CBP/p300 inhibitors as promising novel anticancer agents

The histone acetyltransferases CBP and p300, often referred to as CBP/p300 due to their sequence homology and functional overlap and co-operation, are emerging as critical drivers of oncogenesis in the past several years. CBP/p300 induces histone H3 lysine 27 acetylation (H3K27ac) at target gene promoters, enhancers and super-enhancers, thereby activating gene transcription. While earlier studies indicate that CBP/p300 deletion/loss can promote tumorigenesis, CBP/p300 have more recently been shown to be over-expressed in cancer cells and drug-resistant cancer cells, activate oncogene transcription and induce cancer cell proliferation, survival, tumorigenesis, metastasis, immune evasion and drug-resistance. Small molecule CBP/p300 histone acetyltransferase inhibitors, bromodomain inhibitors, CBP/p300 and BET bromodomain dual inhibitors and p300 protein degraders have recently been discovered. The CBP/p300 inhibitors and degraders reduce H3K27ac, down-regulate oncogene transcription, induce cancer cell growth inhibition and cell death, activate immune response, overcome drug resistance and suppress tumor progression in vivo. In addition, CBP/p300 inhibitors enhance the anticancer efficacy of chemotherapy, radiotherapy and epigenetic anticancer agents, including BET bromodomain inhibitors; and the combination therapies exert substantial anticancer effects in mouse models of human cancers including drug-resistant cancers. Currently, two CBP/p300 inhibitors are under clinical evaluation in patients with advanced and drug-resistant solid tumors or hematological malignancies. In summary, CBP/p300 have recently been identified as critical tumorigenic drivers, and CBP/p300 inhibitors and protein degraders are emerging as promising novel anticancer agents for clinical translation.

Repressing MYC by targeting BET synergizes with selective inhibition of PI3Kα against B cell lymphoma

Phosphatidylinositol 3-kinase (PI3K) δ-specific inhibitors have been approved for the therapy of certain types of B cell lymphoma (BCL). However, their clinical use is limited by the substantial toxicity and lack of efficacy in other types of BCL. Emerging evidence indicates that PI3Kα plays important roles in the progression of B cell lymphoma. In this study, we revealed that PI3Kα was important for the PI3K signaling and proliferation in BCL cells. A novel clinical PI3Kα-selective inhibitor CYH33 possessed superior activity against BCL compared to the marketed PI3Kα-selective inhibitor Alpelisib and PI3Kδ-selective inhibitor Idelalisib. Though CYH33 was able to inhibit PI3K/AKT signaling in tested BCL cells, differential activity against proliferation was observed. Transcriptome profiling revealed that CYH33 down-regulated "MYC-targets" gene set in sensitive but not resistant cells. CYH33 inhibited c-MYC transcription in sensitive cells, which was attributed to a decrease in acetylated H3 bound to the promoter and super-enhancer region of c-MYC. Accordingly, CYH33 treatment resulted in phosphorylation and proteasomal degradation of the histone acetyltransferase p300. An unbiased screening with drugs approved or in clinical trials for the therapy of BCL identified that the clinical BET (Bromodomain and Extra Terminal domain) inhibitor OTX015 significantly potentiated the activity of CYH33 against BCL in vitro and in vivo, which was associated with enhanced inhibition on c-MYC expression and induction of cell cycle arrest and apoptosis. Our findings provide the rationale of combined CYH33 with BET inhibitors for the therapy of B cell lymphoma.

Epigenetic inactivation of hydroxymethylglutaryl CoA synthase reduces ketogenesis and facilitates tumor cell motility in clear cell renal carcinoma

Previously, we have reported that the dysregulation of ketogenesis plays an important role in the carcinogenesis of clear cell renal cell carcinoma (ccRCC). Here, we demonstrate decreased expression of the HMGCS2 gene in ccRCC, a critical enzyme for the synthesis of the ketone body β-hydroxybutyrate (β-OHB). We found that the reduced transcription of the HMGCS2 gene in ccRCC cells was significantly correlated to a higher relative methylation rate in its promotor region. The higher methylation rate in the region of the transcription start site and 1st exon of the HMGCS2 gene was, in turn, correlated with a worse clinical outcome for patients. The transcription of HMGCS2 was possible to restore by treatment with 5-aza-2'-deoxycytidine and with the histone deacetylase inhibitor β-OHB. Therefore, the low levels of the HMGCS2 enzyme in ccRCC may be the consequence of hypermethylation of the HMGCS2 promotor. The ensuing reduction in the ketone body levels further suppresses the transcription of HMGCS2 via a feedback loop. Ectopic expression of HMGCS2 attenuates the migration and invasion of ccRCC but does not affect the proliferative capacity of ccRCC cells in vitro. In addition, we showed that ectopic expression of HMGCS2 boosts the intracellular levels of β-OHB and that exogenously applied β-OHB suppresses the motility and invasion of ccRCC. Our study reveals crosstalk between genes that regulate metabolism and their metabolites, thus providing a better understanding of the epigenetic mechanism involved in ccRCC carcinogenesis and suggesting opportunities for metabolic therapy of tumors. Initially, we suggest that the mRNA level of HMGCS2 could serve as a potentially valuable diagnostic (AUC = 0.918, p < 0.001) and prognostic biomarker.

