The proteasome inhibitor bortezomib interacts synergistically with histone deacetylase inhibitors to induce apoptosis in Bcr/Abl+ cells sensitive and resistant to STI571

Promoting reactive oxygen species accumulation to overcome tyrosine kinase inhibitor resistance in cancer

BACKGROUND

In tumor treatment, protein tyrosine kinase inhibitors (TKIs) have been extensively utilized. However, the efficacy of TKI is significantly compromised by drug resistance. Consequently, finding an effective solution to overcome TKI resistance becomes crucial. Reactive oxygen species (ROS) are a group of highly active molecules that play important roles in targeted cancer therapy including TKI targeted therapy. In this review, we concentrate on the ROS-associated mechanisms of TKI lethality in tumors and strategies for regulating ROS to reverse TKI resistance in cancer.

MAIN BODY

Elevated ROS levels often manifest during TKI therapy in cancers, potentially causing organelle damage and cell death, which are critical to the success of TKIs in eradicating cancer cells. However, it is noteworthy that cancer cells might initiate resistance pathways to shield themselves from ROS-induced damage, leading to TKI resistance. Addressing this challenge involves blocking these resistance pathways, for instance, the NRF2-KEAP1 axis and protective autophagy, to promote ROS accumulation in cells, thereby resensitizing drug-resistant cancer cells to TKIs. Additional effective approaches inducing ROS generation within drug-resistant cells and providing exogenous ROS stimulation.

CONCLUSION

ROS play pivotal roles in the eradication of tumor cells by TKI. Harnessing the accumulation of ROS to overcome TKI resistance is an effective and widely applicable approach.

HDAC inhibitors: Promising agents for leukemia treatment

The essential role of epigenetic modification in the pathogenesis of a series of cancers have gradually been recognized. Histone deacetylase (HDACs), as well-known epigenetic modulators, are responsible for DNA repair, cell proliferation, differentiation, apoptosis and angiogenesis. Studies have shown that aberrant expression of HDACs is found in many cancer types. Thus, inhibition of HDACs has provided a promising therapeutic approach alternative for these patients. Since HDAC inhibitor (HDACi) vorinostat was first approved by the Food and Drug Administration (FDA) for treating cutaneous T-cell lymphoma (CTCL) in 2006, the combination of HDAC inhibitors with other molecules such as chemotherapeutic drugs has drawn much attention in current cancer treatment, especially in hematological malignancies therapy. Up to now, there have been more than twenty HDAC inhibitors investigated in clinic trials with five approvals being achieved. Indeed, Histone deacetylase inhibitors promote or enhance several different anticancer mechanisms and therefore are in evidence as potential antileukemia agents. In this review, we will focus on possible mechanisms by how HDAC inhibitors exert therapeutic benefit and their clinical utility in leukemia.

Phase 1 study of belinostat (PXD-101) and bortezomib (Velcade, PS-341) in patients with relapsed or refractory acute leukemia and myelodysplastic syndrome

We report the results of a phase 1 dose-escalation study of belinostat and bortezomib in adult patients with acute leukemia or MDS or CML with blast crisis. Thirty-eight patients received IV belinostat days 1-5 and 8-12 with IV bortezomib days 1, 4, 8, and 11 every 21 days. QTc prolongation was the only identified DLT. The RP2Ds were 1.3 mg/m² bortezomib and 1000 mg/m² belinostat. One patient with highly refractory MLL-ENL rearranged biphenotypic AML with multiple karyotypic aberrations had a complete pathologic and karyotypic response. One patient with post-MPN AML remained on study with stable disease (SD) for 32 cycles. Whole-exome sequencing revealed no aberrations in the first patient and a hyper-mutator genotype in the second. Eighteen patients had a best response of SD. We conclude that this treatment strategy is feasible but has limited activity in this population. Nevertheless, the factors that predict exceptional responses to this strategy warrant further investigation.

An investigation of the mechanisms underlying the proteasome inhibitor bortezomib resistance in PC3 prostate cancer cell line

The phenomenon of acquired resistance to chemotherapeutic agents is a long-standing conundrum in cancer treatment. To help delineate drug resistance mechanisms and pave the way for the development of novel strategies, we generated a PC3 prostate cancer cell line resistant to proteasome inhibitor bortezomib for the first time. The resistant cells were found to have an IC₅₀ value of 359.6 nM, whereas the IC₅₀ value of parental cells was 82.6 nM after 24 h of treatment with varying doses of bortezomib. The resistant cells were also partly cross-resistant to the novel proteasome inhibitor carfilzomib; however, they were not resistant to widely used chemotherapeutic agent vincristine sulfate, indicating that enhanced cellular drug efflux via the multidrug resistance (MDR) transporters is not the molecular basis of the resistance. Since both bortezomib and carfilzomib target and inhibit the chymotrypsin-related activity residing in the β5 subunit of the proteasome (PSMB5), we next examined its expression and found surprisingly no significant alteration in the expression profile of the mature form. However, a significant increase in the accumulation of the precursor form of PSMB5 in response to 100 nM bortezomib was observed in the parental cells without a significant accumulation in the resistant cells. The results presented here thus suggest that the molecular mechanisms causing resistance to proteasome inhibitors need to be examined in-depth to overcome the resistance to ubiquitin-proteasome pathway inhibitors in cancer treatment.

Overexpression of miR-4433 by suberoylanilide hydroxamic acid suppresses growth of CML cells and induces apoptosis through targeting Bcr-Abl

Background: Targeting Bcr-Abl is the key for the treatment of CML. Although great progress has been achieved for the treatment of CML patients in chronic stage, effective drugs with good safety are not available for those in advanced stages of CML patients. In present study, a histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), was used to screen for microRNA that can target Bcr-Abl.

Methods: RT-qPCR was used to determine Bcr-Abl and miR-4433 transcription level in CML cells. In CML cells, Proteins including PARP, caspase-3, acetyl-histone 3, histone 3 and Bcr-Abl, as well as Bcr-Abl downstream proteins were detected using western blot. Cell viability and apoptosis were monitored respectively by MTS assay and flow cytometry. The correlation between miR-4433 and Bcr-Abl was determined by luciferase reporter assay. The anti-tumor effect of miR-4433 to K562 cells was evaluated by nude mouse xenograft model in vivo.

Results: SAHA up-regulated the acetylation level of histone 3, and effectively inhibited Bcr-Abl mRNA level and its downstream signal transduction pathway, while inhibiting the growth of CML cells and inducing apoptosis. Furthermore, bioinformatics tools predicted that miR-4433 is a putative microRNA targeting Bcr-Abl and that the expression level of miR-4433 was significantly increased after SAHA treatment in K562 cells. Luciferase activity analysis revealed that miR-4433 directly targets Bcr-Abl. Additionally, transient expression of miR-4433 abrogated Bcr-Abl activity and its downstream signaling pathways while inducing apoptosis in K562 cells. Moreover, stable expression of miR-4433 suppressed Bcr-Abl and its downstream signaling pathway, and inhibited the growth of K562 cells in vitro and the growth of K562-xenografts in nude mice.

Conclusion: miR-4433 was identified as a microRNA targeting Bcr-Abl, which may be subject to epigenetic regulation of SAHA, a histone deacetylase inhibitor that has been approved by the US FDA for the treatment of cutaneous T-cell lymphoma. The findings of this study provide a molecular basis from another angle for the use of SAHA in the treatment of CML.

