Malignant Pleural Mesothelioma Cell Proliferation Research Articles

APE-1/Ref-1 Inhibition Blocks Malignant Pleural Mesothelioma Cell Proliferation and Migration: Crosstalk between Oxidative Stress and Epithelial Mesenchymal Transition (EMT) in Driving Carcinogenesis and Metastasis.

Malignant pleural mesothelioma (MPM) is an aggressive cancer associated with asbestos exposure. MPM pathogenesis has been related both to oxidative stress, evoked by and in response to asbestos fibers exposure, and epithelial mesenchymal transition (EMT), an event induced by oxidative stress itself and related to cancer proliferation and metastasis. Asbestos-related primary oxidative damage is counteracted in the lungs by various redox-sensitive factors, often hyperactivated in some cancers. Among these redox-sensitive factors, Apurinic-apyrimidinic endonuclease 1 (APE-1)/Redox effector factor 1 (Ref-1) has been demonstrated to be overexpressed in MPM and lung cancer, but the molecular mechanism has not yet been fully understood. Moreover, asbestos exposure has been associated with induced EMT events, via some EMT transcription factors, such as Twist, Zeb-1 and Snail-1, in possible crosstalk with oxidative stress and inflammation events. To demonstrate this hypothesis, we inhibited/silenced Ref-1 in MPM cells; as a consequence, both EMT (Twist, Zeb-1 and Snail-1) markers and cellular migration/proliferation were significantly inhibited. Taken as a whole, these results show, for the first time, crosstalk between oxidative stress and EMT in MPM carcinogenesis and invasiveness, thus improving the knowledge to better address a preventive and therapeutic approach against this aggressive cancer.

Important functional role of the protein osteopontin in the progression of malignant pleural mesothelioma.

Malignant Pleural Mesothelioma (MPM) is an aggressive cancer of the mesothelial lining associated with exposure to airborne non-degradable asbestos fibers. Its poor response to currently available treatments prompted us to explore the biological mechanisms involved in its progression. MPM is characterized by chronic non-resolving inflammation; in this study we investigated which inflammatory mediators are mostly expressed in biological tumor samples from MPM patients, with a focus on inflammatory cytokines, chemokines and matrix components. Expression and quantification of Osteopontin (OPN) was detected in tumor and plasma samples of MPM patients by mRNA, immunohistochemistry and ELISA. The functional role of OPN was investigated in mouse MPM cell lines in vivo using an orthotopic syngeneic mouse model. In patients with MPM, the protein OPN was significantly more expressed in tumors than in normal pleural tissues and predominantly produced by mesothelioma cells; plasma levels were elevated in patients and associated with poor prognosis. However, modulation of OPN levels was not significantly different in a series of 18 MPM patients receiving immunotherapy with durvalumab alone or with pembrolizumab in combination with chemotherapy, some of whom achieved a partial clinical response. Two established murine mesothelioma cell lines: AB1 and AB22 of sarcomatoid and epithelioid histology, respectively, spontaneously produced high levels of OPN. Silencing of the OPN gene (Spp1) dramatically inhibited tumor growth in vivo in an orthotopic model, indicating that OPN has an important promoting role in the proliferation of MPM cells. Treatment of mice with anti-CD44 mAb, blocking a major OPN receptor, significantly reduced tumor growth in vivo. These results demonstrate that OPN is an endogenous growth factor for mesothelial cells and inhibition of its signaling may be helpful to restrain tumor progression in vivo. These findings have translational potential to improve the therapeutic response of human MPM.

CircPLK1 Acts as a Carcinogenic Driver to Promote the Development of Malignant Pleural Mesothelioma by Governing the miR-1294/HMGA1 Pathway.