C646 Protects Against DSS-Induced Colitis Model by Targeting NLRP3 Inflammasome

Numerous pieces of evidence have identified that the NLRP3 inflammasome plays a pivotal role in the development and pathogenesis of colitis. Targeting the NLRP3 inflammasome represents a potential therapeutic treatment. Our previous studies have suggested that acetylation of NLRP3 is indispensable to NLRP3 inflammasome activation, and some acetyltransferase inhibitors could suppress the NLRP3 inflammasome activation. Here, we identified that C646, an inhibitor of histone acetyltransferase p300, exerts anti-inflammatory effects in DSS-induced colitis mice by targeting the NLRP3 inflammasome. Mechanistically, C646 not only inhibits NF-κB activation, leading to the decreased expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) and NLRP3, but also suppresses the NLRP3 inflammasome assembly by disrupting the interaction between NLRP3 and ASC. In addition, C646 attenuated the LPS-induced acute systemic inflammation model. Thus, our results demonstrate the ability of C646 to suppress the NLRP3 inflammasome activity and its potential application in the treatment of inflammatory bowel disease.

BRD4 inhibition boosts the therapeutic effects of epidermal growth factor receptor-targeted chimeric antigen receptor T cells in glioblastoma

Glioblastoma (GBM) is the deadliest brain malignancy without effective treatments. Here, we reported that epidermal growth factor receptor-targeted chimeric antigen receptor T cells (EGFR CAR-T) were effective in suppressing the growth of GBM cells in vitro and xenografts derived from GBM cell lines and patients in mice. However, mice soon acquired resistance to EGFR CAR-T cell treatment, limiting its potential use in the clinic. To find ways to improve the efficacy of EGFR CAR-T cells, we performed genomics and transcriptomics analysis for GBM cells incubated with EGFR CAR-T cells and found that a large cohort of genes, including immunosuppressive genes, as well as enhancers in vicinity are activated. BRD4, an epigenetic modulator functioning on both promoters and enhancers, was required for the activation of these immunosuppressive genes. Accordingly, inhibition of BRD4 by JQ1 blocked the activation of these immunosuppressive genes. Combination therapy with EGFR CAR-T cells and JQ1 suppressed the growth and metastasis of GBM cells and prolonged survival in mice. We demonstrated that transcriptional modulation by targeting epigenetic regulators could improve the efficacy of immunotherapy including CAR-T, providing a therapeutic avenue for treating GBM in the clinic.

C646 inhibits G2/M cell cycle-related proteins and potentiates anti-tumor effects in pancreatic cancer

The activity of histone acetyltransferases (HATs) plays a central role in an epigenetic modification in cooperation with HDACs (histone deacetyl transferases). It is likely that malfunction of this enzymatic machinery controlling epigenetic modification is relevant to carcinogenesis and tumor progression. However, in pancreatic cancer, the clinical relevance of HAT activity and histone acetylation has remained unclear. We identified that H3 acetylation was expressed in all pancreatic cancer patients, indicating that H3 acetylation may be essential in pancreatic cancer cells. We also found that the HAT inhibitor C646 augmented anti-tumor effects in vitro by inhibiting cell proliferation and cell cycle progression concomitantly with suppression of acetylated H3K9 and H3K27 expression. C646 or p300 and CBP (CREB-binding protein)-specific siRNA treatment inhibited the transcription of the G2/M cell cycle regulatory proteins cyclin B1 and CDK1 (cyclin-dependent kinase 1). C646 treatment also inhibited tumor growth in vivo in a xenograft mouse model. C646 could be an effective therapeutic agent for pancreatic cancer. The epigenetic status of pancreatic cancers based on their level of histone H3 acetylation may influence patient survival. Epigenetic stratification according to H3K27 acetylation could be useful for predicting disease prognosis as well as the therapeutic efficacy of C646 in pancreatic cancer.

Targeting Triple-Negative Breast Cancer with Combination Therapy of EGFR CAR T Cells and CDK7 Inhibition

EGFR-targeted chimeric antigen receptor (CAR) T cells are potent and specific in suppressing the growth of triple-negative breast cancer (TNBC) in vitro and in vivo. However, in this study, a subset of mice soon acquired resistance, which limits the potential use of EGFR CAR T cells. We aimed to find a way to overcome the observed resistance. Transcriptomic analysis results revealed that EGFR CAR T-cell treatment induced a set of immunosuppressive genes, presumably through IFNγ signaling, in EGFR CAR T-cell-resistant TNBC tumors. The EGFR CAR T-cell-induced immunosuppressive genes were associated with EGFR CAR T-cell-activated enhancers and were especially sensitive to THZ1, a CDK7 inhibitor we screened out of a panel of small molecules targeting epigenetic modulators. Accordingly, combination therapy with THZ1 and EGFR CAR T cells suppressed immune resistance, tumor growth, and metastasis in TNBC tumor models, including human MDA-MB-231 cell-derived and TNBC patient-derived xenografts, and mouse EMT6 cell-derived allografts. Taken together, we demonstrated that transcriptional modulation using epigenetic inhibitors could overcome CAR T-cell therapy-induced immune resistance, thus providing a therapeutic avenue for treating TNBC in the clinic.