The role of proteasome activity for activating and inhibitory signalling in human platelets

Platelets express key proteins of the proteasome system, but its functional role in the regulation of platelet integrity, however, is not fully understood yet. Therefore, this study evaluated activating and inhibitory platelet signalling pathways using the potent and selective proteasome inhibitor bortezomib. In washed platelets, the effect of bortezomib on viability and on aggregation was assessed. In addition, fibrinogen binding and CD62P expression were determined. The influence on activating and inhibitory signalling was detected by phosphorylation levels of essential messenger molecules. Platelet viability was maintained after incubation with 0.01 μM to 1 μM bortezomib, but tampered with 100 μM bortezomib. Agonist-induced aggregation was only reduced under 100 μM bortezomib and with weak induction by 10 μM adenosine diphosphate. Similarly, phosphorylated kinase levels of the activating signalling pathways were not affected by 0.01 μM to 1 μM bortezomib. In contrast, proteasome inhibition resulted in the reduction of inhibitor-induced vasodilator-stimulated phosphoprotein phosphorylation, accompanied with the partial decrease of induced inhibition of fibrinogen binding and CD62P expression. In conclusion, platelet activation and aggregation are not dependent on proteasome activity. Instead, inhibitory signalling is partially attenuated under proteasome inhibition. Supramaximal inhibitory concentrations of bortezomib (above 1 μM) lead to heterogeneous effects on activating or inhibitory systems, probably caused by decreasing platelet viability.

Proteasome inhibitor b-AP15 induces enhanced proteotoxicity by inhibiting cytoprotective aggresome formation

Proteasome inhibitors have been shown to induce cell death in cancer cells by triggering an acute proteotoxic stress response characterized by accumulation of poly-ubiquitinated proteins, ER stress and the production of reactive oxygen species. The aggresome pathway has been described as an escape mechanism from proteotoxicity by sequestering toxic cellular aggregates. Here we show that b-AP15, a small-molecule inhibitor of proteasomal deubiquitinase activity, induces poly-ubiquitin accumulation in absence of aggresome formation. b-AP15 was found to affect organelle transport in treated cells, raising the possibility that microtubule-transport of toxic protein aggregates is inhibited, leading to enhanced cytotoxicity. In contrast to the antiproliferative effects of the clinically used proteasome inhibitor bortezomib, the effects of b-AP15 are not further enhanced by the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA). Our results suggest an inhibitory effect of b-AP15 on the transport of misfolded proteins, resulting in a lack of aggresome formation, and a strong proteotoxic stress response.

Copper(II) Bis(diethyldithiocarbamate) Induces the Expression of Syndecan-4, a Transmembrane Heparan Sulfate Proteoglycan, via p38 MAPK Activation in Vascular Endothelial Cells

Proteoglycans synthesized by vascular endothelial cells are important for regulating cell function and the blood coagulation-fibrinolytic system. Since we recently reported that copper(II) bis(diethyldithiocarbamate) (Cu(edtc)₂) modulates the expression of some molecules involving the antioxidant and blood coagulation systems, we hypothesized that Cu(edtc)₂ may regulate the expression of proteoglycans and examined this hypothesis using a bovine aortic endothelial cell culture system. The experiments showed that Cu(edtc)₂ induced the expression of syndecan-4, a transmembrane heparan sulfate proteoglycan, in a dose- and time-dependent manner. This induction required the whole structure of Cu(edtc)₂—the specific combination of intramolecular copper and a diethyldithiocarbamate structure—as the ligand. Additionally, the syndecan-4 induction by Cu(edtc)₂ depended on the activation of p38 mitogen-activated protein kinase (MAPK) but not the Smad2/3, NF-E2-related factor2 (Nrf2), or epidermal growth factor receptor (EGFR) pathways. p38 MAPK may be a key molecule for inducing the expression of syndecan-4 in vascular endothelial cells.

A Phase II Trial of Bortezomib and Vorinostat in Mantle Cell Lymphoma and Diffuse Large B-cell Lymphoma

BACKGROUND

The proteasome inhibitor bortezomib has demonstrated marked preclinical activity when combined with the histone deacetylase inhibitor vorinostat in leukemia, multiple myeloma, and mantle cell lymphoma (MCL) cells. The present study evaluated the efficacy and safety of the combination in patients with relapsed or refractory MCL and diffuse large B-cell lymphoma (DLBCL).

PATIENTS AND METHODS

The present multicenter, nonrandomized phase II trial used a Simon 2-stage design with 3 cohorts: cohort A, MCL with no previous bortezomib (including untreated MCL); cohort B, MCL with previous bortezomib; and cohort C, relapsed or refractory DLBCL with no previous bortezomib. Vorinostat (400 mg) was administered orally on days 1 to 5 and 8 to 12 before bortezomib (1.3 mg/m2), which was administered intravenously on days 1, 4, 8, and 11 of each 21-day cycle.

RESULTS

For the 65 treated patients (22 in cohort A, 4 in cohort B, and 39 in cohort C), the overall response rate was 31.8%, 0%, and 7.7%, respectively. The median progression-free survival was 7.6 months for cohort A and 1.8 months for cohort C. In cohort A, 7 patients had a partial response (PRs), 5 had stable disease (SD), 7 had progressive disease (PD), 1 was not assessed, and 2 were not evaluable. In cohort B, 2 had SD and 2 had PD. In cohort C, 3 had a PR, 8 had SD, 23 had PD, and 5 were not assessed. Baseline NF-κB activation, measured as nuclear RelA by immunohistochemistry, did not correlate with clinical response.

CONCLUSION

The combination of bortezomib and vorinostat is safe and has modest activity in MCL and limited activity in DLBCL.

Reactive oxygen species in haematopoiesis: leukaemic cells take a walk on the wild side

Oxidative stress is related to ageing and degenerative diseases, including cancer. However, a moderate amount of reactive oxygen species (ROS) is required for the regulation of cellular signalling and gene expression. A low level of ROS is important for maintaining quiescence and the differentiation potential of haematopoietic stem cells (HSCs), whereas the level of ROS increases during haematopoietic differentiation; thus, suggesting the importance of redox signalling in haematopoiesis. Here, we will analyse the importance of ROS for haematopoiesis and include evidence showing that cells from leukaemia patients live under oxidative stress. The potential sources of ROS will be described. Finally, the level of oxidative stress in leukaemic cells can also be harnessed for therapeutic purposes. In this regard, the reliance of front-line anti-leukaemia chemotherapeutics on increased levels of ROS for their mechanism of action, as well as the active search for novel compounds that modulate the redox state of leukaemic cells, will be analysed.

The BCR-ABL/NF-κB signal transduction network: a long lasting relationship in Philadelphia positive Leukemias

The Nuclear Factor-kappa B (NF-κB) family of transcription factors plays a key role in cancer pathogenesis due to the ability to promote cellular proliferation and survival, to induce resistance to chemotherapy and to mediate invasion and metastasis. NF-κB is recruited through different mechanisms involving either canonical (RelA/p50) or non-canonical pathways (RelB/p50 or RelB/p52), which transduce the signals originated from growth-factors, cytokines, oncogenic stress and DNA damage, bacterial and viral products or other stimuli. The pharmacological inhibition of the NF-κB pathway has clearly been associated with significant clinical activity in different cancers. Almost 20 years ago, NF-κB was described as an essential modulator of BCR-ABL signaling in Chronic Myeloid Leukemia and Philadelphia-positive Acute Lymphoblastic Leukemia. This review summarizes the role of NF-κB in BCR-ABL-mediated leukemogenesis and provides new insights on the long lasting BCR-ABL/NF-κB connection.

