Transforming growth factor-beta: antisense RNA-mediated inhibition affects anchorage-independent growth, tumorigenicity and tumor-infiltrating T-cells in malignant mesothelioma

Neutrophils in cancer: dual roles through intercellular interactions

Neutrophils, the most abundant immune cells in human blood, play crucial and diverse roles in tumor development. In the tumor microenvironment (TME), cancer cells regulate the recruitment and behaviors of neutrophils, transforming some of them into a pro-tumor phenotype. Pro-tumor neutrophils interact with cancer cells in various ways to promote cancer initiation, growth, and metastasis, while anti-tumor neutrophils interact with cancer cells to induce senescence and death. Neutrophils can also interact with other cells in TME, including T cells, macrophages, stromal cells, etc. to exert anti- or pro-tumor functions. In this review, we will analyze the anti- and pro-tumor intercellular interactions mediated by neutrophils, with a focus on generalizing the mechanisms underlying the interaction of neutrophils with tumor cells and T cells. Furthermore, we will provide an overview of cancer treatment strategies targeting neutrophil-mediated cellular interactions.

How Our Continuing Studies of the Pre-clinical Inbred Mouse Models of Mesothelioma Have Influenced the Development of New Therapies

Asbestos-induced preclinical mouse models of mesothelioma produce tumors that are very similar to those that develop in humans and thus represent an ideal platform to study this rare, universally fatal tumor type. Our team and a number of other research groups have established such models as a stepping stone to new treatments, including chemotherapy, immunotherapy and other approaches that have been/are being translated into clinical trials. In some cases this work has led to changes in mesothelioma treatment practice and over the last 30 years these models and studies have led to trials which have improved the response rate in mesothelioma from less than 10% to over 50%. Mouse models have had a vital role in that improvement and will continue to play a key role in the future success of mesothelioma immunotherapy. In this review we focus only on these original inbred mouse models, the large number of preclinical studies conducted using them and their contribution to current and future clinical therapy for mesothelioma.

The Multifaceted Role of TGF-β in Gastrointestinal Tumors

Simple Summary

The transforming growth factor β signaling pathway elicits a broad range of physiological re-sponses, and its misregulation has been related to cancer. The secreted cytokine TGFβ exerts a tumor-suppressive effect that counteracts malignant transformation. However, once tumor has developed, TGFβ can support tumor progression regulating epithelial to mesenchymal transition, invasion and metastasis, stimulating fibrosis, angiogenesis and immune suppression. Here we review the dichotomous role of TGF-β in the progression of gastrointestinal tumors, as well as its intricate crosstalk with other signaling pathways. We also discuss about the therapeutic strate-gies that are currently explored in clinical trials to counteract TGF-β functions.

Abstract

Transforming growth factor-beta (TGF-β) is a secreted cytokine that signals via serine/threonine kinase receptors and SMAD effectors. Although TGF-β acts as a tumor suppressor during the early stages of tumorigenesis, it supports tumor progression in advanced stages. Indeed, TGF-β can modulate the tumor microenvironment by modifying the extracellular matrix and by sustaining a paracrine interaction between neighboring cells. Due to its critical role in cancer development and progression, a wide range of molecules targeting the TGF-β signaling pathway are currently under active clinical development in different diseases. Here, we focused on the role of TGF-β in modulating different pathological processes with a particular emphasis on gastrointestinal tumors.

Biomarkers for Malignant Pleural Mesothelioma-A Novel View on Inflammation

Malignant pleural mesothelioma (MPM) is an aggressive disease with limited treatment response and devastating prognosis. Exposure to asbestos and chronic inflammation are acknowledged as main risk factors. Since immune therapy evolved as a promising novel treatment modality, we want to reevaluate and summarize the role of the inflammatory system in MPM. This review focuses on local tumor associated inflammation on the one hand and systemic inflammatory markers, and their impact on MPM outcome, on the other hand. Identification of new biomarkers helps to select optimal patient tailored therapy, avoid ineffective treatment with its related side effects and consequently improves patient's outcome in this rare disease. Additionally, a better understanding of the tumor promoting and tumor suppressing inflammatory processes, influencing MPM pathogenesis and progression, might also reveal possible new targets for MPM treatment. After reviewing the currently available literature and according to our own research, it is concluded that the suppression of the specific immune system and the activation of its innate counterpart are crucial drivers of MPM aggressiveness translating to poor patient outcome.

On-Target Anti-TGF-β Therapies Are Not Succeeding in Clinical Cancer Treatments: What Are Remaining Challenges?

Metastasis is the leading cause of death for cancer patients. During cancer progression, the initial detachment of cells from the primary tumor and the later colonization of a secondary organ are characterized as limiting steps for metastasis. Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are opposite dynamic multistep processes that enable these critical events in metastasis by altering the phenotype of cancer cells and improving their ability to migrate, invade and seed at distant organs. Among the molecular pathways that promote tumorigenesis in late-stage cancers, transforming growth factor-β (TGF-β) is described as an EMT master inducer by controlling different genes and proteins related to cytoskeleton assembly, cell-cell attachment and extracellular matrix remodeling. Still, despite the successful outcomes of different TGF-β pharmacological inhibitors in cell culture (in vitro) and animal models (in vivo), results in cancer clinical trials are poor or inconsistent at least, highlighting the existence of crucial components in human cancers that have not been properly explored. Here we review most recent findings to provide perspectives bridging the gap between on-target anti-TGF-β therapies in vitro and in pre-clinical models and the poor clinical outcomes in treating cancer patients. Specifically, we focus on (i) the dual roles of TGF-β signaling in cancer metastasis; (ii) dynamic signaling; (iii) functional differences of TGF-β free in solution vs. in exosomes; (iv) the regulatory effects of tumor microenvironment (TME) – particularly by cancer-associated fibroblasts – on TGF-β signaling pathway. Clearly identifying and establishing those missing links may provide strategies to revitalize and clinically improve the efficacy of TGF-β targeted therapies.

On-Target Anti-TGF-β Therapies Are Not Succeeding in Clinical Cancer Treatments: What Are Remaining Challenges?

