Anti-tumor activity of K1-LysPE38QQR, an immunotoxin targeting mesothelin, a cell-surface antigen overexpressed in ovarian cancer and malignant mesothelioma

A bispecific antibody that targets the membrane-proximal region of mesothelin and retains high anticancer activity in the presence of shed mesothelin

Mesothelin (MSLN) is a cell-surface protein that is expressed on many cancers, which makes it a popular target for antibody-based cancer therapy. However, MSLN is shed from cancer cells at high levels via proteases that cleave at its membrane-proximal C-terminal region. Shed MSLN accumulates in patient fluids and tumors and can block antibody-based MSLN-targeting drugs from killing cancer cells. A previously established monoclonal antibody (mAb), 15B6, binds MSLN at its protease-sensitive C-terminal region and does not bind shed MSLN. 15B6 variable fragment (Fv)-derived chimeric antigen receptor (CAR) T cells are not inhibited by shed MSLN and kill tumors in mice more effectively than mAb SS1 Fv-derived CAR T cells, which bind an epitope retained in shed MSLN. Here, we have established 15B6 Fv-derived MSLN x CD3 bispecific antibodies (BsAbs) that target MSLN-expressing cancers. We identified our lead candidate, BsAb 5, after screening multiple 15B6-derived BsAb formats in vitro for cytotoxic activity. BsAb 5 activates T cells to kill various cancer cell lines in a MSLN-specific manner. MSLN 296-591 His, a recombinant protein mimicking shed MSLN, does not inhibit 15B6-derived BsAb 5 but completely inhibits humanized SS1-derived BsAb 7. Furthermore, BsAb 5 inhibits and delays tumor growth and is not inhibited by MSLN 296-585 His in mice. Our findings indicate that by targeting the protease-sensitive region of MSLN, BsAb 5 has high MSLN-specific anticancer activity that is not inhibited by shed MSLN. BsAb 5 may be a promising immunotherapy candidate for MSLN-expressing cancers.

The Role of Mesothelin in Activation of Portal Fibroblasts in Cholestatic Liver Injury

Fibrosis is a common consequence of abnormal wound healing, which is characterized by infiltration of myofibroblasts and formation of fibrous scar. In liver fibrosis, activated Hepatic Stellate Cells (aHSCs) and activated Portal Fibroblasts (aPFs) are the major contributors to the origin of hepatic myofibroblasts. aPFs are significantly involved in the pathogenesis of cholestatic fibrosis, suggesting that aPFs may be a primary target for anti-fibrotic therapy in cholestatic injury. aPFs are distinguishable from aHSCs by specific markers including mesothelin (Msln), Mucin 16 (Muc16), and Thymus cell antigen 1 (Thy1, CD90) as well as fibulin 2, elastin, Gremlin 1, ecto-ATPase nucleoside triphosphate diphosphohydrolase 2. Msln plays a critical role in activation of PFs, via formation of Msln-Muc16-Thy1 complex that regulates TGFβ1/TGFβRI-mediated fibrogenic signaling. The opposing pro- and anti-fibrogenic effects of Msln and Thy1 are key components of the TGFβ1-induced activation pathway in aPFs. In addition, aPFs and activated lung and kidney fibroblasts share similarities across different organs with expression of common markers and activation cascade including Msln-Thy1 interaction. Here, we summarize the potential function of Msln in activation of PFs and development of cholestatic fibrosis, offering a novel perspective for anti-fibrotic therapy targeting Msln.

The role of Mesothelin signaling in Portal Fibroblasts in the pathogenesis of cholestatic liver fibrosis

Liver fibrosis develops in response to chronic toxic or cholestatic injury, and is characterized by apoptosis of damaged hepatocytes, development of inflammatory responses, and activation of Collagen Type I producing myofibroblasts that make liver fibrotic. Two major cell types, Hepatic Stellate Cells (HSCs) and Portal Fibroblasts (PFs) are the major source of hepatic myofibroblasts. Hepatotoxic liver injury activates Hepatic Stellate Cells (aHSCs) to become myofibroblasts, while cholestatic liver injury activates both aHSCs and Portal Fibroblasts (aPFs). aPFs comprise the major population of myofibroblasts at the onset of cholestatic injury, while aHSCs are increasingly activated with fibrosis progression. Here we summarize our current understanding of the role of aPFs in the pathogenesis of cholestatic fibrosis, their unique features, and outline the potential mechanism of targeting aPFs in fibrotic liver.

