Serum diagnostic markers for malignant pleural mesothelioma: a narrative review

Background and Objective

The prognosis of patients with malignant pleural mesothelioma (MPM) is poor, and early diagnosis is key to improving the prognosis. Pleural biopsy is the gold reference for diagnosing MPM, but it is an invasive method that can cause operation-related complications such as bleeding and infection. Serum biomarkers, with the advantages of mini-invasiveness, short turnaround time and objectiveness, represent a promising diagnostic tool for MPM.

Methods

We searched the PubMed database to identify clinical studies published between 1990 to July 2022 that investigated the diagnostic accuracy of serum biomarkers for MPM. The major findings of the verified studies were summarized.

Key Content and Findings

Currently, there are many available serum markers for MPM, including mesothelin, soluble mesothelin-related peptides, osteopontin, fibulin-3, high mobility group box 1, and microRNA. Systematic review and meta-analysis evidence indicates that the sensitivity and specificity of these serum markers are less than 0.90. In addition, a large portion of previous studies have limitations, especially the representativeness of the study cohort.

Conclusions

The diagnostic accuracy of currently available serum biomarkers is unsatisfactory, and further studies are needed to investigate novel serum biomarkers.

Metastases to Meningiomas: A Comprehensive Literature Review Including Mediating Proteins

Approximately 5-15% of solid tumors metastasizing to the central nervous system metastasize to the leptomeninges. Less common, is metastasis to leptomeningeal meningiomas. These are primarily carcinomas of the breast and lung. Awareness of this phenomenon is critical to the evaluation of meningiomas, especially since the metastases may be the first indication of an occult tumor elsewhere in the body. Lack of clear demarcation between the metastasis and meningioma parenchyma, as well as histological features similar to the meningioma, may hinder recognition. The mechanisms underlying metastases anchoring and spread along the leptomeninges are not established. However, several cell adhesion molecules are thought to contribute to this phenomenon. E cadherin is a cell adhesion molecule present in meningioma cells. Binding to endothelium by adhesion molecules such as ICAM, B1 integrin, P-selectin, PECAM-1, CXCL12 and SDF-1 have also been proposed as part of the mechanisms underlying breast carcinoma metastases. In addition, the leptomeninges and meningiomas express mesothelin that acts as an anchoring protein coupling with mucin-16. Consequently, metastatic tumor cell mucin and mesothelin may also facilitate the anchoring of metastases to meningiomas.

Tear Proteome Revealed Association of S100A Family Proteins and Mesothelin with Thrombosis in Elderly Patients with Retinal Vein Occlusion

Tear samples collected from patients with central retinal vein occlusion (CRVO; n = 28) and healthy volunteers (n = 29) were analyzed using a proteomic label-free absolute quantitative approach. A large proportion (458 proteins with a frequency > 0.6) of tear proteomes was found to be shared between the study groups. Comparative proteomic analysis revealed 29 proteins (p < 0.05) significantly differed between CRVO patients and the control group. Among them, S100A6 (log (2) FC = 1.11, p < 0.001), S100A8 (log (2) FC = 2.45, p < 0.001), S100A9 (log2 (FC) = 2.08, p < 0.001), and mesothelin ((log2 (FC) = 0.82, p < 0.001) were the most abundantly represented upregulated proteins, and β2-microglobulin was the most downregulated protein (log2 (FC) = −2.13, p < 0.001). The selected up- and downregulated proteins were gathered to customize a map of CRVO-related critical protein interactions with quantitative properties. The customized map (FDR < 0.01) revealed inflammation, impairment of retinal hemostasis, and immune response as the main set of processes associated with CRVO ischemic condition. The semantic analysis displayed the prevalence of core biological processes covering dysregulation of mitochondrial organization and utilization of improperly or topologically incorrect folded proteins as a consequence of oxidative stress, and escalating of the ischemic condition caused by the local retinal hemostasis dysregulation. The most significantly different proteins (S100A6, S100A8, S100A9, MSLN, and β2-microglobulin) were applied for the ROC analysis, and their AUC varied from 0.772 to 0.952, suggesting probable association with the CRVO.