Therapeutic Strategies against Epstein-Barr Virus-Associated Cancers Using Proteasome Inhibitors

Epstein-Barr virus (EBV) is closely associated with several lymphomas (endemic Burkitt lymphoma, Hodgkin lymphoma and nasal NK/T-cell lymphoma) and epithelial cancers (nasopharyngeal carcinoma and gastric carcinoma). To maintain its persistence in the host cells, the virus manipulates the ubiquitin-proteasome system to regulate viral lytic reactivation, modify cell cycle checkpoints, prevent apoptosis and evade immune surveillance. In this review, we aim to provide an overview of the mechanisms by which the virus manipulates the ubiquitin-proteasome system in EBV-associated lymphoid and epithelial malignancies, to evaluate the efficacy of proteasome inhibitors on the treatment of these cancers and discuss potential novel viral-targeted treatment strategies against the EBV-associated cancers.

The Search for Potent, Small-Molecule HDACIs in Cancer Treatment: A Decade After Vorinostat

Histone deacetylases (HDACs) play a crucial role in the remodeling of chromatin, and are involved in the epigenetic regulation of gene expression. In the last decade, inhibition of HDACs came out as a target for specific epigenetic changes associated with cancer and other diseases. Until now, more than 20 HDAC inhibitors (HDACIs) have entered clinical studies, and some of them (e.g., vorinostat, romidepsin) have been approved for the treatment of cutaneous T-cell lymphoma. This review provides an overview of current knowledge, progress, and molecular mechanisms of HDACIs, covering a period from 2011 until 2015.

A phase 1 study of bortezomib and romidepsin in patients with chronic lymphocytic leukemia/small lymphocytic lymphoma, indolent B-cell lymphoma, peripheral T-cell lymphoma, or cutaneous T-cell lymphoma

A phase 1 study was conducted to determine the dose-limiting toxicities and maximum-tolerated dose (MTD) for bortezomib followed by romidepsin on days 1, 8, and 15 in patients with relapsed/refractory CLL/SLL or B- or T-cell lymphoma. Eighteen treated patients were evaluable for response. The MTD was 1.3 mg/m² bortezomib and 10 mg/m² romidepsin; median treatment duration was 3 cycles at this dose. The dose-limiting toxicities were grade 3 fatigue, vomiting, and chills. Two patients had partial responses, one lasting >2 years, 8 had stable disease, and 8 had progressive disease. The median duration of stable disease was 3.5 cycles. Correlative studies examining expression of NF-кB, XIAP, Bcl-xL, and Bim yielded variable results. The safety profile was consistent with that reported for single-agent bortezomib and romidepsin. This regimen has modest activity in heavily pretreated patients with relapsed/refractory CLL or B- or T-cell lymphoma. NCT00963274.

Induction of MAPK- and ROS-dependent autophagy and apoptosis in gastric carcinoma by combination of romidepsin and bortezomib

Proteasome inhibitors and histone deacetylase (HDAC) inhibitors can synergistically induce apoptotic cell death in certain cancer cell types but their combinatorial effect on the induction of autophagy remains unknown. Here, we investigated the combinatorial effects of a proteasome inhibitor, bortezomib, and an HDAC inhibitor, romidepsin, on the induction of apoptotic and autophagic cell death in gastric carcinoma (GC) cells. Isobologram analysis showed that low nanomolar concentrations of bortezomib/romidepsin could synergistically induce killing of GC cells. The synergistic killing was due to the summative effect of caspase-dependent intrinsic apoptosis and caspase-independent autophagy. The autophagic cell death was dependent on the activation of MAPK family members (ERK1/2 and JNK), and generation of reactive oxygen species (ROS), but was independent of Epstein-Barr virus infection. In vivo, bortezomib/romidepsin also significantly induced apoptosis and autophagy in GC xenografts in nude mice. This is the first report demonstrating the potent effect of combination of HDAC and proteasome inhibitors on the induction of MAPK- and ROS-dependent autophagy in addition to caspase-dependent apoptosis in a cancer type.

How do tumor cells respond to HDAC inhibition?

It is now well recognized that mutations, deregulated expression, and aberrant recruitment of epigenetic readers, writers, and erasers are fundamentally important processes in the onset and maintenance of many human tumors. The molecular, biological, and biochemical characteristics of a particular class of epigenetic erasers, the histone deacetylases (HDACs), have been extensively studied and small-molecule HDAC inhibitors (HDACis) have now been clinically approved for the treatment of human hemopoietic malignancies. This review explores our current understanding of the biological and molecular effects on tumor cells following HDACi treatment. The predominant responses include induction of tumor cell death and inhibition of proliferation that in experimental models have been linked to therapeutic efficacy. However, tumor cell-intrinsic responses to HDACi, including modulating tumor immunogenicity have also been described and may have substantial roles in mediating the antitumor effects of HDACi. We posit that the field has failed to fully reconcile the biological consequences of exposure to HDACis with the molecular events that underpin these responses, however progress is being made. Understanding the pleiotrophic activities of HDACis on tumor cells will hopefully fast track the development of more potent and selective HDACi that may be used alone or in combination to improve patient outcomes.

Childhood relapsed acute lymphoblastic leukemia: Biology and recent treatment progress

Acute lymphoblastic leukemia (ALL) is the most frequent cancer in children. Despite remarkable improvement in the prognosis of childhood ALL over the past few decades, the treatment of relapsed ALL is still challenging. The prognosis of first ALL relapse is associated with time of relapse after initial therapy, sites of relapse, and immunophenotype. More recently, response to treatment, which is evaluated by assessment of minimal residual disease (MRD), has been found to be clinically significant in relapsed ALL as well as in the initially diagnosed disease. Utilizing these factors, risk-oriented treatment stratification for first ALL relapse has been established. In the standard-risk group for first ALL relapse, intensification of conventional ALL-type therapy can provide a cure in approximately 70% of patients. It is important to assess MRD after reinduction therapy to determine the indications for stem cell transplantation in the standard-risk group. In contrast, no standardized therapy has been established for the high-risk group, which accounts for more than half of relapsed ALL patients. Recent studies have shed light on the clonal origin of relapsed ALL, which usually exists as a minor subclone at the time of initial diagnosis. Clonal selection and evolution take place during chemotherapy, resulting in distinct genetic and epigenetic characteristics of relapsed ALL, some of which are linked to drug resistance, a common and problematic feature of ALL after relapse. To overcome resistance to standard ALL-type therapy, and considering the heterogeneous biological background of high-risk relapsed ALL, innovative therapies using new agents are necessary.

