Antisense therapy for malignant mesothelioma with oligonucleotides targeting the bcl-xl gene product

The role of BCL-2 family proteins and therapeutic potential of BH3-mimetics in malignant pleural mesothelioma

Introduction: With limited recent therapeutic changes, malignant pleural mesothelioma (MPM) is associated with poor survival and death within 12 months, making it one of the most lethal malignancies. Due to unregulated asbestos use in developing countries and home renovation exposures, cases of MPM are likely to present for decades. As MPM is largely driven by dysregulation of tumor suppressor genes, researchers have examined other mechanisms of subverting tumor proliferation and spread. Over-expression of pro-survival BCL-2 family proteins impairs cells from undergoing apoptosis, and BH3-mimetics  targeting them are a novel treatment option across various cancers, though have not been widely investigated in MPM.Areas covered: This review provides an overview of MPM and its current treatment landscape. It summarizes the role of BCL-2 family proteins in tumorigenesis and the therapeutic potential of BH3-mimetics . Finally, it discusses the role of BCL-2 proteins in MPM and the pre-clinical rationale for investigating BH3-mimetics as a therapeutic strategy.Expert opinion: As a disease without readily actionable oncogene driver mutations and with modest benefit from immune checkpoint inhibition, novel therapeutic options are urgently needed for MPM. Hence, BH3-mimetics provide a promising treatment option, with evidence supporting dependence on pro-survival BCL-2 proteins for MPM cell survival.

BCL-XL is an actionable target for treatment of malignant pleural mesothelioma

Despite having one of the lowest survival rates of all cancers, there have been no new approved treatments for malignant pleural mesothelioma (MPM) in over a decade. Standard-of-care treatment relies on Cisplatin plus Pemetrexed chemotherapy. Here, we tested a suite of BH3-mimetic drugs targeting BCL-2 pro-survival proteins of the intrinsic apoptotic pathway. We found BCL-XL is the dominant pro-survival protein in a panel of cell lines in vitro, though potent, synergistic cell killing occurred with MCL-1 co-targeting. This correlates with high-level expression of BCL-XL and MCL-1 in cell lines and a large cohort of patient tumour samples. BCL-XL inhibition combined with Cisplatin also enhanced cell killing. In vivo BCL-XL inhibition was as effective as Cisplatin, and the combination enhanced tumour growth control and survival. Genetic ablation of MCL-1 also enhanced the effects of BCL-XL inhibitors, in vivo. Combined, these data provide a compelling rationale for the clinical investigation of BH3-mimetics targeting BCL-XL in MPM.

Variation in apoptotic gene expression in cervical cancer through oligonucleotide microarray profiling

OBJECTIVE

The current study aimed to investigate the molecular basis of cervical cancer development using a microarray to identify the differentially expressed genes. This study also aimed to detect apoptosis genes and proteins to find those genes most aberrantly expressed in cervical cancer and to explore the cause of Uighur cervical cancer.

METHODS

An analysis of gene expression profiles obtained from cervical cancer cases was performed. Total RNA was prepared from 10 samples of cervical carcinoma and normal cervix and was hybridized to Affymetrix oligonucleotide microarrays with probe sets complementary to more than 20,000 transcripts. Several genes of the apoptosis pathway, which were differentially regulated, included BCL2, BCLXL, and c-IAP1. These were validated by quantitative reverse transcription-polymerase chain reaction and immunohistochemical staining on an independent set of cancer and control specimens.

RESULTS

Unsupervised hierarchical clustering of the expression data readily distinguished the normal cervix from cancer. Supervised analysis of gene expression data identified 1,326 and 1,432 genes that were upregulated and downregulated, respectively; a set of genes belonging to the apoptosis pathways were upregulated or downregulated in patients with cervical cancer. BCL2, BCLXL, and c-IAP1 were found to be upregulated in late-stage cancer compared to early-stage cancer.

CONCLUSIONS

These findings provide a new understanding of the gene expression profile in cervical cancer. BCL2, BCLXL, and c-IAP1 might be involved in cancer progression. The pathway analysis of expression data showed that the BCL2, BCLXL, and c-IAP1 genes were coordinately differentially regulated between cancer and normal cases. Our results may serve as basis for further development of biomarkers for the diagnosis and treatment of cervical cancer.

The role of key genes and pathways involved in the tumorigenesis of Malignant Mesothelioma

Malignant Mesothelioma (MM) is a very aggressive cancer with low survival rates and often diagnosed at an advanced stage. Several players have been implicated in the development of this cancer, such as asbestos, erionite and the simian virus 40 (SV40). Here, we have reviewed the involvement of erionite, SV40, as well as, the role of several genes (p16(INK4a), p14(ARF), NF2, LATS2, SAV, CTNNB1 and among others), the pathways (RAS, PI3K, Wnt, BCL and Hippo), and their respective roles in the development of MM.

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.