Immunotherapy targeting mesothelin in acute myeloid leukemia

Mesothelin (MSLN) is an emerging target that exists in soluble and membrane-associated forms. It is usually used for the diagnosis and treatment of MSLN-positive solid tumors. Interestingly, recent studies have shown that MSLN is highly expressed in 36% of acute myeloid leukemia (AML) patients and barely expressed in normal hematopoietic cells, which makes MSLN a promising target for the treatment of AML. It has been shown that MSLN is detectable as a diagnostic marker in its soluble form. Although the mechanism of action is unclear, MSLN remains a promising target for immunotherapy. Most MSLN research has been conducted in solid tumors, and less research has been conducted in hematopoietic tumors. Increasing research on MSLN is underway in AML, a hematopoietic neoplasm. For example, MSLN is related to extramedullary disease, minimal residual disease, and relapse in AML patients. Decreasing the expression of MSLN reduces the severity of the disease course. This information suggests that MSLN may be an ideal target for the treatment of many AML-related diseases to improve the prognosis and survival rate. At present, there are a few immunotherapies targeting MSLN in AML in preclinical and clinical trials, such as antibody-drug conjugates, bispecific T-cell engagers, and chimeric antigen receptor-T cells, which opens new room for the treatment of MSLN-related AML.

Construction of a 124I-Labeled Specific Antibody for the Noninvasive Detection of Mesothelin-Overexpressing Tumors

Mesothelin (MSLN) is a molecular biomarker of many types of solid tumors, such as mesothelioma, pancreatic cancer, and colon cancer. Owing to the significant difference in expression between cancer cells and normal cells, mesothelin has been widely used as a key target in cancer immunotherapy. In this study, we used iodine isotope (^nat/124/125I)-labeled mesothelin antibodies to noninvasively detect MSLN expression in mice with LS174T colon cancer. The ¹²⁴I-labeled MSLN antibody showed a high radiochemical purity (RCP, >99%) and specific activity (20.8-67.8 GBq/μmol) after purification and was stable in 5% HSA and PBS (>95% RCP at 8 days). Western blot analysis indicated that the LS174T cells showed a higher MSLN protein level than the HepG2 cells. The half maximal effective concentration (EC₅₀) values of the MSLN antibody and ^natI-anti-MSLN were 34.77 ± 3.72 ng/mL and 32.60 ± 2.52 ng/mL (P = 0.63), respectively. The dissociation constant of ¹²⁴I-anti-MSLN binding to MSLN protein was 16.0 nM. The radiotracer showed a significantly higher uptake in LS174T cells than in HepG2 tumor cells (1.56 ± 0.09 vs 0.81 ± 0.03, P = 0.0016) 2 days postinjection. The LS174T mouse models showed extremely low organ uptake and high tumor uptake 96 h after the injection of ¹²⁴I-anti-MSLN, and the T/M values were much higher than those of the other imaging groups (10.56 ± 1.20 for ¹²⁴I-anti-MSLN in LS174T mice vs 3.27 ± 0.20 for ¹²⁴I-anti-MSLN in HepG2 mice vs 3.53 ± 0.2 for ¹²⁴I-IgG in LS174T mice). The immunochemical histology results showed that LS174T tumors were strongly positive (+++) for MSLN, while those in the HepG2 group showed slight expression (+). The dosimetry estimation study showed that the effective dose of ¹²⁴I-anti-MSLN was 0.185 mSv/MBq, which is within the range of acceptable doses for further nuclear medicine translational research. Taken together, these results suggest that this radiotracer has the potential for detecting mesothelin-overexpressing tumors.

Mesothelin‑specific T cell cytotoxicity against triple negative breast cancer is enhanced by 40s ribosomal protein subunit 3‑treated self‑differentiated dendritic cells

Triple negative breast cancer (TNBC) lacks targeted treatment resulting in poor prognosis. Targeting overexpressing mesothelin (MSLN) using MSLN‑specific T cells is an attractive treatment approach and the aim of the present study. The expression of MSLN in human TNBC paraffin sections was analyzed by immunohistochemistry. Lentiviral vector harbored granulocyte‑macrophage colony stimulating factor (GM‑CSF), interleukin‑4 (IL‑4) and MSLN cDNAs was constructed to generate self‑differentiated myeloid‑derived antigen‑presenting‑cells reactive against tumor expressing MSLN dendritic cell (MSLN‑SmartDC) for MSLN‑specific T cell activation. The results showed high MSLN in 32.8% of all breast cancer subtypes and 57% in TNBC. High MSLN was significantly associated with TNBC subtype and the absence of estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2. MSLN‑SmartDC exhibited comparable phenotype to DC generated by exogenous cytokine treatment and an addition of 40s ribosomal protein subunit 3 (RPS3), a toll‑like receptor 4 ligand, enhanced DC maturation and function by upregulation of CD40, CD80 and CD83 expressions and IL‑12p70 secretion. MSLN‑specific CD8+CD69+ IFN‑γ+ T cells were detected in T cells activated by both MSLN‑SmartDC and RPS3‑MSLN‑SmartDC. MSLN‑specific T cells activated by these DCs showed more specific killing capability against naturally expressed MSLN‑HCC70 and artificially MSLN‑overexpressing MDA‑MB‑231 compared with parental MDA‑MB‑231 in both two dimensional (2D)‑ and 3D‑culture systems. In conclusion, the results demonstrated the efficacy of MSLN‑SmartDC to promote MSLN‑specific T cells response against TNBC and RPS3 can enhance the cytolytic activity of these T cells providing an alternative treatment approach for patients with TNBC.

