TREM1/Dap12-based CAR-T cells show potent antitumor activity

Aim: Chimeric antigen receptor-engineered T (CAR-T) cells have gained huge success in treating hematological malignancies, yet the CD3ζ-based CAR-T therapies have not shown comparable clinical benefits in solid tumors. We designed an alternative chimeric immunoreceptor in which a single-chain variable fragment was fused to the transmembrane-cytoplasmic domains of triggering receptor expressed on myeloid (TREM1), which may show potent antitumor activity. Methods: To generate TREM1/DNAX activation protein of 12 kDa (Dap12)-based CAR-T cells, TREM1 along with DAP12 was transduced into T cells. Results: TREM1/Dap12-based CAR-T cells showed more lysis in vitro and a similar antitumor effect in mouse models compared with CD19BBζ CAR-T cells. Conclusion: In this study, we designed a TREM1/Dap12-based CAR, which was not reported previously and demonstrated that TREM1/Dap12-based CAR-T cells had potent antitumor activity in vitro and in vivo.

Mesothelin expression and its prognostic role according to microsatellite instability status in colorectal adenocarcinoma

The cell-surface glycoprotein, mesothelin, is normally present on mesothelial cells. Overexpression of mesothelin has been reported in many tumors and is correlated with poor outcome. We investigated the clinicopathologic significance of mesothelin expression in colorectal adenocarcinoma with microsatellites instability (MSI) status.Mesothelin expression was evaluated immunohistochemically in tissue microarray blocks from 390 colorectal adenocarcinoma samples. Mesothelin expression was interpreted according to the intensity and extent. A score of 2 was considered high expression. We analyzed the correlation between mesothelin expression and clinicopathologic characteristics.High mesothelin expression was observed in 177 (45.4%) out of 390 colorectal adenocarcinoma samples and was significantly associated with high histologic grade (P = .037), lymphatic invasion (P = .028), lymph node metastasis (P = .028), and high AJCC stage (P = .026). Kaplan-Meier survival curves revealed no significant difference between patients with high mesothelin expression and patients with low mesothelin expression in both recurrence-free survival (RFS) and cancer-specific survival (P = .609 and P = .167, respectively). In subgroup survival analyses, high mesothelin expression was associated with poor RFS in the MSI-High group of colorectal adenocarcinoma (P = .004).High mesothelin expression was significantly associated with aggressive phenotypes and poor patient outcome in MSI-High colorectal adenocarcinoma.

Diagnostic value of soluble mesothelin-related peptides in pleural effusion for malignant pleural mesothelioma: An updated meta-analysis

BACKGROUND

Soluble mesothelin-related peptide (SMRP) is a widely studied tumor marker for diagnosing malignant pleural mesothelioma (MPM). This study discussed the diagnostic value of SMRPs in pleural effusion (PE) for MPM.

METHODS

Medline, Embase, Web of Science, and Cochrane library system were systematically searched on the data of SMRPs in PE for MPM diagnosis. Pooled diagnostic sensitivity, specificity, and symmetric receiver operating characteristic curve were calculated.

RESULTS

Thirteen studies fulfilled the inclusion criteria and a total of 3359 cases including 759 MPM cases, 1061 non-MM (malignant mesothelioma) malignant PE, and 1539 benign PE were brought into this meta-analysis. The pooled results of SMRPs in PE for diagnosing MPM were as follows: sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio were 0.68 (95% confidence interval [CI]: 0.64-0.72), 0.91 (95% CI: 0.86-0.94), 7.8 (95% CI: 5.0-12.0), 0.35 (95% CI: 0.31-0.40), and 22 (95% CI: 14-35), respectively. The area under the summary receiver operating characteristic curves (AUC) was 0.75 (95% CI: 0.72-0.80). Subgroup analyzes revealed that the AUC of cohort group using histological diagnosis could be improved to 0.86 (95% CI: 0.83, 0.89). The Deek's funnel plot asymmetry test showed no publication bias.

CONCLUSION

Although the sensitivity of SMRPs was low, PE-SMRPs can be a good indicator of the existence of MPM.

