Homoharringtonine and SAHA synergistically enhance apoptosis in human acute myeloid leukemia cells through upregulation of TRAIL and death receptors

Investigating the synergistic potential of TRAIL and SAHA in inducing apoptosis in MOLT-4 cancer cells

INTRODUCTION

T-cell acute lymphoblastic leukemia is characterized by its fast progression rate and high complications. TRAIL can be used to trigger apoptosis in cancer cells with minimal effects on normal cells, but most of cancer cells develop resistance to this agent through various mechanisms. HDAC inhibitors like SAHA can be used to make cancer cells more susceptible to TRAIL-induced apoptosis. In this study, this hypothesis was tested on MOLT-4 cancer cell line.

MATERIALS AND METHODS

The cells were divided into six groups including the control group, TRAIL 50 nM, TRAIL 100 nM, SAHA 2 μM, SAHA 2 μM + TRAIL 50 nM, and SAHA 2 μM + TRAIL 100 nM. Apoptosis was evaluated by flowcytometry after 24, 48 and 72 h. The expression levels of c-flip, DR4, DR5, CHOP, NF-κB, STAT3, Akt, and PI3K genes were investigated by quantitative real-time PCR. Data were analyzed using two-way variance analysis with Tukey's and Dunnett's multiple comparisons tests, and statistical significance was defined as having a p-value less than 0.05.

RESULTS

Groups exposed to the combination of SAHA with TRAIL demonstrated the maximum apoptosis in MOLT-4 cells by increasing the expression of DR4, DR5, and CHOP and decreasing the expression of c-flip, STAT3, PI3k, Akt, and NF-kB genes.

CONCLUSION

It can be concluded that SAHA increases the sensitivity of MOLT-4 cells to TRAIL-mediated apoptosis, which can be used as a strategy to overcome resistance to TRAIL in leukemic patients.

Regulation of anoikis by extrinsic death receptor pathways

Metastatic cancer cells can develop anoikis resistance in the absence of substrate attachment and survive to fight tumors. Anoikis is mediated by endogenous mitochondria-dependent and exogenous death receptor pathways, and studies have shown that caspase-8-dependent external pathways appear to be more important than the activity of the intrinsic pathways. This paper reviews the regulation of anoikis by external pathways mediated by death receptors. Different death receptors bind to different ligands to activate downstream caspases. The possible mechanisms of Fas-associated death domain (FADD) recruitment by Fas and TNF receptor 1 associated-death domain (TRADD) recruitment by tumor necrosis factor receptor 1 (TNFR1), and DR4- and DR5-associated FADD to induce downstream caspase activation and regulate anoikis were reviewed. This review highlights the possible mechanism of the death receptor pathway mediation of anoikis and provides new insights and research directions for studying tumor metastasis mechanisms. Video Abstract.

Ribosome-Directed Therapies in Cancer

The human ribosomes are the cellular machines that participate in protein synthesis, which is deeply affected during cancer transformation by different oncoproteins and is shown to provide cancer cell proliferation and therefore biomass. Cancer diseases are associated with an increase in ribosome biogenesis and mutation of ribosomal proteins. The ribosome represents an attractive anti-cancer therapy target and several strategies are used to identify specific drugs. Here we review the role of different drugs that may decrease ribosome biogenesis and cancer cell proliferation.

The Metabolic Signature of AML Cells Treated With Homoharringtonine

Acute myeloid leukemia (AML) is a hematologic malignancy. The overall prognosis is poor and therapeutic strategies still need to be improved. Studies have found that abnormalities in metabolisms promote the survival of AML cells. In recent years, an increasing number of studies have reported the effectiveness of a protein synthesis inhibitor, homoharringtonine (HHT), for the treatment of AML. In this study, we demonstrated that HHT effectively inhibited AML cells, especially MV4-11, a cell line representing human AML carrying the poor prognostic marker FLT3-ITD. We analyzed the transcriptome of MV4-11 cells treated with HHT, and identified the affected metabolic pathways including the choline metabolism process. In addition, we generated a line of MV4-11 cells that were resistant to HHT. The transcriptome analysis showed that the resistant mechanism was closely related to the ether lipid metabolism pathway. The key genes involved in these processes were AL162417.1, PLA2G2D, and LPCAT2 by multiple intergroup comparison and Venn analysis. In conclusion, we found that the treatment of HHT significantly changed metabolic signatures of AML cells, which may contribute to the precise clinical use of HHT and the development of novel strategies to treat HHT-resistant AML.