Proteasome inhibitor MG-132 enhances histone deacetylase inhibitor SAHA-induced cell death of chronic myeloid leukemia cells by an ROS-mediated mechanism and downregulation of the Bcr-Abl fusion protein

Recently, there has been progress in the treatment of chronic myeloid leukemia (CML). However, novel therapeutic strategies are required in order to address the emerging problem of imatinib resistance. Histone deacetylase inhibitors (HDACi) and proteasome inhibitors are promising alternatives, and may be amenable to integration with current therapeutic approaches. However, the mechanisms underlying the interaction between these two agents remain unclear. The present study assessed the cytotoxic effect of the HDACi, suberoylanilide hydroxamic acid (SAHA), in combination with the proteasome inhibitor, MG-132, in imatinib-sensitive K562 and imatinib-resistant K562G cells, and investigated the mechanism underlying this effect. Cell viability was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method and protein expression levels were determined by western blotting. Reactive oxygen species (ROS) generation levels were observed under a fluorescence microscope The results indicated that SAHA and MG-132 act in a synergistic manner to induce cell death in K562 and K562G cells. This effect was associated with Bcr-Abl downregulation and the production of ROS. Notably, the ROS scavenger, N-acetyl-L-cysteine, almost fully reversed the cell death and Bcr-Abl downregulation that was induced by the combination of SAHA and MG-132. By contrast, the pan-caspase inhibitor, z-VAD-fmk, only partially reversed the cell death induced by these two drugs in CML cells. These results indicated that increased intracellular ROS levels are important in the induction of cell death and the downregulation of Bcr-Abl. In conclusion, the present results suggested that combined SAHA and MG-132 may be a promising treatment for CML.

Targeted therapies for ER+/HER2- metastatic breast cancer

The majority of breast cancers present with estrogen receptor (ER)-positive and human epidermal growth factor receptor (HER2)-negative features and might benefit from endocrine therapy. Although endocrine therapy has notably evolved during the last decades, the invariable appearance of endocrine resistance, either primary or secondary, remains an important issue in this type of tumor. The improvement of our understanding of the cancer genome has identified some promising targets that might be responsible or linked to endocrine resistance, including alterations affecting main signaling pathways like PI3K/Akt/mTOR and CCND1/CDK4-6 as well as the identification of new ESR1 somatic mutations, leading to an array of new targeted therapies that might circumvent or prevent endocrine resistance. In this review, we have summarized the main targeted therapies that are currently being tested in ER+ breast cancer, the rationale behind them, and the new agents and combinational treatments to come.

The ubiquitin-proteasome system: opportunities for therapeutic intervention in solid tumors

The destruction of proteins via the ubiquitin-proteasome system is a multi-step, complex process involving polyubiquitination of substrate proteins, followed by proteolytic degradation by the macromolecular 26S proteasome complex. Inhibitors of the proteasome promote the accumulation of proteins that are deleterious to cell survival, and represent promising anti-cancer agents. In multiple myeloma and mantle cell lymphoma, treatment with the first-generation proteasome inhibitor, bortezomib, or the second-generation inhibitor, carfilzomib, has demonstrated significant therapeutic benefit in humans. This has prompted United States Food and Drug Administration (US FDA) approval of these agents and development of additional second-generation compounds with improved properties. There is considerable interest in extending the benefits of proteasome inhibitors to the treatment of solid tumor malignancies. Herein, we review progress that has been made in the preclinical development and clinical evaluation of different proteasome inhibitors in solid tumors. In addition, we describe several novel approaches that are currently being pursued for the treatment of solid tumors, including drug combinatorial strategies incorporating proteasome inhibitors and the targeting of components of the ubiquitin-proteasome system that are distinct from the 26S proteasome complex.

Toward understanding induction of oxidative stress and apoptosis by proteasome inhibitors

SIGNIFICANCE

Proteasome inhibitors (PIs) are used in the clinic for the treatment of hematopoietic malignancies. PI inhibitors induce endoplasmatic reticulum (ER) stress and oxidative stress, disruption of signaling pathways, mitochondrial dysfunction, and, eventually, cell death by apoptosis. PIs designated as clinical candidates include natural product derivatives and compounds developed by rational design and feature a wide diversity of structural elements. The vast amount of literature on this topic underscores PIs significance in driving basic research alongside therapeutic benefit.

RECENT ADVANCES

Research in recent years has brought an in-depth insight into the molecular mechanisms of PI-induced apoptosis. However, there are some paradoxes and controversies in the literature. In this review, the advances and uncertainties, in particular on the time course events that make cells commit to apoptosis, are discussed. In addition, some mechanisms of evolved PI resistance are presented, and speculations on the difference in sensitivity between cell or tumor types are brought forward. The review concludes by giving an outlook of recent methods that may be employed to describe the system biology of how PIs impact cell survival decisions.

CRITICAL ISSUES

The biology of ER stress, reactive oxygen species (ROS) production, and apoptosis as induced by PIs is not well understood. Absorbed by the strong focus on PIs, one might overlook the importance of proteasome activity activators or modulators and the study of enzymatic pathways that lie up- or downstream from the proteasome function.

FUTURE DIRECTIONS

An increased understanding of the systems biology at mRNA and protein levels and the kinetics behind the interaction between PIs and cells is imperative. The design and synthesis of subunit specific inhibitors for each of the seven known proteasome activities and for the enzymes associated to proteasomes will aid in unraveling biology of the ubiquitin-proteasome system in relation to ER stress, ROS production, and apoptosis and will generate leads for therapeutic intervention.

(-)-Epigallocatechin-3-gallate induces cancer cell apoptosis via acetylation of amyloid precursor protein

Epigenetic modifications are involved in cancer pathogenesis, and HDACis are considered potential therapeutic agents. We and others have shown the inhibitory activity of EGCG on HDAC1. But little is known about the effect of EGCG as on epigenetic regulation in cancer. Here, we try to demonstrate that EGCG acts as an HDACi downregulated APP expression, which was pathophysiologically upregulated in cancers and exerts a key role in cancer cell growth. We used PC-12 cells, SK-N-SH cells and primary tumor tissues for our analysis. Male 4-week-old athymic nude mice were used for heterotopic tumor growth assay. We employed Western blotting analysis to detect Bcl-2, Bax, APP, caspase-3, caspase-7, HDAC1 and H4Ac. We used AnnexinV-FITC and TUNEL staining for apoptosis detection. Tumor tissues were examined by immunohistochemical staining. We demonstrated that EGCG suppresses the growth of xenografted adrenal pheochromocytoma. Flow cytometry analysis and TUNEL staining showed that EGCG induced the apoptosis. Treatment with EGCG resulted in decrease in Bcl-2 but increase in Bax and activated caspase-3 and caspase-7. HDAC inhibitor EGCG leaded to hyperacetylated histone H4 by immunofluorescence. EGCG decreased APP levels by immunofluorescence staining and Western blot analysis. Silencing specific to HDAC1 leaded to caspase-3 and caspase-7 activation and cleavage. Our results are the first to demonstrate a functional interaction between EGCG and APP in suppression tumor growth, and provide a new epigenetic effects of EGCG on antitumor.

Histone deacetylase inhibitor (HDACI) mechanisms of action: emerging insights

Initially regarded as "epigenetic modifiers" acting predominantly through chromatin remodeling via histone acetylation, HDACIs, alternatively referred to as lysine deacetylase or simply deacetylase inhibitors, have since been recognized to exert multiple cytotoxic actions in cancer cells, often through acetylation of non-histone proteins. Some well-recognized mechanisms of HDACI lethality include, in addition to relaxation of DNA and de-repression of gene transcription, interference with chaperone protein function, free radical generation, induction of DNA damage, up-regulation of endogenous inhibitors of cell cycle progression, e.g., p21, and promotion of apoptosis. Intriguingly, this class of agents is relatively selective for transformed cells, at least in pre-clinical studies. In recent years, additional mechanisms of action of these agents have been uncovered. For example, HDACIs interfere with multiple DNA repair processes, as well as disrupt cell cycle checkpoints, critical to the maintenance of genomic integrity in the face of diverse genotoxic insults. Despite their pre-clinical potential, the clinical use of HDACIs remains restricted to certain subsets of T-cell lymphoma. Currently, it appears likely that the ultimate role of these agents will lie in rational combinations, only a few of which have been pursued in the clinic to date. This review focuses on relatively recently identified mechanisms of action of HDACIs, with particular emphasis on those that relate to the DNA damage response (DDR), and discusses synergistic strategies combining HDACIs with several novel targeted agents that disrupt the DDR or antagonize anti-apoptotic proteins that could have implications for the future use of HDACIs in patients with cancer.

