Bortezomib sensitizes malignant human glioma cells to TRAIL, mediated by inhibition of the NF-{kappa}B signaling pathway

YM-155 potentiates the effect of ABT-737 in malignant human glioma cells via survivin and Mcl-1 downregulation in an EGFR-dependent context

Antiapoptotic proteins are commonly overexpressed in gliomas, contributing to therapeutic resistance. We recently reported that clinically achievable concentrations of the Bcl-2/Bcl-xL inhibitor ABT-737 failed to induce apoptosis in glioma cells, with persistent expression of survivin and Mcl-1. To address the role of these mediators in glioma apoptosis resistance, we analyzed the effects of YM-155, a survivin suppressant, on survival on a panel of glioma cell lines. YM-155 inhibited cell growth and downregulated survivin and Mcl-1 in a dose- and cell line-dependent manner. While U373, LN18, LNZ428, T98G, LN229, and LNZ308 cells exhibited an IC(50) of 10 to 75 nmol/L, A172 cells were resistant (IC(50) ∼ 250 nmol/L). No correlation was found between sensitivity to YM-155 and baseline expression of survivin or cIAP-1/cIAP-2/XIAP. However, strong correlation was observed between EGF receptor (EGFR) activation levels and YM-155 response, which was confirmed using EGFR-transduced versus wild-type cells. Because we postulated that decreasing Mcl-1 expression may enhance glioma sensitivity to ABT-737, we examined whether cotreatment with YM-155 promoted ABT-737 efficacy. YM-155 synergistically enhanced ABT-737-induced cytotoxicity and caspase-dependent apoptosis. Downregulation of Mcl-1 using short hairpin RNA also enhanced ABT-737-inducing killing, confirming an important role for Mcl-1 in mediating synergism between ABT-737 and YM-155. As with YM-155 alone, sensitivity to YM-155 and ABT-737 inversely correlated with EGFR activation status. However, sensitivity could be restored in highly resistant U87-EGFRvIII cells by inhibition of EGFR or its downstream pathways, highlighting the impact of EGFR signaling on Mcl-1 expression and the relevance of combined targeted therapies to overcome the multiple resistance mechanisms of these aggressive tumors.

Vorinostat and bortezomib synergistically cause ubiquitinated protein accumulation in prostate cancer cells

PURPOSE

Protein ubiquitination is a novel strategy used to treat malignancies. We investigated whether the histone deacetylase inhibitor vorinostat (Cayman Chemical, Ann Arbor, Michigan) and the proteasome inhibitor bortezomib (LC Laboratories, Woburn, Massachusetts) would synergistically cause the accumulation of ubiquitinated proteins in prostate cancer cells.

MATERIALS AND METHODS

LNCaP, PC-3 and DU 145 cells (ATCC™) were treated with vorinostat and/or bortezomib. Cell viability and induction of apoptosis were assessed. In vivo efficacy was evaluated in a murine subcutaneous tumor model using PC-3 cells. The influence of androgen receptor expression on bortezomib efficacy was examined using RNA interference. Changes in the expression of ubiquitinated proteins, cell cycle associated proteins and acetylated histone were evaluated.

RESULTS

Androgen receptor expression seemed to decrease bortezomib activity. PC-3 and DU 145 cells were more susceptible to bortezomib than LNCaP cells and the silencing of androgen receptor expression in LNCaP cells enhanced bortezomib activity. Vorinostat and bortezomib synergistically induced apoptosis, inhibited prostate cancer cell growth and suppressed tumor growth in a murine xenograft model. The combination decreased cyclin D1 and cyclin-dependent kinase 4 expression, and increased p21 expression. The combination synergistically caused the accumulation of ubiquitinated proteins and histone acetylation. This histone acetylation was a consequence of the accumulation of ubiquitinated proteins.

