Antitumor effects of a novel sulfur‐containing hydroxamate histone deacetylase inhibitor H40

Histone deacetylase (HDAC) inhibitors are among the most promising targeted anticancer agents and are potent inducers of growth arrest, differentiation, and/or apoptotic cell death of transformed cells. In this study, antitumor effects of a novel sulfur‐containing hydroxamate HDAC inhibitor, H40, were observed and compared with a typical HDAC inhibitor SAHA. In biochemical HDAC assay, H40 showed a potent HDAC inhibition. It induced histone H3 hyperacetylation, correlating with inhibition of cancer cell proliferation, induction of cell differentiation and cell cycle blockage. A broad cytotoxicity was observed across cell lines from different tumor entities. The autophagy rather than apoptosis inducing activity for both H40 and SAHA was observed in prostate cancer PC‐3M cells. HDAC inhibitor‐induced p21^CIP/WAF1 expression was evident in PC‐3M and HL‐60 cell lines. The in vivo efficacy of H40 against a murine prostate carcinoma TRAMP‐C2 was compared with that of SAHA, which showed that H40 exerted a favorable antitumor action when only administered twice a week. We conclude that H40 might have clinical value in cancer chemotherapy and warrants further investigation in this regard. © 2008 Wiley‐Liss, Inc.     

Inhibition of histone deacetylase enhances the anti-proliferative action of antiestrogens on breast cancer cells and blocks tamoxifen-induced proliferation of uterine cells

Here we report a novel potential therapeutic strategy using histone deacetylase (HDAC) inhibitors to enhance the action of hormonal therapy agents in estrogen receptor alpha (ERα)-positive breast cancer. HDAC inhibitors [trichostatin A (TSA), suberoylanilide hydroxamic acid (SAHA) and valproic acid (VPA)], inhibited proliferation of MCF-7 breast cancer cells and, in combination with tamoxifen inhibited proliferation better than with either agent alone. VPA, an anti-convulsant drug with HDAC inhibitory activity, enhanced tamoxifen action at doses within the concentration range used for anti-convulsive therapy. VPA cooperated with tamoxifen in a variety of ERα-positive cell lines and was also effective when combined with other antiestrogens, and with aromatase inhibition. VPA enhanced antiestrogen action by promoting cell death via apoptosis without affecting cell cycling. Some of this action may be due to VPA’s ability to induce the pro-apoptotic gene Bik, which is also induced by antiestrogens. Remarkably, VPA blocked the undesirable pro-proliferative action of tamoxifen on uterine endometrial cells. Our in vitro results suggest that VPA and other HDAC inhibitors have the potential to enhance hormonal therapy for ERα-positive breast cancer and simultaneously reverse the adverse effects of antiestrogens in the uterus.     

Romidepsin (FK228), a potent histone deacetylase inhibitor,induces apoptosis through the generation of hydrogen peroxide

Romidepsin (FK228) is a potent histone deacetylase (HDAC) inhibitor, which has a potent anticancer activity, but its molecular mechanism is unknown. We investigated the mechanism of FK228‐induced apoptosis in the human leukemia cell line HL‐60 and its hydrogen peroxide (H₂O₂)‐resistant sub‐clone, HP100, and the human colon cancer cell line Caco‐2. Cytotoxicity and DNA ladder formation induced by FK228 could be detected in HL‐60 cells after a 24‐h incubation, whereas they could not be detected in HP100 cells. Trichostatin A (TSA), an HDAC inhibitor, induced DNA ladder formation in both HL‐60 and HP100 cells. In contrast, FK228 inhibited HDAC activity in both HL‐60 and HP100 cells to a similar extent. These findings suggest that FK228‐induced apoptosis involves H₂O₂‐mediated pathways and that TSA‐induced apoptosis does not. Flow cytometry revealed H₂O₂ formation and a change in mitochondrial membrane potential (Δψm) in FK228‐treated cells. FK228 also induced apoptosis in Caco‐2 cells, which was prevented by N‐acetyl‐cysteine, suggesting that reactive oxygen species participate in apoptosis in various types of tumor cells. Interestingly, in a cell‐free system, FK228 generated superoxide (O₂^?) in the presence of glutathione, suggesting that H₂O₂ is derived from dismutation of O₂^? produced through redox‐cycle of FK228. Therefore, in addition to HDAC inhibition, H₂O₂ generated from FK228 may participate in its apoptotic effect. (Cancer Sci 2010;)     

