Functional differences between wild-type and mutant-type BRCA1-associated protein 1 tumor suppressor against malignant mesothelioma cells

Effects of Combined Therapeutic Targeting of AXL and ATR on Pleural Mesothelioma Cells

Few treatment options exist for pleural mesothelioma (PM), which is a progressive malignant tumor. However, the efficacy of molecular-targeted monotherapy is limited, and further therapeutic strategies are warranted to treat PM. Recently, the cancer cell-cycle checkpoint inhibitors have attracted attention because they disrupt cell-cycle regulation. Here, we aimed to establish a novel combinational therapeutic strategy to inhibit the cell-cycle checkpoint kinase, ATR in PM cells. The siRNA screening assay showed that anexelekto (AXL) knockdown enhanced cell growth inhibition when exposed to ATR inhibitors, demonstrating the synergistic effects of the ATR and AXL combination in some PM cells. The AXL and ATR inhibitor combination increased cell apoptosis via the Bim protein and suppressed cell migration when compared with each monotherapy. The combined therapeutic targeting of AXL and ATR significantly delayed regrowth compared with monotherapy. Thus, optimal AXL and ATR inhibition may potentially improve the PM outcome.

Deubiquitinase BAP1 regulates stability of BRCA1 protein and inactivates the NF-κB signaling to protect mice from sepsis-induced acute kidney injury

Sepsis and its associated organ dysfunction syndrome is a leading cause of death in critically ill patients. Breast cancer susceptibility protein 1 (BRCA1)-associated protein 1 (BAP1) is a potential regulator in immune regulation and inflammatory responses. This study aims to investigate the function of BAP1 in sepsis-induced acute kidney injury (AKI). A mouse model with sepsis-induced AKI was induced by cecal ligation and puncture, and renal tubular epithelial cells (RTECs) were treated with lipopolysaccharide (LPS) to mimic an AKI condition in vitro. BAP1 was significantly poorly expressed in the kidney tissues of model mice and the LPS-treated RTECs. Artificial upregulation of BAP1 ameliorated the pathological changes, tissue injury and inflammatory responses in kidney tissues of the mice, and it reduced the LPS-induced injury and apoptosis of the RTECs. BAP1 was found to interact with BRCA1 and enhance stability of BRCA1 protein through deubiquitination modification. Further downregulation of BRCA1 activated the nuclear factor-kappa B (NF-κB) signaling pathway and blocked the protective roles of BAP1 in sepsis-induced AKI. In conclusion, this study demonstrates that BAP1 protects mice from sepsis-induced AKI through enhancing stability of BRCA1 protein and inactivating the NF-κB signaling.

CAMK2D: a novel molecular target for BAP1-deficient malignant mesothelioma

Malignant mesothelioma (MMe) is a rare but aggressive malignancy. Although the molecular genetics of MMe is known, including BRCA1-associated protein-1 (BAP1) gene alterations, the prognosis of MMe patients remains poor. Here, we generated BAP1 knockout (BAP1-KO) human mesothelial cell clones to develop molecular-targeted therapeutics based on genetic alterations in MMe. cDNA microarray and quantitative RT-PCR (qRT-PCR) analyses revealed high expression of a calcium/calmodulin-dependent protein kinase type II subunit delta (CAMK2D) gene in the BAP1-KO cells. CAMK2D was highly expressed in 70% of the human MMe tissues (56/80) and correlated with the loss of BAP1 expression, making it a potential diagnostic and therapeutic target for BAP1-deficient MMe. We screened an anticancer drugs library using BAP1-KO cells and successfully identified a CaMKII inhibitor, KN-93, which displayed a more potent and selective antiproliferative effect against BAP1-deficient cells than cisplatin or pemetrexed. KN-93 significantly suppressed the tumor growth in mice xenografted with BAP1-deficient MMe cells. This study is the first to provide a potential molecular-targeted therapeutic approach for BAP1-deficient MMe.

