New Agents in the Management of Advanced Mesothelioma

Malignant mesothelioma tumours: molecular pathogenesis, diagnosis, and therapies accompanying clinical studies

The pathetic malignant mesothelioma (MM) is a extremely uncommon and confrontational tumor that evolves in the mesothelium layer of the pleural cavities (inner lining- visceral pleura and outer lining- parietal pleura), peritoneum, pericardium, and tunica vaginalis and is highly resistant to standard treatments. In mesothelioma, the predominant pattern of lesions is a loss of genes that limit tumour growth. Despite the worldwide ban on the manufacture and supply of asbestos, the prevalence of mesothelioma continues to increase. Mesothelioma presents and behaves in a variety of ways, making diagnosis challenging. Most treatments available today for MM are ineffective, and the median life expectancy is between 10 and 12 months. However, in recent years, considerable progress has already been made in understanding the genetics and molecular pathophysiology of mesothelioma by addressing hippo signaling pathway. The development and progression of MM are related to many important genetic alterations. This is related to NF2 and/or LATS2 mutations that activate the transcriptional coactivator YAP. The X-rays, CT scans, MRIs, and PET scans are used to diagnose the MM. The MM are treated with surgery, chemotherapy, first-line combination chemotherapy, second-line treatment, radiation therapy, adoptive T-cell treatment, targeted therapy, and cancer vaccines. Recent clinical trials investigating the function of surgery have led to the development of innovative approaches to the treatment of associated pleural effusions as well as the introduction of targeted medications. An interdisciplinary collaborative approach is needed for the effective care of persons who have mesothelioma because of the rising intricacy of mesothelioma treatment. This article highlights the key findings in the molecular pathogenesis of mesothelioma, diagnosis with special emphasis on the management of mesothelioma.

Trimethylamine N-oxide: role in cell senescence and age-related diseases

INTRODUCTION

Hayflick and Moorhead first demonstrated cell senescence as the irreversible growth arrest of cells after prolonged cultivation. Telomere shortening and oxidative stress are the fundamental mechanisms that drive cell senescence. Increasing studies have shown that TMAO is closely associated with cellular aging and age-related diseases. An emerging body of evidence from animal models, especially mice, has identified that TMAO contributes to senescence from multiple pathways and appears to accelerate many neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. However, the specific mechanism of how TMAO speeds aging is still not completely clear.

MATERIAL AND METHODS

In this review, we summarize some key findings in TMAO, cell senescence, and age-related diseases. We focused particular attention on the potential mechanisms for clinical transformation to find ways to interfere with the aging process.

CONCLUSION

TMAO can accelerate cell senescence by causing mitochondrial damage, superoxide formation, and promoting the generation of pro-inflammatory factors.

A Phase II Study of Pazopanib in Patients with Malignant Pleural Mesothelioma: NCCTG N0623 (Alliance)

PURPOSE

Preclinical and clinical data have shown promise in using antiangiogenic agents to treat malignant pleural mesothelioma (MPM). We conducted this phase II study to evaluate the efficacy and toxicity of single-agent pazopanib in patients with MPM.

MATERIALS AND METHODS

Patients with MPM who had received 0-1 prior chemotherapy regimens were eligible to receive pazopanib at a dose of 800 mg daily. The primary endpoint was progression-free survival rate at 6 months (PFS6), with a preplanned interim analysis for futility. Secondary endpoints included overall survival (OS), PFS, adverse events assessment and clinical benefit (complete response, partial response [PR], and stable disease [SD]).

