Histone deacetylase inhibitors in malignant pleural mesothelioma: preclinical rationale and clinical trials

Unraveling Novel Strategies in Mesothelioma Treatments Using a Newly Synthetized Platinum(IV) Compound

Malignant mesothelioma is a rare tumor associated with asbestos exposure. Mesothelioma carcinogenesis is related to enhanced reactive oxygen species (ROS) production and iron overload. Despite the recent advances in biomedical sciences, to date the only available treatments include surgery in a small fraction of patients and platinum-based chemotherapy in combination with pemetrexed. In this view, the purpose of this study was to evaluate the therapeutic potential of the newly synthetized platinum prodrug Pt(IV)Ac-POA compared to cisplatin (CDDP) on human biphasic mesothelioma cell line MSTO-211H using different complementary techniques, such as flow-cytometry, transmission electron microscopy (TEM), and immunocytochemistry. Healthy mesothelial cell lines Met-5A were also employed to assess the cytotoxicity of the above-mentioned compounds. Our in vitro results showed that Pt(IV)Ac-POA significantly interfere with iron metabolisms and more importantly is able to trigger cell death, through different pathways, including ferroptosis, necroptosis, and apoptosis, in neoplastic cells. On the other hand, CDDP triggers mainly apoptotic and necrotic cell death. In conclusion, Pt(IV)Ac-POA may represent a new promising pharmacological agent in the treatment of malignant mesothelioma.

YAP/TAZ-TEAD signalling axis: A new therapeutic target in malignant pleural mesothelioma

The Hippo signalling pathway, a highly conserved signalling cassette, regulates organ size by controlling cell growth, apoptosis and stem cell self-renewal. The tumourigenic potential of this pathway is largely attributed to the activity of YAP/TAZ, which activate the TEAD1-4 transcription factors, leading to the expression of genes involved in cell proliferation and suppression of cell death. Aberrant regulation of the YAP/TAZ-TEAD signalling axis is commonly observed in malignant pleural mesothelioma (MPM), an insidious neoplasm of the pleural tissue that lines the chest cavity and covers the lungs with poor prognosis. Given the limited effectiveness of current treatments, targeting the YAP/TAZ-TEAD signalling cascade has emerged as a promising therapeutic strategy in MPM. Several inhibitors of the YAP/TAZ-TEAD signalling axis are presently undergoing clinical development, with the goal of advancing them to clinical use in the near future.

Updates in Management of Malignant Pleural Mesothelioma

OPINION STATEMENT

Malignant pleural mesothelioma (MPM) is an aggressive asbestos-associated thoracic malignancy that is usually incurable. As demonstrated in the landmark MARS2 trial, surgical resection does not improve survival outcomes and its role in managing MPM is limited. Whilst platinum-pemetrexed chemotherapy in combination with bevacizumab was the standard first-line approach for unresectable disease, landmark phase 3 trials have now established the role of immune checkpoint inhibitors (CPIs) in the upfront management of unresectable disease: either nivolumab-ipilimumab or carboplatin-pemetrexed-pembrolizumab. Patient selection for optimal strategy remains an ongoing question. For relapsed disease novel genomic-based therapies targeting a range of aberrations including losses of the tumour suppressor genes BAP1, CDKN2A and NF2, are being evaluated. Nonetheless, the future of MPM therapeutics holds promise. Here we overview current treatment strategies in the management of MPM.

Target Therapy in Malignant Pleural Mesothelioma: Hope or Mirage?

Malignant Pleural Mesothelioma (MPM) is a rare neoplasm that is typically diagnosed in a locally advanced stage, making it not eligible for radical surgery and requiring systemic treatment. Chemotherapy with platinum compounds and pemetrexed has been the only approved standard of care for approximately 20 years, without any relevant therapeutic advance until the introduction of immune checkpoint inhibitors. Nevertheless, the prognosis remains poor, with an average survival of only 18 months. Thanks to a better understanding of the molecular mechanisms underlying tumor biology, targeted therapy has become an essential therapeutic option in several solid malignancies. Unfortunately, most of the clinical trials evaluating potentially targeted drugs for MPM have failed. This review aims to present the main findings of the most promising targeted therapies in MPM, and to explore possible reasons leading to treatments failures. The ultimate goal is to determine whether there is still a place for continued preclinical/clinical research in this area.

Biological basis for novel mesothelioma therapies

Mesothelioma is an aggressive cancer that is associated with exposure to asbestos. Although asbestos is banned in several countries, including the UK, an epidemic of mesothelioma is predicted to affect middle-income countries during this century owing to their heavy consumption of asbestos. The prognosis for patients with mesothelioma is poor, reflecting a failure of conventional chemotherapy that has ultimately resulted from an inadequate understanding of its biology. However, recent work has revolutionised the study of mesothelioma, identifying genetic and pathophysiological vulnerabilities, including the loss of tumour suppressors, epigenetic dysregulation and susceptibility to nutrient stress. We discuss how this knowledge, combined with advances in immunotherapy, is enabling the development of novel targeted therapies.