BAP1 loss induces mitotic defects in mesothelioma cells through BRCA1-dependent and independent mechanisms

The tumour suppressor BRCA1-associated protein 1 (BAP1) is the most frequently mutated cancer gene in mesothelioma. Here we report novel functions for BAP1 in mitotic progression highlighting the relationship between BAP1 and control of genome stability in mesothelioma cells with therapeutic implications. Depletion of BAP1 protein induced proteasome-mediated degradation of BRCA1 in mesothelioma cells while loss of BAP1 correlated with BRCA1 loss in mesothelioma patient tumour samples. BAP1 loss also led to mitotic defects that phenocopied the loss of BRCA1 including spindle assembly checkpoint failure, centrosome amplification and chromosome segregation errors. However, loss of BAP1 also led to additional mitotic changes that were not observed upon BRCA1 loss, including an increase in spindle length and enhanced growth of astral microtubules. Intriguingly, these consequences could be explained by loss of expression of the KIF18A and KIF18B kinesin motors that occurred upon depletion of BAP1 but not BRCA1, as spindle and astral microtubule defects were rescued by re-expression of KIF18A and KIF18B, respectively. We therefore propose that BAP1 inactivation causes mitotic defects through BRCA1-dependent and independent mechanisms revealing novel routes by which mesothelioma cells lacking BAP1 may acquire genome instability and exhibit altered responses to microtubule-targeted agents.

Malignant pleural mesothelioma: an update

Malignant mesotheliomas are rare types of cancers that affect the mesothelial surfaces, usually the pleura and peritoneum. They are associated with asbestos exposure, but due to a latency period of more than 30 years and difficult diagnosis, most cases are not detected until they reach advanced stages. Treatment options for this tumor type are very limited and survival ranges from 12 to 36 months. This review discusses the molecular physiopathology, current diagnosis, and latest therapeutic options for this disease.

Co-occurrence of BAP1 and SF3B1 mutations in uveal melanoma induces cellular senescence

Uveal melanoma (UM) is the most common intraocular tumor in adults. Recurrent mutations in BRCA1‐associated protein 1 (BAP1) and splicing factor 3B subunit 1 (SF3B1) display a mutually exclusive pattern in UM, but the underlying mechanism is unknown. We show that combined BAP1 deficiency and SF3B1 hotspot mutation lead to senescence and growth arrest in human UM cells. Although p53 protein expression is induced, deletion of TP53 (encoding p53) only modestly rescues the observed senescent phenotype. UM cells with BAP1 loss or SF3B1 mutation are more sensitive to chemotherapeutic drugs compared with their isogenic parental cells. Transcriptome analysis shows that DNA‐repair genes are downregulated upon co‐occurrence of BAP1 deletion and SF3B1 mutation, thus leading to impaired DNA damage response and the induction of senescence. The co‐occurrence of these two mutations reduces invasion of UM cells in zebrafish xenograft models and suppresses growth of melanoma xenografts in nude mice. Our findings provide a mechanistic explanation for the mutual exclusivity of BAP1 and SF3B1 mutations in human UM.

Malignant Pleural Mesothelioma Interactome with 364 Novel Protein-Protein Interactions

Malignant pleural mesothelioma (MPM) is an aggressive cancer affecting the outer lining of the lung, with a median survival of less than one year. We constructed an 'MPM interactome' with over 300 computationally predicted protein-protein interactions (PPIs) and over 2400 known PPIs of 62 literature-curated genes whose activity affects MPM. Known PPIs of the 62 MPM associated genes were derived from Biological General Repository for Interaction Datasets (BioGRID) and Human Protein Reference Database (HPRD). Novel PPIs were predicted by applying the HiPPIP algorithm, which computes features of protein pairs such as cellular localization, molecular function, biological process membership, genomic location of the gene, and gene expression in microarray experiments, and classifies the pairwise features as interacting or non-interacting based on a random forest model. We validated five novel predicted PPIs experimentally. The interactome is significantly enriched with genes differentially ex-pressed in MPM tumors compared with normal pleura and with other thoracic tumors, genes whose high expression has been correlated with unfavorable prognosis in lung cancer, genes differentially expressed on crocidolite exposure, and exosome-derived proteins identified from malignant mesothelioma cell lines. 28 of the interactors of MPM proteins are targets of 147 U.S. Food and Drug Administration (FDA)-approved drugs. By comparing disease-associated versus drug-induced differential expression profiles, we identified five potentially repurposable drugs, namely cabazitaxel, primaquine, pyrimethamine, trimethoprim and gliclazide. Preclinical studies may be con-ducted in vitro to validate these computational results. Interactome analysis of disease-associated genes is a powerful approach with high translational impact. It shows how MPM-associated genes identified by various high throughput studies are functionally linked, leading to clinically translatable results such as repurposed drugs. The PPIs are made available on a webserver with interactive user interface, visualization and advanced search capabilities.

