组蛋白去乙酰化酶抑制剂MS-275对人宫颈癌SiHa细胞增殖及凋亡的影响

目的： 观察组蛋白去乙酰化酶抑制剂MS-275对人宫颈癌SiHa细胞增殖和凋亡的影响,并探讨其可能的机制。 方法： 以MS-275（0、5、10、20 μmol/L）作用于人宫颈癌SiHa细胞,MTT法检测细胞的增殖,流式细胞术检测细胞的凋亡,Western blotting法检测细胞内乙酰化组蛋白H4（acetylhistone4,Ac-H4）水平,RT-PCR检测p21和p53 mRNA的表达。 结果： MS-275作用后,人宫颈癌SiHa细胞增殖受到抑制、细胞凋亡增加,20 μmol/L MS-275作用下,细胞增殖率仅为（1395±891）%,凋亡率高达（3838±178）%,显著高于其他各组（P< 001）。MS-275作用后,细胞内Ac-H4水平增加（P< 001）,p21和p53 mRNA表达增加（均P< 001）。 结论： MS-275可抑制人宫颈癌SiHa细胞的增殖,诱导SiHa细胞凋亡;上调p21和p53表达、提高组蛋白乙酰化水平可能是其作用机制之一。     

Enhanced radiation-induced cell killing and prolongation of gammaH2AX foci expression by the histone deacetylase inhibitor MS-275

Histone deacetylase (HDAC) inhibitors are undergoing clinical evaluation for cancer therapy. Because HDAC modulates chromatin structure and gene expression, parameters considered to influence radioresponse, we have investigated the effects of the HDAC inhibitor MS-275 on the radiosensitivity of two human tumor cell lines (DU145 prostate carcinoma and U251 glioma). Acetylation status of histones H3 and H4 was determined as a function of time after MS-275 addition to and removal from culture medium. Histone acetylation increased by 6 h after MS-275 addition, reaching a maximum between 24 and 48 h of exposure; providing fresh drug-free medium then resulted in a decrease in histone acetylation that began by 6 h and approached untreated levels by 16 h. Treatment of cells with MS-275 for 48 h followed by irradiation had little or no effect on radiation-induced cell death. However, exposure to MS-275 before and after irradiation resulted in an increase in radiosensitivity with dose enhancement factors of 1.9 and 1.3 for DU145 and U251 cells, respectively. This MS-275 treatment protocol did not result in a redistribution of the cells into a more radiosensitive phase of the cell cycle or in an increase in apoptosis. However, MS-275 did modify the time course of gammaH2AX expression in irradiated cells. Whereas there was no significant difference in radiation-induced gammaH2AX foci at 6 h, the number of cells expressing gammaH2AX foci was significantly greater in the MS-275-treated cells at 24 h after irradiation. These results indicate that MS-275 can enhance radiosensitivity and suggest that this effect may involve an inhibition of DNA repair.     

组蛋白去乙酰酶抑制剂MS-275抑制膀胱癌的实验研究

背景与目的:染色质核心组蛋白的乙酰化水平受组蛋白乙酰转移酶和组蛋白去乙酰酶(HDAC)的控制,它与基因表达调控密切相关、HDACs功能异常与肿瘤的发生发展有关,组蛋白去乙酰酶抑制剂(HDAC Is)通过抑制HDACs而抗肿瘤。本文研究HDAC I类药物之一MS-275对人膀胱癌T24细胞的抑制作用,为临床应用提供有价值的实验依据。方法:将不同浓度的MS-275作用于T24细胞,用MTT法检测生长抑制作用,用平板克隆形成试验测定细胞增殖能力的影响,分别采用光学显微镜、透射电子显微镜及AnnexinV、PI双标流式细胞术观察和检测细胞的凋亡情况。结果:MS-275对人膀胱癌T24细胞的生长抑制作用存在明显的剂量、时间依赖关系,0.5μmol/L作用72 h的抑制率为9.34%±3.57%,而8μmol/L作用120 h达94.84%±1.33%。克隆形成率从阴性对照组的55.67%±6.51%降至4μmol/L组的2.33%±0.58%。显微镜下可观察到大量的凋亡形态特征的细胞。流式细胞术检测示,作用48 h后的凋亡率在1μmol/L组、2μmol/L组和4μmol/L组分别为24.19%、30.77%和38.51%,明显高于阴性对照组(2.49%)。结论:组蛋白去乙酰酶抑制剂类药物具有体外抗膀胱癌作用,其重要作用机制之一是诱导膀胱癌细胞凋亡,并有望成为新的抗膀胱肿瘤药物。     