RESULTS

Thirty-four evaluable patients were enrolled, with a median age of 73 years (49-84). The trial was closed early because of lack of efficacy at the preplanned interim analysis. Only 8 patients (28.6%; 95% confidence interval [CI], 13.2-48.7%) in the first 28 evaluable were progression-free at 6 months. PFS6 was 32.4% (95% CI, 17.4-50.5). There were 2 PR (5.9%) and 16 SD (47.1%). The overall median PFS and OS were 4.2 months (95% CI, 2.0-6.0) and 11.5 months (95% CI: 5.3-18.2), respectively. The median PFS and OS for the previously untreated patients was 5.4 months (95% CI, 2.7-8.5) and 16.6 months (95% CI, 6.6-30.6), respectively; and 2.0 months (95% CI, 1.3-4.2) and 5.0 months (95% CI: 3.0-11.9), respectively, for the previously treated patients. Grade 3 or higher adverse events were observed in 23 patients (67.6%).

CONCLUSION

Single-agent pazopanib was poorly tolerated in patients with MPM. The primary endpoint of PFS6 was not achieved in the current study. ClinicalTrials.gov identification number. NCT00459862.

IMPLICATIONS FOR PRACTICE

Single-agent pazopanib did not meet its endpoint in this phase II trial in malignant mesothelioma. Pazopanib is well tolerated in mesothelioma patients with a manageable toxicity profile. There is a need to better identify signals of angiogenesis that can be targeted in mesothelioma. Encouraging findings in frontline treatment warrant further investigations in combination with chemotherapy or immunotherapy.

Novel systemic therapy against malignant pleural mesothelioma

Malignant pleural mesothelioma is an aggressive tumor of the pleura with an overall poor prognosis. Even with surgical resection, for which only a subset of patients are eligible, long term disease free survival is rare. Standard first-line systemic treatment consists of a platinum analog, an anti-metabolite, and sometimes anti-angiogenic therapy, but there is currently no well-established standard therapy for refractory or relapsed disease. This review focuses on efforts to develop improved systemic therapy for the treatment of malignant pleural mesothelioma (MPM) including cytotoxic systemic therapy, a variety of tyrosine kinase inhibitors and their downstream effector pathways, pharmacologic targeting of the epigenome, novel approaches to target proteins expressed on mesothelioma cells (such as mesothelin), arginine depletion therapy, and the emerging role of immunotherapy. Overall, these studies demonstrate the challenges of improving systemic therapy for MPM and highlight the need to develop therapeutic strategies to control this disease.

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.

Combination effect of photodynamic therapy using NPe6 with pemetrexed for human malignant pleural mesothelioma cells

To identify a possible new treatment modality for malignant pleural mesothelioma (MPM), we examined whether combination treatment consisting of pemetrexed chemotherapy and photodynamic therapy (PDT) using the photosensitizer NPe6, enhanced the antitumor effect in both in vitro and in vivo models. We also investigated preclinical treatment schedules. Four human malignant mesothelioma cell lines (MSTO‑211H, H2052, H2452 and H28) were assayed using the WST assay after treatment with pemetrexed and NPe6‑PDT. The treatment schedule for the combination treatment was examined using nude mice. Pemetrexed pre‑treatment enhanced the lethal effect of NPe6‑PDT in the four malignant mesothelioma cell lines, but NPe6‑PDT followed by pemetrexed treatment did not enhance cell lethality in the in vitro assay. Pemetrexed pre‑treatment did not enhance the intracellular accumulation of NPe6, which is one of the determinants of the antitumor effect of PDT. In nude mice injected with MSTO‑211H cells and then treated using a combination of pemetrexed and NPe6‑PDT (10 mg/kg NPe6, 10 J/cm(2) laser irradiation), the tumor volume decreased by 50% but subsequently increased, reaching the pre‑treatment value after 14 days. Pemetrexed treatment followed by NPe6‑PDT resulted in an 80% reduction in the tumor size and inhibited re‑growth. NPe6‑PDT followed by pemetrexed treatment resulted in a 60% reduction in tumor size but did not inhibit re‑growth. NPe6‑PDT induced the expression of thymidylate synthase (TS), which confers resistance to pemetrexed, and NPe6‑PDT followed by pemetrexed treatment did not enhance the treatment outcome in vivo. In conclusion, combination treatment, consisting of pemetrexed followed by NPe6‑PDT, should be further investigated as a new treatment modality for MPM. In the future, this combination treatment may contribute to a reduction in local recurrence and a prolonged survival period in patients with MPM.

