Cullin 4B Ubiquitin Ligase Is Important for Cell Survival and Regulates TGF-β1 Expression in Pleural Mesothelioma

We previously demonstrated that cullin 4B (CUL4B) upregulation was associated with worse outcomes of pleural mesothelioma (PM) patients, while the overexpression of its paralog CUL4A was not associated with clinical outcomes. Here, we aimed to identify the distinct roles of CUL4B and CUL4A in PM using an siRNA approach in PM cell lines (ACC Meso-1 and Mero82) and primary culture. The knockdown of CUL4B and CUL4A resulted in significantly reduced colony formation, increased cell death, and delayed cell proliferation. Furthermore, similar to the effect of CUL4A knockdown, downregulation of CUL4B led to reduced expression of Hippo pathway genes including YAP1, CTGF, and survivin. Interestingly, CUL4B and not CUL4A knockdown reduced TGF-β1 and MMP2 expression, suggesting a unique association of CUL4B with this pathway. However, the treatment of PM cells with exogenous TGF-β1 following CUL4B knockdown did not rescue PM cell growth. We further analyzed ACC Meso-1 xenograft tumor tissues treated with the cullin inhibitor, pevonedistat, which targets protein neddylation, and observed the downregulation of human TGF-β1 and MMP2. In summary, our data suggest that CUL4B overexpression is important for tumor cell growth and survival and may drive PM aggressiveness via the regulation of TGF-β1 expression and, furthermore, reveal a new mechanism of action of pevonedistat

Evaluation of imaging techniques for the assessment of tumour progression in an orthotopic rat model of malignant pleural mesothelioma

OBJECTIVES An orthotopic rat tumour recurrence model for malignant pleural mesothelioma (MPM) provides clinical similarity to patients and is useful for drug testing combined with surgical intervention. Importantly, a reliable imaging method is required allowing for noninvasive and repetitive evaluation of the tumour load. We compared the tumour load assessed by bioluminescence and magnetic resonance imaging (MRI) to the macroscopic tumour volume as a reference standard. METHODS A total of 500 000 syngeneic rat MPM cells transfected with luciferase were implanted underneath the parietal pleura of immunocompetent rats (n = 13). From the second day after implantation, bioluminescence measurements of the tumour load expressed as the maximum bioluminescent intensity (photon/second) were performed daily after intraperitoneal injection of the luciferase substrate, d-luciferin, to observe the first occurrence of tumour. Six days after the first detection of tumour, bioluminescence, MRI and macroscopic tumour volume measurement were conducted. For MRI, a 4.7-Tesla small animal imager equipped with a (1)H whole-body rat coil was employed using T2-weighted fast spin-echo sequences. Tumour burden (mm(3)) was quantified from magnetic resonance transverse images by two independent readers by manual segmentation. Finally, the tumour burden assessed by bioluminescence and MRI was correlated (Pearson's correlation) with the macroscopic measurement of tumour (ellipsoid) volume. RESULTS In all rats, a single tumour nodule was found at the inoculation site with a median macroscopic volume of 46 mm(3) (18-377 mm(3)). For tumour burden quantification of MRIs, we observed good interobserver correlation (R(2) = 0.81, P < 0.0001) as well as significant association with the macroscopic tumour volume (R(2) = 0.59, P = 0.002). However, the signal intensity of bioluminescence did not correspond to the macroscopic tumour volume (R(2) = 0.01, P = 0.76). CONCLUSIONS MRI is a reliable and reproducible noninvasive in vivo imaging method for MPM tumour burden assessment for the present MPM mode

Deletions of CDKN2A and MTAP Detected by Copy-Number Variation Array Are Associated with Loss of p16 and MTAP Protein in Pleural Mesothelioma