Effects of the histone acetylase inhibitor C646 on growth and differentiation of adipose-derived stem cells

As an important histone acetylase, the transcriptional coactivator P300/CBP affects target gene expression and plays a role in the maintenance of stem cell characteristics and differentiation potential. In this study, we explored the action of a highly effective selective histone acetylase inhibitor, C646, on goat adipose-derived stem cells (gADSCs), and investigated the impact of histone acetylation on the growth characteristics and the differentiation potential of ADSCs. We found that C646 blocked the cell proliferation, arrested the cell cycle, and triggered apoptosis. Notably, immunocytochemistry and western blot analyses showed that the acetylation level of histone H3K9 was increased. Moreover, although real-time quantitative PCR and western blot confirmed that P300 expression was inhibited under these conditions, the expression level of two other histone acetylases, TIP60 and PCAF, was significantly increased. Furthermore, C646 clearly promoted the differentiation of gADSCs into adipocytes and had an impact on their differentiation into neuronal cells. This study provides new insights into the epigenetic regulation of stem cell differentiation and may represent an experimental basis for the comprehension of stem cell characteristics and function. Furthermore, it is of great relevance for the application of adult stem cells to somatic cell cloning, which may improve the efficiency of large livestock cloning and foster the production of transgenic animals.

Carbon ion triggered immunogenic necroptosis of nasopharyngeal carcinoma cells involving necroptotic inhibitor BCL-x

To explore the potential and mechanisms of necroptosis, a form of immunogenic cell death, induced by carbon ion as compared to photon beams in established photon resistant- (PR-) and sensitive nasopharyngeal carcinoma (NPC) cells. MLKL is considered a central executor of necroptosis and phosphorylation of MLKL (p-MLKL) was a critical event of necroptosis. The clonogenic survival and DNA microarray demonstrated that after repeated photon irradiation, radiosensitive NPC cells became apoptosis-resistant but could be effectively inhibited by carbon ion irradiation. The relative biologic effectiveness (RBE) at D10 and D37 were 2.15 and 2.78 for PR-NPC cells. Carbon ion induced delayed DNA damage repair, cell cycle arrest, cytogenetic damage, morphological change and cell necrosis, indicating the possibility of necroptosis in both PR- and sensitive NPC cell types. The lower expression of necroptotic inhibitors (caspase-8 and Bcl-x) and higher level of MLKL in PR-NPC cells showed it was relatively more predisposed to necroptosis compared to the sensitive cells. Subsequent experiments demonstrated the significant upregulation of p-MLKL in the PR-NPC cells treated by carbon ion (4 Gy) compared with photon irradiation at both physical (4 Gy) and RBE (10 Gy) doses (P≤0.0001). Moreover, carbon ion induced a robust (up to 28 folds) p-MLKL in the PR-NPC cells as well as sensitive cells (up to 6-fold) coupled with a lower level of BCL-x expression and increased GM-CSF implicated in resculputure of immune system. These results suggested that carbon ion could induce necroptosis of NPC cells, especially in PR-NPC cells, and its mechanisms involve BCL-x.

Advances in Epigenetic Cancer Therapeutics

Cancer has traditionally been hailed a genetic disease, dictated by successive genetic aberrations which alter gene expression. Yet, recent advances in molecular sequencing technologies, enabling the characterisation of cancer patient phenotypes on a large scale, have highlighted epigenetic changes as a hallmark of cancer. Epigenetic modifications, including DNA methylation and demethylation and histone modifications, have been found to play a key role in the pathogenesis of a wide variety of cancers through the regulation of chromatin state, gene expression and other nuclear events. Targeting epigenetic aberrations offers remarkable promise as a potential anti-cancer therapy given the reversible nature of epigenetic changes. Hence, epigenetic therapy has emerged as a rapidly advancing field of cancer research. A plethora of epigenetic therapies which inhibit enzymes of post-translational histone modifications, so-called 'writers', 'erasers' and 'readers', have been developed, with several epigenetic inhibitor agents approved for use in routine clinical practice. Epigenetic therapeutics inhibit the methylation or demethylation and acetylation or deacetylation of DNA and histone proteins. Their targets include writers (DNA methyltransferases [DNMT], histone acetyltransferases [HAT] and histone deacetylases [HDAC]) and erasers (histone demethylases [HDM] and histone methylases [HMT]). With new epigenetic mechanisms increasingly being elucidated, a vast array of targets and therapeutics have been brought to the fore. This review discusses recent advances in cancer epigenetics with a focus on molecular targets and mechanisms of action of epigenetic cancer therapeutics.

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.

Defining COMMD4 as an anti-cancer therapeutic target and prognostic factor in non-small cell lung cancer

Background

Non-small cell lung cancers (NSCLC) account for 85–90% of all lung cancers. As drug resistance critically impairs chemotherapy effectiveness, there is great need to identify new therapeutic targets. The aims of this study were to investigate the prognostic and therapeutic potential of the copper-metabolism-domain-protein, COMMD4, in NSCLC.

Methods

The expression of COMMD4 in NSCLC was investigated using bioinformatic analysis, immunoblotting of immortalised human bronchial epithelial (HBEC) and NSCLC cell lines, qRT-PCR and immunohistochemistry of tissue microarrays. COMMD4 function was additionally investigated in HBEC and NSCLC cells depleted of COMMD4, using small interfering RNA sequences.