MSLN Correlates With Immune Infiltration and Chemoresistance as a Prognostic Biomarker in Ovarian Cancer

Mesothelin (MSLN) is a glycoprotein with various expression degrees in different tumors including mesothelioma, ovarian cancer, pancreatic cancer, etc. MSLN is considered to play an important role in cell survival, proliferation, and tumor progression. Although the expression of MSLN in tumors makes it a potential therapeutic target, its mechanism of action is still unclear, especially its correlation with immune cells infiltration in the tumor microenvironment has not been investigated. In this study, we detected the overexpression of MSLN in ovarian cancer using database analysis and tissue-array staining. We further evaluated the diagnostic value of MSLN and found it was associated with poor overall survival in ovarian cancer. In addition, the high expression of MSLN was significantly related to the immune-related genes and chemoresistant genes. We confirmed the overexpression of MSLN in the chemoresistant ovarian cancer cell lines. Our research suggests that MSLN participates in a variety of pathways related to the suppression of immune activation and promotion of chemoresistance, leading to a poor prognosis in ovarian cancer.

Mesothelial cell-derived antigen-presenting cancer-associated fibroblasts induce expansion of regulatory T cells in pancreatic cancer

Recent studies have identified a unique cancer-associated fibroblast (CAF) population termed antigen-presenting CAFs (apCAFs), characterized by the expression of major histocompatibility complex class II molecules, suggesting a function in regulating tumor immunity. Here, by integrating multiple single-cell RNA-sequencing studies and performing robust lineage-tracing assays, we find that apCAFs are derived from mesothelial cells. During pancreatic cancer progression, mesothelial cells form apCAFs by downregulating mesothelial features and gaining fibroblastic features, a process induced by interleukin-1 and transforming growth factor β. apCAFs directly ligate and induce naive CD4+ T cells into regulatory T cells (Tregs) in an antigen-specific manner. Moreover, treatment with an antibody targeting the mesothelial cell marker mesothelin can effectively inhibit mesothelial cell to apCAF transition and Treg formation induced by apCAFs. Taken together, our study elucidates how mesothelial cells may contribute to immune evasion in pancreatic cancer and provides insight on strategies to enhance cancer immune therapy.

The Role of Mesothelin Expression in Serous Ovarian Carcinoma: Impacts on Diagnosis, Prognosis, and Therapeutic Targets

Mesothelin (MSLN) is a protein expressed in the mesothelial cell lining of the pleura, peritoneum, and pericardium; its biological functions in normal cells are still unknown. Experimental studies using knockout mice have suggested that this molecule does not play an important role in development and reproduction. In contrast, it has been observed that this molecule is produced in abnormal amounts in several malignant neoplasms, such as mesotheliomas and pancreatic adenocarcinomas. Many molecular studies have also demonstrated that mesothelin is overexpressed in HSOCs. Here, we discuss the current knowledge of mesothelin and focus on its role in clinical and pathological diagnoses, as well as its impact on the prognosis of HSOC. Moreover, regarding the binding of MSLN to the ovarian cancer antigen CA125, which has been demonstrated in many studies, we also report on signal transduction pathways that may play an important role in the spread and neoplastic progression of this lethal neoplasm. Given that mesothelin is overexpressed in many solid tumours and has antigenic properties, this molecule could be considered an antigenic target for the treatment of many malignancies. Consequently, we also review the literature to report on mesothelin-targeting therapies for HSOC that have been recently investigated in many clinical studies.

