Reduced Folate Carrier and Folylpolyglutamate Synthetase, but not Thymidylate Synthase Predict Survival in Pemetrexed-Treated Patients Suffering from Malignant Pleural Mesothelioma

Evening Primrose Extract Modulates TYMS Expression via SP1 Transcription Factor in Malignant Pleural Mesothelioma

PURPOSE

To determine the mechanism of EPE in downregulating TYMS in MPM cancer.

METHODS

The TYMS mRNA expression with epithelial-to-mesenchymal transition biomarkers and nuclear factor SP1 was assessed using the GEO database in a data set of MPM patients (GSE51024). Invasive MPM cell lines were in vitro models for the investigation of TYMS expression after EPE treatment. The tyms promoter SP1 binding sequences were determined using Genomatix v 3.4 software Electrophoretic mobility shift and dual-luciferase reporter assays revealed specific SP1 motifs in the interaction of EPE and reference compounds. Chromatin immunoprecipitation and Re-ChIP were used for the co-occupancy study.

RESULTS

In MPM patients, a positive correlation of overexpressed TYMS with mesenchymal TWIST1, FN1 and N-cadherin was observed. EPE and its major components, gallic and ellagic acid (GA and EA, respectively), downregulated TYMS in invasive MPM cells by interacting with particular SP1 motifs on the tyms promoter. The luciferase constructs confirmed the occupation of two SP1 regulatory regions critical for the promotion of TYMS expression. Both EPE and reference standards influenced SP1 translocation into the nucleus.

CONCLUSION

EPE components reduced TYMS expression by occupation of SP1 motifs on the tyms promoter and reversed the EMT phenotype of invasive MPM cells. Further in-depth analysis of the molecular docking of polyphenol compounds with SP1 regulatory motifs is required.

Mesothelin expression remodeled the immune-matrix tumor microenvironment predicting the risk of death in patients with malignant pleural mesothelioma

Background

The combination of immunobiological agents with immune checkpoint proteins is a promising treatment for malignant pleural mesothelioma (MPM). Mesothelin and anti-PD-L1 antibody-drug conjugates specifically target malignant neoplastic cells, inhibit the migration and invasion of neoplastic cells, and restore the immune landscape. In this study, we confirmed the importance of mesothelin and examined the relationship between mesothelin and the immune landscape of the tumor microenvironment (TME) in two MPM cohorts.

Methods

The discovery cohort included 82 MPM cases. Tissue microarray slides were generated, and samples were processed for hematoxylin & eosin staining, immunohistochemistry, and immunofluorescence assays. The relationship between mesothelin, biomarkers of histogenesis, histological aggressiveness, PD-L1, immune cells (CD4, CD8, CD20, CD68), and collagen type I and type V fibers was evaluated by quantitative digital analyses. The outcome was the survival time until death from disease recurrence. The exploratory cohort included 87 malignant mesothelioma (MESO) patients from The Cancer Genome Atlas database.

Results

Most patients were male (70.7%) with a history of asbestos exposure (53.7%) and with the epithelioid subtype (89%). Surgical resection was performed in 85.4% of patients, and 14.6% received chemotherapy; 59.8% of patients died from disease extension to the mediastinum. Low tumor mesothelin expression was associated with tumor necrosis and nuclear grade 1, whereas high mesothelin expression was significantly associated with the epithelioid histotype and high density of T cells CD8+, macrophages CD68+, and collagen type I fibers. Cox multivariate analysis showed a high risk of death for non-operated patients [hazard ratio (HR), 3.42 (1.15-10.16)] with low tumor mesothelin levels [HR, 2.58 (1.09-6.10)] and high PD-L1 and low infiltration of T cells CD4+ [HR, 3.81 (1.58-9.18)]. In the exploratory cohort, low mesothelin and high COL1A1 and COL5A1 expression were associated with poor overall survival.

Conclusion

Tumor mesothelin expression associated with the TME immune landscape predicts the risk of death for patients with MPM and could be a new target for immunotherapy in MPM.

