MTORC2 is a physiological hydrophobic motif kinase of S6 Kinase 1.

Ribosomal protein S6 kinase 1 (S6K1), a major downstream effector molecule of mTORC1, regulates cell growth and proliferation by modulating protein translation and ribosome biogenesis. We have recently identified eIF4E as an intermediate in transducing signals from mTORC1 to S6K1 and further demonstrated that the role of mTORC1 is restricted to inducing eIF4E phosphorylation and interaction with S6K1. This interaction relieves S6K1 auto-inhibition and facilitates its hydrophobic motif (HM) phosphorylation and activation as a consequence. These observations underscore a possible involvement of mTORC1 independent kinase in mediating HM phosphorylation. Here, we report mTORC2 as an in-vivo/physiological HM kinase of S6K1. We show that rapamycin-resistant S6K1 truncation mutant ∆NH∆CT continues to display HM phosphorylation with selective sensitivity toward Torin-1. We also show that HM phosphorylation of wildtype S6K1and ∆NH∆CT depends on the presence of mTORC2 regulatory subunit-rictor. Furthermore, truncation mutagenesis and molecular docking analysis reveal the involvement of a conserved 19 amino acid stretch of S6K1 in mediating interaction with rictor. We finally show that deletion of the 19 amino acid region from wildtype S6K1 results in loss of interaction with rictor, with a resultant loss of HM phosphorylation regardless of the presence of functional TOS motif. Our data demonstrate that mTORC2 acts as a physiological HM kinase that can activate S6K1 after its auto-inhibition is overcome by mTORC1. We, therefore, propose a novel mechanism for S6K1 regulation where mTOR complexes 1 and 2 act in tandem to activate the enzyme.

Expanding the view of the molecular mechanisms of autophagy pathway.

Autophagy is an evolutionarily conserved multistep degradation mechanism in eukaryotes, that maintains cellular homoeostasis by replenishing cells with nutrients through catabolic lysis of the cytoplasmic components. This critically coordinated pathway involves sequential processing events that begin with initiation, nucleation, and elongation of phagophores, followed by the formation of  double-membrane vesicles known as autophagosomes. Finally, autophagosomes migrate towards and fuse with lysosomes in mammals and vacuoles in yeast and plants, for the eventual degradation of the intravesicular cargo. Here, we review the recent advances in our understanding of the molecular events that define the process of autophagy.

mTORC1 induces eukaryotic translation initiation factor 4E interaction with TOS-S6 kinase 1 and its activation.

Eukaryotic translation initiation factor 4E was recently shown to be a substrate of mTORC1, suggesting it may be a mediator of mTORC1 signaling. Here, we present evidence that eIF4E phosphorylated at S209 interacts with TOS motif of S6 Kinase1 (S6K1). We also show that this interaction is sufficient to overcome rapamycin sensitivity and mTORC1 dependence of S6K1. Furthermore, we show that eIF4E-TOS interaction relieves S6K1 from auto-inhibition due to carboxy terminal domain (CTD) and primes it for hydrophobic motif (HM) phosphorylation and activation in mTORC1 independent manner. We conclude that the role of mTORC1 is restricted to engaging eIF4E with S6K1-TOS motif to influence its state of HM phosphorylation and inducing its activation.

Eukaryotic Initiation Factor 4E phosphorylation acts a switch for its binding to 4E-BP1 and mRNA cap assembly.

Translational regulation has invited considerable interest consequent of its circumstantial dysregulation during cancer genesis. eIF4E (Eukaryotic Initiation Factor 4E) has been identified as an important factor involved in tumor progression by way of instrumenting the convergence of oncogenic signals for up-regulation of Cap-dependent translation. In the backdrop of dramatic eIF4E over-expression in a large population of human cancers, we suggest that the tumorigenic property of eIF4E is strictly attributed to its phosphorylation state. We provide evidence that while phosphorylated eIF4E fails to be sequestered by 4E-BP1, its dephosphorylated form shows overwhelming binding with 4E-BP1 without any consideration to the state of 4E-BP1 phosphorylation to suggest that eIF4E-4EBP1 binding is governed by eIF4E phosphorylation instead of 4E-BP1. We also show that eIF4E engages in Cap-assembly formation preferably in a phosphorylation-dependent manner to suggest that eIF4E phosphorylation rather than 4E-BP1 regulates its availability for Cap-assembly.