Molecular Fingerprints of Malignant Pleural Mesothelioma: Not Just a Matter of Genetic Alterations

Malignant pleural mesothelioma (MPM) is a clinical emergency of our time. Being strongly associated with asbestos exposure, incidence of this cancer is ramping up these days in many industrialized countries and it will soon start to increase in many developing areas where the use of this silicate derivate is still largely in use. Deficiency of reliable markers for the early identification of these tumors and the limited efficacy of the currently available therapeutic options are the basis of the impressive mortality rate of MPM. These shortcomings reflect the very poor information available about the molecular basis of this disease. Results of the recently released deep profiling studies point to the epigenome as a central element in MPM development and progression. First, MPM is characterized by a low mutational burden and a highly peculiar set of mutations that hits almost exclusively epigenetic keepers or proteins controlling chromatin organization and function. Furthermore, asbestos does not seem to be associated with a distinctive mutational signature, while the precise mapping of epigenetic changes caused by this carcinogen has been defined, suggesting that alterations in epigenetic features are the driving force in the development of this disease. Last but not least, consistent evidence also indicates that, in the setting of MPM, chromatin rewiring and epigenetic alterations of cancer cells heavily condition the microenvironment, including the immune response. In this review we aim to point to the relevance of the epigenome in MPM and to highlight the dependency of this tumor on chromatin organization and function. We also intend to discuss the opportunity of targeting these mechanisms as potential therapeutic options for MPM.

Epigenetic modulation and understanding of HDAC inhibitors in cancer therapy

The role of genetic and epigenetic factors in tumor initiation and progression is well documented. Histone deacetylases (HDACs), histone methyl transferases (HMTs), and DNA methyl transferases. (DNMTs) are the main proteins that are involved in regulating the chromatin conformation. Among these, histone deacetylases (HDAC) deacetylate the histone and induce gene repression thereby leading to cancer. In contrast, histone acetyl transferases (HATs) that include GCN5, p300/CBP, PCAF, Tip 60 acetylate the histones. HDAC inhibitors are potent drug molecules that can induce acetylation of histones at lysine residues and induce open chromatin conformation at tumor suppressor gene loci and thus resulting in tumor suppression. The key processes regulated by HDAC inhibitors include cell-cycle arrest, chemo-sensitization, apoptosis induction, upregulation of tumor suppressors. Even though FDA approved drugs are confined mainly to haematological malignancies, the research on HDAC inhibitors in glioblastoma multiforme and triple negative breast cancer (TNBC) are providing positive results. Thus, several combinations of HDAC inhibitors along with DNA methyl transferase inhibitors and histone methyl transferase inhibitors are in clinical trials. This review focuses on how HDAC inhibitors regulate the expression of coding and non-coding genes with specific emphasis on their anti-cancer potential.

Biomarker-guided targeted and immunotherapies in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a lethal thoracic malignancy whose incidence is still increasing worldwide. MPM is characterized by frequent inactivation of tumor-suppressor genes (TSGs), e.g., the homozygous deletion of CDKN2A/2B and various genetic alterations that inactivate BAP1, NF2, LATS1/2, and TP53. The leading cause for the poor prognosis of patients with MPM is the lack of effective treatment options, with conventional chemotherapy being the standard of care in the clinic, which has remained unchanged for almost 20 years. Precision oncology, a burgeoning effort to provide precise cancer treatment tailored to unique molecular changes in individual patients, has made tremendous progress in the last decade in several cancers, but not in MPM. Recent studies indicate a high degree of tumor heterogeneity in MPM and the importance to optimize histological and molecular classifications for improved treatment. In this review, we provide an up-to-date overview of recent advances in MPM by focusing on new stratifications of tumor subgroups, specific vulnerabilities associated with functional loss of TSGs and other biomarkers, and potential clinical implications. The molecularly based subdivisions not only deepen our understanding of MPM pathobiology, but more importantly, they may raise unprecedented new hopes for personalized treatment of MPM patients with biomarker-guided targeted and immunotherapies.

The Use of Immunohistochemistry, Fluorescence in situ Hybridization, and Emerging Epigenetic Markers in the Diagnosis of Malignant Pleural Mesothelioma (MPM): A Review

Malignant pleural mesothelioma (MPM) is an aggressive asbestos related disease that is generally considered to be difficult to diagnose, stage and treat. The diagnostic process is continuing to evolve and requires highly skilled pathology input, and generally an extensive list of biomarkers for definitive diagnosis. Diagnosis of MPM requires histological evidence of invasion by malignant mesothelial cells often confirmed by various immunohistochemical biomarkers in order to separate it from pleural metastatic carcinoma. Often when invasion of neoplastic mesothelial cells into adjacent tissue is not apparent, further immunohistochemical testing - namely BAP1 and MTAP, as well as FISH testing for loss of p16 (CDKN2A) are used to separate reactive mesothelial proliferation due to benign processes, from MPM. Various combinations of these markers, such as BAP1 and/or MTAP immunohistochemistry alongside FISH testing for loss of p16, have shown excellent sensitivity and specificity in the diagnosis of MPM. Additionally, over the recent years, research into epigenetic marker use in the diagnosis of MPM has gained momentum. Although still in their research stages, various markers in DNA methylation, long non-coding RNA, micro RNA, circular RNA, and histone modifications have all been found to support diagnosis of MPM with generally good sensitivity and specificity. Many of these studies are however, limited by small sample sizes or other study limitations and further research into the area would be beneficial. Epigenetic markers show promise for use in the future to facilitate the diagnosis of MPM.