Combination of SAHA and bortezomib up-regulates CDKN2A and CDKN1A and induces apoptosis of Epstein-Barr virus-positive Wp-restricted Burkitt lymphoma and lymphoblastoid cell lines

Epstein-Barr virus (EBV) latent proteins exert anti-apoptotic effects on EBV-transformed lymphoid cells by down-regulating BCL2L11 (BIM), CDKN2A (p16(INK4A) ) and CDKN1A (p21(WAF1) ). However, the potential therapeutic effects of targeting these anti-apoptotic mechanisms remain unexplored. Here, we tested both in vitro and in vivo effects of the combination of histone deacetylase (HDAC) and proteasome inhibitors on the apoptosis of six endemic Burkitt lymphoma (BL) lines of different latency patterns (types I and III and Wp-restricted) and three lymphoblastoid cell lines (LCLs). We found that the combination of HDAC and proteasome inhibitors (e.g. SAHA/bortezomib) synergistically induced the killing of Wp-restricted and latency III BL and LCLs but not latency I BL cells. The synergistic killing was due to apoptosis, as evidenced by the high percentage of annexin V positivity and strong cleavage of PARP1 (PARP) and CASP3 (caspase-3). Concomitantly, SAHA/bortezomib up-regulated the expression of CDKN2A and CDKN1A but did not affect the level of BCL2L11 or BHRF1 (viral homologue of BCL2). The apoptotic effects were dependent on reactive oxygen species generation. Furthermore, SAHA/bortezomib suppressed the growth of Wp-restricted BL xenografts in nude mice. This study provides the rationale to test the novel application of SAHA/bortezomib on the treatment of EBV-associated Wp-restricted BL and post-transplant lymphoproliferative disorder.

Carfilzomib and oprozomib synergize with histone deacetylase inhibitors in head and neck squamous cell carcinoma models of acquired resistance to proteasome inhibitors

Acquired resistance to proteasome inhibitors represents a considerable impediment to their effective clinical application. Carfilzomib and its orally bioavailable structural analog oprozomib are second-generation, highly-selective, proteasome inhibitors. However, the mechanisms of acquired resistance to carfilzomib and oprozomib are incompletely understood, and effective strategies for overcoming this resistance are needed. Here, we developed models of acquired resistance to carfilzomib in two head and neck squamous cell carcinoma cell lines, UMSCC-1 and Cal33, through gradual exposure to increasing drug concentrations. The resistant lines R-UMSCC-1 and R-Cal33 demonstrated 205- and 64-fold resistance, respectively, relative to the parental lines. Similarly, a high level of cross-resistance to oprozomib, as well as paclitaxel, was observed, whereas only moderate resistance to bortezomib (8- to 29-fold), and low level resistance to cisplatin (1.5- to 5-fold) was seen. Synergistic induction of apoptosis signaling and cell death, and inhibition of colony formation followed co-treatment of acquired resistance models with carfilzomib and the histone deacetylase inhibitor (HDACi) vorinostat. Synergism was also seen with other combinations, including oprozomib plus vorinostat, or carfilzomib plus the HDACi entinostat. Synergism was accompanied by upregulation of proapoptotic Bik, and suppression of Bik attenuated the synergy. The acquired resistance models also exhibited elevated levels of MDR-1/P-gp. Inhibition of MDR-1/P-gp with reversin 121 partially overcame carfilzomib resistance in R-UMSCC-1 and R-Cal33 cells. Collectively, these studies indicate that combining carfilzomib or oprozomib with HDAC or MDR-1/P-gp inhibitors may be a useful strategy for overcoming acquired resistance to these proteasome inhibitors.

Proteasome inhibitor carfilzomib interacts synergistically with histone deacetylase inhibitor vorinostat in Jurkat T-leukemia cells

In the present study, we investigated the interactions between proteasome inhibitor carfilzomib (CFZ) and histone deacetylase inhibitor vorinostat in Jurkat T-leukemia cells. Coexposure of cells to minimally lethal concentrations of CFZ with very low concentration of vorinostat resulted in synergistic antiproliferative effects and enhanced apoptosis in Jurkat T-leukemia cells, accompanied with the sharply increased reactive oxygen species (ROS), the striking decrease in the mitochondrial membrane potential (MMP), the increased release of cytochrome c, the enhanced activation of caspase-9 and -3, and the cleavage of PARP. The combined treatment of Jurkat cells pre-treated with ROS scavengers N-acetylcysteine (NAC) significantly blocked the loss of mitochondrial membrane potential, suggesting that ROS generation was a former event of the loss of mitochondrial membrane potential. Furthermore, NAC also resulted in a marked reduction in apoptotic cells, indicating a critical role for increased ROS generation by combined treatment. In addition, combined treatment arrested the cell cycle in G2-M phase. These results imply that CFZ interacted synergistically with vorinostat in Jurkat T-leukemia cells, which raised the possibility that the combination of carfilzomib with vorinostat may represent a novel strategy in treating T-cell Leukemia.

Combination of proteasome and class I HDAC inhibitors induces apoptosis of NPC cells through an HDAC6-independent ER stress-induced mechanism

The current paradigm stipulates that inhibition of histone deacetylase (HDAC) 6 is essential for the combinatorial effect of proteasome and HDAC inhibitors for the treatment of cancers. Our study aims to investigate the effect of combining different class I HDAC inhibitors (without HDAC6 action) with a proteasome inhibitor on apoptosis of nasopharyngeal carcinoma (NPC). We found that combination of a proteasome inhibitor, bortezomib, and several class I HDAC inhibitors, including MS-275, apicidin and romidepsin, potently induced killing of NPC cells both in vitro and in vivo. Among the drug pairs, combination of bortezomib and romidepsin (bort/romidepsin) was the most potent and could induce apoptosis at low nanomolar concentrations. The apoptosis of NPC cells was reactive oxygen species (ROS)- and caspase-dependent but was independent of HDAC6 inhibition. Of note, bort/romidepsin might directly suppress the formation of aggresome through the downregulation of c-myc. In addition, two markers of endoplasmic reticulum (ER) stress-induced apoptosis, ATF-4 and CHOP/GADD153, were upregulated, whereas a specific inhibitor of caspase-4 (an initiator of ER stress-induced apoptosis) could suppress the apoptosis. When ROS level in the NPC cells was reduced to the untreated level, ER stress-induced caspase activation was abrogated. Collectively, our data demonstrate a model of synergism between proteasome and class I HDAC inhibitors in the induction of ROS-dependent ER stress-induced apoptosis of NPC cells, independent of HDAC6 inhibition, and provide the rationale to combine the more specific and potent class I HDAC inhibitors with proteasome inhibitors for the treatment of cancers.