Rucaparib in patients with BAP1-deficient or BRCA1-deficient mesothelioma (MiST1): an open-label, single-arm, phase 2a clinical trial

BACKGROUND

Malignant mesothelioma remains an incurable cancer, with no effective treatments in the setting of relapsed disease. Homologous recombination deficiency predicts sensitivity to poly (ADP-ribose) polymerase (PARP) inhibitors. In mesothelioma, BRCA1-associated protein 1 carboxy-terminal hydrolase (BAP1), which regulates DNA repair, is frequently mutated. We aimed to test the hypothesis that BAP1-deficient or BRCA1-deficient mesotheliomas would be sensitive to PARP inhibition by rucaparib.

METHODS

We did a single-centre, open-label, single-arm, phase 2a trial in Leicester, UK, with prospective molecular stratification (Mesothelioma-Stratified Therapy 1 [MiST1]). Patients aged 18 years or older who had radiologically progressing, histologically confirmed, malignant mesothelioma after at least one course of systemic treatment; with cytoplasmic-BAP1-deficient or BRCA1-deficient mesothelioma (pleural or peritoneal or other primary localisation), and who met the other inclusion criteria, were deemed eligible. All eligible patients who consented to take part were given rucaparib 600 mg twice a day orally, for six cycles of 28 days, or until disease progression, unacceptable toxicity, withdrawal of consent, or death. Response was measured by CT scan every 6 weeks. The primary outcome was disease control (complete response, partial response, or stable disease) at 12 weeks in all patients who received study drug; secondary outcomes were the safety and toxicity profile, objective response rate (proportion of complete or partial responses), and disease control rate at 24 weeks. Recruitment is now closed. This trial is registered with ClinicalTrials.gov, NCT03654833.

FINDINGS

Between Feb 9 and June 10, 2019, we enrolled 26 molecularly and clinically eligible patients. Ten (38%) of 26 patients were BAP1 negative and BRCA1 negative, 23 patients (89%) were BAP1 negative, and 13 patients (50%) were BRCA1 negative. Disease control rate at 12 weeks was 58% (95% CI 37-77; 15 of 26 patients), and at 24 weeks was 23% (9-44; six of 26 patients). Rucaparib was well tolerated, with 15 (9%) of 166 adverse events being grade 3 or 4, which were seen in nine (35%) of 26 patients, and there were no deaths. The most common grade 1-2 adverse events were nausea (18 [69%] of 26 patients), fatigue (14 patients [54%]), and decreased appetite (ten patients [38%]). The most common grade 3-4 adverse events were upper respiratory tract infection (three patients [12%]) and anaemia (three patients [12%]). All six cycles of rucaparib were received by eight (31%) of 26 patients. One or more dose reductions occurred in nine patients (35%).

INTERPRETATION

Rucaparib in patients with BAP1-negative or BRCA1-negative mesothelioma met the prespecified criteria for success, showing promising activity with manageable toxicity. Further investigation of homologous recombination deficiency mutations is planned to refine the identification of predictive biomarkers for PARP inhibition in mesothelioma.

FUNDING

University of Leicester (Leicester, UK), Asthma UK and British Lung Foundation Partnership, and the Victor Dahdaleh Foundation (Toronto, ON, Canada).

