• Users Online: 439
  • Home
  • Print this page
  • Email this page
Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 

 Table of Contents  
Year : 2018  |  Volume : 9  |  Issue : 2  |  Page : 86-92

Valproic acid, a histone deacetylase inhibitor, enhances radiosensitivity in breast cancer cell line

1 Biochemistry and Metabolic Disorders Research Center, Golestan University of Medical Sciences, Gorgan, Iran
2 Laboratory Sciences Research Center, Golestan University of Medical Sciences, Gorgan, Iran
3 Babol University of Medical Sciences, Babol, Iran
4 Department of Biochemistry and Biophysics, Faculty of Medicine, Golestan University of Medical Sciences, Gorgan, Iran

Date of Web Publication22-May-2018

Correspondence Address:
Dr. Alireza Khoshbin Khoshnazar
Department of Biochemistry and Biophysics, Faculty of Medicine, Golestan University of Medical Sciences, Gorgan
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jrcr.jrcr_37_17

Rights and Permissions

Purpose: Valproic acid (VPA) is used mainly for the treatment of epilepsy and other seizure disorders, however, it is known to be one of histone deacetylase (HDAC) inhibitors. HDACIs have represented roles in radiation-sensitizing of cancer cells. This study is aimed to study to evaluate the radiosensitizing capability of VPA in MCF-7 breast cancer cell line. Materials and Methods: Cell viability and apoptosis were assayed using MTT and TUNEL assays, respectively and caspase-8 and caspase-9 activities were measured by commercially available kits. Results: Our finding showed that pre treatment of cells with VPA, notably enhanced apoptotic cell death in MCF-7 cell line. Our results showed that VPA sensitizes cancer cells against radiation. Conclusion: Valproic acid could be a beneficial radio-sensitizer in breast cancer radiotherapy.

Keywords: MCF-7 cell, radiosensitizer, valproic acid

How to cite this article:
Yarmohamadi A, Asadi J, Gharaei R, Mir M, Khoshnazar AK. Valproic acid, a histone deacetylase inhibitor, enhances radiosensitivity in breast cancer cell line. J Radiat Cancer Res 2018;9:86-92

How to cite this URL:
Yarmohamadi A, Asadi J, Gharaei R, Mir M, Khoshnazar AK. Valproic acid, a histone deacetylase inhibitor, enhances radiosensitivity in breast cancer cell line. J Radiat Cancer Res [serial online] 2018 [cited 2020 Jul 3];9:86-92. Available from: http://www.journalrcr.org/text.asp?2018/9/2/86/232983

  Introduction Top

Breast cancer is the second prevalent cancer worldwide after lung cancer, while it is the most prevalent and the first cause of cancer-related mortality among females.[1],[2]

Valproic acid (VPA, 2- pentatonic propyl acid) is a branched eight-carbon fatty acid, which is often used for the treatment of epilepsy, bipolar, and migraine's diseases.[3] Recently, it has been shown that VPA is a histone deacetylase (HDAC) inhibitor.[4],[5] HDAC inhibitors are considered as a new class of anticancer agents. In fact, several HDACI including hydroxamate, suberoylanilide hydroxamic acid (SAHA), depsipeptide, and the cyclic tetrapeptide have shown acceptable anticancer functions in both hematologic and solid cancers in clinical trials.[6],[7] HDAC inhibitors inhibit proliferation and induce cell growth arrest, cell-cycle arrest, and apoptosis in cancer cell lines in both cell culture and in vivo.[8],[9] Selective toxicity on numerous cancer cell lines is one of the potential benefits of HDAC inhibitors so that they are nontoxic to normal cells.[10] There are two suggested pathways which define HDACI function: modulation of tertiary chromatin structure and acetylation and alteration of nonhistone proteins such as transcription factor p53. It is a protein which affects the expression of more than 150 genes that contribute in the arrest of cell-cycle checkpoints or apoptosis induction.[11] These findings accelerated the evaluation of VPA as an anticancer treatment factor.

