Journal of Cancer Research and Therapeutics

: 2018  |  Volume : 14  |  Issue : 10  |  Page : 576--582

Trichostatin A induces apoptosis in oral squamous cell carcinoma cell lines independent of hyperacetylation of histones

Boonsil Jang1, Lee-Han Kim1, Seung-Youp Lee2, Kyung-Eun Lee3, Ji-Ae Shin1, Sung-Dae Cho1,  
1 Department of Oral Pathology, School of Dentistry, Institute of Oral Bioscience and Biodegradable Material, Chonbuk National University, Jeonju 561-756, Republic of Korea
2 Department of Orthodontics, School of Dentistry, Chonbuk National University, Jeonju 561-756, Republic of Korea
3 Department of Oral Medicine, School of Dentistry, Research Institute of Clinical Medicine of Chonbuk National University-Biomedical Research Institute, Chonbuk National University Hospital, Jeonju 561-712, Republic of Korea

Correspondence Address:
Sung-Dae Cho
Department of Oral Pathology, School of Dentistry, Institute of Oral Bioscience and Biodegradable Material, Chonbuk National University, Jeonju 561.756
Republic of Korea


Aim of Study: To investigate the apoptotic event of trichostatin A (TSA) and its associated mechanism in oral squamous cell carcinoma (OSCC) lines. Materials and Methods: HSC-3 and Ca9.22 cell lines were evaluated using a trypan blue exclusion assay, histone isolation, soft agar assay, live/dead assay, 4%,6-diamidino-2-phenylindole staining, JC-1 mitochondrial membrane potential (MMP) assay, and Western blot analysis to demonstrate the anticancer activity of TSA. Results: TSA decreased OSCC cell viability and proliferation without affecting the histone acetylation. TSA-induced caspase-dependent or -independent apoptosis according to cell types, TSA enhanced the expression levels of Bim protein by dephosphorylating ERK1/2 pathway in HSC-3 cells. TSA also damaged MMP and increased cytosolic apoptosis-inducing factor (AIF) in Ca9.22 cells. Conclusion: The present study suggests that TSA may be a potential anticancer drug candidate for the treatment of OSCC through the induction of apoptosis.

How to cite this article:
Jang B, Kim LH, Lee SY, Lee KE, Shin JA, Cho SD. Trichostatin A induces apoptosis in oral squamous cell carcinoma cell lines independent of hyperacetylation of histones.J Can Res Ther 2018;14:576-582

How to cite this URL:
Jang B, Kim LH, Lee SY, Lee KE, Shin JA, Cho SD. Trichostatin A induces apoptosis in oral squamous cell carcinoma cell lines independent of hyperacetylation of histones. J Can Res Ther [serial online] 2018 [cited 2022 Jun 25 ];14:576-582
Available from:

Full Text


Histone deacetylases (HDACs) are important regulators of gene expression that remove the acetyl group from histones resulting in gene repression. Numerous studies have indicated that abnormal expression of HDACs in human tumors can be linked to key events of carcinogenesis.[1],[2],[3] Recently, Chang et al.[4] demonstrated that overexpression of HDAC in oral squamous cell carcinoma (OSCC) tissue was associated with advanced tumor size, metastasis, and shorter overall survival implying the possibility of being a good biomarker. In this concept, HDAC inhibitors were thought to be potentially effective anticancer drug candidates for the treatment of OSCC. Trichostatin A (TSA)[5] originally identified as an antibiotic against fungi was a classic HDAC inhibitor. It was found that TSA can suppress the growth of several types of malignant tumors and promote tumor cell apoptosis.[6],[7] However, previous studies have not properly explained the antitumor activity of TSA in OSCC cell lines.