Mesothelin-targeted second generation CAR-T cells inhibit growth of mesothelin-expressing tumors in vivo

Non-small cell lung cancer (NSCLC) and mesothelioma are renowned for being diagnosed at a late stage and poor prognosis. Although surgery, chemotherapy, and radiotherapy have yielded successful outcomes, the improvement on the survival rate of NSCLC and mesothelioma have been less marked. Recently, adoptive immunotherapy, particularly chimeric antigen receptor T (CAR-T) cell therapy demonstrated promise for improving the survival of acute lymphoblastic leukemia with minimum toxicity. However, its application in solid tumors still warrants in-depth investigations and multiple consistent trial results, particularly in eliminating 'off-tumor' toxicity. To explore CAR-T therapy in NSCLC and mesothelioma, second-generation CAR-T cells were constructed targeting mesothelin (MSLN), which is abundant in NSCLC and mesothelioma but is under expressed in normal tissues. The second-generation design incorporated co-stimulatory CD28 and 4-1BB signaling domains to enhance the proliferation. Following the successful analysis of CAR-T cells by flow cytometry, cytotoxicity experiments were performed using the LDH kit to verify the killing effect of CAR-T cells on target cells. Otherwise, the in vivo killing tumor activity of MSLN CAR-T cells was verified by constructing a mouse model using tumor-derived cells from patients to inoculate the mice. When the effector-to-target ratio is >0.5:1, CAR-T MSLN cells exhibited significantly higher ability to kill tumor cells than T cells. In in vivo experiments, mice whose tail vein was injected with CAR-T MSLN cells demonstrated significantly slower tumor growth. Without continuous administration, both groups became gradually synchronized in growth of tumor size, which suggests that the persistence of CAR-T cells is an important issue in preclinical studies.

SS1P Immunotoxin Induces Markers of Immunogenic Cell Death and Enhances the Effect of the CTLA-4 Blockade in AE17M Mouse Mesothelioma Tumors

SS1P is an anti-mesothelin immunotoxin composed of a targeting antibody fragment genetically fused to a truncated fragment of Pseudomonas exotoxin A. Delayed responses reported in mesothelioma patients receiving SS1P suggest that anti-tumor immunity is induced. The goal of this study is to evaluate if SS1P therapy renders mesothelioma tumors more sensitive to cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) immune checkpoint blockade. We evaluated the ability of SS1P to induce adenosine triphosphate (ATP) secretion and calreticulin expression on the surface of AE17M mouse mesothelioma cells. Both properties are associated with immunogenic cell death. Furthermore, we treated these tumors with intra-tumoral SS1P and systemic CTLA-4. We found that SS1P increased the release of ATP from AE17M cells in a dose and time-dependent manner. In addition, SS1P induced calreticulin expression on the surface of AE17M cells. These results suggest that SS1P promotes immunogenic cell death and could sensitize tumors to anti-CTLA-4 based therapy. In mouse studies, we found that the combination of anti-CTLA-4 with intra-tumoral SS1P induced complete regressions in most mice and provided a statistically significant survival benefit compared to monotherapy. The surviving mice were protected from tumor re-challenge, indicating the development of anti-tumor immunity. These findings support the use of intra-tumoral SS1P in combination with anti-CTLA-4.

DNAX-activating protein 10 co-stimulation enhances the anti-tumor efficacy of chimeric antigen receptor T cells

Chimeric antigen receptor (CAR) T cell immunotherapies have shown remarkable efficacy in treating multiple types of hematological malignancies but are not sufficiently effective at treating solid tumors. NKG2D is a strong activating receptor for NK cells and a co-stimulatory receptor for T cells. NKG2D signal transduction depends on DNAX-activating protein 10 (DAP10). Here, we introduced the cytoplasmic domain of DAP10 into the second-generation CARs M28z and G28z to generate M28z10 and G28z10, which target mesothelin (MSLN) and glypican 3 (GPC3), respectively. T cells expressing M28z10 or G28z10 showed enhanced and prolonged effector function against MSLN+ lung cancer or GPC3+ hepatocellular carcinoma cell lines in culture and secreted elevated levels of cytokines, including IL-2, IFN-γ, granzyme B, and GM-CSF. In addition, M28z10 CAR-T cells showed greater anti-tumor activity than those expressing M28z in both A549 cell line xenografts and human lung cancer patient-derived xenografts (PDX). Similarly, G28z10 exhibited higher efficacy in causing tumor regression than did G28z in hepatocellular carcinoma PDX. Therefore, our results show that DAP10 signaling contributes to the function of CAR-T cells in both lung cancer and hepatocellular carcinoma and can enhance the efficacy of CAR-T cells.

