Histone deacetylase inhibitors: Potential in cancer therapy

The role of histone deacetylases (HDAC) and the potential of these enzymes as therapeutic targets for cancer, neurodegenerative diseases and a number of other disorders is an area of rapidly expanding investigation. There are 18 HDACs in humans. These enzymes are not redundant in function. Eleven of the HDACs are zinc dependent, classified on the basis of homology to yeast HDACs: Class I includes HDACs 1, 2, 3, and 8; Class IIA includes HDACs 4, 5, 7, and 9; Class IIB, HDACs 6 and 10; and Class IV, HDAC 11. Class III HDACs, sirtuins 1–7, have an absolute requirement for NAD⁺, are not zinc dependent and generally not inhibited by compounds that inhibit zinc dependent deacetylases. In addition to histones, HDACs have many nonhistone protein substrates which have a role in regulation of gene expression, cell proliferation, cell migration, cell death, and angiogenesis. HDAC inhibitors (HDACi) have been discovered of different chemical structure. HDACi cause accumulation of acetylated forms of proteins which can alter their structure and function. HDACi can induce different phenotypes in various transformed cells, including growth arrest, apoptosis, reactive oxygen species facilitated cell death and mitotic cell death. Normal cells are relatively resistant to HDACi induced cell death. Several HDACi are in various stages of development, including clinical trials as monotherapy and in combination with other anti‐cancer drugs and radiation. The first HDACi approved by the FDA for cancer therapy is suberoylanilide hydroxamic acid (SAHA, vorinostat, Zolinza), approved for treatment of cutaneous T‐cell lymphoma. J. Cell. Biochem. 107: 600–608, 2009. © 2009 Wiley‐Liss, Inc.     

Vimentin,colon cancer progression and resistance to butyrate and other HDACis

Dietary fibre protects against colorectal cancer (CRC) most likely through the activity of its fermentation product, butyrate. Butyrate functions as a histone deacetylase inhibitor (HDACi) that hyperactivates Wnt signalling and induces apoptosis of CRC cells. However, individuals who consume a high‐fibre diet may still develop CRC; therefore, butyrate resistance may develop over time. Furthermore, CRC cells that are resistant to butyrate are cross‐resistant to clinically relevant therapeutic HDACis, suggesting that the development of butyrate resistance in vivo can result in HDACi‐resistant CRCs. Butyrate/HDACi‐resistant CRC cells differ from their butyrate/HDACi‐sensitive counterparts in the expression of many genes, including the gene encoding vimentin (VIM) that is usually expressed in normal mesenchymal cells and is involved in cancer metastasis. Interestingly, vimentin is overexpressed in butyrate/HDACi‐resistant CRC cells although Wnt signalling is suppressed in such cells and that VIM is a Wnt activity‐targeted gene. The expression of vimentin in colonic neoplastic cells could be correlated with the stage of neoplastic progression. For example, comparative analyses of LT97 microadenoma cells and SW620 colon carcinoma cells revealed that although vimentin is not detectable in LT97 cells, it is highly expressed in SW620 cells. Based upon these observations, we propose that the differential expression of vimentin contributes to the phenotypic differences between butyrate‐resistant and butyrate‐sensitive CRC cells, as well as to the differences between early‐stage and metastatic colorectal neoplastic cells. We discuss the hypothesis that vimentin is a key factor integrating epithelial to mesenchymal transition, colonic neoplastic progression and resistance to HDACis.     

Inhibition of histone deacetylase as a new mechanism of teratogenesis

Histone deacetylases (HDACs) are nuclear and cytoplasmic enzymes that deacetylate a number of substrates, of which histones are the best known and described in the literature. HDACs are present in eukaryotic and bacteria cells, and are fundamental for a number of cellular functions, including correct gene expression. Surprisingly, only up to 20% of the whole genome is controlled by HDACs, but key processes for survival, proliferation, and differentiation have been strictly linked to HDAC enzyme functioning. The use of HDAC inhibitors (HDACi) has been proposed for the treatment of neoplastic diseases. Their effectiveness has been suggested for a number of liquid and solid tumors, particularly acute promyelocytic leukemia (APL). The role of HDACs in embryo development is currently under investigation. Published data indicate knockout phenotype analysis to be of particular interest, in which a number of HDACs play a key role during development. Little data have been published on the effects of HDACi on embryonic development, although for valproic acid (VPA), literature from the 1980s described its teratogenic effects in experimental animals and humans. To date, all tested HDACi have shown teratogenic effects similar to those described for VPA when tested in zebrafish, Xenopus laevis, and mice. HDACs were also able to alter embryo development in invertebrates and plants. A model, similar to that proposed in APL, involving retinoic acid receptors (RAR) and tissue specific Hox gene expression, is suggested to explain the HDAC effects on embryo development.     