Pseudomonas Exotoxin-Based Immunotoxins: Over Three Decades of Efforts on Targeting Cancer Cells With the Toxin

Cancer is one of the prominent causes of death worldwide. Despite the existence of various modalities for cancer treatment, many types of cancer remain uncured or develop resistance to therapeutic strategies. Furthermore, almost all chemotherapeutics cause a range of side effects because they affect normal cells in addition to malignant cells. Therefore, the development of novel therapeutic agents that are targeted specifically toward cancer cells is indispensable. Immunotoxins (ITs) are a class of tumor cell-targeted fusion proteins consisting of both a targeting moiety and a toxic moiety. The targeting moiety is usually an antibody/antibody fragment or a ligand of the immune system that can bind an antigen or receptor that is only expressed or overexpressed by cancer cells but not normal cells. The toxic moiety is usually a protein toxin (or derivative) of animal, plant, insect, or bacterial origin. To date, three ITs have gained Food and Drug Administration (FDA) approval for human use, including denileukin diftitox (FDA approval: 1999), tagraxofusp (FDA approval: 2018), and moxetumomab pasudotox (FDA approval: 2018). All of these ITs take advantage of bacterial protein toxins. The toxic moiety of the first two ITs is a truncated form of diphtheria toxin, and the third is a derivative of Pseudomonas exotoxin (PE). There is a growing list of ITs using PE, or its derivatives, being evaluated preclinically or clinically. Here, we will review these ITs to highlight the advances in PE-based anticancer strategies, as well as review the targeting moieties that are used to reduce the non-specific destruction of non-cancerous cells. Although we tried to be as comprehensive as possible, we have limited our review to those ITs that have proceeded to clinical trials and are still under active clinical evaluation.

Immunotoxins: From Design to Clinical Application

The Special Issue of Biomolecules entitled "Immunotoxins, From Design to Clinical Application" contains seven reviews related to immunotoxins [...].

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.

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.

Novel mesothelin antibody-drug conjugates: current evidence and future role in the treatment of ovarian cancer

Introduction: Ovarian cancer is the deadliest gynecologic malignancy in the United States, and effective therapies for recurrent, advanced, and progressive disease are limited. Mesothelin is known to be expressed in ovarian cancers, and antibody-drug conjugates targeting mesothelin are a promising novel therapeutic agent.Areas Covered: This article reviews the currently available literature of anti-mesothelin antibody-drug conjugates as a novel treatment for ovarian cancer. Preclinical in vitro and in vivo data as well as clinical results are reviewed for each available agent. Additionally, adverse effects are covered.Expert Opinion: Anti-mesothelin antibody-drug conjugates and their combination with chemotherapeutic agents have undergone phase II trials with encouraging results and demonstrated favorable adverse effect profiles. Phase III data will be necessary to establish its role in ovarian cancer, particularly in recurrent, advanced, or progressive disease.

Mesothelin-Targeted Recombinant Immunotoxins for Solid Tumors

Mesothelin (MSLN) is a cell surface glycoprotein normally expressed only on serosal surfaces, and not found in the parenchyma of vital organs. Many solid tumors also express MSLN, including mesothelioma and pancreatic adenocarcinoma. Due to this favorable expression profile, MSLN represents a viable target for directed anti-neoplastic therapies, such as recombinant immunotoxins (iToxs). Pre-clinical testing of MSLN-targeted iTox’s has yielded a strong body of evidence for activity against a number of solid tumors. This has led to multiple clinical trials, testing the safety and efficacy of the clinical leads SS1P and LMB-100. While promising clinical results have been observed, neutralizing anti-drug antibody (ADA) formation presents a major challenge to overcome in the therapeutic development process. Additionally, on-target, off-tumor toxicity from serositis and non-specific capillary leak syndrome (CLS) also limits the dose, and therefore, impact anti-tumor activity. This review summarizes existing pre-clinical and clinical data on MSLN-targeted iTox’s. In addition, we address the potential future directions of research to enhance the activity of these anti-tumor agents.