Results

Bioinformatic analysis and in vitro analysis of COMMD4 transcripts showed that COMMD4 levels were upregulated in NSCLC and elevated COMMD4 was associated with poor prognosis in adenocarcinoma (ADC). Immunoblotting demonstrated that COMMD4 expression was upregulated in NSCLC cells and siRNA-depletion of COMMD4, decreased cell proliferation and reduced cell viability. Cell death was further enhanced after exposure to DNA damaging agents. COMMD4 depletion caused NSCLC cells to undergo mitotic catastrophe and apoptosis.

Conclusions

Our data indicate that COMMD4 may function as a prognostic factor in ADC NSCLC. Additionally, COMMD4 is a potential therapeutic target for NSCLC, as its depletion induces cancer cell death.

Binding mechanism of spinosine and venenatine molecules with p300 HAT enzyme: Molecular screening, molecular dynamics and free-energy analysis

The chromatin modification is regulated by the histone acetyltransferase (HAT) and histone deacetyltransferase (HDAC) enzymes; abnormal function of these enzymes leads to several malignant diseases. The inhibition of these enzymes using natural ligand molecules is an emerging technique to cure these diseases. The in vitro analysis of natural molecules, venenatine, spinosine, palmatine and taxodione are giving the best inhibition rate against p300 HAT enzyme. However, the detailed understanding of binding and the stability of these molecules with p300 HAT is not yet known. The aim of the present study is focused to determine the binding strength of the molecules from molecular dynamics simulation analysis. The docking analysis confirms that, the venenatine (-6.97 kcal/mol - conformer 8), spinosine (-6.52 kcal/mol conformer -10), palmatine (-5.72 kcal/mol conformer-3) and taxodione (-4.99 kcal/mol conformer-4) molecules form strong hydrogen bonding interactions with the key amino acid residues (Arg1410, Thr1411 and Trp1466) present in the active site of p300. In the molecular dynamics (MD) simulation, the spinosine retain these key interactions with the active site amino acid residues (Arg1410, Thr1411, and Trp1466) than venenatine and are stable throughout the simulation. The RMSD value of spinosine (0.5 to 1.3 Å) and venenatine (0.3 to 1.3 Å) are almost equal during the MD simulation. However, during the MD simulation, the intermolecular interaction between venenatine and the active site amino acid residues (Arg1410, Thr1411, and Trp1466) decreased on comparing with the spinosine-p300 interaction. The binding free energy of the spinosine (-15.30 kcal/mol) is relatively higher than the venenatine (-11.8 kcal/mol); this increment is attributed to the strong hydrogen bonding interactions of spinosine molecule with the active site amino acid residues of p300.

Inhibition of acetylation of histones 3 and 4 attenuates aortic valve calcification

Aortic valve calcification develops in patients with chronic kidney disease who have calcium and phosphate metabolic disorders and poor prognoses. There is no effective treatment except valve replacement. However, metabolic disorders put patients at high risk for surgery. Increased acetylation of histones 3 and 4 is present in interstitial cells from human calcific aortic valves, but whether it is involved in aortic valve calcification has not been studied. In this study, we found that treating cultured porcine aortic valve interstitial cells with a high-calcium/high-phosphate medium induced calcium deposition, apoptosis, and expression of osteogenic marker genes, producing a phenotype resembling valve calcification in vivo. These phenotypic changes were attenuated by the histone acetyltransferase inhibitor C646. C646 treatment increased the levels of class I histone deacetylase members and decreased the acetylation of histones 3 and 4 induced by the high-calcium/high-phosphate treatment. Conversely, the histone deacetylase inhibitor suberoylanilide hydroxamic acid promoted valve interstitial cell calcification. In a mouse model of aortic valve calcification induced by adenine and vitamin D treatment, the levels of acetylated histones 3 and 4 were increased in the calcified aortic valves. Treatment of the models with C646 attenuated aortic valve calcification by restoring the levels of acetylated histones 3 and 4. These observations suggest that increased acetylation of histones 3 and 4 is part of the pathogenesis of aortic valve calcification associated with calcium and phosphate metabolic disorders. Targeting acetylated histones 3 and 4 may be a potential therapy for inoperable aortic valve calcification in chronic kidney disease patients.

Three-dimensional analysis reveals altered chromatin interaction by enhancer inhibitors harbors TCF7L2-regulated cancer gene signature

Distal regulatory elements influence the activity of gene promoters through chromatin looping. Chromosome conformation capture (3C) methods permit identification of chromatin contacts across different regions of the genome. However, due to limitations in the resolution of these methods, the detection of functional chromatin interactions remains a challenge. In the current study, we employ an integrated approach to define and characterize the functional chromatin contacts of human pancreatic cancer cells. We applied tethered chromatin capture to define classes of chromatin domains on a genome-wide scale. We identified three types of structural domains (topologically associated, boundary, and gap) and investigated the functional relationships of these domains with respect to chromatin state and gene expression. We uncovered six distinct sub-domains associated with epigenetic states. Interestingly, specific epigenetically active domains are sensitive to treatment with histone acetyltransferase (HAT) inhibitors and decrease in H3K27 acetylation levels. To examine whether the subdomains that change upon drug treatment are functionally linked to transcription factor regulation, we compared TCF7L2 chromatin binding and gene regulation to HAT inhibition. We identified a subset of coding RNA genes that together can stratify pancreatic cancer patients into distinct survival groups. Overall, this study describes a process to evaluate the functional features of chromosome architecture and reveals the impact of epigenetic inhibitors on chromosome architecture and identifies genes that may provide insight into disease outcome.