Bcl-2 family proteins modulate mitochondrial membrane potential (MMP) to control the fate of cells to die, and thus it is necessary to target these proteins for inducing cancer cell death. Bim, a proapoptotic BH3-only protein of the Bcl-2 family members, can be upregulated to trigger cytochrome c release from mitochondria causing apoptotic cell death. The Bim-deficient mice increased the number of lymphoid and myeloid cells.[8] Bim deficiency also can result in the formation and growth of the tumors in nude mice.[9] These findings suggest that Bim is possibly a critical molecule of apoptosis in chemotherapy. Apoptosis-inducing factor (AIF) was known to be a novel apoptotic effector that induces chromatin condensation and DNA fragmentation.[10] AIF is located in the mitochondria, which is critical for providing energy to support cellular functions. It may be released from mitochondria into cytosol causing caspase-independent cell death when cells got certain stress such as the treatment with genotoxic agents.[5],[11] Thus, AIF can be a very important target for caspase-independent apoptosis against cancer treatment.

The goal of our study was to investigate how TSA exerts its anticancer effect in human OSCC cell lines. To this end, we used two OSCC cell lines, HSC-3 and Ca9.22. With this study, we are the first to demonstrate that TSA can induce caspase-dependent or caspase-independent apoptosis according to cell type.

 Materials and Methods

Chemicals and antibodies

TSA and 4',6-diamidino-2-phenylindole (DAPI) were supplied by Sigma–Aldrich (Sigma–Aldrich, Louis, MI, USA). Z-VAD-FMK was obtained from R & D Systems (Minneapolis, MN, USA). Antibodies against AIF, actin and α-tubulin, were purchased from Santa Cruz Biotechnology, Inc., (Santa Cruz, CA, USA). Antibodies against acetyl-histone H3 and H2A (Lys5), cleaved caspase 3, cleaved PARP, Bim, Bax, Bak, Bcl-xL, Bcl-2, phospho-ERK, and total ERK were bought from Cell Signaling Technology, Inc., (Cell Signaling Technology, Charlottesville, VA, USA). COX4 antibody was obtained from Abcam (Abcam, Cambridge, UK).

Cell culture and chemical treatment

HSC-3 and Ca9.22 human OSCC cell lines were kindly provided from Prof. Shindo (Hokkaido, Japan). Both cell lines were cultured in Dulbecco's modified essential medium (DMEM; Welgene, Dae-gu, Korea) supplemented with 10% fetal bovine serum at 37°C in a 5% CO2 incubator.

Trypan blue exclusion assay

HSC-3 and Ca9.22 cells were treated with different concentrations of TSA (62.5, 125, 250, and 500 nM) for 24 h, and the number of viable cells was counted using a hemocytometer with trypan blue (0.4%). Each experiment was carried out in triplicate, and the results were expressed as means ± standard deviation for each treatment group.

Histone isolation

To verify an HDAC inhibiting activity of TSA, acid-soluble proteins were extracted as follows. Isolated nuclei were mixed with 0.4 N sulfuric acid and incubated for 3 h on ice. After centrifugation at 15,000 rpm for 5 min at 4°C, the dissolved histones in the supernatant were precipitated with 20% trichloroacetic acid overnight at −80°C. The tubes were centrifuged and washed with acetone. The pellets were collected by centrifugation at 15,000 rpm for 5 min at 4°C and then dissolved in distilled water.

Live/dead assay

Cell death was further investigated using the live/dead viability/cytotoxicity kit (Invitrogen, Carlsbad, CA, USA) according to the manufacturer's instructions. Briefly, HSC-3 and Ca9.22 cells were seeded in 60 mm2 dishes, treated with different concentrations of TSA for 24 h, and harvested by trypsinization. Cell pellets were resuspended with calcein acetoxymethyl ester (2 μM) and ethidium homodimer (4 μM) at room temperature (RT) for 30 min, followed by washing with ice-cold PBS. Dead cells were finally observed with a fluorescence microscope (×200).

4',6-diamidino-2-phenylindole staining

Nuclear condensation and fragmentation were determined by DAPI staining. Both cell lines were treated with TSA for 24 h and fixed in 100% ethanol overnight at −20°C. The next day, the cells were washed with ice-cold PBS (3X), fixed with 100% methanol at RT for 10 min, and then stained with DAPI solution (2 μg/ml). DAPI-stained cells were observed using a fluorescence microscope (×400).