BRCA1/MAD2L1 Deficiency Disrupts the Spindle Assembly Checkpoint to Confer Vinorelbine Resistance in Mesothelioma

Mesothelioma is a universally lethal cancer lacking effective therapy. The spindle poison vinorelbine exhibits clinical activity in the relapsed setting, and in preclinical models requires BRCA1 to initiate apoptosis. However, the mechanisms underlying this regulation and the clinical implications have not been explored. Here, we show that BRCA1 silencing abrogated vinorelbine-induced cell-cycle arrest, recruitment of BUBR1 to kinetochores, and apoptosis. BRCA1 silencing led to codepletion of MAD2L1 at the mRNA and protein levels consistent with its status as a transcriptional target of BRCA1 Silencing of MAD2L1 phenocopied BRCA1 and was sufficient to confer resistance to vinorelbine. This was recapitulated in cell lines selected for resistance to vinorelbine, which acquired loss of both BRCA1 and MAD2L1 expression. Following ex vivo vinorelbine in 20 primary tumor explants, apoptotic response rate was 59% in BRCA1/MAD2L1-positive explants compared with 0% in BRCA1/MAD2L1-negative explants. In 48 patients, BRCA1 and/or MAD2L1 loss of expression was not prognostic; however, in a subset of patients treated with vinorelbine, survival was shorter for patients lacking BRCA1/MAD2L1 expression compared with double-positive patients (5.9 vs. 36.7 months, P = 0.03). Our data implicate BRCA1/MAD2L1 loss as a putative predictive marker of resistance to vinorelbine in mesothelioma and warrant prospective clinical evaluation.

Large-scale analysis of BAP1 expression reveals novel associations with clinical and molecular features of malignant pleural mesothelioma

BRCA1‐associated protein‐1 (BAP1) expression is commonly lost in several tumors including malignant pleural mesothelioma (MPM). Presence or absence of immunohistochemical BAP1 nuclear staining in tumor cells is currently used for differential diagnosis of MPM. In this study, a large cohort of 596 MPM tumors with available clinical data was analyzed to examine associations of BAP1 staining pattern with clinical and molecular features that may reflect the impact of BAP1 mutation on MPM biology. Cases were classified according to the BAP1 staining pattern of tumor cells. Exome and RNA‐sequencing data were available for subsets of cases. Levels of mRNA encoding claudin 15 (CLDN15) and vimentin (VIM) were determined using RT‐qPCR on 483 cases to estimate the relative proportions of epithelial‐like and mesenchymal‐like components in each tumor. Four BAP1 staining patterns were observed: single‐pattern nuclear staining (36%), single‐pattern cytoplasmic staining (25%), single‐pattern absent staining (12%), and combinations of these staining patterns (27%). This study confirmed prior reports that nuclear BAP1 is more frequently associated with wild‐type BAP1 and sarcomatoid histology. However, no associations between BAP1 staining pattern(s) and mutations in specific protein domains and/or mutation type were observed. BAP1 staining patterns were significantly associated (p < 0.001) with BAP1 gene expression, MPM histologic subtypes, molecular clusters, and markers of epithelial‐to‐mesenchymal transition. Frequent observation of combinations of BAP1 staining patterns in MPM tumors indicated intra‐tumoral heterogeneity of BAP1 status. Cytoplasmic BAP1 staining was identified as a putative indicator of favorable prognosis in non‐epithelioid MPM. In conclusion, novel significant associations among different BAP1 staining patterns and subgroups of MPM tumors were observed, suggesting that the role of BAP1 in tumor progression may be more complex than its presumed tumor suppressor function. Cytoplasmic staining was identified as a putative indicator of favorable prognosis in non‐epithelioid MPM, potentially addressing a critical need in clinical decision‐making in this disease. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Functional Genomic Screen in Mesothelioma Reveals that Loss of Function of BRCA1-Associated Protein 1 Induces Chemoresistance to Ribonucleotide Reductase Inhibition