The Future of Mesothelioma Research: Basic Science Research

Our current understanding of mesothelioma in terms of disease induction, development, and treatment is underpinned by decades of basic laboratory science. In this chapter, we discuss the tools that have been developed to aid our understanding of mesothelioma such as cell lines and animal models. We then go on to detail the current use and understanding of conventional therapies for mesothelioma, e.g. chemotherapy, surgery, and radiotherapy, plus their mechanisms of action, and why they may be ineffective. Finally, we discuss a range of newer treatments that are either undergoing clinical trials or are still in the earlier stages of preclinical investigation. These include a growing number of immunotherapies (e.g. checkpoint inhibitors), plus targeted therapies, the search for clinical biomarkers to predict whether patients with mesothelioma might respond to particular treatments, and combined therapies where conventional treatments may be added to newer drugs. The strategy of repositioning existing drugs, approved for other diseases, to treat mesothelioma is also discussed.

Chemical Profiling of Primary Mesothelioma Cultures Defines Subtypes with Different Expression Profiles and Clinical Responses

Purpose: Finding new treatment options for patients with malignant pleural mesothelioma is challenging due to the rarity and heterogeneity of this cancer type. The absence of druggable targets further complicates the development of new therapies. Current treatment options are therefore limited, and prognosis remains poor.Experimental Design: We performed drug screening on primary mesothelioma cultures to guide treatment decisions of corresponding patients that were progressive after first- or second-line treatment.Results: We observed a high concordance between in vitro results and clinical outcomes. We defined three subgroups responding differently to the anticancer drugs tested. In addition, gene expression profiling yielded distinct signatures that segregated the differently responding subgroups. These genes signatures involved various pathways, most prominently the fibroblast growth factor pathway.Conclusions: Our primary mesothelioma culture system has proved to be suitable to test novel drugs. Chemical profiling of primary mesothelioma cultures allows personalizing treatment for a group of patients with a rare tumor type where clinical trials are notoriously difficult. This personalized treatment strategy is expected to improve the poor prospects of patients with mesothelioma. Clin Cancer Res; 24(7); 1761-70. ©2017 AACRSee related commentary by John and Chia, p. 1513.

Advances in systemic therapy for malignant mesothelioma: future perspectives

Malignant mesothelioma is a rare and aggressive form of cancer affecting the mesothelium. This mainly occupational disease is becoming more common in those countries where asbestos has been used for industrial applications. Notwithstanding the progress made in the field, patients do not survive more than 12 months on average with standard treatment. With the advent of next generation sequencing, it is now possible to study the mutational landscape of each tumor with the aim of identifying the genetic aberrations driving tumorigenesis. This review encompasses the latest research in the field, with particular attention to new chemotherapy combinatorial regimens, molecular targets and immunotherapies, providing a comprehensive picture of the current and future treatment options for malignant mesothelioma patients.

Targeting the epigenome in malignant pleural mesothelioma

Malignant pleural mesotheliomas (MPM) are notoriously refractory to conventional treatment modalities. Recent insights regarding epigenetic alterations in MPM provide the preclinical rationale for the evaluation of novel combinatorial regimens targeting the epigenome in these neoplasms.

Promising in vivo efficacy of the BET bromodomain inhibitor OTX015/MK-8628 in malignant pleural mesothelioma xenografts

It has recently been reported that a large proportion of human malignant pleural mesothelioma (MPM) cell lines and patient tissue samples present high expression of the c-MYC oncogene. This gene drives several tumorigenic processes and is overexpressed in many cancers. Although c-MYC is a strategic target to restrain cancer processes, no drugs acting as c-MYC inhibitors are available. The novel thienotriazolodiazepine small-molecule bromodomain inhibitor OTX015/MK-8628 has shown potent antiproliferative activity accompanied by c-MYC downregulation in several tumor types. This study was designed to evaluate the growth inhibitory effect of OTX015 on patient-derived MPM473, MPM487 and MPM60 mesothelioma cell lines and its antitumor activity in three patient-derived xenograft models, MPM473, MPM487 and MPM484, comparing it with cisplatin, gemcitabine and pemetrexed, three agents which are currently used to treat MPM in the clinic. OTX015 caused a significant delay in cell growth both in vitro and in vivo. It was the most effective drug in MPM473 xenografts and showed a similar level of activity as the most efficient treatment in the other two MPM models (gemcitabine in MPM487 and cisplatin in MPM484). In vitro studies showed that OTX015 downregulated c-MYC protein levels in both MPM473 and MPM487 cell lines. Our findings represent the first evidence of promising therapeutic activity of OTX015 in mesothelioma.

The resistance related to targeted therapy in malignant pleural mesothelioma: Why has not the target been hit yet?

Malignant pleural mesothelioma (MPM) is an aggressive tumor of the pleura with a poor prognosis. The most active first-line regimens are platinum compounds and pemetrexed. There is no standard second-line treatment in MPM. Advances in the understanding of tumor molecular biology have led to the development of several targeted treatments, which have been evaluated in clinical trials. Unfortunately none of the explored targeted treatments can currently be recommended as routine treatment in MPM. We reviewed the biological pathways involved in MPM, the clinical trials about targeted therapy, and possible related mechanisms of resistance. We suggest that specific genetic markers are needed as targets of selective therapy. By this way the selection of patients based on the molecular profile may facilitate a therapeutic strategy that allows the use of the most appropriate drug for each patient.