CONCLUSIONS

Vorinostat and bortezomib inhibit the growth of prostate cancer cells synergistically by causing ubiquitinated proteins to accumulate in cells. The current study provides a framework for testing the combination in patients with advanced prostate cancer.

Bortezomib and TRAIL: a perfect match for apoptotic elimination of tumour cells?

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine that selectively eradicates tumour cells via specific cell surface receptors and is intensively explored for use as a novel anticancer approach. To enhance the efficacy of TRAIL receptor agonists the proteasome inhibitor bortezomib is one of the most potent sensitizers. Here we review the main mechanisms underlying bortezomib-dependent TRAIL sensitization, including stimulation of apoptosis by increasing expression of TRAIL receptors, reduction of cFLIP and enhancement of caspase 8 activation, and modulation of Bcl-2 family proteins and inhibitor of apoptosis proteins (IAPs). Concomitantly, pro-survival signals are suppressed such as elicited by NF-κB and Akt. The different preclinical tumour models explored with this combination, including primary tumour (stem) cells, stroma co-culture and mice models, are discussed, as well as possible hurdles for clinical activity. Collectively, anticipating a solid rationale for bortezomib-TRAIL combination and very promising preclinical results, its clinical activity remains to be demonstrated.

The inhibitory effect of MSCs expressing TRAIL as a cellular delivery vehicle in combination with cisplatin on hepatocellular carcinoma

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been demonstrated to induce cell apoptosis in many types of tumors, while many hepatocellular carcinoma (HCC) cells display high resistance to TRAIL. Another outstanding limitation of TRAIL is the short half-life in vivo. Stem cell-based therapies provide a promising approach for the treatment of many types of tumors because of the ability of tropism. Therefore, as a new therapeutic strategy, the combination of chemotherapeutic agents and TRAIL gene modified MSCs (TRAIL-MSCs) would improve the therapeutic efficacy of HCC in vivo. This is the first time to show the potential of combination of chemotherapeutic agents and MSCs as a gene vector in the therapy of HCC.

ABT-737 synergizes with bortezomib to induce apoptosis, mediated by Bid cleavage, Bax activation, and mitochondrial dysfunction in an Akt-dependent context in malignant human glioma cell lines

We observed that glioma cells are differentially sensitive to N-{4-[4-(4'-chloro-biphenyl-2-ylmethyl)-piperazin-1-yl]-benzoyl}-4-(3-dimethylamino-1-phenylsulfanylmethyl-propylamino)-3-nitro-benzenesulfonamide (ABT-737) and administration of ABT-737 at clinically achievable doses failed to induce apoptosis. Although elevated Bcl-2 levels directly correlated with sensitivity to ABT-737, overexpression of Bcl-2 did not influence sensitivity to ABT-737. To understand the molecular basis for variable and relatively modest sensitivity to the Bcl-2 homology domain 3 mimetic drug ABT-737, the abundance of Bcl-2 family members was assayed in a panel of glioma cell lines. Bcl-2 family member proteins, Bcl-xL, Bcl-w, Mcl-1, Bax, Bak, Bid, and Noxa, were found to be expressed ubiquitously at similar levels in all cell lines tested. We then examined the contribution of other apoptosis-resistance pathways to ABT-737 resistance. Bortezomib, an inhibitor of nuclear factor-kappaB (NF-κB), was found to enhance sensitivity of ABT-737 in phosphatase and tensin homolog on chromosome 10 (PTEN)-wild type, but not PTEN-mutated glioma cell lines. We therefore investigated the association between phosphatidylinositol 3-kinase (PI3K)/Akt activation and resistance to the combination of ABT-737 and bortezomib in PTEN-deficient glioma cells. Genetic and pharmacological inhibition of PI3K inhibition sensitized PTEN-deficient glioma cells to bortezomib- and ABT-737-induced apoptosis by increasing cleavage of Bid protein, activation and oligomerization of Bax, and loss of mitochondrial membrane potential. Our data further suggested that PI3K/Akt-dependent protection may occur upstream of the mitochondria. This study demonstrates that interference with multiple apoptosis-resistance signaling nodes, including NF-κB, Akt, and Bcl-2, may be required to induce apoptosis in highly resistant glioma cells, and therapeutic strategies that target the PI3K/Akt pathway may have a selective role for cancers lacking PTEN function.