Metastasis is the leading cause of death for cancer patients. During cancer progression, the initial detachment of cells from the primary tumor and the later colonization of a secondary organ are characterized as limiting steps for metastasis. Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are opposite dynamic multistep processes that enable these critical events in metastasis by altering the phenotype of cancer cells and improving their ability to migrate, invade and seed at distant organs. Among the molecular pathways that promote tumorigenesis in late-stage cancers, transforming growth factor-β (TGF-β) is described as an EMT master inducer by controlling different genes and proteins related to cytoskeleton assembly, cell-cell attachment and extracellular matrix remodeling. Still, despite the successful outcomes of different TGF-β pharmacological inhibitors in cell culture (in vitro) and animal models (in vivo), results in cancer clinical trials are poor or inconsistent at least, highlighting the existence of crucial components in human cancers that have not been properly explored. Here we review most recent findings to provide perspectives bridging the gap between on-target anti-TGF-β therapies in vitro and in pre-clinical models and the poor clinical outcomes in treating cancer patients. Specifically, we focus on (i) the dual roles of TGF-β signaling in cancer metastasis; (ii) dynamic signaling; (iii) functional differences of TGF-β free in solution vs. in exosomes; (iv) the regulatory effects of tumor microenvironment (TME) - particularly by cancer-associated fibroblasts - on TGF-β signaling pathway. Clearly identifying and establishing those missing links may provide strategies to revitalize and clinically improve the efficacy of TGF-β targeted therapies.

Detection of TGF-β in pleural effusions for diagnosis and prognostic stratification of malignant pleural mesothelioma

OBJECTIVES

Malignant pleural mesothelioma (MPM) is an aggressive malignancy with dismal prognosis but variable course of disease. To support diagnosis and to risk stratify patients, more reliable biomarkers are warranted. Emerging evidence underlines a functional role of transforming growth factor-beta (TGF-β) in MPM tumorigenesis though its utility as a clinical biomarker remains unexplored.

MATERIALS AND METHODS

Corresponding pleural effusions and serum samples taken at primary diagnosis were analyzed for TGF-β by ELISA, and for mesothelin (SMRP) by chemiluminescence enzyme immunoassay. Tumor load was quantified in MPM patients by volumetric analysis of chest CT scans. All findings were correlated with clinicopathological characteristics.

RESULTS

In total 48 MPM patients, 24 patients with non-malignant pleural disease (NMPD) and 30 patients with stage IV lung cancer were enrolled in this study. Pleural effusions from MPM patients had significantly higher TGF-β levels than from NMPD or lung cancer patients (p < 0.0001; AUC for MPM vs NMPD: 0.78, p = 0.0001). Both epithelioid and non-epithelioid MPM were associated with higher TGF-β levels (epithelioid: p < 0.05; non-epithelioid: p < 0.0001) and levels of TGF-β correlated with disease stage (p = 0.003) and with tumor volume (p = 0.002). Interestingly, high TGF-β levels in pleural effusion, but not in serum, was significantly associated with inferior overall survival (TGF-beta ≥14.36 ng/mL: HR 3.45, p = 0.0001). This correlation was confirmed by multivariate analysis. In contrast, effusion SMRP levels were exclusively high in epithelioid MPM, negatively correlated with effusion TGF-β levels and did not provide prognostic information.

CONCLUSION

TGF-β levels determined in pleural effusion may be a promising biomarker for diagnosis and prognostic stratification of MPM.

Inhibition of collagen production delays malignant mesothelioma tumor growth in a murine model

Malignant mesothelioma is an aggressive fibrous tumor, predominantly of the pleura, with a very poor prognosis. Cell-matrix interactions are recognized important determinants of tumor growth and invasiveness but the role of the extracellular matrix in mesothelioma is unknown. Mesothelioma cells synthesize collagen as well as transforming growth factor-beta (TGF-β), a key regulator of collagen production. This study examined the effect of inhibiting collagen production on mesothelioma cell proliferation in vitro and tumor growth in vivo. Collagen production by mesothelioma cells was inhibited by incubating cells in vitro with the proline analogue thiaproline (thiazolidine-4-carboxylic acid) or by oral administration of thiaproline in a murine tumor model. Cell cytotoxicity was measured using neutral red uptake and lactate dehydrogenase assays. Proliferation was measured by tritiated thymidine incorporation, and inflammatory cell influx, proliferation, apoptosis and angiogenesis in tumors examined by immunohistochemical labelling. Tumor size was determined by tumor weight and collagen production was measured by HPLC. Thiaproline at non-toxic doses significantly reduced basal and TGF-β-induced collagen production by over 50% and cell proliferation by over 65%. In vivo thiaproline administration inhibited tumor growth at 10 days, decreasing the median tumor weight by 80%. The mean concentration of collagen was 50% lower in the thiaproline-treated tumors compared with the controls. There were no significant differences in vasculature or inflammatory cell infiltration but apoptosis was increased in thiaproline treated tumors at day 10. In conclusion, these observations strongly support a role for collagen in mesothelioma growth and establish the potential for inhibitors of collagen synthesis in mesothelioma treatment.

Intracavitary Therapeutics for Pleural Malignancies

Pleural malignancies remain a serious therapeutic challenge, and are frequently refractory to standard treatment; however, they have the advantage of occurring in an enclosed cavity readily accessible for examination, biopsy, and serial sampling. Novel therapeutics can be administered via intracavitary delivery to maximize efficacy by targeting the site of involvement and potentially mitigating the adverse effects of systemic therapies. The easy accessibility of the pleural space lends itself well to repeated sampling and analysis to determine efficacy and toxicity of a given treatment paradigm. These factors support the rationale for delivery of novel therapeutics directly into the pleural space.

Successful combined intratumoral immunotherapy of established murine mesotheliomas requires B-cell involvement

Combination immunotherapy has resulted in a number of impressive outcomes in mouse models and clinical settings. In this study, we report that a timed triple immunotherapy (TTI) protocol using 3 agonist antibodies (anti-CD25mAb, anti-TGF-βmAb, and anti-CTLA-4mAb) produced complete clearance of established AB1 murine mesothelioma tumors. Combining all 3 agonist antibodies into a single cocktail for intratumoral injection was as effective as the TTI in tumor eradication. Cured mice showed elevated levels of tumor-specific IgG antibodies at 95 days posttreatment. Time-course studies of tumor clearance showed (1) that IgG levels were not elevated during tumor clearance and (2) that B-cell numbers were increased in the tumor-draining lymph nodes and spleens during tumor clearance. Finally, employment of B-cell knockout mice indicated a significant role for B cells in the successful eradication of the established tumors by the triple immunotherapy cocktail.

The timing of TGF-β inhibition affects the generation of antigen-specific CD8+ T cells

BACKGROUND

Transforming growth factor (TGF)-β is a potent immunosuppressive cytokine necessary for cancer growth. Animal and human studies have shown that pharmacologic inhibition of TGF-β slows the growth rate of established tumors and occasionally eradicates them altogether. We observed, paradoxically, that inhibiting TGF-β before exposing animals to tumor cells increases tumor growth kinetics. We hypothesized that TGF-β is necessary for the anti-tumor effects of cytotoxic CD8+ T lymphocytes (CTLs) during the early stages of tumor initiation.

