Synergistic antileukemic interactions between 2-medroxyestradiol (2-ME) and histone deacetylase inhibitors involve Akt down-regulation and oxidative stress

The emerging roles of HDACs and their therapeutic implications in cancer

Deregulation of protein post-translational modifications is intensively involved in the etiology of diseases, including degenerative diseases, inflammatory injuries, and cancers. Acetylation is one of the most common post-translational modifications of proteins, and the acetylation levels are controlled by two mutually antagonistic enzyme families, histone acetyl transferases (HATs) and histone deacetylases (HDACs). HATs loosen the chromatin structure by neutralizing the positive charge of lysine residues of histones; whereas HDACs deacetylate certain histones, thus inhibiting gene transcription. Compared with HATs, HDACs have been more intensively studied, particularly regarding their clinical significance. HDACs extensively participate in the regulation of proliferation, migration, angiogenesis, immune escape, and therapeutic resistance of cancer cells, thus emerging as critical targets for clinical cancer therapy. Compared to HATs, inhibitors of HDAC have been clinically used for cancer treatment. Here, we enumerate and integratethe mechanisms of HDAC family members in tumorigenesis and cancer progression, and address the new and exciting therapeutic implications of single or combined HDAC inhibitor (HDACi) treatment.

Development, Optimization and Evaluation of 2-Methoxy-Estradiol Loaded Nanocarrier for Prostate Cancer

The therapeutic efficacy of antineoplastic agents possessing a selective target to the nucleus of the cancer cells could be enhanced through novel formulation approaches. Thus, toward the improvement of the anticancer potential of 2-methoxy estradiol (2 ME) on prostate cancer, the drug was entrapped into the hydrophobic micelles core formulated with Phospholipon 90G and d-α-tocopheryl polyethylene glycol succinate (TPGS). Optimization of the formulation was done by Box-Behnken statistical design using Statgraphics software to standardize percentages of TPGS and phospholipid to obtain the smallest particle size. The optimized formulation was found to be spherical with nanometer size of 152 ± 5.2 nm, and low PDI (0.234). The entrapment efficiency of the micelles was 88.67 ± 3.21% with >93% release of 2 ME within 24 h. There was a 16-fold increase in apoptosis and an 8-fold increase in necrosis of the PC-3 cells when incubated with 2 ME micellar delivery compared to control cells (2.8 ± 0.2%). This increased apoptosis was further correlated with increased BAX expression (11.6 ± 0.7) and decreased BCL-2 expression (0.29 ± 0.05) in 2 ME micelles treated cells when compared to the control group. Further, loss of mitochondrial membrane potential (∼50-fold) by the drug-loaded micelles and free drug compared to control cells was found to be due to the generation of ROS. Findings on cell cycle analysis revealed the significant arrest of the G2-M phase of the PC-3 cells when incubated with the optimized formulation. Simultaneously, a significantly increased number of cells in pre-G1 revealed the maximum apoptotic potential of the drug when delivered via micellar formulation. Finally, upregulation of caspase-9, p53, and NO, with downregulation of TNF-α, NF-κβ, and inflammatory mediators of the PC-3 cells established the superiority of the micellar approach against prostate cancer. In summary, the acquired results highlighted the potentiality of the 2 ME-micellar delivery tool for controlling the growth of prostate cancer cells for improved efficacy.

BIM upregulation and ROS-dependent necroptosis mediate the antitumor effects of the HDACi Givinostat and Sorafenib in Hodgkin lymphoma cell line xenografts