Eukaryotic initiation factor 4E is a novel effector of mTORC1 signaling pathway in cross talk with Mnk1.

Cellular signals that influence Cap-dependent translation have assumed significant relevance in the backdrop of their enforced dysregulation during oncogenesis. Eukaryotic initiation factor 4E(eIF4E), the mRNA cap-binding protein, has emerged as a key player to facilitate tumor progression through upregulated cap-dependent translation synchronized with enhanced cell division. We provide evidence that eIF4E phosphorylation is regulated by mTORC1 by virtue of its interaction with Raptor through a novel TPTPNPP motif and consequent phosphorylation invitro and in vivo in a Rapamycin-sensitive manner. While we show that phosphorylation pattern of eIF4E responds faithfully to Rapamycin inhibition, the prolonged exposure to Rapamycin rescues the loss of eIF4E phosphorylation through Mnk1 activation. We also present evidence that eIF4E interacts with the amino terminal domain of S6K1 in a phospho-dependent manner, and this interaction is instrumental in overriding Rapamycin inhibition of S6K1. The data endorses eIF4E as a regulatory subunit that modulates the functional attributes of mTOR effectors to synchronize cap-dependent translation with growth assertion.

Eukaryotic Initiation Factor 4E (eIF4E) sequestration mediates 4E-BP1 response to rapamycin.

The cap dependent translation initiation is a tightly controlled process of cooperative ternary complex formation by 4E-BP1, eIF4E and the 5' cap of eukaryotic mRNA in response to environmental cues like glucose, nutrients and growth factor levels. Based on the well-described effects of mTORC1/rapamycin complex on 4E-BP1 phosphorylation/s, it is generally accepted that rapamycin is a global inhibitor of cap-dependent translation. We have previously shown that 4E-BP1 resistance to rapamycin was overcome by the stoichiometric abundance of S6K1. Now we present evidence that the TOS-bearing amino terminal domain of S6K1 is sufficient to relieve the rapamycin resistance of 4E-BP1 as TOS deleted variants of S6K1, active or inactive with regard to S6K1 activity failed to bring about relief of 4E-BP1 resistance to rapamycin. We also show that the reciprocal inactivation of S6K1 by abundance of 4E-BP1 gets accomplished only with intact TOS motif in the protein. The data presented in this study identifies eIF4E and not Raptor as a cellular factor responsible to regulate rapamycin sensitivity of 4E-BP1 suggesting that the phosphorylation dynamics and rapamycin sensitivity of 4E-BP1 and S6K1 are regulated independently.

PI3K target based novel cyano derivative of betulinic acid induces its signalling inhibition by down-regulation of pGSK3ß and cyclin D1 and potentially checks cancer cell proliferation.

In spite of the Betulinic acid (BA) being recognized as anticancerous source; its further use in clinical development is greatly hampered because of its poor pharmacokinetic properties. To circumvent these limitations, we synthesized a PI3K target based library of 18 triazole based derivatives and we identified a C-3 cyano analog of betulinic acid (CBA) with significant cell death effects with 5-7 fold higher potency than BA in various cancers. Importantly, no such report is available demonstrating the involvement of BA or its structural analogs in the modulation of PI3K pathway. Using, human leukemia HL-60 cells as a model, we for the first time report that CBA decreased expression of PI3K p110α, p85α, and pAKT in HL-60. Furthermore, we could find significant depletion of pGSK3ß, cyclin D1 and increased expression of p21/cip, p27/Kip proteins. CBA induced G0/G1 cell cycle arrest, increased sub-G0 DNA fraction and annexin V binding of the cells besides imparting the typical surface features of cell death. Also, this target specific inhibition was associated with mitochondrial apoptosis as was reflected by expression studies of various proteins together with reactive oxygen species generation and decline in mitochondrial trans membrane potential. The apoptotic effectors i.e., caspase 8 and caspase 9 were found to get upregulated besides PI3K associated DNA repair enzyme i.e., PARP cleavage was observed. Thus, our results elucidated that CBA or other BA based small molecules inhibit PI3K/AKT pathway with induction of subsequent cancer cell death which may be useful therapeutic strategy against leukemias and possibly other cancers.

Plant-derived protease inhibitors LC-pi (Lavatera cashmeriana) inhibit human lung cancer cell proliferation in vitro.