Anetumab ravtansine inhibits tumor growth and shows additive effect in combination with targeted agents and chemotherapy in mesothelin-expressing human ovarian cancer models

Despite the recent advances in the treatment of ovarian cancer, it remains an area of high unmet medical need. Epithelial ovarian cancer is associated with high levels of mesothelin expression, and therefore, mesothelin is an attractive candidate target for the treatment of this disease. Herein, we investigated the antitumor efficacy of the mesothelin-targeting antibody-drug conjugate (ADC) anetumab ravtansine as a novel treatment option for ovarian cancer in monotherapy and in combination with the antitumor agents pegylated liposomal doxorubicin (PLD), carboplatin, copanlisib and bevacizumab. Anetumab ravtansine showed potent antitumor activity as a monotherapy in ovarian cancer models with high mesothelin expression. No activity was seen in mesothelin-negative models. The combination of anetumab ravtansine with PLD showed additive anti-proliferative activity in vitro, which translated into improved therapeutic in vivo efficacy in ovarian cancer cell line- and patient-derived xenograft (PDX) models compared to either agents as a monotherapy. The combination of anetumab ravtansine with the PI3Kα/δ inhibitor copanlisib was additive in the OVCAR-3 and OVCAR-8 cell lines in vitro, showing increased apoptosis in response to the combination treatment. In vivo, the combination of anetumab ravtansine with copanlisib resulted in more potent antitumor activity than either of the treatments alone. Likewise, the combination of anetumab ravtansine with carboplatin or bevacizumab showed improved in vivo efficacy in the ST081 and OVCAR-3 models, respectively. All combinations were well-tolerated. Taken together, these data support the development of anetumab ravtansine for ovarian cancer treatment and highlight its suitability for combination therapy with PLD, carboplatin, copanlisib, or bevacizumab.

The Potential of CAR T Cell Therapy in Pancreatic Cancer

Pancreatic cancer has a dismal prognosis and effective treatment options are limited. It is projected to be the second most common cause of cancer related mortality in the United States by 2030 and there is urgent unmet need for novel systemic treatment options. Immunotherapy with antibodies targeting PD-1, PD-L1, CTLA-4 has not shown clinical activity in unselected pancreatic cancer, emphasizing the need for combination immunotherapy approaches or other therapeutic strategies. As such, chimeric antigen receptor (CAR) T cell therapy represents an emerging therapeutic option for pancreatic cancer. This modality utilizes genetically engineered T cells that are redirected to specific cancer-associated antigens to elicit potent cytotoxic activity. This review summarizes the available preclinical data and highlights early phase clinical trials using CAR T cell approaches in pancreatic cancer, a disease state that is gaining attention as a conduit for cell therapy. Future directions in application of CAR T cell therapy are also considered including its ability to be directed against novel epitopes and combined with other therapeutic regimens.

The anti-mesothelin monoclonal antibody amatuximab enhances the anti-tumor effect of gemcitabine against mesothelin-high expressing pancreatic cancer cells in a peritoneal metastasis mouse model

Pancreatic cancer often has a very poor prognosis, even after complete resection. The recurrence of hepatic and peritoneal metastases is an important prognostic factor; therefore, the development of improved adjuvant therapy is urgently required. Mesothelin is a cell surface glycoprotein whose expression is restricted to a variety of cancer types, including pancreatic cancer. This expression pattern makes mesothelin an attractive target for cancer therapy, and several agents targeting mesothelin are currently in clinical trials. Here, we used the chimerized high-affinity anti-mesothelin monoclonal antibody amatuximab to investigate its effect on peritoneal metastasis. We used the AsPC-1 pancreatic cancer cell line engineered to express Gaussia luciferase (Gluc), (AsPC-1-Gluc) for in vivo experiments. Results showed that while amatuximab was not directly cytotoxic on an AsPC-1-Gluc tumor cells in a peritoneal metastasis model, it prevented the formation of tumor growth. In combination therapy with gemcitabine, amatuximab exhibited synergistic killing. Our results suggest that blockade of mesothelin by amatuximab may be a useful strategy for preventing the peritoneal dissemination of pancreatic cancer under an adjuvant setting.

Nuclear grading, BAP1, mesothelin and PD-L1 expression in malignant pleural mesothelioma: prognostic implications