BDNF/TrkB signaling protects HT-29 human colon cancer cells from EGFR inhibition

The clinical success of targeted treatment of colorectal cancer (CRC) is often limited by resistance to anti-epidermal growth factor receptor (EGFR) therapy. The neurotrophin brain-derived neurotrophic factor (BDNF) and its receptor TrkB have recently emerged as anticancer targets, and we have previously shown increased BDNF levels in CRC tumor samples. Here we report the findings from in vitro experiments suggesting that BDNF/TrkB signaling can protect CRC cells from the antitumor effects of EGFR blockade. The anti-EGFR monoclonal antibody cetuximab reduced both cell proliferation and the mRNA expression of BDNF and TrkB in human HT-29 CRC cells. The inhibitory effect of cetuximab on cell proliferation and survival was counteracted by the addition of human recombinant BDNF. Finally, the Trk inhibitor K252a synergistically enhanced the effect of cetuximab on cell proliferation, and this effect was blocked by BDNF. These results provide the first evidence that increased BDNF/TrkB signaling might play a role in resistance to EGFR blockade. Moreover, it is possible that targeting TrkB could potentiate the anticancer effects of anti-EGFR therapy.     

靶点药物Cetuximab(C225)研究新进展

在许多肿瘤组织中均有表皮生长因子受体(epidermal growthfactor receptor,EGFR)的过表达,它的失调与肿瘤对化疗和放疗的耐受以及不良预后相关,为肿瘤的治疗提供了一个理想的分子靶点.Cetuximab(C225)是特异性EGFR单克隆抗体,与化疗或放疗联合应用时具有协同作用,具有毒副作用少、靶向性好等优点.Cetuximab(C225)已被批准用于对伊利替康抵抗的结直肠癌和头颈部鳞癌的治疗,对非小细胞肺癌、乳腺癌、胰腺癌等具有EGFR高表达肿瘤治疗的临床试验正在进行之中,为肿瘤治疗开辟了一个全新的领域.     

Resveratrol as a Pan-HDAC Inhibitor Alters the Acetylation Status of Jistone Proteins in Human-Derived Hepatoblastoma Cells

The polyphenolic alcohol resveratrol has demonstrated promising activities for the prevention and treatment of cancer. Different modes of action have been described for resveratrol including the activation of sirtuins, which represent the class III histone deacetylases (HDACs). However, little is known about the activity of resveratrol on the classical HDACs of class I, II and IV, although these classes are involved in cancer development or progression and inhibitors of HDACs (HDACi) are currently under investigation as promising novel anticancer drugs. We could show by in silico docking studies that resveratrol has the chemical structure to inhibit the activity of different human HDAC enzymes. In vitro analyses of overall HDAC inhibition and a detailed HDAC profiling showed that resveratrol inhibited all eleven human HDACs of class I, II and IV in a dose-dependent manner. Transferring this molecular mechanism into cancer therapy strategies, resveratrol treatment was analyzed on solid tumor cell lines. Despite the fact that hepatocellular carcinoma (HCC) is known to be particularly resistant against conventional chemotherapeutics, treatment of HCC with established HDACi already has shown promising results. Testing of resveratrol on hepatoma cell lines HepG2, Hep3B and HuH7 revealed a dose-dependent antiproliferative effect on all cell lines. Interestingly, only for HepG2 cells a specific inhibition of HDACs and in turn a histone hyperacetylation caused by resveratrol was detected. Additional testing of human blood samples demonstrated a HDACi activity by resveratrol ex vivo. Concluding toxicity studies showed that primary human hepatocytes tolerated resveratrol, whereas in vivo chicken embryotoxicity assays demonstrated severe toxicity at high concentrations. Taken together, this novel pan-HDACi activity opens up a new perspective of resveratrol for cancer therapy alone or in combination with other chemotherapeutics. Moreover, resveratrol may serve as a lead structure for chemical optimization of bioavailability, pharmacology or HDAC inhibition.     