Computational genomic analysis of PARK7 interactome reveals high BBS1 gene expression as a prognostic factor favoring survival in malignant pleural mesothelioma

The aim of our study was to assess the differential gene expression of Parkinson protein 7 (PARK7) interactome in malignant pleural mesothelioma (MPM) using data mining techniques to identify novel candidate genes that may play a role in the pathogenicity of MPM. We constructed the PARK7 interactome using the ConsensusPathDB database. We then interrogated the Oncomine Cancer Microarray database using the Gordon Mesothelioma Study, for differential gene expression of the PARK7 interactome. In ConsensusPathDB, 38 protein interactors of PARK7 were identified. In the Gordon Mesothelioma Study, 34 of them were assessed out of which SUMO1, UBC3, KIAA0101, HDAC2, DAXX, RBBP4, BBS1, NONO, RBBP7, HTRA2, and STUB1 were significantly overexpressed whereas TRAF6 and MTA2 were significantly underexpressed in MPM patients (network 2). Furthermore, Kaplan-Meier analysis revealed that MPM patients with high BBS1 expression had a median overall survival of 16.5 vs. 8.7 mo of those that had low expression. For validation purposes, we performed a meta-analysis in Oncomine database in five sarcoma datasets. Eight network 2 genes (KIAA0101, HDAC2, SUMO1, RBBP4, NONO, RBBP7, HTRA2, and MTA2) were significantly differentially expressed in an array of 18 different sarcoma types. Finally, Gene Ontology annotation enrichment analysis revealed significant roles of the PARK7 interactome in NuRD, CHD, and SWI/SNF protein complexes. In conclusion, we identified 13 novel genes differentially expressed in MPM, never reported before. Among them, BBS1 emerged as a novel predictor of overall survival in MPM. Finally, we identified that PARK7 interactome is involved in novel pathways pertinent in MPM disease.

Vorinostat in patients with advanced malignant pleural mesothelioma who have progressed on previous chemotherapy (VANTAGE-014): a phase 3, double-blind, randomised, placebo-controlled trial

BACKGROUND

Vorinostat is a histone deacetylase inhibitor that changes gene expression and protein activity. On the basis of the clinical benefit reported in patients with malignant pleural mesothelioma treated in a phase 1 study of vorinostat, we designed this phase 3 trial to investigate whether vorinostat given as a second-line or third-line therapy improved patients' overall survival.

METHODS

This double-blind, randomised, placebo-controlled trial was done in 90 international centres. Patients with measurable advanced malignant pleural mesothelioma and disease progression after one or two previous systemic regimens were eligible. After stratification for Karnofsky performance status, histology, and number of previous chemotherapy regimens, patients were randomly assigned (1:1) by use of an interactive voice response system with a block size of four to either treatment with vorinostat or placebo. Patients received oral vorinostat 300 mg (or matching placebo) twice daily on days 1, 2, 3, 8, 9, 10, 15, 16, and 17 of a 21-day cycle. The primary endpoints were overall survival and safety and tolerability of vorinostat. The primary efficacy comparison was done in the intention-to-treat population, and safety and tolerability was assessed in the treated population. This trial is registered with ClinicalTrials.gov, number NCT00128102.

FINDINGS

From July 12, 2005, to Feb 14, 2011, 661 patients were enrolled and randomly assigned to receive either vorinostat (n=329) or placebo (n=332) and included in the intention-to-treat analysis. Median overall survival for vorinostat was 30·7 weeks (95% CI 26·7-36·1) versus 27·1 weeks (23·1-31·9) for placebo (hazard ratio 0·98, 95% CI 0·83-1·17, p=0·86). The most common grade 3 or worse adverse events for patients treated with vorinostat were fatigue or malaise (51 [16%] patients in the vorinostat group vs 25 [8%] in the placebo group]) and dyspnoea (35 [11%] vs 45 [14%]).

INTERPRETATION

In this randomised trial, vorinostat given as a second-line or third-line therapy did not improve overall survival and cannot be recommended as a therapy for patients with advanced malignant pleural mesothelioma.

FUNDING

Merck & Co.

New and emerging therapeutic options for malignant pleural mesothelioma: review of early clinical trials

Malignant pleural mesothelioma (MPM) is a rare tumor that is challenging to control. Despite some benefit from using the multimodality-approach (surgery, combination chemotherapy and radiation), survival remains poor. However, current research produced a list of potential therapies. Here, we summarize significant new preclinical and early clinical developments in treatment of MPM, which include mesothelin specific antibody and toxin therapies, interleukin-4 (IL-4) receptor toxins, dendritic cell vaccines, immune checkpoint inhibitors, and gene-based therapies. In addition, several local modalities such as photodynamic therapy, postoperative lavage using betadine, and cryotherapy for local recurrence, have also shown to be effective for local control of disease.