For malignant pleural mesothelioma (MPM), histopathological subtype is one of the most important prognostic factors. Several immunohistochemical stains whose expressions have possible therapeutic implications have been identified in MPM such as BAP1, mesothelin and PD-L1. The aim of our work was to evaluate the clinical significance and prognostic implications of BAP1, mesothelin and PD-L1 expression in 117 patients with a diagnosis of MPM who were diagnosed in our institution between 2002 and 2017. We also correlated this immunohistochemical profile to a recently described nuclear grading and to histopathological subtype. Mesothelin expression, BAP1 loss and PD-L1 expression were associated with histopathological subtype (p < 0.0001), BAP1 loss was more frequent in epithelioid subtype whereas PD-L1 expression was more frequent in non-epithelioid subtype. For epithelioid MPM, BAP1 expression was associated with overall survival (p = 0.034), with a longer survival when BAP1 expression is lost. Necrosis and nuclear grading are associated with overall survival (p = 0.0048 and <0.0001, respectively), with longer survival when necrosis was absent and for grade I. For non-epithelioid MPM, overall survival was not related to clinical, histopathological or immunohistochemical expression of BAP1, mesothelin or PD-L1. In multivariate analysis, grade I for nuclear grading was an independent prognostic factor associated with overall survival (p < 0.0001). In epithelioid and non-epithelioid MPM, we analysed overall survival in subgroups with combined mesothelin, BAP1 and PD-L1 expression. In epithelioid MPM, BAP1 retained/mesothelin negativity/PD-L1 > 1%, and BAP1 retained/mesothelin positivity/PD-L1 > 1% profiles, are associated with shorter overall survival. In non-epithelioid MPM, BAP1 loss/mesothelin negativity/PD-L1 > 1% is associated with shorter overall survival. Our work confirms that nuclear grading in epithelioid MPM is a strong and independent prognosis factor. Moreover, this study on several promising immunohistochemical stains whose expressions have possible therapeutic implications identifies subgroups with a poor prognosis.

The Impact of Mesothelin in the Ovarian Cancer Tumor Microenvironment

Ovarian cancer is the deadliest gynecological disease among U.S. women. Poor 5-year survival rates (<30%) are due to presentation of most women at diagnosis with advanced stage disease with widely disseminated intraperitoneal metastasis. However, when diagnosed before metastatic propagation the overall 5-year survival rate is >90%. Metastasizing tumor cells grow rapidly and aggressively attach to the mesothelium of all organs within the peritoneal cavity, including the parietal peritoneum and the omentum, producing secondary lesions. In this review, the involvement of mesothelin (MSLN) in the tumor microenvironment is discussed. MSLN, a 40kDa glycoprotein that is overexpressed in many cancers including ovarian and mesotheliomas is suggested to play a role in cell survival, proliferation, tumor progression, and adherence. However, the biological function of MSLN is not fully understood as MSLN knockout mice do not present with an abnormal phenotype. Conversely, MSLN has been shown to bind to the ovarian cancer antigen, CA-125, and thought to play a role in the peritoneal diffusion of ovarian tumor cells. Although the cancer-specific expression of MSLN makes it a potential therapeutic target, more studies are needed to validate the role of MSLN in tumor metastasis.

Identification of a novel HLA-A24-restricted cytotoxic T lymphocyte epitope peptide derived from mesothelin in pancreatic cancer

Pancreatic cancer involves highly malignant tumors, and the development of new therapeutic strategies is critical. Mesothelin is overexpressed in infiltrating pancreatic cancer cells and plays an important role in the invasion and migration processes. In this study, we focused on mesothelin as a tumor-specific antigen target for a pancreatic cancer vaccine. We first investigated the mesothelin-derived epitope peptide restricted to HLA-A^*2402. A total of 19 candidate peptides were synthesized, and we then determined their potential to induce peptide-specific cytotoxic T lymphocytes (CTLs). Peptide-specific CTLs were induced by five peptides derived from mesothelin, and these CTLs successfully exhibited peptide-specific IFN-γ production. After the expansion of each CTL, two CTL lines were established, which were induced by mesothelin-10-5 peptide (AFYPGYLCSL). These CTL lines exhibited peptide-specific cytotoxicity and IFN-γ production. Moreover, we were able to generate mesothelin-10-5 peptide-specific CTL clones. These CTL clones also had specific cytotoxic activity against HLA-A^*2402-positive pancreatic cancer cells that endogenously expressed mesothelin. These results indicate that the mesothelin-10-5 peptide is a novel HLA-A^*2402 restricted CTL epitope and that it is a promising candidate target for antigen-specific immunotherapy against pancreatic cancers.

Antitumor-specific T-cell responses induced by oncolytic adenovirus ONCOS-102 (AdV5/3-D24-GM-CSF) in peritoneal mesothelioma mouse model

Oncolytic adenoviral immunotherapy activates the innate immune system with subsequent induction of adaptive tumor‐specific immune responses to fight cancer. Hence, oncolytic viruses do not only eradicate cancer cells by direct lysis, but also generate antitumor immune response, allowing for long‐lasting cancer control and tumor reduction. Their therapeutic effect can be further enhanced by arming the oncolytic adenovirus with costimulatory transgenes and/or coadministration with other antitumor therapies. ONCOS‐102 has already been found to be well tolerated and efficacious against some types of treatment‐refractory tumors, including mesothelin‐positive ovarian cancer (NCT01598129). It induced local and systemic CD8+ T‐cell immunity and upregulated programmed death ligand 1. These results strongly advocate the use of ONCOS‐102 in combination with other therapeutic strategies in advanced and refractory tumors, especially those expressing the mesothelin antigen. The in vivo work presented herein describes the ability of the oncolytic adenovirus ONCOS‐102 to induce mesothelin‐specific T‐cells after the administration of the virus in bagg albino (BALB/c) mice with mesothelin‐positive tumors. We also demonstrate the effectiveness of the interferon‐γ the enzyme‐linked immunospot (ELISPOT) assay to detect the induction of T‐cells recognizing mesothelin, hexon, and E1A antigens in ONCOS‐102‐treated mesothelioma‐bearing BALB/c mice. Thus, the ELISPOT assay could be useful to monitor the progress of therapy with ONCOS‐102.

