Histone deacetylase inhibitors and 15-deoxy-Delta12,14-prostaglandin J2 synergistically induce apoptosis

Pathological and pharmacological functions of the metabolites of polyunsaturated fatty acids mediated by cyclooxygenases, lipoxygenases, and cytochrome P450s in cancers

Oxylipins have garnered increasing attention because they were consistently shown to play pathological and/or pharmacological roles in the development of multiple cancers. Oxylipins are the metabolites of polyunsaturated fatty acids via both enzymatic and nonenzymatic pathways. The enzymes mediating the metabolism of PUFAs include but not limited to lipoxygenases (LOXs), cyclooxygenases (COXs), and cytochrome P450s (CYPs) pathways, as well as the down-stream enzymes. Here, we systematically summarized the pleiotropic effects of oxylipins in different cancers through pathological and pharmacological aspects, with specific reference to the enzyme-mediated oxylipins. We discussed the specific roles of oxylipins on cancer onset, growth, invasion, and metastasis, as well as the expression changes in the associated metabolic enzymes and the associated underlying mechanisms. In addition, we also discussed the clinical application and potential of oxylipins and related metabolic enzymes as the targets for cancer prevention and treatment. We found the specific function of most oxylipins in cancers, especially the underlying mechanisms and clinic applications, deserves and needs further investigation. We believe that research on oxylipins will provide not only more therapeutic targets for various cancers but also dietary guidance for both cancer patients and healthy humans.

Inhibition of phospholipase D2 augments histone deacetylase inhibitor-induced cell death in breast cancer cells

BACKGROUND

Histone deacetylase (HDAC) inhibitors are promising anticancer drugs but their effect on tumor treatment has been disappointing mainly due to the acquisition of HDAC inhibitor resistance. However, the mechanisms underlying such resistance remain unclear.

METHODS

In this study, we performed Western blot, q-PCR, and promoter assay to examine the expression of HDAC inhibitor-induced phospholipase D2 (PLD2) in MDA-MB231and MDA-MB435 breast cancer cells. Apoptosis and proliferation were analyzed by flow cytometry. In addition to invasion and migration assay, angiogenesis was further measured using in vitro tube formation and chick embryo chorioallantoic membrane model.

RESULTS

HDAC inhibitors including suberoylanilide hydroxamic acid (SAHA), trichostatin, and apicidin, induce expression of PLD2 in a transcriptional level. SAHA upregulates expression of PLD2 via protein kinase C-ζ in breast cancer cells and increases the enzymatic activity of PLD. The combination treatment of SAHA with PLD2 inhibitor significantly enhances cell death in breast cancer cells. Phosphatidic acid, a product of PLD activity, prevented apoptosis promoted by cotreatment with SAHA and PLD2 inhibitor, suggesting that SAHA-induced PLD2 expression and subsequent activation of PLD2 might confers resistance of breast cancer cells to HDAC inhibitor. The combinational treatment of the drugs significantly suppressed invasion, migration, and angiogenesis, compared with that of either treatment.

CONCLUSION

These findings provide further insight into elucidating the advantages of combination therapy with HDAC and PLD2 inhibitors over single-agent strategies for the treatment of cancer.

Reactive Oxygen Species-Mediated Mitochondrial Dysfunction Triggers Sodium Valproate-Induced Cytotoxicity in Human Colorectal Adenocarcinoma Cells

BACKGROUND

Colorectal cancer (CRC) is one of the frequently diagnosed cancers worldwide. Currently used chemotherapeutic drugs have several side effects. Histone deacetylase (HDAC) enzyme inhibitors possess potential anti-cancer effects. Therefore, we investigated the cytotoxic potential of sodium valproate, a HDAC inhibitor in human colorectal adenocarcinoma (HT-29) cells.