The Inhibitory Effects of Anti-ERC/Mesothelin Antibody 22A31 on Colorectal Adenocarcinoma Cells, within a Mouse Xenograft Model

Simple Summary

The expression of Renal Carcinoma (ERC)/mesothelin is overexpressed in malignancies such as mesothelioma, pancreatic cancer, and ovarian cancer, and molecular-targeted therapies against ERC/mesothelin have been developed to treat them. Recently, it was revealed that ERC/mesothelin is also expressed in colorectal cancer; thus, this protein is expected to be a therapeutic target in colorectal cancer. In this study, we demonstrated that anti-ERC/mesothelin antibody 22A31 suppressed the growth of colorectal cancer cells subcutaneously xenografted on the back of mice. This is the first report to show the effectiveness of an anti-ERC/mesothelin antibody for the treatment of colorectal cancer in vivo.

Abstract

The expression of Renal Carcinoma (ERC)/mesothelin is enhanced in a variety of cancers. ERC/mesothelin contributes to cancer progression by modulating cell signals that regulate proliferation and apoptosis. Based on such biological insights, ERC/mesothelin has become a molecular target for the treatment of mesothelioma, pancreatic cancer, and ovarian cancer. Recent studies revealed about 50–60% of colorectal adenocarcinomas also express ERC/mesothelin. Therefore, colorectal cancer can also be a potential target of the treatment using an anti-ERC/mesothelin antibody. We previously demonstrated an anti-tumor effect of anti-ERC antibody 22A31 against mesothelioma. In this study, we investigated the effect of 22A31 on a colorectal adenocarcinoma cell line, HCT116. The cells were xenografted into BALB/c nu/nu mice. All mice were randomly allocated to either an antibody treatment group with 22A31 or isotype-matched control IgG1κ. We compared the volume of subsequent tumors, and tumors were pathologically assessed by immunohistochemistry. Tumors treated with 22A31 were significantly smaller than those treated with IgG1κ and contained significantly fewer mitotic cells with Ki67 staining. We demonstrated that 22A31 exhibited a growth inhibitory property on HCT116. Our results implied that ERC/mesothelin-targeted therapy might be a promising treatment for colorectal cancer.

Interpatient variability in mesothelin expression necessitates its evaluation before gastric cancer immunotherapy

Aims: Mesothelin (MSLN) was applied for the immunotherapy of ovarian cancer and mesothelioma with a minimum expression of 60% to obtain a clinical response. Here, the authors evaluated MSLN expression as a potential target of gastric adenocarcinoma immunotherapy. Materials & methods: The expression of MSLN was evaluated by immunohistochemistry and was reported in primary tumor (PT) and metastatic tumor (MT) sites. Results: The results showed that only 17.1% and 13.5% of the patients had 60% or more MSLN expression in PT and MT sites, respectively. The expression of MSLN in PTs and MTs was not influenced by Lauren classification, neoadjuvant therapy or tumor stage. Conclusions: Interpatient variability in MSLN expression necessitates its evaluation before MSLN-based gastric cancer immunotherapy.

Mesothelin Expression Is Not Associated with the Presence of Cancer Stem Cell Markers SOX2 and ALDH1 in Ovarian Cancer

Mesothelin (MSLN) overexpression (OE) is a frequent finding in ovarian carcinomas and increases cell survival and tumor aggressiveness. Since cancer stem cells (CSCs) contribute to pathogenesis, chemoresistance and malignant behavior in ovarian cancer (OC), we hypothesized that MSLN expression could be creating a favorable environment that nurtures CSCs. In this study, we analyzed the expression of MSLN and CSC markers SOX2 and ALDH1 by immunohistochemistry (IHC) in different model systems: primary high-grade serous carcinomas (HGSCs) and OC cell lines, including cell lines that were genetically engineered for MSLN expression by either CRISPR-Cas9-mediated knockout (Δ) or lentivirus-mediated OE. Cell lines, wild type and genetically engineered, were evaluated in 2D and 3D culture conditions and xenografted in nude mice. We observed that MSLN was widely expressed in HGSC, and restricted expression was observed in OC cell lines. In contrast, SOX2 and ALDH1 expression was limited in all tissue and cell models. Most importantly, the expression of CSC markers was independent of MSLN expression, and manipulation of MSLN expression did not affect CSC markers. In conclusion, MSLN expression is not involved in driving the CSC phenotype.