CBP/p300 inhibitor C646 prevents high glucose exposure induced neuroepithelial cell proliferation

BACKGROUND

Maternal diabetes related neural tube defects (NTDs) are a result of oxidative stress and apoptosis. However, the molecular mechanism behind the pathogenesis is not fully understood. Here, we report that high glucose exposure-induced epigenetic changes influence histone H4 acetylation and neuroepithelial cell proliferation. We also show that the acetyltransferase inhibitor C646 can prevent high glucose induced changes in histone H4 acetylation and neuroepithelial cell proliferation.

METHODS

By using LC-MS/MS as an unbiased approach, we screened the histone acetylation profile in an E9 neuroepithelial cell line (NE-4C) under high glucose exposure. We further explored the mechanism in cells in vitro and in maternal diabetes-induced mouse embryos in vivo.

RESULTS

We identified 35 core histone acetylation marks in normal E9 neuroepithelial cells, whereas high glucose exposure resulted in novel acetylation sites on H4K31 and H4K44. Acetylation levels of embryonic development associated H4K5/K8/K12/K16 increased in neuroepithelial cells exposed to high glucose in vitro and in brain tissue from maternal diabetes induced exencephalic embryos in vivo. Further, mRNA level of histone acetyltransferase CBP encoded gene Crebbp was significantly increased both in vitro and in vivo. The addition of C646, a selective inhibitor for CBP/p300, significantly rescued increase of H4K5/K8/K12/K16 acetylation levels and H3S10pi-labeled neuroepithelial cell proliferation induced by high glucose exposure.

CONCLUSION

Our data provide complementary insights for potential mechanisms of maternal diabetes induced NTDs.

Along the Central Dogma-Controlling Gene Expression with Small Molecules

The central dogma of molecular biology, that DNA is transcribed into RNA and RNA translated into protein, was coined in the early days of modern biology. Back in the 1950s and 1960s, bacterial genetics first opened the way toward understanding life as the genetically encoded interaction of macromolecules. As molecular biology progressed and our knowledge of gene control deepened, it became increasingly clear that expression relied on many more levels of regulation. In the process of dissecting mechanisms of gene expression, specific small-molecule inhibitors played an important role and became valuable tools of investigation. Small molecules offer significant advantages over genetic tools, as they allow inhibiting a process at any desired time point, whereas mutating or altering the gene of an important regulator would likely result in a dead organism. With the advent of modern sequencing technology, it has become possible to monitor global cellular effects of small-molecule treatment and thereby overcome the limitations of classical biochemistry, which usually looks at a biological system in isolation. This review focuses on several molecules, especially natural products, that have played an important role in dissecting gene expression and have opened up new fields of investigation as well as clinical venues for disease treatment.

The Genomic Landscape and Pharmacogenomic Interactions of Clock Genes in Cancer Chronotherapy

Cancer chronotherapy, treatment at specific times during circadian rhythms, endeavors to optimize anti-tumor effects and to lower toxicity. However, comprehensive characterization of clock genes and their clinical relevance in cancer is lacking. We systematically characterized the alterations of clock genes across 32 cancer types by analyzing data from The Cancer Genome Atlas, Cancer Therapeutics Response Portal, and The Genomics of Drug Sensitivity in Cancer databases. Expression alterations of clock genes are associated with key oncogenic pathways, patient survival, tumor stage, and subtype in multiple cancer types. Correlations between expression of clock genes and of other genes in the genome were altered in cancerous versus normal tissues. We identified interactions between clock genes and clinically actionable genes by analyzing co-expression, protein-protein interaction, and chromatin immunoprecipitation sequencing data and also found that clock gene expression is correlated to anti-cancer drug sensitivity in cancer cell lines. Our study provides a comprehensive analysis of the circadian clock across different cancer types and highlights potential clinical utility of cancer chronotherapy.

Paradoxical induction of growth arrest and apoptosis by EGF via the up-regulation of PTEN by activating Redox factor-1/Egr-1 in human lung cancer cells

Epidermal growth factor (EGF) signaling promotes cell proliferation and survival in several types of cancer. Here, however, we showed that EGF inhibits proliferation and promotes programmed cell death in non-small cell lung cancer (NSCLC) cells. In A549 cells, EGF increased redox factor-1 (Ref-1) expression and the association of Ref-1 with zinc finger-containing transcriptional regulator (EGR1) via activation of p22phox, RAC1, and an NADPH oxidase subunit. EGF increased p22phox and RAC1 expression through activation of purinergic receptors (P2Y). Elevated Ref-1/EGR1 levels increased phosphatase and tensin homolog (PTEN) levels, leading to inhibition of the Akt pathway. EGF-induced PTEN upregulation increased apoptosis and autophagy-induced damage in A549 cells, whereas Ref-1 knockdown blocked EGF-induced PTEN upregulation in an NADPH oxidase p22phox subunit-independent manner. In addition, p22phox knockdown restored EGF-induced effects, implying that changes in P2Y activity caused by EGF, which activates NADPH oxidase via RAC1, influenced Ref-1-mediated redox regulation. Finally, EGF similarly attenuated cell proliferation and promoted autophagy and apoptosis in vivo in a xenograft model using A549 cells. These findings reveal that EGF-induced redox signaling is linked to Ref-1-induced death in NSCLC cells.

