Immunotherapy strategies for mesothelioma - the role of tumor specific neoantigens in a new era of precision medicine

Mesothelioma Mouse Models with Mixed Genomic States of Chromosome and Microsatellite Instability

Malignant mesothelioma (MMe) is a rare malignancy originating from the linings of the pleural, peritoneal and pericardial cavities. The best-defined risk factor is exposure to carcinogenic mineral fibers (e.g., asbestos). Genomic studies have revealed that the most frequent genetic lesions in human MMe are mutations in tumor suppressor genes. Several genetically engineered mouse models have been generated by introducing the same genetic lesions found in human MMe. However, most of these models require specialized breeding facilities and long-term exposure of mice to asbestos for MMe development. Thus, an alternative model with high tumor penetrance without asbestos is urgently needed. We characterized an orthotopic model using MMe cells derived from Cdkn2a+/-;Nf2+/- mice chronically injected with asbestos. These MMe cells were tumorigenic upon intraperitoneal injection. Moreover, MMe cells showed mixed chromosome and microsatellite instability, supporting the notion that genomic instability is relevant in MMe pathogenesis. In addition, microsatellite markers were detectable in the plasma of tumor-bearing mice, indicating a potential use for early cancer detection and monitoring the effects of interventions. This orthotopic model with rapid development of MMe without asbestos exposure represents genomic instability and specific molecular targets for therapeutic or preventive interventions to enable preclinical proof of concept for the intervention in an immunocompetent setting.

How Our Continuing Studies of the Pre-clinical Inbred Mouse Models of Mesothelioma Have Influenced the Development of New Therapies

Asbestos-induced preclinical mouse models of mesothelioma produce tumors that are very similar to those that develop in humans and thus represent an ideal platform to study this rare, universally fatal tumor type. Our team and a number of other research groups have established such models as a stepping stone to new treatments, including chemotherapy, immunotherapy and other approaches that have been/are being translated into clinical trials. In some cases this work has led to changes in mesothelioma treatment practice and over the last 30 years these models and studies have led to trials which have improved the response rate in mesothelioma from less than 10% to over 50%. Mouse models have had a vital role in that improvement and will continue to play a key role in the future success of mesothelioma immunotherapy. In this review we focus only on these original inbred mouse models, the large number of preclinical studies conducted using them and their contribution to current and future clinical therapy for mesothelioma.

Clinicopathological characteristics of primary peritoneal epithelioid mesothelioma of clear cell type: A case report

RATIONALE

Primary peritoneal epithelioid mesothelioma of clear cell type is an extremely rare entity composed of clear cytoplasm. It is challenging to diagnose because of the morphological resemblance to clear cell tumor.

PATIENTS CONCERNS

A 69-year-old male patient had swollen lymph nodes in the right inguinal region for 7 months and was constipated for 1 month.

DIAGNOSIS

The patient was diagnosed as peritoneal epithelioid mesothelioma of clear cell type based on computed tomography scan, pathology, immunohistochemistry, special staining and whole-exome sequencing. This patient harbored VHL gene alteration in exon 1 and homologous recombination defect (with a score of 45). This finding indicated that this patient might be sensitive to platinum-based therapy and Poly ADP-ribose Polymerase (PARP) inhibitor. This patient carried no microsatellite instability, a low level of tumor mutation burden, and a high extent of intratumoral heterogeneity. Eighteen neoantigens were detected.

INTERVENTIONS

The patient received surgery-based multidisciplinary treatment by integrating cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC). HIPEC was administered with docetaxel 120 mg plus cisplatin 120 mg, at 43°C, for 60 minutes. After operation, the patient received intravenous (IV) chemotherapy with docetaxel 60 mg, pemetrexed 750 mg and cisplatin 100 mg, and then intraperitoneal (IP) chemotherapy with docetaxel 40 mg. The patient received interventional therapy of hepatic artery embolization for 5 times.

OUTCOMES

Regular follow-up was performed until Oct 14, 2020. The patient died 31.6 months later owing to incomplete intestinal obstruction.

LESSONS

Primary peritoneal epithelioid mesothelioma of clear cell type needs to be differentiated from a variety of clear cell tumors. This disease is characterized by specific genetic alteration. Whole-exome sequencing contributes to guide individualized therapy. CRS-HIPEC helps achieve long-term overall survival.