Plant flavone apigenin inhibits HDAC and remodels chromatin to induce growth arrest and apoptosis in human prostate cancer cells: In vitro and in vivo study

Apigenin (4′,5,7,‐trihydroxyflavone), an anticancer agent, selectively toxic to cancer cells induces cell cycle arrest and apoptosis through mechanisms that have not been fully elucidated. Our studies indicate that apigenin‐mediated growth inhibitory responses are due to inhibition of class I histone deacetylases (HDACs) in prostate cancer cells. Treatment of PC‐3 and 22Rv1 cells with apigenin (20–40 µM) resulted in the inhibition of HDAC enzyme activity, specifically HDAC1 and HDAC3 at the protein and message level. Apigenin‐mediated HDAC inhibition resulted in global histone H3 and H4 acetylation, as well as localized hyperacetylation of histone H3 on the p21/waf1 promoter. A corresponding increase was observed in p21/waf1 and bax protein and mRNA expression after apigenin exposure, consistent with the use of HDAC inhibitor, trichostatin A. The downstream events demonstrated cell cycle arrest and induction of apoptosis in both cancer cells. Studies of PC‐3 xenografts in athymic nude mice further demonstrated that oral intake of apigenin at doses of 20 and 50 µg/mouse/d over an 8‐wk period resulted in a marked reduction in tumor growth, HDAC activity, and HDAC1 and HDAC3 protein expression at both doses of apigenin. An increase in p21/waf1 expression was observed in apigenin‐fed mice, compared to the control group. Furthermore, apigenin intake caused a significant decrease in bcl2 expression with concomitant increase in bax, shifting the bax/bcl2 ratio in favor of apoptosis. Our f indings confirm for the first time that apigenin inhibits class I HDACs, particularly HDAC1 and HDAC3 and its exposure results in reversal of aberrant epigenetic events that promote malignancy. © 2011 Wiley Periodicals, Inc.     

Anti-invasive effects and proapoptotic activity induction by the rexinoid IIF and valproic acid in combination on colon cancer cell lines

In this study, we investigated the antiproliferative and anti-invasive mechanism action of sodium valproate (VPA), an inhibitor of histone deacetylase (HDAC) activity, in combination with the rexinoid 6-OH-11-O-hydroxyphenanthrene (IIF), a ligand of retinoid X receptor (RXR), in the HT-29 and LoVo colon cancer cell lines. VPA inhibited HDAC-1 and increased RXRγ expression. VPA and IIF reduced viability in a dose- and time-dependent manner. The combined use of VPA and IIF enhanced the apoptosis induction. In particular, the BCL2 level decreased, while levels of BAX, cleaved caspase-3 and caspase-9 increased. The same treatment also reduced invasiveness of HT-29 cell line through the inhibition of metalloproteinase-9 (MMP9) expression, and MMP9 and MMP2 activity, with an increase of tissue inhibitors of MMPs TIMP1 and TIMP2. In conclusion, VPA and IIF have strong proapoptotic and anti-invasive effects in the HT-29 colon cancer cell line and their effects are enhanced when used together.     

