The diagnosis of malignant pleural mesothelioma is difficult, with the most common differential diagnoses being benign pleural diseases and metastatic adenocarcinomas (ADCA). To identify novel markers that would be able to improve diagnostic accuracy, we performed a genome-wide gene expression analysis on tumor cell lines established from pleural effusions (malignant pleural mesothelioma and lung ADCA). This analysis led to the identification of genes encoding novel and pertinent cellular and soluble markers, for which the expression was validated by real-time RT-PCR. Immunohistochemical staining of tumor biopsy specimens with anti-type III collagen antibodies showed positive labeling for mesothelioma cells but not for ADCA cells. Using enzyme-linked immunosorbent assay, we showed that the C-C motif chemokine 2 (CCL2) concentration was significantly higher in pleural effusions from patients with mesothelioma (n = 61) than in subjects with ADCA (n = 25) or with benign pleural effusions (n = 15): median (inter-quartile range) = 2.99 ng/ml (1.76 to 6.01) vs 0.99 ng/ml (0.51 to 1.83) and 1.47 ng/ml (0.80 to 1.56), respectively, P < 0.0001. Conversely, the galectin-3 concentration was lower in mesothelioma: 11.50 ng/ml (6.73 to 23.53) vs 24.74 ng/ml (20.42 to 70.35) and 17.64 ng/ml (14.81 to 24.68), respectively, P < 0.0001. The areas under the curve for CCL2 were 0.8030 and 0.7716 for the differentiation of mesothelioma from ADCA or benign pleural effusions, respectively. Similarly, the areas under the curve obtained for galectin-3 were 0.7980 and 0.6923, respectively. In conclusion, type III collagen, CCL2, and galectin-3 are promising new diagnostic markers for mesothelioma. (Am J Pathol 2011, 178:1033-1042 DOI: 10.1016/j.ajpath.2010.12.014)

Malignant pleural mesothelioma (MPM) is an aggressive tumour with a limited response to conventional therapy. The aim of this study was to evaluate the anticancer effect of a DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (5-azaCdR), and two histone deacetylase inhibitors, valproic acid (VPA) and suberoylanilide hydroxamic acid (SAHA). Human mesothelioma cells were treated with each epigenetic drug, either alone or in combinations. The cytotoxic effects on treated cells and the expression of specific tumour antigens were evaluated. The recognition of treated cells by a specific CD8+ T-cell clone was also measured. Additionally, the effect of combined treatments was tested in a murine model of mesothelioma. We showed that VPA and SAHA synergised with 5-azaCdR to kill MPM cells and induce tumour antigen expression in the remaining living tumour cells. As a consequence, tumour cells expressing these antigens were recognised and lysed by specific CD8+ cytotoxic T-cells. In vivo, treatment with 5-azaCdR/VPA inhibited tumour growth, and promoted lymphocyte infiltration and an immune response against tumour cells. Appropriate epigenetic drug combinations, in addition to inducing mesothelioma cell death, also affect the immunogenic status of these cells. This property could be exploited in clinical investigations to develop MPM treatments combining chemotherapeutic and immunotherapeutic approaches.

Elevated amounts of soluble mesothelin‐related proteins (SMRP) have already been reported in sera and pleural effusions from mesothelioma patients, providing a useful diagnostic marker for malignant pleural mesothelioma (MPM). However, the origin of SMRP is not yet understood. Production of SMRP could be related to abnormal splicing events leading to synthesis of a secreted protein (release) or to an enzymatic cleavage from membrane‐bound mesothelin (ectodomain shedding). To test these hypotheses, we used a panel of mesothelioma cells established in culture from pleural effusions of MPM patients. Our in vitro results confirmed specific mesothelin expression and SMRP production in supernatants from epithelioid MPM cell lines, thus providing a relevant cellular model to study soluble mesothelin production mechanisms. The expression of mesothelin‐encoding RNA variants was screened by reverse transcription–polymerase chain reaction experiments. Protease involvement in mesothelin cleavage from the cellular surface was investigated by treatment of MPM cells with GM6001, a broad‐spectrum MMP‐ and ADAM‐family inhibitor. GM6001 treatment significantly impaired SMRP production by MPM cell lines, in favor of an enzymatic‐mediated shedding process. In addition, a splice variant transcript of mesothelin (variant 3) was detected in these MPM cell lines, in accordance with the release of a secreted part of the protein. Our results indicate that both mechanisms could be implicated in soluble mesothelin production by epithelioid mesothelioma cells. (Cancer Sci 2008; 99: 590–594)