Advances in the biology of malignant pleural mesothelioma

Malignant pleural mesothelioma is a highly aggressive cancer with a very poor prognosis. Although the mechanism of carcinogenesis is not fully understood, approximately 80% of malignant pleural mesothelioma can be attributed to asbestos fiber exposure. This disease is largely unresponsive to conventional chemotherapy or radiotherapy, and most patients die within 10-17 months of their first symptoms. Currently, malignant pleural mesothelioma therapy is guided by clinical stage and patient characteristics rather than by the histological or molecular features of the tumor. Several molecular pathways involved in malignant pleural mesothelioma have been identified; these include cell cycle regulation, apoptosis, growth factor pathways, and angiogenesis. Unfortunately, several agents targeting these processes, including erlotinib, gefitinib, and imatinib, have proven ineffective in clinical trials. A greater understanding of the molecular pathways involved in malignant pleural mesothelioma is needed to develop better diagnostics, therapeutics, and preventative measures. Moreover, understanding the biological basis of mesothelioma progression may facilitate personalized treatment approaches, and early identification of poor prognostic indicators may help reduce the heterogeneity of the clinical response. This paper reviews advances in the molecular biology of malignant pleural mesothelioma in terms of pathogenesis, the major molecular pathways and the associated therapeutic strategies, and the roles of biomarkers.

Biomarkers for early detection of malignant mesothelioma: diagnostic and therapeutic application

Malignant mesothelioma (MM) is a rare and aggressive tumour of the serosal cavities linked to asbestos exposure. Improved detection methods for diagnosing this type of neoplastic disease are essential for an early and reliable diagnosis and treatment. Thus, focus has been placed on finding tumour markers for the non-invasive detection of MM. Recently, some blood biomarkers have been described as potential indicators of early and advanced MM cancers. The identification of tumour biomarkers alone or in combination could greatly facilitate the surveillance procedure for cohorts of subjects exposed to asbestos, a common phenomenon in several areas of western countries.

Relevance of Bcl-x expression in different types of endometrial tissues

OBJECTIVES

To explore the roles of Bcl-xl and Bcl-xs in the development and progression of endometrial carcinoma, and to analyze the correlation between Bcl-xl and Bcl-xs.

METHODS

RT-PCR and Western-blot assay were applied to detect the expressions of Bcl-xl and Bcl-xs in endometrial tissues of various histomorphologic types.

RESULTS

The Bcl-xl expression levels of simple and atypical hyperplasia endometrial tissues were not significantly different from that of normal endometrial tissue (both P > 0.05). On contrary, Bcl-xl expression in endometrial carcinoma tissue was significantly higher than the normal endometrial tissue (P = 0.00), which was correlated with the pathological grading of endometrial carcinoma (F = 5.33, P = 0.02). In addition, Bcl-xs mRNA level in simple hyperplasia endometrial tissue had no significant difference compared to that in normal endometrial tissue (P = 0.12), while the levels of atypical hyperplasia and endometrial carcinoma endometrial tissues were significantly different from the normal endometrial tissue (both P = 0.00). Furthermore, level of Bcl-xs mRNA was correlated with the clinical staging and lymph node metastasis of the endometrial carcinoma (P < 0.05). The expressions of Bcl-xl and Bcl-xs were negatively correlated with each other (r = -0.76).

CONCLUSION

The abnormal expressions of Bcl-xs and Bcl-xl were one of the molecular mechanisms for the pathogenesis of endometrial carcinoma, and altered ratio between these two might involve in the onset of endometrial carcinoma.

Downregulation of Bcl-xL and Mcl-1 is sufficient to induce cell death in mesothelioma cells highly refractory to conventional chemotherapy

Malignant pleural mesothelioma (MPM) is an aggressive tumor with poor prognosis and limited response to platinum-based chemotherapy. Several lines of evidence support a role for the anti-apoptotic protein Bcl-x(L) in MPM chemoresistance. Since it has been recently suggested that Mcl-1 cooperates with Bcl-x(L) for protection against cell death, we investigated the response of mesothelioma cell lines to the downregulation of Bcl-x(L) (alone or in combination with cisplatin) and the potential interest of its concomitant inhibition with that of Mcl-1. Using RNA interference, we showed that Bcl-x(L) depletion sensitized two highly chemoresistant mesothelioma cell lines to cisplatin and that under this treatment, one cell line, MSTO-211H, displayed an apoptotic type of cell death, whereas the other, NCI-H28, evidenced mainly necrotic-type cell death. Otherwise, the inhibition of Mcl-1 by cisplatin may contribute to this induction of cell death observed after Bcl-x(L) downregulation. Strikingly, we observed that the simultaneous inhibition of Bcl-x(L) and Mcl-1 using small interfering RNA (siRNA) induced a massive cell death in the absence of chemotherapy and was sufficient to avoid escape to treatment in MSTO-211H cells. In NCI-H28, the addition of a low cisplatin concentration allowed to impede the long-term recovery observed after treatment by the siRNA combination. Together, these findings provide a strong molecular basis for the clinical evaluation of therapies targeting both Bcl-x(L) and Mcl-1, alone or in combination with conventional chemotherapy, for the treatment of MPM.