Radiotherapy is commonly used for cancer treatment. Loss of clonogenic potential is the main mechanism which radiation kills most of the tumor cells.[12] Ionizing radiation (IR) imposes one of the worst DNA impairments, DNA double-stranded breaks.[12],[13] Ataxia telangiectasia mutated (ATM) kinase exhibits the first response to DNA damage. ATM kinase triggers a cascade of response through signal transduction to downstream elements for cell-cycle arrest and induction of repair and finally cell death if the damage is irreparable.[14] However, IR induces apoptosis or cell-cycle arrest, but its effects are heterogeneous in various cell lines.[15]

Radiation therapy is an accepted approach in cancer therapy, and worldwide data indicate that approximately 50% of cancer patients are treated with radiation either for therapeutic or palliative purposes.[16] However, relapse of tumors is still an issue of concern and so on suggests the necessity of using other agents to sensitize cancer cells and improve the therapeutic idea of radiotherapy.[16],[17],[18] Therefore, the development of such compounds has been actively pursued to reach better clinical results.

It was demonstrated that HDACI can serve as a radiation sensitizer in different types of tumor cells both in vivo and in vitro.[19],[20],[21] It seems that the mechanism which HDACI can act as a radiation sensitizer is to block HDAC activity and therefore acetylation of core histone resulting in chromatin structure decondense. DNA in decondensed chromatin is more sensitive to DNA damage caused by radiotherapy.[22] Trichostatin A (TSA) is a radiation sensitizer in K562 cells. Treatment of cells by TSA before irradiation decreases cell viability.[23] Furthermore, SAHA decreases cell viability and increases induced apoptosis caused by irradiation in prostate and glioma cancer cell lines.[24] In this study, we proposed to assess potent radiation enhancer properties of VPA on MCF-7 breast cancer cell line. In this context, we evaluated the effect of VPA and IR alone and combined on cytotoxicity and apoptosis including the makers of extrinsic and intrinsic apoptotic pathways (caspases 8 and 9).

  Materials and Methods Top

Cell culture and treatments: MCF-7 human breast cancer cells (obtained from Pasteur Institute, Tehran, Iran) were grown in a humidified atmosphere of 95% air and 5% CO2 (v/v) at 37°C Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 2 mM L-glutamine, 1% nonessential amino acids, 100 U/ml streptomycin, 100 U/ml penicillin, and 10% heat-inactivated fetal bovine serum. All reagents were purchased from Gibco, Germany. Cells were maintained in an exponential growth phase, and experiments were performed on cells that were collected at a density of 4–7 × 105 cell/ml. The cell lines in a maximum range of up to 20 passages were used for this study. In typical experiments, MCF-7 cells (5 × 105 ml) in complete DMEM medium were treated with 0.5, 2, 4, 8, 16, 32, and 64 mM VPA (Sigma Aldrich, Germany), for 24, 48, and 72 h at 37°C. The VPA was dissolved in phosphate buffer saline (PBS) to a stock concentration of 100 mM and stored at −20°C. The exponentially growing, untreated MCF-7 cells and cells that had been pretreated with VPA, irradiated using g-rays from Cobalt 60 source (Theratron teletherapy unit) at a dose rate of 0.63 Gy/min. Cells were exposed to doses of 0, 2, 4, and 6 Gy of g-rays.

3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay

To determine cell viability, specified numbers (8 × 103) of cells were seeded in individual wells of 96well plates and incubated for 24 h at 37°C before treatment with various concentrations of VPA for 24, 48, and 72 h. Subsequently, cells were washed with PBS, and 20 μl of sterile 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) (5 mg/ml, Sigma Aldrich) was added to each well which were incubated at 37°C for 4 h. Supernatant media containing MTT were discarded, and 200 μl dimethyl sulfoxide was added in each well. Plate was gently mixed at darkness for 15 min, and absorbance was recorded at 492 nm to evaluate cell proliferation. The percentage cell prolifeartion was determined by comparing the optical density (OD) of the drug-treated cells with that of untreated controls. All experiments were repeated at least thrice.

Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling assay

For apoptosis detection, adherent and floating cells were harvested and analyzed for DNA fragmentation by terminal deoxynucleotidyl transferase deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) assay and propidium iodide (PI) staining with the APO-BrdU TUNEL assay kit (Invitrogen) according to the manufacturer's recommendation. Briefly, MCF-7 cells were fixed in paraformaldehyde and were stored in 70% (v/v) ethanol at −20°C for 24 h. Then, ethanol was removed by centrifugation, and cells were resuspended in washing buffer, mixed with 50 μl of DNA labeling solution and incubated for 60 min at 37°C. After addition of rinse buffer, the cell suspension was centrifuged to remove the buffer; 100 L of antibody solution was added to each cell pellet and incubated for 30 min in darkness at room temperature. Then, 60 μl PI/RNase A solution was added and incubated for 30 min in darkness at room temperature. Then, 20 μl of the homogeneous mixture of cell suspension was dropped onto a slide before being covered with a cover slip. The apoptotic cells were determined by counting cells showing green fluorescence staining over an orange–red PI counter-staining. Viable and apoptotic cells were observed and quantified. All assays were performed in triplicate.

Caspase-8 and caspase-9 activity assays

Induction of apoptosis in MCF-7 cells was determined by measuring the activities of caspase-8 and caspase-9 with the colorimetric assay kits (R and D systems) according to the protocols suggested by the manufacturer. Briefly, after treatment, cells were washed with cold PBS and harvested by scraping, then centrifuged (250 × g for 10 min) and incubated for 10 min in cell lysis buffer. Cell lysates were centrifuged (10,000 × g for 1 min), and 10 μl of that was loaded in triplicate on 96-well plate, then 50 μl of caspase assay buffer was added to each one. Then, 5 μl of the colorimetric caspase-8 and caspase-9 substrates (IETD-pNA and LEHD-pNA, respectively) was added separately to each well. The plates were incubated for 2 h at room temperature in darkness. Finally, colorimetric signal was determined by measuring the absorbance at 405 nm. The protocol was repeated thrice for each assay.

Statistical analysis

The data were analyzed using SPSS (version 16) software (SPSS Inc, Chicago, USA). Kolmogorov–Smirnov test was used to measure the normality of data distribution. In the cases of normality, one-way analysis of variance was used followed by post hoc Tukey's test. The statistical significance was considered at P < 0.05 level.

  Results Top

Evaluation of growth inhibition by valproic acid

The effect of VPA on the viability of the MCF-7 cell line was assessed by the MTT assay. VPA inhibited the proliferation of MCF-7 cells in a time and dosedependent manner, as shown in [Figure 1].
Figure 1: Effect of valproic acid on cell viability. MCF-7 cell was treated for 24, 48, and 72 h with valproic acid (0–64 mM), and cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay after the indicated times. (a) MCF-7 cells after 24 h treatment, (b) MCF-7 cells after 48 h treatment, and (c) MCF-7 cells after 72 h treatment. The results are the means of three independent experiments with six repetitive treatments (*P < 0.05 and ***P < 0.0001)

Click here to view

A Concentration of 0.5 mM VPA resulted in a cell survival equal to 90%; however, at higher concentrations, the reduction in viability was obtained at the highest level of statistical significance. In summary, the results indicated that the cells treated with VPA showed marked decrease in proliferation, which was found to be statistically significant (P < 0.0001) as compared to control [Figure 1]. Using LD50 obtained in our previous work,[25] the doses 4 mM and 8 mM at 48 h period were selected for the current experiment.

Deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling

Increased apoptosis of MCF-7 cells using combined IR and VPA. To determine the effect of IR and/or VPA on MCF-7 cells, apoptosis was evaluated by TUNEL assay. MCF-7 cells were treated with VPA (4 and 8 mM) for 48 h than irradiated with, IR (2 and 4 Gy), apoptotic cells showed green fluorescence, while the red fluorescence was an indication of viable cells [26] [Figure 2].
Figure 2: The effect of valproic acid and ionizing radiation treatment on MCF-7 cell line, assessed by terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling staining assay technique (Apo-BrdU), double stained with fluorescein Br-deoxyuridine triphosphate and PI solution: (a) untreated cells (b) treatment of cells with 4 mM (c) 8 mM (d) 2 Gy (e) 4 Gy (f) 4 mm + 2 Gy (g) 4 mm + 4 Gy (h) 8 mm + 2 Gy (i) 8 mm + 4 Gy. Viable cells show red nuclei (yellow arrow) whereas apoptotic cells show yellow to greenish nuclei (white arrow) (Mag × 20)