Relapsed/refractory Hodgkin's lymphoma (HL) is an unmet medical need requiring new therapeutic options. Interactions between the histone deacetylase inhibitor Givinostat and the RAF/MEK/ERK inhibitor Sorafenib were examined in HDLM-2 and L-540 HL cell lines. Exposure to Givinostat/Sorafenib induced a synergistic inhibition of cell growth (range, 70-80%) and a marked increase in cell death (up to 96%) due to increased H3 and H4 acetylation and strong mitochondrial injury. Gene expression profiling indicated that the synergistic effects of Givinostat/Sorafenib treatment are associated with the modulation of cell cycle and cell death pathways. Exposure to Givinostat/Sorafenib resulted in sustained production of reactive oxygen species (ROS) and activation of necroptotic cell death. The necroptosis inhibitor Necrostatin-1 prevented Givinostat/Sorafenib-induced ROS production, mitochondrial injury, activation of BH3-only protein BIM and cell death. Knockdown experiments identified BIM as a key signaling molecule that mediates Givinostat/Sorafenib-induced oxidative death of HL cells. Furthermore, in vivo xenograft studies demonstrated a 50% reduction in tumor burden (P<0.0001), a 5- to 15-fold increase in BIM expression (P < 0.0001) and a fourfold increase in tumor necrosis in Givinostat/Sorafenib-treated animals compared with mice that received single agents. These results provide a rationale for exploring Givinostat/Sorafenib combination in relapsed/refractory HL.

6-Shogaol induces apoptosis in human leukemia cells through a process involving caspase-mediated cleavage of eIF2α

Background

6-Shogaol is a promising antitumor agent isolated from dietary ginger (Zingiber officinale). However, little is known about the efficacy of 6-shogaol on leukemia cells. Here we investigated the underlying mechanism of 6-shogaol induced apoptosis in human leukemia cells in vitro and in vivo.

Methods

Three leukemia cell lines and primary leukemia cells were used to investigate the apoptosis effect of 6-shogaol. A shotgun approach based on label-free proteome with LC-CHIP Q-TOF MS/MS was employed to identify the cellular targets of 6-shogaol and the differentially expressed proteins were analyzed by bioinformatics protocols.

Results

The present study indicated that 6-shogaol selectively induced apoptosis in transformed and primary leukemia cells but not in normal cells. Eukaryotic translation initiation factor 2 alpha (eIF2α), a key regulator in apoptosis signaling pathway, was significantly affected in both Jurkat and U937 proteome profiles. The docking results suggested that 6-shogaol might bind well to eIF2α at Ser51 of the N-terminal domain. Immunoblotting data indicated that 6-shogaol induced apoptosis through a process involving dephosphorylation of eIF2α and caspase activation–dependent cleavage of eIF2α. Furthermore, 6-shogaol markedly inhibited tumor growth and induced apoptosis in U937 xenograft mouse model.

Conclusion

The potent anti-leukemia activity of 6-shogaol found both in vitro and in vivo in our study make this compound a potential anti-tumor agent for hematologic malignancies.

The Cytotoxicity Mechanism of 6-Shogaol-Treated HeLa Human Cervical Cancer Cells Revealed by Label-Free Shotgun Proteomics and Bioinformatics Analysis

Cervical cancer is one of the most common cancers among women in the world. 6-Shogaol is a natural compound isolated from the rhizome of ginger (Zingiber officinale). In this paper, we demonstrated that 6-shogaol induced apoptosis and G2/M phase arrest in human cervical cancer HeLa cells. Endoplasmic reticulum stress and mitochondrial pathway were involved in 6-shogaol-mediated apoptosis. Proteomic analysis based on label-free strategy by liquid chromatography chip quadrupole time-of-flight mass spectrometry was subsequently proposed to identify, in a non-target-biased manner, the molecular changes in cellular proteins in response to 6-shogaol treatment. A total of 287 proteins were differentially expressed in response to 24 h treatment with 15 μM 6-shogaol in HeLa cells. Significantly changed proteins were subjected to functional pathway analysis by multiple analyzing software. Ingenuity pathway analysis (IPA) suggested that 14-3-3 signaling is a predominant canonical pathway involved in networks which may be significantly associated with the process of apoptosis and G2/M cell cycle arrest induced by 6-shogaol. In conclusion, this work developed an unbiased protein analysis strategy by shotgun proteomics and bioinformatics analysis. Data observed provide a comprehensive analysis of the 6-shogaol-treated HeLa cell proteome and reveal protein alterations that are associated with its anticancer mechanism.