Chromatin modifiers and the promise of epigenetic therapy in acute leukemia

Hematopoiesis is a tightly regulated process involving the control of gene expression that directs the transition from hematopoietic stem and progenitor cells to terminally differentiated blood cells. In leukemia, the processes directing self-renewal, differentiation and progenitor cell expansion are disrupted, leading to the accumulation of immature, non-functioning malignant cells. Insights into these processes have come in stages, based on technological advances in genetic analyses, bioinformatics and biological sciences. The first cytogenetic studies of leukemic cells identified chromosomal translocations that generate oncogenic fusion proteins and most commonly affect regulators of transcription. This was followed by the discovery of recurrent somatic mutations in genes encoding regulators of the signal transduction pathways that control cell proliferation and survival. Recently, studies of global changes in methylation and gene expression have led to the understanding that the output of transcriptional regulators and the proliferative signaling pathways are ultimately influenced by chromatin structure. Candidate gene, whole-genome and whole-exome sequencing studies have identified recurrent somatic mutations in genes encoding epigenetic modifiers in both acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL). In contrast to the two-hit model of leukemogenesis, emerging evidence suggests that these epigenetic modifiers represent a class of mutations that are critical to the development of leukemia and affect the regulation of various other oncogenic pathways. In this review, we discuss the range of recurrent, somatic mutations in epigenetic modifiers found in leukemia and how these modifiers relate to the classical leukemogenic pathways that lead to impaired cell differentiation and aberrant self-renewal and proliferation.

Development of histone deacetylase inhibitors for cancer treatment

Histone deacetylase (HDAC) inhibitors are an exciting new addition to the arsenal of cancer therapeutics. The inhibition of HDAC enzymes by HDAC inhibitors shifts the balance between the deacetylation activity of HDAC enzymes and the acetylation activity of histone acetyltransferases, resulting in hyperacetylation of core histones. Exposure of cancer cells to HDAC inhibitors has been associated with a multitude of molecular and biological effects, ranging from transcriptional control, chromatin plasticity, protein-DNA interaction to cellular differentiation, growth arrest and apoptosis. In addition to the antitumor effects seen with HDAC inhibitors alone, these compounds may also potentiate cytotoxic agents or synergize with other targeted anticancer agents. The exact mechanism by which HDAC inhibitors cause cell death is still unclear and the specific roles of individual HDAC enzymes as therapeutic targets has not been established. However, emerging evidence suggests that the effects of HDAC inhibitors on tumor cells may not only depend on the specificity and selectivity of the HDAC inhibitor, but also on the expression patterns of HDAC enzymes in the tumor tissue. In this review, the recent advances in the understanding and clinical development of HDAC inhibitors, as well as their current role in cancer therapy, will be discussed.

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.

Superior antimitogenic and chemosensitization activities of the combination treatment of the histone deacetylase inhibitor apicidin and proteasome inhibitors on human colorectal cancer cells

Despite the effectiveness of histone deacetylase inhibitors, proteasome inhibitors and cytotoxic drugs on human cancers, none of these types of treatments by themselves has been sufficient to eradicate the disease. The combination of different modalities may hold enormous potential for eliciting therapeutic results. In the current study, we examined the effects of treatment with the histone deacetylase inhibitor (HDACI) apicidin (APC) in combination with proteasome inhibitors on human colorectal cancer cells. The molecular mechanisms of the combined treatments and their potential to sensitize colorectal cancer cells to chemotherapies were also investigated. Cancer cells were exposed to the agents alone and in combination, and cell growth inhibition was determined by MTT and colony formation assays. HDAC, proteasome and NF-κB activities as well as reactive oxygen species (ROS) were monitored. Cell cycle perturbation and induction of apoptosis were assessed by flow cytometry. The expression of cell cycle/apoptosis- and cytoprotective/stress-related genes was determined by quantitative PCR and EIA, respectively. The potentiation of cancer cell sensitivity to chemotherapies upon APC/PI combination treatment was also studied. The combination of APC and MG132, PI-1 or epoxomicin potently inhibited cancer cell growth, disrupted the cell cycle, induced apoptosis, decreased NF-κB activity and increased ROS production. These events were accompanied by the altered expression of genes associated with the cell cycle, apoptosis and cytoprotection/stress regulation. The combination treatment markedly enhanced the chemosensitivity of colorectal cancer cells (50-3.7 x 10(4)-fold) in a drug-, APC/PI combination- and colorectal cancer subtype-dependent manner. The results of this study have implications for the development of com-binatorial treatments that include HDACIs, PIs and conventional chemotherapeutic drugs, suggesting a potential therapeutic synergy with general applicability to various types of cancers.

Combination of bortezomib and mitotic inhibitors down-modulate Bcr-Abl and efficiently eliminates tyrosine-kinase inhibitor sensitive and resistant Bcr-Abl-positive leukemic cells

Emergence of resistance to Tyrosine-Kinase Inhibitors (TKIs), such as imatinib, dasatinib and nilotinib, in Chronic Myelogenous Leukemia (CML) demands new therapeutic strategies. We and others have previously established bortezomib, a selective proteasome inhibitor, as an important potential treatment in CML. Here we show that the combined regimens of bortezomib with mitotic inhibitors, such as the microtubule-stabilizing agent Paclitaxel and the PLK1 inhibitor BI2536, efficiently kill TKIs-resistant and -sensitive Bcr-Abl-positive leukemic cells. Combined treatment activates caspases 8, 9 and 3, which correlate with caspase-induced PARP cleavage. These effects are associated with a marked increase in activation of the stress-related MAP kinases p38MAPK and JNK. Interestingly, combined treatment induces a marked decrease in the total and phosphorylated Bcr-Abl protein levels, and inhibits signaling pathways downstream of Bcr-Abl: downregulation of STAT3 and STAT5 phosphorylation and/or total levels and a decrease in phosphorylation of the Bcr-Abl-associated proteins CrkL and Lyn. Moreover, we found that other mitotic inhibitors (Vincristine and Docetaxel), in combination with bortezomib, also suppress the Bcr-Abl-induced pro-survival signals and result in caspase 3 activation. These results open novel possibilities for the treatment of Bcr-Abl-positive leukemias, especially in the imatinib, dasatinib and nilotinib-resistant CML cases.

A phase I study of vorinostat in combination with bortezomib in patients with advanced malignancies

BACKGROUND

A phase I study to assess the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), pharmacokinetics (PK) and antitumor activity of vorinostat in combination with bortezomib in patients with advanced solid tumors.

METHODS

Patients received vorinostat orally once daily on days 1-14 and bortezomib intravenously on days 1, 4, 8 and 11 of a 21-day cycle. Starting dose (level 1) was vorinostat (400 mg) and bortezomib (0.7 mg/m(2)). Bortezomib dosing was increased using a standard phase I dose-escalation schema. PKs were evaluated during cycle 1.

RESULTS

Twenty-three patients received 57 cycles of treatment on four dose levels ranging from bortezomib 0.7 mg/m(2) to 1.5 mg/m(2). The MTD was established at vorinostat 400 mg daily and bortezomib 1.3 mg/m(2). DLTs consisted of grade 3 fatigue in three patients (1 mg/m(2),1.3 mg/m(2) and 1.5 mg/m(2)) and grade 3 hyponatremia in one patient (1.5 mg/m(2)). The most common grade 1/2 toxicities included nausea (60.9%), fatigue (34.8%), diaphoresis (34.8%), anorexia (30.4%) and constipation (26.1%). Objective partial responses were observed in one patient with NSCLC and in one patient with treatment-refractory soft tissue sarcoma. Bortezomib did not affect the PKs of vorinostat; however, the Cmax and AUC of the acid metabolite were significantly increased on day 2 compared with day 1.