Hydroxyurea (HU) and 1-β-d-arabino-furanosylcytosine (AraC) are two compounds used to inhibit DNA repair in the comet assay and thereby increase its sensitivity. We used RNA synthesis and comet assays to assess the cytotoxic and genotoxic effects of HU and AraC in the HepG2 cells after 1, 5, or 21 h of exposure to concentrations used to inhibit DNA repair. HU was genotoxic between 2 and 10 mM after 1 h of exposure and cytotoxic after 21 h. The presence of AraC (10, 50, or 100 μM) increased the DNA damage caused by HU (10 mM) suggesting a potentiation of the genotoxic effect. The interaction between the two inhibitors started after 5 h but was not dependent on the concentrations of AraC. Consequently, careful attention is required when employing a combination of HU and AraC, as their mechanisms of action could interfere with the interpretation of the data from genotoxicity assays.

AIM:To explore different effects of 12 beticolins, Cercospora beticola toxins, on ras-transformed adrenocortical cell growth inhibition and their functional mechanism.METHODS:Beticolin-induced inhibition was measured with survival cell number determined by an automated photocolorimetric method. The penetration of beticolin was examined by confocal microscopy. Ras protein determined by Lowry method were separated by 14 % SDS-PAGE and electroblotted to Immobilon-P transfer membrane and detected with pan-Ras (Ab-3) monoclonal antibody. The Ca2+ chelation by beticolin was investigated using a calcium ionophore.RESULTS:Cell growth inhibition was found dose- and time-dependently at submicromolar level for beticolin-1, -2, and -13 (IC50 </= 250 nmol/L) and for beticolin-0, 6, and -11 (400 nmol/L < IC50 </= 500 nmol/L). The inhibition by beticolin-1 was immediate, independent of cell culture step and not reversible for 3-day treatment. Beticolin-3 and -4 were slightly active (1 micromol/L < IC50 </= 2 micromol/L) and beticolin-7, -9, -12, and -5 were inactive at micromolar level. The beticolin-induced cell growth inhibition was correlated with the hydrophobicity of these compounds. Beticolin-1 fluorescence in RTAC cells was detected by confocal microscopy whereas beticolin-3 and -12 were not even after a 24 h incubation period. Beticolin-1-induced cell growth inhibition was partially reverted by calcium ionophore suggesting a role of intracellular Ca2+ chelation by beticolin-1 on cell growth inhibition. Furthermore, beticolin-1 blocked up Ras p21 translocation to membrane and induced accumulation of Ras in the cytosol as an inactive form by different ways.CONCLUSION:Beticolins with high hydrophobicity inhibit tumorigenic cell proliferation by different ways.

To test the Kirsten‐Ras (Ki‐Ras) alternative prenylation hypothesis in malignant transformation, we used a novel farnesyltransferase inhibitor competitive to farnesyl‐pyrophosphate, RPR130401, and a CaaX peptidomimetic geranylgeranyltransferase‐1 inhibitor GGTI‐298. In Ki‐Ras‐overexpressing transformed adrenocortical cells, RPR130401 at 1–10 μM inhibited very efficiently the [ 3 H]farnesyl but not [ 3 H]geranylgeranyl transfer to Ras. However, proliferation of these cells was only slightly sensitive to RPR130401 (IC 50 =30 μM). GGTI‐298 inhibited the growth of these cells with an IC 50 of 11 μM but cell lysis was observed at 15 μM. The combination of 10 μM RPR130401 and 10 μM GGTI‐298 inhibited efficiently (80%) cell proliferation. These combined inhibitors but not each inhibitor alone blocked the cell cycle in G 0 /G 1 and disrupted MAP kinase activation. Thus, combination of two inhibitors, at non‐cytotoxic concentrations, acting on the farnesyl‐pyrophosphate binding site of the farnesyltransferase and the CaaX binding site of the geranylgeranyltransferase‐1 respectively is an efficient strategy for disrupting Ki‐Ras tumorigenic cell proliferation.