Prediction of improved survival in patients with pancreatic cancer via IL-21 enhanced detection of mesothelin epitope-reactive T-cell responses

Most patients with pancreatic cancer present with extensive metastasis at diagnosis, with a 5-year survival rate of approximately 5%, despite chemotherapy and surgery. New treatment modalities are needed to improve survival. Mesothelin is a tumor-associated antigen (TAA) in patients with pancreatic cancer that could be used to gauge cellular immune responses directed against transformed cells since up to 100 percent of pancreatic ductal adenocarcinoma cells have been shown to strongly express mesothelin. A prospective, observational study was carried out in twenty-six, chemotherapy-naïve patients with resectable pancreatic ductal adenocarcinoma. Participants were between 48 and 81 years (median age: 64.5 years), 15 males and 11 females. All participants were clinically followed-up between 439 and 853 days post-surgery (n=14) or until death (n=12). Peripheral blood drawn on the day of surgery was stimulated with a mesothelin peptide pool (42 peptides, non-overlapping), individual mesothelin peptides, positive (anti-CD3 antibody, OKT3) and negative controls (medium) with or without adding IL-21. Kaplan-Meier estimators were used to gauge patients’ survival pattern in relation to mesothelin-specific IFN-γ responses. A survival benefit was linked with IFN-γ responses to peptides corresponding to mature mesothelin (p=0.018) and targeted recognition of the mesothelin_601-615 epitope (MQEALSGTPCLLGPG) (p=0.006) in the presence of IL-21. Conversely, production of high levels of IFN-γ to OKT3 stimulation with IL-21 conditioning was associated with reduced survival of patients (p=0.016). Gauging anti-Mesothelin- directed immune responses will aid to identify patients i) in need of a more intensive clinical follow-up and ii) who may benefit from immunotherapeutic approaches targeting mesothelin.

CA125 suppresses amatuximab immune-effector function and elevated serum levels are associated with reduced clinical response in first line mesothelioma patients

The tumor-shed antigen CA125 has recently been found to bind certain monoclonal antibodies (mAbs) and suppress immune-effector mediated killing through perturbation of the Fc domain with CD16a and CD32a Fc-γ activating receptors on immune-effector cells. Amatuximab is a mAb targeting mesothelin whose mechanism of action utilizes in part antibody-dependent cellular cytotoxicity (ADCC). It is being tested for its therapeutic activity in patients with mesothelioma in combination with first line standard-of-care. To determine if CA125 has immunosuppressive effects on amatuximab ADCC and associated clinical outcomes, post hoc subgroup analysis of patients from a Phase 2 study with primary diagnosed stage III/IV unresectable mesothelioma treated with amatuximab plus cisplatin and pemetrexed were conducted. Analysis found patients with baseline CA125 levels no greater than 57 U/m (∼3X the upper limit of normal) had a 2 month improvement in progression free survival (HR = 0.43, p = 0.0062) and a 7 month improvement in overall survival (HR = 0.40, p = 0.0022) as compared to those with CA125 above 57 U/mL. In vitro studies found that CA125 was able to bind amatuximab and perturb ADCC activity via decreased Fc-γ-receptor engagement. These data suggest that clinical trial designs of antibody-based drugs in cancers producing CA125, including mesothelioma, should consider stratifying patients on baseline CA125 levels for mAbs that are experimentally determined to be bound by CA125.