The deregulation of circular RNAs (circRNAs) is involved in cancer development. CircRNA polo-like kinase 1 (circPLK1) was reported to promote breast cancer development. However, the role of circPLK1 in malignant pleural mesothelioma (MPM) is unclear. The expression of circPLK1, miR-1294, and high mobility group AT-hook 1 (HMGA1) mRNA was measured by quantitative real-time PCR (qPCR). Cell viability was detected by CCK-8 assay. Colony formation ability was monitored by colony formation assay. Cell proliferation was detected by EdU assay. Cell migration and cell invasion were monitored by transwell assay. Cancer cell stemness was investigated by sphere formation assay. The protein levels of marker proteins and HMGA1 expression were measured by western blot analysis. The binding relationship between miR-1294 and circPLK1 or HMGA1 was validated by pull-down assay, dual-luciferase reporter assay or RIP assy. Animal study was performed to disclose the role of circPLK1 in vivo. Exosomes were identified by transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). CircPLK1 was upregulated in MPM tumor tissues and cell lines. CircPLK1 knockdown suppressed the proliferation, migration, invasion and stemness of MPM cells. CircPLK1 contained a binding site for miR-1294 and thus bound to miR-1294 to sequester its expression. Inhibition of miR-1294 reversed the effects of circPLK1 knockdown. HMGA1 was a target of miR-1294, and circPLK1 bound to miR-1294 to increase the expression of HMGA1. MiR-1294 restoration also suppressed the proliferation, migration, invasion and stemness of MPM cells, while these effects were abolished by HMGA1 overexpression. In addition, circPLK1 knockdown inhibited tumor growth in vivo. CircPLK1 was overexpressed in exosomes derived from serum of MPM patients. CircPLK1 knockdown inhibited MPM cell proliferation, migration, invasion and stemness by targeting the miR-1294/HMGA1 pathway.

Identification of novel COX-2 / CYP19A1 axis involved in the mesothelioma pathogenesis opens new therapeutic opportunities

BackgroundBased on previous studies highlighting that the induction of cyclooxygenase-2 (COX-2) and high prostaglandin E2 (PGE2) levels contribute to the pathogenesis of malignant pleural mesothelioma (MPM), and that aromatase (CYP19A1), an enzyme that plays a key role in estrogen biosynthesis, along with estradiol (E2) were expressed in MPM, this study aimed to investigate the possible interplay between COX-2 and CYP19A1 in the pathogenesis of mesothelioma, as well as the underlying mechanism.MethodsThe interaction between COX-2 and CYP19A1 was first investigated on different MPM lines upon PGE2, and COX-2 inhibitor (rofecoxib) treatment by western blot, RT-PCR. The key regulatory pathways involved in the COX-2 and CYP19A1 axis were further studied in MPM cells, after rofecoxib and exemestane (CYP19A1 inhibitor) treatment in monotherapy and in combination, by cell cycle distribution, western blot, and combination index analysis. To explore the role of COX-2/CYP19A1 axis in 3D preclinical models of MPM cells, we analyzed the effect of combination of COX-2 and CYP19A1 inhibitors in mesosphere formation. Immunohistochemical analysis of MPM mesosphere and specimens was utilized to evaluate the involvement of COX-2 on the CYP19A1 activity and the relationship between E2 and COX-2.ResultsPGE2 or rofecoxib treatment caused in MPM cells an increased or decreased, respectively, CYP19A1 expression at mRNA and protein levels. The effect of rofecoxib and exemestane combination in MPM cell proliferation was synergistic. Activation of caspase-3 and cleavage of PARP confirmed an apoptotic death for MPM cell lines. Increased expression levels of p53, p21, and p27, downregulation of cyclin D1 and inhibition of Akt activation (pAKT) were also found. The antagonistic effect of rofecoxib and exemestane combination found only in one cell line, was reverted by pretreatment with MK2206, a pAKT inhibitor, indicating pAKT as an actionable mediator in the COX-2-CYP19A1 axis. Reduction of size and sphere-forming efficiency in MPM spheres after treatment with both inhibitor and a decrease in COX-2 and E2 staining was found. Moreover, immunohistochemical analysis of 46 MPM samples showed a significant positive correlation between COX-2 and E2.ConclusionsCollectively, the results highlighted a novel COX-2/CYP19A1 axis in the pathogenesis of MPM that can be pharmacologically targeted, consequently opening up new therapeutic options.

Inhibition of Human Malignant Pleural Mesothelioma Growth by Mesenchymal Stromal Cells.