6-Shogaol induces apoptosis in human hepatocellular carcinoma cells and exhibits anti-tumor activity in vivo through endoplasmic reticulum stress

6-Shogaol is an active compound isolated from Ginger (Zingiber officinale Rosc). In this work, we demonstrated that 6-shogaol induces apoptosis in human hepatocellular carcinoma cells in relation to caspase activation and endoplasmic reticulum (ER) stress signaling. Proteomic analysis revealed that ER stress was accompanied by 6-shogaol-induced apoptosis in hepatocellular carcinoma cells. 6-shogaol affected the ER stress signaling by regulating unfolded protein response (UPR) sensor PERK and its downstream target eIF2α. However, the effect on the other two UPR sensors IRE1 and ATF6 was not obvious. In prolonged ER stress, 6-shogaol inhibited the phosphorylation of eIF2α and triggered apoptosis in SMMC-7721 cells. Salubrinal, an activator of the PERK/eIF2α pathway, strikingly enhanced the phosphorylation of eIF2α in SMMC-7721 cells with no toxicity. However, combined treatment with 6-shogaol and salubrinal resulted in significantly increase of apoptosis and dephosphorylation of eIF2α. Overexpression of eIF2α prevented 6-shogaol-mediated apoptosis in SMMC-7721 cells, whereas inhibition of eIF2α by small interfering RNA markedly enhanced 6-shogaol-mediated cell death. Furthermore, 6-shogaol-mediated inhibition of tumor growth of mouse SMMC-7721 xenograft was associated with induction of apoptosis, activation of caspase-3, and inactivation of eIF2α. Altogether our results indicate that the PERK/eIF2α pathway plays an important role in 6-shogaol-mediated ER stress and apoptosis in SMMC-7721 cells in vitro and in vivo.

Preclinical evaluation of dual PI3K-mTOR inhibitors and histone deacetylase inhibitors in head and neck squamous cell carcinoma

Background:

We examine the potential value of a series of clinically relevant PI3K-mTOR inhibitors alone, or in combination with histone deacetylase inhibitors, in a model of head and neck squamous cell carcinoma (HNSCC).

Methods:

Head and neck squamous cell carcinoma cell lines, human keratinocyte and HNSCC xenograft models were treated with histone deacetylase inhibitors (HDACIs) and new generation PI3K and dual PI3K-mTOR inhibitors either alone or in combination. Cell and tumour tissue viability and proliferation were then determined in vitro and in vivo.

Results:

Phosphatidylinositol-3-phosphate kinase, AKT and dual PI3K-mTOR inhibitors caused marked in vitro enhancement of cytotoxicity induced by HDACIs in HNSCC cancer cells. This effect correlates with AKT inhibition and is attenuated by expression of constitutively active AKT. Histone deacetylase inhibitor and phosphatidylinositol-3-phosphate kinase inhibitors (PI3KIs) inhibited tumour growth in xenograft models of HNSCC. Importantly, we observed intratumoural HDAC inhibition and PI3K inhibition as assessed by histone H3 acetylation status and phospho-AKT staining, respectively. However, we saw no evidence of improved efficacy with an HDACI/PI3KI combination.

Interpretation:

That PI3K and dual PI3K-mTOR inhibitors possess antitumour effect against HNSCC in vivo.

The HDAC inhibitor depsipeptide transactivates the p53/p21 pathway by inducing DNA damage

Histone deacetylase (HDAC) inhibitors have been proven to be effective therapeutic agents to kill cancer cells through inhibiting HDAC activity or altering the structure of chromatin. As a potent HDAC inhibitor, depsipeptide not only modulates histone deacetylation but also activates non-histone protein p53 to inhibit cancer cell growth. However, the mechanism of depsipeptide-induced p53 transactivity remains unknown. Here, we show that depsipeptide causes DNA damage through induction of reactive oxygen species (ROS) generation, as demonstrated by a comet assay and by detection of the phosphorylation of H2AX. Depsipeptide induced oxidative stress was confirmed to relate to a disturbance in reduction-oxidation (redox) reactions through inhibition of the transactivation of thioredoxin reductase (TrxR) in human cancer cells. Upon treatment with depsipeptide, p53 phosphorylation at threonine 18 (Thr18) was specifically induced. Furthermore, we also demonstrated that phosphorylation of p53 at Thr18 is required for p53 acetylation at lysine 373/382 and for p21 expression in response to depsipeptide treatment. Our results demonstrate that depsipeptide plays an anti-neoplastic role by generating ROS to elicit p53/p21 pathway activation.