CONCLUSIONS

This combination was generally well-tolerated at doses that achieved clinical benefit. The MTD was established at vorinostat 400 mg daily × 14 days and bortezomib 1.3 mg/m(2) on days 1, 4, 8 and 11 of a 21-day cycle.

A Phase I study of intermittently dosed vorinostat in combination with bortezomib in patients with advanced solid tumors

BACKGROUND

Accumulating evidence shows evidence of efficacy with the combination of vorinostat and bortezomib in solid tumors. We previously examined a once-daily continuous dosing schedule of vorinostat in combination with bortezomib which was well tolerated in cycles 1 and 2; however, there was concern regarding the tolerability through multiple cycles. This study was conducted to evaluate an intermittent dosing schedule of vorinostat with bortezomib.

METHODS

Vorinostat was initially administered orally twice daily on days 1-14 with bortezomib IV on days 1, 4, 8, and 11 of a 21 day cycle. Two DLTs (elevated ALT and fatigue) were observed at dose level 1, thus the protocol was amended to administer vorinostat intermittently twice daily on days 1-4 and 8-11.

RESULTS

29 patients were enrolled; 13 men and 16 women. Common cancer types included sarcoma, pancreatic, colorectal, GIST, and breast. The most common Grade 3-4 toxicities at any dose level included thrombocytopenia, fatigue, increased ALT, elevated INR, and diarrhea. DLTs in the intermittent dosing scheduled included thrombocytopenia and fatigue. The Cmax and AUC for the intermittent dosing regimen were similar to those observed in the daily dosing. In this heavily pretreated population, stable disease was observed in patients with sarcoma, colorectal adenocarcinoma and GIST.

CONCLUSIONS

The MTD was established at vorinostat 300 mg BID on days 1-4 and 8-11 and bortezomib 1.3 mg/m(2) IV on days 1, 4, 8, and 11 of a 21 day cycle. Tolerability was not improved with the intermittent dosing schedule of vorinostat when compared to continuous dosing.

The promise and failures of epigenetic therapies for cancer treatment

Genetic mutations and gross structural defects in the DNA sequence permanently alter genetic loci in ways that significantly disrupt gene function. In sharp contrast, genes modified by aberrant epigenetic modifications remain structurally intact and are subject to partial or complete reversal of modifications that restore the original (i.e. non-diseased) state. Such reversibility makes epigenetic modifications ideal targets for therapeutic intervention. The epigenome of cancer cells is extensively modified by specific hypermethylation of the promoters of tumor suppressor genes relative to the extensive hypomethylation of repetitive sequences, overall loss of acetylation, and loss of repressive marks at microsatellite/repeat regions. In this review, we discuss emerging therapies targeting specific epigenetic modifications or epigenetic modifying enzymes either alone or in combination with other treatment regimens. The limitations posed by cancer treatments elicit unintended epigenetic modifications that result in exacerbation of tumor progression are also discussed. Lastly, a brief discussion of the specificity restrictions posed by epigenetic therapies and ways to address such limitations is presented.

Redox control of leukemia: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) play both positive and negative roles in the proliferation and survival of a cell. This dual nature has been exploited by leukemia cells to promote growth, survival, and genomic instability-some of the hallmarks of the cancer phenotype. In addition to altered ROS levels, many antioxidants are dysregulated in leukemia cells. Together, the production of ROS and the expression and activity of antioxidant enzymes make up the primary redox control of leukemia cells. By manipulating this system, leukemia cells gain proliferative and survival advantages, even in the face of therapeutic insults. Standard treatment options have improved leukemia patient survival rates in recent years, although relapse and the development of resistance are persistent challenges. Therapies targeting the redox environment show promise for these cases. This review highlights the molecular mechanisms that control the redox milieu of leukemia cells. In particular, ROS production by the mitochondrial electron transport chain, NADPH oxidase, xanthine oxidoreductase, and cytochrome P450 will be addressed. Expression and activation of antioxidant enzymes such as superoxide dismutase, catalase, heme oxygenase, glutathione, thioredoxin, and peroxiredoxin are perturbed in leukemia cells, and the functional consequences of these molecular alterations will be described. Lastly, we delve into how these pathways can be potentially exploited therapeutically to improve treatment regimens and promote better outcomes for leukemia patients.

A focus on the preclinical development and clinical status of the histone deacetylase inhibitor, romidepsin (depsipeptide, Istodax(®))

Romidepsin (Istodax(®), depsipeptide, FR901228, FK228, NSC 630176) is a cyclic peptide, broad-spectrum, potent histone deacetylase inhibitor, with activity mainly against class I histone deacetylase enzymes. In this article, we give an overview of the putative modes of action, such as effects on gene expression, cell cycle regulation, apoptosis induction, DNA repair, protein acetylation and induction of autophagy. Romidepsin has mainly been developed as a therapy for hematologic malignancies and is approved by the US FDA for the treatment of cutaneous T-cell lymphomas. This report outlines the laboratory and clinical development of the compound as a single agent that has more recently been evaluated in combination with other anticancer therapeutics, such as proteasome inhibitors.

Histone deacetylase inhibitors and rational combination therapies

Histone deacetylase inhibitors (HDACIs) are epigenetically acting agents that modify chromatin structure and by extension, gene expression. However, they may influence the behavior and survival of transformed cells by diverse mechanisms, including promoting expression of death- or differentiation-inducing genes while downregulating the expression of prosurvival genes; acting directly to increase oxidative injury and DNA damage; acetylating and disrupting the function of multiple proteins, including DNA repair and chaperone proteins; and interfering with the function of corepressor complexes. Notably, HDACIs have been shown in preclinical studies to target transformed cells selectively, and these agents have been approved in the treatment of certain hematologic malignancies, for example, cutaneous T-cell lymphoma and peripheral T-cell lymphoma. However, attempts to extend the spectrum of HDACI activity to other malignancies, for example, solid tumors, have been challenging. This has led to the perception that HDACIs may have limited activity as single agents. Because of the pleiotropic actions of HDACIs, combinations with other antineoplastic drugs, particularly other targeted agents, represent a particularly promising avenue of investigation. It is likely that emerging insights into mechanism(s) of HDACI activity will allow optimization of this approach, and hopefully, will expand HDACI approvals to additional malignancies in the future.