Background: Malignant Pleural Mesothelioma (MPM) is an aggressive tumor that has a significant incidence related to asbestos exposure with no effective therapy and poor prognosis. The role of mesenchymal stromal cells (MSCs) in cancer is controversial due to their opposite effects on tumor growth and in particular, only a few data are reported on MSCs and MPM. Methods: We investigated the in vitro efficacy of adipose tissue-derived MSCs, their lysates and secretome against different MPM cell lines. After large-scale production of MSCs in a bioreactor, their efficacy was also evaluated on a human MPM xenograft in mice. Results: MSCs, their lysate and secretome inhibited MPM cell proliferation in vitro with S or G0/G1 arrest of the cell cycle, respectively. MSC lysate induced cell death by apoptosis. The efficacy of MSC was confirmed in vivo by a significant inhibition of tumor growth, similar to that produced by systemic administration of paclitaxel. Interestingly, no tumor progression was observed after the last MSC treatment, while tumors started to grow again after stopping chemotherapeutic treatment. Conclusions: These data demonstrated for the first time that MSCs, both through paracrine and cell-to-cell interaction mechanisms, induced a significant inhibition of human mesothelioma growth. Since the prognosis for MPM patients is poor and the options of care are limited to chemotherapy, MSCs could provide a potential new therapeutic approach for this malignancy.

Metformin Induces Apoptosis and Inhibits Notch1 in Malignant Pleural Mesothelioma Cells.

Malignant pleural mesothelioma (MPM) is an aggressive asbestos-related cancer arising from the mesothelial cells lining the pleural cavity. MPM is characterized by a silent clinical progression and a highly resistance to conventional chemo/radio-therapies. MPM patients die in a few months/years from diagnosis. Notch signaling is a well-conserved cell communication system, which regulates many biological processes. In humans, the dysregulation of Notch pathway potentially contributes to cancer onset/progression, including MPM. Metformin is the first-line drug used to treat type 2 diabetes mellitus. Metformin is proven to be an effective antitumor drug in preclinical models of different types of cancer. To date, clinical efficacy is being studied in many clinical trials. In this study, the anti-proliferative effect of metformin on MPM cells and the putative involvement of Notch1 as a mediator of metformin activities, were investigated. MPM cells showed high levels of Notch1 activation compared to normal pleural mesothelial cells. Furthermore, metformin treatment hampered MPM cell proliferation and enhanced the apoptotic process, accompanied by decreased Notch1 activation.

2-Deoxy-glucose Enhances the Effect of Cisplatin and Pemetrexed in Reducing Malignant Pleural Mesothelioma Cell Proliferation But Not Spheroid Growth.

Malignant pleural mesothelioma (MPM) is a therapy-resistant neoplasm of the pleura. Standard chemotherapy consists of a combination of cisplatin (CPDD) and pemetrexed (PEM). The aim of this study was to assess whether inhibition of aerobic glycolysis by 2-deoxy-glucose (2DG) would enhance the effects of standard chemotherapy. MeT-5A, M14K, MSTO and ZL34 cell lines were used. Cell viability with 2DG and cell proliferation and spheroid formation with CPDD+PEM alone and with 2-DG were tested. Viability with 2-DG was dose-dependent. Cell proliferation with CPDD+PEM on 2D surface was reduced in all cell types, 2-DG inclusion demonstrated a synergistic effect in MSTO and ZL34 cells. Spheroid growth in 3D with CPDD+PEM or CPDD+PEM+2-DG lowered spheroid growth in all cell types. 2-DG synergizes with CPDD+PEM in lowering MPM cell proliferation in 2D to <20%. In 3D MPM spheroid growth 2-DG synergism with CPDD+PEM treatment is not maintained.

Overcoming palbociclib resistance by combined treatment with PI3K/AKT/mTOR inhibitors in mesothelioma cells

Carcinogenesis of malignant pleural mesothelioma (MPM) is strictly associated with chronic exposure of mesothelial cells from the pleura to asbestos fibers and MPM incidence is expected to peak in the next years. Extensive genome analyses of patient-derived MPM tumors revealed that the most frequent mutational event involves the inactivation of the CDKN2A gene that encodes for the cell cycle inhibitors p16$^{\rm INK4a}$ and p14$^{\rm ARF}$ with consequent constitutive activation of CDK4/6 - cyclin D complexes. Therefore, inhibition of the latter complexes may represent a new option for the treatment of MPM patients. However, despite the efficacy of the specific CDK4/6 inhibitor palbociclib in blocking MPM cell proliferation, acquired resistance inevitably occurs. Herein, palbocilib-resistant clones isolated after stepwise exposure of MSTO-211H cells to gradually increasing drug concentrations, showed a reduction in Rb protein levels as well as in the cell cycle inhibitor p21$^{\rm waf1}$, accompanied by increased phosphorylation of AKT and p70S6K. Simultaneous treatment of resistant clones with both palbociclib and specific PI3K/AKT/mTOR inhibitors produced an additive effect in terms of reduction in cell growth, without any signs of senescence but with increased cell death. In MSTO-211H sensitive cells, this combination drug treatment significantly delayed the adaptation to palbociclib, suggesting that this treatment approach may prevent or at least retard the emergence of palbociclib resistance. Collectively, these results suggest that the combination of palbociclib with PI3K/AKT/mTOR inhibitors may overcome the acquisition of resistance to palbociclib treatment and could represent a potential therapeutic approach to treat cancers with acquired resistance to CDK4/6 inhibitors in the presence of activation of the AKT/mTOR signaling pathway.