METHODS

MTT assay was used to analyze the cytotoxicity of HT-29 cells. Intracellular reactive oxygen species (ROS) induction was evaluated by dichloro-dihydro-fluorescein diacetate staining. Dual staining with acridine orange/ethidium bromide was used to investigate the morphology-related apoptotic cell death. Mitochondrial membrane potential was analyzed by rhodamine 123 staining. E-cadherin protein expression was examined by immunofluorescence staining.

RESULTS

Sodium valproate at 2 and 4 mM/mL treatments significantly induced cytotoxicity. Increased intracellular ROS expression was observed in the cells treated with sodium valproate. This treatment also induced mitochondrial dissipation, apoptosis-related morphological damage, and E-cadherin expression in HT-29 cells.

CONCLUSIONS

Our present results suggest that sodium valproate is cytotoxic to HT-29 cells due to its pro-oxidative and apoptosis inducing potential. Sodium valproate can be used as an adjuvant along with standard chemotherapeutic agents in CRC patients after necessary in vivo and clinical studies.

Biotinylation enhances the anticancer effects of 15d‑PGJ2 against breast cancer cells

15-Deoxy-∆12,14-prostaglandin J2 (15d‑PGJ2) is a natural agonist of peroxisome proliferator-activated receptor γ (PPARγ) that displays anticancer activity. Various studies have indicated that the effects of 15d‑PGJ2 are due to both PPARγ-dependent and -independent mechanisms. In the present study, we examined the effects of a biotinylated form of 15d‑PGJ2 (b‑15d‑PGJ2) on hormone-dependent MCF‑7 and triple‑negative MDA‑MB‑231 breast cancer cell lines. b‑15d‑PGJ2 inhibited cell proliferation more efficiently than 15d‑PGJ2 or the synthetic PPARγ agonist, efatutazone. b‑15d‑PGJ2 was also more potent than its non-biotinylated counterpart in inducing apoptosis. We then analyzed the mechanisms underlying this improved efficiency. It was found not to be the result of biotin receptor-mediated increased incorporation, since free biotin in the culture medium did not decrease the anti-proliferative activity of b‑15d‑PGJ2 in competition assays. Of note, b‑15d‑PGJ2 displayed an improved PPARγ agonist activity, as measured by transactivation experiments. Molecular docking analyses revealed a similar insertion of b‑15d‑PGJ2 and 15d‑PGJ2 into the ligand binding domain of PPARγ via a covalent bond with Cys285. Finally, PPARγ silencing markedly decreased the cleavage of the apoptotic markers, poly(ADP-ribose) polymerase 1 (PARP‑1) and caspase‑7, that usually occurs following b‑15d‑PGJ2 treatment. Taken together, our data indicate that biotinylation enhances the anti-proliferative and pro-apoptotic activity of 15d‑PGJ2, and that this effect is partly mediated via a PPARγ-dependent pathway. These results may aid in the development of novel therapeutic strategies for breast cancer treatment.

15-Deoxy-Δ12,14-prostaglandin J2 activates PI3K-Akt signaling in human breast cancer cells through covalent modification of the tumor suppressor PTEN at cysteine 136

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), one of the terminal products of cyclooxygenase-2-catalized arachidonic acid metabolism, has been shown to stimulate breast cancer cell proliferation and migration through Akt activation, but the underlying mechanisms remain poorly understood. In the present study, we investigated the effects of 15d-PGJ₂ on the activity of PTEN, the inhibitor of the phosphoinositide 3-kinase (PI3K)-Akt axis, in human breast cancer (MCF-7) cells. Since the α,β-unsaturated carbonyl moiety in the cyclopentenone ring of 15d-PGJ₂ is electrophilic, we hypothesized that 15d-PGJ₂-induced Akt phosphorylation might result from the covalent modification and subsequent inactivation of PTEN that has several critical cysteine residues. When treated to MCF-7 cells, 15d-PGJ₂ bound to PTEN, and this was abolished in the presence of the thiol-reducing agent dithiothreitol. A mass spectrometric analysis by using recombinant and endogenous PTEN protein revealed that the cysteine 136 residue (Cys¹³⁶) of PTEN is covalently modified upon treatment with 15d-PGJ₂. Notably, the ability of 15d-PGJ₂ to covalently bind to PTEN as well as to induce Akt phosphorylation was abolished in the cells expressing a mutant form of PTEN in which Cys¹³⁶ was replaced by serine (C136S-PTEN). The present study demonstrates for the first time that electrophilic 15d-PGJ₂ directly binds to cysteine 136 of PTEN and provides new insight into PTEN loss in cancer progression associated with chronic inflammation. These observations suggest that 15d-PGJ₂ can undergo nucleophilic addition to PTEN, presumably at Cys¹³⁶, thereby inactivating this tumor suppressor protein with concomitant Akt activation.