Targeting the Human 80S Ribosome in Cancer: From Structure to Function and Drug Design for Innovative Adjuvant Therapeutic Strategies

The human 80S ribosome is the cellular nucleoprotein nanomachine in charge of protein synthesis that is profoundly affected during cancer transformation by oncogenic proteins and provides cancerous proliferating cells with proteins and therefore biomass. Indeed, cancer is associated with an increase in ribosome biogenesis and mutations in several ribosomal proteins genes are found in ribosomopathies, which are congenital diseases that display an elevated risk of cancer. Ribosomes and their biogenesis therefore represent attractive anti-cancer targets and several strategies are being developed to identify efficient and specific drugs. Homoharringtonine (HHT) is the only direct ribosome inhibitor currently used in clinics for cancer treatments, although many classical chemotherapeutic drugs also appear to impact on protein synthesis. Here we review the role of the human ribosome as a medical target in cancer, and how functional and structural analysis combined with chemical synthesis of new inhibitors can synergize. The possible existence of oncoribosomes is also discussed. The emerging idea is that targeting the human ribosome could not only allow the interference with cancer cell addiction towards protein synthesis and possibly induce their death but may also be highly valuable to decrease the levels of oncogenic proteins that display a high turnover rate (MYC, MCL1). Cryo-electron microscopy (cryo-EM) is an advanced method that allows the visualization of human ribosome complexes with factors and bound inhibitors to improve our understanding of their functioning mechanisms mode. Cryo-EM structures could greatly assist the foundation phase of a novel drug-design strategy. One goal would be to identify new specific and active molecules targeting the ribosome in cancer such as derivatives of cycloheximide, a well-known ribosome inhibitor.

Adjuvant Epigenetic Therapy of Decitabine and Suberoylanilide Hydroxamic Acid Exerts Anti-Neoplastic Effects in Acute Myeloid Leukemia Cells

Atypical epigenetic processes including histone acetylation and DNA methylation have been identified as a fundamental theme in hematologic malignancies. Such mechanisms modify gene expression and prompt, in part at least, the initiation and progression of several malignancies including acute myeloid leukemia. In the current study we determined the effects of treating KG-1 and U937 acute myeloid leukemia (AML) cells, in vitro, with the HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA), or with a DNMT inhibitor, decitabine (DAC), or their combination, on cell proliferation, cell cycle progression, apoptosis, and expression of apoptosis-related proteins. Each of SAHA and DAC attenuated cell proliferation and induced cell cycle arrest and apoptotic cell death of KG-1 and U937 cell lines. Besides, their sequential combination improved the obtained anti-neoplastic effect: significant augmentation of growth inhibition and apoptosis induction as compared to cells treated with either drug alone. This effect was featured by the upregulated expression of Bax, cytochrome c1, p21, and cleaved caspases 8, 9, and 3, signifying the activation of both the intrinsic and extrinsic pathways of apoptosis. The sequential combination of SAHA and DAC causes a profound antitumorigenic effect in AML cell lines by inducing the expression of tumor suppressor genes.