The objective of this study was to check the anticancer activity of purified protease inhibitors of Lavatera cashmeriana viz LC-pi I, II, III, and IV (Lavatera cashmeriana protease inhibitors) on A549 (lung) cell. It was found that LC-pi I and II significantly inhibited the proliferation of A549 cells with IC50 value of 54 µg/ml and 38 µg/ml, respectively, whereas inhibition by LC-pi III and IV was negligible. LC-pi I and II were further found to inhibit formation of colonies in a dose-dependent manner. Also, both inhibitors were found to induce apoptosis causing chromatin condensation and DNA fragmentation, without loss of mitochondrial membrane potential. Cell cycle revealed a significant increase of subG0/G1 phase cells that are apoptotic cells. We also demonstrated a dose-dependent decrease in migration of A549 cells on cell migration assay by both inhibitors. Taken together, we demonstrate that LC-pi I and II inhibited proliferation through arresting cells before apoptosis, inducing apoptosis and inhibiting cell migration in human lung cancer cells, but the study warrants further investigation. Our results support the notion that plant protease inhibitors may have the potential to advance as chemopreventive agents.

Essential oil composition of Senecio graciliflorus DC: comparative analysis of different parts and evaluation of antioxidant and cytotoxic activities.

The essential oil of different parts of Senecio graciliflorus DC was obtained by hydrodistillation and analysed by GC-FID and GC-MS for the first time. A total of 17, 20, 19 and 17 constituents were identified comprising 99.90, 95.50, 98.93 and 95.96% of the essential oil of flower, leaf, stem and root parts of Senecio graciliflorus respectively. Monoterpene hydrocarbons predominated in the essential oil with 85.28% in flower, 57.53% in leaf, 67.74% in stem and 64.98% in root oil. α-pinene, cis-ocimene, 1,2,3-trimethylcyclohexane and ß-pinene were the major constituents of the essential oil. The flower essential oil exhibited a strong antioxidant potential displaying IC50 values of 21.6±0.6 and 26.0±1.0µg/ml in DPPH and hydroxyl radical assays respectively. On the other hand the essential oil of flower and root displayed highest cytotoxicity against lung (A-549) cancer cell lines (IC50=19.1±0.9 and 21.3±1.1µg/ml respectively. This study which represents the first report of the essential oil composition and bioevaluation of Senecio graciliflorus, can serve as a new source of cytotoxic and antioxidant activity.

Comparative studies for screening of bioactive constituents from various parts of Incarvillea emodi.

A comparative study was performed on various parts (shoots, roots and flowers) of Incarvillea emodi. The alcoholic extracts of different parts were fractionated with solvents of different polarity and studied for the determination of total polyphenol content and total antioxidant potential. Furthermore, we have isolated major iridoid glucosides from the dried flowers of I. emodi followed by the comparative cytotoxicity studies of these iridoids against five different human cancer cell lines. The results have demonstrated that ethyl acetate fraction of all parts have higher phenolic content (167.87-294.31 mg/g as gallic acid equivalent) and higher total antioxidant potential (252.95-384.64 mg/g as trolox equivalent). The results of in vitro cytotoxicity studies have indicated that boschnaloside (2) possesses promising anticancer potential against three human cancer cell lines, THP-1, A-549 and PC-3, which belong to leukaemia, lung and prostate cancers, respectively, while plantarenaloside (1) expressed relevant cytotoxic activity against THP-1 cell lines of leukaemia.

Click chemistry inspired facile synthesis and bioevaluation of novel triazolyl analogs of Ludartin.

A convenient and modular synthesis involving diastereoselective Michael addition followed by regioselective Huisgen 1,3-dipolar cycloaddition reaction was carried out to furnish 1,4-disubstituted-1,2,3-triazoles of Ludartin. This reaction scheme involving Michael addition followed by regioselective Huisgen 1,3-dipolar cycloaddition reaction leading to the formation of triazolyl analogs is being reported for the first time. All the triazolyl products were characterised using spectral data analysis. Sulphorhodamine B cytotoxicity screening of the resulting products against a panel of five human cancerous cell-lines revealed that few of the analogs display promising broad spectrum cytotoxic effect. Among all the synthesized compounds, only 3q displayed the best cytotoxic effect with IC50 values of 12, 11, 38, 39 and 8.5 µM but less than the standard Ludartin (1) with IC50 values of 6.3, 7.4, 7.5, 6.9 and 0.5 µM against human neuroblastoma (T98G), lung (A-549), prostate (PC-3), colon (HCT-116) and breast (MCF-7) cancer cell lines, respectively. The present synthesis was designed based on the previous literature reports of Ludartin as an aromatase inhibitor. Our work provides an initial study on structure-activity relationship of triazolyl analogs of sesquiterpene lactones in general and Ludartin (1) in particular.