Development of Anti-Human Mesothelin-Targeted Chimeric Antigen Receptor Messenger RNA-Transfected Peripheral Blood Lymphocytes for Ovarian Cancer Therapy

CD19-targeted chimeric antigen receptor (CAR) engineered T/natural killer (NK)-cell therapies can result in durable clinical responses in B-cell malignancies. However, CAR-based immunotherapies have been much less successful in solid cancers, in part due to "on-target off-tumor" toxicity related to expression of target tumor antigens on normal tissue. Based on preliminary observations of safety and clinical activity in proof-of-concept clinical trials, tumor antigen-specific messenger RNA (mRNA) CAR transfection into selected, activated, and expanded T/NK cells may permit prospective control of "on-target off-tumor" toxicity. To develop a commercial product for solid tumors, mesothelin was selected as an antigen target based on its association with poor prognosis and overexpression in multiple solid cancers. It was hypothesized that selecting, activating, and expanding cells ex vivo prior to mRNA CAR transfection would not be necessary, thus simplifying the complexity and cost of manufacturing. Now, the development of anti-human mesothelin mRNA CAR transfected peripheral blood lymphocytes (CARMA-hMeso) is reported, demonstrating the manufacture and cryopreservation of multiple cell aliquots for repeat administrations from a single human leukapheresis. A rapid, automated, closed system for cGMP-compliant transfection of mRNA CAR in up to 20 × 10⁹ peripheral blood lymphocytes was developed. Here we show that CARMA-hMeso cells recognize and lyse tumor cells in a mesothelin-specific manner. Expression of CAR was detectable over approximately 7 days in vitro, with a progressive decline of CAR expression that appears to correlate with in vitro cell expansion. In a murine ovarian cancer model, a single intraperitoneal injection of CARMA-hMeso resulted in the dose-dependent inhibition of tumor growth and improved survival of mice. Furthermore, repeat weekly intraperitoneal administrations of the optimal CARMA-hMeso dose further prolonged disease control and survival. No significant off-target toxicities were observed. These data support further investigation of CARMA-hMeso as a potential treatment for ovarian cancer and other mesothelin-expressing cancers.

Recombinant immunotoxins with albumin-binding domains have long half-lives and high antitumor activity

Recombinant immunotoxins (RITs) are chimeric proteins consisting of a Fv that binds to a cancer cell and a portion of a protein toxin. One of these, Moxetumomab pasudotox, was shown to be effective in treating patients with some leukemias, where the cells are readily accessible to the RIT. However, their short half-life limits their efficacy in solid tumors, because penetration into the tumors is slow. Albumin and agents bound to albumin have a long half-life in the circulation. To increase the time tumor cells are exposed to RITs, we have produced and evaluated variants that contain either an albumin-binding domain (ABD) from Streptococcus or single-domain antibodies from Llama. We have inserted these ABDs into RITs targeting mesothelin, between the Fv and the furin cleavage site. We find that these proteins can be produced in large amounts, are very cytotoxic to mesothelin-expressing cancer cell lines, and have a high affinity for human or mouse serum albumin. In mice, the RIT containing an ABD from Streptococcus has a longer half-life and higher antitumor activity than the other two. Its half-life in the circulation of mice ranges from 113 to 194 min compared with 13 min for an RIT with no ABD. Cell uptake studies show the RIT enters the target cell bound to serum albumin. We conclude that RITs with improved half-lives and antitumor activity should be evaluated for the treatment of cancer in humans.

Preclinical Evaluation of Mesothelin-Specific Ligands for SPECT Imaging of Triple-Negative Breast Cancer

Mesothelin is a cell-surface glycoprotein restricted to mesothelial cells overexpressed in several types of cancer, including triple-negative breast cancer not responding to trastuzumab or hormone-based therapies. Mesothelin-targeting therapies are currently being developed. However, the identification of patients potentially eligible for such a therapeutic strategy remains challenging. The objective of this study was to perform the radiolabeling and preclinical evaluation of ^99mTc-A1 and ^99mTc-C6, two antimesothelin single-domain antibody (sdAb)-derived imaging agents. Methods: A1 and C6 were radiolabeled with ^99mTc and evaluated in vitro on recombinant protein and cells, as well as in vivo in xenograft mouse models of the triple-negative breast cancer cell lines HCC70 (mesothelin-positive) and MDA-MB-231 (mesothelin-negative). Results: Both ^99mTc-A1 and ^99mTc-C6 bound mesothelin with high affinity in vitro, with ^99mTc-A1 affinity being 2.4-fold higher than that of ^99mTc-C6 (dissociation constant, 43.9 ± 4.0 vs. 107 ± 16 nM, P < 0.05). ^99mTc-A1 and ^99mTc-C6 remained stable in vivo in murine blood (>80% at 2 h) and ex vivo in human blood (>90% at 6 h). In vivo ^99mTc-A1 uptake (percentage injected dose) in HCC70 tumors was 5-fold higher than in MDA-MB-231 tumors and 1.5-fold higher than that of ^99mTc-C6 (2.34% ± 0.36% vs. 0.48% ± 0.18% and 1.56% ± 0.43%, respectively, P < 0.01) and resulted in elevated tumor-to-background ratios. In vivo competition experiments demonstrated the specificity of ^99mTc-A1 uptake in HCC70 tumors. Conclusion: Mesothelin-positive tumors were successfully identified by SPECT using ^99mTc-A1 and ^99mTc-C6. Considering its superior characteristics, ^99mTc-A1 was selected as the most suitable tool for further clinical translation.