组蛋白去乙酰化酶抑制剂MS-275在体外抑制胃癌细胞的实验研究

背景与目的:组蛋白去乙酰化酶抑制剂(histone deacetylase inhibitors,HDACis)对于很多肿瘤细胞具有选择性的诱导凋亡及分化作用,而对正常细胞的细胞毒性作用很低,这一选择性杀伤作用使HDACis成为目前抗肿瘤分子靶向药物的研究热点.本文研究了HDACis MS-275对人胃癌细胞SGC-7901、人胃黏膜正常细胞GES-1和张氏肝细胞(CHANG-LIVER)的选择性作用及机制,为HDACis的临床应用提供了理论依据.方法:不同终浓度MS-275处理SGC-7901细胞、GES-1和张氏肝细胞,用WST-1方法检测药物对细胞的生长抑制作用;AnnexinV、PI双标流式细胞术检测MS-275对肿瘤细胞SGC-7901和正常细胞的选择性杀伤作用;TUNEL染色观察肿瘤细胞核内凋亡情况.结果:MS-275对胃癌细胞SGC-7901具有明显的生长抑制作用,并且这种作用具有时间及剂量依赖性;MS-275的杀伤作用具有选择性,对正常细胞GES-1和张氏肝细胞并不表现出促凋亡作用;TUNEL染色证明MS-275能诱导SGC-7901细胞核内发生DNA断裂,是细胞发生凋亡的重要指标.结论:MS-275具有体外选择性杀伤胃癌细胞的作用,对正常细胞没有明显的杀伤作用,有希望成为新一代的胃癌临床治疗的肿瘤分子靶向药物.     

组蛋白去乙酰化转移酶抑制剂MS-275对胃癌细胞增殖的影响

目的：探讨组蛋白去乙酰化转移酶抑制剂MS-275对胃癌细胞（MKN-45）和人正常胃黏膜细胞（GES-1）及张氏肝细胞（changliver）生长及凋亡的影响。方法：用不同浓度的MS-275分别处理体外培养的胃癌细胞和人正常胃黏膜细胞及张氏肝细胞,用水溶性四唑盐（WST-1）法检测对细胞的增殖抑制作用;流式细胞仪和TUNEL法检测细胞凋亡情况。结果：MS-275可明显抑制胃癌细胞的生长且呈时间和浓度依赖性,细胞凋亡率明显增加,但对正常细胞没有促凋亡作用。低浓度的MS-275能诱导MKN-45细胞发生G0/G1期阻滞,随着药物处理时间的延长,可以明显检测到G0/G1期比例增大。结论：去乙酰化转移酶抑制剂MS-275对胃癌细胞MKN-45具有选择性细胞毒作用,为其临床应用提供了有价值的实验依据,有望成为新的抗胃癌药物。     

The histone deacetylase inhibitor MS-275 interacts synergistically with fludarabine to induce apoptosis in human leukemia cells