Ranpirnase and its potential for the treatment of unresectable malignant mesothelioma

Ribonucleases are a superfamily of enzymes which operate at the crossroads of transcription and translation, catalyzing the degradation of RNA; they can be cytotoxic because the cleavage of RNA renders indecipherable its information. Ranpirnase is a novel ribonuclease which preferentially degrades tRNA, thus leading to inhibition of protein synthesis and, ultimately, to cytostasis and cytotoxicity. Ranpirnase has demonstrated antitumor activity both in vitro and in vivo in several tumor models. The maximum tolerated dose emerging from phase I studies was 960 g/m², with renal toxicity as the main dose-limiting toxicity. A large phase II trial showed that ranpirnase has disease-modifying activity against malignant mesothelioma. Ranpirnase proved to be superior to doxorubicin in a phase III trial, while preliminary results of another large, phase III trial, suggest that the combination of ranpirnase and doxorubicin could be more effective than doxorubicin alone. In all the above studies, ranpirnase seems to act mainly as a cytostatic rather than a cytotoxic drug, stabilizing progressive disease and potentially prolonging patients’ survival. Ranpirnase may thus find its niche in combination with doxorubicin for mesothelioma as a second-line therapy, where no standard of care presently exists.

Review on clinical trials of targeted treatments in malignant mesothelioma

PURPOSE

Malignant mesothelioma (MM) is an aggressive tumor of the serosal surfaces with a poor prognosis. Advances in the understanding of tumor biology have led to the development of several targeted treatments, which have been evaluated in clinical trials. This article is a comprehensive review of all clinical trials evaluating the effect of targeted treatments in MM.

METHODS

An extensive literature search was performed in January 2011 using pubmed and medline. No constraints on publication date were applied.

RESULTS

Thirty-two trials exploring 17 different targeted agents in MM were found. Treatment in first- and second-line targeted agents induced response rates ranging from 0-14% and 0-16%, respectively. The tyrosine kinase inhibitor sunitinib induced partial response in 10% and stable disease in 66% of MPM patients as second-line treatment. A preliminary analysis of a phase II/III trial suggests that addition of bevacizumab to pemetrexed and cisplatin first-line treatment significantly improves disease control (CR + PR + SD) in the bevacizumab arm (73.5%) compared with treatment with pemetrexed and cisplatin without bevacizumab (43.2%) (P = 0.010). Another phase II trial did not observe any significant clinical benefit of adding of bevacizumab to gemcitabine and cisplatin.

CONCLUSIONS

Disease stabilization is reported in some patients with several targeted treatments and might be beneficial in subgroups of patients or in combination with classic chemotherapy. None of the hitherto explored targeted treatments can currently be recommended as standard treatment in MM.

HER1-targeted 86Y-panitumumab possesses superior targeting characteristics than 86Y-cetuximab for PET imaging of human malignant mesothelioma tumors xenografts

Malignant mesothelioma (MM), a rare form of cancer is often associated with previous exposure to fibrous minerals, such as asbestos. Asbestos exposure increases HER1-activity and expression in pre-clinical models. Additionally, HER1 over-expression is observed in the majority of MM cases. In this study, the utility of HER1-targeted chimeric IgG₁, cetuximab, and a human IgG₂, panitumumab, radiolabeled with ⁸⁶Y, were evaluated for PET imaging to detect MM non-invasively in vivo, and to select an antibody candidate for radioimmunotherapy (RIT).

Methods

Radioimmunoconjugates (RICs) of cetuximab and panitumumab were prepared by conjugation with CHX-A’’-DTPA followed by radiolabeling with ⁸⁶Y. The HER1 expression of NCI-H226, NCI-H2052, NCI-H2452 and MSTO-211H human mesothelioma cells was characterized by flow cytometry. In vivo biodistribution, pharmacokinetic analysis, and PET imaging were performed in tumor bearing athymic mice.