METHODS

BALB/c mice were pretreated with a blocking soluble TGF-β receptor (sTGF-βR, TGF-β-blockade group, n=20) or IgG2a (Control group, n=20) before tumor inoculation. Tumor size was followed for 6 weeks. In vivo lymphocyte assays and depletion experiments were then performed to investigate the immunological basis of our results. Lastly, animals were pretreated with either sTGF-βR (n=6) or IgG2a (n=6) prior to immunization with an adenoviral vector encoding the human papillomavirus E7 gene (Ad.E7). One week later, flow cytometry was utilized to measure the number of splenic E7-specific CD8+ T cells.

RESULTS

Inhibition of TGF-β before the injection of tumor cells resulted in significantly larger average tumor volumes on days 11, 17, 22, 26 and 32 post tumor-inoculation (p < 0.05). This effect was due to the inhibition of CTLs, as it was not present in mice with severe combined immunodeficiency (SCID) or those depleted of CD8+ T cells. Furthermore, pretreatment with sTGF-βR inhibited tumor-specific CTL activity in a Winn Assay. Tumors grew to a much larger size when mixed with CD8+ T cells from mice pretreated with sTGF-βR than when mixed with CD8+ T cells from mice in the control group: 96 mm3 vs. 22.5 mm3, respectively (p < 0.05). In addition, fewer CD8+ T cells were generated in Ad.E7-immunized mice pretreated with sTGF-βR than in mice from the control group: 0.6% total CD8+ T cells vs. 1.9%, respectively (p < 0.05).

CONCLUSIONS

These studies provide the first in vivo evidence that TGF-β may be necessary for anti-tumor immune responses in certain cancers. This finding has important implications for our understanding of anti-tumor immune responses, the role of TGF-β in the immune system, and the future development of TGF-β inhibiting drugs.

Intracavitary therapeutics for pleural malignancies

Pleural malignancies are ideal for novel therapeutic approaches because they are invariably fatal. Intrapleural (IP) chemotherapy has only marginal benefit in pleural malignancies, but may prove efficacious with hyperthermic chemotherapy administered in combination with maximal tumor debulking. IP immunotherapies may be most effective in those patients with early-stage pleural malignancy, and may prove superior to standard pleurodesis methods in control of effusion and prolongation of survival. Immunogene therapy may be unable to successfully treat bulky tumors on its own, but success may be achieved with combination approaches that combine debulking surgery and chemotherapy with IP genetic immunotherapy.

Targeting macrophages rescues age-related immune deficiencies in C57BL/6J geriatric mice

Changes to innate cells, such as macrophages and myeloid-derived suppressor cells (MDSCs), during aging in healthy or tumor-bearing hosts are not well understood. We compared macrophage subpopulations and MDSCs from healthy young (6-8 weeks) C57BL/6J mice to those from healthy geriatric (24-28 months) mice. Spleens, lymph nodes, and bone marrow of geriatric hosts contained significantly more M2 macrophages and MDSCs than their younger counterparts. Peritoneal macrophages from geriatric, but not young, mice co-expressed CD40 and CX3CR1 that are usually mutually exclusively expressed by M1 or M2 macrophages. Nonetheless, macrophages from geriatric mice responded to M1 or M2 stimuli similarly to macrophages from young mice, although they secreted higher levels of TGF-β in response to IL-4. We mimicked conditions that may occur within tumors by exposing macrophages from young vs. geriatric mice to mesothelioma or lung carcinoma tumor cell-derived supernatants. While both supernatants skewed macrophages toward the M2-phenotype regardless of age, only geriatric-derived macrophages produced IL-4, suggesting a more immunosuppressive tumor microenvironment will be established in the elderly. Both geriatric- and young-derived macrophages induced allogeneic T-cell proliferation, regardless of the stimuli used, including tumor supernatant. However, only macrophages from young mice induced T-cell IFN-γ production. We examined the potential of an IL-2/agonist anti-CD40 antibody immunotherapy that eradicates large tumors in young hosts to activate macrophages from geriatric mice. IL-2-/CD40-activated macrophages rescued T-cell production of IFN-γ in geriatric mice. Therefore, targeting macrophages with IL-2/anti-CD40 antibody may improve innate and T-cell immunity in aging hosts.

Suppression of activin A signals inhibits growth of malignant pleural mesothelioma cells

BACKGROUND

Activins control the growth of several tumour types including thoracic malignancies. In the present study, we investigated their expression and function in malignant pleural mesothelioma (MPM).

METHODS

The expression of activins and activin receptors was analysed by quantitative PCR in a panel of MPM cell lines. Activin A expression was further analysed by immunohistochemistry in MPM tissue specimens (N=53). Subsequently, MPM cells were treated with activin A, activin receptor inhibitors or activin-targeting siRNA and the impact on cell viability, proliferation, migration and signalling was assessed.

RESULTS

Concomitant expression of activin subunits and receptors was found in all cell lines, and activin A was overexpressed in most cell lines compared with non-malignant mesothelial cells. Similarly, immunohistochemistry demonstrated intense staining of tumour cells for activin A in a subset of patients. Treatment with activin A induced SMAD2 phosphorylation and stimulated clonogenic growth of mesothelioma cells. In contrast, treatment with kinase inhibitors of activin receptors (SB-431542, A-8301) inhibited MPM cell viability, clonogenicity and migration. Silencing of activin A expression by siRNA oligonucleotides further confirmed these results and led to reduced cyclin D1/3 expression.

CONCLUSION

Our study suggests that activin A contributes to the malignant phenotype of MPM cells via regulation of cyclin D and may represent a valuable candidate for therapeutic interference.

Clinical role of pleural effusion MMP-3 levels in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive malignant tumor of mesothelial origin associated with asbestos exposure. MPM exhibits a limited response to conventional chemotherapy and radiotherapy. This, early diagnosis of MPM is essential. Malignant tumor progression requires the destruction of the basement membrane, which is constructed from extracellular matrix (ECM) materials. Various types of human tumor cells are reported to produce ECM-degrading proteases that are important in tumor progression. Among this group of proteolytic enzymes, matrix metalloproteinases (MMPs) are thought to be important due to their wide degrading function. We investigated the pleural effusion MMP-3 levels of patients with MPM and compared them with those of a population with non-malignant pleuritis or lung cancer involving malignant pleural effusion. The pleural effusion MMP-3 concentrations of 52 MPM patients and 67 non-MPM patients were measured. The results showed that the MPM patients had significantly higher pleural effusion MMP-3 levels than the population with non-malignant pleuritis. The overall survival of the MPM patients with lower pleural effusion MMP-3 levels was longer than that of patients with higher pleural effusion MMP-3 levels. Our data therefore suggest a clinical role of pleural effusion MMP-3 levels in malignant pleural mesothelioma.