Interactions between the novel benzamide histone deacetylase (HDAC) inhibitor MS-275 and fludarabine were examined in lymphoid and myeloid human leukemia cells in relation to mitochondrial injury, signal transduction events, and apoptosis. Prior exposure of Jurkat lymphoblastic leukemia cells to a marginally toxic concentration of MS-275 (e.g., 500 nM) for 24 h sharply increased mitochondrial injury, caspase activation, and apoptosis in response to a minimally toxic concentration of fludarabine (500 nM), resulting in highly synergistic antileukemic interactions and loss of clonogenic survival. Simultaneous exposure to MS-275 and fludarabine also led to synergistic effects, but these were not as pronounced as observed with sequential treatment. Similar interactions were noted in the case of (a) other human leukemia cell lines (e.g., U937, CCRF-CEM); (b) other HDAC inhibitors (e.g., sodium butyrate); and (c) other nucleoside analogues (e.g., 1-beta-D-arabinofuranosylcytosine, gemcitabine). Potentiation of fludarabine lethality by MS-275 was associated with acetylation of histones H3 and H4, down-regulation of the antiapoptotic proteins XIAP and Mcl-1, enhanced cytosolic release of proapoptotic mitochondrial proteins (e.g., cytochrome c, Smac/DIABLO, and apoptosis-inducing factor), and caspase activation. It was also accompanied by the caspase-dependent down-regulation of p27(KIP1), cyclins A, E, and D(1), and cleavage and diminished phosphorylation of retinoblastoma protein. However, increased lethality of the combination was not associated with enhanced fludarabine triphosphate formation or DNA incorporation and occurred despite a slight reduction in the S-phase fraction. Prior exposure to MS-275 attenuated fludarabine-mediated activation of MEK1/2, extracellular signal-regulated kinase, and Akt, and enhanced c-Jun NH(2)-terminal kinase phosphorylation; furthermore, inducible expression of constitutively active MEK1/2 or Akt significantly diminished MS-275/fludarabine-induced lethality. Combined exposure of cells to MS-275 and fludarabine was associated with a significant increase in generation of reactive oxygen species; moreover, both the increase in reactive oxygen species and apoptosis were largely attenuated by coadministration of the free radical scavenger L-N-acetylcysteine. Finally, prior administration of MS-275 markedly potentiated fludarabine-mediated generation of the proapoptotic lipid second messenger ceramide. Taken together, these findings indicate that the HDAC inhibitor MS-275 induces multiple perturbations in signal transduction, survival, and cell cycle regulatory pathways that lower the threshold for fludarabine-mediated mitochondrial injury and apoptosis in human leukemia cells. They also provide insights into possible mechanisms by which novel, clinically relevant HDAC inhibitors might be used to enhance the antileukemic activity of established nucleoside analogues such as fludarabine.     

The histone deacetylase inhibitor MS-275 induces caspase-dependent apoptosis in B-cell chronic lymphocytic leukemia cells.

MS-275 is a histone deacetylase (HDAC) inhibitor that has been reported to mediate its cytotoxic effect through generation of reactive oxygen species (ROS) in proliferating hematopoietic cell lines. We examined efficacy of MS-275 in nonproliferating chronic lymphocytic leukemia (CLL) cells from patients. In these cells, MS-275 demonstrated an in vitro LC(50) that was one log lower than for normal mononuclear cells. Following MS-275 treatment, histones H3 and H4 showed increased acetylation and HDAC enzymatic activity was reduced. Caspase-8, -9, and -3 were activated, and caspase substrates PARP and BID were cleaved. Additionally, FLICE-inhibitory protein (FLIP) was downmodulated following MS-275 incubation. MS-275 treatment caused detectable ROS generation after 15 h of incubation, which was blocked by the caspase inhibitor Z-VAD-fmk. Overexpression of Bcl-2 protein protected against MS-275-induced apoptosis. These data demonstrate that MS-275 is a promising therapy for the treatment of CLL, but that in contrast to previous reports, ROS generation does not precede commitment to apoptosis. Similar to many other therapeutic targets, MS-275-mediated apoptosis is reduced by overexpression of Bcl-2, justifying strategies to combine HDAC inhibitors with Bcl-2 antagonists.     