Targeting CD26 suppresses proliferation of malignant mesothelioma cell via downmodulation of ubiquitin-specific protease 22

Malignant pleural mesothelioma (MPM) is an aggressive malignancy arising from mesothelial lining of pleura. It is associated with a poor prognosis, partly due to the lack of a precise understanding of the molecular mechanisms associated with its malignant behavior. In the present study, we expanded on our previous studies on cell cycle control of MPM cells by targeting CD26 molecule with humanized anti-CD26 monoclonal antibody (HuCD26mAb), focusing particularly on ubiquitin-specific protease 22 (USP22). We showed that USP22 protein expression is detected in clinical specimens of MPM and that USP22 knockdown, as well as CD26 knockdown, significantly inhibits the growth and proliferation of MPM cells in vitro and in vivo. Moreover, depletion of both USP22 and CD26 suppresses MPM cell proliferation even more profoundly. Furthermore, expression levels of USP22 correlate with those of CD26. HuCD26mAb treatment induces a decrease in USP22 level through its interaction with the CD26 molecule, leading to increased levels of ubiquitinated histone H2A and p21. By demonstrating a CD26-related linkage with USP22 in MPM cell inhibition induced by HuCD26mAb, our present study hence characterizes USP22 as a novel target molecule while concurrently suggesting a new therapeutic strategy for MPM.

Nintedanib Is Active in Malignant Pleural Mesothelioma Cell Models and Inhibits Angiogenesis and Tumor Growth In Vivo.

Purpose: Malignant pleural mesothelioma (MPM) is an aggressive thoracic tumor type with limited treatment options and poor prognosis. The angiokinase inhibitor nintedanib has shown promising activity in the LUME-Meso phase II MPM trial and thus is currently being evaluated in the confirmatory LUME-Meso phase III trial. However, the anti-MPM potential of nintedanib has not been studied in the preclinical setting.Experimental Design: We have examined the antineoplastic activity of nintedanib in various in vitro and in vivo models of human MPM.Results: Nintedanib's target receptors were (co)expressed in all the 20 investigated human MPM cell lines. Nintedanib inhibited MPM cell growth in both short- and long-term viability assays. Reduced MPM cell proliferation and migration and the inhibition of Erk1/2 phosphorylation were also observed upon nintedanib treatment in vitro Additive effects on cell viability were detected when nintedanib was combined with cisplatin, a drug routinely used for systemic MPM therapy. In an orthotopic mouse model of human MPM, survival of animals receiving nintedanib per os showed a favorable trend, but no significant benefit. Nintedanib significantly reduced tumor burden and vascularization and prolonged the survival of mice when it was administered intraperitoneally. Importantly, unlike bevacizumab, nintedanib demonstrated significant in vivo antivascular and antitumor potential independently of baseline VEGF-A levels.Conclusions: Nintedanib exerts significant antitumor activity in MPM both in vitro and in vivo These data provide preclinical support for the concept of LUME-Meso trials evaluating nintedanib in patients with unresectable MPM. Clin Cancer Res; 24(15); 3729-40. ©2018 AACR.

Critical role of the Ror-family of receptor tyrosine kinases in invasion and proliferation of malignant pleural mesothelioma cells.

Malignant pleural mesothelioma (MPM) is a highly aggressive tumor with poor prognosis and closely related to exposure to asbestos. MPM is a heterogeneous tumor with three main histological subtypes, epithelioid, sarcomatoid, and biphasic types, among which sarcomatoid type shows the poorest prognosis. The Ror-family of receptor tyrosine kinases, Ror1 and Ror2, is expressed in various types of tumor cells at higher levels and affects their aggressiveness. However, it is currently unknown whether they are expressed in and involved in aggressiveness of MPM. Here, we show that Ror1 and Ror2 are expressed in clinical specimens and cell lines of MPM with different histological features. Studies using MPM cell lines indicate that expression of Ror2 is associated tightly with high invasiveness of MPM cells, whereas Ror1 can contribute to their invasion in the absence of Ror2. However, both Ror1 and Ror2 promote proliferation of MPM cells. We also show that promoted invasion and proliferation of MPM cells by Ror signaling can be mediated by the Rho-family of small GTPases, Rac1, and Cdc42. These findings elucidate the critical role of Ror signaling in promoting invasion and proliferation of MPM cells.