Clinical significance of pleural effusion mesothelin in malignant pleural mesothelioma

BACKGROUND

Malignant pleural mesothelioma (MPM) is an aggressive malignant tumor of mesothelial origin associated with asbestos exposure. MPM has a limited response to conventional chemotherapy and radiotherapy, so early diagnosis of MPM is very important. This study investigated the pleural effusion mesothelin levels in patients with MPM and compared them to those of a population with a non-malignant pleuritis or lung cancer involving malignant pleural effusion.

METHODS

The pleural effusion mesothelin concentrations were measured in 45 MPM patients and 53 non-MPM individuals (24 individuals with non-malignant pleural effusions and 29 individuals with lung cancer involving malignant pleural effusion).

RESULTS

This study demonstrated that patients with MPM had significantly higher pleural effusion mesothelin levels than a population with non-malignant pleuritis or lung cancer involving malignant pleural effusion. The difference in overall survival between the groups with pleural effusion mesothelin levels lower and higher than the assumed cut-off of 10 nM was significant.

CONCLUSIONS

The data suggest that the pleural effusion mesothelin concentration could be useful as an aid for the diagnosis of MPM.

Chemotherapy delivered after viral immunogene therapy augments antitumor efficacy via multiple immune-mediated mechanisms

The most widely used approach to cancer immunotherapy is vaccines. Unfortunately, the need for multiple administrations of antigens often limits the use of one of the most effective vaccine approaches, immunogene therapy using viral vectors, because neutralizing antibodies are rapidly produced. We hypothesized that after viral immunogene therapy "primed" an initial strong antitumor immune response, subsequent "boosts" could be provided by sequential courses of chemotherapy. Three adenoviral (Ad)-based immunogene therapy regimens were administered to animals with large malignant mesothelioma and lung cancer tumors followed by three weekly administrations of a drug regimen commonly used to treat these tumors (Cisplatin/Gemcitabine). Immunogene therapy followed by chemotherapy resulted in markedly increased antitumor efficacy associated with increased numbers of antigen-specific, activated CD8(+) T-cells systemically and within the tumors. Possible mechanisms included: (i) decreases in immunosuppressive cells such as myeloid-derived suppressor cells (MDSC), T-regulatory cells (T-regs), and B-cells, (ii) stimulation of memory cells by intratumoral antigen release leading to efficient cross-priming, (iii) alteration of the tumor microenvironment with production of "danger signals" and immunostimulatory cytokines, and (iv) augmented trafficking of T-cells into the tumors. This approach is currently being tested in a clinical trial and could be applied to other trials of viral immunogene therapy.

Kinetics of host cell recruitment during dissemination of diffuse malignant peritoneal mesothelioma

Diffuse malignant mesothelioma is an aggressive tumor which displays a median survival of 11.2 months and a 5-year survival of less than 5% emphasizing the need for more effective treatments. This study uses an orthotopic model of malignant mesothelioma established in syngeneic, immunocompetent C57Bl/6 mice which produce malignant ascites and solid tumors that accurately replicate the histopathology of the human disease. Host stromal and immune cell accumulation within malignant ascites and solid tumors was determined using immunofluorescent labeling with confocal microscopy and fluorescence-activated cell sorting. An expression profile of cytokines and chemokines was produced using quantitative real-time PCR arrays. Tumor spheroids and solid tumors show progressive growth and infiltration with host stromal and immune cells including macrophages, endothelial cells, CD4(+) and CD8(+) lymphocytes, and a novel cell type, myeloid derived suppressor cells (MDSCs). The kinetics of host cell accumulation and inflammatory mediator expression within the tumor ascites divides tumor progression into two distinct phases. The first phase is characterized by progressive macrophage and T lymphocyte recruitment, with a cytokine profile consistent with regulatory T lymphocytes differentiation and suppression of T cell function. The second phase is characterized by decreased expression of macrophage chemotactic and T-cell regulating factors, an increase in MDSCs, and increased expression of several cytokines which stimulate differentiation of MDSCs. This cellular and expression profile suggests a mechanism by which host immune cells promote diffuse malignant mesothelioma progression.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12307-010-0048-1) contains supplementary material, which is available to authorized users.

Monocyte chemoattractant protein-1 blockade inhibits lung cancer tumor growth by altering macrophage phenotype and activating CD8+ cells

The role of chemokines in the pathogenesis of lung cancer has been increasingly appreciated. Monocyte chemoattractant protein-1 (MCP-1, also known as CCL2) is secreted from tumor cells and associated tumor stromal cells. The blockade of CCL2, as mediated by neutralizing antibodies, was shown to reduce tumorigenesis in several solid tumors, but the role of CCL2 in lung cancer remains controversial, with evidence of both protumorigenic and antitumorigenic effects. We evaluated the effects and mechanisms of CCL2 blockade in several animal models of non-small-cell lung cancer (NSCLC). Anti-murine-CCL2 monoclonal antibodies were administered in syngeneic flank and orthotopic models of NSCLC. CCL2 blockade significantly slowed the growth of primary tumors in all models studied, and inhibited lung metastases in a model of spontaneous lung metastases of NSCLC. In contrast to expectations, no significant effect of treatment was evident in the number of tumor-associated macrophages recruited into the tumor after CCL2 blockade. However, a change occurred in the polarization of tumor-associated macrophages to a more antitumor phenotype after CCL2 blockade. This was associated with the activation of cytotoxic CD8(+) T lymphocytes (CTLs). The antitumor effects of CCL2 blockade were completely lost in CB-17 severe combined immunodeficient mice or after CD8 T-cell depletion. Our data from NSCLC models show that CCL2 blockade can inhibit the tumor growth of primary and metastatic disease. The mechanisms of CCL2 blockade include an alteration of the tumor macrophage phenotype and the activation of CTLs. Our work supports further evaluation of CCL2 blockade in thoracic malignancies.

Immunological alterations found in mesothelioma patients and supporting experimental evidence

It is common knowledge that exposure to asbestos causes asbestos-related diseases, such as asbestosis, lung cancer and malignant mesothelioma, not only in people who have had long-term contact with asbestos in their work environment but also in residents living near factories that handle asbestos. Since the summer of 2005, these revelations turned into a large medical problem and caused and social unrest. We have focused on the immunological effects of both asbestos and silica on the human immune system. In this brief review, we introduce immunological alterations found in patients with malignant mesothelioma and describe the experimental background in which these were found. Analyzing the immunological effects of asbestos may improve our understanding of the biological effects of asbestos.

