Well-differentiated papillary mesothelioma (WDPM) is an uncommon mesothelial proliferation that is most commonly encountered as an incidental finding in the peritoneal cavity. There is controversy in the literature about whether WDPM is a neoplasm or a reactive process and, if neoplastic, whether it is a variant or precursor of epithelial malignant mesothelioma or is a different entity. Using whole exome sequencing of five WDPMs of the peritoneum, we have identified distinct mutations in EHD1, ATM, FBXO10, SH2D2A, CDH5, MAGED1, and TP73 shared by WDPM cases but not reported in malignant mesotheliomas. Furthermore, we show that WDPM is strongly enriched with C > A transversion substitution mutations, a pattern that is also not found in malignant mesotheliomas. The WDPMs lacked the alterations involving BAP1, SETD2, NF2, CDKN2A/B, LASTS1/2, PBRM1, and SMARCC1 that are frequently found in malignant mesotheliomas. We conclude that WDPMs are neoplasms that are genetically distinct from malignant mesotheliomas and, based on observed mutations, do not appear to be precursors of malignant mesotheliomas.

Although considered a disease of the elderly, a subset of patients with mesothelioma are young (<40 years). The goal of this study was to understand their characteristics and outcomes. The Surveillance, Epidemiology, and End Results (SEER) database was used to extract mesothelioma cases (1990-2010). We modeled Kaplan-Meyer survival curves stratified by site of disease, and age of presentation. 2% (207 of 12345) of mesothelioma patients are young. Sex distribution is comparable among the young (51% males, 49% females); males predominated (78%, 22%) in the older cohort. Frequency of pleural and peritoneal mesothelioma are similar in the young (47%, 48% respectively); pleural disease predominated in the old (90%, 9%). Cancer-directed surgeries are more frequent in the young. Regardless of histologic subtype, young patients with pleural (11 vs. 8 months) and peritoneal (not reached vs. 10 months) mesothelioma had significantly improved overall survival. In multivariate analysis, younger age was an independent prognostic factor. Although rare, mesothelioma do occur in the young; their characteristics are distinct from those of older patients. Further studies are needed to understand the interplay between genetic susceptibility and mineral fiber carcinogenesis in the pathogenesis of mesothelioma in the young.

Malignant pleural mesothelioma (MPM) is a rare and aggressive cancer that arises from the mesothelial surface of the pleural and peritoneal cavities, the pericardium, and rarely, the tunica vaginalis. The incidence of MPM is expected to increase worldwide in the next two decades. However, even with the use of multimodality treatment, MPM remains challenging to treat, with a 5-year survival rate of less than 5%. The International Association for the Study of Lung Cancer has gathered experts in different areas of mesothelioma research and management to summarize the most significant scientific advances and new frontiers related to mesothelioma therapeutics.

BACKGROUND: While asbestos has long been known to cause mesothelioma, quantitative exposure-response data on the relation of mesothelioma risk and exposure to chrysotile asbestos are sparse. METHODS: Quantitative relationships of mortality from mesothelioma and pleural cancer were investigated in an established cohort of 5397 asbestos textile manufacturing workers in North Carolina, USA. Eligible workers were those employed between 1950 and 1973 with mortality follow-up through 2003. Individual exposure to chrysotile fibres was estimated on the basis of 3420 air samples covering the entire study period linked to work history records. Exposure coefficients adjusted for age, race, and time-related covariates were estimated by Poisson regression. RESULTS: Positive, statistically significant associations were observed between mortality from all pleural cancer (including mesothelioma) and time since first exposure (TSFE) to asbestos (rate ratio [RR], 1.19; 95% confidence interval [CI], 1.06-1.34 per year), duration of exposure, and cumulative asbestos fibre exposure (RR, 1.15; 95% CI, 1.04-1.28 per 100 f-years/mL; 10-year lag). Analyses of the shape of exposure-response functions suggested a linear relationship with TSFE and a less-than-linear relationship with cumulative exposure. Restricting the analysis to years when mesothelioma was coded as a unique cause of death yielded stronger but less precise associations. CONCLUSIONS: These observations support with quantitative data the conclusion that chrysotile causes mesothelioma and encourage exposure-response analyses of mesothelioma in other cohorts exposed to chrysotile.