Bromodomain inhibition exerts its therapeutic potential in malignant pleural mesothelioma by promoting immunogenic cell death and changing the tumor immune-environment

ABSTRACTSystemic treatment of malignant pleural mesothelioma (MPM) is moderately active for the intrinsic pharmacological resistance of MPM cell and its ability to induce an immune suppressive environment. Here we showed that the expression of bromodomain (BRD) proteins BRD2, BRD4 and BRD9 was significantly higher in human primary MPM cells compared to normal mesothelial cells (HMC). Nanomolar concentrations of bromodomain inhibitors (BBIs) JQ1 or OTX015 impaired patient-derived MPM cell proliferation and induced cell-cycle arrest without affecting apoptosis. Importantly, BBIs primed MPM cells for immunogenic cell death, by increasing extracellular release of ATP and HMGB1, and by promoting membrane exposure of calreticulin and ERp57. Accordingly, BBIs activated dendritic cell (DC)-mediated phagocytosis and expansion of CD8+ T-lymphocyte clones endorsed with antitumor cytotoxic activity. BBIs reduced the expression of the immune checkpoint ligand PD-L1 in MPM cells; while both CD8+ and CD4+ T-lymphocytes co-cultured with JQ1-treated MPM cells decreased PD-1 expression, suggesting a disruption of the immune-suppressive PD-L1/PD-1 axis. Additionally, BBIs reduced the expansion of myeloid-derived suppressor cells (MDSC) induced by MPM cells. Finally, a preclinical model of MPM confirmed that the anti-tumor efficacy of JQ1 was largely due to its ability to restore an immune-active environment, by increasing intra-tumor DC and CD8+ T-lymphocytes, and decreasing MDSC. Thereby, we propose that, among novel drugs, BBIs should be investigated for MPM treatment for their combined activity on both tumor cells and surrounding immune-environment.

Tamoxifen Suppresses the Growth of Malignant Pleural Mesothelioma Cells.

Malignant pleural mesothelioma (MPM) is a rare but highly aggressive malignancy most often associated with exposure to asbestos. Recent evidence points to oestrogen receptor (ER)-β having a tumour-suppressor role in MPM progression, and this raises the question of whether selective modulators of ERs could play a role in augmenting MPM therapy. We investigated the action of tamoxifen in inhibiting the growth and modulating the cisplatin sensitivity of four MPM cell lines. Tamoxifen inhibited the growth of MPM cells and also modulated their sensitivity to cisplatin. The MPM cell lines expressed ERβ, but the actions of tamoxifen were not blocked by antagonism of nuclear ERs. Tamoxifen treatment repressed the expression of cyclins by MPM cells, resulting in cell-cycle arrest and caspase-3-coupled apoptosis signaling. The ER-independent actions of tamoxifen on MPM cell proliferation and cell-cycle progression may have clinical benefits for a subset of patients with MPM.

P2X7 targeting inhibits growth of human mesothelioma.

Malignant pleural mesothelioma (MPM) is an aggressive tumor refractory to anti-blastic therapy. MPM cells show several genetic and biochemical defects, e.g. overexpression of oncogenes, downregulation of onco-suppressor genes, dysregulation of microRNA, or alteration of intracellular Ca2+ homeostasis and of apoptosis. No information is as yet available on purinergic signalling in this tumor. Signalling via the P2×7 (P2RX7 or P2×7R) purinergic receptor is attracting increasing attention as a pathway involved in cancer cell death or proliferation. In this report we show that the P2×7R is expressed by three MPM cell lines established from MPM patients but not by mesothelial cells from healthy subjects (healthy mesothelial cells, HMCs). MPM cell proliferation was inhibited by in vitro incubation in the presence of selective P2×7R antagonists, as well as by stimulation with the P2×7R agonist BzATP. Systemic administration of the selective P2×7R blocker AZ10606120 inhibited in vivo growth of MPM tumors whether implanted subcutaneously (s.c.) or intraperitoneally (i.p.). Our findings suggest that the P2×7R might be a novel target for the therapy of mesothelioma.