One Third of Malignant Pleural Mesothelioma Shows High Immunohistochemical Expression of MSLN or CXCR4 Which Indicates Potent Candidates for Endo-Radiotherapy

Malignant pleural mesothelioma (MPM) is a mainly asbestos-related tumour associated with a very poor prognosis. Therapeutic approaches include multimodal therapy and chemotherapeutics, with cisplatin being the drug of choice, but response rates of only up to 14% indicate very poor outcomes. Effective treatment options are lacking. Besides the diagnostic usage of radioligands in positron emission tomography (PET)/computed tomography (CT), the endo-radioligand therapy with Lu177 has been proven as a powerful tool in cancer therapy. Mesothelin (MSLN) and C-XC chemokine receptor 4 (CXCR4) are membrane-bound proteins, expressed in certain cancers, and thus are promising targets for endo-radiotherapy. A significant portion of high MSLN- or CXCR4-expressing tumors within the MPM may open the field for this sophisticated treatment approach in the near future. Formalin-fixed, paraffin-embedded (FFPE) tumour specimens from 105 patients suffering from MPM and treated at the Lung Cancer Centre of Essen and at the Helios Klinikum Emil von Behring Berlin were screened. The tumour samples were arranged in tissue microarrays. We immunohistochemically stained the tumour samples against MSLN and CXCR4. The protein expressions of the stainings were scored by a pathologist by using a semiquantitative method. The data obtained were correlated with the clinical outcome. Overall, 77.1% of the analysed tumours showed CXCR4 protein expression (25.7% of them at high expression level (Score 3)). 48.6% of all samples showed an overall strong staining (Score ≥ 2), 59% of the investigated tumours showed MSLN protein expression (10.5% of them at high expression (Score 3)), and 36.2% of all samples showed an overall strong staining (Score ≥ 2). Our results show significant tissue expression levels, for both CXCR4 and MSLN protein, in a major portion of clinical MPM samples. One-third of patients showed outstanding immunoexpression of at least one of these markers, making them interesting candidates for radioligand-based PET/CT diagnostics and follow-up and furthermore may profit from endo-radiotherapy.

Uncovering cancer vulnerabilities by machine learning prediction of synthetic lethality

BACKGROUND

Synthetic lethality describes a genetic interaction between two perturbations, leading to cell death, whereas neither event alone has a significant effect on cell viability. This concept can be exploited to specifically target tumor cells. CRISPR viability screens have been widely employed to identify cancer vulnerabilities. However, an approach to systematically infer genetic interactions from viability screens is missing.

METHODS

Here we describe PAn-canceR Inferred Synthetic lethalities (PARIS), a machine learning approach to identify cancer vulnerabilities. PARIS predicts synthetic lethal (SL) interactions by combining CRISPR viability screens with genomics and transcriptomics data across hundreds of cancer cell lines profiled within the Cancer Dependency Map.

RESULTS

Using PARIS, we predicted 15 high confidence SL interactions within 549 DNA damage repair (DDR) genes. We show experimental validation of an SL interaction between the tumor suppressor CDKN2A, thymidine phosphorylase (TYMP) and the thymidylate synthase (TYMS), which may allow stratifying patients for treatment with TYMS inhibitors. Using genome-wide mapping of SL interactions for DDR genes, we unraveled a dependency between the aldehyde dehydrogenase ALDH2 and the BRCA-interacting protein BRIP1. Our results suggest BRIP1 as a potential therapeutic target in ~ 30% of all tumors, which express low levels of ALDH2.

CONCLUSIONS

PARIS is an unbiased, scalable and easy to adapt platform to identify SL interactions that should aid in improving cancer therapy with increased availability of cancer genomics data.

Impact of hypoxia on chemoresistance of mesothelioma mediated by the proton-coupled folate transporter, and preclinical activity of new anti-LDH-A compounds

BACKGROUND

Expression of proton-coupled folate transporter (PCFT) is associated with survival of mesothelioma patients treated with pemetrexed, and is reduced by hypoxia, prompting studies to elucidate their correlation.

METHODS

Modulation of glycolytic gene expression was evaluated by PCR arrays in tumour cells and primary cultures growing under hypoxia, in spheroids and after PCFT silencing. Inhibitors of lactate dehydrogenase (LDH-A) were tested in vitro and in vivo. LDH-A expression was determined in tissue microarrays of radically resected malignant pleural mesothelioma (MPM, N = 33) and diffuse peritoneal mesothelioma (DMPM, N = 56) patients.