Isolation and antiproliferative activity of Lotus corniculatus lectin towards human tumour cell lines.

The objective of the study was to investigate the anti cancer activity of a lectin isolated from Lotus corniculatus seeds. A tetrameric 70kDa galactose specific lectin was purified using two step simple purification protocol which involved affinity chromatography on AF-BlueHC650M and gel filtration on Sephadex G-100. The lectin was adsorbed on AF-BlueHC650M and desorbed using 1M NaCl in the starting buffer. Gel filtration on Sephadex G-100 yielded a major peak absorbance that gave two bands of 15kDa and 20kDa in SDS PAGE. Hemagglutination activity was completely preserved, when the temperature was in the range of 20-60°C. However, drastic reduction in activity occurred at temperatures above 60°C. Full hemagglutination activity was retained at ambient pH 4-12. Thereafter no activity was observed above pH 13. Hemaglutination of the lectin was inhibited by d-galactose. The lectin showed a strong antiproliferative activity towards human leukemic (THP-1) cancer cells followed by lung cancer (HOP62) cells and HCT116 with an IC50 of 39µg/ml and 50µg/ml and 60µg/ml respectively. Flow cytometry analysis showed an increase in the percentage of cells in sub G0G1 phase confirming that Lotus corniculatus lectin induced apoptosis. Morphological observations showed that Lotus corniculatus lectin (LCL) treated THP-1 cells displayed apparent apoptosis characteristics such as nuclear fragmentation, appearance of membrane enclosed apoptotic bodies and DNA fragmentation. Lotus corniculatus lectin (LCL) effectively inhibits the cell migration in a dose dependent manner as indicated by the wound healing assay.

Synthesis and biological evaluation of ursolic acid-triazolyl derivatives as potential anti-cancer agents.

A series of ursolic acid-1-phenyl-1H-[1,2,3]triazol-4-ylmethylester congeners have been designed and synthesized in an attempt to develop potent antitumor agents. A regioselective approach using Huisgen 1,3-dipolar cycloaddition reaction of ursolic acid-alkyne derivative with various aromatic azides was employed to target an array of triazolyl derivatives in an efficient manner. Their structures were confirmed by using (1)H NMR, (13)C NMR, IR and MS analysis. All the compounds were evaluated for anti-cancer activity against a panel of four human cancer cell lines including A-549 (lung), MCF-7 (breast), HCT-116 (colon), THP-1 (leukemia) and a normal human epithelial cell line (FR-2) using sulforhodamine-B assay. The pharmacological results showed that most of the compounds displayed high level of antitumor activities against the tested cancer cell lines compared with ursolic acid. Compounds 7b, 7g, 7p and 7r were found to be the most potent compounds in this study.

Synthesis and biological evaluation of amino analogs of Ludartin: potent and selective cytotoxic agents.

Diverse amino analogs of Ludartin, a cytotoxic guaianolide and a position isomer of an anticancer drug, Arglabin were prepared through Michael type addition at its highly active α-methylene-γ-lactone motif. The semisynthetic derivatives were subjected to sulphorhodamine B cytotoxicity assay against a panel of four different human cancer cell lines viz. lung (A-549), leukemia (THP-1), prostate (PC-3) and colon (HCT-116) to look into structure-activity relationship. Few of the analogs displayed potent selective cytotoxicity compared to the parent molecule-Ludartin (1). (11R)-13-(Diethyl amine)-11,13-dihydroludartin (6) and (11R)-13-(piperidine)-11,13-dihydroludartin (10) showed almost same cytotoxicity against leukemia cell lines (THP-1) as that of parent molecule-Ludartin, but were more active against colon (HCT-116) cancer cells. (11R)-13-(Morpholine)-11,13-dihydroludartin (11) displayed selectively better cytotoxicity against Leukemia cancer cells (THP-1) exhibiting IC50 of 2.8 µM. (11R)-13-(6-Nitroindazole)-11,13-dihydroludartin (17) was four times more potent than Ludartin with selective cytotoxic effects against prostate cancer cells (2.2 µM) while as (11R)-13-(6-nitroindazole)-11,13-dihydroludartin (18) exhibited three-fold selective cytotoxicity for Lung (A-549) cancer cell lines exhibiting IC50 of 2.6 µM.