Click here to view

Based on these figures, there were no observable apoptotic cells seen in the untreated control cells (99% viability) [Figure 2]a. An induction of TUNEL positive cells was observed in the presence of each single factor, while the combined treatment produced a remarkable increase of apoptosis compared to the untreated control cells (P > 0.0001). Reduced size and impaired morphology of cells nuclei were obviously seen in treated cells in comparison to control cells. All of the mentioned alterations are indicating chromatin condensation and DNA fragmentation which are the underlying mechanisms of cell apoptosis.[27]

Quantification of apoptotic cells was reported as the percentage of apoptotic cells among total cells. Five to six high-power fields were selected randomly, and the total number of cells was counted manually [Figure 3].
Figure 3: The percentage of apoptotic cells in the treated group in comparison to control cells assayed by terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling method. V4: 4 mM valproic acid, V8: 8 mM valproic acid, R2: 2 Gy, R4: 4 Gy, V4 + R2: 4 mM valproic acid + 2 Gy, V4 + R4: 4 mM valproic acid +4 Gy V8 + R2: 8 Mm valproic acid + 2 Gy, V8 + R4: 8 mM + 4 Gy (***P < 0.0001)

Click here to view

Caspase activity

Mechanism of apoptosis induction to further elucidate the mechanism of VPA and IR on the increase of apoptosis or its enhancement of IR exposure, caspase-8 and caspase-9 activities were measured as the markers of extrinsic and internal apoptosis pathways, respectively. Caspase-8 activity increased about 4.4- and 6.4-fold for 4 and 8 mM concentrations of VPA, also 3.4- and 5-fold for 2 and 4 Gy, respectively, as compared to untreated cells [Figure 4]. Caspase-8 activity increased about 7.5-fold for 4 mM concentration combined with 4 Gy radiation, also 7.2-fold for 8 mM concentration of VPA together with 4 Gy of radiation, compared with control group.
Figure 4: Effect of valproic acid on caspase-8 and caspase-9 induction in MCF-7 cells. Caspase 8 (a) and 9 (b) activities in cells treated with valproic acid and irradiation; Activities (absorbance/mg protein) were measured spectrophotometrically at a wavelength of 405 nm. V4:4 mM valproic acid, V8: 8 mm valproic acid, R2: 2 Gy, R4: 4 Gy, V4 + R2: 4 mm valproic acid + 2 Gy, V4 + R4: 4 mm valproic acid + 4 Gy V8 + R2: 8 mm valproic acid + 2 Gy, V8 + R4: 8 mm + 4 Gy. Caspase activities are presented as mean ± standard deviation (n = 3). ***P < 0.0001

Click here to view

On the other hand, caspase-9 activity increased about 4.5- and 7.4-fold for 4 and 8 mM concentrations of VPA also 3.7- and 4.9-fold for 2 and 4 Gy, respectively, as compared to untreated cells. Caspase-9 activity increased about 5.6-fold for 4 mM concentration combined with 2 Gy radiation, also 7.6-fold for 4 mM concentration of VPA together with 4 Gy of radiation and finally 8.5-fold for synchronous usage of 8 mM concentration of VPA together with 4 Gy of radiation compared with control group [Figure 4]. This concentration-dependent increase was statistically significant (P < 0.0001).

  Discussion Top

In this study, we aimed to survey the effects of VPA and radiation on viability and apoptosis of MCF-7 cell line. Our results showed that VPA is an antiproliferative agent in MCF-7 cell line which notably decreases cell viability in a dose- and time-dependent manner. These results are concordant with the previous surveys which claimed the reduction of cell viability in case of VPA treatment.[25],[28] HDACIs are suggested to exhibit antiproliferative actions through several mechanisms, including: cell-cycle arrest, differentiation, and apoptosis induction.[29],[30] TSA, oxamflatin, MS-275, butyrate, and SAHA are considered as the members of HDACIs family, which induce the expression of CDKN1A gene, resulting in p21 encoding and finally cell-cycle arrest G1.[31],[32],[33],[34]