The multifaceted role of lysine acetylation in cancer: prognostic biomarker and therapeutic target

Lysine acetylation is a post-translational modification that regulates gene transcription by targeting histones as well as a variety of transcription factors in the nucleus. Recently, several reports have demonstrated that numerous cytosolic proteins are also acetylated and that this modification, affecting protein activity, localization and stability has profound consequences on their cellular functions. Interestingly, most non-histone proteins targeted by acetylation are relevant for tumorigenesis. In this review, we will analyze the functional implications of lysine acetylation in different cellular compartments, and will examine our current understanding of lysine acetyltransferases family, highlighting the biological role and prognostic value of these enzymes and their substrates in cancer. The latter part of the article will address challenges and current status of molecules targeting lysine acetyltransferase enzymes in cancer therapy.

Protective effect of α-lipoic acid against radiation-induced fibrosis in mice

Radiation-induced fibrosis (RIF) is one of the most common late complications of radiation therapy. We found that α-lipoic acid (α-LA) effectively prevents RIF. In RIF a mouse model, leg contracture assay was used to test the in vivo efficacy of α-LA. α-LA suppressed the expression of pro-fibrotic genes after irradiation, both in vivo and in vitro, and inhibited the up-regulation of TGF-β1-mediated p300/CBP activity. Thus, α-LA prevents radiation-induced fibrosis (RIF) by inhibiting the transcriptional activity of NF-κB through inhibition of histone acetyltransferase activity. α-LA is a new therapeutic methods that can be used in the prevention-treatment of RIF.

Integrative analysis to identify oncogenic gene expression changes associated with copy number variations of enhancer in ovarian cancer

Enhancers are short regulatory regions (50-1500 bp) of DNA that control the tissue-specific activation of gene expression by long distance interaction with targeting gene regions. Recently, genome-wide identification of enhancers in diverse tissues and cell lines was achieved using high-throughput sequencing. Enhancers have been associated with malfunctions in cancer development resulting from point mutations in regulatory regions. However, the potential impact of copy number variations (CNVs) on enhancer regions is unknown. To learn more about the relationship between enhancers and cancer, we integrated the CNVs data on enhancers and explored their targeting gene expression pattern in high-grade ovarian cancer. Using human enhancer-gene interaction data with 13,691 interaction pairs between 7,905 enhancers and 5,297 targeting genes, we found that the 2,910 copy number gain events of enhancer are significantly correlated with the up-regulation of targeting genes. We further identified that a number of highly mutated super-enhancers, with concordant gene expression change on their targeting genes. We also identified 18 targeting genes by super-enhancers with prognostic significance for ovarian cancer, such as the tumour suppressor CDKN1B. We are the first to report that abundant copy number variations on enhancers could change the expression of their targeting genes which would be valuable for the design of enhancer-based cancer treatment strategy.

One-step Protocol for Evaluation of the Mode of Radiation-induced Clonogenic Cell Death by Fluorescence Microscopy

Research on ionizing radiation (IR)-induced clonogenic cell death is important for understanding the effect of IR on malignant tumors and normal tissues. Here, we describe a quick and cost-effective one-step assay for simultaneously assessing the major modes of clonogenic cell death induced by IR, i.e., apoptosis, mitotic catastrophe, and cellular senescence. In this method, cells grown on a cover slip are irradiated with X-rays and stained with 4',6-diamidino-2-phenylindole dihydrochloride (DAPI). Using fluorescence microscopy, apoptosis, mitotic catastrophe, and cellular senescence are identified based on the characteristic morphologies of the DAPI-stained nuclei. Apoptosis is determined by the presence of apoptotic bodies (i.e., condensed and fragmented nuclei). Mitotic catastrophe is determined by the presence of nuclei that exhibit two or more distinct lobes and micronuclei. Cellular senescence is determined by the presence of senescence-associated heterochromatic foci (i.e., nuclear DNA containing 30-50 bright, dense foci). This approach allows the experimenter to easily screen for clonogenic cell death modes using various cell lines, treatment settings, and/or time points, with the goal of elucidating the mechanisms of cell death in the target cells and conditions of interest.

Selective p300 inhibitor C646 inhibited HPV E6-E7 genes, altered glucose metabolism and induced apoptosis in cervical cancer cells

High risk HPV infection is a causative factor of cervical cancer. The constitutive expression of HPV E6-E7 genes is important for the maintenance of cancer phenotypes. The cellular transcription co-activator p300 plays a crucial role in the regulation of HPV genes thus it was targeted for the inhibition of HPV-associated cervical cancer. In the present study, HPV positive cervical cells were treated with C646, a selective inhibitor of p300, to investigate its influence on HPV E6-E7 expression and cancer cell growth. Results of RT-qPCR, Western-blot and promoter activity assays showed that C646 inhibited the transcription of HPV E6-E7, which was accompanied with the accumulation of p53 protein. Meanwhile, cell proliferation was suppressed, glucose metabolism was disrupted and apoptosis was induced via the intrinsic pathway. Generally, the anti-cervical cancer potential of C646 was demonstrated and a novel mechanism was proposed in this study.