Current issues in malignant pleural mesothelioma evaluation and management

Malignant pleural mesothelioma (MPM) is an uncommon disease most often associated with occupational asbestos exposure and is steadily increasing in worldwide incidence. Patients typically present at an older age, with advanced clinical stage and other medical comorbidities, making management quite challenging. Despite great efforts, the prognosis of MPM remains poor, especially at progression after initial treatment. Macroscopic complete resection of MPM can be achieved through extrapleural pneumonectomy (EPP) or extended (ie, radical) pleurectomy (e-P/D) in selected patients and can result in prolonged survival when incorporated into a multimodality approach. Given the morbidity associated with surgical resection of MPM, optimizing identification of appropriate patients is essential. Unfortunately, most patients are not candidates for EPP or e-P/D due to advanced stage, age, and/or medical comorbidity. Pemetrexed and platinum combination chemotherapy has become the cornerstone of therapy for patients with unresectable disease because the combination is associated with improved survival and quality of life in treated patients. However, MPM eventually becomes resistant to initial therapy, and benefit to further lines of therapy has not been substantiated in randomized clinical trials. Translational research has provided exciting insights into tumorigenesis, biomarkers, and immune response in MPM, leading to the development of multiple novel therapeutic agents that are currently in clinical trials. These advances hold the promise of a new era in the treatment of MPM and suggest that this disease will not be left behind in the war on cancer.

New histone deacetylase inhibitors improve cisplatin antitumor properties against thoracic cancer cells

Histone deacetylase inhibitors (HDACi) have shown promising antitumor effects on numerous cancer cells including malignant pleural mesothelioma (MPM) and lung adenocarcinoma (ADCA) cells. However, clinical trials using these compounds alone have shown limited efficacy against solid tumors. Therefore, new molecules are being developed and combinations with classical chemotherapeutic drugs are being tested. Here, we have evaluated on three MPM and three lung ADCA cell lines the antitumor potential of four new HDACi compounds, either alone or in combination with cisplatin. These effects were compared with those of vorinostat, an HDACi approved for cancer treatments. First, we characterized the HDAC mRNA expression profiles of tumor cells and showed an increase of the classI/classII HDAC ratio. We then treated cancer cells with these new HDACi and observed a cell-death induction and an increase of HDACi target genes and proteins expression. This was particularly evident for NODH compound (pan-HDACi) which had similar effects at nanomolar concentrations as micromolar concentrations of vorinostat. Interestingly, we observed that the HDACi/cisplatin combination strongly increased cell-death and limited resistance-phenotype emergence as compared with results obtained when the drugs were used alone. These results could be exploited to develop MPM and lung ADCA treatments combining chemotherapeutic approaches.

New insights into understanding the mechanisms, pathogenesis, and management of malignant mesotheliomas

Malignant mesothelioma (MM) is a relatively rare but devastating tumor that is increasing worldwide. Yet, because of difficulties in early diagnosis and resistance to conventional therapies, MM remains a challenge for pathologists and clinicians to treat. In recent years, much has been revealed regarding the mechanisms of interactions of pathogenic fibers with mesothelial cells, crucial signaling pathways, and genetic and epigenetic events that may occur during the pathogenesis of these unusual, pleiomorphic tumors. These observations support a scenario whereby mesothelial cells undergo a series of chronic injury, inflammation, and proliferation in the long latency period of MM development that may be perpetuated by durable fibers, the tumor microenvironment, and inflammatory stimuli. One culprit in sustained inflammation is the activated inflammasome, a component of macrophages or mesothelial cells that leads to production of chemotactic, growth-promoting, and angiogenic cytokines. This information has been vital to designing novel therapeutic approaches for patients with MM that focus on immunotherapy, targeting growth factor receptors and pathways, overcoming resistance to apoptosis, and modifying epigenetic changes.

Vorinostat eliminates multicellular resistance of mesothelioma 3D spheroids via restoration of Noxa expression

When grown in 3D cultures as spheroids, mesothelioma cells acquire a multicellular resistance to apoptosis that resembles that of solid tumors. We have previously found that resistance to the proteasome inhibitor bortezomib in 3D can be explained by a lack of upregulation of Noxa, the pro-apoptotic BH3 sensitizer that acts via displacement of the Bak/Bax-activator BH3-only protein, Bim. We hypothesized that the histone deacetylase inhibitor vorinostat might reverse this block to Noxa upregulation in 3D. Indeed, we found that vorinostat effectively restored upregulation of Noxa protein and message and abolished multicellular resistance to bortezomib in the 3D spheroids. The ability of vorinostat to reverse resistance was ablated by knockdown of Noxa or Bim, confirming the essential role of the Noxa/Bim axis in the response to vorinostat. Addition of vorinostat similarly increased the apoptotic response to bortezomib in another 3D model, the tumor fragment spheroid, which is grown from human mesothelioma ex vivo. In addition to its benefit when used with bortezomib, vorinostat also enhanced the response to cisplatin plus pemetrexed, as shown in both 3D models. Our results using clinically relevant 3D models show that the manipulation of the core apoptotic repertoire may improve the chemosensitivity of mesothelioma. Whereas neither vorinostat nor bortezomib alone has been clinically effective in mesothelioma, vorinostat may undermine chemoresistance to bortezomib and to other therapies thereby providing a rationale for combinatorial strategies.