A Novel Small-Molecule Inhibitor of Transforming Growth Factor β Type I Receptor Kinase (SM16) Inhibits Murine Mesothelioma Tumor Growth In vivo and Prevents Tumor Recurrence after Surgical Resection

Malignant mesothelioma is an aggressive and lethal pleural cancer that overexpresses transforming growth factor beta (TGFbeta). We investigated the efficacy of a novel small-molecule TGFbeta type I receptor (ALK5) kinase inhibitor, SM16, in the AB12 syngeneic model of malignant mesothelioma. SM16 inhibited TGFbeta signaling seen as decreased phosphorylated Smad2/3 levels in cultured AB12 cells (IC(50), approximately 200 nmol/L). SM16 penetrated tumor cells in vivo, suppressing tumor phosphorylated Smad2/3 levels for at least 3 h following treatment of tumor-bearing mice with a single i.p. bolus of 20 mg/kg SM16. The growth of established AB12 tumors was significantly inhibited by 5 mg/kg/d SM16 (P < 0.001) delivered via s.c. miniosmotic pumps over 28 days. The efficacy of SM16 was a result of a CD8+ antitumor response because (a) the antitumor effects were markedly diminished in severe combined immunodeficient mice and (b) CD8+ T cells isolated from spleens of mice treated with SM16 showed strong antitumor cytolytic effects whereas CD8+ T cells isolated from spleens of tumor-bearing mice treated with control vehicle showed minimal activity. Treatment of mice bearing large tumors with 5 mg/kg/d SM16 after debulking surgery reduced the extent of tumor recurrence from 80% to <20% (P < 0.05). SM16 was also highly effective in blocking and regressing tumors when given p.o. at doses of 0.45 or 0.65 g/kg in mouse chow. Thus, SM16 shows potent activity against established AB12 malignant mesothelioma tumors using an immune-mediated mechanism and can significantly prevent tumor recurrence after resection of bulky AB12 malignant mesothelioma tumors. These data suggest that ALK5 inhibitors, such as SM16, offer significant potential for the treatment of malignant mesothelioma and possibly other cancers.

Biology and management of malignant pleural mesothelioma

Malignant mesothelioma is an aggressive tumour, with a poor prognosis and an increasing incidence as a result of widespread exposure to asbestos. The results of the treatments available are poor. Surgery and radiotherapy have a limited role in highly selected patients and systemic therapy is the only potential treatment option for the majority of patients. Despite some definite activity of the novel antifolates such as pemetrexed and raltitrexed, the results, even in combination with platinating agents, are still modest, with a median survival of approximately one year. The better understanding of the biology of mesothelioma makes the assessment of a number of targeted agents particularly interesting. Unfortunately, the targeted agents imatinib, gefitinib, erlotinib and thalidomide have been shown to be ineffective in unselected patients. Studies with anti-angiogenesis agents are ongoing. An improvement of the knowledge of major molecular pathways involved in malignant mesothelioma is needed in order to define proper targets for the systemic treatment of this disease.

Intracerebral and intrathecal infusion of the TGF-beta 2-specific antisense phosphorothioate oligonucleotide AP 12009 in rabbits and primates: toxicology and safety

Here, we provide first evidence that long-term continuous infusion of highly purified antisense phosphorothioate oligodeoxynucleotides (S-ODN) into brain parenchyma is well tolerated and thus highly suitable for in vivo application. AP 12009 is an S-ODN for the therapy of malignant glioma. It is directed against human transforming growth factor-beta (TGF-beta2) mRNA. In the clinical setting, AP 12009 is administered intratumorally by continuous infusion directly into the brain tumor. In view of this clinical application, the focus of our data is on local toxicology studies in rabbits and monkeys to evaluate the safety of AP 12009. AP 12009 was administered either by intrathecal bolus injection into the subarachnoidal space of the lumbar region of both cynomolgus monkeys and rabbits or by continuous intraparenchymatous infusion directly into the brain tissue of rabbits. Intrathecal bolus administration of 0.1 ml of 500 microM AP 12009 showed neither clinical signs of toxicity nor macroscopically visible or histomorphologic changes. After a 7-day intraparenchymatous continuous infusion of 500 microM AP 12009 at 1 microl/h in rabbits, there was no evidence of toxicity except for local mild to moderate lymphocytic leptomeningoencephalitis. Additionally, AP 12009 showed good tolerability in safety pharmacology as well as in acute toxicity studies and 4-week subchronic toxicity studies in mice, rats, and monkeys. This favorable safety profile proves the suitability of AP 12009 for local administration in brain tumor patients from the point of view of toxicology.

Cytogenetic and molecular genetic changes in malignant mesothelioma

Malignant mesothelioma (MM) results from the accumulation of a number of acquired genetic events, especially deletions, which lead to the inactivation of multiple onco-suppressor genes in a multistep cascade mechanism. Past asbestos exposure represents the major risk factor for MM, and the link between asbestos fibers and MM has been largely proved by several epidemiologic and experimental studies. Asbestos fibers induce DNA and chromosomal damage. Most MM cases have shown multiple chromosomal abnormalities. Chromosomal losses are more common than gains. The most common cytogenetic abnormality in MM is a deletion in 9p21, the locus of CDKN2A, a tumor suppressor gene (TSG). The deletion of CDKN2A is a negative prognostic factor in MM. Loss of TSG CDKN2A/p14(ARF) is also common in MM and mutations in NF2 occur in approximately half of the cases. Despite the ban on asbestos use in Western countries, the incidence of MM is increasing, and asbestos is still used in developing countries. This epidemiologic situation calls for further research. Ongoing studies are already applying high-throughput genomic profiling methods in MM. Genetic alterations observed in MM may be useful in differential diagnosis between lung cancer and MM, as diagnostic markers or therapeutic targets, and as indicators of premalignancy for primary prevention and health surveillance.

Major carcinogenic pathways identified by gene expression analysis of peritoneal mesotheliomas following chemical treatment in F344 rats

This study was performed to characterize the gene expression profile and to identify the major carcinogenic pathways involved in rat peritoneal mesothelioma (RPM) formation following treatment of Fischer 344 rats with o-nitrotoluene (o-NT) or bromochloracetic acid (BCA). Oligo arrays, with over 20,000 target genes, were used to evaluate o-NT- and BCA-induced RPMs, when compared to a non-transformed mesothelial cell line (Fred-PE). Analysis using Ingenuity Pathway Analysis software revealed 169 cancer-related genes that were categorized into binding activity, growth and proliferation, cell cycle progression, apoptosis, and invasion and metastasis. The microarray data were validated by positive correlation with quantitative real-time RT-PCR on 16 selected genes including igf1, tgfb3 and nov. Important carcinogenic pathways involved in RPM formation included insulin-like growth factor 1 (IGF-1), p38 MAPkinase, Wnt/beta-catenin and integrin signaling pathways. This study demonstrated that mesotheliomas in rats exposed to o-NT- and BCA were similar to mesotheliomas in humans, at least at the cellular and molecular level.