Sorafenib inhibits ERK1/2 and MCL-1(L) phosphorylation levels resulting in caspase-independent cell death in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive, rapidly progressive malignancy without effective therapy. We evaluate sorafenib efficacy and impact on the cellular pro-survival machinery in vitro, efficacy of sorafenib as monotherapy and in combination with the naturally occurring death receptor agonist, TRAIL using human MPM cell lines, MSTO-211H, M30, REN, H28, H2052 and H2452. In vitro studies of the six MPM lines demonstrated single agent sensitivity to the multikinase inhibitor sorafenib and resistance to TRAIL. H28 and H2452 demonstrated augmented apoptosis with the addition of TRAIL to sorafenib in vitro. Treated cell lines demonstrated sorafenib-induced rapid dephosphorylation of AKT followed shortly by near complete dephosphorylation of the constitutively phosphorylated ERK1/2. Sorafenib therapy also decreased phosphorylation of B-Raf and mTOR in several cell lines. Within 3 h of sorafenib treatment, a number of known pro-survival molecules were dephosphorylated and/or downregulated in expression including MCL-1(L), c-FLIP(L), survivin and cIAP(1). These changes and eventual cell death did not elicit significant caspase-3 activation or PARP cleavage and pretreatment with the pan-caspase inhibitor, Z-VAD-FMK, did not block sorafenib efficacy but did block the effect of TRAIL monotherapy. Pre-treatment with Z-VAD-FMK did not block the synergistic effect of TRAIL and sorafenib in H28. In summary, single agent treatment with sorafenib results in widespread inhibition of the pro-survival machinery in vitro leading to cell death via a primarily caspase-independent mechanism. Combining sorafenib therapy with TRAIL, may be useful in order to provide a more efficient death signal and this synergistic effect appears to be caspase-independent. Pilot in vivo data demonstrates promising evidence of therapeutic efficacy in human tumor bearing xenograft nu/nu mice. We document single agent activity of sorafenib against MPM, unravel novel effects of sorafenib on anti-apoptotic signaling mediators, and suggest the combination of sorafenib plus TRAIL as possible therapy for clinical testing in MPM.

Up-regulation of Bcl-xl by hepatocyte growth factor in human mesothelioma cells involves ETS transcription factors

Bcl-xl and the hepatocyte growth factor (HGF) receptor c-Met are both highly expressed in mesotheliomas, where they protect cells from apoptosis and can confer resistance to conventional therapeutic agents. In our current study, we investigate a model for the transcriptional control of Bcl-xl that involves ETS transcription factors and the HGF/Met axis. In addition, the effects of activated c-Met on the phosphorylation of the ETS family transcriptional factors were examined. The transient expression of ETS-2 and PU.1 cDNAs in mesothelioma cell lines resulted in an increase in the promoter activity of Bcl-xl and consequently in its mRNA and protein expression levels, whereas the transcriptional repressor Tel suppressed Bcl-xl transcription. The activation of the HGF/Met axis led to rapid phosphorylation of ETS family transcription factors in mesothelioma cells through the mitogen-activated protein kinase pathway and via nuclear accumulation of ETS-2 and PU.1. A chromatin immunoprecipitation assay further demonstrated that the activation of c-Met enhanced the binding of ETS transcriptional factors to the Bcl-x promoter. Finally, we determined the Bcl-xl and phosphorylated c-Met expression levels in mesothelioma patient samples; these data suggest a strong correlation between Bcl-xl and phosphorylated c-Met levels. Taken together, these findings support a role for c-Met as an inhibitor of apoptosis and an activator of Bcl-xl.

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.

MicroRNA let-7a down-regulates MYC and reverts MYC-induced growth in Burkitt lymphoma cells

Regulation of the MYC oncogene remains unclear. Using 10058-F4, a compound that inhibits MYC-MAX transcription factor, MYC protein and gene expression were down-regulated in Namalwa cells, a Burkitt lymphoma. Compound 10058-F4 decreased MYC mRNA (45%), MYC protein (50%), and cell growth (32%). MYC-MAX transcription factor was disrupted 24 h after treatment, resulting in transcriptional inhibition of target genes. Because microRNAs (miRNA) disrupt mRNA translation, let-7a, let-7b, and mir-98 were selected using bioinformatics for targeting MYC. Inhibition of MYC-MAX transcription factor with 10058-F4 increased levels of members of the let-7 family. In inhibited cells at 24 h, let-7a, let-7b, and mir-98 were induced 4.9-, 1.3-, and 2.4-fold, respectively, whereas mir-17-5p decreased 0.23-fold. These results were duplicated using microRNA multianalyte suspension array technology. Regulation of MYC mRNA by let-7a was confirmed by transfections with pre-let-7a. Overexpression of let-7a (190%) decreased Myc mRNA (70%) and protein (75%). Down-regulation of Myc protein and mRNA using siRNA MYC also elevated let-7a miRNA and decreased Myc gene expression. Inverse coordinate regulation of let-7a and mir-17-5p versus Myc mRNA by 10058-F4, pre-let-7a, or siRNA MYC suggested that both miRNAs are Myc-regulated. This supports previous results in lung and colon cancer where decreased levels of the let-7 family resulted in increased tumorigenicity. Here, pre-let-7a transfections led to down-regulation of expression of MYC and its target genes and antiproliferation in lymphoma cells. These findings with let-7a add to the complexity of MYC regulation and suggest that dysregulation of these miRNAs participates in the genesis and maintenance of the lymphoma phenotype in Burkitt lymphoma cells and other MYC-dysregulated cancers.