Inhibition of autophagy induced by TSA sensitizes colon cancer cell to radiation

Radiotherapy is one of the main treatments for clinical cancer therapy. However, its application was limited due to lack of radiosensitivity in some cancers. Trichostatin A (TSA) is a classic histone deacetylases inhibitor (HDACi) that specifically inhibits the biochemical functions of HDAC and is demonstrated to be an active anticancer drug. However, whether it could sensitize colon cancer to radiation is not clear. Our results showed that TSA enhanced the radiosensitivity of colon cancer cells as determined by CCK-8 and clonogenic survival assay. Moreover, apoptotic cell death induced by radiation was enhanced by TSA treatment. Additionally, TSA also induced autophagic response in colon cancer cells, while autophagy inhibition led to cell apoptosis and enhanced the radiosensitivity of colon cancer cells. Our data suggested that inhibition of cytoprotective autophagy sensitizes cancer cell to radiation, which might be further investigated for clinical cancer radiotherapy.     

Cancer cells become susceptible to natural killer cell killing after exposure to histone deacetylase inhibitors due to glycogen synthase kinase-3-dependent expression of MHC class I-related chain A and B

We show that histone deacetylase (HDAC) inhibitors lead to functional expression of MHC class I-related chain A and B (MICA/B) on cancer cells, making them potent targets for natural killer (NK) cell-mediated killing through a NK group 2, member D (NKG2D) restricted mechanism. Blocking either apoptosis or oxidative stress caused by HDAC inhibitor treatment did not affect MICA/B expression, suggesting involvement of a separate signal pathway not directly coupled to induction of cell death. HDAC inhibitor treatment induced glycogen synthase kinase-3 (GSK-3) activity and down-regulation of GSK-3 by small interfering RNA or by different inhibitors showed that GSK-3 activity is essential for the induced MICA/B expression. We thus present evidence that cancer cells which survive the direct induction of cell death by HDAC inhibitors become targets for NKG2D-expressing cells like NK cells, gammadelta T cells, and CD8 T cells.     

HDAC3 overexpression and colon cancer cell proliferation and differentiation

An immunohistochemical analysis of human colorectal adenocarcinomas showed that cancer cells express widely varying levels of HDAC3. The SW480 colon cancer cell line was found to express high levels of HDAC3 compared to other colon cancer cell lines. p21 was poorly induced in SW480 cells relative to the lower HDAC3-expressing HT-29 cells. RNAi-induced reduction of HDAC3 in SW480 cells increased their constitutive, butyrate-, TSA-, and TNF-alpha-induced expression of p21, but did not cause all the gene expression changes induced upon general histone deacetylase (HDAC) inhibition. SW480 cells with lower HDAC3 expression appeared to be poised for gene expression responses with increased histone H4-K12 acetylation, but not K5, K8, or K16 acetylation. Even though p21 was readily activated in HT29 cells, HDAC3 siRNA nonetheless stimulated p21 expression in these cells to a greater degree than HDAC1 and HDAC2 siRNA. SW480 cells with lower HDAC3 levels displayed an enhanced cell cycle arrest and growth inhibition by butyrate, but without changes in apoptosis or sensitivity to chemotherapeutic agents. As reported for other colon cancer cell lines, butyrate induced the rapid downregulation of the secretory cell differentiation markers mucin 2 and intestinal trefoil factor in SW480 cells. Interestingly, selective HDAC3 inhibition was sufficient to downregulate these genes. Our data support a central role for HDAC3 in regulating the cell proliferation and differentiation of colon cancer cells and suggest a potential mechanism by which colon cancers may become resistant to luminal butyrate.     

SAHA inhibits the growth of colon tumors by decreasing histone deacetylase and the expression of cyclin D1 and survivin