Mitotic catastrophe is a putative mechanism underlying the weak correlation between sensitivity to carbon ions and cisplatin

In cancer therapy today, carbon ion radiotherapy is used mainly as monotherapy, whereas cisplatin is used concomitantly with X-ray radiotherapy. The effectiveness of concomitant carbon ions and cisplatin is unclear. To obtain the information on the mechanisms potentially shared between carbon ions or X-rays and cisplatin, we assessed the correlation of sensitivity to the single treatments. In 20 human cancer cell lines, sensitivity to X-rays strongly correlated with sensitivity to cisplatin, indicating the presence of potentially shared target mechanisms. Interestingly, the correlation of sensitivity to carbon ions and cisplatin was much weaker than that of sensitivity to X-rays and cisplatin, indicating the presence of potentially different target mechanisms between carbon ions and cisplatin. Assessment of clonogenic cell death by 4′,6-diamidino-2-phenylindole dihydrochloride staining showed that mitotic catastrophe was more efficiently induced by carbon ions than by the same physical dose of X-rays, while apoptosis and senescence were not. These data indicate that the correlation of sensitivity to carbon ions and cisplatin is weaker than that of sensitivity to X-rays and cisplatin, which are helpful as biological basis to understand the potentially shared mechanism among these treatments. Further investigation is mandatory to elucidate the clinical efficacy of carbon ions and cisplatin combination.

Acetylation Reader Proteins: Linking Acetylation Signaling to Genome Maintenance and Cancer

Chromatin-based DNA damage response (DDR) pathways are fundamental for preventing genome and epigenome instability, which are prevalent in cancer. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) catalyze the addition and removal of acetyl groups on lysine residues, a post-translational modification important for the DDR. Acetylation can alter chromatin structure as well as function by providing binding signals for reader proteins containing acetyl-lysine recognition domains, including the bromodomain (BRD). Acetylation dynamics occur upon DNA damage in part to regulate chromatin and BRD protein interactions that mediate key DDR activities. In cancer, DDR and acetylation pathways are often mutated or abnormally expressed. DNA damaging agents and drugs targeting epigenetic regulators, including HATs, HDACs, and BRD proteins, are used or are being developed to treat cancer. Here, we discuss how histone acetylation pathways, with a focus on acetylation reader proteins, promote genome stability and the DDR. We analyze how acetylation signaling impacts the DDR in the context of cancer and its treatments. Understanding the relationship between epigenetic regulators, the DDR, and chromatin is integral for obtaining a mechanistic understanding of genome and epigenome maintenance pathways, information that can be leveraged for targeting acetylation signaling, and/or the DDR to treat diseases, including cancer.

Interferon-microRNA signalling drives liver precancerous lesion formation and hepatocarcinogenesis

OBJECTIVE

Precancerous lesion, a well-established histopathologically premalignant tissue with the highest risk for tumourigenesis, develops preferentially from activation of DNA damage checkpoint and persistent inflammation. However, little is known about the mechanisms by which precancerous lesions are initiated and their physiological significance.

DESIGN

Laser capture microdissection was used to acquire matched normal liver, precancerous lesion and tumour tissues. miR-484(-/-), Ifnar1(-/-) and Tgfbr2(△hep) mice were employed to determine the critical role of the interferon (IFN)-microRNA pathway in precancerous lesion formation and tumourigenesis. RNA immunoprecipitation (RIP), pull-down and chromatin immunoprecipitation (ChIP) assays were applied to explore the underlying mechanisms.

RESULTS

miR-484 is highly expressed in over 88% liver samples clinically. DEN-induced precancerous lesions and hepatocellular carcinoma were dramatically impaired in miR-484(-/-) mice. Mechanistically, ectopic expression of miR-484 initiates tumourigenesis and cell malignant transformation through synergistic activation of the transforming growth factor-β/Gli and nuclear factor-κB/type I IFN pathways. Specific acetylation of H3K27 is indispensable for basal IFN-induced continuous transcription of miR-484 and cell transformation. Convincingly, formation of precancerous lesions were significantly attenuated in both Tgfbr2(△hep) and Ifnar1(-/-) mice.

CONCLUSIONS

These findings demonstrate a new protumourigenic axis involving type I IFN-microRNA signalling, providing a potential therapeutic strategy to manipulate or reverse liver precancerous lesions and tumourigenesis.

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.

Inhibition of p300 histone acetyltransferase activity in palate mesenchyme cells attenuates Wnt signaling via aberrant E-cadherin expression

p300 is a multifunctional transcriptional coactivator that interacts with numerous transcription factors and exhibits protein/histone acetyltransferase activity. Loss of p300 function in humans and in mice leads to craniofacial defects. In this study, we demonstrated that inhibition of p300 histone acetyltransferase activity with the compound, C646, altered the expression of several genes, including Cdh1 (E-cadherin) in mouse maxillary mesenchyme cells, which are the cells that give rise to the secondary palate. The increased expression of plasma membrane-bound E-cadherin was associated with reduced cytosolic β-catenin, that led to attenuated signaling through the canonical Wnt pathway. Furthermore, C646 reduced both cell proliferation and the migratory ability of these cells. These results suggest that p300 histone acetyltransferase activity is critical for Wnt-dependent palate mesenchymal cell proliferation and migration, both processes that play a significant role in morphogenesis of the palate.