The future of therapy for relapsed/refractory multiple myeloma: emerging agents and novel treatment strategies

Treatment of relapsed or refractory multiple myeloma (MM) continues to present a therapeutic challenge. The immunomodulatory drugs (IMiDs) thalidomide and lenalidomide, and the proteasome inhibitor (PI) bortezomib, have dramatically improved clinical outcomes for patients with newly diagnosed and relapsed/refractory MM. However, nearly all patients will eventually relapse or become refractory to these drugs. Numerous agents are currently in development for the treatment of relapsed/refractory MM. Those farthest along in clinical development include new IMiDs (pomalidomide), new PIs (eg, carfilzomib, MLN9708, and marizomib), histone deacetylase inhibitors (eg, panobinostat and vorinostat), monoclonal antibodies (eg, elotuzumab, siltuximab, and BT062), and signal transduction modulators (eg, perifosine). These emerging agents with diverse mechanisms of action have demonstrated promising anti-tumor activity in patients with relapsed/refractory MM, and rationally designed combinations with established agents are being investigated in the clinic. These new agents are creating opportunities to target multiple pathways, overcome resistance, and improve clinical outcomes, particularly for those patients who are refractory to approved novel agents. This article describes emerging antimyeloma agents in mid-stage to late-stage clinical development, and highlights the novel treatment approaches and combination strategies being evaluated in the relapsed/refractory setting.

Dendritic cell-based immunotherapy in mesothelioma

Mesothelioma is a rare thoracic malignancy with a dismal prognosis. Current treatment options are scarce and clinical outcomes are rather disappointing. Due to the immunogenic nature of mesothelioma, several studies have investigated immunotherapeutic strategies to improve the prognosis of patients with mesothelioma. In the last decade, progress in knowledge of the modulation of the immune system to attack the tumor has been remarkable, but the optimal strategy for immunotherapy has yet to be unraveled. Because of their potent antigen-presenting capacity, dendritic cells are acknowledged as a promising agent in immunotherapeutic approaches in a number of malignancies. This review gives an update and provides a future perspective in which immunotherapy may improve the outcome of mesothelioma therapy.

Sphingosine kinase 1 is required for mesothelioma cell proliferation: role of histone acetylation

Background

Malignant pleural mesothelioma (MPM) is a devastating disease with an overall poor prognosis. Despite the recent advances in targeted molecular therapies, there is a clear and urgent need for the identification of novel mesothelioma targets for the development of highly efficacious therapeutics.

Methodology/Principal Findings

In this study, we report that the expression of Sphingosine Kinase 1 (SphK1) protein was preferentially elevated in MPM tumor tissues (49 epithelioid and 13 sarcomatoid) compared to normal tissue (n = 13). In addition, we also observed significantly elevated levels of SphK1 and SphK2 mRNA and SphK1 protein expression in MPM cell lines such as H2691, H513 and H2461 compared to the non-malignant mesothelial Met5 cells. The underlying mechanism appears to be mediated by SphK1 induced upregulation of select gene transcription programs such as that of CBP/p300 and PCAF, two histone acetyl transferases (HAT), and the down regulation of cell cycle dependent kinase inhibitor genes such as p27Kip1 and p21Cip1. In addition, using immunoprecipitates of anti-acetylated histone antibody from SphK inhibitor, SphK-I2 treated Met5A and H2691 cell lysates, we also showed activation of other cell proliferation related genes, such as Top2A (DNA replication), AKB (chromosome remodeling and mitotic spindle formation), and suppression of p21 CIP1 and p27KIP1. The CDK2, HAT1 and MYST2 were, however, unaffected in the above study. Using SphK inhibitor and specific siRNA targeting either SphK1 or SphK2, we also unequivocally established that SphK1, but not SphK2, promotes H2691 mesothelioma cell proliferation. Using a multi-walled carbon nanotubes induced peritoneal mesothelioma mouse model, we showed that the SphK1−/− null mice exhibited significantly less inflammation and granulamatous nodules compared to their wild type counterparts.

Conclusions/Significance

The lipid kinase SphK1 plays a positive and essential role in the growth and development of malignant mesothelioma and is therefore a likely therapeutic target.

Molecular pathogenesis of malignant mesothelioma

Malignant mesothelioma is a rare, highly aggressive cancer arising from mesothelial cells that line the pleural cavities. Approximately 80% of mesothelioma cases can be directly attributed to asbestos exposure. Additional suspected causes or co-carcinogens include other mineral fibres, simian virus 40 (SV40) and radiation. A mesothelioma epidemic in Turkey has demonstrated a probable genetic predisposition to mineral fibre carcinogenesis and studies of human tissues and animal models of mesothelioma have demonstrated genetic and epigenetic events that contribute to the multistep process of mineral fibre carcinogenesis. Several growth factors and their receptors have a significant role in the oncogenesis, progression and resistance to therapy of mesothelioma. Epidermal growth factor (EGF), hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF) and insulin-like growth factor (IGF) have been shown as targets for therapy based on promising preclinical data. However, clinical trials of tyrosine kinase inhibitors in mesothelioma have been disappointing. Bcl-XL is an important antiapoptotic member of the Bcl-2 family and is overexpressed in several solid tumours, including mesothelioma. Reduction of Bcl-XL expression in mesothelioma induces apoptosis and engenders sensitisation to cytotoxic chemotherapeutic agents. Pharmacological inhibitors of antiapoptotic Bcl-2 family members continue to undergo refinement and have shown promise in mesothelioma.

Molecular changes in mesothelioma with an impact on prognosis and treatment

CONTEXT

In recent decades, research on malignant pleural mesothelioma (MPM) has been developed to improve patients' outcomes by increasing the level of confidence in MPM diagnosis and prognosis.

OBJECTIVE

To summarize data on genetic and epigenetic abnormalities in MPM that may be of interest for a better management of patients with MPM.