Results

In vivo studies demonstrated high HER1 tumor uptake of both RICs. Significant reduction in tumor uptake was observed in mice co-injected with excess mAb (0.1 mg), demonstrating that uptake in the tumor was receptor specific. Significant differences were observed in the in vivo characteristics of the RICs. The blood clearance T_½α of ⁸⁶Y-cetuximab (0.9–1.1 h) was faster than ⁸⁶Y-panitumumab (2.6–3.1 h). Also, the tumor area under the curve (AUC) to liver AUC ratios of ⁸⁶Y-panitumumab were 1.5 to 2.5 times greater than ⁸⁶Y-cetuximab as observed by the differences in PET tumor to background ratios, which could be critical when imaging orthotopic tumors and concerns regarding radiation doses to normal organs such as the liver.

Conclusion

This study demonstrates the more favorable HER1-targeting characteristics of ⁸⁶Y-panitumumab than ⁸⁶Y-cetuximab for non-invasive assessment of the HER1 status of MM by PET imaging. Due to lower liver uptake, panitumumab based immunoconjugates may fare better in therapy than corresponding cetuximab based immunoconjugates.

Ribonucleases as potential modalities in anticancer therapy

Antitumor ribonucleases are small (10-28 kDa) basic proteins. They were found among members of both, ribonuclease A and T1 superfamilies. Their cytotoxic properties are conferred by enzymatic activity, i.e., the ability to catalyze cleavages of phosphodiester bonds in RNA. They bind to negatively charged cell membrane, enter cells by endocytosis and translocate to cytosol where they evade mammalian protein ribonuclease inhibitor and degrade RNA. Here, we discuss structures, functions and mechanisms of antitumor activity of several cytotoxic ribonucleases with particular emphasis to the amphibian Onconase, the only enzyme of this class that reached clinical trials. Onconase is the smallest, very stable, less catalytically efficient and more cytotoxic than most RNase A homologues. Its cytostatic, cytotoxic and anticancer effects were extensively studied. It targets tRNA, rRNA, mRNA as well as the non-coding RNA (microRNAs). Numerous cancer lines are sensitive to Onconase; their treatment with 10-100 nM enzyme leads to suppression of cell cycle progression, predominantly through G(1), followed by apoptosis or cell senescence. Onconase also has anticancer properties in animal models. Many effects of this enzyme are consistent with the microRNAs, one of its critical targets. Onconase sensitizes cells to a variety of anticancer modalities and this property is of particular interest, suggesting its application as an adjunct to chemotherapy or radiotherapy in treatment of different tumors. Cytotoxic RNases as exemplified by Onconase represent a new class of antitumor agents, with an entirely different mechanism of action than the drugs currently used in the clinic. Further studies on animal models including human tumors grafted on severe combined immunodefficient (SCID) mice and clinical trials are needed to explore clinical potential of cytotoxic RNases.

Lymph node dissection in primary intrahepatic malignant mesothelioma: case report and implications for diagnosis and therapy

INTRODUCTION

In this rare case of intrahepatic malignant mesothelioma with subsequent lymph node metastases, hepatic segmentectomy in combination with repeated lymphadenectomy resulted in prolonged survival, currently 37 months after initial diagnosis.

DISCUSSION

Immunohistochemically, vascular endothelial growth factor receptor-1 expressing tumor cells were surrounded by a dense D 2-40-positive lymphangiovascular network, suggesting tumor induced lymphangiogenesis correlating to 2-deoxy-2[(18)F]fluoro-d-glucose-positron emission tomography/computed tomography-positive recurrent intraabdominal and intrathoracic lymphatic tumor spread. Therefore, extended lymphadenectomy during primary tumor resection and combined adjuvant chemotherapy with promising anticancer agents possessing antilymphangiogenic and antimetabolite properties should be considered to prolong survival in cases of extrathoracic malignant mesothelioma. Additionally, as shown in our case, individual operative concepts and (sometimes) multiple operations can be beneficial for highly selected patients. Importantly, a case-by-case optimized antitumor regimen requires interdisciplinary expertise and consensus of all involved faculties.