A Glimpse in the Future of Malignant Mesothelioma Treatment

Malignant mesothelioma (MMe) is a rare neoplasm with few therapeutic options available. The landscape of effective therapy for this disease remained unchanged in the last two decades. Recently, however, the introduction of Immune Checkpoint Inhibitors (ICIs) led to small, but nevertheless, promising improvements. However, many efforts are still needed to radically improve the prognosis of MMe. In this review, we analyze all those therapeutic strategies for MMe that are still in a preclinical or early clinical phase of development. In particular, we focus on novel antiangiogenic drugs and their possible combination with immunotherapy. Furthermore, we describe also more complex strategies such as microRNA-loaded vectors, oncolytic viruses, and engineered lymphocytes.

Immunotherapeutic Targeting of Mesothelin Positive Pediatric AML Using Bispecific T Cell Engaging Antibodies

Simple Summary

Immunotherapy development in pediatric AML has been slow due to the paucity of validated AML-specific targets. We recently identified mesothelin (MSLN) as a therapeutic target in pediatric AML. Mice receiving T cell engaging bispecific antibodies (BsAbs) targeting MSLN and CD3 achieved complete remission and durable responses in two MSLN-positive patient-derived xenograft (PDX) models. This is a first report showing MSLN-targeting BsAbs are a viable immunotherapy for MSLN-positive pediatric AML.

Abstract

Advances in the treatment of pediatric AML have been modest over the past four decades. Despite maximally intensive therapy, approximately 40% of patients will relapse. Novel targeted therapies are needed to improve outcomes. We identified mesothelin (MSLN), a well-validated target overexpressed in some adult malignancies, to be highly expressed on the leukemic cell surface in a subset of pediatric AML patients. The lack of expression on normal bone marrow cells makes MSLN a viable target for immunotherapies such as T-cell engaging bispecific antibodies (BsAbs) that combine two distinct antibody-variable regions into a single molecule targeting a cancer-specific antigen and the T-cell co-receptor CD3. Using antibody single-chain variable region (scFv) sequences derived from amatuximab-recognizing MSLN, and from either blinatumomab or AMG330 targeting CD3, we engineered and expressed two MSLN/CD3-targeting BsAbs: MSLN^AMA-CD3^L2K and MSLN^AMA-CD3^AMG, respectively. Both BsAbs promoted T-cell activation and reduced leukemic burden in MV4;11:MSLN xenografted mice, but not in those transplanted with MSLN-negative parental MV4;11 cells. MSLN^AMA-CD3^AMG induced complete remission in NTPL-146 and DF-5 patient-derived xenograft models. These data validate the in vivo efficacy and specificity of MSLN-targeting BsAbs. Because prior MSLN-directed therapies appeared safe in humans, MSLN-targeting BsAbs could be ideal immunotherapies for MSLN-positive pediatric AML patients.

Host Mesothelin Expression Increases Ovarian Cancer Metastasis in the Peritoneal Microenvironment

Mesothelin (MSLN), a glycoprotein normally expressed by mesothelial cells, is overexpressed in ovarian cancer (OvCa) suggesting a role in tumor progression, although the biological function is not fully understood. OvCa has a high mortality rate due to diagnosis at advanced stage disease with intraperitoneal metastasis. Tumor cells detach from the primary tumor as single cells or multicellular aggregates (MCAs) and attach to the mesothelium of organs within the peritoneal cavity producing widely disseminated secondary lesions. To investigate the role of host MSLN in the peritoneal cavity we used a mouse model with a null mutation in the MSLN gene (MSLN^KO). The deletion of host MSLN expression modified the peritoneal ultrastructure resulting in abnormal mesothelial cell surface architecture and altered omental collagen fibril organization. Co-culture of murine OvCa cells with primary mesothelial cells regardless of MSLN expression formed compact MCAs. However, co-culture with MSLN^KO mesothelial cells resulted in smaller MCAs. An allograft tumor study, using wild-type mice (MSLN^WT) or MSLN^KO mice injected intraperitoneally with murine OvCa cells demonstrated a significant decrease in peritoneal metastatic tumor burden in MSLN^KO mice compared to MSLN^WT mice. Together, these data support a role for host MSLN in the progression of OvCa metastasis.