RESULTS

Overexpression of hypoxia marker CAIX was associated with low PCFT expression and decreased MPM cell growth inhibition by pemetrexed. Through integration of PCR arrays in hypoxic cells and spheroids and following PCFT silencing, we identified the upregulation of LDH-A, which correlated with shorter survival of MPM and DMPM patients. Novel LDH-A inhibitors enhanced spheroid disintegration and displayed synergistic effects with pemetrexed in MPM and gemcitabine in DMPM cells. Studies with bioluminescent hypoxic orthotopic and subcutaneous DMPM athymic-mice models revealed the marked antitumour activity of the LDH-A inhibitor NHI-Glc-2, alone or combined with gemcitabine.

CONCLUSIONS

This study provides novel insights into hypoxia/PCFT-dependent chemoresistance, unravelling the potential prognostic value of LDH-A, and demonstrating the preclinical activity of LDH-A inhibitors.

A Phase II Study of Pemetrexed in Patients with Recurrent Thymoma and Thymic Carcinoma

INTRODUCTION

Thymoma and thymic carcinoma (TC) are neoplastic diseases with reported chemosensitivity to a broad range of agents. However, because of the rarity of these diseases, few prospective trials have been conducted in patients with advanced thymic malignancies. We conducted a prospective phase II trial to evaluate the clinical activity of pemetrexed, a multitargeted antifolate agent, in previously treated patients with thymoma and TC.

METHODS

A total of 27 previously treated patients (16 with thymoma and 11 with TC) with advanced, unresectable disease were treated with pemetrexed, 500 mg/m², intravenously every 3 weeks for a maximum of six cycles or until undue toxicity or progressive disease. All patients received folic acid, vitamin B₁₂, and steroid prophylaxis.

RESULTS

The median number of cycles administered was 6 (range 1-6). Nine patients with a total of 14 events had grade 3 toxicities; no grade 4 toxicities were noted. In 26 fully evaluable patients, two complete and three partial responses (according to the Response Evaluation Criteria in Solid Tumors) were documented (all in patients with stage IVA thymoma, except for one partial response with stage IVA TC). A total of 14 patients completed the full six cycles of treatment, 7 patients progressed while undergoing therapy, 5 patients discontinued therapy because of intolerance, and 1 patient discontinued therapy because of progressive Morvan syndrome. The median progression-free survival time for all patients was 10.6 months (12.1 months for those with thymoma versus 2.9 months for those with TC). With 23 deaths at data cutoff, the median overall survival time was 28.7 months (46.4 months for those with thymoma versus 9.8 months for those with TC).

CONCLUSIONS

Pemetrexed is an active agent in this heavily pretreated population of patients with recurrent thymic malignancies, especially thymoma.

Inhibition of MDM2 via Nutlin-3A: A Potential Therapeutic Approach for Pleural Mesotheliomas with MDM2-Induced Inactivation of Wild-Type P53

Previously, our group demonstrated that nuclear expression of E3 ubiquitin ligase (MDM2) in malignant pleural mesothelioma (MPM) is significantly associated with decreased overall survival. A possible explanation may be that overexpression of MDM2 leads to a proteasomal degradation of TP53 that eventually results in a loss of TP53-induced apoptosis and senescence. It is well known from other tumor entities that restoration of TP53 activity, e.g., by MDM2 inhibition, results in an instant TP53-induced stress and/or DNA damage response of cancer cells. Nutlin-3A (a cis-imidazoline analogue) has been described as a potent and selective MDM2 inhibitor preventing MDM2-TP53-interaction by specific binding to the hydrophobic TP53-binding pocket of MDM2. In the present study, the effects of MDM2 inhibition in MPM via Nutlin-3A and standard platinum based chemotherapeutic agents were comparatively tested in three MPM cell lines (NCI-H2052, MSTO-211H, and NCI-H2452) showing different expression profiles of TP53, MDM2, and its physiological inhibitor of MDM2—P14/ARF. Our in vitro experiments on MPM cell lines revealed that Nutlin-3A in combination with cisplatin resulted in up to 9.75 times higher induction of senescence (p=0.0050) and up to 5 times higher apoptosis rate (p=0.0067) compared to the commonly applied cisplatin and pemetrexed regimens. Thus Nutlin-3A, a potent inhibitor of MDM2, is associated with a significant induction of senescence and apoptosis in MPM cell lines, making Nutlin-3A a promising substance for a targeted therapy in the subgroup of MPM showing MDM2 overexpression.