Downregulation of Nrf2 by the combination of TRAIL and Valproic acid induces apoptotic cell death of TRAIL-resistant papillary thyroid cancer cells via suppression of Bcl-xL

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) represents an effective agent for the treatment of many cancers, though the majority of thyroid cancers are found to be resistant. Therefore it would be necessary to identify agents capable of increasing the sensitivity of these cancers to TRAIL-mediated cell death. Here, we examined the therapeutic effect and its underlying mechanism of combination treatment of TRAIL and histone deacetylase inhibitor, Valproic acid (VPA) in vitro using human papillary thyroid cancer (PTC) cells and in vivo using an orthotopic mouse model of PTC. TRAIL-VPA combination therapy synergistically induced apoptotic cell death in TRAIL-resistant PTC through caspase activation. In addition, downregulation of antioxidant transcription factor, Nrf2 by co-treatment of TRAIL-VPA induces cell death via suppression of Bcl-xL in vitro and in vivo; these effects were further enhanced following siRNA inhibition of these proteins in combination with TRAIL or TRAIL-VPA. Taken together, VPA sensitized TRAIL-resistant PTC cells to apoptotic cell death through involvement of Nrf2 and Bcl-xL. Thus, the combination of VPA and TRAIL may be a promising therapy for TRAIL-resistant PTC.

Eicosanoid pathway in colorectal cancer: Recent updates

Enzymatic metabolism of the 20C polyunsaturated fatty acid (PUFA) arachidonic acid (AA) occurs via the cyclooxygenase (COX) and lipoxygenase (LOX) pathways, and leads to the production of various bioactive lipids termed eicosanoids. These eicosanoids have a variety of functions, including stimulation of homeostatic responses in the cardiovascular system, induction and resolution of inflammation, and modulation of immune responses against diseases associated with chronic inflammation, such as cancer. Because chronic inflammation is essential for the development of colorectal cancer (CRC), it is not surprising that many eicosanoids are implicated in CRC. Oftentimes, these autacoids work in an antagonistic and highly temporal manner in inflammation; therefore, inhibition of the pro-inflammatory COX-2 or 5-LOX enzymes may subsequently inhibit the formation of their essential products, or shunt substrates from one pathway to another, leading to undesirable side-effects. A better understanding of these different enzymes and their products is essential not only for understanding the importance of eicosanoids, but also for designing more effective drugs that solely target the inflammatory molecules found in both chronic inflammation and cancer. In this review, we have evaluated the cancer promoting and anti-cancer roles of different eicosanoids in CRC, and highlighted the most recent literature which describes how those molecules affect not only tumor tissue, but also the tumor microenvironment. Additionally, we have attempted to delineate the roles that eicosanoids with opposing functions play in neoplastic transformation in CRC through their effects on proliferation, apoptosis, motility, metastasis, and angiogenesis.

Peroxisome proliferator-activated receptor γ ligand troglitazone and TRAIL synergistically induce apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known to cause apoptosis in several types of malignant tumor cells through its interaction with the death domain-containing receptor, death receptor 5 (DR5). In the present study, we showed that co-treatment with troglitazone (TGZ), a synthetic ligand of peroxisome proliferator-activated receptor γ (PPARγ), and TRAIL synergistically induced apoptosis through DR5 upregulation in human colon cancer DLD-1 cells. TGZ elevated DR5 expression at the promoter level through the CCAAT/enhancer-binding protein homologous protein (CHOP) binding site. These results suggest that combined treatment with TGZ and TRAIL may be promising as a new therapy against malignant tumors.