Epigenetic Regulation of TRAIL Signaling: Implication for Cancer Therapy

One of the main characteristics of carcinogenesis relies on genetic alterations in DNA and epigenetic changes in histone and non-histone proteins. At the chromatin level, gene expression is tightly controlled by DNA methyl transferases, histone acetyltransferases (HATs), histone deacetylases (HDACs), and acetyl-binding proteins. In particular, the expression level and function of several tumor suppressor genes, or oncogenes such as c-Myc, p53 or TRAIL, have been found to be regulated by acetylation. For example, HATs are a group of enzymes, which are responsible for the acetylation of histone proteins, resulting in chromatin relaxation and transcriptional activation, whereas HDACs by deacetylating histones lead to chromatin compaction and the subsequent transcriptional repression of tumor suppressor genes. Direct acetylation of suppressor genes or oncogenes can affect their stability or function. Histone deacetylase inhibitors (HDACi) have thus been developed as a promising therapeutic target in oncology. While these inhibitors display anticancer properties in preclinical models, and despite the fact that some of them have been approved by the FDA, HDACi still have limited therapeutic efficacy in clinical terms. Nonetheless, combined with a wide range of structurally and functionally diverse chemical compounds or immune therapies, HDACi have been reported to work in synergy to induce tumor regression. In this review, the role of HDACs in cancer etiology and recent advances in the development of HDACi will be presented and put into perspective as potential drugs synergizing with TRAIL's pro-apoptotic potential.

Natural Agents-Mediated Targeting of Histone Deacetylases

In the past few years, basic and clinical scientists have witnessed landmark achievements in many research projects, such as those conducted by the US National Institutes of Health Roadmap Epigenomics Mapping Consortium, the International Human Epigenome Consortium, The Cancer Genome Atlas Network and the International Cancer Genome Consortium, which have provided near-complete resolution of epigenetic landscape in different diseases. Furthermore, genome sequencing of tumors has provided compelling evidence related to frequent existence of mutations in readers, erasers and writers of epigenome in different cancers. Histone acetylation is an intricate mechanism modulated by two opposing sets of enzymes and deeply studied as a key biological phenomenon in 1964 by Vincent Allfrey and colleagues. The research group suggested that this protein modification contributed substantially in transcriptional regulation. Subsequently, histone deacetylases (HDACs), histone acetyltransferases and acetyl-Lys-binding proteins were identified as transcriptional mediators, which further deepened our comprehension regarding biochemical modifications. Overwhelmingly increasing high-impact research is improving our understanding of this molecularly controlled mechanism; moreover, quantification and identification of lysine acetylation by mass spectrometry has added new layers of information. We partition this multi-component review into how both activity and expression of HDAC are targeted using natural agents. We also set spotlight on how oncogenic fusion proteins tactfully utilize HDAC-associated nano-machinery to modulate expression of different genes and how HDAC inhibitors regulate TRAIL-induced apoptosis in cancer cells. HDAC inhibitors have been reported to upregulate expression of TRAIL receptors and protect TRAIL from proteasomal degradation. Deeper understanding of HDAC biology will be useful for stratification and selection of patients who are responders, non-responders and poor-responders for HDACi therapy, and for the rational design of combination studies using HDACi.

Omacetaxine mepesuccinate induces apoptosis and cell cycle arrest, promotes cell differentiation, and reduces telomerase activity in diffuse large B‑cell lymphoma cells

Clinical studies have demonstrated that omacetaxine mepesuccinate exerts beneficial effects on acute myelogenous leukemia. It has been suggested that omacetaxine mepesuccinate, used alone or with interferon-α or cytarabine, induces remission in patients with chronic myelogenous leukemia. These effects are possibly mediated by its ability to induce apoptosis of leukemia cells and inhibit the activity of telomerase. To determine whether omacetaxine mepesuccinate is beneficial in diffuse large B-cell lymphoma (DLBCL), two DLBCL cell lines [a germinal center B cell-like subtype (GCB) and an activated B cell-like subtype (ABC)] were treated with omacetaxine mepesuccinate at various concentrations for different durations. The present study indicated that omacetaxine mepesuccinate exerts proapoptotic effects in the two cell types in a dose- and time-dependent manner. The ABC subtype demonstrated increased sensitivity compared with the GCB subtype. At 40 ng/ml, omacetaxine mepesuccinate exhibited a marked proapoptotic effect on DLBCL cells compared with the other tumor cells investigated. Furthermore, omacetaxine mepesuccinate induced cell cycle arrest at G₀/G₁ phase, and promoted cell terminal differentiation of pro-B cells. The present study also demonstrated that omacetaxine mepesuccinate exerted its antitumor effect by reducing telomerase activity. In conclusion, the present study demonstrated that omacetaxine mepesuccinate may induce apoptosis and cell cycle arrest, promote cell differentiation, and reduce telomerase activity in DLBCL cells, thus aiding the development of omacetaxine mepesuccinate-based DLBCL therapeutic strategies.