Interspecies differences in plasma protein binding of MS-275, a novel histone deacetylase inhibitor

MS-275 (MS-27–275; 3-pyridylmethyl-N-{4-[(2-aminophenyl)-carbamoyl]-benzyl-carbamate) is a histone deacetylase inhibitor under clinical development as an anticancer agent. Here, we examined the role of protein binding as a possible determinant of the pharmacokinetic behavior of MS-275. The distribution of MS-275 in plasma was studied in vitro using equilibrium dialysis and ex vivo in five cancer patients receiving the drug orally at a dose of 10 mg/m². The dialysis method uses a tracer amount of [G−³H]MS-275 on a 96-well microdialysis plate with a 5-kDa cut-off membrane, and requires 250 μl sample. The time to equilibrium was established to be within 5 h, and the mean unbound fraction of MS-275 (f _u) over a presumed therapeutic concentration range in healthy volunteer human plasma was 0.188±0.0075 as compared to 0.168±0.0144 in cancer patients. The binding was concentration-independent, indicating a low affinity, possibly non-specific and non-saturable process. MS-275 was found to bind in decreasing order to plasma > α₁-acid glycoprotein > albumin. Among 19 tested drugs, a slightly increased f _u was observed in the presence of only ibuprofen (f _u, 0.236±0.001) and metoclopramide (f _u, 0.270±0.042), suggesting weakly competitive displacement from protein-binding sites (P<0.01). Compared to humans, f _u was significantly higher in plasma from mouse (0.376), rat (0.393), rabbit (0.355), dog (0.436), and pig (0.439) (P<0.01), which may explain, in part, the species-dependent pharmacokinetic profile of MS-275 observed previously.     

组蛋白去乙酰化酶抑制剂MS-275诱导骨髓瘤细胞株U266凋亡过程中Survivin的表达

背景与目的：组蛋白去乙酰化酶抑制剂（histone deacetylase inhibitors,HDACi）是-类具有抗肿瘤活性的新型药物,主要通过诱导细胞凋亡发挥作用。本实验研究HDACi（MS-275）对人骨髓瘤细胞系U266细胞增殖和凋亡的影响及其与Survivin表达的关系。方法：将不同浓度的MS-275作用于U266细胞不同时间后,用台盼蓝拒染法观察药物对细胞活力的影响：通过瑞氏-姬姆萨染色观察药物作用后细胞形态学的变化;用流式细胞仪分析细胞周期;用Westernblot检测Survivin、P21和Cdk4等的蛋白表达,以及凋亡信号通路中Caspase-3活化及蛋白聚ADP核糖聚合酶[poly（ADP—ribose）polymerase,PARP]的裂解情况。结果：MS-275呈时间和剂量依赖性抑制U266细胞增殖,阻断细胞周期于G0／G1期。MS-275作用U266细胞48h时的Ic50为1．39μmol／L：2μmol／L的MS-275作用U266细胞24h后,G／G,期细胞占66．39％．36h后G0／G1期细胞占89．80％。瑞氏-姬姆萨染色显示细胞形态发生明显变化。Western blot检测结果显示。MS-275作用U266细胞后,Survivin和Cdk4表达下降,P21表达增加,Caspase3被裂解活化,其底物蛋白PARP发生剪切。结论：MS-275抑制人多发性骨髓瘤细胞系U266增殖并诱导细胞凋亡,可能与下调Survivin蛋白的表达有关。     

Hypermethylation-associated inactivation of retinoic acid receptor beta in human esophageal squamous cell carcinoma.