Anti-proliferative effects of simocyclinone D8 (SD8), a novel catalytic inhibitor of topoisomerase II

INTRODUCTION

Simocyclinone D-8 (SD8), a semi-synthetic compound derived from yeast, has been shown to decrease the proliferation of MCF-7 breast cancer cells. It has been shown to be a potent bacterial DNA gyrase inhibitor, a homologue of human topoisomerase II (hTopoII). We tested SD8 activity alone and in combination with cisplatin against malignant mesothelioma (MM) and non-small cell cancer (NSCLC) cell lines.

METHODS

Inhibition of hTopoII supercoiling function by SD8 and a known hTopoII poison, etoposide, were done by in vitro assay using purified hTopoII and kinetoplast DNA as the substrate. The DNA products were analyzed by agarose gel electrophoresis after treatment with increasing concentrations of each drug. Mesothelioma cell lines (H2373, H2461 and H2596) and NSCLC cell lines (H2030, H460, and H2009) grown in RPMI with 10% calf serum were used. Non-malignant mesothelial cells, LP9, were grown in 1:1 ratio of MCDB:199E medium supplemented with 15% calf serum, 0.4 microg/mL hydrocortisone, and 15 ng/mL epidermal grown factor. Cell proliferation assays were performed in 96-well plates using the CCK-8 kit (Dojindo inc.). Cells were treated for 72 h with various SD8 concentrations and controls containing equal volume of the vehicle, DMSO. Treated cells were assayed for the induction of apoptosis with poly ADP-ribose polymerase-1 (PARP) cleavage assay.

RESULTS

Biochemical assays revealed that the IC(50) for hTopoII inhibition was 100 microM for SD8 and 400 microM for etoposide. SD8 inhibited hTopoII function without inducing DNA cleavage events. SD8 inhibited the growth of NSCLC and Mesothelioma cells with IC(50) ranging from 75-125 microM. Furthermore, SD8 was not toxic to non-transformed primary mesothelial cell line, LP9 at the IC(50) doses. SD8 induced apoptosis in all cell lines tested.

CONCLUSIONS

SD8 inhibits hTopoII in vitro without inducing DNA strands breaks and has significant activity against NSCLC and MM cell lines. While doses required for SD8 anticancer activity are unlikely to be achieved in vivo, chemical modifications to SD8 to increase its potency could lead to improved therapies for these diseases.

The cytotoxic ribonuclease onconase targets RNA interference (siRNA)

Onconase (Onc), a ribonuclease from oocytes of Northern Leopard frogs (Rana pipiens) is cytostatic and cytotoxic to a variety of tumor lines in vitro, inhibits growth of tumors in animal in vivo models and enhances sensitivity of tumor cells to a number of other cytotoxic agents with diverse mechanism of action. In Phase III clinical trials Onc demonstrated significant efficacy in patients with malignant mesothelioma that failed prior chemotherapy. We previously postulated that the antitumor activity of Onc and the observed synergisms with other antitumor modalities at least in part may be mediated by targeting RNA interference (RNAi). In the present study we observed that the silencing of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene in human lung adenocarcinoma A549 cells by siRNA was effectively prevented by Onc. While transfection of cells with GAPDH siRNA reduced expression of this protein by nearly 70%, the expression was restored in the cells exposed to 0.8 muM Onc for 48 or 72 h. The data thus provide evidence that one of the targets of Onc is siRNA, likely within the RNA-induced silencing complex (RISC). In light of the findings that microRNAs are involved in tumor pathogenesis as well as in enhancing cell resistance to anticancer therapy the present data may provide explanation for both, the antitumor Onc activity and its propensity to enhance effectiveness of cytotoxic drugs.