Inhibition of histone deacetylase 2 increases apoptosis and p21Cip1/WAF1 expression, independent of histone deacetylase 1

Histone deacetylases (HDACs) 1 and 2 share a high degree of homology and coexist within the same protein complexes. Despite their close association, each possesses unique functions. We show that the upregulation of HDAC2 in colorectal cancer occurred early at the polyp stage, was more robust and occurred more frequently than HDAC1. Similarly, while the expression of HDACs1 and 2 were increased in cervical dysplasia and invasive carcinoma, HDAC2 expression showed a clear demarcation of high-intensity staining at the transition region of dysplasia compared to HDAC1. Upon HDAC2 knockdown, cells displayed an increased number of cellular extensions reminiscent of cell differentiation. There was also an increase in apoptosis, associated with increased p21Cip1/WAF1 expression that was independent of p53. These results suggest that HDACs, especially HDAC2, are important enzymes involved in the early events of carcinogenesis, making them candidate markers for tumor progression and targets for cancer therapy.     

Histone deacetylases inhibitor MS-275 suppresses human esophageal squamous cell carcinoma cell growth and progression via the PI3K/Akt/mTOR pathway

Esophageal squamous cell carcinoma (ESCC) is a malignant tumor with low survival rate, so new therapies are urgently needed. Histone deacetylases (HDACs) play a critical role in tumorigenesis, and HDACs inhibition is a potential therapeutic target in ESSC. In our study, we evaluated the effect and molecular mechanism of MS-275 (an inhibitor of HDACs) on ESCC cells. We found that HDAC1 and HDAC2 were overexpressed in ESCC tissues and related with clinical pathological features of patients with ESCC. MS-275 markedly reduced HDAC1 and HDAC2 expression, whereas increased the level of AcH3 and AcH2B. MS-275 suppressed proliferation and clonogenicity of ESCC cells in a concentration-dependent manner. In addition, MS-275 induced apoptosis, arrested cell cycle, and inhibited migration, epithelial–mesenchymal transition, and sphere-forming ability of ESCC cells in vitro. Moreover, p-Akt1 and p-mTOR were downregulated by MS-275. Finally, MS-275 significantly inhibited tumor growth in vivo. Taken together, HDAC1 and HDAC2 are associated with the progression of ESCC, and MS-275 hinders the progression and stemness of ESCC cells by suppressing the PI3K/Akt/mTOR pathway. Our findings show that MS-275 inhibits ESCC cells growth in vitro and in vivo, which is a potential drug for the ESCC therapy.     

Synthesis and structure–activity relationships of novel hybrid ferrocenyl compounds based on a bicyclic core skeleton for breast cancer therapy

Breast cancer is the most frequent cancer in women worldwide, and incidence is increasing year by year. Although current selective estrogen receptor modulators (SERMs) have clear advantages in the treatment of hormone-responsive breast cancer, they are ineffective for ER(−). In this study, we describe the design and synthesis of a series of dual-acting estrogen receptor (ER) and histone deacetylase (HDAC) inhibitors with incorporation of the ferrocenyl moiety, leading to novel hybrid ferrocenyl complexes (FcOBHS–HDACis) for breast cancer therapy. It is worth to note that these ferrocenyl conjugates could not only potently inhibit HDACs and the proliferation of ERα positive (ER(+)) breast cancer cells (MCF-7), but also show significant antiproliferative effect on ER(−) breast cancer cells (MDA-MB-231). Thus, the FcOBHS–HDACi conjugates represent a novel approach to the development of efficiently dual-acting agents for treatment of breast cancer.     

Proliferation of Colorectal Cancer Is Promoted by Two Signaling Transduction Expression Patterns: ErbB2/ErbB3/AKT and MET/ErbB3/MAPK

One of the recent breakthroughs in cancer research is the identification of activating mutations in various receptor tyrosine kinase(RTK) pathways in many cancers including colorectal cancer(CRC). We hypothesize that, alternative to mutations, overexpression of various oncogenic RTKs may also underpin CRC pathogenesis, and different RTK may couple with distinct downstream signaling pathways in different subtypes of human CRC. By immunohistochemistry, we show here that RTK members ErbB2, ErbB3 and c-Met were in deed differentially overexpressed in colorectal cancer patient samples leading to constitutive activation of RTK signaling pathways. Using ErbB2 specific inhibitor Lapatinib and c-Met specific inhibitor PHA-665752, we further demonstrated that this constitutive activation of RTK signaling is necessary for the survival of colorectal cancer cells. Furthermore, we show that RTK overexpression pattern dictates the use of downstream AKT and/or MAPK pathways. Our data are important additions to current oncogenic mutation models, and further explain the clinical variation in therapeutic responses of colorectal cancer. Our findings advocate for more personalized therapy tailored to individual patients based on their type of RTK expression in addition to their mutation status.     