CDKN2A deletion is a common alteration in pleural mesothelioma (PM) and frequently associated with co-deletion of MTAP. Since the standard detection method for CDKN2A deletion and FISH analysis is relatively expensive, we here investigated the suitability of inexpensive p16 and MTAP IHC by comparing concordance between IHC and OncoScan CNV arrays on samples from 52 PM patients. Concordance was determined using Cohen's kappa statistics. Loss of CDKN2A was associated with co-deletion of MTAP in 71% of cases. CDKN2A-MTAP copy-number normal cases were also IHC positive in 93% of cases for p16 and 100% for MTAP, while homozygous deletion of CDKN2A-MTAP was always associated with negative IHC for both proteins. In cases with heterozygous CDKN2A-MTAP loss, IHC expression of p16 and MTAP was negative in 100% and 71%, respectively. MTAP and p16 IHC showed high sensitivity (MTAP 86.5%, p16 100%) and specificity (MTAP 100%, p16 93.3%) for the detection of any gene loss. Loss of MTAP expression occurred exclusively in conjunction with loss of p16 labeling. Both p16 and MTAP IHC showed high concordance with Oncoscan CNV arrays (kappa = 0.952, p < 0.0001, and kappa = 0.787, p < 0.0001 respectively). We recommend combined MTAP and p16 immunohistochemistry to confirm the diagnosis of PM

Hedgehog Signaling in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a cancer associated with exposure to asbestos fibers, which accumulate in the pleural space, damage tissue and stimulate regeneration. Hedgehog signaling is a pathway important during embryonic mesothelium development and is inactivated in adult mesothelium. The pathway is reactivated in some MPM patients with poor clinical outcome, mainly mediated by the expression of the ligands. Nevertheless, mutations in components of the pathway have been observed in a few cases. Data from different MPM animal models and primary culture suggest that both autocrine and paracrine Hedgehog signaling are important to maintain tumor growth. Drugs inhibiting the pathway at the level of the smoothened receptor (Smo) or glioma-associated protein transcription factors (Gli) have been used mostly in experimental models. For clinical development, biomarkers are necessary for the selection of patients who can benefit from Hedgehog signaling inhibition

Heterogeneity in Malignant Pleural Mesothelioma

Despite advances in malignant pleural mesothelioma therapy, life expectancy of affected patients remains short. The limited efficiency of treatment options is mainly caused by inter- and intra-tumor heterogeneity of mesotheliomas. This diversity can be observed at the morphological and molecular levels. Molecular analyses reveal a high heterogeneity (i) between patients; (ii) within different areas of a given tumor in terms of different clonal compositions; and (iii) during treatment over time. The aim of the present review is to highlight this diversity and its therapeutic implications

Heterogeneity in Malignant Pleural Mesothelioma

Despite advances in malignant pleural mesothelioma therapy, life expectancy of affected patients remains short. The limited efficiency of treatment options is mainly caused by inter- and intra-tumor heterogeneity of mesotheliomas. This diversity can be observed at the morphological and molecular levels. Molecular analyses reveal a high heterogeneity (i) between patients; (ii) within different areas of a given tumor in terms of different clonal compositions; and (iii) during treatment over time. The aim of the present review is to highlight this diversity and its therapeutic implications

Importance of Cullin4 Ubiquitin Ligase in Malignant Pleural Mesothelioma

Neurofibromatosis type 2 (NF2), the tumor suppressor frequently lost in malignant pleural mesothelioma (MPM), suppresses tumorigenesis in part by inhibiting the Cullin4 ubiquitin ligase (CUL4) complex in the nucleus. Here, we evaluated the importance of CUL4 in MPM progression and tested the efficacy of cullin inhibition by pevonedistat, a small molecule inhibiting cullin neddylation. CUL4 paralogs (CUL4A and CUL4B) were upregulated in MPM tumor specimens compared to nonmalignant pleural tissues. High gene and protein expressions of CUL4B was associated with a worse progression-free survival of MPM patients. Among 13 MPM cell lines tested, five (38%) were highly sensitive to pevonedistat (half maximal inhibitory concentration of cell survival IC$_{50}$ < 0.5 µM). This remained true in a 3D spheroid culture. Pevonedistat treatment caused the accumulation of CDT1 and p21 in both sensitive and resistant cell lines. However, the treatment induced S/G2 cell cycle arrest and DNA rereplication predominantly in the sensitive cell lines. In an in vivo mouse model, the pevonedistat treatment significantly prolonged the survival of mice bearing both sensitive and resistant MPM tumors. Pevonedistat treatment reduced growth in sensitive tumors but increased apoptosis in resistant tumors. The mechanism in the resistant tumor model may be mediated by reduced macrophage infiltration, resulting from the suppression of macrophage chemotactic cytokines, C-C motif chemokine ligand 2 (CCL2), expression in tumor cells