Involvement of reactive oxygen species in 2-methoxyestradiol-induced apoptosis in human neuroblastoma cells

Neuroblastoma is the most common extra-cranial solid tumor in children. Despite advances in the treatment of childhood cancer, outcomes for children with advanced-stage neuroblastoma remain poor. Here we reported that 2-methoxyestradiol (2-ME) inhibited the proliferation and induced apoptosis in human neuroblastoma SK-N-SH and SH-SY5Y cells. 2-ME treatment also resulted in the generation of ROS and the loss of mitochondrial membrane potential in SK-N-SH and SH-SY5Y, indicating that 2-ME-induced apoptosis is mediated by ROS. This is supported by the results that have shown that co-treatment with antioxidants, VC, L-GSH and MitoQ(10), decreased 2-ME-induced generation of ROS and the loss of the mitochondrial membrane potential, increased the Bcl-2/Bax ratio, decreased 2-ME-induced activation of caspase-9 and caspase-3 and the up-regulation of apoptosis-inducing factor (AIF), and prevented 2-ME-induced apoptosis in SK-N-SH and SH-SY5Y cells. These results suggested that oxidative stress plays an important role in 2-ME-induced apoptotic death of human neuroblastoma cells.

PRL-3, a metastasis associated tyrosine phosphatase, is involved in FLT3-ITD signaling and implicated in anti-AML therapy

Combination with other small molecule drugs represents a promising strategy to improve therapeutic efficacy of FLT3 inhibitors in the clinic. We demonstrated that combining ABT-869, a FLT3 inhibitor, with SAHA, a HDAC inhibitor, led to synergistic killing of the AML cells with FLT3 mutations and suppression of colony formation. We identified a core gene signature that is uniquely induced by the combination treatment in 2 different leukemia cell lines. Among these, we showed that downregulation of PTP4A3 (PRL-3) played a role in this synergism. PRL-3 is downstream of FLT3 signaling and ectopic expression of PRL-3 conferred therapeutic resistance through upregulation of STAT (signal transducers and activators of transcription) pathway activity and anti-apoptotic Mcl-1 protein. PRL-3 interacts with HDAC4 and SAHA downregulates PRL-3 via a proteasome dependent pathway. In addition, PRL-3 protein was identified in 47% of AML cases, but was absent in myeloid cells in normal bone marrows. Our results suggest such combination therapies may significantly improve the therapeutic efficacy of FLT3 inhibitors. PRL-3 plays a potential pathological role in AML and it might be a useful therapeutic target in AML, and warrant clinical investigation.

Overcoming resistance to histone deacetylase inhibitors in human leukemia with the redox modulating compound β-phenylethyl isothiocyanate

Mechanisms of action and resistance of histone deacetylase inhibitors (HDACIs) are not well understood. A gene expression analysis performed in a phase 1 trial of vorinostat in leukemia indicated that overexpression of genes involved in antioxidant defense was associated with clinical resistance. We hypothesized that nonepigenetic mechanisms may be involved in resistance to HDACI therapy in leukemia. Here we confirmed up-regulation of a series of antioxidants in a pan-HDACI-resistant leukemia cell line HL60/LR. Vorinostat induced reactive oxygen species (ROS) through nicotinamide adenine dinucleotide phosphate oxidase in leukemia cells. An increase in ROS resulted in translocation of nuclear factor E2-related factor 2 from cytosol to nucleus, leading to up-regulation of antioxidant genes, including a majority of glutathione-associated enzymes as a cellular protective mechanism. Addition of β-phenylethyl isothiocyanate, a natural compound capable of depleting cellular glutathione, significantly enhanced the cytotoxicity of vorinostat in leukemia cell lines and primary leukemia cells by inhibiting the cytoprotective antioxidant response. These results suggest that ROS plays an important role in action of vorinostat and that combination with a redox-modulating compound increases sensitivity to HDACIs and also overcomes vorinostat resistance. Such a combination strategy may be an effective therapeutic regimen and have potential clinical application in leukemia.