DATA SOURCES

Data were obtained from scientific publications on genetic and epigenetic abnormalities in MPM by studying gene mutations, DNA methylation, and gene and microRNA expression profiling.

CONCLUSIONS

Molecular changes in MPM consist in altered expression and in activation or inactivation of critical genes in oncogenesis, especially tumor suppressor genes at the INK4 and NF2 loci. Activation of membrane receptor tyrosine kinases and deregulation of signaling pathways related to differentiation, survival, proliferation, apoptosis, cell cycle control, metabolism, migration, and invasion have been demonstrated. Alterations that could be targeted at a global level (methylation) have been recently reported. Experimental research has succeeded especially in abolishing proliferation and triggering apoptosis in MPM cells. So far, targeted clinical approaches focusing on receptor tyrosine kinases have had limited success. Molecular analyses of series of MPM cases have shown that defined alterations are present in MPM subsets, consistent with interindividual variations of molecular alterations, and suggesting that identification of patient subgroups will be essential to develop more specific therapies.

Targeting histone deacetylases: development of vorinostat for the treatment of cancer

Reversible histone acetylation on lysine residues, regulated by the opposing activities of histone acetyltransferases and histone deacetylases (HDACs), plays an important role in the regulation of gene expression. Aberrant gene expression resulting from increased HDAC activity and histone hypoacetylation has been observed in human tumors and genetic knockdown studies support a role of HDACs in cancer. Treatment with small-molecule inhibitors of HDAC activity results in anti-tumor effects in a variety of transformed cell lines. Several HDAC inhibitors are in clinical development and show anti-tumor activity in cancer patients. Vorinostat (suberoylanilide hydroxamic acid) was the first HDAC inhibitor approved for the treatment of cancer and will be the focus of this article.

Novel therapies in phase II and III trials for malignant pleural mesothelioma

Mesothelioma is a rare malignancy of the pleura with limited therapeutic options. Despite the desperate need to develop better treatment for this disease, the rarity of the tumor type creates formidable challenges in clinical research. Nonetheless, several novel agents are under investigation. Most efforts are directed toward improving standard first-line therapy with pemetrexed and cisplatin, or developing effective second-line treatments. Several classes of drugs are being explored, including those that impact DNA transcription, cell-cycle progression, angiogenesis, and immune tolerance. This article describes several ongoing or recently completed phase II and III trials using novel agents vorinostat, everolimus, CBP501, MORAb-009, NGR-hTNF, WT1 vaccine, bevacizumab, cediranib, and thalidomide.

Medical treatment of mesothelioma: anything new?

In the present report, we review the current standard and investigational treatments of malignant pleural mesothelioma (MPM). Several studies have reported the use of gemcitabine and cisplatin as an induction chemotherapy in combination with extrapleural pneumonectomy (EPP) and thoracic radiation in a combined-modality approach for resectable MPM. Since the combination of cisplatin with pemetrexed was applied as the standard first-line regimen for unresectable MPM, the combination as an induction chemotherapy regimen has been proven effective in phase 2 trials. In addition, intensity-modulated radiation therapy and proton therapy have been introduced as new radiation methods into the combined modality. Hyperthermic intraoperative chemotherapy following EPP appears effective with acceptable toxicity. In addition, clinical studies that include molecular targeting agents, immunotherapy, and gene therapy have all been conducted. Thus, although there are numerous hopeful treatments for MPM, the benefits of these regimens remain to be proven in a randomized clinical setting.

Vorinostat/SAHA-induced apoptosis in malignant mesothelioma is FLIP/caspase 8-dependent and HR23B-independent

INTRODUCTION

Malignant pleural mesothelioma (MPM) is a rapidly fatal malignancy that is increasing in incidence. The caspase 8 inhibitor FLIP is an anti-apoptotic protein over-expressed in several cancer types including MPM. The histone deacetylase (HDAC) inhibitor Vorinostat (SAHA) is currently being evaluated in relapsed mesothelioma. We examined the roles of FLIP and caspase 8 in regulating SAHA-induced apoptosis in MPM.

METHODS

The mechanism of SAHA-induced apoptosis was assessed in 7 MPM cell lines and in a multicellular spheroid model. SiRNA and overexpression approaches were used, and cell death was assessed by flow cytometry, Western blotting and clonogenic assays.

RESULTS

RNAi-mediated FLIP silencing resulted in caspase 8-dependent apoptosis in MPM cell line models. SAHA potently down-regulated FLIP protein expression in all 7 MPM cell lines and in a multicellular spheroid model of MPM. In 6/7 MPM cell lines, SAHA treatment resulted in significant levels of apoptosis induction. Moreover, this apoptosis was caspase 8-dependent in all six sensitive cell lines. SAHA-induced apoptosis was also inhibited by stable FLIP overexpression. In contrast, down-regulation of HR23B, a candidate predictive biomarker for HDAC inhibitors, significantly inhibited SAHA-induced apoptosis in only 1/6 SAHA-sensitive MPM cell lines. Analysis of MPM patient samples demonstrated significant inter-patient variations in FLIP and caspase 8 expressions. In addition, SAHA enhanced cisplatin-induced apoptosis in a FLIP-dependent manner.

CONCLUSIONS

These results indicate that FLIP is a major target for SAHA in MPM and identifies FLIP, caspase 8 and associated signalling molecules as candidate biomarkers for SAHA in this disease.