Immunohistochemically detectable metallothionein expression in malignant pleural mesotheliomas is strongly associated with early failure to platin-based chemotherapy

Background

Malignant pleural mesothelioma (MPM) is a biologically highly aggressive tumor arising from the pleura with a dismal prognosis. Cisplatin is the drug of choice for the treatment of MPM, and carboplatin seems to have comparable efficacy. Nevertheless, cisplatin treatment results in a response rate of merely 14% and a median survival of less than seven months. Due to their role in many cellular processes, methallothioneins (MTs) have been widely studied in various cancers. The known heavy metal detoxifying effect of MT-I and MT-II may be the reason for heavy metal drug resistance of various cancers including MPM.

Methods

105 patients were retrospectively analyzed immunohistochemically for their MT expression levels. Survival analysis was done by Cox-regression, and statistical significance determined using likelihood ratio, Wald test and Score (logrank) tests.

Results

Cox-regression analyses were done in a linear and logarithmic scale revealing a significant association between expression of MT and shortened overall survival (OS) in a linear (p=0.0009) and logarithmic scale (p=0.0003). Reduced progression free survival (PFS) was also observed for MT expressing tumors (linear: p=0.0134, log: p=0.0152).

Conclusion

Since both, overall survival and progression-free survival are negatively correlated with detectable MT expression in MPM, our results indicate a possible resistance to platin-based chemotherapy associated with MT expression upregulation, found exclusively in progressive MPM samples. Initial cell culture studies suggest promoter DNA hypomethylation and expression of miRNA-566 a direct regulator of copper transporter SLC31A1 and a putative regulator of MT1A and MT2A gene expression, to be responsible for the drug resistance.

Folic acid phenotype (FAP) is a superior biomarker predicting response to pemetrexed-based chemotherapy in malignant pleural mesothelioma

BACKGROUND

Malignant pleural mesothelioma (MPM) is a rare tumor linked to a dismal prognosis. Even the most effective chemotherapeutical regime of pemetrexed combined with cisplatin leads to a remission-rate of only about 40%. The reasons for the rather poor efficacy remain largely unknown.

RESULTS

Phenotypes were significantly associated with progression (p=0.0279) and remission (p=0.0262). Cox-regression revealed significant associations between SLC19A1/TYMS-ratio (p=0.0076) as well as FPGS/TYMS-ratio (p=0.0026) and OS. For differentiation by risk-groups, COXPH identified a strong correlation (p=0.0008).

METHODS

56 MPM specimens from patients treated with pemetrexed were used for qPCR analysis. Phenotypes and risk groups were defined by their expression levels of members of the folic acid metabolism and correlated to survival and objective response.

CONCLUSION

Our results indicate that the balance between folic acid uptake, activation and metabolism plays a crucial role in response to pemetrexed-based chemotherapy and the prognosis of MPM patients. Implementing this marker profile in MPM stratification may help to individualize MPM-therapy more efficiently.

Role of proton-coupled folate transporter in pemetrexed resistance of mesothelioma: clinical evidence and new pharmacological tools

BACKGROUND

Thymidylate synthase (TS) has a predictive role in pemetrexed treatment of mesothelioma; however, additional chemoresistance mechanisms are poorly understood. Here, we explored the role of the reduced-folate carrier (RFC/SLC19A1) and proton-coupled folate transporter (PCFT/SLC46A1) in antifolate resistance in mesothelioma.

PATIENTS AND METHODS

PCFT, RFC and TS RNA and PCFT protein levels were determined by quantitative RT-PCR of frozen tissues and immunohistochemistry of tissue-microarrays, respectively, in two cohorts of pemetrexed-treated patients. Data were analyzed by t-test, Fisher's/log-rank test and Cox proportional models. The contribution of PCFT expression and PCFT-promoter methylation to pemetrexed activity were evaluated in mesothelioma cells and spheroids, through 5-aza-2'-deoxycytidine-mediated demethylation and siRNA-knockdown.

RESULTS

Pemetrexed-treated patients with low PCFT had significantly lower rates of disease control, and shorter overall survival (OS), in both the test (N = 73, 11.3 versus 20.1 months, P = 0.01) and validation (N = 51, 12.6 versus 30.3 months, P = 0.02) cohorts. Multivariate analysis confirmed PCFT-independent prognostic role. Low-PCFT protein levels were also associated with shorter OS. Patients with both low-PCFT and high-TS levels had the worst prognosis (OS, 5.5 months), whereas associations were neither found for RFC nor in pemetrexed-untreated patients. PCFT silencing reduced pemetrexed sensitivity, whereas 5-aza-2'-deoxycytidine overcame resistance.