Mechanisms of synergistic antileukemic interactions between valproic acid and cytarabine in pediatric acute myeloid leukemia

PURPOSE

To determine the possibility of synergistic antileukemic activity and the underlying molecular mechanisms associated with cytarabine combined with valproic acid (VPA; a histone deacetylase inhibitor and a Food and Drug Administration-licensed drug for treating both children and adults with epilepsy) in pediatric acute myeloid leukemia (AML).

EXPERIMENTAL DESIGN

The type and extent of antileukemic interactions between cytarabine and VPA in clinically relevant pediatric AML cell lines and diagnostic blasts from children with AML were determined by MTT assays and standard isobologram analyses. The effects of cytarabine and VPA on apoptosis and cell cycle distributions were determined by flow cytometry analysis and caspase enzymatic assays. The effects of the two agents on DNA damage and Bcl-2 family proteins were determined by Western blotting.

RESULTS

We showed synergistic antileukemic activities between cytarabine and VPA in four pediatric AML cell lines and nine diagnostic AML blast samples. t(8;21) AML blasts were significantly more sensitive to VPA and showed far greater sensitivities to combined cytarabine and VPA than non-t(8;21) AML cases. Cytarabine and VPA cooperatively induced DNA double-strand breaks, reflected in induction of γH2AX and apoptosis, accompanied by activation of caspase-9 and caspase-3. Further, VPA induced Bim expression and short hairpin RNA knockdown of Bim resulted in significantly decreased apoptosis induced by cytarabine and by cytarabine plus VPA.

CONCLUSIONS

Our results establish global synergistic antileukemic activity of combined VPA and cytarabine in pediatric AML and provide compelling evidence to support the use of VPA in the treatment of children with this deadly disease.

Histone deacetylase inhibitors: current status and overview of recent clinical trials

Histone deacetylase (HDAC) inhibitors are a new group of anticancer agents that have a potential role in the regulation of gene expression, induction of cell death, apoptosis and cell cycle arrest of cancer cells by altering the acetylation status of chromatin and other non-histone proteins. In clinical trials, HDAC inhibitors have demonstrated promising antitumour activity as monotherapy in cutaneous T-cell lymphoma and other haematological malignancies. In solid tumours, several HDAC inhibitors have been shown to be efficacious as single agents; however, results of most clinical trials were in favour of using HDAC inhibitors either prior to the initiation of chemotherapy or in combination with other treatments. Currently, the molecular basis of response to HDAC inhibitors in patients is not fully understood. In this review, we summarize the current status of HDAC inhibitors, as single agents or in combination with other agents in different phases of clinical trials. In most of the clinical trials, HDAC inhibitors were tolerable and exerted biological or antitumor activity. HDAC inhibitors have been studied in phase I, II and III clinical trials with variable efficacy. The combination of HDAC inhibitors with other anticancer agents including epigenetic or chemotherapeutic agents demonstrated favourable clinical outcome.

Proteomic analysis identifies protein targets responsible for depsipeptide sensitivity in tumor cells

Depsipeptide FR901228 (FK228) is a new kind of histone deacetylase inhibitors (HDACi) that induces growth arrest and cell death in a variety of tumor cells. Though its effects on oncogene expression and degradation have been documented, the detailed mechanism of FK228-induced cytotoxicity is still undefined. In this study, a differential proteomic analysis was performed to identify proteins associated with FK228-induced cytotoxicity in human lung cancer cells. Two-dimensional gel electrophoresis (2-DE) revealed a distinct protein profile of H322 cells in response to FK228 treatment, and 45 protein spots with significant alteration were screened. In total, 27 proteins were identified by mass spectrometry and involved in signal transduction, transcriptional regulation, metabolism, cytoskeletal organization, and protein folding, synthesis and degradation, consistent with multiple effects of FK228 on tumor cells. Notably, a novel target protein, thioredoxin reductase (TrxR), was identified, which is downregulated in FK228-sensitive cancer cells, but upregulated in resistant cells. The expression level of TrxR was negatively correlated with ROS accumulation, DNA damage and apoptosis, implicating TrxR in FK228-induced apoptosis and HDACi sensitivity in cancer cells. Thus, proteomic analysis provides new information about target proteins important for FK228-induced cytotoxicity in cancer cells.