Anti-Mesothelin CAR T cell therapy for malignant mesothelioma

Malignant mesothelioma (MM) is a treatment-resistant tumor originating in the mesothelial lining of the pleura or the abdominal cavity with very limited treatment options. More effective therapeutic approaches are urgently needed to improve the poor prognosis of MM patients. Chimeric Antigen Receptor (CAR) T cell therapy has emerged as a novel potential treatment for this incurable solid tumor. The tumor-associated antigen mesothelin (MSLN) is an attractive target for cell therapy in MM, as this antigen is expressed at high levels in the diseased pleura or peritoneum in the majority of MM patients and not (or very modestly) present in healthy tissues. Clinical trials using anti-MSLN CAR T cells in MM have shown that this potential therapeutic is relatively safe. However, efficacy remains modest, likely due to the MM tumor microenvironment (TME), which creates strong immunosuppressive conditions and thus reduces anti-MSLN CAR T cell tumor infiltration, efficacy and persistence. Various approaches to overcome these challenges are reviewed here. They include local (intratumoral) delivery of anti-MSLN CAR T cells, improved CAR design and co-stimulation, and measures to avoid T cell exhaustion. Combination therapies with checkpoint inhibitors as well as oncolytic viruses are also discussed. Preclinical studies have confirmed that increased efficacy of anti-MSLN CAR T cells is within reach and offer hope that this form of cellular immunotherapy may soon improve the prognosis of MM patients.

Repurposing Quinacrine for Treatment of Malignant Mesothelioma: In-Vitro Therapeutic and Mechanistic Evaluation

Malignant mesothelioma (MM) is a rare type of cancer primarily affecting mesothelial cells lining the pleural cavity. In this study, we propose to repurpose quinacrine (QA), a widely approved anti-malarial drug, for Malignant Pleural Mesothelioma (MPM) treatment. QA demonstrates high degree of cytotoxicity against both immortalized and primary patient-derived cell lines with sub-micromolar 50% inhibitory concentration (IC₅₀) values ranging from 1.2 µM (H2452) to 5.03 µM (H28). Further, QA also inhibited cellular migration and colony formation in MPM cells, demonstrated using scratch and clonogenic assays, respectively. A 3D-spheroid cell culture experiment was performed to mimic in-vivo tumor conditions, and QA was reported to be highly effective in this simulated cellular model. Anti-angiogenic properties were also discovered for QA. Autophagy inhibition assay was performed, and results revealed that QA successfully inhibited autophagy process in MPM cells, which has been cited to be one of the survival pathways for MPM. Annexin V real-time apoptosis study revealed significant apoptotic induction in MPM cells following QA treatment. Western blots confirmed inhibition of autophagy and induction of apoptosis. These studies highlight anti-mesothelioma efficacy of QA at low doses, which can be instrumental in developing it as a stand-alone treatment strategy for MPM.

Telomerase Reverse Transcriptase Promoter Mutations Identify a Genomically Defined and Highly Aggressive Human Pleural Mesothelioma Subgroup

PURPOSE

Human malignant pleural mesothelioma (MPM) is characterized by dismal prognosis. Consequently, dissection of molecular mechanisms driving malignancy is of key importance. Here we investigate whether activating mutations in the telomerase reverse transcriptase (TERT) gene promoter are present in MPM and associated with disease progression, cell immortalization, and genomic alteration patterns.

EXPERIMENTAL DESIGN

TERT promoters were sequenced in 182 MPM samples and compared with clinicopathologic characteristics. Surgical specimens from 45 patients with MPM were tested for in vitro immortalization. The respective MPM cell models (N = 22) were analyzed by array comparative genomic hybridization, gene expression profiling, exome sequencing as well as TRAP, telomere length, and luciferase promoter assays.

RESULTS

TERT promoter mutations were detected in 19 of 182 (10.4%) MPM cases and significantly associated with advanced disease and nonepithelioid histology. Mutations independently predicted shorter overall survival in both histologic MPM subtypes. Moreover, 9 of 9 (100%) mutated but only 13 of 36 (36.1%) wild-type samples formed immortalized cell lines. TERT promoter mutations were associated with enforced promoter activity and TERT mRNA expression, while neither telomerase activity nor telomere lengths were significantly altered. TERT promoter-mutated MPM cases exhibited distinctly reduced chromosomal alterations and specific mutation patterns. While BAP1 mutations/deletions were exclusive with TERT promoter mutations, homozygous deletions at the RBFOX1 and the GSTT1 loci were clearly enriched in mutated cases.