Loss of function of BRCA1-associated protein 1 (BAP1) is observed in about 50% of malignant pleural mesothelioma (MPM) cases. The aim of this study was to investigate whether this aspect could be exploited for targeted therapy. A genetically engineered model was established expressing either functional or nonfunctional BAP1, and whole-genome siRNA synthetic lethality screens were performed assessing differentially impaired survival between the two cell lines. The whole-genome siRNA screen unexpectedly revealed 11 hits (FDR < 0.05) that were more cytotoxic to BAP1-proficient cells. Two actionable targets, ribonucleotide reductase (RNR) catalytic subunit M1 (RRM1) and RNR regulatory subunit M2 (RRM2), were validated. In line with the screen results, primary mesothelioma (BAP1 ^+/-) overexpressing BAP1 C91A (catalytically dead mutant) was more resistant to RNR inhibition, while BAP1 knockdown in the BAP1-proficient cell lines rescued the cells from their vulnerability to RNR depletion. Gemcitabine and hydroxyurea were more cytotoxic in BAP1-proficient cell line-derived spheroids compared with BAP1 deficient. Upregulation of RRM2 upon gemcitabine and hydroxyurea treatment was more profound in BAP1 mut/del cell lines. Increased lethality mediated by RNR inhibition was observed in NCI-H2452 cells reconstituted with BAP1-WT but not with BAP1 C91A. Upregulation of RRM2 in NCI-H2452-BAP1 WT spheroids was modest compared with control or C91A mutant. Together, we found that BAP1 is involved in the regulation of RNR levels during replication stress. Our observations reveal a potential clinical application where BAP1 status could serve as predictive or stratification biomarker for RNR inhibition-based therapy in MPM.

BAP1 expression is prognostic in breast and uveal melanoma but not colon cancer and is highly positively correlated with RBM15B and USP19

BAP1 is a tumor suppressor gene important to the development and prognosis of many cancers, especially uveal melanoma (UM). Its role in more common cancers such as breast and colon cancer is largely unknown. We collected the transcriptome profiling data sets from the TCGA uveal melanoma (TCGA-UVM), breast cancer (TCGA-BRCA), and colon cancer (TCGA-COAD) projects to analyze the expression of BAP1. We found that patients with UM and breast cancer, but not colon cancer, who died had a lower level of BAP1 gene expression compared to surviving patients. Importantly, in breast cancer patients, the lowest BAP1 expression levels corresponded to the dead young patients (age at diagnosis < 46). Since the number of cases in TCGA-BRCA was much higher than TCGA-UVM, we obtained highly correlated genes with BAP1 in invasive breast carcinomas. Then, we tested if these genes are also highly correlated with BAP1 in UM and colon cancer. We found that BAP1 is highly positively correlated with RBM15B and USP19 expression in invasive breast carcinoma, UM, and colon adenocarcinoma. All three genes are located in close proximity on the 3p21 tumor suppressor region that is commonly altered in many cancers.

BAP1 mutations in high-grade meningioma: implications for patient care

We have recently shown that the breast cancer (BRCA)1-associated protein-1 tumor suppressor gene (BAP1) is inactivated in a subset of clinically aggressive meningiomas that display rhabdoid histomorphology. Immunohistochemistry for BAP1 protein provides a rapid and inexpensive method for screening suspected cases. Notably, some patients with BAP1-mutant meningiomas have germline BAP1 mutations and BAP1 tumor predisposition syndrome (TPDS). It appears that nearly all patients with germline BAP1 mutations develop malignancies by age 55, most frequently uveal melanoma, cutaneous melanoma, pleural or peritoneal malignant mesothelioma, or renal cell carcinoma, although other cancers have also been associated with BAP1 TPDS. Therefore, when confronted with a patient with a potentially high-grade rhabdoid meningioma, it is important that neuropathologists assess the BAP1 status of the tumor and that the patient's family history of cancer is carefully ascertained. In the appropriate clinical setting, genetic counseling and germline BAP1 DNA sequencing should be performed. A cancer surveillance program for individuals who carry germline BAP1 mutations may help identify tumors such as uveal melanoma, cutaneous melanoma, and renal cell carcinoma at early and treatable stages. Because BAP1-mutant meningiomas are rare tumors, multi-institutional efforts will be needed to evaluate therapeutic strategies and to further define the clinicopathologic features of these tumors.

Patterns of BAP1 protein expression provide insights into prognostic significance and the biology of uveal melanoma