Valproic acid resensitizes cisplatin-resistant ovarian cancer cells

Although certain inhibitors of histone deacetylases have been shown to induce cytotoxicity alone or in combination with chemotherapeutic agents in cancer cells, the molecular mechanism is not clear. The goal of the present study was to determine whether the antiseizure drug valproic acid (2-propylpentanoic acid; VPA), which is also able to inhibit histone deacetylase, exhibits synergistic cytotoxicity with cisplatin, and the possible pathways for this. Our results clearly show that VPA not only exhibits synergistic cytotoxicity with cisplatin in all of the ovarian carcinoma cells tested, but also can resensitize the cells that have acquired resistance to cisplatin. Consistent with the increased cytotoxicity, cotreatment with VPA was shown to upregulate the cisplatin-mediated DNA damage revealed by phosphorylation of ataxia telangiectasia mutation and histone H2AX. Reactive oxygen species accumulation and tumor suppressor phosphatase and tensin homolog (PTEN) overexpression, which could contribute to the enhanced cytotoxicity, were also observed to be upregulated by VPA. Because PTEN knockdown by small interference RNA or antioxidant treatment can reduce cisplatin-mediated cytotoxicity, it is suggested that upregulation of PTEN and reactive oxygen species by VPA contributes to the enhancement of cisplatin-mediated cytotoxicity. These results with resensitization of cisplatin-resistant cells particularly may provide benefits in the treatment of ovarian cancer patients.

Metabolic regulation of manganese superoxide dismutase expression via essential amino acid deprivation

Organisms respond to available nutrient levels by rapidly adjusting metabolic flux, in part through changes in gene expression. A consequence of adaptations in metabolic rate is the production of mitochondria-derived reactive oxygen species. Therefore, we hypothesized that nutrient sensing could regulate the synthesis of the primary defense of the cell against superoxide radicals, manganese superoxide dismutase. Our data establish a novel nutrient-sensing pathway for manganese superoxide dismutase expression mediated through essential amino acid depletion concurrent with an increase in cellular viability. Most relevantly, our results are divergent from current mechanisms governing amino acid-dependent gene regulation. This pathway requires the presence of glutamine, signaling via the tricarboxylic acid cycle/electron transport chain, an intact mitochondrial membrane potential, and the activity of both the MEK/ERK and mammalian target of rapamycin kinases. Our results provide evidence for convergence of metabolic cues with nutrient control of antioxidant gene regulation, revealing a potential signaling strategy that impacts free radical-mediated mutations with implications in cancer and aging.

Mechanisms of resistance to histone deacetylase inhibitors and their therapeutic implications

Histone deacetylase inhibitors (HDI) are a promising new approach to the treatment of cancer. HDIs have been shown to induce differentiation, cell cycle arrest, and apoptosis in a variety of transformed cell lines; inhibit tumor growth in animal models; and show antitumor activity in clinical trials. Vorinostat, which has shown clinical responses in approximately 30% of patients with advanced cutaneous T-cell lymphoma, is the first HDI approved for the treatment of cancer, and it is currently being evaluated in other indications. A better understanding of the molecular determinants of resistance to HDIs may provide the basis for therapeutic combinations with improved clinical efficacy. Poor response to treatment could be linked to systemic factors like pharmacokinetics or to tumor-specific factors both at the level of the malignant cells (tumor intrinsic) or the tumor microenvironment. This review focuses on the tumor intrinsic mechanisms of drug resistance (excluding mechanism of acquired resistance due to chronic exposure). In particular, attention is given to selected mechanisms that are relevant across chemical classes of HDIs and that can aid in the design of rational combination strategies.