ERK1/2 and p38 MAP kinase control MMP-2, MT1-MMP, and TIMP action and affect cell migration: a comparison between mesothelioma and mesothelial cells

Pleural malignant mesothelioma is a locally aggressive tumor of mesothelial cell origin. In other tumor types high expression of matrix metalloproteinase (MMP)-2, together with membrane-type1-MMP (MT1-MMP), and low levels of the tissue inhibitor of MMP (TIMP)-2 have been correlated with aggressive tumor progression and low survival rates. Therefore, we compared the expression and activation of these three factors and their regulation by two mesothelioma associated growth factors, platelet-derived growth factor (PDGF)-BB, and transforming growth factor (TGF)-beta1 in six human mesothelioma and one mesothelial cell line. Polymerase chain reaction (PCR), immunoblotting, zymography, and small inhibitory RNAs (siRNA) were used to study gene expression, protein activation, and signal transduction. To proof the relevance of our in vitro data immunohistochemistry was performed in tissue sections. PDGF-BB induced, while TGF-beta1 inhibited cell proliferation. PDGF-BB was a chemoattractant for mesothelial cells, and its effect was increased in the presence of TGF-beta1. TGF-beta1 stimulated the de novo synthesis of pro-MMP-2 in both cell types. Pro-MMP-2 synthesis involved p38 MAP kinase. In cell culture and tissue sections only mesothelial cells expressed MT1-MMP. Migration of mesothelioma cells was dependent on the presence of MT1-MMP. Migration, but not proliferation of mesothelioma cells was inhibited by oleoyl-N-hydroxylamide, TIMP-2, and siRNA for MT1-MMP. Our data suggest that in mesothelioma cells the phosphorylation of p38 MAP kinase is deregulated and is involved in pro-MMP-2 expression. Mesothelioma progression depends on an interaction with mesothelial cells that provide MT1-MMP necessary to activate pro-MMP-2 to facilitate migration through an extracellular matrix (ECM) layer.

Soluble type II transforming growth factor-beta receptor inhibits established murine malignant mesothelioma tumor growth by augmenting host antitumor immunity

PURPOSE

Transforming growth factor (TGF)-beta blockade has been proposed as an anticancer therapy; however, understanding which tumor patients might benefit most from such therapy is crucial. An ideal target of such inhibitory therapy might be malignant mesothelioma (MM), a highly lethal, treatment-resistant malignancy of mesothelial cells of the pleura and peritoneum that produces large amounts of TGF-beta. The purpose of this study was to explore the possible therapeutic utility of TGF-beta blockade on MM.

EXPERIMENTAL DESIGN

To evaluate this hypothesis, we tested the effects of a soluble TGF-beta type II receptor (sTGF-beta R) that specifically inhibits TGF-beta1 and TGF-beta 3 in three different murine MM tumor models, AB12 and AC29 (which produce large amounts of TGF-beta) and AB1 (which does not produce TGF-beta).

RESULTS

Tumor growth of both established AB12 and AC29 tumors was inhibited by sTGF-beta R. In contrast, AB1 tumors showed little response to sTGF-beta R. The mechanism of these antitumor effects was evaluated and determined to be primarily dependent on immune-mediated responses because (a) the antitumor effects were markedly diminished in severe combined immunodeficient mice or mice depleted of CD8(+) T cells and (b) CD8(+) T cells isolated from spleens of mice treated with sTGF-beta R showed strong antitumor cytolytic effects, whereas CD8(+) T cells isolated from spleens of tumor-bearing mice treated with of control IgG2a showed no antitumor cytolytic effects.

CONCLUSIONS

Our data suggest that TGF-beta blockade of established TGF-beta-secreting MM should be explored as a promising strategy to treat patients with MM and other tumors that produce TGF-beta.

Integration of Multimodality Approaches in the Management of Malignant Pleural Mesothelioma

More than half a century after the first descriptions of mesothelioma as a pathologic entity, satisfactory treatment is still elusive. Although relatively uncommon, the incidence of mesothelioma will most likely increase over the next 10-20 years. Advances have been made in understanding the pathogenesis, diagnosis, and staging, but they have not translated into markedly improved survival. Some use palliative treatment as the primary means of therapy even now. On the other hand, a cadre of individuals have studied how surgery, chemotherapy, and radiation therapy affect the disease. Although each individual modality has had limited success by itself, a multimodality approach has been documented to improve survival and quality of life. In addition, intriguing discoveries in immunology and gene profiling and therapy promise hope for further improvement. In this article, we will illustrate the current views on integrating these different approaches and delineate areas of active research.

IL-2 intratumoral immunotherapy enhances CD8+ T cells that mediate destruction of tumor cells and tumor-associated vasculature: a novel mechanism for IL-2

Therapeutic use of IL-2 can generate antitumor immunity; however, a variety of different mechanisms have been reported. We injected IL-2 intratumorally (i.t.) at different stages of growth, using our unique murine model of mesothelioma (AE17; and AE17 transfected with secretory OVA (AE17-sOVA)), and systematically analyzed real-time events as they occurred in vivo. The majority of mice with small tumors when treatment commenced displayed complete tumor regression, remained tumor free for >2 mo, and survived rechallenge with AE17 tumor cells. However, mice with large tumors at the start of treatment failed to respond. Timing experiments showed that IL-2-mediated responses were dependent upon tumor size, not on the duration of disease. Although i.t. IL-2 did not alter tumor Ag presentation in draining lymph nodes, it did enhance a previously primed, endogenous, tumor-specific in vivo CTL response that coincided with regressing tumors. Both CD4(+) and CD8(+) cells were required for IL-2-mediated tumor eradication, because IL-2 therapy failed in CD4(+)-depleted, CD8(+)-depleted, and both CD4(+)- and CD8(+)-depleted C57BL/6J animals. Tumor-infiltrating CD8(+) T cells, but not CD4(+) T cells, increased in association with a marked reduction in tumor-associated vascularity. Destruction of blood vessels required CD8(+) T cells, because this did not occur in nude mice or in CD8(+)-depleted C57BL/6J mice. These results show that repeated doses of i.t. (but not systemic) IL-2 mediates tumor regression via an enhanced endogenous tumor-specific CTL response concomitant with reduced vasculature, thereby demonstrating a novel mechanism for IL-2 activity.