Pilot Study to Evaluate Serum Soluble Mesothelin-Related Peptide (SMRP) as Marker for Clinical Monitoring of Pleural Mesothelioma (PM): Correlation with Modified RECIST Score

A soluble mesothelin-related peptide (SMRP) is the only FDA-approved biomarker for diagnosis of pleural mesothelioma (PM) and the most used for monitoring treatment. Radiological assessment of PM, based on modified RECIST (mRECIST) criteria, is challenging. This pilot study was designed to evaluate whether SMRP levels correlated over time with mRECIST score. Serial serum samples from PM patients were collected and SMRP levels were measured and compared with the mRECIST score obtained through centralized CT scans by blinded review. The within-patient SMRP-mRECIST relationship over time was estimated through a normal random-effects regression approach applied to the log-transformed mRECIST score. Overall, 58 PM patients were included (46 males and 12 females) with a median age at diagnosis of 67 years (min–max = 48–79), 44 (76%) with epithelioid and 14 (24%) with non-epithelioid histology. The total number of SMRP measurements and CT scans considered for analysis was 183. There was a statistically significant correlation between SMRP and mRECIST score in the 2 cohorts considered both separately and jointly. These results, although exploratory, suggest that SMRP measurement might be considered as an adjunct to monitor PM patients in order to delay CT scans time interval, thus warranting further investigation.

Development of mesothelin-specific CAR NK-92 cells for the treatment of gastric cancer

Background: The application of chimeric antigen receptor (CAR) NK cells in solid tumors is hindered by lack of tumor-specific targets and inefficient CAR NK cell efficacy. It has been reported that mesothelin (MSLN) may be an ideal immunotherapy target for gastric cancer. However, the feasibility of using anti-MSLN CAR NK cells to treat gastric cancer remains to be studied.

Methods: MSLN expression in primary human gastric cancer, normal tissues and cell lines were detected. MSLN and CD19 targeted CAR NK-92 (MSLN- and CD19-CAR NK) cells were constructed, purified and verified. N87, MKN-28, AGS and Huh-7 cells expressing the GFP and luciferase genes were transduced. Cell- and patient-derived xenograft (PDX) were established via NSG mice. The ability of MSLN-CAR NK cells to kill MSLN-positive gastric cancer cells were evaluated in vitro and in vivo.

Results: MSLN-CAR NK cells can specifically kill MSLN-positive gastric cancer cells (N87, MKN-28 and AGS), rather than MSLN negative cell (Huh-7), in vitro. Moreover, compared with parental NK-92 cells and CD19-CAR NK cells, stronger cytokine secretions were secreted in MSLN-CAR NK cells cocultured with N87, MKN-28 and AGS. Furthermore, MSLN-CAR NK cells can effectively eliminate gastric cancer cells in both subcutaneous and intraperitoneal tumor models. They could also significantly prolong the survival of intraperitoneally tumor-bearing mice. More importantly, the potent antitumor effect and considerable NK cell infiltration were observed in the patient-derived xenograft treated with MSLN-CAR NK cells, which further warranted the therapeutic effects of MSLN-CAR NK cells to treat gastric cancer.

Conclusion: These results demonstrate that MSLN-CAR NK cells possess strong antitumor activity and represent a promising therapeutic approach to gastric cancer.

Hitting the Bull's-Eye: Mesothelin's Role as a Biomarker and Therapeutic Target for Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer with limited treatment options and poor prognosis. MPM originates from the mesothelial lining of the pleura. Mesothelin (MSLN) is a glycoprotein expressed at low levels in normal tissues and at high levels in MPM. Many other solid cancers overexpress MSLN, and this is associated with worse survival rates. However, this association has not been found in MPM, and the exact biological role of MSLN in MPM requires further exploration. Here, we discuss the current research on the diagnostic and prognostic value of MSLN in MPM patients. Furthermore, MSLN has become an attractive immunotherapy target in MPM, where better treatment strategies are urgently needed. Several MSLN-targeted monoclonal antibodies, antibody-drug conjugates, immunotoxins, cancer vaccines, and cellular therapies have been tested in the clinical setting. The biological rationale underpinning MSLN-targeted immunotherapies and their potential to improve MPM patient outcomes are reviewed.

Prevalence of mesothelin expression in peritoneal disease from colorectal and appendiceal cancers

BACKGROUND

Mesothelin is a cell surface glycoprotein overexpressed in 28%-58% of colorectal cancer (CRC). We hypothesized that CRC mesothelin expression contributes to peritoneal spread and that it is selectively overexpressed in those with peritoneal metastasis versus distant metastasis.

METHODS

This case-controlled study involved mesothelin immunohistochemistry staining of tumor specimens from patients with metastatic CRC/appendiceal cancers between 2017 and 2019. Staining reactivity was graded from trace to 4+ (low ≤1+; high >1+). Staining patterns were characterized on global (focal/patchy/diffuse) and cellular (apical/cytoplasmic) levels. Immunostaining of normal mesothelial cells served as internal control.