Synergistic induction of apoptosis by HMG-CoA reductase inhibitor and histone deacetylases inhibitor in HeLa cells

HMG-CoA reductase inhibitors and histone deacetylases (HDACs) inhibitors have been shown to induce apoptosis in a variety of cells, which could potentially be used as an anticancer therapy in addition to the designated applications. In the present study, we explored the possible synergistic pro-apoptotic effects and the underlying mechanisms when the two classes of inhibitors were combined. Exposure of HeLa cells to the combined treatment of mevastatin (an inhibitor of HMG-CoA reductase) and trichostatin A (TSA) (an inhibitor of HDACs) synergistically induced apoptosis. Mevastatin treatment transcriptionally and translationally up-regulated RhoA expression in the cells by negative feedback mechanism. While TSA enhanced mevastatin-induced RhoA up-regulation, more importantly, it also accelerated mevastatin-mediated depletion of membrane-bound (geranylgeranylated) RhoA. Moreover, TSA treatment down-regulated protein geranylgeranyl transferase-I (GGTase-I) beta subunit expression, which is one of the key enzymes for protein geranylgeranylation. Taken together, TSA down-regulated GGTase-I beta expression, hence enhanced the statin-induced depletion of geranylgeranylated RhoA, which could be an important mechanism for the synergistic induction of the apoptosis.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid induces growth inhibition and enhances gemcitabine-induced cell death in pancreatic cancer

PURPOSE

Pancreatic cancer is an aggressive human malignancy that is generally refractory to chemotherapy. Histone deacetylase inhibitors are novel agents that modulate cell growth and survival. In this study, we sought to determine whether a relatively new histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), inhibits pancreatic cancer cell growth.

EXPERIMENTAL DESIGN

The effects of SAHA on the growth of three pancreatic cancer cell lines (BxPC3, COLO-357, and PANC-1) were examined with respect to cell cycle progression, p21 induction and localization, and interactions with the nucleoside analogue gemcitabine.

RESULTS

SAHA induced a G(1) cell cycle arrest in BxPC-3 cells and COLO-357 cells but not in PANC-1 cells. This arrest was dependent, in part, on induction of p21 by SAHA, as p21 was not induced in PANC-1 cells, and knockdown of p21 using small interfering RNA oligonucleotides nearly completely suppressed the effects of SAHA on cell cycle arrest in COLO-357 and partly attenuated the effects of SAHA in BxPC-3. COLO-357 and BxPC-3 cells, but not PANC-1 cells, were also sensitive to gemcitabine. In the gemcitabine-resistant PANC-1 cells, a 48-h cotreatment with SAHA rendered the cells sensitive to the inhibitory and proapoptotic effects of gemcitabine. An additive effect on growth inhibition by SAHA and gemcitabine was observed in COLO-357 and BxPC-3 cells. Moreover, analysis of p21 distribution in COLO-357 cells revealed that SAHA induced the cytoplasmic localization of both p21 and phospho-p21.

CONCLUSIONS

These data indicate that SAHA exerts proapoptotic effects in pancreatic cancer cells, in part, by up-regulating p21 and sequestering it in the cytoplasm, raising the possibility that SAHA may have therapeutic potential in the treatment of pancreatic cancer.

Mechanisms of interferon-beta-induced survival in fetal and neonatal primary astrocytes

BACKGROUND

We have previously shown that interferon-beta (IFN-beta) is a potent promoter of astrocyte survival. Although the mechanism(s) by which IFN-beta promotes astrocyte survival have not been completely elucidated, it has been shown that IFN-beta directly stimulates survival signaling pathways. In the present report, we took advantage of the differences in the susceptibility of fetal and neonatal astrocytes to apoptosis to further investigate the mechanism(s) underlying the antiapoptotic effect of IFN-beta.

METHODS

Primary monolayer cultures of cortical astrocytes were established from neonatal (3- to 6-day-old) or fetal (embryonic days: E15 or E17) Sprague-Dawley rat cerebral cortices. Apoptotic cell death was determined by fluorescent-microscopic analysis of staining patterns of cell DNA with Hoechst 33258, and determination of annexin V binding.Akt phosphorylation was detected by Western blottingusing a commercial kit that allows specific recognition of both non-phosphorylated and serine-phosphorylated Akt.

RESULTS

In the present work, we have found that primary astrocytes obtained from neonatal rats are resistant to apoptosis induced by serum starvation, though cell death may be induced by combining serum starvation with sodium butyrate treatment. This effect is counteracted by IFN-beta treatment through a mechanism that involves phosphatidylinositol 3-kinase stimulation.