Western blot analysis

Whole cell lysates were extracted with lysis buffer, and protein samples were quantified using a DC Protein Assay (Bio-Rad Laboratories, Hercules, CA, USA). Equal amounts of protein were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to immunoblot PVDF membranes (Bio-Rad Laboratories). The membranes were blocked with 5% skim milk in tris-buffered saline and Tween 20 for 1 h 30 min at RT and maintained overnight at 4°C with designated primary antibodies, followed by incubation with HRP-conjugated secondary antibody at RT for 1 h 30 min. Antibody-bound proteins were detected using an ECL Western blotting luminol reagent (Santa Cruz, CA, USA).

JC-1 assay

Alterations in MMP were measured using the MMP detection kit (Stratagene, La Jolla, CA, USA). Ca9.22 cells were treated with TSA, incubated with 1X JC-1 Reagent for 15 min at 37°C in 5% CO2 incubator, and washed with PBS (3X). JC-1 fluorescence was measured using a microplate reader (Plate Chameleon, HIDEX).

Preparation of cytosolic and mitochondrial fractions

Cell pellets were suspended for 1 min at RT in plasma membrane extraction buffer containing 0.05% digitonin. Following a centrifugation step at 15,000 g at 4°C for 5 min, the supernatant (cytosolic fraction) was separated from the pellet, which consisted of cellular debris (mitochondrial fraction). The pellets were resuspended in plasma membrane extraction buffer containing 0.5% Triton X-100 and centrifuged at 15,000 g at 4°C for 5 min. The supernatant from the last centrifugation contains mitochondrial proteins.

Statistical analysis

The data were analyzed for statistical significance using a Student's t-test, and P value compared with vehicle control was considered statistically significant.


Trichostatin A blocks viability of HSC-3 and Ca9.22 cells without affecting histone acetylation

We first examined a growth-inhibitory effect of TSA on HSC-3 and Ca9.22 cells using trypan blue exclusion assay. Both cell lines were treated with 62.5, 125, 250, and 500 nM of TSA for 24 h. TSA efficiently blocked the viability of HSC-3 and Ca9.22 cells in a concentration-dependent manner compared with DMSO-treated groups [Figure 1]a. To verify whether the antigrowth activity of TSA was mediated through the hyperacetylation of histones, we isolated histones and performed Western blot analysis using a specific antibody against acetyl-histones H2A and H3. HSC-3 and Ca9.22 cells treated with TSA for 24 h did not exhibit an increase in acetylation over the control except only HSC-3 cells treated with 500 nM of TSA whereas SAHA (4 μM)-treated HSC-3 cells as a positive control clearly caused hyperacetylation of histones [Figure 1]b. Overall, these results suggest that TSA can exert the antiproliferative activity oral cancer cell lines regardless of histone acetylation.{Figure 1}

Trichostatin A augments caspase-dependent or -independent apoptosis in oral cancer cell lines

To characterize the apoptotic response induced by TSA, a live/dead assay was carried out. As shown in [Figure 2]a, TSA clearly increased red fluorescence-positive cells implying the increasing number of dead cells in HSC-3 and Ca9.22 cells. Next, we tested whether the nuclear morphological change was being affected by TSA. Both cell lines treated with TSA displayed nuclear condensation and fragmentation, which are typical apoptotic features while DMSO-treated cells had an intact nucleus [Figure 2]b. To examine the effect of TSA on the expression of apoptosis-regulating proteins in both cell lines, Western blot analysis using antibodies against cleaved PARP and cleaved caspase 3 was implemented. The results demonstrated that higher concentrations of TSA dramatically induced cleaved PARP and cleaved caspase 3 [Figure 3]a. To evaluate whether caspase 3 is associated in TSA-induced apoptosis, we then confirmed the dependency of caspase 3 in TSA-mediated PARP cleavage using a pan-caspase inhibitor, z-VAD-FMK. We found that z-VAD-FMK partly prevented caspase-related PARP cleavage in HSC-3 cells, but the apoptotic event triggered by TSA was not blocked by the z-VAD-FMK in Ca9.22 cells [Figure 3]b. These findings suggest that TSA-induced apoptotic cell death is mediated by either a caspase-dependent or -independent pathway dependent on cell types.{Figure 2}{Figure 3}