Bortezomib-induced sensitization of malignant human glioma cells to vorinostat-induced apoptosis depends on reactive oxygen species production, mitochondrial dysfunction, Noxa upregulation, Mcl-1 cleavage, and DNA damage

Glioblastomas are invasive tumors with poor prognosis despite current therapies. Histone deacetylase inhibitors (HDACIs) represent a class of agents that can modulate gene expression to reduce tumor growth, and we and others have noted some antiglioma activity from HDACIs, such as vorinostat, although insufficient to warrant use as monotherapy. We have recently demonstrated that proteasome inhibitors, such as bortezomib, dramatically sensitized highly resistant glioma cells to apoptosis induction, suggesting that proteasomal inhibition may be a promising combination strategy for glioma therapeutics. In this study, we examined whether bortezomib could enhance response to HDAC inhibition in glioma cells. Although primary cells from glioblastoma multiforme (GBM) patients and established glioma cell lines did not show significant induction of apoptosis with vorinostat treatment alone, the combination of vorinostat plus bortezomib significantly enhanced apoptosis. The enhanced efficacy was due to proapoptotic mitochondrial injury and increased generation of reactive oxygen species. Our results also revealed that combination of bortezomib with vorinostat enhanced apoptosis by increasing Mcl-1 cleavage, Noxa upregulation, Bak and Bax activation, and cytochrome c release. Further downregulation of Mcl-1 using shRNA enhanced cell killing by the bortezomib/vorinostat combination. Vorinostat induced a rapid and sustained phosphorylation of histone H2AX in primary GBM and T98G cells, and this effect was significantly enhanced by co-administration of bortezomib. Vorinostat/bortezomib combination also induced Rad51 downregulation, which plays an important role in the synergistic enhancement of DNA damage and apoptosis. The significantly enhanced antitumor activity that results from the combination of bortezomib and HDACIs offers promise as a novel treatment for glioma patients.

Different effects of bortezomib on the expressions of various protein kinase C isoenzymes in T cells of patients with systemic lupus erythematosus and in Jurkat cells

The effects of proteosome inhibitor Bortezomib (BZ) were studied in vitro for 24 h on the protein kinase C (PKC) profiles, rates of proliferation and apoptosis in Jurkat cells and lymphocytes of 10 patients with systemic lupus erythematosus (SLE) and nine healthy subjects. The expressions of PKC proteins, the rates of proliferation and apoptosis were determined. The effects of BZ were different in the Jurkat and lupus T cells. Whereas BZ elevated the expression of PKC θ, δ and ξ isoenzymes in the Jurkat cells, it was unable to do that in the lupus T cells. BZ induced a dose-dependent increase in the apoptosis of Jurkat cells, while decreased the proliferation. The same effect of BZ was observed on the apoptosis of lymphocytes both in SLE and healthy subjects at concentrations higher than the therapeutic dose. We conclude that BZ treatment in vitro was not able to restore the SLE-specific defect (decrease) in the expression of PKC isoenzymes in the T cells as it was expected. This can be a limiting factor in the positive clinical effects of BZ in lupus.

Targeting p53 as a therapeutic strategy in sensitizing TRAIL-induced apoptosis in cancer cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been intensively studied as a cancer therapeutic agent due to its unique ability to induce apoptosis in malignant cells but not in normal cells. However, as more human cancer cells are reported to be resistant to TRAIL treatment, it is important to develop new therapeutic strategies to overcome this resistance. p53 is an important tumor suppressor that is widely involved in cellular responses to various stresses. In this mini-review, we aim to provide an overview of the intricate relationship between p53 and the TRAIL-mediated apoptosis pathway, and to summarize the current approaches of targeting p53 as a therapeutic strategy to sensitize TRAIL-induced apoptosis in human cancer cells. Although in some cases TRAIL kills cancer cells in a p53-independent manner, it is believed that in cancers with wild-type and functional p53, targeting p53 may be an important strategy for overcoming TRAIL-resistance in cancer therapy.