RESULTS

Thirty-one patients were identified: 11 peritoneal (study) and 20 distant metastasis (control). The control group did not include appendiceal cancers. The study group had greater proportion of high staining reactivity (55% vs. 5%; odds ratio [OR] = 20.4, 95% confidence interval [CI] 1.96-211.8). The study group had more diffuse (36% vs. 0%; OR = 22.2, 95% CI 1.1-465.3) and cytoplasmic staining patterns (73% vs. 28%; OR = 6.9, 95% CI 1.3-37.2).

CONCLUSION

Mesothelin expression is higher in CRC/appendiceal cancers with peritoneal metastasis than those with distant metastasis. Immunohistochemistry staining patterns suggestive of propensity towards peritoneal metastasis include diffuse and cytoplasmic staining. Mesothelin may be a potential target for novel treatments of CRC/appendiceal carcinoma with peritoneal involvement.

Immunotherapy-based targeting of MSLN+ activated portal fibroblasts is a strategy for treatment of cholestatic liver fibrosis

We investigated the role of mesothelin (Msln) and thymocyte differentiation antigen 1 (Thy1) in the activation of fibroblasts across multiple organs and demonstrated that Msln^-/- mice are protected from cholestatic fibrosis caused by Mdr2 (multidrug resistance gene 2) deficiency, bleomycin-induced lung fibrosis, and UUO (unilateral urinary obstruction)-induced kidney fibrosis. On the contrary, Thy1^-/- mice are more susceptible to fibrosis, suggesting that a Msln-Thy1 signaling complex is critical for tissue fibroblast activation. A similar mechanism was observed in human activated portal fibroblasts (aPFs). Targeting of human MSLN⁺ aPFs with two anti-MSLN immunotoxins killed fibroblasts engineered to express human mesothelin and reduced collagen deposition in livers of bile duct ligation (BDL)-injured mice. We provide evidence that antimesothelin-based therapy may be a strategy for treatment of parenchymal organ fibrosis.

Emerging biological therapies for the treatment of malignant pleural mesothelioma

Introduction: Malignant pleural mesothelioma (MPM) has limited treatment options with minimal new therapy approvals for unresectable disease in the past 15 years. However, considerable work has occurred to develop immunotherapies and biomarker driven therapy to improve patient outcomes over this period.Areas covered: This review examines current standard of care systemic therapy in the first- and second line setting. The last 12 months has seen 2 significant trials (Checkmate 743 and CONFIRM) which provide evidence supporting the role of immunotherapy in the management of MPM. Further trials are underway to assess the role of combination chemoimmunotherapy and personalized therapy. Additionally, a large number of clinical trials are ongoing to assess the efficacy of oncoviral, dendritic cell, anti-mesothelin and chimeric antigen receptor T cell therapy in the treatment of MPM.Expert opinion: Recent Phase III trial results have established a role for immunotherapy in the management of MPM. The optimal sequencing and combination of chemotherapy and immunotherapy remains to be determined. Novel therapies for MPM are promising however efficacy remains to be determined and issues remain regarding access to and delivery of these therapies.

In Vitro and In Vivo Comparison of 3,2-HOPO Versus Deferoxamine-Based Chelation of Zirconium-89 to the Antimesothelin Antibody Anetumab

Introduction: [²²⁷Th]Th-3,2-HOPO-MSLN-mAb, a mesothelin (MSLN)-targeted thorium-227 therapeutic conjugate, is currently in phase I clinical trial; however, direct PET imaging using this conjugate is technically challenging. Thus, using the same MSLN antibody, we synthesized 3,2-HOPO and deferoxamine (DFO)-based zirconium-89 antibody conjugates, [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb and [⁸⁹Zr]Zr-DFO-MSLN-mAb, respectively, and compared them in vitro and in vivo.

Methods: [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb and [⁸⁹Zr]Zr-DFO-MSLN-mAb were evaluated in vitro to determine binding affinity and immunoreactivity in HT29-MSLN and PDX (NCI-Meso16, NCI-Meso21) cells. For both the zirconium-89 conjugates, in vivo studies (biodistribution/imaging) were performed at days 1, 3, and 6, from which tissue uptake was determined.