We studied the effects of suberoylanilide hydroxamic acid (SAHA), a histone deacetylase (HDAC) inhibitor, on colon cancer. The expression of HDACs in colorectal cancer specimens and the effects of SAHA on colon cancer cells and tumors of nude mice were assessed. Treatment with SAHA (3 μm) for 72 h induced downregulation of different subtypes of HDAC proteins and also induced acetylation of histone 3 and histone 4. SAHA significantly inhibited the expression of the oncogenic protein c-myc and also increased the expression of the p53 and Rb proteins. The immunohistochemical staining of HDACs, including HDAC1, HDAC2, HDAC3, and HDAC4, was significantly increased in colorectal adenocarcinoma specimens compared to healthy control tissues. In addition, murine studies showed that 100 mg/kg SAHA administered by intraperitoneal injection significantly induced tumor necrosis and inhibited the growth of colon tumors. Immunohistochemistry of the tumor tissues from nude mice revealed that SAHA inhibited the expression of different subtypes of histone deacetylase, the anti-apoptotic proteins cyclin D1, survivin, and also inhibited cell proliferative as determined by Ki67 expression. SAHA inhibited the growth of colon tumors by decreasing histone deacetylases and the expression of cyclin D1 and survivin in nude mice.     

Aberrant expression of proteinase‐activated receptor 4 promotes colon cancer cell proliferation through a persistent signaling that involves Src and ErbB‐2 kinase

Thrombin is now recognized as an important factor in many cancers. Here, we examined the expression and role of the recently discovered thrombin receptor PAR4, in human colon cancer cells. PAR4 mRNA was found in 10 out of 14 (71%) human colon cancer cell lines tested but not in epithelial cells isolated from normal human colon. This finding is in line with immunostaining results of PAR4 in human colon tumors and its absence in normal human colonic mucosa. Investigation of the functional significance of the aberrant expression of PAR4 in colon cancer cells revealed (i) a prompt increase in intracellular calcium concentration on challenge with PAR4‐specific agonist AP4 (100 μM) and (ii) marked mitogenic response (2.5‐fold increase in cell number) in a dose‐dependent manner on treatment with AP4 (0.1–300 μM). Analysis of the signaling pathways downstream of PAR4 activation in HT29 cells showed (i) a sustained phosphorylation of extracellular signal‐related kinase 1/2 (ERK1/2) and (ii) the involvement of epidermal growth factor receptor B‐2 (ErbB‐2) but not of epidermal growth factor receptor in PAR4‐induced mitogen‐activated protein kinase activation. Tyrphostin AG1478, the ErbB inhibitor, reversed the action of AP4 on ERK1/2 and ErbB‐2 phosphorylation and HT29 cell growth. Finally, the Src inhibitor PP2 abrogated ErbB‐2 and ERK phosphorylation and HT29 cell proliferation, suggesting the essential role of Src activity in PAR4‐induced phosphorylation of ErbB‐2. These data highlight the role of PAR4 as a new important player in the control of colon tumors and underline the critical role of ErbB‐2 transactivation. © 2008 Wiley‐Liss, Inc.     

Combination of proteasome and class I HDAC inhibitors induces apoptosis of NPC cells through an HDAC6‐independent ER stress‐induced mechanism

The current paradigm stipulates that inhibition of histone deacetylase (HDAC) 6 is essential for the combinatorial effect of proteasome and HDAC inhibitors for the treatment of cancers. Our study aims to investigate the effect of combining different class I HDAC inhibitors (without HDAC6 action) with a proteasome inhibitor on apoptosis of nasopharyngeal carcinoma (NPC). We found that combination of a proteasome inhibitor, bortezomib, and several class I HDAC inhibitors, including MS‐275, apicidin and romidepsin, potently induced killing of NPC cells both in vitro and in vivo. Among the drug pairs, combination of bortezomib and romidepsin (bort/romidepsin) was the most potent and could induce apoptosis at low nanomolar concentrations. The apoptosis of NPC cells was reactive oxygen species (ROS)‐ and caspase‐dependent but was independent of HDAC6 inhibition. Of note, bort/romidepsin might directly suppress the formation of aggresome through the downregulation of c‐myc. In addition, two markers of endoplasmic reticulum (ER) stress‐induced apoptosis, ATF‐4 and CHOP/GADD153, were upregulated, whereas a specific inhibitor of caspase‐4 (an initiator of ER stress‐induced apoptosis) could suppress the apoptosis. When ROS level in the NPC cells was reduced to the untreated level, ER stress‐induced caspase activation was abrogated. Collectively, our data demonstrate a model of synergism between proteasome and class I HDAC inhibitors in the induction of ROS‐dependent ER stress‐induced apoptosis of NPC cells, independent of HDAC6 inhibition, and provide the rationale to combine the more specific and potent class I HDAC inhibitors with proteasome inhibitors for the treatment of cancers.     