PURPOSE: The purpose of this study was to investigate the mechanism of altered retinoic acid receptor beta (RARbeta) expression during esophageal squamous carcinogenesis. EXPERIMENTAL DESIGN: Samples were collected from Linzhou, China. The hypermethylation of CpG islands in the promoter region of the RARbeta gene was examined by methylation-specific PCR in human esophageal squamous cell carcinoma (ESCC) samples, as well as in neighboring tissues with normal epithelium, basal cell hyperplasia, and dysplasia. RARbeta mRNA expression was determined by in situ hybridization. The DNA methyltransferase inhibitor 2'-deoxy-5-azacytidine was used to treat the ESCC cell line, and the DNA hypermethylation status and mRNA expression level were examined. RESULTS: Two of 17 (12%) normal, 9 of 21 basal cell hyperplasia (43%), 7 of 12 dysplasia (58%), and 14 of 20 ESCC (70%) samples had hypermethylation of the RARbeta promoter region. The loss of RARbeta mRNA expression was highly concordant with RARbeta promoter CpG island hypermethylation when individual samples were considered in the correlation analysis. Good statistical correlation between hypermethylation and loss of RARbeta expression was revealed. Frequencies of hypermethylation appeared to increase with the progression of carcinogenesis. In samples from the same patients, if hypermethylation was detected in earlier lesions, it was usually observed in more severe lesions. In the ESCC cell line KYSE 510, 2'-deoxy-5-azacytidine partially reversed CpG island hypermethylation and restored RARbeta mRNA expression. CONCLUSIONS: The results suggest that hypermethylation of RARbeta promoter region is an important mechanism for RARbeta gene silencing in esophageal squamous carcinogenesis.     

Molecular profiling of embryonal carcinoma cells following retinoic acid or histone deacetylase inhibitor treatment

Regulation of tissue homeostasis is crucial to disease prevention; cell division, cell cycle arrest, differentiation and apoptosis have to be tightly controlled in order to maintain this homeostasis. Retinoic acid (RA) and the histone deacetylase inhibitors (HDACIs) have profound effects on these processes and thus may be critical regulators of homeostasis. Consequently, RA and/or histone deacetylase inhibitors are currently being tested in clinical trials for a variety of cancers. Unfortunately, little is known of the overall affect of these compounds on cellular gene expression. Therefore, we decided to compare the effects of all-trans retinoic acid (ATRA) and a particular HDACI-Trichostatin A (TSA)-on an embryonal carcinoma (EC) cell line (F9) using gene chip analysis. We have focused particular attention on those genes that may be differentially affected by these compounds. Within the parameters established for this study, only 116 of the 12,488 genes examined were similarly regulated by ATRA and TSA: 75 positively and 41 negatively. An additional 70 genes were affected by only one of the compounds and 19 genes were actually inversely regulated. The gene set inversely regulated by ATRA and TSA includes several important patterning genes as well as the crucial tumor suppressor/promoter, transforming growth factor beta 1 (TGFbeta1). Promoter analysis suggests a motif that may regulate one set of these genes. This study provides the first comprehensive comparison of global gene expression on EC cells as affected by ATRA and a HDAC inhibitor (TSA); reveals new targets for ATRA and HDAC inhibitors; identifies a new regulatory motif; demonstrates that ATRA and HDAC inhibitors do not always act synergistically on gene expression; and examines particular questions regarding their concurrent clinical application.     

Antineoplastic action of 5-aza-2'-deoxycytidine and histone deacetylase inhibitor and their effect on the expression of retinoic acid receptor beta and estrogen receptor alpha genes in breast carcinoma cells