Combined inhibition of DNA methyltransferase and histone deacetylase restores caspase-8 expression and sensitizes SCLC cells to TRAIL

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising drug for the treatment of tumors; however, a number of cancer cells are resistant to this cytokine. Among the mechanisms of resistance of small cell lung carcinomas (SCLCs) to TRAIL is the lack of caspase-8 expression. Although methylation of the caspase-8 promoter has been suggested as the main mechanism of caspase-8 silencing, we showed that reduction of the enzymes involved in DNA methylation, DNA methyltransferases (DNMT) 1, 3a and 3b, was not sufficient to significantly restore caspase-8 expression in SCLC cells, signifying that other mechanisms are involved in caspase-8 silencing. We found that combination of the DNMT inhibitor decitabine with an inhibitor of histone deacetylase (HDAC) significantly increased caspase-8 expression in SCLC cells at the RNA and protein levels. Among all studied HDAC inhibitors, valproic acid (VPA) and CI-994 showed prolonged effects on histone acetylation, while combination with decitabine produced the most prominent effects on caspase-8 re-expression. Moreover, a significant reduction of survivin and cIAP-1 proteins level was observed after treatment with VPA. The combination of two drugs sensitized SCLC cells to TRAIL-induced apoptosis, involving mitochondrial apoptotic pathway and was accompanied by Bid cleavage, activation of Bax, and release of cytochrome c. Both initiator caspase-8 and -9 were required for the sensitization of SCLC cells to TRAIL. Thus, efficient restoration of caspase-8 expression in SCLC cells is achieved when a combination of DNMT and HDAC inhibitors is used, suggesting a combination of decitabine and VPA or CI-994 as a potential treatment for sensitization of SCLC cells lacking caspase-8 to TRAIL.

Potential usage of proteasome inhibitor bortezomib (Velcade, PS-341) in the treatment of metastatic melanoma: basic and clinical aspects

Protein degradation by proteasome is essential to the regulation of important cellular functions including cell cycle progression, proliferation, differentiation and apoptosis. Abnormal proteasomal degradation of key regulatory proteins perturbs the normal dynamics of these cellular processes culminating in uncontrolled cell cycle progression and decreased apoptosis leading to the characteristic cancer cell phenotype. Proteasome inhibitors are a novel group of therapeutic agents designed to oppose the increased proteasomal degradation observed in various cancers while restoring key cellular functions such as apoptosis, cell cycle progression, and the inhibition of angiogenesis. Several proteasome inhibitors have been evaluated in pre- and clinical studies for their potential usage in clinical oncology. Bortezomib (Velcade, PS-341) is the first Food and Drug Administration-approved proteasome inhibitor for the treatment of multiple myeloma and mantle cell lymphoma. Bortezomib's ability to preferentially induce toxicity and cell death in tumor cells while rendering healthy cells unaffected makes it a powerful therapeutic agent and has extended its use in other types of malignancies. The ability of bortezomib and other proteasome inhibitors to synergize with conventional therapies in killing tumors in various in vitro and in vivo models makes this class of drugs a powerful tool in overcoming acquired and inherent resistance observed in many cancers. This is achieved through modulation of aberrant cellular survival signal transduction pathways and their downstream anti-apoptotic gene products. This review will discuss the anti-neoplastic effects of various proteasome inhibitors in a variety of cancers with a special emphasis on bortezomib, its mechanism of action and role in cancer therapy. We further discuss the potential use of bortezomib in the treatment of metastatic melanoma.