Malignant tumours of the heart: a review of tumour type, diagnosis and therapy

Primary cardiac neoplasms are rare and occur less commonly than metastatic disease of the heart. In this overview, current published studies concerning malignant neoplasms of the heart are reviewed, together with some insights into their aetiology, diagnosis and management. We searched medline using the subject 'cardiac neoplasms'. We selected about 110 articles from between 1973 and 2006, of which 76 sources were used to complete the review. Sarcomas are the most common cardiac tumours and include myxosarcoma, liposarcoma, angiosarcoma, fibrosarcoma, leiomyosarcoma, osteosarcoma, synovial sarcoma, rhabdomyosarcoma, neurofibrosarcoma, malignant fibrous histiocytoma and undifferentiated sarcoma. The classic symptoms of cardiac tumours are intracardiac obstruction, signs of systemic embolisation, and systemic or constitutional symptoms. However, serious complications including stroke, myocardial infarction and even sudden death from arrhythmia may be the first signs of a tumour. Echocardiography and angiography are essential diagnostic tools for evaluating cardiac neoplasms. Computed tomography and magnetic resonance imaging studies have improved the diagnostic approach in recent decades. Successful treatment for benign cardiac tumours is usually achieved by surgical resection. Unfortunately, resection of the tumour is not always feasible. The prognosis after surgery is usually excellent in the case of benign tumours, but the prognosis of malignant tumours remains dismal. In conclusion, there are limited published data concerning cardiac neoplasms. Therefore, a high level of suspicion is required for early diagnosis. Surgery is the cornerstone of therapy. However, a multi-treatment approach, including chemotherapy, radiation as well as evolving approaches such as gene therapy, might provide a better palliative and curative result.

Update on the molecular biology of malignant mesothelioma

Malignant mesothelioma (MM) is a highly aggressive tumor with a very poor prognosis. The disease is largely unresponsive to conventional chemotherapy or radiotherapy, and most patients die within 10-17 months of the first symptoms. Novel, more effective therapeutic strategies are needed for this inexorably fatal disease. Improvement in our understanding of the molecular biology of MM has identified promising new candidates for targeted treatments. In this review the key molecular signaling pathways, including vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), Wnt, and the cell cycle control genes p53, pRb, and bcl-2 that appear to play an important role in the pathogenesis of MM are explored.

Therapeutic potential of antisense oligodeoxynucleotides to down-regulate thymidylate synthase in mesothelioma

Malignant mesothelioma is an aggressive tumor of the serosal surfaces of the lungs, heart, and abdomen. Survival rates are poor and effective treatments are not available. However, recent therapeutic regimens targeting thymidylate synthase (TS) in malignant mesothelioma patients have shown promise. We have reported the use of an antisense oligodeoxynucleotide targeting TS mRNA (antisense TS ODN 83) to inhibit growth of human tumor cells. To test the potential for antisense targeting of TS mRNA in treatment of malignant mesothelioma, we assessed and compared the effects of antisense TS ODN 83 on three human malignant mesothelioma cell lines (211H, H2052, and H28) and human nonmalignant mesothelioma cells (HT29 colorectal adenocarcinoma, HeLa cervical carcinoma, and MCF7 breast tumor cell lines). We report that ODN 83 applied as a single agent effectively reduced TS mRNA and protein in malignant mesothelioma cell lines. Furthermore, it inhibited malignant mesothelioma growth significantly more effectively than it inhibited growth of nonmalignant mesothelioma human tumor cell lines: a difference in susceptibility was not observed in response to treatment with TS protein-targeting drugs. In malignant mesothelioma cells, antisense TS both induced apoptotic cell death and reduced proliferation. In nonmalignant mesothelioma cells, only reduced proliferation was observed. Thus, antisense TS-mediated induction of apoptosis may be the basis for the high malignant mesothelioma sensitivity to antisense targeting of TS. Further preclinical and clinical study of TS antisense oligodeoxynucleotides, alone and in combination with TS-targeting chemotherapy drugs, in mesothelioma is warranted.

Cisplatin and TNF-alpha downregulate transcription of Bcl-xL in murine malignant mesothelioma cells

Malignant mesothelioma (MM) is an aggressive and highly chemo-resistant tumour. In this study, we examined cisplatin-induced apoptosis in mouse models of this disease and investigated the role of constitutive and inducible expression of apoptosis related genes in this process. All of the four mouse MM cell lines examined expressed Bax, Bcl-xL, c-Myc, and caspase-3 but not Bcl-2. Cisplatin-induced apoptosis characterised by DNA fragmentation and cell death while caspase-3/7 was activated in 3 of 4 cell lines. Quantitation of basal gene expression showed significant differences but there was no correlation between single genes and cisplatin sensitivity. In the AC29 and AB1 models, both cisplatin and TNF-alpha downregulated Bcl-xL gene expression, indicating that this gene was a common transcriptional target in these cells. The findings of the present study provide insights into apoptotic mechanisms in mesothelioma cells and show similar patterns of gene expression to that reported in the human disease.

Up-regulation of EphB4 in mesothelioma and its biological significance

PURPOSE

Mesothelioma is a rare malignancy that is incurable and carries a short survival despite surgery, radiation, or chemotherapy. This study was designed to identify novel targets for diagnostic, prognostic, and therapeutic approaches.