Regression of AK7 malignant mesothelioma established in immunocompetent mice following intratumoral gene transfer of interferon gamma

Malignant mesothelioma (MM) is a lethal tumor linked with a prior exposure to asbestos in which limited progress has been made so far using conventional therapies. MM is an example of a "nonimmunogenic" tumor characterized by a fibrous stroma and an absence of infiltrating T lymphocytes. High levels of transforming growth factor-beta (TGF-beta) produced by mesothelioma cells have been related to the immune tolerance towards the tumor. In order to evaluate the effect of local delivery of cytokines such as interferon gamma (IFN-gamma) by gene transfer, we characterized and used a murine model, AK7, which appeared very similar to human mesothelioma. AK7 cells expressed low levels of major histocompatibility class I and class II antigens and secreted high levels of latent TGF-beta. The TGF-beta pathway in AK7 cells is operative but inefficient because endogenous TGF-beta is predominantly inactive. Treatment of pre-established AK7 tumors by direct intratumoral injection of an adenovirus vector expressing murine IFN-gamma, Ad.mIFN-gamma, led to significant tumor regression. Peripheral tumor infiltration by CD4+ and CD8+ T lymphocytes in the treated tumors appeared to be because of the induction of an immune response. Tumor relapse was observed, which could be due to local TGF-beta secretion by remaining tumor cells.

Localised spontaneous regression in mesothelioma -- possible immunological mechanism

Malignant mesothelioma (MM) is an aggressive tumor usually associated with asbestos exposure. Although it can remain stable for prolonged periods, it has not been described to spontaneously regress. MM tumors are thought to be immunogenic based both on animal studies and on the good responses in some humans treated with immunotherapy. Here we present a case of pleural MM in which a transient spontaneous regression was associated with tumor tissue infiltration with mononuclear cells and serological evidence of anti-MM reactivity. The patient's tumor eventually progressed and with this progression there was evidence of loss of serological reactivity to some, but not all, of her MM antigens. The patient survived for 20 months and, in contrast to her initial biopsy, no significant lymphoid infiltrate was detected in her MM tissue at post mortem examination.

Dengue virus binding to human leukocyte cell lines: receptor usage differs between cell types and virus strains

Monocyte macrophages (Mphi) are thought to be the principal target cells for the dengue viruses (DV), the cause of dengue fever and hemorrhagic fever. Cell attachment is mediated by the virus envelope (E) protein, but the host-cell receptors remain elusive. Currently, candidate receptor molecules include proteins, Fc receptors, glycosaminoglycans (GAGs) and lipopolysaccharide binding CD14-associated molecules. Here, we show that in addition to Mphi, cells of the T- and B-cell lineages, and including cells lacking GAGs, can bind and become infected with DV. The level of virus binding varied widely between cell lines and, notably, between virus strains within a DV serotype. The latter difference may be ascribable to one or more amino acid differences in domain II of the E protein. Heparin had no significant effect on DV binding, while heparinase treatment of cells in all cases increased DV binding, further supporting the contention that GAGs are not required for DV binding and infection of human cells. In contrast to a recent report, we found that lipopolysaccharide (LPS) had either no effect or enhanced DV binding to, and infection of, various human leukocyte cell lines, while in all virus-cell combinations, depletion of Ca(2+)/Mg(2+) enhanced DV binding. This argues against involvement of beta(2) integrins in virus-host cell interactions, a conclusion in accord with the demonstration of three virus binding membrane proteins of < 75 kDa. Collectively, the results of this study question the purported exclusive importance of the E protein domain III in DV binding to host cells and point to a far more complex interaction between various target cells and, notably, individual DV strains.

Cross-presentation of tumour antigens: evaluation of threshold, duration, distribution and regulation

The development of technology to measure antigen presentation in the secondary lymphoid system has provided the opportunity of analysing components of the host antitumour immune response that have, until now, been unavailable for study. In particular, this technology has enabled us to evaluate threshold levels of tumour antigen required for cross-presentation in draining lymph nodes, the duration of this antigen presentation and processes that regulate tumour antigen presentation. Thus, we have been able to dissect out the relationship between antigen presentation and the resultant development of effector function in class I-restricted T cells, as well as the role of regulatory CD4 cells. We have also used this technology to evaluate the effects of antitumour therapy on local antigen cross-presentation.

Emerging translational therapies for mesothelioma

Malignant pleural mesothelioma remains a therapeutic and diagnostic problem. Translational mechanisms for treatment of the disease are emerging from newly learned characteristics of the tumor on a molecular, cellular, and extracellular basis. Although slow to reach the clinical arena, these potential strategies do show proof of principle in the in vitro and in vivo settings, and some, including adenoviral molecular chemotherapy, have completed phase I testing. This review describes the rationale and status of these newer treatment ideas.

Loss of differentiation of 4NQO-induced rat malignant oral keratinocytes correlates with metastatic dissemination and is associated with a reduced cellular response to TGF-beta1 and an altered receptor profile

This study examined the metastatic capacity of clonal populations of 4NQO-induced rat malignant oral keratinocytes following orthotopic transplantation to athymic mice. Polygonal and spindle cells formed well-differentiated squamous cell carcinomas (keratin positive and vimentin negative) and undifferentiated spindle cell tumours (keratin negative and vimentin positive), respectively, in almost 100% of animals at the site of inoculation (floor of mouth). Transplantation of 5x 10(6) cells of either cell type at high cell density resulted in approximately 50% of animals forming pulmonary metastases. By contrast, inoculation of 2x 10(6) differentiated polygonal cells resulted in the formation of significantly fewer pulmonary metastases than the undifferentiated spindle cells. A single well-differentiated clone of polygonal cells and 3 of 4 of the undifferentiated spindle cell lines produced comparable levels of TGF-beta1. One undifferentiated spindle cell line expressed significantly more TGF-beta1 and, following transplantation orthotopically, fewer animals formed pulmonary metastases despite the formation of primary tumours in almost all grafted animals, suggesting that TGF-beta1 can act as a tumour suppressor in this cell type. All cell lines produced comparable amounts of TGF-beta2. The clones of polygonal cells were markedly inhibited and the spindle cells were only partially inhibited by exogenous TGF-beta1. Both cell types expressed high-affinity TGF-beta cell surface receptors; the ratio of type I to type II TGF-beta receptors was 1.0:<3.0 in the spindle cells and 1.0:17.9 in the polygonal clone. The results suggest that differentiated rat malignant oral keratinocytes are less aggressive and have a decreased potential to metastasise than their undifferentiated spindle cell counterparts. This may be attributable, in part, to a change in TGF-beta receptor profile leading to the partial loss of response to exogenous TGF-beta1.