CONCLUSIONS

These findings identify for the first time PCFT as a novel mesothelioma prognostic biomarker, prompting prospective trials for its validation. Moreover, preclinical data suggest that targeting PCFT-promoter methylation might eradicate pemetrexed-resistant cells characterized by low-PCFT expression.

microRNAs are differentially regulated between MDM2-positive and negative malignant pleural mesothelioma

Background

Malignant pleural mesothelioma (MPM) is a highly aggressive tumour first-line treated with a combination of cisplatin and pemetrexed. MDM2 and P14/ARF (CDKN2A) are upstream regulators of TP53 and may contribute to its inactivation. In the present study, we now aimed to define the impact of miRNA expression on this mechanism.

Material and Methods

24 formalin-fixed paraffin-embedded (FFPE) tumour specimens were used for miRNA expression analysis of the 800 most important miRNAs using the nCounter technique (NanoString). Significantly deregulated miRNAs were identified before a KEGG-pathway analysis was performed.

Results

17 miRNAs regulating TP53, 18 miRNAs regulating MDM2, and 11 miRNAs directly regulating CDKN2A are significantly downregulated in MDM2-expressing mesotheliomas. TP53 is downregulated in MDM2-negative tumours through miRNAs with a miSVR prediction score of 11.67, RB1 with a prediction score of 8.02, MDM2 with a prediction score of 4.50 and CDKN2A with a prediction score of 1.27.

Conclusion

MDM2 expression seems to impact miRNA expression levels in MPM. Especially, miRNAs involved in TP53-signaling are strongly decreased in MDM2-positive mesotheliomas. A better understanding of its tumour biology may open the chance for new therapeutic approaches and thereby augment patients' outcome.

Dual Targeting of Epithelial Ovarian Cancer Via Folate Receptor α and the Proton-Coupled Folate Transporter with 6-Substituted Pyrrolo[2,3-d]pyrimidine Antifolates

Folate uptake in epithelial ovarian cancer (EOC) involves the reduced folate carrier (RFC) and the proton-coupled folate transporter (PCFT), both facilitative transporters and folate receptor (FR) α. Although in primary EOC specimens, FRα is widely expressed and increases with tumor stage, PCFT was expressed independent of tumor stage (by real-time RT-PCR and IHC). EOC cell line models, including cisplatin sensitive (IGROV1 and A2780) and resistant (SKOV3 and TOV112D) cells, expressed a 17-fold range of FRα and similar amounts (within ∼2-fold) of PCFT. Novel 6-substituted pyrrolo[2,3-d]pyrimidine thienoyl antifolates AGF94 and AGF154 exhibited potent antiproliferative activities toward all of the EOC cell lines, reflecting selective cellular uptake by FRα and/or PCFT over RFC. When IGROV1 cells were pretreated with AGF94 at pH 6.8, clonogenicity was potently inhibited, confirming cell killing. FRα was knocked down in IGROV1 cells with lentiviral shRNAs. Two FRα knockdown clones (KD-4 and KD-10) showed markedly reduced binding and uptake of [³H]folic acid and [³H]AGF154 by FRα, but maintained high levels of [³H]AGF154 uptake by PCFT compared to nontargeted control cells. In proliferation assays, KD-4 and KD-10 cells preserved in vitro inhibition by AGF94 and AGF154, compared to a nontargeted control, attributable to residual FRα- and substantial PCFT-mediated uptake. KD-10 tumor xenografts in severe-compromised immune-deficient mice were likewise sensitive to AGF94 Collectively, our results demonstrate the substantial therapeutic potential of novel 6-substituted pyrrolo[2,3-d]pyrimidine antifolates with dual targeting of PCFT and FRα toward EOCs that express a range of FRα, along with PCFT, as well as cisplatin resistance. Mol Cancer Ther; 16(5); 819-30. ©2017 AACR.