EXPERIMENTAL DESIGN

The expression and functional significance of the receptor tyrosine kinase EphB4 was studied in vitro and in a murine model of mesothelioma.

RESULTS

EphB4 was highly expressed in mesothelioma cell lines and primary tumor tissues but not in normal mesothelium. Knockdown of EphB4 using small interfering RNA and antisense oligodeoxynucleotide showed reduction in cell survival, migration, and invasion. EphB4 knockdown initiated a caspase-8-mediated apoptosis and down-regulation of the anti-apoptotic protein bcl-xl. EphB4 knockdown also resulted in reduced phosphorylation of Akt and down-regulation of matrix metalloproteinase-2 transcription. In addition, murine tumor xenograft studies using EphB4 oligodeoxynucleotides showed a marked reduction in tumor growth accompanied by a specific decline in EphB4 protein levels, reduced cell division, apoptosis in tumor tissue, and decreased microvascular density.

CONCLUSIONS

EphB4 is expressed in mesothelioma, provides a survival advantage to tumor cells, and is therefore a potential novel therapeutic target.

Receptor tyrosine kinase and phosphoinositide-3 kinase signaling in malignant mesothelioma

OBJECTIVE

The phosphoinositide-3 kinase signaling pathway is implicated in the development of malignancy and promotes cell-cycle progression and resistance to apoptosis. Malignant mesothelioma tumor specimens demonstrate high levels of the phosphoinositide-3 kinase downstream mediator phosphorylated Akt. Exposure of mesothelioma cell lines to LY294002, a phosphoinositide-3 kinase inhibitor, results in apoptotic cell death and decreased phosphorylated Akt in vitro and tumor burden reduction in vivo. Phosphoinositide-3 kinase is activated by cell-surface receptor tyrosine kinases. We sought to determine which receptors are present in mesothelioma and their role in cellular survival and phosphoinositide-3 kinase signaling.

METHODS

Western blot analysis was performed to determine the relative expression of epidermal growth factor receptor, insulin-like growth factor receptor, and platelet-derived growth factor receptor in the mesothelioma cell lines I-45 and REN and the mesothelial line Met5a. After exposure of mesothelioma lines to kinase inhibitors, a cell viability assay was performed, cell-cycle analysis was performed to determine the percentage of apoptosis, and Western blot analysis was performed for phosphorylated Akt.

RESULTS

Inhibition of epidermal growth factor receptor resulted in apoptotic cell death and Akt hypophosphorylation in mesothelioma cell lines. Insulin-like growth factor receptor inhibition led to apoptotic cell death without affecting Akt phosphorylation. Platelet-derived growth factor receptor inhibition did not affect cellular survival or phosphoinositide-3 kinase signaling.

CONCLUSION

In malignant mesothelioma constitutive activation of phosphoinositide-3 kinase/Akt results in cellular survival and contributes to the malignant phenotype. We have demonstrated that epidermal growth factor receptor inhibition leads to apoptotic cell death through downregulation of phosphoinositide-3 kinase signaling in mesothelioma cell lines, whereas insulin-like growth factor receptor inhibition leads to apoptosis independent of phosphoinositide-3 kinase. Epidermal growth factor receptor, insulin-like growth factor receptor, and phosphoinositide-3 kinase inhibition might be clinically relevant in malignant mesothelioma.

Molecular prognostic markers in malignant mesothelioma

Malignant mesothelioma remains a highly lethal cancer. Recent advances in both surgical and medical therapy have improved survival, but the treatments remain toxic and selection of appropriate patients for these therapies is difficult. Research into the molecular pathways involved in the development of mesothelioma should yield information that will guide therapeutic decisions in the near future. In particular, expression of EGFR and VEGF receptor hold promise to alter standards of patient care in the next few years. Alterations in cell cycle control proteins such as p16, p21, and p27 also offer information on prognosis and represent potential targets for therapy.

Metastasis in pleural mesothelioma. Immunohistochemical markers for disseminated disease

AIMS

To examine 13 cases of mesothelioma with metastases and compare these with 29 biopsy samples of patients without metastases. Metastatic disease was defined as tumour in which tumour appeared in a different cavity/tissue of the body and which showed no direct spread. Consequently, mediastinal nodal and parenchymal lung spread was excluded.

METHODS AND RESULTS

Standard sections were prepared and stained according to the manufacturers' protocols. The antibodies used were MIB-1, nm23, Bcl-2, MMP-9, EMMPRIN (CD147) and alpha-catenin. Scoring employed a grading system (0/1/2/3), and was performed by two pathologists independently. The tissues revealed no significant staining differences for MIB-1, Bcl-2, MMP-9 or EMMPRIN, and therefore no linkage to metastatic potential was determined. Alpha-Catenin showed a diminished level of expression in cases of metastatic mesothelioma (P = 0.024), possibly reflecting dimished catenin-cadherin binding and paralleling data from other tumours. nm23 showed greater staining in metastatic tumours when compared with the controls (P = 0.001). Intriguingly, the nm23 staining pattern was the reverse of that expected. This reversed pattern has been noted before in other tumours and therefore a biological prognostic event may exist for this antibody test and mesothelioma metastasis.