Insulin-like growth factor-II renders LIM 2405 human colon cancer cells resistant to butyrate-induced apoptosis: a potential mechanism for colon cancer cell survival in vivo

Butyrate has potent anti-tumorigenic effects on many colon cancer cell lines, including inhibition of growth and promotion of apoptosis in vitro. Nevertheless, despite the butyrate concentration in the colonic lumen being sufficient to result in the death of almost all cells in vitro, colon cancers still develop and grow in vivo, suggesting that cancer cells must develop mechanisms by which they escape the effects of butyrate observed in vitro. Insulin-like growth factor-II (IGF-II) is an autocrine growth factor in many colon cancer cells. The aim of this study was to determine whether IGF-II influences butyrate-mediated apoptosis in LIM 2405 human colon cancer cells. Butyrate and trichostatin A, both of which are histone deacetylase inhibitors although the latter is more specific, induced apoptosis as determined by floating cell counting, Hoechst 33258 staining, DNA laddering and a cell death detection ELISA. IGF-II inhibited the effects of both agents. Butyrate but not trichostatin A also induced LIM 2405 cell migration. In contrast to the above results, IGF-II enhanced butyrate-induced cell migration. Levels of IGF binding protein-3 (IGFBP-3), which may induce apoptosis by IGF-dependent or -independent mechanisms, were increased by butyrate and trichostatin A; IGF-II augmented this effect. It is therefore unlikely that IGFBP-3 mediates butyrate-induced apoptosis. We suggest that IGF-II inhibits the pro-apoptotic effect of butyrate downstream of histone deacetylase inhibition. In contrast, IGF-II promotes histone deacetylase-dependent IGFBP-3 expression and histone deacetylase-independent migration. IGF-II may promote tumour growth by mediating the development of resistance to the pro-apoptotic effects of butyrate.     

HDAC inhibitors restore BRAF‐inhibitor sensitivity by altering PI3K and survival signalling in a subset of melanoma

Mutations in BRAF activate oncogenic MAPK signalling in almost half of cutaneous melanomas. Inhibitors of BRAF (BRAFi) and its target MEK are widely used to treat melanoma patients with BRAF mutations but unfortunately acquired resistance occurs in the majority of patients. Resistance results from mutations or non‐genomic changes that either reactivate MAPK signalling or activate other pathways that provide alternate survival and growth signalling. Here, we show the histone deacetylase inhibitor (HDACi) panobinostat overcomes BRAFi resistance in melanoma, but this is dependent on the resistant cells showing a partial response to BRAFi treatment. Using patient‐ and in vivo‐derived melanoma cell lines with acquired BRAFi resistance, we show that combined treatment with the BRAFi encorafenib and HDACi panobinostat in 2D and 3D culture systems synergistically induced caspase‐dependent apoptotic cell death. Key changes induced by HDAC inhibition included decreased PI3K pathway activity associated with a reduction in the protein level of a number of receptor tyrosine kinases, and cell line dependent upregulation of pro‐apoptotic BIM or NOXA together with reduced expression of anti‐apoptotic proteins. Independent of these changes, panobinostat reduced c‐Myc and pre‐treatment of cells with siRNA against c‐Myc reduced BRAFi/HDACi drug‐induced cell death. These results suggest that a combination of HDAC and MAPK inhibitors may play a role in treatment of melanoma where the resistance mechanisms are due to activation of MAPK‐independent pathways.     

Effects of valproic acid on the cell cycle and apoptosis through acetylation of histone and tubulin in a scirrhous gastric cancer cell line

Background

Management of peritoneal dissemination is the most critical problem in gastric cancer. This study was performed to investigate the inhibitory effects of valproic acid (VPA) on a highly peritoneal-seeding cell line of human scirrhous gastric cancer, OCUM-2MD3, and to explore the mechanism and the potential of VPA.