The combination of sorafenib and everolimus shows antitumor activity in preclinical models of malignant pleural mesothelioma.

BackgroundMalignant Pleural Mesothelioma (MPM) is an aggressive tumor arising from mesothelial cells lining the pleural cavities characterized by resistance to standard therapies. Most of the molecular steps responsible for pleural transformation remain unclear; however, several growth factor signaling cascades are known to be altered during MPM onset and progression. Transducers of these pathways, such as PIK3CA-mTOR-AKT, MAPK, and ezrin/radixin/moesin (ERM) could therefore be exploited as possible targets for pharmacological intervention. This study aimed to identify ‘druggable’ pathways in MPM and to formulate a targeted approach based on the use of commercially available molecules, such as the multikinase inhibitor sorafenib and the mTOR inhibitor everolimus.MethodsWe planned a triple approach based on: i) analysis of immunophenotypes and mutational profiles in a cohort of thoracoscopic MPM samples, ii) in vitro pharmacological assays, ii) in vivo therapeutic approaches on MPM xenografts. No mutations were found in ‘hot spot’ regions of the mTOR upstream genes (e.g. EGFR, KRAS and PIK3CA).ResultsPhosphorylated mTOR and ERM were specifically overexpressed in the analyzed MPM samples. Sorafenib and everolimus combination was effective in mTOR and ERM blockade; exerted synergistic effects on the inhibition of MPM cell proliferation; triggered ROS production and consequent AMPK-p38 mediated-apoptosis. The antitumor activity was displayed when orally administered to MPM-bearing NOD/SCID mice.ConclusionsERM and mTOR pathways are activated in MPM and ‘druggable’ by a combination of sorafenib and everolimus. Combination therapy is a promising therapeutic strategy against MPM.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-015-1363-1) contains supplementary material, which is available to authorized users.

Adenosine Deaminase Inhibitor EHNA Exhibits a Potent Anticancer Effect Against Malignant Pleural Mesothelioma

Background/Aims: Malignant pleural mesothelioma (MPM) is an aggressive malignant tumor and an effective therapy has been little provided as yet. The present study investigated the possibility for the adenosine deaminase (ADA) inhibitor EHNA as a target of MPM treatment. Methods: MTT assay, TUNEL staining, monitoring of intracellular adenosine concentrations, and Western blotting were carried out in cultured human MPM cell lines without and with knocking-down ADA. The in vivo effect of EHNA was assessed in mice inoculated with NCI-H2052 MPM cells. Results: EHNA induced apoptosis of human MPM cell lines in a concentration (0.01-1 mM)- and treatment time (24-48 h)-dependent manner, but such effect was not obtained with another ADA inhibitor pentostatin. EHNA increased intracellular adenosine concentrations in a treatment time (3-9 h)-dependent manner. EHNA-induced apoptosis of MPM cells was mimicked by knocking-down ADA, and the effect was neutralized by the adenosine kinase inhibitor ABT-702. EHNA clearly suppressed tumor growth in mice inoculated with NCI-H2052 MPM cells. Conclusion: The results of the present study show that EHNA induces apoptosis of MPM cells by increasing intracellular adenosine concentrations, to convert to AMP, and effectively prevents MPM cell proliferation. This suggests that EHNA may be useful for treatment of the tragic neoplasm MPM.

Abstract 742: Antitumor activity of Trametinib, a MEK1/2 inhibitor, in malignant pleural mesothelioma cells in vitro