Aberrant lysine acetylation in tumorigenesis: Implications in the development of therapeutics

The 'language' of covalent histone modifications translates environmental and cellular cues into gene expression. This vast array of post-translational modifications on histones are more than just covalent moieties added onto a protein, as they also form a platform on which crucial cellular signals are relayed. The reversible lysine acetylation has emerged as an important post-translational modification of both histone and non-histone proteins, dictating numerous epigenetic programs within a cell. Thus, understanding the complex biology of lysine acetylation and its regulators is essential for the development of epigenetic therapeutics. In this review, we will attempt to address the complexities of lysine acetylation in the context of tumorigenesis, their role in cancer progression and emphasize on the modalities developed to target lysine acetyltransferases towards cancer treatment.

Epigenetic regulation of proliferation and invasion in hepatocellular carcinoma cells by CBP/p300 histone acetyltransferase activity

Altered epigenetic control of gene expression plays a substantial role in tumor development and progression. Accumulating studies suggest that somatic mutations of CREB binding proteins (CBP)/p300 occur in some cancer cells. CBP/p300 possess histone acetyltransferase (HAT) activity, and are involved in many cellular processes. In this study, we investigated the expression and functional role of CBP/p300 in hepatocellular carcinoma (HCC) using the specific inhibitor C646 of CBP/p300 HAT activity. We examined its effect on several apoptosis-related proteins and invasion-related genes. The results showed that CBP/p300 were highly expressed in HCC tissues and that expression of p300, but not of CBP, was strongly correlated with the malignant character of HCC. C646 inhibited proliferation of HCC cell lines in a dose dependent manner. C646 significantly augmented TRAIL-induced apoptotic sensitivity, which was accompanied by reduced levels of survivin, in HepG2, HLE and SK-HEP1 cells. C646 significantly inhibited invasion of Huh7, HLE and SK-HEP1 cells. The level of matrix metallopeptidase 15 (MMP15) mRNA expression was significantly reduced, whereas the level of laminin alpha 3 (LAMA3) and secreted phosphoprotein 1 (SPP1) mRNA expression was significantly increased in Huh7 cells following exposure to C646. In conclusion, our results suggest that CBP/p300 HAT activity has an important role in malignant transformation, proliferation, apoptotic sensitivity and invasion in HCC. CBP/p300 could be a promising therapeutic target in HCC.

3,3'-Diindolylmethane: A Promising Sensitizer of γ-Irradiation

Purpose. Radiotherapy is an effective treatment modality in the clinical treatment of breast cancer. The present work investigated the effect of 3,3′-diindolylmethane (DIM) on γ-irradiation sensitizing human breast carcinoma. Methods. Cell survival, intracellular ROS levels, cell cycle distribution, cell apoptosis, and expression of proteins related to apoptosis were measured with MTT assays, flow cytometry, and Western blot analysis, respectively. Results. In vitro DIM plus γ-irradiation arrested the activity of G2/M phase cell cycle, increased intracellular ROS level, significantly suppressed PARP (poly ADP-ribose polymerase), and enhanced γ-irradiation-induced apoptosis, thereby inhibiting the proliferation of MCF-7 cells. Conclusion. These data provide a rationale for the use of DIM as a promising sensitizer of γ-irradiation.

Successful strategies in the discovery of small-molecule epigenetic modulators with anticancer potential

As a class, epigenetic enzymes have been identified as clear targets for cancer therapeutics based on their broad hyperactivity in solid and hematological malignancies. The search for effective inhibitors of histone writers and of histone erasers has been a focus of drug discovery efforts both in academic and pharmaceutical laboratories and has led to the identification of some promising leads. This review focuses on the discovery strategies and preclinical evaluation studies of a subset of the more advanced compounds that target histone writers or histone erasers. The specificity and anticancer potential of these small molecules is discussed within the context of their development pipeline.

Functional Role of G9a Histone Methyltransferase in Cancer

Post-translational modifications of DNA and histones are epigenetic mechanisms, which affect the chromatin structure, ultimately leading to gene expression changes. A number of different epigenetic enzymes are actively involved in the addition or the removal of various covalent modifications, which include acetylation, methylation, phosphorylation, ubiquitination, and sumoylation. Deregulation of these processes is a hallmark of cancer. For instance, G9a, a histone methyltransferase responsible for histone H3 lysine 9 (H3K9) mono- and dimethylation, has been observed to be upregulated in different types of cancer and its overexpression has been associated with poor prognosis. Key roles played by these enzymes in various diseases have led to the hypothesis that these molecules represent valuable targets for future therapies. Several small molecule inhibitors have been developed to specifically block the epigenetic activity of these enzymes, representing promising therapeutic tools in the treatment of human malignancies, such as cancer. In this review, the role of one of these epigenetic enzymes, G9a, is discussed, focusing on its functional role in regulating gene expression as well as its implications in cancer initiation and progression. We also discuss important findings from recent studies using epigenetic inhibitors in cell systems in vitro as well as experimental tumor growth and metastasis assays in vivo.