Oncolytic bacteria: past, present and future

More than a century ago, independent groups raised the possibility of using bacteria to selectively infect tumours. Such treatment induces an immune reaction that can cause tumour rejection and protect the patient against further recurrences. One of the first holistic approximations to use bacteria in cancer treatment was performed by William Coley, considered the father of immune-therapy, at the end of XIX century. Since then, many groups have used different bacteria to test their antitumour activity in animal models and patients. The basis for this reactivity implies that innate immune responses activated upon bacteria recognition, also react against the tumour. Different publications have addressed several aspects of oncolytic bacteria. In the present review, we will focus on revisiting the historical aspects using bacteria as oncolytic agents and how they led to the current clinical trials. In addition, we address the molecules present in oncolytic bacteria that induce specific toxic effects against the tumors as well as the activation of host immune responses in order to trigger antitumour immunity. Finally, we discuss future perspectives that could be considered in the different fields implicated in the implementation of this kind of therapy in order to improve the current use of bacteria as oncolytic agents.

Mesothelin as a biomarker for targeted therapy

CAR-T cell therapy targeting CD19 has achieved remarkable success in the treatment of B cell malignancies, while various solid malignancies are still refractory for lack of suitable target. In recent years, a large number of studies have sought to find suitable targets with low “on target, off tumor” concern for the treatment of solid tumors. Mesothelin (MSLN), a tumor-associated antigen broadly overexpressed on various malignant tumor cells, while its expression is generally limited to normal mesothelial cells, is an attractive candidate for targeted therapy. Strategies targeting MSLN, including antibody-based drugs, vaccines and CAR-T therapies, have been assessed in a large number of preclinical investigations and clinical trials. In particular, the development of CAR-T therapy has shown great promise as a treatment for various types of cancers. The safety, efficacy, doses, and pharmacokinetics of relevant strategies have been evaluated in many clinical trials. This review is intended to provide a brief overview of the characteristics of mesothelin and the development of strategies targeting MSLN for solid tumors. Further, we discussed the challenges and proposed potential strategies to improve the efficacy of MSLN targeted immunotherapy.

Mesothelial to mesenchyme transition as a major developmental and pathological player in trunk organs and their cavities

The internal organs embedded in the cavities are lined by an epithelial monolayer termed the mesothelium. The mesothelium is increasingly implicated in driving various internal organ pathologies, as many of the normal embryonic developmental pathways acting in mesothelial cells, such as those regulating epithelial-to-mesenchymal transition, also drive disease progression in adult life. Here, we summarize observations from different animal models and organ systems that collectively point toward a central role of epithelial-to-mesenchymal transition in driving tissue fibrosis, acute scarring, and cancer metastasis. Thus, drugs targeting pathways of mesothelium’s transition may have broad therapeutic benefits in patients suffering from these diseases.

Tim Koopmans and Yuval Rinkevich review recent findings linking the mesothelium’s embryonic programs that drive epithelial-to-mesenchyme transition with adult pathologies, such as fibrosis, acute scarring, and cancer metastasis. They highlight new avenues for drug development that would target pathways of the mesothelium’s mesenchymal transition.

Molecular medicine - To be or not to be

Molecular medicine is founded on the synergy between Chemistry, Physics, Biology and Medicine, with the ambitious goal of tackling diseases from a molecular perspective. This Review aims at retracing a personal outlook of the birth and development of molecular medicine, as well as at highlighting some of the most urgent challenges linked to aging and represented by incurable neurodegenerative diseases caused by protein misfolding. Furthermore, we emphasize the emerging role of the retromer dysfunctions and improper protein sorting in Alzheimer's disease and other important neurological disordered.

Immune therapies for malignant mesothelioma

Malignant mesothelioma (MM) is a rare disease which can develop in pleura, pericardium or peritoneum and in which the therapies available have limited efficacy and are associated with various side effects. Therefore, there is a need for more targeted and more effective therapies which are able to halt the disease progression. Among them immune therapies actively or passively directed against various structures of the MM cells seem to be particularly promising given their inhibitory potential demonstrated in both experimental and early clinical studies. Mesothelin in particular seem to be not only a biomarker of disease activity but also a therapeutic target. This review discusses the immune therapies currently investigated for MM.