CONCLUSIONS

IFN-beta can be considered as a neuroprotective agent and, therefore, part of its beneficial effects in multiple sclerosis (MS) treatment may depend on its capacity to protect astrocytes against the apoptotic cell death that occurs in the course of the MS lesions.

Antitumor activity of suberoylanilide hydroxamic acid against thyroid cancer cell lines in vitro and in vivo

PURPOSE

The histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), has multiple antitumor effects against a variety of human cancers.

EXPERIMENTAL DESIGN

We treated several anaplastic and papillary thyroid cancer cell lines with SAHA to determine if it could inhibit the growth of these cells in vitro and in vivo.

RESULTS

SAHA effectively inhibited 50% clonal growth of the anaplastic thyroid cancer cell lines, ARO and FRO, and the papillary thyroid cancer cell line, BHP 7-13, at 1.3x10(-7) to 5x10(-7) mol/L, doses that are achievable in patients. In concert with growth inhibition, SAHA down-regulated the expression of cyclin D1 and up-regulated levels of p21WAF1. Annexin V and cleavage of poly(ADP)ribose polymerase were both increased by exposure of the thyroid cancer cells to SAHA. Expression of the death receptor 5 (DR5) gene was also increased by SAHA, but the combination of the DR5 ligand, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), with SAHA had little effect compared with SAHA alone. Of note, the combination of paclitaxel, doxorubicin, or paraplatin with SAHA enhanced cell killing of the thyroid cancer cells. In addition, murine studies showed that SAHA administered daily by i.p. injection at 100 mg/kg inhibited the growth of human thyroid tumor cells.

CONCLUSION

Our data indicate that SAHA is a plausible adjuvant therapy for thyroid cancers.

Adaphostin and bortezomib induce oxidative injury and apoptosis in imatinib mesylate-resistant hematopoietic cells expressing mutant forms of Bcr/Abl

Effects of the tyrphostin adaphostin and bortezomib were examined in Bcr/Abl+ leukemia cell resistant to imatinib mesylate secondary to Bcr/Abl point mutations. Adaphostin was equally effective in inducing mitochondrial damage, caspase activation, JNK activation, and Raf-1, phospho-Stat3 and -Stat5 inactivation in mutant and wild-type cells, but differentially down-regulated phospho-Bcr/Abl. Adaphostin and bortezomib synergistically induced apoptosis in wild-type and mutant cells, including T315I mutants. Notably, adaphostin+/-bortezomib potently induced ROS and lethality in mutant cells, effects attenuated by the antioxidant NAC. These findings indicate that adaphostin+/-bortezomib circumvent imatinib resistance due to Bcr/Abl point mutations most likely through ROS generation.

The role of the NADPH oxidase complex, p38 MAPK, and Akt in regulating human monocyte/macrophage survival

M-CSF induces PI 3-kinase activation, resulting in reactive oxygen species (ROS) production. Previously, we reported that ROS mediate macrophage colony-stimulating factor (M-CSF)-induced extracellular regulated kinase (Erk) activation and monocyte survival. In this work, we hypothesized that M-CSF-stimulated ROS products modulated Akt1 and p38 activation. Furthermore, we sought to clarify the source of these ROS and the role of ROS and Akt in monocyte/macrophage survival. Macrophages from p47(phox-/-) mice, lacking a key component of the NADPH oxidase complex required for ROS generation, had reduced cell survival and Akt1 and p38 mitogen-activated protein kinase (MAPK) phosphorylation compared with wild-type macrophages in response to M-CSF stimulation, but had no difference in M-CSF-stimulated Erk. To understand how ROS affected monocyte survival and signaling, we observed that NAC and DPI decreased cell survival and Akt1 and p38 MAPK phosphorylation. Using bone marrow-derived macrophages from mice expressing constitutively activated Akt1 (Myr-Akt1) or transfecting Myr-Akt1 constructs into human peripheral monocytes, we concluded that Akt is a positive regulator of monocyte survival. Moreover, the p38 MAPK inhibitor, SB203580, inhibited p38 activity and M-CSF-induced monocyte survival. These findings demonstrate that ROS generated from the NADPH oxidase complex contribute to monocyte/macrophage survival induced by M-CSF via regulation of Akt and p38 MAPK.