Apoptosis is the other selective mechanism by anticancer agents. This process is triggered by extrinsic (receptor-dependent) or intrinsic (mitochondrial) pathways modulated by caspase-8 and caspase-9 enzymatic activity, respectively.[35] The results of the TUNEL assay showed that VPA strongly induced apoptosis in MCF-7 cell line. These findings were confirmed when performing caspase-8 and caspase-9 activity evaluation for mentioned cells. It seems that HDACI itself and cell type are the two major factors which determine the specific pathway to be used in apoptosis induction. For instance, SAHA includes intrinsic pathway through cleavage and activation of Bcl-2 which results in mitochondrial membrane damage and ROS production.[36] On the other hand, apicidin exploits fas/fas ligand expression in leukemia cells and desipeptide involve TNF to activate caspase-8 and trigger apoptosis extrinsic pathway.[37],[38] Vandermeers et al. reported that VPA activated both intrinsic and extrinsic pathways by hyperactivation of histone H3, p21 overexpression, bid cleavage and cytochrome C release from mitochondria in malignant mesothelioma [39] whereas Catalano et al. could not find the effect of VPA on caspase-8 pathway in thyroid tumor cells and their results limited just in caspase-9 pathway in this issue.[28]

We also assessed the radiation sensitizing potency of VPA in MCF-7 cell line by a 48 h period of VPA pretreatment, before radiation. We understood that VPA is an efficient radiation sensitizer in MCF-7 cells and therefore, are in concurrence with those from the previous report.[40],[41],[42] Our data from TUNEL assay demonstrated that the treatment of cells with VPA before irradiation enhances apoptotic cell from 32% to 45% at 4 mM and from 43% to 58% at 8 mM in 2 Gy; these changes were 32%–52% at 4 mM and 34%–66% at 8 mM for 4 Gy radiation [Figure 3]. Similarly, caspase-8 and caspase-9 assays indicate that pretreatment with VPA potentates radiation-induced apoptosis in MCF-7 cells in a pattern just like what we concluded in the TUNEL assay [Figure 4]. Irradiation can cause an increase in levels of p53 by recruiting ATM proteins, and ultimately results in an increase in the level of the cyclin-dependent kinase inhibitory protein p21.[43]

Some of the reported mechanisms which claim the synergistic effect of HDACIs on radiation enhancement include inhibition of DNA damage repair pathways, resulting in radiation sensitizing actions by involving the protein kinases, ATM, ataxia telangiectasia-related proteins and 53PB1 which all have important roles in DNA damage cascades.[23],[42],[44],[45] HDACIs also can induce gene expression alteration or changing the acetylation status of p53 protein, which is a known substrate for HATs and HDACs.[46] Acetylated p53 can stimulate its sequence-specific DNA binding activity to modulate proapoptotic responses in cancer cells.[47]

One of the common problems of clinical oncology is the occurrence of tumors relapse in radiotherapy.[17] Hence, sensitizing the cancer cell to radiation-induced DNA damage and apoptosis by radiation-sensitizing agents such as VPA, seem to be an efficient approach to conflict against this problem. Our findings showed that VPA is a potent radiation-sensitizer in MCF-7 breast cancer cell line. We could show that VPA utilization before radiation can enhance cell death and apoptosis in vitro that could be an application strategy to enhance radiosensitivity of breast cancer cells in the clinic.