CONCLUSIONS

TERT promoter mutations independently predict a dismal course of disease in human MPM. The altered genomic aberration pattern indicates that TERT promoter mutations identify a novel, highly aggressive MPM subtype presumably based on a specific malignant transformation process.

Nivolumab resulting in persistently elevated troponin levels despite clinical remission of myocarditis and myositis in a patient with malignant pleural mesothelioma: case report

Malignant pleural mesothelioma (MPM) remains a deadly disease with limited therapeutic options beyond platinum/pemetrexed chemotherapy. Immune checkpoint inhibitors have demonstrated modest benefit in the second to later-line settings. An MPM patient from our institute developed myocarditis and myositis after 2 cycles of second-line nivolumab. Despite immunosuppression with corticosteroids and mycophenolate mofetil, there was ongoing rise in troponin levels which remained elevated for months. The patient developed an impressive but brief response following cessation of nivolumab. Myocarditis and myositis are rare complications of immune checkpoint inhibitors. Clinicians should be aware of these possible complications as myocarditis can result in mortality.

Malignant Pleural Mesothelioma: State-of-the-Art on Current Therapies and Promises for the Future

Malignant pleural mesothelioma (MPM) is a rare, aggressive cancer of the pleural surface associated with asbestos exposure. The median survival of MPM patients is a mere 8-14 months, and there are few biomarkers and no cure available. It is hoped that, eventually, the incidence of MPM will drop and remain low and constant, given that most nations have banned the use of asbestos, but in the meantime, the incidence in Europe is still growing. The exact molecular mechanisms that explain the carcinogenicity of asbestos are not known. Standard therapeutic strategies for MPM include surgery, often coupled with chemotherapy and/or radiotherapy, in a small percentage of eligible patients and chemotherapy in tumors considered unresectable with or without adjuvant radiotherapy. In recent years, several new therapeutic avenues are being explored. These include angiogenesis inhibitors, synthetic lethal treatment, miRNA replacement, oncoviral therapies, and the fast-growing field of immunotherapy alone or in combination with chemotherapy. Of particular promise are the multiple options offered by immunotherapy: immune checkpoint inhibitors, tumor vaccines, and therapies taking advantage of tumor-specific antigens, such as specific therapeutic antibodies or advanced cell-based therapies exemplified by the CAR-T cells. This review comprehensively presents both old and new therapeutic options in MPM, focusing on the results of the numerous recent and on-going clinical trials in the field, including the latest data presented at international meetings (AACR, ASCO, and ESMO) this year, and concludes that more work has to be done in the framework of tailored therapies to identify reliable targets and novel biomarkers to impact MPM management.

Identification of a CD8+ T-cell response to a predicted neoantigen in malignant mesothelioma

Neoantigens present unique and specific targets for personalized cancer immunotherapy strategies. Given the low mutational burden yet immunotherapy responsiveness of malignant mesothelioma (MM) when compared to other carcinogen-induced malignancies, identifying candidate neoantigens and T cells that recognize them has been a challenge. We used pleural effusions to gain access to MM tumor cells as well as immune cells in order to characterize the tumor-immune interface in MM. We characterized the landscape of potential neoantigens from SNVs identified in 27 MM patients and performed whole transcriptome sequencing of cell populations from 18 patient-matched pleural effusions. IFNγ ELISpot was performed to detect a CD8+ T cell responses to predicted neoantigens in one patient. We detected a median of 68 (range 7–258) predicted neoantigens across the samples. Wild-type non-binding to mutant binding predicted neoantigens increased risk of death in a model adjusting for age, sex, smoking status, histology and treatment (HR: 33.22, CI: 2.55–433.02, p = .007). Gene expression analysis indicated a dynamic immune environment within the pleural effusions. TCR clonotypes increased with predicted neoantigen burden. A strong activated CD8+ T-cell response was identified for a predicted neoantigen produced by a spontaneous mutation in the ROBO3 gene. Despite the challenges associated with the identification of bonafide neoantigens, there is growing evidence that these molecular changes can provide an actionable target for personalized therapeutics in difficult to treat cancers. Our findings support the existence of candidate neoantigens in MM despite the low mutation burden of the tumor, and may present improved treatment opportunities for patients.