Comprehensive identification of genes driven by ERV9-LTRs reveals TNFRSF10B as a re-activatable mediator of testicular cancer cell death

The long terminal repeat (LTR) of human endogenous retrovirus type 9 (ERV9) acts as a germline-specific promoter that induces the expression of a proapoptotic isoform of the tumor suppressor homologue p63, GTAp63, in male germline cells. Testicular cancer cells silence this promoter, but inhibitors of histone deacetylases (HDACs) restore GTAp63 expression and give rise to apoptosis. We show here that numerous additional transcripts throughout the genome are driven by related ERV9-LTRs. 3' Rapid amplification of cDNA ends (3'RACE) was combined with next-generation sequencing to establish a large set of such mRNAs. HDAC inhibitors induce these ERV9-LTR-driven genes but not the LTRs from other ERVs. In particular, a transcript encoding the death receptor DR5 originates from an ERV9-LTR inserted upstream of the protein coding regions of the TNFRSF10B gene, and it shows an expression pattern similar to GTAp63. When treating testicular cancer cells with HDAC inhibitors as well as the death ligand TNF-related apoptosis-inducing ligand (TRAIL), rapid cell death was observed, which depended on TNFRSF10B expression. HDAC inhibitors also cooperate with cisplatin (cDDP) to promote apoptosis in testicular cancer cells. ERV9-LTRs not only drive a large set of human transcripts, but a subset of them acts in a proapoptotic manner. We propose that this avoids the survival of damaged germ cells. HDAC inhibition represents a strategy of restoring the expression of a class of ERV9-LTR-mediated genes in testicular cancer cells, thereby re-enabling tumor suppression.

Synergistic combination of histone deacetylase inhibitor suberoylanilide hydroxamic acid and oncolytic adenovirus ZD55-TRAIL as a therapy against cervical cancer

Oncolytic adenoviruses (OA) have been investigated as virotherapeutic agents for the treatment of cervical cancer and thus far results are promising. However, the cytotoxicity of the viruses requires improvement. The present study demonstrated that this can be achieved by combining ZD55-TRAIL, an OA containing the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene, with the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA). It was demonstrated that these agents act synergistically to kill HeLa cells by inducing G2 growth arrest and apoptosis. Notably, in a mouse xenograft model, ZD55-TRAIL/SAHA combination inhibited tumor growth. At the molecular level, it was found that upregulation of IκBα and the p50 and p65 subunits of nuclear factor-κB induced by ZD55-TRAIL, can be abrogated by SAHA treatment. These data strongly suggested that ZD55-TRAIL/SAHA co-treatment may serve as an effective therapeutic strategy against cervical cancer.

Phenethyl isothiocyanate sensitizes glioma cells to TRAIL-induced apoptosis

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) is a promising antitumor therapy. However, many cancer cells, including malignant glioma cells, tend to be resistant to TRAIL, highlighting the need for strategies to overcome TRAIL resistance. Here we show that in combination with phenethyl isothiocyanate (PEITC), exposure to TRAIL induced apoptosis in TRAIL-resistant glioma cells. Subtoxic concentrations of PEITC significantly potentiated TRAIL-induced cytotoxicity and apoptosis in glioma cells. PEITC dramatically upregulated DR5 receptor expression but had no effects on DR4 receptor. PEITC enhances TRAIL-induced apoptosis through the downregulation of cell survival proteins and the upregulation of DR5 receptors through actions on the ROS-induced-p53.