Ranpirnase as a potential antitumor ribonuclease treatment for mesothelioma and other malignancies

Ranpirnase, originally isolated from oocytes of the northern leopard frog (Rana pipiens), is a member of the pancreatic RNase A superfamily of ribonucleases. Ranpirnase exerts antiproliferative and cytotoxic effects in vitro and in vivo and has been shown to act synergistically with different cancer therapeutic agents. The cytotoxic and cytostatic effects of ranpirnase are the consequence of tRNA degradation that results in the disruption of protein translation and the induction of programmed cell death (apoptosis). Ranpirnase has been shown to target malignant cells both in human cancer cell lines and in animal models, and has demonstrated efficacy in the treatment of several human cancers in clinical studies. Most clinical studies have been conducted in patients with malignant mesothelioma, and a confirmatory Phase IIIb trial is currently underway for the treatment of this disease. Owing to its selective destruction of malignant cells and favorable toxicology profile, ranpirnase is a promising antitumor agent with ideal attributes that are generally lacking in conventional cytotoxic drugs.

Remarkable enhancement of cytotoxicity of onconase and cepharanthine when used in combination on various tumor cell lines

Onconase (Onc), a ribonuclease from oocytes or early embryos of Northern Leopard frog (Rana pipiens), is cytostatic and cytotoxic to a variety of tumor lines in vitro, inhibits growth of tumors in animal in vivo models and is currently in Phase IIIb clinical trials for malignant mesothelioma where it displays antitumor activity with minor overall toxicity to the patient. One of the characteristic features of Onc is a synergism with a variety of other antitumor modalities. Cepharanthine (Cep), a biscoclaurine alkaloid from Stephania cepharantha Hayata, is widely used in Japan to treat variety of ailments. It also shows low toxicity to patients. The aim of the present study was to assess the interaction of these two drugs on different tumor cell lines. When human promyelocytic leukemia HL-60, histiomonocytic lymphoma U937, multiple myeloma RPMI-8228, prostate carcinoma DU 145 and prostate adenocarcinoma LNCaP cells were exposed to relatively low concentrations of Onc or Cep their growth rates were somewhat suppressed but the cells were still able to proliferate. Cell growth, however, was totally abolished in each of these cell lines when treated with Onc and Cep combined. The frequency of apoptosis was also many-fold higher in cultures treated with a combination of Onc and Cep than in respective cultures treated with Onc or Cep alone. The mechanism of the observed synergism is unclear but it may be associated with the Onc activity in targeting microRNAs and/or NFkappaB and Cep activity also targeting NFkappaB. The data suggest that the combination of these two drugs, that individually express a low toxic profile, may have strong antitumor potential.

Bcl-xL antisense oligonucleotide and cisplatin combination therapy extends survival in SCID mice with established mesothelioma xenografts

Bcl-xL functions as a dominant regulator of apoptotic cell death and is implicated in chemotherapeutic resistance of malignant pleural mesothelioma (MPM). Mesothelioma cell lines demonstrate increasing levels of Bcl-xL as resistant clones are selected in vitro. Moreover, upon introduction of antisense oligonucleotides specific to Bcl-xL mRNA, MPM cells are sensitized to chemotherapeutic agents. Here we describe the therapeutic effects of a novel combination therapy, Bcl-xL antisense oligonucleotide (ASO 15999) and cisplatin, on mesothelioma cell lines in vitro and in vivo; in addition, efficacy of ASO 15999 in decreasing tumor load as well as its effect on survival in an animal model. Finally, we initiated preliminary toxicity studies involved with intraperitoneal (IP) injections of ASO 15999 into mice. This novel combination, with doses of cisplatin four times below established IC(50) levels, significantly decreased viability of MPM cell lines after 48 hr. The growth of established mouse flank human tumor xenografts was reduced with intra-tumor administration of ASO 15999. Local spread and development of IP xenografts was reduced with treatments of ASO alone, and survival of mice afflicted with these xenografts was prolonged after administration of ASO alone and ASO 15999 + cisplatin combination therapy. These findings suggest that ASO 15999 sensitizes MPM cell lines to the toxic effects of cisplatin. ASO 15999 induced reduction of Bcl-xL is effective in slowing the progression of human mesothelioma cell lines both in vitro and in vivo. More notably, the combination of Bcl-xL ASO and cisplatin extends survival in an orthotopic tumor xenograft model.