The authors would like to thank biochemistry laboratory of faculty of medicine of Golestan University of medical sciences. We would like thank specially Mr. Mohamad Mostakhdem Hashemi for his useful comments.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Jemal A, Siegel R, Xu J, Ward E. Cancer statistics, 2010. CA Cancer J Clin 2010;60:277-300.  Back to cited text no. 1
Bunz F. Principles of Cancer Genetics. Verlag Berlin Heidelberg: Springer Science & Business Media; 2007.  Back to cited text no. 2
Blaheta RA, Cinatl J Jr. Anti-tumor mechanisms of valproate: A novel role for an old drug. Med Res Rev 2002;22:492-511.  Back to cited text no. 3
Göttlicher M, Minucci S, Zhu P, Krämer OH, Schimpf A, Giavara S, et al. Valproic acid defines a novel class of HDAC inhibitors inducing differentiation of transformed cells. EMBO J 2001;20:6969-78.  Back to cited text no. 4
Zhang L, Wang G, Wang L, Song C, Leng Y, Wang X, et al. VPA inhibits breast cancer cell migration by specifically targeting HDAC2 and down-regulating survivin. Mol Cell Biochem 2012;361:39-45.  Back to cited text no. 5
Kelly WK, Marks PA. Drug insight: Histone deacetylase inhibitors – Development of the new targeted anticancer agent suberoylanilide hydroxamic acid. Nat Clin Pract Oncol 2005;2:150-7.  Back to cited text no. 6
Piekarz R, Bates S. A review of depsipeptide and other histone deacetylase inhibitors in clinical trials. Curr Pharm Des 2004;10:2289-98.  Back to cited text no. 7
Harikrishnan KN, Karagiannis TC, Chow MZ, El-Osta A. Effect of valproic acid on radiation-induced DNA damage in euchromatic and heterochromatic compartments. Cell Cycle 2008;7:468-76.  Back to cited text no. 8
Takai N, Desmond JC, Kumagai T, Gui D, Said JW, Whittaker S, et al. Histone deacetylase inhibitors have a profound antigrowth activity in endometrial cancer cells. Clin Cancer Res 2004;10:1141-9.  Back to cited text no. 9
Rosato RR, Grant S. Histone deacetylase inhibitors in clinical development. Expert Opin Investig Drugs 2004;13:21-38.  Back to cited text no. 10
Appella E, Anderson CW. Post-translational modifications and activation of p53 by genotoxic stresses. Eur J Biochem 2001;268:2764-72.  Back to cited text no. 11
Howell S. Resistance to apoptosis in prostate cancer cells. Mol Urol 2000;4:225-9.  Back to cited text no. 12
Bartek J, Lukas J. DNA repair: Damage alert. Nature 2003;421:486-8.  Back to cited text no. 13
Khanna KK, Jackson SP. DNA double-strand breaks: Signaling, repair and the cancer connection. Nat Genet 2001;27:247-54.  Back to cited text no. 14
Zhang Y, Adachi M, Zhao X, Kawamura R, Imai K. Histone deacetylase inhibitors FK228, N-(2-aminophenyl)-4-[N-(pyridin-3-yl-methoxycarbonyl) amino- methyl] benzamide and m-carboxycinnamic acid bis-hydroxamide augment radiation-induced cell death in gastrointestinal adenocarcinoma cells. Int J Cancer 2004;110:301-8.  Back to cited text no. 15
Mundt AJ, Roeske JC. Principles of radiation oncology. In: Oncologic Therapies. Verlag Berlin Heidelberg: Springer; 2003. p. 9-17.  Back to cited text no. 16
Zietman AL, DeSilvio ML, Slater JD, Rossi CJ Jr., Miller DW, Adams JA, et al. Comparison of conventional-dose vs. high-dose conformal radiation therapy in clinically localized adenocarcinoma of the prostate: A Randomized controlled trial. JAMA 2005;294:1233-9.  Back to cited text no. 17
Zelefsky MJ, Fuks Z, Hunt M, Lee HJ, Lombardi D, Ling CC, et al. High dose radiation delivered by intensity modulated conformal radiotherapy improves the outcome of localized prostate cancer. J Urol 2001;166:876-81.  Back to cited text no. 18
Entin-Meer M, Yang X, VandenBerg SR, Lamborn KR, Nudelman A, Rephaeli A, et al. In vivo efficacy of a novel histone deacetylase inhibitor in combination with radiation for the treatment of gliomas. Neuro Oncol 2007;9:82-8.  Back to cited text no. 19
Kim IA, Shin JH, Kim IH, Kim JH, Kim JS, Wu HG, et al. Histone deacetylase inhibitor-mediated radiosensitization of human cancer cells: Class differences and the potential influence of p53. Clin Cancer Res 2006;12:940-9.  Back to cited text no. 20
Entin-Meer M, Rephaeli A, Yang X, Nudelman A, VandenBerg SR, Haas-Kogan DA, et al. Butyric acid prodrugs are histone deacetylase inhibitors that show antineoplastic activity and radiosensitizing capacity in the treatment of malignant gliomas. Mol Cancer Ther 2005;4:1952-61.  Back to cited text no. 21
Chen X, Wong P, Radany E, Wong JY. HDAC inhibitor, valproic acid, induces p53-dependent radiosensitization of colon cancer cells. Cancer Biother Radiopharm 2009;24:689-99.  Back to cited text no. 22
Karagiannis TC, Harikrishnan KN, El-Osta A. The histone deacetylase inhibitor, trichostatin A, enhances radiation sensitivity and accumulation of gammaH2A.X. Cancer Biol Ther 2005;4:787-93.  Back to cited text no. 23
Chinnaiyan P, Vallabhaneni G, Armstrong E, Huang SM, Harari PM. Modulation of radiation response by histone deacetylase inhibition. Int J Radiat Oncol Biol Phys 2005;62:223-9.  Back to cited text no. 24