Uveal melanoma (UM) is a rare aggressive intraocular tumour with a propensity for liver metastases, occurring in ∼50% of patients. The tumour suppressor BAP1 is considered to be key in UM progression. Herein, we present the largest study to date investigating cellular expression patterns of BAP1 protein in 165 UMs, correlating these patterns to prognosis. Full clinical, histological, genetic, and follow‐up data were available for all patients. BAP1 gene sequencing was performed on a subset of 26 cases. An independent cohort of 14 UMs was examined for comparison. Loss of nuclear BAP1 (nBAP1) protein expression was observed in 54% (88/165) UMs. nBAP1 expression proved to be a significant independent prognostic parameter: it identified two subgroups within monosomy 3 (M3) UM, which are known to have a high risk of metastasis. Strikingly, nBAP1‐positiveM3 UMs were associated with prolonged survival compared to nBAP1‐negative M3 UMs (Log rank, p = 0.014). nBAP1 protein loss did not correlate with a BAP1 mutation in 23% (6/26) of the UMs analysed. Cytoplasmic BAP1 protein (cBAP1) expression was also observed in UM: although appearing ‘predominantly diffuse’ in most nBAP1‐negative UM, a distinct ‘focal perinuclear’ expression pattern – localized immediately adjacent to the cis Golgi – was seen in 31% (18/59). These tumours tended to carry loss‐of‐function BAP1 mutations. Our study demonstrates loss of nBAP1 expression to be the strongest prognostic marker in UM, confirming its importance in UM progression. Our data suggest that non‐genetic mechanisms account for nBAP1 loss in a small number of UMs. In addition, we describe a subset of nBAP1‐negative UM, in which BAP1 is sequestered in perinuclear bodies, most likely within Golgi, warranting further mechanistic investigation.

Novel ATP-competitive Akt inhibitor afuresertib suppresses the proliferation of malignant pleural mesothelioma cells

Malignant pleural mesothelioma (MPM), an asbestos-related occupational disease, is an aggressive and incurable tumor of the thoracic cavity. Despite recent advances in MPM treatment, overall survival of patients with MPM is very low. Recent studies have implicated that PI3K/Akt signaling is involved in MPM cell survival and development. To investigate the effects of Akt inhibitors on MPM cell survival, we examined the effects of nine selective Akt inhibitors, namely, afuresertib, Akti-1/2, AZD5363, GSK690693, ipatasertib, MK-2206, perifosine, PHT-427, and TIC10, on six MPM cell lines, namely, ACC-MESO-4, Y-MESO-8A, MSTO-211H, NCI-H28, NCI-H290, and NCI-H2052, and a normal mesothelial cell line MeT-5A. Comparison of IC₅₀ values of the Akt inhibitors showed that afuresertib, an ATP-competitive specific Akt inhibitor, exerted tumor-specific effects on MPM cells. Afuresertib significantly increased caspase-3 and caspase-7 activities and apoptotic cell number among ACC-MESO-4 and MSTO-211H cells. Moreover, afuresertib strongly arrested the cell cycle in the G₁ phase. Western blotting analysis showed that afuresertib increased the expression of p21^WAF1/CIP1 and decreased the phosphorylation of Akt substrates, including GSK-3β and FOXO family proteins. These results suggest that afuresertib-induced p21 expression promotes G₁ phase arrest by inducing FOXO activity. Furthermore, afuresertib significantly enhanced cisplatin-induced cytotoxicity. Interestingly, results of gene set enrichment analysis showed that afuresertib modulated the expression E2F1 and MYC, which are associated with fibroblast core serum response. Together, these results suggest that afuresertib is a useful anticancer drug for treating patients with MPM.

Uveal Melanoma Nuclear BRCA1-Associated Protein-1 Immunoreactivity Is an Indicator of Metastasis

PURPOSE

To examine the BRCA1-associated protein-1 (BAP1) expression of primary uveal melanomas without and with metastasis, and to analyze the correlation between the BAP1 immunoreactivity of primary uveal melanoma and other clinicopathologic features.

DESIGN

Retrospective case series.

PARTICIPANTS

Forty patients with uveal melanoma (mean age, 57.98±14.75 years) were included in this analysis, of whom 20 had no metastatic disease and 20 had metastasis.

METHODS

Medical records and histology slides of patients with primary uveal melanoma treated by enucleation were reviewed. BAP1 expression was evaluated by immunohistochemical staining of formalin-fixed, paraffin-embedded sections. Immunoreactivity in the nucleus and cytoplasm were graded by estimating the percentage of primary tumor cells showing a positive staining of their nucleus or cytoplasm per 1 high-power field 200× (grades 0-3).

MAIN OUTCOME MEASURES

Tumor size, histologic features, nuclear and cytoplasmic BAP1 immunoreactivity grade, and patient outcome, including development of metastasis.