Multidisciplinary treatment of malignant pleural mesothelioma

The incidence of malignant pleural mesothelioma (MPM) is increasing worldwide, and is predicted to peak in the next 10-20 years. Difficulties in MPM diagnosis and staging, especially of early disease, have thwarted the development of a universally accepted therapeutic approach. Single modality therapies (surgery, radiotherapy, chemotherapy) have generally failed to significantly prolong patient survival. As a result, multimodality treatment regimens have been developed. Radical surgery with extrapleural pneumonectomy and adjuvant treatments has become the preferred option in early disease, but the benefits of such an aggressive approach have been questioned because of significant treatment-related morbidity and mortality. In the past few years, there have been several major advances in the management of patients with MPM, including more accurate staging and patient selection, improvements in surgical techniques and postoperative care, novel chemotherapy regimens with definite activity such as antifolate (pemetrexed or raltitrexed)-platinum combinations, and new radiotherapy techniques such as intensity-modulated radiation therapy. Induction chemotherapy followed by surgery and adjuvant radiotherapy has shown promising results. A number of molecular alterations occurring in MPM have been reported, providing broader insights into its biology and leading to the identification of new targets for therapy. However, currently available treatments still appear to have modest results. Further studies are needed to provide evidence-based recommendations for the treatment of early and advanced stages of this disease.

Advances in the systemic therapy of malignant pleural mesothelioma

Malignant pleural mesothelioma is an aggressive thoracic malignancy associated with exposure to asbestos, and its incidence is anticipated to increase during the first half of this century. Chemotherapy is the mainstay of treatment, yet sufficiently robust evidence to substantiate the current standard of care has emerged only in the past 5 years. This Review summarizes the evidence supporting the clinical activity of chemotherapy, discusses the use of end points for its assessment and examines the influence of clinical and biochemical prognostic factors on the natural history of malignant pleural mesothelioma. Early-phase clinical trials of second-line and novel agents are emerging from an increased understanding of mesothelioma cell biology. Coupled with high-quality translational research, such developments have real potential to improve the outlook of patients at a time of increasing incidence.

In vivo loss of expression of argininosuccinate synthetase in malignant pleural mesothelioma is a biomarker for susceptibility to arginine depletion

PURPOSE

Malignant pleural mesothelioma (MPM) is an increasing health burden on many societies worldwide and, being generally resistant to conventional treatment, has a poor prognosis with a median survival of <1 year. Novel therapies based on the biology of this tumor seek to activate a proapoptotic cellular pathway. In this study, we investigated the expression and biological significance of argininosuccinate synthetase (AS), a rate-limiting enzyme in arginine production.

EXPERIMENTAL DESIGN

Initially, we documented down-regulation of AS mRNA in three of seven MPM cell lines and absence of AS protein in four of seven MPM cell lines. We confirmed that the 9q34 locus, the site of the AS gene, was intact using a 1-Mb comparative genomic hybridization array; however, there was aberrant promoter CpG methylation in cell lines lacking AS expression, consistent with epigenetic regulation of transcription. To investigate the use of AS negativity as a therapeutic target, arginine was removed from the culture medium of the MPM cell lines.

RESULTS

In keeping with the cell line data, 63% (52 of 82) of patients had tumors displaying reduced or absent AS protein, as assessed using a tissue microarray. Cell viability declined markedly in the AS-negative cell lines 2591 and MSTO but not in the AS-positive cell line, 28. This response was apparent by day 4 and maintained by day 9 in vitro. Arginine depletion induced BAX conformation change and mitochondrial inner membrane depolarization selectively in AS-negative MPM cells.