A novel HDAC inhibitor OBP-801 and a PI3K inhibitor LY294002 synergistically induce apoptosis via the suppression of survivin and XIAP in renal cell carcinoma

Renal cell carcinoma (RCC) is resistant to traditional cancer therapies such as radiation therapy and chemotherapy. The use of targeted therapies has improved the clinical outcomes of patients with metastatic RCC. However, most patients acquire resistance against targeted therapies over time. We report that the combination of the novel histone deacetylase (HDAC) inhibitor OBP-801, also known as YM753 and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 synergistically inhibits cell growth and induces apoptosis in RCC cells. This combination activated caspase-3, -8 and -9 and the pan-caspase inhibitor zVAD-fmk significantly reduced the apoptotic response to the treatment with OBP-801 and LY294002. Moreover, the combined treatment induced intracellular reactive oxygen species (ROS) and the radical scavenger N-acetyl-L-cysteine (NAC) blocked the intracellular ROS and apoptosis induced by OBP-801 and LY294002. The co-treatment with OBP-801 and LY294002 markedly decreased survivin and the X-linked inhibitor of apoptosis protein (XIAP) protein levels, but Bcl-2 family members were not altered by the OBP-801/LY294002 co-treatment. These alterations were restored by NAC treatment. The transient transfection of survivin and XIAP reduced the apoptotic response to the OBP-801/LY294002 co-treatment. Additionally, OBP-801 was significantly more effective than SAHA, another HDAC inhibitor, in the combination with LY294002 against 786-O cells. Taken together, these results strongly suggest the combination of OBP-801 and LY294002 to be a promising treatment for RCC.

Utilization of the cellular stress response to sensitize cancer cells to TRAIL-mediated apoptosis

INTRODUCTION

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) is a promising death ligand who has received significant attention due to its specific anti-cancer activity. Recently, a number of clinical trials involving either recombinant soluble TRAIL or agonistic death receptor (DR) antibodies have even been initiated. One major caveat in TRAIL-based anti-cancer therapies is that a considerable number of cancer cells are notorious resistant to apoptosis induction by TRAIL. Overcoming this primary or secondary evolved resistance is an utmost important goal of present cancer research. The current literature suggests that TRAIL resistance is mediated by a number of endogenous factors.

AREAS COVERED

According to recent research, stress-related transcription factors have acquired a pivotal role in the sensitization of highly resistant cancer cells, for example, pancreatic cancer and glioblastoma cells, to TRAIL-mediated cell death. Out of this transcription factor family, C/EBP-homologous protein (CHOP) is linked to the control of DR-mediated apoptosis by modulation of several apoptotic and anti-apoptotic factors. Stress responses in certain organelles, such as endoplasmic reticulum (ER) and mitochondria, are potent inductors of CHOP expression. This report focuses on the influence of stress responses on endogenous or acquired resistance to extrinsic apoptosis in tumor cells and summarizes recent findings and results. The Medline and ClinicalTrials database with key words were used for this review.

EXPERT OPINION

A potential novel treatment strategy for highly treatment-resistant tumors is the induction of a cellular stress response in cancer cells. The induction of an organelle-related stress response, such as nuclear, ER and mitochondrial stress, leads to a dramatic sensitization of a broad variety of cancer cells of different tumor entities to the apoptotic ligand, TRAIL. Importantly, non-neoplastic cells are not sensitized to TRAIL-mediated cell death through the unfolded protein response in most instances, suggesting that this treatment is not only of high efficacy, but even more less of unwanted toxicity in patients.