Cullin 4A (Cul4A) is important in cell survival, development, growth and the cell cycle, but its role in mesothelioma has not been studied. For the first time, we identified amplification of the Cul4A gene in four of five mesothelioma cell lines. Consistent with increased Cul4A gene copy number, we found that Cul4A protein was overexpressed in mesothelioma cells as well. Cul4A protein was also overexpressed in 64% of primary malignant pleural mesothelioma (MPM) tumours. Furthermore, knockdown of Cul4A with shRNA in mesothelioma cells resulted in up-regulation of p21 and p27 tumour suppressor proteins in a p53-independent manner in H290, H28 and MS-1 mesothelioma cell lines. Knockdown of Cul4A also resulted in G0/G1 cell cycle arrest and decreased colony formation in H290, H28 and MS-1 mesothelioma cell lines. Moreover, G0/G1 cell cycle arrest was partially reversed by siRNA down-regulation of p21 and/or p27 in Cul4A knockdown H290 cell line. In the contrary, overexpression of Cul4A resulted in down-regulation of p21 and p27 proteins and increased colony formation in H28 mesothelioma cell line. Both p21 and p27 showed faster degradation rates in Cul4A overexpressed H28 cell line and slower degradation rates in Cul4A knockdown H28 cell line. Our study indicates that Cul4A amplification and overexpression play an oncogenic role in the pathogenesis of mesothelioma. Thus, Cul4A may be a potential therapeutic target for MPM.

Malignant mesothelioma is an aggressive cancer that is resistant to current therapy. The poor prognosis of mesothelioma has been associated with elevated Yes-associated protein (YAP) activity. In this study, we evaluated the effect of targeting YAP in mesothelioma. First, we comprehensively studied YAP activity in five mesothelioma cell lines (211H, H2052, H290, MS-1 and H2452) and one normal mesothelial cell line (LP9). We found decreased phospho-YAP to YAP protein ratio and consistently increased GTIIC reporter activity in 211H, H2052 and H290 compared to LP9. The same three cell lines (IC₅₀ s < 1 μM) were more sensitive than LP9 (IC₅₀ = 3.5 μM) to the YAP/TEAD inhibitor verteporfin. We also found that verteporfin significantly reduced YAP protein level, mRNA levels of YAP downstream genes and GTIIC reporter activity in the same three cell lines, indicating inhibition of YAP signaling by verteporfin. Verteporfin also impaired invasion and tumoursphere formation ability of H2052 and H290. To validate the effect of specific targeting YAP in mesothelioma cells, we down-regulated YAP by siRNA. We found siYAP significantly decreased YAP transcriptional activity and impaired invasion and tumoursphere formation ability of H2052 and H290. Furthermore, forced overexpression of YAP rescued GTIIC reporter activity and cell viability after siYAP targeting 3'UTR of YAP. Finally, we found concurrent immunohistochemistry staining of ROCK2 and YAP (P < 0.05). Inhibition of ROCK2 decreased GTIIC reporter activity in H2052 and 211H suggesting that Rho/ROCK signaling also contributed to YAP activation in mesothelioma cells. Our results indicate that YAP may be a potential therapeutic target in mesothelioma.

Mesothelioma affects mostly older individuals who have been occupationally exposed to asbestos. The global mesothelioma incidence and mortality rates are unknown, because data are not available from developing countries that continue to use large amounts of asbestos. The incidence rate of mesothelioma has decreased in Australia, the United States, and Western Europe, where the use of asbestos was banned or strictly regulated in the 1970s and 1980s, demonstrating the value of these preventive measures. However, in these same countries, the overall number of deaths from mesothelioma has not decreased as the size of the population and the percentage of old people have increased. Moreover, hotspots of mesothelioma may occur when carcinogenic fibers that are present in the environment are disturbed as rural areas are being developed. Novel immunohistochemical and molecular markers have improved the accuracy of diagnosis; however, about 14% (high-resource countries) to 50% (developing countries) of mesothelioma diagnoses are incorrect, resulting in inadequate treatment and complicating epidemiological studies. The discovery that germline BRCA1-asssociated protein 1 (BAP1) mutations cause mesothelioma and other cancers (BAP1 cancer syndrome) elucidated some of the key pathogenic mechanisms, and treatments targeting these molecular mechanisms and/or modulating the immune response are being tested. The role of surgery in pleural mesothelioma is controversial as it is difficult to predict who will benefit from aggressive management, even when local therapies are added to existing or novel systemic treatments. Treatment outcomes are improving, however, for peritoneal mesothelioma. Multidisciplinary international collaboration will be necessary to improve prevention, early detection, and treatment.