Vafaiyan Z, Gharaei R, Asadi J. The correlation between telomerase activity and bax/Bcl-2 ratio in valproic acid-treated MCF-7 breast cancer cell line. Iran J Basic Med Sci 2015;18:700-4.  Back to cited text no. 25
Ahmad U, Ahmed I, Keong YY, Abd Manan N, Othman F. Inhibitory and apoptosis-inducing effects of newcastle disease virus strain AF2240 on mammary carcinoma cell line. Biomed Res Int 2015;2015:127828.  Back to cited text no. 26
Choudhari MK, Haghniaz R, Rajwade JM, Paknikar KM. Anticancer activity of Indian stingless bee propolis: An in vitro study. Evid Based Complement Alternat Med 2013;2013:928280.  Back to cited text no. 27
Catalano MG, Fortunati N, Pugliese M, Costantino L, Poli R, Bosco O, et al. Valproic acid induces apoptosis and cell cycle arrest in poorly differentiated thyroid cancer cells. J Clin Endocrinol Metab 2005;90:1383-9.  Back to cited text no. 28
Marks PA, Richon VM, Breslow R, Rifkind RA. Histone deacetylase inhibitors as new cancer drugs. Curr Opin Oncol 2001;13:477-83.  Back to cited text no. 29
Vigushin DM, Coombes RC. Histone deacetylase inhibitors in cancer treatment. Anticancer Drugs 2002;13:1-3.  Back to cited text no. 30
Davis T, Kennedy C, Chiew YE, Clarke CL, deFazio A. Histone deacetylase inhibitors decrease proliferation and modulate cell cycle gene expression in normal mammary epithelial cells. Clin Cancer Res 2000;6:4334-42.  Back to cited text no. 31
Munster PN, Troso-Sandoval T, Rosen N, Rifkind R, Marks PA, Richon VM, et al. The histone deacetylase inhibitor suberoylanilide hydroxamic acid induces differentiation of human breast cancer cells. Cancer Res 2001;61:8492-7.  Back to cited text no. 32
Richon VM, Sandhoff TW, Rifkind RA, Marks PA. Histone deacetylase inhibitor selectively induces p21WAF1 expression and gene-associated histone acetylation. Proc Natl Acad Sci U S A 2000;97:10014-9.  Back to cited text no. 33
Sambucetti LC, Fischer DD, Zabludoff S, Kwon PO, Chamberlin H, Trogani N, et al. Histone deacetylase inhibition selectively alters the activity and expression of cell cycle proteins leading to specific chromatin acetylation and antiproliferative effects. J Biol Chem 1999;274:34940-7.  Back to cited text no. 34
Thompson CB. Apoptosis in the pathogenesis and treatment of disease. Science 1995;267:1456-62.  Back to cited text no. 35
Ruefli AA, Ausserlechner MJ, Bernhard D, Sutton VR, Tainton KM, Kofler R, et al. The histone deacetylase inhibitor and chemotherapeutic agent suberoylanilide hydroxamic acid (SAHA) induces a cell-death pathway characterized by cleavage of bid and production of reactive oxygen species. Proc Natl Acad Sci U S A 2001;98:10833-8.  Back to cited text no. 36
Kwon SH, Ahn SH, Kim YK, Bae GU, Yoon JW, Hong S, et al. Apicidin, a histone deacetylase inhibitor, induces apoptosis and fas/Fas ligand expression in human acute promyelocytic leukemia cells. J Biol Chem 2002;277:2073-80.  Back to cited text no. 37
Aron JL, Parthun MR, Marcucci G, Kitada S, Mone AP, Davis ME, et al. Depsipeptide (FR901228) induces histone acetylation and inhibition of histone deacetylase in chronic lymphocytic leukemia cells concurrent with activation of caspase 8-mediated apoptosis and down-regulation of c-FLIP protein. Blood 2003;102:652-8.  Back to cited text no. 38
Vandermeers F, Hubert P, Delvenne P, Mascaux C, Grigoriu B, Burny A, et al. Valproate, in combination with pemetrexed and cisplatin, provides additional efficacy to the treatment of malignant mesothelioma. Clin Cancer Res 2009;15:2818-28.  Back to cited text no. 39
Van Nifterik KA, Van den Berg J, Slotman BJ, Lafleur MV, Sminia P, Stalpers LJ, et al. Valproic acid sensitizes human glioma cells for temozolomide and γ-radiation. J Neurooncol 2012;107:61-7.  Back to cited text no. 40
Rezacova M, Zaskodova D, Vavrova J, Vokurkova D, Tichy A. Antileukemic activity of the combination of ionizing radiation with valproic acid in promyelocytic leukemia cells HL-60. Neoplasma 2008;55:519-25.  Back to cited text no. 41
Camphausen K, Cerna D, Scott T, Sproull M, Burgan WE, Cerra MA, et al. Enhancement of in vitro and in vivo tumor cell radiosensitivity by valproic acid. Int J Cancer 2005;114:380-6.  Back to cited text no. 42
Pawlik TM, Keyomarsi K. Role of cell cycle in mediating sensitivity to radiotherapy. Int J Radiat Oncol Biol Phys 2004;59:928-42.  Back to cited text no. 43
Kim GD, Choi YH, Dimtchev A, Jeong SJ, Dritschilo A, Jung M, et al. Sensing of ionizing radiation-induced DNA damage by ATM through interaction with histone deacetylase. J Biol Chem 1999;274:31127-30.  Back to cited text no. 44
Zgheib O, Huyen Y, DiTullio RA Jr., Snyder A, Venere M, Stavridi ES, et al. ATM signaling and 53BP1. Radiother Oncol 2005;76:119-22.  Back to cited text no. 45
Luo J, Su F, Chen D, Shiloh A, Gu W. Deacetylation of p53 modulates its effect on cell growth and apoptosis. Nature 2000;408:377-81.  Back to cited text no. 46
Fu M, Wang C, Zhang X, Pestell RG. Acetylation of nuclear receptors in cellular growth and apoptosis. Biochem Pharmacol 2004;68:1199-208.  Back to cited text no. 47