Discovery of mesothelin and exploiting it as a target for immunotherapy

We have recently reported that an immunotoxin targeting mesothelin produced durable major tumor regressions in patients with extensive treatment-refractory mesothelioma. These unprecedented tumor responses have prompted us to review how mesothelin was discovered and the advances that led to these tumor responses. This review is not comprehensive but focuses on major developments over the past 20 years since mesothelin was first identified in our laboratory. Mesothelin is a cell-surface glycoprotein whose expression in normal human tissues is restricted to mesothelial cells. Because it is highly expressed by many solid tumors, it is an attractive immunotherapy target. Antibody-based therapies currently in clinical trials include an immunotoxin, a chimeric monoclonal antibody, and an antibody drug conjugate. In addition, a mesothelin tumor vaccine and a mesothelin- chimeric antigen receptor are being evaluated in the clinic. SS1P, an anti-mesothelin immunotoxin, was the first mesothelin-directed therapy to enter the clinic, and its use showed that mesothelin-targeted therapy was safe in patients. More importantly, our recent work has shown that SS1P in combination with pentostatin and cyclophosphamide can result in durable tumor regression in patients with advanced mesothelioma and opens up the possibility that such an approach can benefit patients with many common cancers.

MSLN gene silencing has an anti-malignant effect on cell lines overexpressing mesothelin deriving from malignant pleural mesothelioma

Genes involved in the carcinogenetic mechanisms underlying malignant pleural mesothelioma (MPM) are still poorly characterized. So far, mesothelin (MSLN) has aroused the most interest. It encodes for a membrane glycoprotein, frequently over-expressed in various malignancies such as MPM, and ovarian and pancreatic cancers. It has been proposed as a diagnostic and immunotherapeutic target with promising results. However, an alternative therapeutic approach seems to rise, whereby synthetic molecules, such as antisense oligonucleotides, could be used to inhibit MSLN activity. To date, such a gene-level inhibition has been attempted in two studies only, both on pancreatic and ovarian carcinoma cell lines, with the use of silencing RNA approaches. With regard to MPM, only one cell line (H2373) has been employed to study the effects of MSLN depletion. Indeed, the knowledge on the role of MSLN in MPM needs expanding. Accordingly, we investigated the expression of MSLN in a panel of three MPM cell lines, i.e., NCI-H28, Mero-14, and IstMes2; one non-MPM cell line was used as reference (Met5A). MSLN knock-down experiments on MSLN-overexpressing cells were also performed through silencing RNA (siRNA) to verify whether previous findings could be generalized to a different set of cell cultures. In agreement with previous studies, transient MSLN-silencing caused decreased proliferation rate and reduced invasive capacity and sphere formation in MSLN-overexpressing Mero-14 cells. Moreover, MSLN-siRNA combined with cisplatin, triggered a marked increase in apoptosis and a decrease in proliferation as compared to cells treated with each agent alone, thereby suggesting a sensitizing effect of siRNA towards cisplatin. In summary, our findings confirm that MSLN should be considered a key molecular target for novel gene-based targeted therapies of cancer.

Mesothelin overexpression is a marker of tumor aggressiveness and is associated with reduced recurrence-free and overall survival in early-stage lung adenocarcinoma

PURPOSE

In an effort to identify molecular markers of tumor aggressiveness and therapeutic targets in lung adenocarcinoma (ADC), we investigated the expression of mesothelin (MSLN) in lung ADC, as well as its biologic and clinical relevance.

EXPERIMENTAL DESIGN

In a training and validation set of patients with early-stage (I-III) lung ADC (n = 1,209), a tissue microarray consisting of tumors and normal lung tissue was used to examine the association between MSLN expression and recurrence-free survival (RFS) and overall survival (OS). The influence of MSLN overexpression on lung ADC was investigated in vitro and in vivo by use of clinically relevant orthotopic and metastatic xenogeneic and syngeneic mouse models.