CONCLUSION

There may be a place for nm23 and possibly alpha-catenin in immunohistochemical assessment of mesothelioma metastatic potential. However, MIB-1, Bcl-2, MMP-9 and EMMPRIN (CD147) do not show significant staining results.

Quantitative evaluation of the apoptosis regulating genes Survivin, Bcl-2 and Bax in inflammatory and malignant pleural lesions

AIM

We aimed to identify defects in the programmed cell death pathway that can be related to pleural malignant mesothelioma (MM) unresponsiveness to chemotherapy.

MATERIALS AND METHODS

We quantified mRNA levels of the apoptosis regulating genes Survivin, member of the IAP family, Bcl-2 and Bax, members of the Bcl-2 family. We studied 22 non-neoplastic pleural samples, comprising normal and inflammatory tissue specimens, and 42 pleural MMs using real-time RT-PCR.

RESULTS

Very low mRNA levels of each apoptotic gene were detected in all normal pleural samples. All three genes displayed increased mRNA levels in inflammatory and tumor specimens. Survivin levels in pleuritis and MMs were significantly increased (333% and 908%, respectively) compared to normal counterparts (p=0.0147 and 0.00349, respectively). Bcl-2 and Bax levels were increased in inflammatory pleural samples (394%, p=0.001 and 188%, p=ns, respectively) and in MMs (94%, p=ns and 88%, p=0.0163, respectively). The Bcl-2/Bax ratio was higher in pleuritis than in MMs, compared to normal pleurae (441%, p=ns and 22%, p=ns, respectively); the difference between Bcl-2/Bax ratio in inflammatory and neoplastic pleural samples was significant (p=0.00375).

CONCLUSIONS

These results suggest that apoptotic defects in pleural MMs are linked to increased levels of Survivin, whereas variations in Bcl-2 and Bax expression appear less significant, although further studies are needed to highlight Bcl-2 family members interactions in apoptosis control. Survivin progressive accumulation from normal pleura to MM suggests this gene may be important in mesothelial cancerogenesis. Survivin overexpression may also be involved in pleural MM resistance to oncological therapies. Therefore, Survivin may represent a promising novel target for selective therapies.

HMBA induces cell death and potentiates doxorubicin toxicity in malignant mesothelioma cells

PURPOSE

Malignant pleural mesothelioma(MM), a rare tumor characterized by high local invasiveness and low metastatic efficiency, is poorly responsive to current therapeutic approaches. The aim of the present study was to evaluate the cytotoxic efficacy of the hybrid polar compound hexamethylene bisacetamide(HMBA), either as a single agent or in combination with the anthracycline doxorubicin (DOX), against MM cells.

METHODS

The MM cell lines MM-B1 and MM-El were treated with HMBA, DOX or with combinations of the two drugs. Cell survival and death were assessed by the MTS assay and trypan blue staining/TUNEL, respectively. The interactions between drugs were evaluated by the method of Kern et al. Western blot analysis was used to investigate the expression of Bcl-2 family proteins.

RESULTS

When administered alone, HMBA dose-dependently decreased the number of viable cells and increased the death rate of MM-B1 and MM-E1 cultures. Combinations of HMBA and DOX achieved a synergistic inhibition of MM cell survival, and the simultaneous administration of HMBA counteracted the resistance induced by DOX in MM-El cells. HMBA,used at cytostatic concentrations, reduced the ratio be-tween antiapoptotic (Bcl-2, Bcl-XL) and proapoptotic(Bax) members of the Bcl-2 family of proteins, thus lowering the threshold for MM cell death commitment.

CONCLUSIONS

HMBA has therapeutic potential in MM both as a single agent and through potentiation of DOX toxicity. These results support future investigations on the feasibility of intrapleural chemotherapy with this hybrid polar compound.

Genetics of malignant pleural mesothelioma: molecular markers and biologic targets

MPM is a poorly understood lethal malignancy. Although the pathobiology of MPM is not completely elucidated, new genomic technology is likely to help shed light on the mechanisms of carcinogenesis through genome-wide screening of tumor-specific gene expression. Related efforts to identify the molecular markers of mesothelioma are pursued with the aim of refining current diagnostic capabilities, predicting prognosis, and designing appropriate trimodality programs. These new genomic tools also will assist efforts to tailor current adjuvant and neoadjuvant therapies, optimizing their effect and furthering research that may lead to new therapeutic options.

Malignant pleural mesothelioma--an update

Exposure to asbestos is the most frequent, but not exclusive, cause of malignant mesothelioma. Clinical features include dyspnea, cough, nonspecific chest pain, weight loss and night sweats. Diagnosis may be complicated by histologic difficulties. Thoracoscopic techniques are proving beneficial, but no one method of imaging has proven superior, and disease staging is inconsistent. Conventional treatments such as chemotherapy, surgery, and radiotherapy have had variable impacts, although chemotherapy is useful in palliation and can improve both survival and quality of life. There is hope for new antimetabolite agents. The role of radical surgery is yet to be evaluated in a large trial. New radiotherapeutic techniques to improve local control are promising. Multimodality treatments appear to be the most successful for management of potentially resectable disease. It is likely that biological markers will improve accuracy in staging and prognosis. With new treatments based on better understanding of the biology of the disease, there is cautious optimism for the future for patients with malignant pleural mesothelioma.