PURPOSE: During tumorigenesis several cancer-related genes can be silenced by aberrant methylation. In many cases these silenced genes can be reactivated by exposure to the DNA methylation inhibitor, 5-aza-2'-deoxycytidine (5-AZA-CdR). Histone acetylation also plays a role in the control of expression of some genes. The aim of this study was to determine the antineoplastic activities of 5-AZA-CdR and trichostatin A (TSA), either administered alone or in combination. in MDA-MB-231 breast carcinoma cells. The effects of these drugs (alone and in combination) on the expression of the tumor suppressor gene, retinoic acid receptor (RAR beta) and of the estrogen receptor alpha gene (ER alpha), whose expression is lost in the cell line used in the study, were also investigated. METHODS: MDA-MB-231 cells were treated with 5-AZA-CdR and TSA and the antitumor activity of these drugs was determined by clonogenic assay. Total RNA was extracted from the treated cells and RT-PCR was used to determine the effect of the treatment on the expression of RAR beta and ER alpha. Methylation-sensitive PCR analysis was used to confirm that lack of expression of both genes was due to hypermethylation of their promoter regions. A single nucleotide primer extension assay was also used to quantify the reduction in DNA methylation following drug treatment. RESULTS: Both 5-AZA-CdR and TSA alone showed significant antineoplastic activity. The combination of the two drugs was synergistic with respect to MDA-MB-231 cell kill. 5-AZA-CdR alone weakly activated the expression of both RAR beta and ER alpha. TSA alone only activated RAR beta, but not ER alpha. The combination of these agents appeared to produce a greater activation of both genes. CONCLUSIONS: The interesting interaction between 5-AZA-CdR and TSA in both cell kill and cancer-related gene reactivation provides a rationale for the use of inhibitors of DNA methylation and histone deacetylation in combination for the chemotherapy of breast cancer.     

Effects of retinoic acid and interferon-gamma on expression of the retinoic acid receptor in mouse renal cell carcinoma

The clinical outcome of interferon-gamma treatment of metastatic renal cell carcinoma remains unsatisfactory. To overcome this, a reagent that has a different action on cancer cells is desired. One such candidate may be 13-cRA (cis retinoic acid), a vitamin A derivative known to markedly regulate the differentiation and proliferation of normal and neoplastic cells. Moreover, 13-cRA demonstrates a remarkable synergistic effect with IFN-gamma in certain types of cancer. We investigated the efficacy of concomitant administration of 13-cRA and IFN-gamma. The in vivo anti-tumor effects were evaluated in a lung metastasis model using a mouse renal cell carcinoma cell line (RenCa). The in vitro anti-tumor effects were also assessed by MTT assay. The presence of retinoic acid receptors (RAR)-alpha, -beta and -gamma was examined by PCR analysis. The influence of IFN-gamma on these retinoic acid receptors was evaluated by Northern blotting. IFN-gamma showed anti-tumor effects both in vivo and in vitro. This effect was enhanced synergistically with concomitant 13-cRA treatment. RenCa cells expressed RAR-alpha, and -gamma, but not -beta according to PCR analysis. IFN-gamma treatment increased the expression level of RAR-alpha and RAR-gamma according to Northern blot analysis. Combination therapy using IFN-gamma and 13-cRA showed synergistic anti-tumor effects, which exceeded those of each therapy alone. Moreover, IFN-gamma treatment increased RAR-alpha and RAR-gamma expression. Thus, the augmented anti-tumor effects of IFN-gamma and 13-cRA may be attributable to enhanced expression of RAR-alpha and RAR-gamma by IFN-gamma treatment.     

Valproic acid, a histone deacetylase inhibitor, enhances radiosensitivity in esophageal squamous cell carcinoma

Histone deacetylase (HDAC) inhibitors have been shown to enhance radiation response in various cancer cell lines. Valproic acid (VPA) has been used in clinical practice for the treatment of epilepsy and other seizure disorders and is also one of the most represented HDAC inhibitors. The aim of this study was to evaluate the radiosensitizing ability of VPA and its mechanisms in four esophageal squamous cell carcinoma (ESCC) cell lines (TE9, TE10, TE11 and TE14). VPA inhibited the viability of all ESCC cells in a dose-dependent manner. The 50% inhibitory concentration (IC50) value of VPA in each cell line was between 1.02-2.15 mM, which is higher than clinically used safe concentrations. VPA induced the hyperacetylation of histones H3 and H4, as well as apoptosis and had a radiosensitizing effect on all four ESCC cell lines at a concentration of 0.5 mM which is equivalent to the therapeutic plasma concentration of anti-epilepsy therapy in humans. The radiosensitization was accompanied by an increase in γH2AX levels, indicating the presence of double-strand breaks (DSBs), and decrease in Rad51 expression, a DSB repair protein. These results suggest that a clinically safe dose of VPA can enhance radiation-induced cytotoxicity in human ESCC cells by chromatin decondensation with histone hyperacetylation and downregulation of Rad51. In conclusion, VPA appears to be a safe and promising radiosensitizer for esophageal cancer radiotherapy.     