Cyclooxygenases and lipoxygenases in cancer

Cancer initiation and progression are multistep events that require cell proliferation, migration, extravasation to the blood or lymphatic vessels, arrest to the metastatic site, and ultimately secondary growth. Tumor cell functions at both primary or secondary sites are controlled by many different factors, including growth factors and their receptors, chemokines, nuclear receptors, cell-cell interactions, cell-matrix interactions, as well as oxygenated metabolites of arachidonic acid. The observation that cyclooxygenases and lipoxygenases and their arachidonic acid-derived eicosanoid products (prostanoids and HETEs) are expressed and produced by tumor cells, together with the finding that these enzymes can regulate cell growth, survival, migration, and invasion, has prompted investigators to analyze the roles of these enzymes in cancer progression. In this review, we focus on the contribution of cyclooxygenase- and lipoxygenase-derived eicosanoids to tumor cell function in vitro and in vivo and discuss hope and tribulations of targeting these enzymes for cancer prevention and treatment.

Eicosanoid signalling pathways in the development and progression of colorectal cancer: novel approaches for prevention/intervention

Arachidonic acid metabolism through cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P-450 epoxygenase (EPOX) pathways leads to the generation of biologically active eicosanoids, including prostanoids, leukotrienes, hydroxyeicosatetraenoic acid, epoxyeicosatrienoic acid and hydroperoxyeicosatetraenoic acids. Eicosanoid expression levels vary during tumor development and progression of a range of malignancies, including colorectal cancer. The actions of these autocoids are also directly influenced by diet, as demonstrated by recent evidence for omega-3 fatty acids in colorectal cancer (CRC) prevention and/or treatment. Eicosanoids regulate CRC development and progression, while inhibition of these pathways has generally been shown to inhibit tumor growth/progression. A progressive sequence of colorectal cancer development has been identified, ranging from normal colon, to colitis, dysplasia, and carcinoma. While both COX and LOX inhibition are both promising candidates for colorectal cancer prevention and/or treatment, there is an urgent need to understand the mechanisms through which these signalling pathways mediate their effects on tumorigenesis. This will allow identification of safer, more effective strategies for colorectal cancer prevention and/or treatment. In particular, binding to/signalling through prostanoid receptors have recently been the subject of considerable interest in this area. In this review, we discuss the role of the eicosanoid signalling pathways in the development and progression of colorectal cancer. We discuss the effects of the eicosanoids on tumor cell proliferation, their roles in cell death induction, effects on angiogenesis, migration, invasion and their regulation of the immune response. Signal transduction pathways involved in these processes are also discussed. Finally, novel approaches targeting these arachidonic acid-derived eicosanoids (using pharmacological or natural agents) for chemoprevention and/or treatment of colorectal cancer are outlined.

COX-derived prostanoid pathways in gastrointestinal cancer development and progression: novel targets for prevention and intervention

Arachidonic acid metabolism through cyclooxygenase (COX) pathways leads to the generation of biologically active eicosanoids. Eicosanoid expression levels vary during development and progression of gastrointestinal (GI) malignancies. COX-2 is the major COX-isoform responsible for G.I. cancer development/progression. COX-2 expression increases during progression from a normal to cancerous state. Evidence from observational studies has demonstrated that chronic NSAID use reduces the risk of cancer development, while both incidence and risk of death due to G.I. cancers were significantly reduced by daily aspirin intake. A number of randomized controlled trials (APC trial, Prevention of Sporadic Adenomatous Polyps trial, APPROVe trial) have also shown a significant protective effect in patients receiving selective COX-2 inhibitors. However, chronic use of selective COX-2 inhibitors at high doses was associated with increased cardiovascular risk, while NSAIDs have also been associated with increased risk. More recently, downstream effectors of COX-signaling have been investigated in cancer development/progression. PGE(2), which binds to both EP and PPAR receptors, is the major prostanoid implicated in the carcinogenesis of G.I. cancers. The role of TXA(2) in G.I. cancers has also been examined, although further studies are required to uncover its role in carcinogenesis. Other prostanoids investigated include PGD(2) and its metabolite 15d-PGJ2, PGF(1α) and PGI(2). Targeting these prostanoids in G.I. cancers has the promise of avoiding cardiovascular toxicity associated with chronic selective COX-2 inhibition, while maintaining anti-tumor reactivity. A progressive sequence from normal to pre-malignant to a malignant state has been identified in G.I. cancers. In this review, we will discuss the role of the COX-derived prostanoids in G.I. cancer development and progression. Targeting these downstream prostanoids for chemoprevention and/or treatment of G.I. cancers will also be discussed. Finally, we will highlight the latest pre-clinical technologies as well as avenues for future investigation in this highly topical research field.