Trichostatin A may induce apoptosis in HSC-3 cells via ERK/Bim signaling

Several studies have reported that modulation of Bcl-2 family proteins by HDAC inhibitors in cancer cells plays a critical role in cancer development and progression.[12],[13],[14] Thus, we determined whether TSA can regulate Bcl-2 family members. The results showed that HSC-3 cells treated with TSA significantly increased the expression level of Bim protein [Figure 4]a, whereas other Bcl-2 family members such as Bax, Bak, Bcl-xL, and Bcl-2 were not altered by TSA (data not shown). Because ERK1/2 pathway is necessary and sufficient to regulate Bim protein,[15] we here evaluated whether TSA could affect ERK1/2 signaling. As shown in [Figure 4]b, TSA significantly dephosphorylated ERK1/2 but did not change total ERK protein. To confirm the relationship between ERK1/2 pathway and Bim protein during TSA-induced apoptosis, we used AZD6244, an MEK/ERK inhibitor. The results showed that AZD6244 dramatically potentiated TSA-induced PARP cleavages through upregulation of Bim protein compared to each single treatment [Figure 4]c.{Figure 4}

Apoptosis-inducing factor may be related to caspase independency of trichostatin A-induced apoptosis in Ca9.22 cells

Next, in order to investigate whether modulation of MMP was involved in TSA-induced apoptosis in Ca9.22 cells, JC-1 assay was performed. The results found that TSA significantly disrupted MMP in a concentration-dependent manner [Figure 5]a. Recently, it has been reported that AIF leads to caspase-independent apoptosis by its translocation into cytosolic from mitochondria.[16] Based on our results that TSA could mediate caspase-independent apoptosis [Figure 3]b, we determined the effect of TSA on cytosolic translocation of AIF in Ca9.22 cells. As shown in [Figure 5]b and [Figure 5]c, cytosolic AIF was increased in a concentration-dependent manner. These suggest that TSA recruits AIF to mediate caspase independency during apoptosis.{Figure 5}


HDAC inhibitors potentially inhibit the proliferation of various cancer cell lines in vitro and tumor growth in animal models.[17],[18],[19] Recently, our group published that new synthetic HDAC inhibitors (Ky2, A248, and A1659) that increased the histone acetylation induced apoptosis by suppressing Sp1 protein in human breast and oral cancer cell lines.[20],[21] These findings suggest that HDAC inhibitors can be possibly apoptotic inducers against various solid tumors including oral cancer. Several studies demonstrated that TSA-induced apoptotic cell death in human liver, ovarian, and lung cancer cells.[22],[23] In the present study, our group also found that TSA significantly suppressed cell viability and increased the number of apoptotic cells in human OSCC cell lines (HSC-3 and Ca9.22) evidenced by live/dead assay and DAPI staining. Similarly, Suzuki et al.[24] demonstrated that TSA inhibited cell growth and induced apoptosis in OSCC cell lines (HSC-4, Ho-1-N-1, and Ho-1-U-1) supporting our data. These strongly suggest that TSA can have a growth-inhibitory activity for the treatment of OSCC through the enhancement of apoptotic cell death. Next, we investigated the intracellular level of acetyl-histones H2A and H3 in both cell lines treated with TSA and the results showed that TSA did not affect the acetylation of histones. Although HDAC inhibitors have direct impact on gene transcription via direct inhibition of HDAC function on histone tail, they may have an indirect mechanism.[25],[26] Thus, we cannot exclude the possibility that TSA may exert its anticancer activities regardless of direct inhibition of HDACs.