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

This article has been cited by
1 Association between interleukin 2 receptor A gene polymorphisms (rs2104286 and rs12722489) with susceptibility to multiple sclerosis in Iranian population
Ramin Pourakbari,Mojgan Hosseini,Saeed Aslani,Mohammad Hosein Ayoubi-joshaghani,Hamed Valizadeh,Leila Roshangar,Majid Ahmadi,Bahareh Shirvani
Meta Gene. 2020; 25: 100750
[Pubmed] | [DOI]

Shelterin Complex at Telomeres: Implications in Ageing

Seyed Mostafa Mir,Sadra Samavarchi Tehrani,Golnaz Goodarzi,Zahra Jamalpoor ?,Asadi Jahanbakhsh,Nafiseh Khelghati,Durdi Qujeq,Mahmood Maniati
Clinical Interventions in Aging. 2020; Volume 15: 827
[Pubmed] | [DOI]
3 HDAC2 Inhibitor Valproic Acid Increases Radiation Sensitivity of Drug-Resistant Melanoma Cells
Bhuvanesh Kalal,Vinitha Pai,Santosh Behera,Hiriyur Somashekarappa
Medical Sciences. 2019; 7(3): 51
[Pubmed] | [DOI]
4 Polyelectrolyte Carboxymethyl Cellulose for Enhanced Delivery of Doxorubicin in MCF7 Breast Cancer Cells: Toxicological Evaluations in Mice Model
Vahid Shafiei-Irannejad,Mahdi Rahimi,Mojtaba Zarei,Roshan Dinparast-isaleh,Saman Bahrambeigi,Alireza Alihemmati,Salman Shojaei,Zarrin Ghasemi,Bahman Yousefi
Pharmaceutical Research. 2019; 36(5)
[Pubmed] | [DOI]


Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

  In this article
Materials and Me...
Article Figures

 Article Access Statistics
    PDF Downloaded210    
    Comments [Add]    
    Cited by others 4    

Recommend this journal