Methods

The effects of VPA on the growth of OCUM-2MD3 cells were assessed by MTT assay. In addition, paclitaxel (PTX) was combined with VPA to evaluate their synergistic effects. HDAC1 and HDAC2 expression were evaluated by western blotting in OCUM-2MD3 cells and other gastric cancer cell lines (TMK-1, MKN-28). The acetylation status of histone H3 and α-tubulin after exposure to VPA were analyzed by western blotting. The activities of cell cycle regulatory proteins and apoptosis-modulating proteins were also examined by western blotting. The effects of VPA in vivo were evaluated in a xenograft model, and apoptotic activity was assessed by TUNEL assay.

Results

OCUM-2MD3 cells showed high levels of HDAC1 and HDAC2 expression compared with TMK-1 and MKN-28. The concentration of VPA required for significant inhibition of cell viability (P < 0.05) was 5 mM at 24 h and 0.5 mM at 48 h and 72 h. The inhibition of VPA with PTX showed dose-dependent and combinatorial effects. VPA increased acetyl-histone H3, acetyl-α-tubulin, and p21WAF1 levels accompanied by upregulation of p27, caspase 3, and caspase 9, and downregulation of bcl-2, cyclin D1, and survivin. In the xenograft model experiment, the mean tumor volume of the VPA-treated group was significantly reduced by 36.4%, compared with that of the control group at 4 weeks after treatment (P < 0.01). The apoptotic index was significantly higher in the VPA-treated group (42.3% ± 3.5%) than in the control group (7.7% ± 2.5%) (P < 0.001).

Conclusions

VPA induced dynamic modulation of histone H3 and α-tubulin acetylation in relation with the anticancer effect and the enhancement of PTX in the OCUM-2MD3 cell line. Therefore, VPA in combination with PTX is expected to be a promising therapy for peritoneal dissemination of scirrhous gastric cancer.     

FK228阻断细胞生存信号通路诱导前列腺癌细胞凋亡

目的：研究组蛋白去乙酰化酶（HDAC）抑制剂FK228诱导前列腺癌细胞系DU145凋亡的作用机制。方法：MTT比色法测定FK228抑制DUl45细胞增殖及其对细胞的杀伤效应；瑞氏-姬姆萨染色观察细胞形态的变化；流式细胞术分析细胞周期的改变；蛋白印迹实验检测细胞内蛋白表达水平的变化。结果：FK228明显抑制DU145细胞体外增殖，并介导细胞死亡；12．5ng／ml FK228作用细胞48h后，细胞存活率降至63．7％；伴有细胞形态改变及细胞周期阻滞于G0／G1期；细胞内多种重要的激酶蛋白，包括EGFR、Her2、Raf-1、Src、Cdk4、Akt及凋亡抑制蛋白Survivin均发生了不同程度的降解，细胞内两条重要的生存信号通路Raf-MEK—ERK及P13K／Akt被阻断，细胞发生凋亡。结论：FK228可以通过清除细胞内重要信号蛋白、阻断细胞生存信号通路来诱导DU145细胞发生凋亡。     

Induction of differentiation of colon cancer cells by combined inhibition of kinases and histone deacetylase

The MAP kinase pathway inhibitor U0126 in combination with butyrate promotes differentiation in some colon cancer cell lines. We examined several inhibitors of histone deacetylase (HDAC) in combination with U0126 and other protein kinase inhibitors to see if these effects are general properties of HDAC inhibitors or butyrate alone. Alkaline phosphatase and peptidase activities were examined as markers for cellular differentiation in the human colon cancer cell lines Caco-2 and HT29 and the minimally transformed NCM460. Several HDAC inhibitors caused greater increases of alkaline phosphatase in the cancer cells than in NCM460, in which butyrate was the only HDAC inhibitor that caused a consistent increase. Unlike the JNK and PKC inhibitors examined, the MEK 1/2 inhibitor U0126 induced alkaline phosphatase activity in Caco-2 as a single agent and caused additive effects with HDAC inhibitors. The PI-3 kinase inhibitor LY294002 had little effect alone but enhanced the response of most HDAC inhibitors as did the raf inhibitor GW5074. In addition to butyrate, several HDAC inhibitors can induce differentiation in colon cancer cells and the responses may be enhanced by U0126, GW5074 and LY294002.     