Since Kerr et al.[27] described a unique morphology of dying cells called apoptosis, it has been developed as an attractive approach of cancer therapy. Caspases are kinds of proapoptotic players sufficient to activate either intrinsic or extrinsic apoptotic pathway. In this study, we have shown that the treatment of OSCC cells with TSA clearly activated caspase 3. However, TSA induced the caspase-dependent apoptosis only in HSC-3 cells. Several studies reported that caspases can play critical roles in the apoptotic responses triggered by TSA.[28],[29] On the other hand, TSA also can induce caspase-independent apoptosis in human gastric and pancreatic cancer cell lines.[30],[31] These findings provide the possibility of both caspase-dependent and -independent apoptotic pathway in TSA-induced cell death of OSCC cells.

HDAC inhibitors can modify the cellular ability of the response to favoring apoptosis. Gene expression profile studies showed that HDAC inhibitors can alter the expression levels of proapoptotic proteins such as Bim, Bax, and Bak.[32],[33] TSA has been shown to increase the transcription of BH3-only proteins to disrupt MMP, induce the release of cytochrome c from the mitochondrial intermembrane space to the cytoplasm and activate caspase-9 during apoptosis[34],[35] meaning that BH3-only proteins can be associated with apoptotic activity of HDAC inhibitors. This study showed that TSA could induce caspase-dependent apoptosis in HSC-3 cells by up-regulation of Bim. In accordance with these data, our group recently published that Bim affects parthenolide-induced apoptosis in oral cancer.[36] The works of Ley et al.[15] demonstrated that ERK1/2 is the major pathway to promote Bim phosphorylation for protein degradation via the proteasome. Our data showed that TSA significantly dephosphorylated ERK1/2 and AZD6244 (an MEK inhibitor) potentiated up-regulation of Bim protein slightly induced by TSA. These data imply that ERK1/2 may mediate Bim protein in TSA-induced apoptosis.

In our study, we observed that z-VAD, a caspase inhibitor, did not prevent TSA-induced apoptosis in Ca9.22 cells suggesting that this phenomenon is mediated by caspase-independent apoptotic pathway. AIF has a unique property to induce apoptosis-like changes in a caspase-independent manner. Recently, our group published that AIF could play an important role in caspase-independent apoptosis in oral cancer cells.[37] Thus, we investigated whether TSA affects the cytosolic expression level of AIF protein and the result showed that it significantly increased AIF expression. Similarly, others also demonstrated that HDAC inhibitors including TSA-induced caspase-independent apoptosis in human pancreatic and lung cancer cell lines, and AIF are involved in HDAC inhibitors-mediated apoptosis strongly supporting our data. These findings suggest that TSA can induce apoptosis in either caspase-dependent or -independent apoptosis in OSCC cells. Collectively, the findings presented here provide the possibility of chemotherapeutic activity of TSA against OSCC.

Financial support and sponsorship

This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (2014R1A1A2055874), the Ministry of Science ICT and Future Planning (2014R1A4A1005309) and research funds of Chonbuk National University in 2011.

Conflicts of interest

There are no conflicts of interest.