Bortezomib and SAHA synergistically induce ROS-driven caspase-dependent apoptosis of nasopharyngeal carcinoma and block replication of Epstein-Barr virus

A novel drug combination of a proteasome inhibitor, bortezomib, and a histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), was tested in nasopharyngeal carcinoma (NPC), both in vitro and in vivo. Dose-response of different concentrations of bortezomib and SAHA on inhibition of cell proliferation of NPC was determined. Mechanisms of apoptosis and effects on lytic cycle activation of Epstein-Barr virus (EBV) were investigated. Combination of bortezomib and SAHA (bortezomib/SAHA) synergistically induced killing of a panel of NPC cell lines. Pronounced increase in sub-G1, Annexin V-positive, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive cell populations were detected after treatment with bortezomib/SAHA when compared with either drug alone. Concomitantly, markedly augmented proteolytic cleavage of PARP, caspase-3, -7, -8, and -9, reactive oxygen species (ROS) generation, and caspase-8-dependent histone acetylation were observed. ROS scavenger, N-acetyl cysteine, diminished the apoptotic effects of bortezomib/SAHA, whereas caspase inhibitor Z-VAD-FMK significantly suppressed the apoptosis without decreasing the generation of ROS. Bortezomib inhibited SAHA's induction of EBV replication and abrogated production of infectious viral particles in NPC cells. Furthermore, bortezomib/SAHA potently induced apoptosis and suppressed the growth of NPC xenografts in nude mice. In conclusion, the novel drug combination of bortezomib and SAHA is highly synergistic in the killing of NPC cells in vitro and in vivo. The major mechanism of cell death is ROS-driven caspase-dependent apoptosis. Bortezomib antagonizes SAHA's activation of EBV lytic cycle in NPC cells. This study provides a strong basis for clinical testing of the combination drug regimen in patients with NPC.

A phase I trial of vorinostat and bortezomib in children with refractory or recurrent solid tumors: a Children's Oncology Group phase I consortium study (ADVL0916)

BACKGROUND

A pediatric Phase I trial was performed to determine the maximum-tolerated dose, dose-limiting toxicities (DLTs), and pharmacokinetics (PK) of vorinostat and bortezomib, in patients with solid tumors.

PROCEDURE

Oral vorinostat was administered on days 1-5 and 8-12 of a 21-day cycle (starting dose 180 mg/m(2) /day with dose escalations to 230 and 300 mg/m(2) /day). Bortezomib (1.3 mg/m(2) i.v.) was administered on days 1, 4, 8, and 11 of the same cycle. PK and correlative biology studies were performed during Cycle 1.

RESULTS

Twenty-three eligible patients [17 male, median age 12 years (range: 1-20)] were enrolled of whom 17 were fully evaluable for toxicity. Cycle 1 DLTs that occurred in 2/6 patients at dose level 3 (vorinostat 300 mg/m(2) /day) were Grade 2 sensory neuropathy that progressed to Grade 4 (n = 1) and Grade 3 nausea and anorexia (n = 1). No objective responses were observed. There was wide interpatient variability in vorinostat PK parameters. Bortezomib disposition was best described by a three-compartment model that demonstrated rapid distribution followed by prolonged elimination. We did not observe a decrease in nuclear factor-κB activity or Grp78 induction after bortezomib treatment in peripheral blood mononuclear cells from solid tumor patients.

CONCLUSION

The recommended Phase 2 dose and schedule is vorinostat (230 mg/m(2) /day PO on days 1-5 and 8-12) in combination with bortezomib (1.3 mg/m(2) /day i.v. on days 1, 4, 8, and 11 of a 21-day cycle) in children with recurrent or refractory solid tumors.

The nuclear factor kappa-B signaling pathway as a therapeutic target against thyroid cancers

BACKGROUND

The nuclear factor kappa-B (NF-κB) proteins, a family of transcription factors found virtually in all cells, are known to play crucial roles in the growth of a number of human malignancies. The ability of NF-κB to target a large number of genes that regulate cell proliferation, differentiation, survival, and apoptosis, provides clues toward its deregulation during the process of tumorigenesis, metastatic progression, and therapeutic resistance of tumors.

SUMMARY

In addition to the signaling pathways known to be involved in thyroid tumorigenesis, such as the mitogen-activated protein kinase and janus kinase cascades, studies implicate the NF-κB pathway in the development of both less aggressive thyroid cancers, papillary and follicular adenocarcinomas, and progression to aggressive thyroid cancers, such as anaplastic adenocarcinomas. A constitutively activated NF-κB pathway also closely links Hashimoto's thyroiditis with increased incidence of thyroid cancers. The NF-κB pathway is becoming one of the major targets for drug development, and a number of compounds have been developed to inhibit this pathway at different levels in cancer cells. Some of these targets have shown promising outcomes in both in vitro and in vivo investigations and a handful of them have shown efficacy in the clinical setting.

CONCLUSIONS

This review discusses the recent findings that demonstrate that the inhibition of NF-κB, alone or with other signaling pathway inhibitors may be of significant therapeutic benefits against aggressive thyroid cancers.

Synergistic anti-cancer effects of resveratrol and chemotherapeutic agent clofarabine against human malignant mesothelioma MSTO-211H cells

Dietary phytochemicals as adjuvants have been suggested to play important roles in enhancing chemotherapeutic potential owing to multitargeted chemopreventive properties and lack of substantial toxicity. Here, we investigated the efficacy of the combined treatment of various phytochemicals with the anticancer drug clofarabine in malignant mesothelioma MSTO-211H cells and normal mesothelial MeT-5A cells. The combined treatment of resveratrol and clofarabine produced a synergistic antiproliferative effect in MSTO-211H cells, but not in MeT-5A cells. In MSTO-211H cells, the nuclear accumulation of Sp1 and the levels of p-Akt, Sp1, c-Met, cyclin D1, and p21 were effectively decreased by the combined treatment of them. In combination with clofarabine, the ability of resveratrol to reduce the contents of Sp1 and its target gene products was also evident in a time- and dose-dependent experiment. The inhibition of phosphoinositide 3-kinase using Ly294002 augmented a decrease in the p21 level induced by their combination, but it showed no significant effects on expression of Sp1 and cyclin D1. Taken together, the data provide evidence that the synergistic antiproliferative effect of resveratrol and clofarabine is linked to the inhibition of Akt and Sp1 activities, and suggest that this combination may have therapeutic value in treatment of malignant mesothelioma.

Synergistic effect of panobinostat and bortezomib on chemoresistant acute myelogenous leukemia cells via AKT and NF-κB pathways

In this study, we investigated the synergistic effects of panobinostat and bortezomib on adriamycin-resistant HL60/ADR cells and refractory acute myelogenous leukemia (AML) primary cells. Combination of both agents had synergistic cytotoxicity on these cells, and increased the sensitivity of HL60/ADR cells to adriamycin. Panobinostat plus bortezomib was shown to modulate multiple apoptotic and drug metabolic related molecules, including activation of caspases, down-regulation of XIAP, Bcl-2 and MRP1. These effects were likely to be mediated via inhibition of AKT and NF-κB pathways. These findings provide evidence for clinic protocols using panobinostat and borezomib to overcome drug resistance in refractory AML patients.

Preclinical cancer chemoprevention studies using animal model of inflammation-associated colorectal carcinogenesis

Inflammation is involved in all stages of carcinogenesis. Inflammatory bowel disease, such as ulcerative colitis and Crohn’s disease is a longstanding inflammatory disease of intestine with increased risk for colorectal cancer (CRC). Several molecular events involved in chronic inflammatory process are reported to contribute to multi-step carcinogenesis of CRC in the inflamed colon. They include over-production of free radicals, reactive oxygen and nitrogen species, up-regulation of inflammatory enzymes in arachidonic acid biosynthesis pathway, up-regulation of certain cytokines, and intestinal immune system dysfunction. In this article, firstly I briefly introduce our experimental animal models where colorectal neoplasms rapidly develop in the inflamed colorectum. Secondary, data on preclinical cancer chemoprevention studies of inflammation-associated colon carcinogenesis by morin, bezafibrate, and valproic acid, using this novel inflammation-related colorectal carcinogenesis model is described.