Abstract Introducion: Malignant pleural mesothelioma (MPM) is a highly aggressive malignancy and there is no approved targeted therapy. The MAPK pathway plays critical roles in the regulation of cell proliferation, growth, differentiation, and survival in multiple solid tumors, including MPM. Trametinib, a selective MEK inhibitor, have a survival benefit in patients with V600 BRAF-mutant metastatic melanoma. FDA approved Trametinib for these patients in May 2013. The effect of Trametinib in MPM cells has not been well studied. Purpose: We examined the effects of Trametinib in MPM cells in vitro. Methods: To examine the effect of Trametinib on the proliferation of MPM cells, we performed cell proliferation assay using four MPM cell lines, NCI-H2452, NCI-H226, NCI-H2052 and MSTO-211H. To examine the effect of Trametinib on intracellular signaling, we performed Western blot analysis in NCI-H226 cell line. Results: Trametinib exhibited potent antiproliferative activity in all four MPM cell lines with IC50 values ranging from 0.5 μM to 44 μM. Trametinib blocked the phosphorylation of ERK until 72 hours and decreased the expression of CD44 in a dose-dependent manner. In addition, the expression of CD44 was inhibited (48-72 hours) after the suppression of ERK phosphorylation by Trametinib. Conclusions: Our results suggest that Trametinib is a promising therapeutic agent for MPM. Citation Format: Hiroyuki Cho, Seiji Matsumoto, Yoshiko Fujita, Ayumi Kuroda, Masaki Hashimoto, Teruhisa Takuwa, Toshi Menju, Makoto Sonobe, Nobuyuki Kondo, Hiroshi Date, Seiki Hasegawa. Antitumor activity of Trametinib, a MEK1/2 inhibitor, in malignant pleural mesothelioma cells in vitro. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 742. doi:10.1158/1538-7445.AM2014-742

Systemic treatment of malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a rare malignancy with limited therapeutic options and its incidence is still increasing in both Europe and the developing nations. Prognosis of MPM patients is poor even if the median survival durations have been slightly improved after the introduction of the up-to-date chemotherapy combination with pemetrexed and cisplatin. There is a continuing unmet need to develop better systemic treatment for this disease, but the rarity of the tumor type creates formidable challenges in clinical trial research. Better understanding of the molecular machinery of MPM leads to the design and synthesis of novel compounds targeted against pathways identified as crucial for MPM cell proliferation and metastasis. Most efforts aim at improving standard first-line therapy, or developing effective second-line treatments. Several classes of drugs are currently being explored either in combination with cisplatin and pemetrexed or as single agent for relapsed or progressive MPM. This review focuses on several ongoing or recently completed clinical trials investigating novel, promising agents as first-line or second-line therapy for advanced MPM.

Platinum–bisphosphonate complexes have proven to be inactive chemotherapeutics targeted for malignant mesothelioma because of inappropriate hydrolysis

Bisphosphonates (BPs), the synthetic analogues of pyrophosphate, are widely used in the treatment of metabolic bone diseases. BPs exhibit a preferential accumulation in malignant pleural mesothelioma (MPM) and, furthermore, nitrogen-containing BPs (n-BPs) show significant inhibition of MPM cell proliferation. We synthesised dinuclear platinum(II) complexes containing a n-BP moiety as bridging ligand and am(m)ines as terminal ligands (Pt–n-BP)s, with the aim of obtaining bifunctional mesothelioma-targeted drugs. We compared the antiproliferative effect of the single drugs (i.e. Pt-model and n-BPs) with that of the preformed Pt–n-BP complexes by means of the combination index (CI) in order to assess the synergistic/additive/antagonistic effect of the two constituents in the resulting conjugates. The combination of the two individual drugs was almost additive, while the preformed Pt–n-BP produced an antagonistic effect. Furthermore, (Pt–n-BP)s neither inhibited the mevalonate pathway (as n-BPs normally do) nor increased the Pt uptake. The minimal biological results of these conjugates could be traced back to a slow and inappropriate hydrolysis, that does not split the adduct into active components.

Overexpression of SOCS3 exhibits preclinical antitumor activity against malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive tumor with poor prognosis for which an effective therapy remains to be established. Our study investigated the therapeutic potential of the suppressor of cytokine signaling 3 (SOCS3), an endogenous inhibitor of intracellular signaling pathways, for treatment of MPM. We infected MPM cells (H226, EHMES-1, MESO-1 and MESO-4) with an adenovirus-expressing SOCS3 (AdSOCS3) to examine the effect of SOCS3 overexpression on MPM cells. SOCS3 overexpression reduced MPM proliferation and induced apoptosis and partial G0/G1 arrest. SOCS3 also inhibited the proliferation of MPM cells via multiple signaling pathways including Janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3), extracellular signal-regulated kinase (ERK), focal adhesion kinase (FAK) and p53 pathways. Notably, AdSOCS3 treatment inhibited tumor growth in an MPM pleural xenograft model. These findings demonstrate that overexpression of SOCS3 has a potent antitumor effect against MPM both in vitro and in vivo and indicate the potential for clinical use of SOCS3 for MPM treatment.