Antiproliferative activity of Lavatera cashmeriana- protease inhibitors towards human cancer cells.

BACKGROUND: Proteases play a regulatory role in a variety of pathologies including cancer, pancreatitis, thromboembolic disorders, viral infections and many others. One of the possible strategies to combat these pathologies seems to be the use of protease inhibitors. LC-pi I, II, III and IV (Lavatera cashmerian-protease inhibitors) have been found in vitro to strongly inhibit trypsin, chymotrypsin and elastase, proteases contributing to tumour invasion and metastasis, indicated possible anticancer effects. The purpose of this study was to check in vitro anticancer activity of these four inhibitors on human lung cancer cell lines. MATERIAL AND METHODS: In order to assess whether these inhibitors induced in vitro cytoxicity, SRB assay was conducted with THP-1 (leukemia), NCIH322 (lung) and Colo205, HCT-116 (colon) lines. RESULTS: LC-pi I significantly inhibited the cell proliferation of all cells tested and also LC-pi II was active in all except HCT-116. Inhibition of cell growth by LC-pi III and IV was negligible. IC50 values of LC-pi I and II for NCIH322, were less compared to other cell lines suggesting that lung cancer cells are more inhibited. CONCLUSION: These investigations might point to future preventive as well as curative solutions using plant protease inhibitors for various cancers, especially in the lung, hence warranting their further investigation.

Synthesis of 3-O-propargylated betulinic acid and its 1,2,3-triazoles as potential apoptotic agents.

Cytotoxic agents from nature are presently the mainstay of anticancer chemotherapy, and the need to reinforce the arsenal of anticancer agents is highly desired. Chemical transformation studies carried out on betulinic acid, through concise 1,2,3-triazole synthesis via click chemistry approach at C-3position in ring A have been evaluated for their cytotoxic potentiation against nine human cancer cell lines. Most of the derivatives have shown higher cytotoxic profiles than the parent molecule. Two compounds i.e. 3{1N(2-cyanophenyl)-1H-1,2,3-triazol-4yl}methyloxy betulinic acid (7) and 3{1N(5-hydroxy-naphth-1yl)-1H-1,2,3-triazol-4yl}methyloxy betulinic acid (13) displayed impressive IC50 values (2.5 and 3.5 µM respectively) against leukemia cell line HL-60 (5-7-fold higher potency than betulinic acid). As evident from various biological end points, inhibition of cell migration and colony formation, mitochondrial membrane disruption followed by DNA fragmentation and apoptosis, is demonstrated.

Induction of apoptosis in human pancreatic MiaPaCa-2 cells through the loss of mitochondrial membrane potential (ΔΨm) by Gentiana kurroo root extract and LC-ESI-MS analysis of its principal constituents.

The objective of the current study was to evaluate the methanolic root extract of Gentiana kurroo for antioxidant and antiproliferative activities as well as to study the effect of the extract on the induction of apoptosis in human pancreatic cancer cell line (MiaPaCa-2). The extract exerted significant antioxidant activity as verified by DPPH, hydroxyl radical, lipid peroxidation and protective oxidative DNA damage assays. The results were comparable to standard antioxidants like α-tocopherol, catechin and BHT used in such experiments. Antioxidant potential of G. kurroo may be attributed to the presence of high phenolic and flavonoid content (73±1.02 and 46±2.05 mg/g extract respectively). The anti-proliferative property of Gentiana kurroo root extract was determined by sulphorhodamine B (SRB) assay against Human colon cancer cell line (HCT-116), Lung carcinoma cell line (A-549), Pancreatic cancer cell line (MiaPaCa-2), Lung cancer cell line (HOP-62) and acute monocytic leukaemia cell line (THP-1). G. kurroo root extract inhibited cancer cell growth depending upon the cell line used and in a dose dependent manner. The extract induced potent apoptotic effects in MiaPaCa-2 cells. The population of apoptotic cells increased from 11.4% in case of control to 49.6% at 100 µg/ml of G. kurroo root extract. The extract also induced a remarkable decrease in mitochondrial membrane potential (ΔΨm) leading to apoptosis of cancer cells used. The main chemical constituents identified by the liquid chromatography-tandem mass spectrometry (LC-ESI-MSMS) were found to be iridoid glucosides (iridoids and secoiridoids), xanthones and flavonoids. Iridoid glucosides are the bitter principles of Gentiana species. Loganic acid, Sweroside, Swertiamarin, Gentiopicroside, Gentisin, Isogentisin, Gentioside, Norswertianolin, Swertianolin, 4″-O-ß-D-glucosyl-6'-O-(4-O-ß-D-glucosylcaffeoyl)-linearoside and Swertisin were the principal compounds present in the methanol root extract of G. kurroo.