A histone deacetylase inhibitor enhances expression of genes inhibiting Wnt pathway and augments activity of DNA demethylation reagent against nonsmall‐cell lung cancer

Development of new inhibitors targeting histone deacetylases (HDACs) with improved efficacy for solid tumor therapy is urgently needed. Here, we report the development of a novel HDAC inhibitor TMU‐35435 and verify it as a single agent and in combination treatment with DNA demethylation reagent 5‐aza‐2′‐deoxycytidine (5‐aza‐dC) in lung cancer preclinical models. TMU‐35435 exerted cancer‐specific cytotoxicity via mitochondria‐mediated apoptosis. Expression microarrays revealed a unique TMU‐35435‐induced gene networks enriched in biological processes, including “negative regulation of cell proliferation” and “Wnt receptor signaling pathway” compared to FDA‐approved HDAC inhibitor SAHA. TMU‐35435 inhibited tumor growth with good pharmacokinetic properties and safety features in lung orthotopic and subcutaneously implanted xenograft models. TMU‐35435 and 5‐aza‐dC showed synergistic antitumor effects through reactivation of tumor suppressor genes and those genes encoding negative regulators of Wnt signaling pathway in vitro and in vivo. Some genes showed additive inhibition of DNA methylation upon TMU‐35435 and 5‐aza‐dC combined treatment. Our findings suggested that TMU‐35435 is a potential HDAC inhibitor for lung cancer treatment as a single agent and in combination with 5‐aza‐dC.     

S-adenosylhomocysteine hydrolase inhibition by 3-deazaneplanocin A analogues induces anti-cancer effects in breast cancer cell lines and synergy with both histone deacetylase and HER2 inhibition

Epigenetic abnormalities including abnormal histone methyltransferase activity contribute to breast cancer pathogenesis. An example is over expression of the polycomb repressive complex (PRC) 2 member enhancer of zeste homolog 2 (EZH2) which is linked to epigenetic silencing and poor prognosis. Recent evidence shows that S-adenosylhomocysteine (AdoHcy) hydrolase inhibitors (AHI) such as 3-deazaneplanocin A (DZNep) modulate chromatin through indirect inhibition of histone methyltransferases including EZH2. We investigated the biological effects of AdoHcy hydrolase inhibition using DZNep and its structural analogues 3-deazaadenosine (DZA) and neplanocin A (Nep A) in breast cancer cells. EZH2 protein expression was decreased and dose dependent growth inhibition occurred with variable potencies in MCF7, MDA-MB-231 and SKBr3 breast cancer cells. Cellular proliferation was inhibited through G₂/M cell cycle arrest and apoptosis. In addition breast cancer cells accumulated cytoplasmic lipid droplets in response to AdoHcy hydrolase inhibition consistent with a differentiating effect. Each analogue induced a similar pattern of biological activity against breast cancer cells but with differences in potency (DZA > DZNep > Nep A). Co-administration with the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) induced synergistic inhibition of breast cancer cell proliferation. Furthermore, the relatively AHI resistant human epidermal growth factor receptor 2 (HER2) positive cell line SKBr3 underwent synergistic growth inhibition in response to co-treatment with the HER2 directed therapeutic antibody trastuzumab. In conclusion, AHI induce growth inhibition, cell cycle arrest, apoptosis and differentiation in breast cancer cells and synergise with HDAC and HER2 inhibition. Targeting histone methyltransferase activity might be of therapeutic value in breast cancer.