Mesothelial cell proliferation and apoptosis

Mesothelial cells line the pleural and peritoneal surfaces, where under normal conditions they proliferate and undergo cell death at a slow rate, thereby maintaining a constant number of cells. These tightly regulated processes are disrupted in malignancy. By developing a better understanding of the mechanisms that regulate cell proliferation and apoptosis in mesothelial and mesothelioma cells, we may be able to develop more effective therapeutic agents that target specific steps in these pathways to induce apoptosis more efficiently. This paper reviews our current knowledge of the signaling pathways involved in the regulation of mesothelial cell proliferation and apoptosis. The latest advancements in identifying proteins that play key roles in the resistance to apoptosis are highlighted.

Defective core-apoptosis signalling in diffuse malignant pleural mesothelioma: opportunities for effective drug development

Because of a lack of effective treatments, survival from diffuse pleural mesothelioma remains poor. Many people do not think that treatments for this disease are effective. The understanding of the biology of mesothelioma relevant to the apoptosis-resistant phenotype has been slow to advance. However, this is now changing, and strategies for rational therapeutic drug development are emerging that have the potential to change the natural history and improve survival in the increasing number of patients that will be diagnosed in the next two decades. This review discusses recent developments in apoptosis biology that are specific to mesothelioma and the therapeutic implications for this aggressive cancer.

Antisense oligonucleotides directed at the bcl-xl gene product augment chemotherapy response in mesothelioma

Objective: Malignant pleural mesothelioma (MPM) is resistant to both conventional chemotherapy and apoptosis. The bcl-2 family proteins are major determinants of apoptotic homeostasis. MPM lines and tumors routinely overexpress the anti-apoptotic protein BCL-XL. We have previously shown that antisense inhibition of BCL-XL in MPM cells leads to apoptosis. We sought to determine whether antisense oligonucleotides directed at the bcl-xl gene product would augment response to a conventional chemotherapeutic agent in human mesothelioma cell lines.

Methods: The human MPM cell lines REN and I-45 were exposed to two bcl-xl antisense oligonucleotides (15999, 16009) and one sense oligonucleotide (113529) construct at varying doses, followed by IC50 cisplatin. Cellular viability was assessed by a calorimetric assay, and apoptosis was evaluated by Hoechst staining, Annexin V staining, and sub-G1 fluorescence-activated cell sorter analysis. Western blot analysis of BCL-2 family proteins was performed following single agent and combined treatment. Isobologram mathematical analysis was used to determine whether or not combination therapies were additive or synergistic.

Results: Cell viability was most affected with the 15999 antisense oligonucleotides plus IC50 cisplatin combination (70% of I-45 and 90% of REN cells killed), and apoptosis was markedly increased with this combination by all measures. Western blot demonstrated 15999 antisense oligonucleotides construct down-regulation of BCL-XL, but no further effect on expression of BCL-2 proteins with cisplatin. Isobologram analysis demonstrated 15999 + cisplatin synergistic effect.

Conclusions: Exposure of human MPM cells to bcl-xl antisense oligonucleotides sensitizes human mesothelioma cells to the conventional chemotherapeutic agent cisplatin. Similar approaches using a combination of molecular and conventional treatment may have clinical utility for this tumor.

Nucleotide-based therapies targeting clusterin chemosensitize human lung adenocarcinoma cells both in vitro and in vivo

Introduction: Lung cancer is highly lethal and resistant to most anticancer interventions. Treatment resistance is mediated, in part, by enhanced expression of cell survival proteins that help facilitate tumor progression. Clusterin is a stress-associated cytoprotective protein up-regulated by various apoptotic triggers in many cancers and confers treatment resistance when overexpressed. The objectives in this study were to evaluate clusterin expression levels in human lung cancer tissue, and to test effects of clusterin silencing using antisense oligonucleotides (ASOs) and short interfering double-stranded RNAs (siRNAs) on chemosensitivity in human lung cancer A549 cells. Methods: Clusterin immunostaining was evaluated in a tissue microarray of 149 spotted human lung cancers. The effects of clusterin ASO or siRNA treatment on clusterin expression and chemosensitivity to paclitaxel was examined in A549 cells in vitro while the ability of clusterin ASO to chemosensitize in vivo was evaluated in immunocompromised mice bearing A549 tumors. Results: More than 80% of human non-small cell lung cancers are immunoreactive for clusterin. Clusterin ASO or siRNA decreased clusterin mRNA expression in A549 cells &gt;75% in a dose-dependent, sequence-specific manner, and significantly enhanced chemosensitivity to paclitaxel in vitro. Characteristic apoptotic DNA laddering was observed after combined treatment with ASO plus paclitaxel, but not with either agent alone. In vivo administration of clusterin ASO, compared to mismatch control oligonucleotide, synergistically enhanced the effects of paclitaxel or gemcitibine to significantly delay A549 tumor growth. Conclusion: These findings identify clusterin as a valid therapeutic target in strategies employing novel multimodality therapy for advanced lung cancer.