Recent development in targeting PI3K-Akt-mTOR signaling for anticancer therapeutic strategies.

Cancer is a diverse class of diseases which differ widely in their cause and biology. The aberrant behavior of cancer reflects up regulation of certain oncogenic signaling pathways that promote proliferation, inhibit apoptosis, and enable the cancer to spread and evoke angiogenesis. Phosphoinositide-3-kinase(PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway controls various biological processes that are important for normal functioning of the cell via cell cycle progression, survival, migration, transcription, translation and metabolism. However, PI3K signaling pathway is dysregulated almost in all cancers which is due to the amplification and genetic mutation of PI3K gene, encoding catalytic and regulatory subunit of PI3K isoforms. The current review focuses on the structural features of various PI3K isoforms including Akt and mTOR and their inhibition using specific small molecule inhibitors in an attempt to achieve an attractive target for cancer prevention and chemotherapy.

Podophyllum hexandrum aqueous extract as a potential free radical scavenger.

The present study was undertaken to evaluate the effect of the aqueous extract of Podophyllum hexandrum against free radical-mediated damage and also explore its anticancer activity. The extract exhibited significant activity in scavenging 1, 1-diphenyl-2-picryl-hydrazyl radicals, (•)OH radical-mediated DNA damage, and lipid peroxide production in rat liver microsomes. The extract was also tested for its reducing abilities. The activity of liver marker enzymes and antioxidant defense enzymes in rat liver homogenate was assessed in control and carbon tetrachloride (CCl(4))-treated animals. It was observed that CCl(4)-induced changes viz., increases in the activities of aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase, a decrease in reduced glutathione as well as decreases in the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione-S-transferase. All these parameters showed reversal when pretreated with aqueous extract of P. hexandrum. Podophylotoxin and etoposide are the two known anticancer agents derived from P. hexandrum and interestingly the aqueous extract of P. hexandrum showed a typical DNA ladder formation in HL-60 cells confirming its role as an inducer of apoptosis. The results obtained suggest that the plant extract exhibits inhibition of and free radical production and lipid peroxidation, increase in antioxidant enzyme activities, revealing its antioxidant properties, and is also able to show potent anticancer activity as depicted by its ability to cause fragmentation of DNA.

Understanding histone deacetylases in the cancer development and treatment: an epigenetic perspective of cancer chemotherapy.

Cancer is a pathologic condition that involves genetic and epigenetic events culminating in neoplastic transformation. Alteration in epigenetic events that regulate the transcriptional activity of genes associated with various signaling pathways can influence multiple stages of tumorigenesis. In cancer cells, an imbalance often exists between histone acetyl transferase and histone deacetylase (HDAC) activities, and current research focuses actively on seeking competitive HDAC inhibitors (HDACi) for chemotherapeutic intervention. HDACi are proving useful for cancer prevention and therapy by virtue of their ability to reactivate the expression of epigenetically silenced genes, including those involved in differentiation, cell cycle regulation, apoptosis, angiogenesis, invasion, and metastasis. Furthermore, epidemiological studies suggest that different diets such as intake of cruciferous vegetables may lower the risk of different cancers, and there is growing interest in identifying the specific chemoprotective constituents and mechanistic insights of their action. Interestingly, it has been observed that cancer cells are more sensitive than nontransformed cells to apoptotic induction by some HDACi. Although the mechanistic basis for this sensitivity is unclear, yet HDACi have emerged as important epigenetic target for single and combinatorial chemotherapy. HDACi derived from diverse sources such as microbial, dietary, and synthetic increase acetylation level of cells and bring about anti-proliferative and apoptotic effects specific to cancer cells by way of their role in cell cycle regulation and expression of epigenetically silenced genes.