Thioredoxin 1 supports colorectal cancer cell survival and promotes migration and invasion under glucose deprivation through interaction with G6PD

Overcoming energy stress is a critical step for cells in solid tumors. Under this stress microenvironment, cancer cells significantly alter their energy metabolism to maintain cell survival and even metastasis. Our previous studies have shown that thioredoxin-1 (Trx-1) expression is increased in colorectal cancer (CRC) and promotes cell proliferation. However, the exact role and mechanism of how Trx-1 is involved in energy stress are still unknown. Here, we observed that glucose deprivation of CRC cells led to cell death and promoted the migration and invasion, accompanied by upregulation of Trx-1. Increased Trx-1 supported CRC cell survival under glucose deprivation. Whereas knockdown of Trx-1 sensitized CRC cells to glucose deprivation-induced cell death and reversed glucose deprivation-induced migration, invasion, and epithelial-mesenchymal transition (EMT). Furthermore, we identified glucose-6-phosphate dehydrogenase (G6PD) interacting with Trx-1 by HuPortTM human protein chip, co-IP and co-localization. Trx-1 promoted G6PD protein expression and activity under glucose deprivation, thereby increasing nicotinamide adenine dinucleotide phosphate (NADPH) generation. Moreover, G6PD knockdown sensitized CRC cells to glucose deprivation-induced cell death and suppressed glucose deprivation-induced migration, invasion, and EMT. Inhibition of Trx-1 and G6PD, together with inhibition of glycolysis using 2-deoxy-D-glucose (2DG), resulted in significant anti-tumor effects in CRC xenografts in vivo. These findings demonstrate a novel mechanism and may represent a new effective therapeutic regimen for CRC.     

Histone Deacetylase Classes I and II Regulate Kaposi's Sarcoma-Associated Herpesvirus Reactivation

In primary effusion lymphoma (PEL) cells infected with latent Kaposi''s sarcoma-associated herpesvirus (KSHV), the promoter of the viral lytic switch gene, Rta, is organized into bivalent chromatin, similar to cellular developmental switch genes. Histone deacetylase (HDAC) inhibitors (HDACis) reactivate latent KSHV and dramatically remodel the viral genome topology and chromatin architecture. However, reactivation is not uniform across a population of infected cells. We sought to identify an HDACi cocktail that would uniformly reactivate KSHV and reveal the regulatory HDACs. Using HDACis with various specificities, we found that class I HDACis were sufficient to reactivate the virus but differed in potency. Valproic acid (VPA) was the most effective HDACi, inducing lytic cycle gene expression in 75% of cells, while trichostatin A (TSA) induced less widespread lytic gene expression and inhibited VPA-stimulated reactivation. VPA was only slightly superior to TSA in inducing histone acetylation of Rta''s promoter, but only VPA induced significant production of infectious virus, suggesting that HDAC regulation after Rta expression has a dramatic effect on reactivation progression. Ectopic HDACs 1, 3, and 6 inhibited TPA-stimulated KSHV reactivation. Surprisingly, ectopic HDACs 1 and 6 stimulated reactivation independently, suggesting that the stoichiometries of HDAC complexes are critical for the switch. Tubacin, a specific inhibitor of the ubiquitin-binding, proautophagic HDAC6, also inhibited VPA-stimulated reactivation. Immunofluorescence indicated that HDAC6 is expressed diffusely throughout latently infected cells, but its expression level and nuclear localization is increased during reactivation. Overall, our data suggest that inhibition of HDAC classes I and IIa and maintenance of HDAC6 (IIb) activity are required for optimal KSHV reactivation.     

The multifaceted influence of histone deacetylases on DNA damage signalling and DNA repair

Histone/protein deacetylases play multiple roles in regulating gene expression and protein activation and stability. Their deregulation during cancer initiation and progression cause resistance to therapy. Here, we review the role of histone deacetylases (HDACs) and the NAD⁺ dependent sirtuins (SIRTs) in the DNA damage response (DDR). These lysine deacetylases contribute to DNA repair by base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), non-homologous end joining (NHEJ), homologous recombination (HR) and interstrand crosslink (ICL) repair. Furthermore, we discuss possible mechanisms whereby these histone/protein deacetylases facilitate the switch between DNA double-strand break (DSB) repair pathways, how SIRTs play a central role in the crosstalk between DNA repair and cell death pathways due to their dependence on NAD⁺, and the influence of small molecule HDAC inhibitors (HDACi) on cancer cell resistance to genotoxin based therapies. Throughout the review, we endeavor to identify the specific HDAC targeted by HDACi leading to therapy sensitization.