Anticancer effects of 15d-prostaglandin-J2 in wild-type and doxorubicin-resistant ovarian cancer cells: novel actions on SIRT1 and HDAC

15-deoxy-delta-12,14-prostaglandin-J₂ (15d-PGJ₂), an arachidonic metabolite and a natural PPARγ agonist, is known to induce apoptosis in tumor cells. In this study, we investigated new therapeutic potentials of 15d-PGJ₂ by determining its anticancer effects in wild-type and doxorubicin-resistant ovarian carcinoma cells. Despite high expression of resistance-inducing genes like MDR1, Bcl2 and Bcl-xl, 15d-PGJ₂ strongly induced apoptosis in doxorubicin-resistant (A2780/AD) cells similar to the wild-type (A2780). This was found to be related to caspase-3/7- and NF-κB pathways but not to its PPARγ agonistic activity. 15d-PGJ₂ also was able to reduce the doxorubicin resistance of A2780/AD cells at low doses as confirmed by the inhibition of gene expression of MDR1 (p-glycoprotein) and SIRT1 (a drug senescence gene). We also investigated effects of 15d-PGJ₂ on cell migration and transformation using a wound-healing assay and morphological analyses, respectively. We found that 15d-PGJ₂ inhibited migration most likely due to NF-κB inhibition and induced transformation of the round-shape A2780/AD cells into elongated epithelial cells due to HDAC1 inhibition. Using a 15d-PGJ₂ analog, we found the mechanism of action of these new activities of 15d-PGJ₂ on SIRT1 and HDAC1 gene expressions and enzyme activities. In conclusion, the present study demonstrates that 15d-PGJ₂ has a high therapeutic potential to kill drug-resistant tumor cells and, the newly described inhibitory effects of this cyclo-oxygenase product on SIRT1 and HDAC will provide new opportunities for cancer therapeutics.

Recombinant immunotoxin anti-c-Met/PE38KDEL inhibits proliferation and promotes apoptosis of gastric cancer cells

Background

Our study aims to evaluate the anti-growth effects of recombinant immunotoxin (IT) anti-c-Met/PE38KDEL on gastric cancer cells, and its mechnisms.

Methods

Gastric cancer cells were treated with increasing doses of IT and c-Met protein was quantified by Western blotting. Cell proliferation was determined by Cell Counting Kit-8 assay (CCK). [³H]-leucine incorporation assay was used to evaluate IT inhibition of protein synthesis. Cell apoptosis was quantified by flow cytometry. Caspase activities were measured using colorimetric protease assays.

Results

Cell growth and protein synthesis of the gastric cancer cell lines were suppressed by IT in a dose- and time-dependent manner. IT also induced apoptosis in a dose-dependent manner. The apoptosis rates of gastric cancer cell lines MKN-45 and SGC7901 were 19.19% and 27.37%, respectively when treated with 50 ng/ml of IT. There were significant increase ofcaspase-3 activity at 24 hr of IT treatment (100 ng/ml) (P < 0.01) in these gastric cancer cell lines.

Conclusions

IT anti-c-Met/PE38KDEL has anti-growth effects on the gastric cancer cell lines in vitro, and it provides an experimental basis for c-Met-targeted therapy towards in vivo testing.