CONCLUSIONS

In summary, we have identified AS negativity as a frequent event in MPM in vivo, leading to susceptibility to cytotoxicity following restriction of arginine. A phase II clinical trial is planned to evaluate the role of arginine depletion in patients with AS-negative MPM.

Preliminary data suggestive of a novel translational approach to mesothelioma treatment: imatinib mesylate with gemcitabine or pemetrexed

BACKGROUND

Malignant mesothelioma is a cancer which is refractory to current treatments. Imatinib mesylate is a selective inhibitor of tyrosine kinases such as bcr-abl, c-Kit, c-Fms and platelet derived growth factor receptor beta (PDGFRbeta). PDGFRbeta is often overexpressed in mesothelioma cells and is a therapeutic target for imatinib in some solid tumours. A study was undertaken to assess whether imatinib alone or combined with chemotherapeutic agents may be effective for treating mesothelioma.

METHODS

Cultures from mesothelioma MMP, REN and ISTMES2 cell lines were treated with imatinib alone or in combination with a chemotherapeutic agent.

RESULTS

Imatinib induced cytotoxicity and apoptosis selectively on PDGFRbeta positive mesothelioma cells via blockade of receptor phosphorylation and interference with the Akt pathway. Of the chemotherapeutic agents tested in combination with imatinib, a synergistic effect was obtained with gemcitabine and pemetrexed.

CONCLUSIONS

This study provides a rationale for a novel translational approach to the treatment of mesothelioma which relies on enhancement of tumour chemosensitivity by inhibition of Akt.

Expression of Cancer-Associated Molecules in Malignant Mesothelioma

Malignant mesothelioma (MM) is a malignant tumor derived from mesothelial cells, native cells of the body cavities. Exposure to asbestos is the most strongly established etiologic factor, predominantly for the most common disease form, pleural mesothelioma. The pathogenesis of MM involves the accumulation of extensive cytogenetic changes, as well as cancer-related phenotypic alterations that facilitate tumor cell survival, invasion and metastasis. This review presents current knowledge regarding the biological characteristics of this disease that are linked to the so-called hallmarks of cancer. In addition, data suggesting that the anatomic site (solid tumor vs. effusion) affects the expression of metastasis-associated and regulatory molecules in MM are presented. Finally, recent work in which high-throughput methodology has been applied to MM research is reviewed. The data obtained in the reviewed research may aid in defining new prognostic markers and therapeutic targets for this aggressive disease in the future.

Management of Malignant Pleural Mesothelioma

Malignant mesothelioma is increasing in incidence globally and has no known cure. Its unique clinical feature of local infiltration along tissue planes makes it a difficult neoplasm to manage. There have been few randomized controlled trials regarding treatment options, although these have increased in recent years, and results are eagerly awaited. This article summarizes important advances in the management of mesothelioma, especially diagnostic and therapeutic aspects.

Role of thioredoxin-1 in apoptosis induction by alpha-tocopheryl succinate and TNF-related apoptosis-inducing ligand in mesothelioma cells

Malignant mesothelioma (MM) is a fatal type of cancer. We studied the role of the redox-active protein thioredoxin-1 (Trx-1) in apoptosis induced in MM cells and their non-malignant counterparts (Met-5A) by alpha-tocopheryl succinate (alpha-TOS) and TNF-related apoptosis-inducing ligand (TRAIL). MM cells were susceptible to alpha-TOS and less to TRAIL, while Met-5A cells were susceptible to TRAIL and resistant to alpha-TOS. MM cells expressed very low level of the Trx-1 protein, which was high in Met-5A cells, while the level of Trx-1 mRNA was similar in all cell lines. Downregulation of Trx-1 further sensitised Met-5A cells to TRAIL but not to alpha-TOS. Our data suggest that the role of Trx-1 in apoptosis modulation is unrelated to its anti-oxidant properties.