The Interaction of Specific Peptide Aptamers With the DNA Binding Domain and the Dimerization Domain of the Transcription Factor Stat3 Inhibits Transactivation and Induces Apoptosis in Tumor Cells

The transcription factor signal transducer and activator of transcription (Stat) 3 is activated through the interleukin-6 family of cytokines and by binding of growth factors to the epidermal growth factor (EGF) receptor. It plays an essential role in embryonic development and assumes specialized tasks in many differentiated tissues. Constitutively activated Stat3 has been found in tumor cell lines and primary tumors and plays a crucial role in tumor cell survival and proliferation. To inhibit the oncogenic action of Stat3 in tumor cells, we have selected short peptides, so-called peptide aptamers, which specifically interact with defined functional domains of this transcription factor. The peptide aptamers were selected from a peptide library of high complexity by an adaptation of the yeast two-hybrid procedure. Peptide aptamers specifically interacting with the Stat3 dimerization domain caused inhibition of DNA binding activity and suppression of transactivation by Stat3 in EGF-responsive cells. Similarly, a peptide aptamer selected for its ability to recognize the Stat3 DNA binding domain inhibited DNA binding and transactivation by Stat3 following EGF stimulation of cells. Peptide aptamers were expressed in bacteria as fusion proteins with a protein transduction domain and introduced into human myeloma cells. This resulted in dose-dependent growth inhibition, down-regulation of Bcl-xL expression, and induction of apoptosis. The inhibition of Stat3 functions through the interaction with peptide aptamers counteracts the transformed phenotype and could become useful in targeted tumor therapy.

The role of bcl-2 family members in non-small cell lung cancer

The treatment of advanced nonsmall cell lung cancer (NSCLC) continues to pose great challenges for the thoracic surgeon. Current therapeutic strategies with chemotherapy and radiation are often ineffective adjuncts to surgery. Accordingly, preclinical research concentration has turned to molecular targets that may prove to be more effective. The Bcl-2 family consists of a homologous network of genes that regulate apoptosis or programmed cell death. Altered expression of members in this family leads to aberrant cell proliferation and malignant growth. This review will discuss the expression and significance of Bcl-2 family members in NSCLC and consider potential methods of intervention that are currently being tested and may have clinical applicability. In addition, the current experience with clinical trials involving Bcl-2 down-regulation in solid organ tumors will be summarized.

Gene therapy of lung cancer

It is estimated that there will be 157,200 deaths from lung cancer in 2003. Current regimens of surgery, chemotherapy and radiation have not significantly changed overall 5-year survival rates for this disease. Thanks to intensive molecular studies over the last three decades, new targets for treatment have been identified, including replacement of tumor suppressor genes, prevention of angiogenesis and tumor growth, and regulation of programmed cell death. Promising advances have been made but obstacles still abound before effective use of these strategies at the patient bedside can occur. One area of concentration lies in developing more accurate and complete delivery of the therapeutic constructs. In the evolution of gene therapy approaches, from beginning theory to translational research, investigators in thoracic malignancies have played a leading role, utilizing a number of methods and delivery vehicles. The objective of this review is to discuss some of the major molecular targets available for manipulation in lung cancer, describe vectors and techniques currently used by thoracic researchers to deliver therapy, and provide the p53 model as an example of progression from bench research to clinical treatment.

Induction of apoptosis and chemosensitization of mesothelioma cells by Bcl-2 and Bcl-xL antisense treatment

Our study was designed to investigate the role of the anti-apoptotic proteins Bcl-2 and Bcl-xL in the chemoresistance of cells derived from malignant pleural mesothelioma. First, we determined the basal expression levels of Bcl-2 and Bcl-xL in mesothelioma cells and examined the effect of their downregulation by antisense oligonucleotides. Bcl-xL mRNA and protein could be readily detected in mesothelioma cell lines, whereas only low levels of Bcl-2 mRNA and protein were found. Preferential downregulation of either Bcl-xL alone or of Bcl-xL and Bcl-2 simultaneously was achieved by treatment with antisense oligonucleotides 4259 and 4625, respectively, whereas the expression of other apoptosis-relevant genes remained unaffected. Treatment with oligonucleotides 4259 or 4625 lowered the apoptosis threshold in ZL34 mesothelioma cells, as indicated by an increase in cell death accompanied by increased caspase-3-like activity, a decrease of the mitochondrial transmembrane potential and the cleavage of procaspase-7 and ICAD. In addition to the direct induction of apoptosis, antisense treatment sensitized ZL34 cells to the cytostatic effect of cisplatin and gemcitabine, with the combination of 4625 and cisplatin being the most effective. Our results demonstrate that Bcl-2 and Bcl-xL antisense treatment facilitates apoptosis in mesothelioma cells and suggest the use of Bcl-2/Bcl-xL bispecific antisense treatment in combination with cisplatin or gemcitabine for therapy of malignant pleural mesothelioma.

Current therapy for malignant mesothelioma

This review briefly summarizes the results of previous systemic (chemotherapy) and local (surgery and radiotherapy) treatment attempted to date for malignant mesothelioma. The prospects for newer modalities, ie molecular and biologic therapies, are also highlighted, including results of both preclinical and early clinical research.