Cell death signaling and anticancer therapy

For a long time, it was commonly believed that efficient anticancer regimens would either trigger the apoptotic demise of tumor cells or induce a permanent arrest in the G₁ phase of the cell cycle, i.e., senescence. The recent discovery that necrosis can occur in a regulated fashion and the increasingly more precise characterization of the underlying molecular mechanisms have raised great interest, as non-apoptotic pathways might be instrumental to circumvent the resistance of cancer cells to conventional, pro-apoptotic therapeutic regimens. Moreover, it has been shown that some anticancer regimens engage lethal signaling cascades that can ignite multiple oncosuppressive mechanisms, including apoptosis, necrosis, and senescence. Among these signaling pathways is mitotic catastrophe, whose role as a bona fide cell death mechanism has recently been reconsidered. Thus, anticancer regimens get ever more sophisticated, and often distinct strategies are combined to maximize efficacy and minimize side effects. In this review, we will discuss the importance of apoptosis, necrosis, and mitotic catastrophe in the response of tumor cells to the most common clinically employed and experimental anticancer agents.

Valproate inhibits colon cancer growth through cell cycle modification in vivo and in vitro

Valproate (VPA) is a well-characterized histone deacetylase inhibitor with anti-neoplastic properties. We analyzed the growth blocking effects and the molecular mode of action of this compound in colorectal cancer cells in vitro and in vivo. Caco-2, SW-480, CX-1 or WIDR cell lines were exposed to VPA (0.25-2 mM) for various time periods. Cell growth, cell cycle progression and apoptosis were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide dye reduction assay and flow cytometry. Cell cycle- and apoptosis-regulating proteins and histone acetylation were assessed by Western blotting. In vivo tumor growth and regulating protein expression under VPA were investigated in a subcutaneous xenograft tumor model. VPA inhibited the growth of all cell lines with cell cycle arrest paralleled by the up-regulation of H3 and H4 acetylation. In vivo tumor growth was substantially depressed by VPA (200 mg/kg bw). Cell cycle proteins (cdk1, cdk2, cdk4, cyclin D, cyclin E, p19, p21 and p27) were differentially altered by VPA. Predominantly cdk1 was decreased and p27 was up-regulated in all models. Apoptosis-related proteins were altered in vivo with up-regulation of bax and down-regulation of bcl-2. VPA exerts anti-neoplastic activity in colorectal tumor cell lines in vitro and in vivo by altering cell cycle regulation.

Epigenetic silencing of peroxisome proliferator-activated receptor γ is a biomarker for colorectal cancer progression and adverse patients' outcome

The relationship between peroxisome proliferator-activated receptor γ (PPARG) expression and epigenetic changes occurring in colorectal-cancer pathogenesis is largely unknown. We investigated whether PPARG is epigenetically regulated in colorectal cancer (CRC) progression. PPARG expression was assessed in CRC tissues and paired normal mucosa by western blot and immunohistochemistry and related to patients' clinicopathological parameters and survival. PPARG promoter methylation was analyzed by methylation-specific-PCR and bisulphite sequencing. PPARG expression and promoter methylation were similarly examined also in CRC derived cell lines. Chromatin immunoprecipitation in basal conditions and after epigenetic treatment was performed along with knocking-down experiments of putative regulatory factors. Gene expression was monitored by immunoblotting and functional assays of cell proliferation and invasiveness. Methylation on a specific region of the promoter is strongly correlated with PPARG lack of expression in 30% of primary CRCs and with patients' poor prognosis. Remarkably, the same methylation pattern is found in PPARG-negative CRC cell lines. Epigenetic treatment with 5'-aza-2'-deoxycytidine can revert this condition and, in combination with trichostatin A, dramatically re-activates gene transcription and receptor activity. Transcriptional silencing is due to the recruitment of MeCP2, HDAC1 and EZH2 that impart repressive chromatin signatures determining an increased cell proliferative and invasive potential, features that can experimentally be reverted. Our findings provide a novel mechanistic insight into epigenetic silencing of PPARG in CRC that may be relevant as a prognostic marker of tumor progression.