Neo-antigen specific T cell responses indicate the presence of metastases before imaging

Non-small cell lung cancer (NSCLC) causes 19% of all Australian cancer deaths, with a 5-year survival post-resection of around 60%. Post-operative recurrence is due to metastases that were undetectable pre-operatively, or growth of microscopic locoregional residual disease. However, post-operative imaging modalities typically only detect more advanced tumours; where PET-CT has a detection limit of 6–7 mm. Detection of small deposits of lung metastatic disease is of importance in order to facilitate early and potentially more effective treatment. In this study, in a murine model of lung metastatic disease, we explore whether neo-antigen specific T cells are a sensitive marker for the detection of lung cancer after primary tumour resection. We determine lung metastatic disease by histology, and then compare detection by PET-CT and neo-antigen specific T cell frequency. Detection of lung metastatic disease within the histology positive group by PET-CT and neo-antigen specific T cell frequency were 22.9% and 92.2%, respectively. Notably, neo-antigen specific T cells in the lung draining lymph node were indicative of metastatic disease (82.8 ± 12.9 spots/10⁵ cells; mean ± SE), compared to healthy lung control (28.5 ± 8.6 spots/10⁵ cells; mean ± SE). Potentially, monitoring tumour neo-antigen specific T cell profiles is a highly sensitive method for determining disease recurrence.

Autophagy facilitates the release of immunogenic signals following chemotherapy in 3D models of mesothelioma

We have previously shown that nearly half of mesothelioma patients have tumors with low autophagy and that these patients have a significantly worse outcome than those with high autophagy. We hypothesized that autophagy may be beneficial by facilitating immunogenic cell death (ICD) of tumor cells following chemotherapy. An important hallmark of ICD is that death of tumor cells is preceded or accompanied by the release of damage-associated molecular pattern molecules (DAMPs), which then can stimulate an antitumor immune response. Therefore, we measured how autophagy affected the release of three major DAMPs: high mobility group box 1 (HMGB1), ATP, and calreticulin following chemotherapy. We found that autophagy in three-dimensional (3D) models with low autophagy at baseline could be upregulated with the cell-permeant Tat-BECN1 peptide and confirmed that autophagy in 3D models with high autophagy at baseline could be inhibited with MRT 68921 or ATG7 RNAi, as we have previously shown. In in vitro 3D spheroids, we found that, when autophagy was high or upregulated, DAMPs were released following chemotherapy; however, when autophagy was low or inhibited, DAMPs release was significantly impaired. Similarly, in ex vivo tumors, when autophagy was high or upregulated, HMGB1 was released following chemotherapy but, when autophagy was low, HMGB1 release was not seen. We conclude that autophagy can be upregulated in at least some tumors with low autophagy and that upregulation of autophagy can restore the release of DAMPs following chemotherapy. Autophagy may be necessary for ICD in this tumor.

Breath Analysis: A Systematic Review of Volatile Organic Compounds (VOCs) in Diagnostic and Therapeutic Management of Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare neoplasm related to asbestos exposure and with high mortality rate. The management of patients with MPM is complex and controversial, particularly with regard to early diagnosis. In the last few years, breath analysis has been greatly implemented with this aim. In this review the strengths of breath analysis and preliminary results in searching breath biomarkers of MPM are highlighted and discussed, respectively. Through a systematic electronic literature search, collecting papers published from 2000 until December 2018, fifteen relevant scientific papers were selected. All papers considered were prospective, comparative, observational case-control studies although every single one pilot and based on a relatively small number of samples. The identification of diagnostic VOCs pattern, through breath sample characterization and the statistical data treatment, allows to obtain a strategic information for clinical diagnostics. To date the collected data provide just preliminary information and, despite the promising results and diagnostic accuracy, conclusions cannot be generalized due to the limited number of individuals included in each cohort study. Furthermore none of studies was externally validated, although validation process is a necessary step towards clinical implementation. Breathomics-based biomarker approach should be further explored to confirm and validate preliminary findings and to evaluate its potential role in monitoring the therapeutic response.