A phase I and pharmacokinetic study of the oral histone deacetylase inhibitor, MS-275, in patients with refractory solid tumors and lymphomas.

PURPOSE: To evaluate the toxicity profile, pharmacologic, and biological properties of 3-pyridylmethyl N-{4-[(2-aminophenyl)carbamoyl]benzyl}carbamate (MS-275), a histone deacetylase inhibitor, when administered orally on three different dosing schedules. EXPERIMENTAL DESIGN: Patients with advanced solid malignancies and lymphomas were treated on three dose schedules: once every other week, twice weekly for 3 weeks every 28 days, and once weekly for 3 weeks every 28 days. First-cycle plasma pharmacokinetics and peripheral blood mononuclear cell histone acetylation were determined. RESULTS: Twenty-seven patients received > or =149 courses of treatment. Hypophosphatemia and asthenia were dose limiting on the weekly and twice-weekly dosing schedules; there was no dose-limiting toxicity on the every other week schedule. Pharmacokinetic variables revealed dose-dependent and dose-proportional increases. Two of 27 patients showed partial remissions, including one patient with metastatic melanoma who had a partial response and has remained on study for >5 years. Six patients showed prolonged disease stabilization. Levels of histone H3 and H4 acetylation in peripheral blood mononuclear cells increased qualitatively but with a high degree of interpatient variation. CONCLUSIONS: MS-275 is well tolerated at doses up to 6 mg/m(2) every other week or 4 mg/m(2) weekly for 3 weeks followed by 1 week of rest and results in biologically relevant plasma concentrations and antitumor activity. Twice-weekly dosing was not tolerable due to asthenia, and further evaluation of this schedule was halted. The recommended dose for further disease-focused studies is 4 mg/m(2) given weekly for 3 weeks every 28 days or 2 to 6 mg/m(2) given once every other week.     

Chemosensitization of oral squamous cell carcinoma cells to cisplatin by histone deacetylase inhibitor, suberoylanilide hydroxamic acid

In the present study, the precise mechanism of the enhancing action of histone deacetylase (HDAC) inhibitors on cisplatin (CDDP)-induced apoptosis was investigated using suberoylanilide hydroxamic acid (SAHA) in human oral squamous cell carcinoma cells (HSC-3). HDAC inhibitors are promising novel compounds for the treatment of cancer, which cooperate with chemotherapeutic agents to induce apoptosis. Apoptosis enhancement of HSC-3 cells by SAHA was accompanied by the activation of caspase-3, -8 and -9, suggesting a mitochondrial-dependent amplification loop. Concomitant treatment (CDDP/SAHA) of cells resulted in the most effective enhancement of apoptosis compared to other timing combinations. By means of cell-cycle synchronization, G0/G1-phase cells proved to be a more sensitive fraction to SAHA action than their synchronized counterparts in other phases. Furthermore, cells treated with SAHA revealed a decrease in intracellular reduced glutathione (GSH) contents. Of importance, the GSH synthesis inhibitor, diethyl maleate, decreased intracellular GSH and enhanced CDDP-induced apoptosis in a similar pattern of timing to SAHA. Thus, SAHA appears to disrupt the intracellular redox balance, which causes maximal apoptosis at the G0/G1 phase arrested by CDDP in HSC-3 cells. These results demonstrate that HDAC inhibitors not only cause a change in the histone acetylation status, but are also able to influence the apoptotic process at several levels, and GSH plays a key role in governing SAHA-dependent enhancement of CDDP-induced apoptosis.