Importance of Cullin4 Ubiquitin Ligase in Malignant Pleural Mesothelioma

Neurofibromatosis type 2 (NF2), the tumor suppressor frequently lost in malignant pleural mesothelioma (MPM), suppresses tumorigenesis in part by inhibiting the Cullin4 ubiquitin ligase (CUL4) complex in the nucleus. Here, we evaluated the importance of CUL4 in MPM progression and tested the efficacy of cullin inhibition by pevonedistat, a small molecule inhibiting cullin neddylation. CUL4 paralogs (CUL4A and CUL4B) were upregulated in MPM tumor specimens compared to nonmalignant pleural tissues. High gene and protein expressions of CUL4B was associated with a worse progression-free survival of MPM patients. Among 13 MPM cell lines tested, five (38%) were highly sensitive to pevonedistat (half maximal inhibitory concentration of cell survival IC50 &lt; 0.5 &micro;M). This remained true in a 3D spheroid culture. Pevonedistat treatment caused the accumulation of CDT1 and p21 in both sensitive and resistant cell lines. However, the treatment induced S/G2 cell cycle arrest and DNA rereplication predominantly in the sensitive cell lines. In an in vivo mouse model, the pevonedistat treatment significantly prolonged the survival of mice bearing both sensitive and resistant MPM tumors. Pevonedistat treatment reduced growth in sensitive tumors but increased apoptosis in resistant tumors. The mechanism in the resistant tumor model may be mediated by reduced macrophage infiltration, resulting from the suppression of macrophage chemotactic cytokines, C-C motif chemokine ligand 2 (CCL2), expression in tumor cells

Importance of excision repair cross-complementation group 1 and ribonucleotide reductase M1 as prognostic biomarkers in malignant pleural mesothelioma treated with platinum-based induction chemotherapy followed by surgery

OBJECTIVES: Survival and response to platinum-based induction chemotherapy are heterogeneous among patients with malignant pleural mesothelioma. The aim of the present study was to assess the prognostic role of DNA repair markers, such as excision repair cross-complementation group 1 and ribonucleotide reductase M1, in multimodally treated patients with malignant pleural mesothelioma. METHODS: Tumor tissue of a malignant pleural mesothelioma cohort (n = 107) treated with platinum/gemcitabine (n = 46) or platinum/pemetrexed (n = 61) induction chemotherapy followed by extrapleural pneumonectomy was assembled on a tissue microarray. Immunohistochemical expression of excision repair cross-complementation group 1 (nuclear) and ribonucleotide reductase M1 (nuclear and cytoplasmic) was assessed for its prognostic impact (association with overall survival or freedom from recurrence). RESULTS: Patients with high nuclear ribonucleotide reductase M1 expression before chemotherapy showed significantly longer freedom from recurrence (P = .03). When specifically analyzed in the subgroup of patients receiving platinum/gemcitabine followed by extrapleural pneumonectomy, high nuclear ribonucleotide reductase M1 was associated with prolonged freedom from recurrence (P = .03) and overall survival (P = .02). Low excision repair cross-complementation group 1 expression in prechemotherapy tumor tissues was associated with significantly longer freedom from recurrence (P = .04). Nuclear ribonucleotide reductase M1 and excision repair cross-complementation group 1 were independent prognosticators of freedom from recurrence in addition to pT stage in multivariate analysis. CONCLUSIONS: In the present study, nuclear ribonucleotide reductase M1 and excision repair cross-complementation group 1 expression were identified as independent prognosticators for freedom from recurrence of malignant pleural mesothelioma in patients undergoing induction chemotherapy followed by extrapleural pneumonectomy