Results: Both the conjugates demonstrated a low nanomolar binding affinity for MSLN and >95% immunoreactivity. In all the three tumor types, biodistribution of [⁸⁹Zr]Zr-DFO-MSLN-mAb resulted in higher tumor uptake(15.88-28-33%ID/g) at all time points compared with [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb(7–13.07%ID/g). [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb femur uptake was always higher than [⁸⁹Zr]Zr-DFO-MSLN-mAb, and imaging results concurred with the biodistribution studies.

Conclusions: Even though the conjugates exhibited a high binding affinity for MSLN, [⁸⁹Zr]Zr-DFO-MSLN-mAb showed a higher tumor and lower femur uptake than [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb. Nevertheless, [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb could be used to study organ distribution and lesion uptake with the caveat of detecting MSLN-positive bone lesions. Clinical trial (NCT03507452).

Mesothelin Expression in Human Tumors: A Tissue Microarray Study on 12,679 Tumors

Mesothelin (MSLN) represents an attractive molecule for targeted cancer therapies. To identify tumors that might benefit from such therapies, tissue microarrays including 15,050 tumors from 122 different tumor types and 76 healthy organs were analyzed for MSLN expression by immunohistochemistry. Sixty-six (54%) tumor types showed at least occasional weak staining, including 50 (41%) tumor types with at least one strongly positive sample. Highest prevalence of MSLN positivity had ovarian carcinomas (serous 97%, clear cell 83%, endometrioid 77%, mucinous 71%, carcinosarcoma 65%), pancreatic adenocarcinoma (ductal 75%, ampullary 81%), endometrial carcinomas (clear cell 71%, serous 57%, carcinosarcoma 50%, endometrioid 45%), malignant mesothelioma (69%), and adenocarcinoma of the lung (55%). MSLN was rare in cancers of the breast (7% of 1138), kidney (7% of 807), thyroid gland (1% of 638), soft tissues (0.3% of 931), and prostate (0 of 481). High expression was linked to advanced pathological tumor (pT) stage (p < 0.0001) and metastasis (p < 0.0001) in 1619 colorectal adenocarcinomas, but unrelated to parameters of malignancy in 1072 breast-, 386 ovarian-, 174 lung-, 757 kidney-, 171 endometrial-, 373 gastric-, and 925 bladder carcinomas. In summary, numerous important cancer types with high-level MSLN expression might benefit from future anti-MSLN therapies, but MSLN’s prognostic relevance appears to be limited.

Malignant mesothelioma: Advances in immune checkpoint inhibitor and mesothelin-targeted therapies

Malignant mesothelioma is an aggressive cancer with a poor prognosis and limited treatment options. For many years, the only US Food and Drug Administration-approved first-line treatment for unresectable mesothelioma was pemetrexed plus cisplatin. However, the recent approval of nivolumab plus ipilimumab as frontline treatment for patients with pleural mesothelioma marks a significant milestone for the treatment of this disease. In this review, the authors describe recent advances in therapeutic strategies for the treatment of patients with advanced, unresectable mesothelioma, highlighting the emerging use of immunotherapy and mesothelin-targeted therapies for the management of malignant mesothelioma.

Chemokine Receptor CCR2b Enhanced Anti-tumor Function of Chimeric Antigen Receptor T Cells Targeting Mesothelin in a Non-small-cell Lung Carcinoma Model

Chimeric antigen receptor (CAR) T cell therapy faces a number of challenges for the treatment of non-small-cell lung carcinoma (NSCLC), and efficient migration of circulating CAR T cells plays an important role in anti-tumor activity. In this study, a CAR specific for tumor antigen mesothelin (Msln-CAR) was co-expressed with cell chemokine receptors CCR2b or CCR4. Findings showed that CCR2b and CCR4 enhanced the migration of Msln-CAR T cell in vitro by transwell assay. When incubated with mesothelin-positive tumor cells, Msln-CCR2b-CAR and Msln-CCR4-CAR T cell specifically exerted potent cytotoxicity and produced high levels of proinflammatory cytokines, including IL-2, IFN-γ, and TNF-α. Furthermore, NSCLC cell line-derived xenograft (CDX) model was constructed by implanting subcutaneously modified A549 into NSG mice. Compared to conventional Msln-CAR T cells, living imaging indicated that Msln-CCR2b-CAR T cells displayed superior anti-tumor function due to enhanced migration and infiltration into tumor tissue shown by immunohistochemistry (IHC) analysis. In addition, histopathological examinations of mice organs showed that no obvious organic damages were observed. This is the first time that CAR T cell therapy combined with chemokine receptor is applied to NSCLC treatment.