Folylpoly-γ-glutamate synthetase: A key determinant of folate homeostasis and antifolate resistance in cancer

Mammalians are devoid of autonomous biosynthesis of folates and hence must obtain them from the diet. Reduced folate cofactors are B9-vitamins which play a key role as donors of one-carbon units in the biosynthesis of purine nucleotides, thymidylate and amino acids as well as in a multitude of methylation reactions including DNA, RNA, histone and non-histone proteins, phospholipids, as well as intermediate metabolites. The products of these S-adenosylmethionine (SAM)-dependent methylations are involved in the regulation of key biological processes including transcription, translation and intracellular signaling. Folate-dependent one-carbon metabolism occurs in several subcellular compartments including the cytoplasm, mitochondria, and nucleus. Since folates are essential for DNA replication, intracellular folate cofactors play a central role in cancer biology and inflammatory autoimmune disorders. In this respect, various folate-dependent enzymes catalyzing nucleotide biosynthesis have been targeted by specific folate antagonists known as antifolates. Currently, antifolates are used in drug treatment of multiple human cancers, non-malignant chronic inflammatory disorders as well as bacterial and parasitic infections. An obligatory key component of intracellular folate retention and intracellular homeostasis is (anti)folate polyglutamylation, mediated by the unique enzyme folylpoly-γ-glutamate synthetase (FPGS), which resides in both the cytoplasm and mitochondria. Consistently, knockout of the FPGS gene in mice results in embryonic lethality. FPGS catalyzes the addition of a long polyglutamate chain to folates and antifolates, hence rendering them polyanions which are efficiently retained in the cell and are now bound with enhanced affinity by various folate-dependent enzymes. The current review highlights the crucial role that FPGS plays in maintenance of folate homeostasis under physiological conditions and delineates the plethora of the molecular mechanisms underlying loss of FPGS function and consequent antifolate resistance in cancer.

Orotate phosphoribosyltransferase is overexpressed in malignant pleural mesothelioma: Dramatically responds one case in high OPRT expression

Objective: Malignant pleural mesothelioma (MPM) is a rare and aggressive, treatment-resistant cancer. Pemetrexed, an inhibitor of thymidylate synthase (TS), is used worldwide for MPM as a first-line chemotherapy regimen. However, there is little consensus for a second-line chemotherapy. S-1, a highly effective dihydropyrimidine dehydrogenase (DPD)-inhibitory fluoropyrimidine, mainly acts via a TS inhibitory mechanism similar to pemetrexed. Orotate phosphoribosyltransferase (OPRT) is a key enzyme related to the first step activation of 5-fluorouracil (5-FU) for inhibiting RNA synthesis. We investigated 5-FU related-metabolism proteins, especially focusing on OPRT expression, in MPM Methods and Patients: Fifteen MPM patients who were diagnosed between July 2004 and December 2013 were enrolled. We examined the protein levels of 5-FU metabolism-related enzymes (TS, DPD, OPRT, and thymidine phosphorylase [TP]) in 14 cases Results: High TS, DPD, OPRT, and TP expressions were seen in 28.6%, 71.4%, 85.7%, and 35.7% of patients, respectively. We found that OPRT expression was extremely high in MPM tissue. We experienced one remarkable case of highly effective S-1 combined therapy for pemetrexed refractory MPM. This case also showed high OPRT protein expression Conclusion: The present study suggests that OPRT expression is high in MPM tumors. Although pemetrexed is mainly used for MPM chemotherapy as a TS inhibitor, S-1 has potential as an anticancer drug not only as a TS inhibitor but also inhibiting RNA synthesis through the OPRT pathway. This is the first report investigating OPRT protein expressions in MPM.

Induction Therapy for Mesothelioma

One particular approach of multimodality treatment for mesothelioma is induction therapy followed by surgery. Among its several advantages, the most important is downstaging of the tumor into a resectable stage, although morbidity and mortality might be increased. In this article we review the principles and outcome of different modalities for induction treatment of mesothelioma.

MDM2 is an important prognostic and predictive factor for platin-pemetrexed therapy in malignant pleural mesotheliomas and deregulation of P14/ARF (encoded by CDKN2A) seems to contribute to an MDM2-driven inactivation of P53

Background:

Malignant pleural mesothelioma (MPM) is a highly aggressive tumour that is first-line treated with a combination of cisplatin and pemetrexed. Until now, predictive and prognostic biomarkers are lacking, making it a non-tailored therapy regimen with unknown outcome. P53 is frequently inactivated in MPM, but mutations are extremely rare. MDM2 and P14/ARF are upstream regulators of P53 that may contribute to P53 inactivation.

Methods:

A total of 72 MPM patients were investigated. MDM2 immunoexpression was assessed in 65 patients. MDM2 and P14/ARF mRNA expression was analysed in 48 patients of the overall collective. The expression results were correlated to overall survival (OS) and progression-free survival (PFS).