Mesothelin-targeted immunotoxin RG7787 has synergistic anti-tumor activity when combined with taxanes

Recombinant immunotoxins (RITs) are antibody-based therapeutics that carry a toxin payload. The RG7787 RIT targets the cancer antigen mesothelin to deliver a recombinantly-engineered, reduced immunogenicity variant of Pseudomonas exotoxin A (PE) to the cytosol where it inhibits protein synthesis. Here we demonstrate that maximal doses of RG7787 temporarily halt growth of pancreatic cancer tumor xenografts, similar to the approved drugs gemcitabine and nab-paclitaxel, however, combination of the RIT with nab-paclitaxel produces durable complete regressions in most mice. Synergy between taxane and anti-MSLN RITs has been previously demonstrated in mouse models, but direct interaction of the combination in cell culture was not observed. Here, we show that this favorable interaction occurs in cell culture, is dependent on the dose and duration of RG7787 exposure, requires the catalytically active PE, and still occurs with RIT targeting a non-MSLN surface antigen. Unexpectedly, the combination does not increase RG7787-mediated protein synthesis inhibition nor perturb downstream apoptotic markers of RIT-mediated killing, but does augment levels of acetylated tubulin, a marker of taxane activity. Taken together, these data suggest that PE increases cell sensitivity to taxane-mediated killing by increasing taxane-mediated microtubule stability and priming cells for apoptosis by decreasing levels of the pro-survival factor Mcl-1.

Near infrared photoimmunotherapy with an anti-mesothelin antibody

Near Infrared-Photoimmunotherapy (NIR-PIT) is a new, highly selective tumor treatment that employs an antibody-photon absorber conjugate (APC). When the APC attaches to its target cell and is exposed to NIR light, highly selective cell killing is observed. NIR-PIT has been demonstrated with a limited number of antibodies. Mesothelin is overexpressed in several malignancies and is emerging as a therapeutic target. A recently humanized antibody (hYP218) has been generated against mesothelin that demonstrates high affinity binding. Here, we describe the efficacy of NIR-PIT, using hYP218 as the antibody within the APC to target a mesothelin expressing A431/H9 cell. The hYP218 antibody was conjugated to a photo-absorber, IR700 and incubated with the cells. The hYP218-IR700 showed specific binding to cells and cell-specific killing was observed in vitro. After implanting A431/H9 cells in an athymic nude mouse, tumor-bearing mice were treated with the following regimen of NIR-PIT; 100 μg of hYP218-IR700 i.v., NIR light was administered at 50 J/cm2 on day 1 after injection and 100 J/cm2 of light on day 2 after injection. The hYP218-IR700 showed high tumor accumulation and a high tumor-background ratio (TBR). Tumor growth was significantly inhibited by NIR-PIT treatment compared with the other control groups (p < 0.001), and significantly prolonged survival (p < 0.0001 vs other groups). Thus, the new anti-mesothelin antibody, hYP218, is suitable as an antibody-drug conjugate for NIR-PIT. Furthermore, NIR-PIT with hYP218-IR700 is a promising candidate for the treatment of mesothelin-expressing tumors that could be readily translated to humans.

Engineered T lymphocytes eliminate lung metastases in models of pancreatic cancer

Pancreatic cancer is known as one of the most lethal cancers in the world. A majority of advanced stage pancreatic cancer patients are diagnosed with distant metastasis and given poor prognoses, calling for a better therapeutic option. Mesothelin, which is overexpressed in pancreatic cancer and other solid tumors, is a potential target for pancreatic cancer immunotherapy. Adoptive transfer of T cells engineered with chimeric antigen receptors (CART cells) was effective for treating CD19-positive leukemia, but it is more difficult for CART cells to eliminate solid tumors. Because distal metastasis is an important malignant behavior of solid tumors, we investigated whether meso-CART cells exert anti-tumor effects against distant metastases. After expressing meso-CAR in human primary T lymphocytes, the resultant meso-CART cells released cytokines in response to and exhibited cytolytic effects on mesothelin-positive tumor cells in vitro. Injection of meso-CART cells into tumor-bearing mice moderately delayed subcutaneous tumor growth and eliminated lung metastases. This is the first study to show that meso-CART cells are effective against lung metastases induced by intravenous injection of pancreatic tumor cells. Our results suggest that meso-CART cells may be an effective clinical treatment for mesothelin-positive primary and metastatic tumors in pancreatic cancer patients.