Background

The Hedgehog (Hh) signaling pathway has been implicated in stem cell maintenance and its activation is aberrant in several types of cancer including mesothelioma. Protein kinase CK2 affects several cell signaling pathways through the mechanism of phosphorylation.

Methods

Protein and mRNA levels of CK2α and Gli1 were tested by quantitative RT-PCR and immunohistochemistry staining in mesothelioma samples and cell lines. Down-regulated Gli1 expression and transcriptional activity were demonstrated by RT-PCR, Western blot and luciferase reporter assay.

Results

In this study, we show that CK2α is over-expressed and a positive regulator of Hegdehog/Gli1 signaling in human malignant pleural mesothelioma. First of all, we found that the mRNA levels of CK2α and Gli1 were broadly elevated and correlated (n = 52, r = 0.401, P < 0.05), compared with LP9 (a normal mesothelial cell line). We then investigated their expression at the protein level, and found that all the 7 mesothelioma cell lines tested showed positive staining in CK2α and Gli1 immunohistochemistry. Correlation analysis by Pearson test for CK2α and Gli1 expression in the 75 mesothelioma tumors and the 7 mesothelioma cell lines showed that the two protein expression was significantly correlated (n = 82, r = 0.554, P < 0.01). Furthermore, we demonstrated that Gli1 expression and transcriptional activity were down-regulated after CK2α was silenced in two mesothelioma cell lines (H28 and H2052). CK2α siRNA also down-regulated the expression of Hh target genes in these cell lines. Moreover, treatment with a small-molecule CK2α inhibitor CX-4945 led to dose-dependent inhibition of Gli1 expression and transcriptional activity. Conversely, forced over-expression of CK2α resulted in an increase in Gli1 transcriptional activity in H28 cells.

Conclusions

Thus, we report for the first time that over-expressed CK2α positively regulate Hh/Gli1 signaling in human mesothelioma.

Malignant pleural mesothelioma (MPM) is an aggressive cancer for which more effective treatments are needed. In this study, strong to moderate staining of MET and ERK5 was detected in 67.1 and 48% of the analyzed 73 human mesothelioma tumors, and significant correlation of MET and ERK5 expression was identified (P<0.05). We evaluated the doublecortin-like kinase 1 (DCLK1) expression in human mesothelioma tumors. Our results showed that 50.7% of the immunohistochemistry analyzed human mesothelioma tumors have strong to moderate staining of DCLK1, and its expression is significantly correlated with MET or ERK5 expression (P<0.05). Also, the upregulation of DCLK1 is correlated with poor prognosis in MPM patients (P=0.0235). To investigate whether DCLK1 is downstream of MET/ERK5 signaling in human mesothelioma, the effect of DCLK1 expression was analyzed after treatments with either the MET inhibitor XL184 or the ERK5 inhibitor XMD8-92 in human mesothelioma cell lines. Our results showed that the MET inhibitor XL184 reduced the expression of phospho‑ERK5 and DCLK1 expression in human mesothelioma cell lines. In addition, the ERK5 inhibitor XMD8-92 reduced the expression of phospho-ERK5 and DCLK1 expression in human mesothelioma cell lines. Furthermore, XML184 and XMD8-92 treatment impaired invasion and tumor sphere formation ability of H290 mesothelioma cells. These results suggest that DCLK1 is regulated by MET/ERK5 signaling in human mesothelioma, and the MET/ERK5/DCLK1 signaling cascade could be further developed into a promising therapeutic target against mesothelioma.