1West AC, Johnstone RW. New and emerging HDAC inhibitors for cancer treatment. J Clin Invest 2014;124:30-9.
2Ellis L, Pili R. Histone deacetylase inhibitors: Advancing therapeutic strategies in hematological and solid malignancies. Pharmaceuticals (Basel) 2010;3:2411-69.
3Anne M, Sammartino D, Barginear MF, Budman D. Profile of panobinostat and its potential for treatment in solid tumors: An update. Onco Targets Ther 2013;6:1613-24.
4Chang HH, Chiang CP, Hung HC, Lin CY, Deng YT, Kuo MY. Histone deacetylase 2 expression predicts poorer prognosis in oral cancer patients. Oral Oncol 2009;45:610-4.
5Oh KH, Yang SW, Park JM, Seol JH, Iemura S, Natsume T, et al. Control of AIF-mediated cell death by antagonistic functions of CHIP ubiquitin E3 ligase and USP2 deubiquitinating enzyme. Cell Death Differ 2011;18:1326-36.
6Smith S, Fox J, Mejia M, Ruangpradit W, Saberi A, Kim S, et al. Histone deacetylase inhibitors selectively target homology dependent DNA repair defective cells and elevate non-homologous endjoining activity. PLoS One 2014;9:e87203.
7Jasek E, Lis GJ, Jasinska M, Jurkowska H, Litwin JA. Effect of histone deacetylase inhibitors trichostatin A and valproic acid on etoposide-induced apoptosis in leukemia cells. Anticancer Res 2012;32:2791-9.
8Bouillet P, Metcalf D, Huang DC, Tarlinton DM, Kay TW, Köntgen F, et al. Proapoptotic Bcl-2 relative Bim required for certain apoptotic responses, leukocyte homeostasis, and to preclude autoimmunity. Science 1999;286:1735-8.
9Tan TT, Degenhardt K, Nelson DA, Beaudoin B, Nieves-Neira W, Bouillet P, et al. Key roles of BIM-driven apoptosis in epithelial tumors and rational chemotherapy. Cancer Cell 2005;7:227-38.
10Daugas E, Susin SA, Zamzami N, Ferri KF, Irinopoulou T, Larochette N, et al. Mitochondrio-nuclear translocation of AIF in apoptosis and necrosis. FASEB J 2000;14:729-39.
11Wesierska-Gadek J, Gueorguieva M, Schloffer D, Uhl M, Wojciechowski J. Non-apoptogenic killing of hela cervical carcinoma cells after short exposure to the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). J Cell Biochem 2003;89:1222-34.
12Locatelli SL, Cleris L, Stirparo GG, Tartari S, Saba E, Pierdominici M, et al. BIM upregulation and ROS-dependent necroptosis mediate the antitumor effects of the HDACi givinostat and sorafenib in hodgkin lymphoma cell line xenografts. Leukemia 2014;28:1861-71.
13Labisso WL, Wirth M, Stojanovic N, Stauber RH, Schnieke A, Schmid RM, et al. MYC directs transcription of MCL1 and eIF4E genes to control sensitivity of gastric cancer cells toward HDAC inhibitors. Cell Cycle 2012;11:1593-602.
14Fiskus W, Sharma S, Qi J, Valenta JA, Schaub LJ, Shah B, et al. Highly active combination of BRD4 antagonist and histone deacetylase inhibitor against human acute myelogenous leukemia cells. Mol Cancer Ther 2014;13:1142-54.
15Ley R, Ewings KE, Hadfield K, Howes E, Balmanno K, Cook SJ. Extracellular signal-regulated kinases 1/2 are serum-stimulated “Bim(EL) kinases” that bind to the BH3-only protein Bim(EL) causing its phosphorylation and turnover. J Biol Chem 2004;279:8837-47.
16Aspe JR, Wall NR. Survivin-T34A: Molecular mechanism and therapeutic potential. Onco Targets Ther 2010;3:247-54.
17Kim YB, Lee KH, Sugita K, Yoshida M, Horinouchi S. Oxamflatin is a novel antitumor compound that inhibits mammalian histone deacetylase. Oncogene 1999;18:2461-70.
18Butler LM, Agus DB, Scher HI, Higgins B, Rose A, Cordon-Cardo C, et al. Suberoylanilide hydroxamic acid, an inhibitor of histone deacetylase, suppresses the growth of prostate cancer cells in vitro and in vivo. Cancer Res 2000;60:5165-70.
19Qiu L, Kelso MJ, Hansen C, West ML, Fairlie DP, Parsons PG. Anti-tumour activity in vitro and in vivo of selective differentiating agents containing hydroxamate. Br J Cancer 1999;80:1252-8.