Tolerogenic nanoparticles restore the antitumor activity of recombinant immunotoxins by mitigating immunogenicity

Protein-based drugs are very active in treating cancer, but their efficacy can be limited by the formation of neutralizing antidrug antibodies (ADAs). Recombinant immunotoxins are proteins that are very effective in patients with leukemia, where immunity is suppressed, but induce ADAs, which compromise their activity, in patients with intact immunity. Here we induced a specific, durable, and transferable immune tolerance to recombinant immunotoxins by combining them with nanoparticles containing rapamycin (SVP-R). SVP-R mitigated the formation of inhibitory ADAs in naïve and sensitized mice, resulting in restoration of antitumor activity. The immune tolerance is mediated by colocalization of the SVP-R and immunotoxin to dendritic cells and macrophages in the spleen and is abrogated by depletion of regulatory T cells. Tolerance induced by SVPs was not blocked by checkpoint inhibitors or costimulatory agonist monoclonal antibodies that by themselves enhance ADA formation.

Biomarkers for Predicting Malignant Pleural Mesothelioma in a Mexican Population

Background: Diagnosis of malignant pleural mesothelioma (MPM) remains a challenge, especially when resources in pathology are limited. The study aimed to evaluate cost-effective tumor markers to predict the probability of MPM in plasma samples in order to accelerate the diagnostic workup of the tissue of potential cases. Methods: We conducted a case-control study stratified by gender, which included 75 incident cases with MPM from three Mexican hospitals and 240 controls frequency-matched by age and year of blood drawing. Plasma samples were obtained to determine mesothelin, calretinin, and thrombomodulin using enzyme-linked immunosorbent assays (ELISAs). We estimated the performance of the markers based on the area under the curve (AUC) and predicted the probability of an MPM diagnosis of a potential case based on the marker concentrations. Results: Mesothelin and calretinin, but not thrombomodulin were significant predictors of a diagnosis of MPM with AUCs of 0.90 (95% CI: 0.85-0.95), 0.88 (95% CI: 0.82-0.94), and 0.51 (95% CI: 0.41-0.61) in males, respectively. For MPM diagnosis in men we estimated a true positive rate of 0.79 and a false positive rate of 0.11 for mesothelin. The corresponding figures for calretinin were 0.81 and 0.18, and for both markers combined 0.84 and 0.11, respectively. Conclusions: We developed prediction models based on plasma concentrations of mesothelin and calretinin to estimate the probability of an MPM diagnosis. Both markers showed a good performance and could be used to accelerate the diagnostic workup of tissue samples in Mexico.

Biomarkers in the diagnosis of pleural diseases: a 2018 update

The use of biomarkers on pleural fluid (PF) specimens may assist the decision-making process and enhance clinical diagnostic pathways. Three paradigmatic examples are heart failure, tuberculosis and, particularly, malignancy. An elevated PF concentration of the amino-terminal fragment of probrain natriuretic peptide (>1500 pg/ml) is a hallmark of acute decompensated heart failure. Adenosine deaminase, interferon-γ and interleukin-27 are three valuable biomarkers for diagnosing tuberculous pleurisy, yet only the first has been firmly established in clinical practice. Diagnostic PF biomarkers for malignancy can be classified as soluble-protein based, immunocytochemical and nucleic-acid based. Soluble markers (e.g. carcinoembryonic antigen (CEA), carbohydrate antigen 15-3, mesothelin) are only indicative of cancer, but not confirmatory. Immunocytochemical studies on PF cell blocks allow: (a) to distinguish mesothelioma from reactive mesothelial proliferations (e.g. loss of BAP1 nuclear expression, complemented by the demonstration of p16 deletion using fluorescence in situ hybridization, indicate mesothelioma); (b) to separate mesothelioma from adenocarcinoma (e.g. calretinin, CK 5/6, WT-1 and D2-40 are markers of mesothelioma, whereas CEA, EPCAM, TTF-1, napsin A, and claudin 4 are markers of carcinoma); and (c) to reveal tumor origin in pleural metastases of an unknown primary site (e.g. TTF-1 and napsin A for lung adenocarcinoma, p40 for squamous lung cancer, GATA3 and mammaglobin for breast cancer, or synaptophysin and chromogranin A for neuroendocrine tumors). Finally, PF may provide an adequate sample for analysis of molecular markers to guide patients with non-small cell lung cancer to appropriate targeted therapies. Molecular testing must include, at least, mutations of epidermal growth-factor receptor and BRAF V600E, translocations of rat osteosarcoma and anaplastic lymphoma kinase, and expression of programmed death ligand 1.