Combined histone deacetylase and cyclooxygenase inhibition achieves enhanced antiangiogenic effects in lung cancer cells

Prostaglandin E2 (PGE2) is an important pro-angiogenic and pro-proliferative cytokine and the key enzymes modulating its levels, cyclooxygenase (COX)-2 and 15-hydroxyprostaglandin dehydrogenase (15-PGDH) play important opposing roles in carcinogenesis. Previously we found loss of 15-PGDH expression in lung cancer and its reactivation leads to strong in vivo tumor-suppressive effect via an antiangiogenic mechanism. Here, we find that HDAC inhibitors (HDACI), such as trichostatin A (TSA) and vorinostat could reactivate 15-PGDH expression but overall induce PGE2 generation and this is the result of concomitant induction of COX-1 and -2 leading to functional promotion of endothelial cell proliferation and capillary formation. Direct TSA treatment inhibits endothelial cell proliferation and capillary formation in our study in line with prior reports as HDACIs have been shown to directly inhibit angiogenesis. The elevation of PGE2 levels induced by HDACI is potently neutralized by indomethacin (INN) or Celecoxib co-treatment and accordingly, angiogenesis is more effectively inhibited when using conditioned medium of co-treatment than either alone confirming that this effect is mediated via the PGE2 axis. Accordingly, blockage of EP2/4 receptors mitigates the stimulation of angiogenesis by excessive PGE2 generation mediated by TSA. In this study, we identify a potentially adverse effect of HDACIs through induction of both 15-PGDH and COX-2 leading to elevated PGE2 levels and thereby stimulation of angiogenesis. Co-treatment of TSA and INN shows more potent anti-angiogenic effects by inducing 15-PGDH and inhibiting COX-2. Overall, our results suggest that combined HDACI and COX inhibition should be explored clinically to achieve more meaningful benefits from HDACI therapy in lung cancer.

Belinostat: clinical applications in solid tumors and lymphoma

INTRODUCTION

Histone deacetylase (HDAC) inhibitors have recently emerged as a novel and active class of anticancer agents. Belinostat is one member of the class that has been tested as a single agent and in combination with other chemotherapies and biological agents in the treatment of solid tumors and lymphoma.

AREAS COVERED

A literature search of pre-clinical and clinical studies of belinostat was performed. The data from these studies were analysed to summarise the progress of belinostat from Phase I to a current pivotal trial in peripheral T-cell lymphoma. The parallel development of appropriate biomarker analysis is also discussed.

EXPERT OPINION

Belinostat has demonstrated significant clinical activity in T-cell lymphomas. Although its activity as a single agent in solid tumors has been less compelling, the emerging results from combination trials are promising. However, the basis for the activity of belinostat, like that of other HDAC inhibitors, remains to be truly defined and the identification of predictive and prognostic biomarkers of activity should be established to further progress the development of this compound.

Epigenetic modulation enhances the therapeutic effect of anti-IL-13R(alpha)2 antibody in human mesothelioma xenografts

PURPOSE

The interleukin-13 receptor α2 (IL-13Rα2) is expressed by a variety of human malignant cells. Here, we have examined the constitutive surface expression and the epigenetic regulation of IL-13Rα2 by human mesothelioma. We have also investigated the therapeutic effect of the DNA methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) and anti-IL-13Rα2 monoclonal antibody on mesothelioma xenografts.

EXPERIMENTAL DESIGN

Cell surface expression of IL-13Rα2 by various lung carcinomas was analyzed using flow cytometry. Therapeutic effects of anti-IL-13Rα2 and 5-aza-dC were investigated using antibody-dependent cellular cytotoxicity and proliferation assays and by monitoring the survival of mesothelioma-bearing mice.

RESULTS

We found that human malignant mesotheliomas expressed surface IL-13Rα2 on their surface and that it was upregulated by treatment with 5-aza-dC. This augmented expression of IL-13Rα2 resulted in growth inhibition of the mesothelioma cells when cocultured with anti-IL-13Rα2 and effector cells, such as splenocytes and peritoneal exudate cells. The growth inhibition of mesothelioma cells was mediated by IFN-γ that was only detected in the supernatant when effector cells were exposed to 5-aza-dC-treated tumors in the presence of anti-IL-13Rα2. Compared with the control or either regimen alone, in vivo administration of anti-IL-13Rα2 in combination with 5-aza-dC significantly prolonged the survival of mice with mesothelioma xenografts.

CONCLUSIONS

These observations indicate a promising role for IL-13Rα2 as a target for antibody treatment in malignant mesothelioma, and, in combination with epigenetic regulation by a DNA methylation inhibitor, suggest the potential for a novel strategy to enhance therapeutic potency.

Challenges and prospects for pharmacotherapy in functional gastrointestinal disorders

Functional gastrointestinal disorders, such as irritable bowel syndrome and functional dyspepsia, are complex conditions with multiple factors contributing to their pathophysiology. As a consequence they are difficult to treat and have posed significant challenges to the pharmaceutical industry when trying to develop new and effective treatments. This review provides an overview of these difficulties and how the industry is reshaping its drug developmental strategies. It describes some of the more significant and encouraging advances that have occurred, and discusses how future research might embrace the opportunities provided by advances in genetic and in particular, epigenetic research.