Advances in the treatment of malignant pleural mesothelioma

Malignant pleural mesothelioma is a neoplasm that is commonly fatal and for which there are no widely accepted curative approaches. Mesothelioma is unresponsive to most chemotherapy and radiotherapy regimens, and it typically recurs even after the most aggressive attempts at surgical resection. Multimodality approaches have been of some benefit in prolonging survival of very highly selected subgroups of patients, but they have had a relatively small impact on the majority of the patients diagnosed with this disease. As the incidence of pleural mesothelioma peaks in the United States and Europe over the next 10 to 20 years, new therapeutic measures will be necessary. This review will discuss the roles of chemotherapy, radiotherapy, surgery, and combined modality approaches in the treatment of pleural mesothelioma, as well as scientific advances made in the past decade that have led to the development of experimental techniques, such as photodynamic therapy, immunotherapy, and gene therapy, that are currently undergoing human clinical trials. These promising new avenues may modify the therapeutic nihilism that is rampant among clinicians dealing with mesothelioma.

Impediments to successful immunotherapy

Over the last decade, there has been a considerable increase in understanding of immune responses against cancers, the antigenic structures on tumor cells recognised by the immune system, and the development of more effective vaccines. There is, however, very limited understanding of why the immune system most often fails to control tumor growth and progression. In some patients, it is difficult to demonstrate immune responses to their tumors, and it may be assumed that this reflects poor recognition of tumor antigens, induction of anergy in lymphocytes, or suppression of immune responses by tumor-derived factors. In other patients, tumor progression appears to occur despite the presence of antibody or cell-mediated responses. This may indicate selection of tumor cells that have lost tumor antigens or HLA antigens by immune responses against the tumor. Tumor cells may also become resistant to mediators of apoptosis, such as Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand used by lymphocytes to kill tumor cells. It is suggested that development of effective immunotherapy will need to include strategies that take into account these limitations of immune responses and classification of tumors according to the treatment approach most likely to succeed.

Primary human mesothelioma cells express class II MHC, ICAM-1 and B7-2 and can present recall antigens to autologous blood lymphocytes

Mesothelioma cells (MMc) are considered to be weakly immunogenic and the experimental approaches attempting to induce an immune response against these cells have been disappointing. Our aim was to investigate whether MMc possess the surface accessory molecules involved in antigen presentation and whether these cells are capable of presenting recall antigens to autologous blood lymphocytes. Four primary MMc cultures were generated from malignant effusions and examined to assess whether the accessory molecules required for antigen presentation were present on their surfaces. Intercellular adhesion molecule-I (ICAM-I; CD54); class I and class II major histocompatibility complex-DR (MHCI and MHCII-DR); B7-1 (CD80.3); and B7-2 (CD86) expression by MMc was studied by immunocytochemical and/or FACScan analysis. MMc were pulsed with purified protein derivative (PPD), Tetanus toxoid (TT) and Candida albicans (CA) bodies, and incubated with autologous lymphocytes. Lymphocyte proliferation was estimated by radionucleotide incorporation. Phenotypic analysis showed the presence of MHCII-DR, ICAM-I and B7-2 on primary MMc cultures, whereas the phenotypic evaluation of 2 established MMc lines did not show the presence of the B7-1 and B7-2 molecules. In addition, MHCII-DR was detectable only after interferon gamma (IFN-gamma) stimulation. Primary MMc cultures acquired the capability to induce lymphocyte proliferation after pulse with the recall antigens. To achieve characterization of these lymphocytes, we generated a PPD-specific CD4+ T-cell clone. PPD-pulsed MMc were shown to specifically induce T-cell clone proliferation through a MHCII-DR-mediated process. We conclude that primary MMc possess the surface molecules required for antigen presentation and can present recall antigens to CD4+ lymphocytes.

A novel transforming growth factor beta2 antisense transcript in mammalian lung

Transforming growth factor (TGF) beta2 gene expression was examined in murine, rat and human lung by in situ hybridization with riboprobes. Hybridization signal was observed in a variety of cells with the sense probe, and Northern-blot analysis with this probe demonstrated the presence of a novel 3.5 kb transcript. This first report suggesting the existance of a natural TGFbeta2 antisense transcript raises the possibility that such a transcript may play a role in regulating TGFbeta2 production.

Gene therapy for malignant pleural mesothelioma

Malignant mesothelioma (MM) is a fatal malignancy refractory to all forms of standard anticancer therapy. This article reports the results of a phase I clinical trial assessing the safety of intrapleural delivery and efficacy of intratumoral gene transfer of recombinant adenovirus (rAd) containing herpes simplex virus thymidine kinase (HSVtk) gene into the pleural space of patients with MM, followed by systematic treatment with the antiviral drug ganciclovir (GCV) for 14 days. AD.RSVtk/GCV gene therapy proved to be well tolerated, with evidence of significant gene transfer particularly at high vector doses and with elimination of preliminary biopsy. Ongoing gene therapy trials for mesothelioma at two other centers, focusing on immunostimulation and using suicide gene therapy as a tumor vaccine, are also reviewed in this article.

TGF beta in prostate cancer: a growth inhibitor that can enhance tumorigenicity

A common feature of cancer cells is the autocrine production of growth promoters and the loss of function of tumor suppressors. In our search for such features of prostate cancer, we discovered that transforming growth factor beta 1 (TGF beta 1) levels are higher in prostate cancer than in normal prostate, and prostate cancer cells can activate endogenously-produced latent TGF beta to a bioactive form. Because TGF beta 1 is a potent growth inhibitor of epithelial cells, it seems paradoxical that malignant epithelial cells make high levels of a growth inhibitor. Even prostate cancer cells can be growth-inhibited by TGF beta 1, but only under specific conditions in vitro (plating at low cell density in serum-free medium), and this response is readily disrupted by growth factors, serum, and extracellular matrix, to all of which the cells are exposed in vivo. This explains why prostate cancer cells are resistant to the growth-inhibitory effect of TGF beta in vivo. In vivo, TGF beta 1 actually enhances prostate tumor growth and metastasis, but not by affecting tumor cell proliferation directly. One possibility is that TGF beta affects the host to allow increased numbers of tumor cells to survive and produce progeny. In addition, since prostate cancer cells can still respond to TGF beta, e.g., by increased cell motility, even under conditions that prevent growth inhibition, the ability of TGF beta to enhance tumorigenicity in vivo might also occur via direct effects on the tumor cells themselves. I will discuss new developments in our understanding of TGF beta action, which provide a framework for elucidating the mechanism by which prostate cancer cells have devised a way to protect themselves from being growth-inhibited by TGF beta 1 in vivo. Since the cells retain the ability to be growth-inhibited by TGF beta, indicating that the TGF beta receptors and signaling pathways for growth inhibition are intact, albeit inactive, it might be possible to reactivate this pathway to achieve a therapeutic benefit in vivo.