RESULTS

Significantly lower (P = 0.025) nuclear BAP1 immunoreactivity was observed in the metastatic melanoma group. Greater tumor thickness, basal diameter, and more advanced TNM stage were associated with an increased odds ratio of developing metastasis (P < 0.05). In addition, tumors with a higher proportion of cells expressing nuclear BAP1 had decreased odds of developing metastatic disease in a multivariate model (P = 0.042). Metastasis-free survival was significantly longer in patients with uveal melanoma with high nuclear BAP1 stain (P = 0.004).

CONCLUSIONS

Time to metastasis differs in patients with primary uveal melanoma with different grades of nuclear BAP1 immunoreactivity. Nuclear BAP1 stain is the only significant independent predictor of metastatic disease in this study. Our data support the role of BAP1 immunohistochemical staining of primary uveal melanoma to evaluate metastatic risk.

Novel insights into mesothelioma biology and implications for therapy

Malignant mesothelioma is a universally lethal cancer that is increasing in incidence worldwide. There is a dearth of effective therapies, with only one treatment (pemetrexed and cisplatin combination chemotherapy) approved in the past 13 years. However, the past 5 years have witnessed an exponential growth in our understanding of mesothelioma pathobiology, which is set to revolutionize therapeutic strategies. From a genomic standpoint, mesothelioma is characterized by a preponderance of tumour suppressor alterations, for which novel therapies are currently in development. Other promising antitumour agents include inhibitors against angiogenesis, mesothelin and immune checkpoints, which are at various phases of clinical trial testing.

Targeting the epigenome in malignant pleural mesothelioma

Malignant pleural mesotheliomas (MPM) are notoriously refractory to conventional treatment modalities. Recent insights regarding epigenetic alterations in MPM provide the preclinical rationale for the evaluation of novel combinatorial regimens targeting the epigenome in these neoplasms.

Switching off malignant mesothelioma: exploiting the hypoxic microenvironment

Malignant mesotheliomas are aggressive, asbestos-related cancers with poor patient prognosis, typically arising in the mesothelial surfaces of tissues in pleural and peritoneal cavity. The relative unspecific symptoms of mesotheliomas, misdiagnoses, and lack of precise targeted therapies call for a more critical assessment of this disease. In the present review, we categorize commonly identified genomic aberrations of mesotheliomas into their canonical pathways and discuss targeting these pathways in the context of tumor hypoxia, a hallmark of cancer known to render solid tumors more resistant to radiation and most chemo-therapy. We then explore the concept that the intrinsic hypoxic microenvironment of mesotheliomas can be Achilles' heel for targeted, multimodal therapeutic intervention.

BAP1 immunohistochemistry and p16 FISH results in combination provide higher confidence in malignant pleural mesothelioma diagnosis: ROC analysis of the two tests

Differentiation of malignant pleural mesothelioma (MPM) from benign mesothelial proliferation remains problematic. Loss of nuclear staining of BRCA1-associated protein 1 (BAP1; detected using immunohistochemistry (IHC)) and homozygous deletion (HD) of p16 (detected using fluorescence in situ hybridization (FISH)) are useful for differentiation of MPM from reactive mesothelial hyperplasia (RMH), but the correlation between BAP1 expression loss and p16 HD has not been fully described. We performed BAP1 IHC and p16-specific FISH for 40 MPM and 20 RMH cases, and measured proportions of cells showing BAP1 expression and p16 HD for each case. The diagnostic accuracy for MPM and the cut-off values of the two methods were assessed using receiver operating characteristic (ROC) analysis. BAP1 expression loss, p16 HD and coexistence of both were present in 27 (67.5 %), 27 (67.5 %) and 17 (42.5 %) MPM cases, respectively. Three MPM cases (7.5 %) and all 20 RMH cases had neither BAP1 loss nor p16 HD. There was no correlation between the results of the two methods. Their combination showed higher sensitivity (92.5 %, 37/40) and estimated probability than BAP1 IHC and p16-specific FISH used alone. BAP1 IHC and p16-specific FISH have independent diagnostic value, and have increased reliability when used in combination, for MPM diagnosis.