20Shin JA, Han G, Kim HJ, Kim HM, Cho SD. Chemopreventive and chemotherapeutic effect of a novel histone deacetylase inhibitor, by specificity protein 1 in MDA-MB-231 human breast cancer cells. Eur J Cancer Prev 2014;23:277-85.
21Shin JA, Han G, Park SK, Lee K, Kim HJ, Cho SD, et al. The in vitro apoptotic effects of A248 and A1659, newly synthetic histone deacetylase inhibitors in oral cancer cells. Oral Dis 2014;20:482-9.
22Zohre S, Kazem NK, Abolfazl A, Mohammad RY, Aliakbar M, Effat A, et al. Trichostatin A-induced apoptosis is mediated by Kruppel-like factor 4 in ovarian and lung cancer. Asian Pac J Cancer Prev 2014;15:6581-6.
23Shi QQ, Zuo GW, Feng ZQ, Zhao LC, Luo L, You ZM, et al. Effect of trichostatin A on anti HepG2 liver carcinoma cells: Inhibition of HDAC activity and activation of Wnt/ß-catenin signaling. Asian Pac J Cancer Prev 2014;15:7849-55.
24Suzuki T, Yokozaki H, Kuniyasu H, Hayashi K, Naka K, Ono S, et al. Effect of trichostatin A on cell growth and expression of cell cycle- and apoptosis-related molecules in human gastric and oral carcinoma cell lines. Int J Cancer 2000;88:992-7.
25Spange S, Wagner T, Heinzel T, Krämer OH. Acetylation of non-histone proteins modulates cellular signalling at multiple levels. Int J Biochem Cell Biol 2009;41:185-98.
26Batta K, Das C, Gadad S, Shandilya J, Kundu TK. Reversible acetylation of non histone proteins: Role in cellular function and disease. Subcell Biochem 2007;41:193-212.
27Kerr JF, Wyllie AH, Currie AR. Apoptosis: A basic biological phenomenon with wide-ranging implications in tissue kinetics. Br J Cancer 1972;26:239-57.
28Henderson C, Mizzau M, Paroni G, Maestro R, Schneider C, Brancolini C. Role of caspases, Bid, and p53 in the apoptotic response triggered by histone deacetylase inhibitors trichostatin-A (TSA) and suberoylanilide hydroxamic acid (SAHA). J Biol Chem 2003;278:12579-89.
29Taghiyev AF, Guseva NV, Sturm MT, Rokhlin OW, Cohen MB. Trichostatin A (TSA) sensitizes the human prostatic cancer cell line DU145 to death receptor ligands treatment. Cancer Biol Ther 2005;4:382-90.
30Wu ZQ, Zhang R, Chao C, Zhang JF, Zhang YQ. Histone deacetylase inhibitor trichostatin A induced caspase-independent apoptosis in human gastric cancer cell. Chin Med J (Engl) 2007;120:2112-8.
31García-Morales P, Gómez-Martínez A, Carrato A, Martínez-Lacaci I, Barberá VM, Soto JL, et al. Histone deacetylase inhibitors induced caspase-independent apoptosis in human pancreatic adenocarcinoma cell lines. Mol Cancer Ther 2005;4:1222-30.
32Zhang XD, Gillespie SK, Borrow JM, Hersey P. The histone deacetylase inhibitor suberic bishydroxamate regulates the expression of multiple apoptotic mediators and induces mitochondria-dependent apoptosis of melanoma cells. Mol Cancer Ther 2004;3:425-35.
33Peart MJ, Smyth GK, van Laar RK, Bowtell DD, Richon VM, Marks PA, et al. Identification and functional significance of genes regulated by structurally different histone deacetylase inhibitors. Proc Natl Acad Sci U S A 2005;102:3697-702.
34Zhao Y, Tan J, Zhuang L, Jiang X, Liu ET, Yu Q. Inhibitors of histone deacetylases target the Rb-E2F1 pathway for apoptosis induction through activation of proapoptotic protein Bim. Proc Natl Acad Sci U S A 2005;102:16090-5.
35Bolden JE, Peart MJ, Johnstone RW. Anticancer activities of histone deacetylase inhibitors. Nat Rev Drug Discov 2006;5:769-84.
36Yu HJ, Jung JY, Jeong JH, Cho SD, Lee JS. Induction of apoptosis by parthenolide in human oral cancer cell lines and tumor xenografts. Oral Oncol 2015;51:602-9.
37Yang IH, Shin JA, Cho SD. Pycnogenol induces nuclear translocation of apoptosis-inducing factor and caspase-independent apoptosis in MC-3 human mucoepidermoid carcinoma cell line. J Cancer Prev 2014;19:265-72.