Results:

OS and PFS correlated highly significantly with MDM2 mRNA and protein expression, showing a dismal prognosis for patients with elevated MDM2 expression (for OS: Score (logrank) test: P⩽0.002, and for PFS: Score (logrank) test; P<0.007). MDM2 was identified as robust prognostic and predictive biomarker for MPM on the mRNA and protein level. P14/ARF mRNA expression reached no statistical significance, but Kaplan–Meier curves distinguished patients with low P14/ARF expression and hence shorter survival from patients with higher expression and prolonged survival.

Conclusions:

MDM2 is a prognostic and predictive marker for a platin–pemetrexed therapy of patients with MPMs. Downregulation of P14/ARF expression seems to contribute to MDM2-overexpression-mediated P53 inactivation in MPM patients.

Downregulation of thymidylate synthase and E2F1 by arsenic trioxide in mesothelioma

Malignant pleural mesothelioma is a global health issue. Arsenic trioxide (ATO) has been shown to suppress thymidylate synthase (TYMS) in lung adenocarcinoma and colorectal cancer, and induce apoptosis in acute promyelocytic leukemia. With TYMS as a putative therapeutic target, the effect of ATO in mesothelioma was therefore studied. A panel of 5 mesothelioma cell lines was used to study the effect of ATO on cell viability, protein expression, mRNA expression and TYMS activity by MTT assay, western blot, qPCR and tritium-release assay, respectively. The knockdown of TYMS and E2F1 was performed with a specific siRNA. Phosphatidylserine externalization and mitochondrial membrane depolarization were measured by Annexin V and JC-1 staining respectively. The in vivo effect of ATO was studied using a nude mouse xenograft model. Application of ATO demonstrated anticancer effects in the cell line model with clinically achievable concentrations. Downregulation of TYMS protein (except H226 cells and 1.25 µM ATO in H2052 cells) and mRNA expression (H28 cells), pRB1 (H28 cells) and E2F1 and TYMS activity (except H226 cells) were also evident. E2F1 knockdown decreased cell viability more significantly than TYMS knockdown. In general, thymidine kinase 1, ribonucleotide reductase M1, c-myc and skp2 were downregulated by ATO. p-c-Jun was downregulated in H28 cells while upregulated in 211H cells. Phosphatidylserine externalization, mitochondrial membrane depolarization, downregulation of Bcl-2 and Bcl-xL, and upregulation of Bak and cleaved caspase-3 were observed. In the H226 xenograft model, the relative tumor growth was aborted, and E2F1 was downregulated while cleaved caspase-3 was elevated and localized to the nucleus in the ATO treatment group. ATO has potent antiproliferative and cytotoxic effects in mesothelioma in vitro and in vivo, partially mediated through E2F1 targeting (less effect through TYMS targeting). There is sound scientific evidence to support the clinical application of ATO in treatment of mesothelioma.

The major facilitative folate transporters solute carrier 19A1 and solute carrier 46A1: biology and role in antifolate chemotherapy of cancer

This review summarizes the biology of the major facilitative membrane transporters, the reduced folate carrier (RFC) (Solute Carrier 19A1) and the proton-coupled folate transporter (PCFT) (Solute Carrier 46A1). Folates are essential vitamins, and folate deficiency contributes to a variety of health disorders. RFC is ubiquitously expressed and is the major folate transporter in mammalian cells and tissues. PCFT mediates the intestinal absorption of dietary folates and appears to be important for transport of folates into the central nervous system. Clinically relevant antifolates for cancer, such as methotrexate and pralatrexate, are transported by RFC, and loss of RFC transport is an important mechanism of methotrexate resistance in cancer cell lines and in patients. PCFT is expressed in human tumors, and is active at pH conditions associated with the tumor microenvironment. Pemetrexed is an excellent substrate for both RFC and PCFT. Novel tumor-targeted antifolates related to pemetrexed with selective membrane transport by PCFT over RFC are being developed. In recent years, there have been major advances in understanding the structural and functional properties and the regulation of RFC and PCFT. The molecular bases for methotrexate resistance associated with loss of RFC transport and for hereditary folate malabsorption, attributable to mutant PCFT, were determined. Future studies should continue to translate molecular insights from basic studies of RFC and PCFT biology into new therapeutic strategies for cancer and other diseases.