RESULTS

MSLN was expressed in 69% of lung ADC tumors, with one in five patients strongly expressing MSLN and no expression in normal lung tissue. Increased MSLN expression was associated with reduced OS [HR = 1.78; 95% confidence interval (CI), 1.26-2.50; P < 0.01] and RFS (HR = 1.67; 95% CI, 1.21-2.27; P < 0.01) in multivariate analyses, even after adjustment for currently known markers of tumor aggressiveness in lung ADC: male sex, smoking history, increasing stage, morphologic pattern, visceral pleural invasion, lymphatic or vascular invasion, and mutation status. In vitro, lung ADC cells overexpressing MSLN demonstrated increased cell proliferation, migration, and invasion; in vivo, mice with MSLN(+) tumors demonstrated decreased survival (P = 0.001).

CONCLUSIONS

MSLN expression in patients with early-stage lung ADC is associated with increased risk of recurrence and reduced OS, indicating that MSLN expression is a molecular marker of tumor aggressiveness and a potential target for therapy.

Lysine at position 222 of the goat prion protein inhibits the binding of monoclonal antibody F99/97.6.1

Prion protein (PrP) is encoded by the PRNP gene, which is highly polymorphic in goats, with polymorphisms encoding amino acid substitutions at the protein level. In the current study, the reactivity of monoclonal antibody (mAb) F99/97.6.1 in binding PrP from goats polymorphic at PRNP codon 222 was investigated. Nervous tissue from 30 scrapie-negative goats with 3 different genotypes (222Q/Q, 222Q/K, and 222K/K) was analyzed by Western blot using mAbs P4 and F99/97.6.1. Although PrP was detected in all 30 samples by mAb P4, detection of PrP by mAb F99/97.6.1 was limited to 222Q/Q (12/12). No PrP was detected by mAb F99/97.6.1 in the 222K/K samples (n = 6), and the signal intensity of mAb F99/97.6.1 for PrP was lower for the 222Q/K samples (12/12 samples). To further investigate these results, additional Western blot analyses were performed, and the PrP signals detected by mAbs F99/97.6.1 and SAF84 were then quantified. The mean F99/SAF84 ratio (± standard deviation) calculated for the 222Q/Q group was 0.73 ± 1.26, and the mean for the 222Q/K group was 0.27 ± 1.31. Statistical analysis of these values evidenced statistically significant differences between the 222Q/Q and 222Q/K samples. The results of the study thus revealed an inhibition by lysine at position 222 on the binding of mAb F99/97.6.1 to goat PrP. This has implications for the use of mAb F99/97.6.1 for diagnostic purposes. Because the 222K allele could be a target for genetic selection in goats, the differential reactivity of mAb F99/97.6.1 could be exploited with a genotyping test setup.

Resolving low-expression cell surface antigens by time-gated orthogonal scanning automated microscopy

We report a highly sensitive method for rapid identification and quantification of rare-event cells carrying low-abundance surface biomarkers. The method applies lanthanide bioprobes and time-gated detection to effectively eliminate both nontarget organisms and background noise and utilizes the europium containing nanoparticles to further amplify the signal strength by a factor of ∼20. Of interest is that these nanoparticles did not correspondingly enhance the intensity of nonspecific binding. Thus, the dramatically improved signal-to-background ratio enables the low-expression surface antigens on single cells to be quantified. Furthermore, we applied an orthogonal scanning automated microscopy (OSAM) technique to rapidly process a large population of target-only cells on microscopy slides, leading to quantitative statistical data with high certainty. Thus, the techniques together resolved nearly all false-negative events from the interfering crowd including many false-positive events.

Inhibition of mesothelin as a novel strategy for targeting cancer cells

Mesothelin, a differentiation antigen present in a series of malignancies such as mesothelioma, ovarian, lung and pancreatic cancer, has been studied as a marker for diagnosis and a target for immunotherapy. We, however, were interested in evaluating the effects of direct targeting of Mesothelin on the viability of cancer cells as the first step towards developing a novel therapeutic strategy. We report here that gene specific silencing for Mesothelin by distinct methods (siRNA and microRNA) decreased viability of cancer cells from different origins such as mesothelioma (H2373), ovarian cancer (Skov3 and Ovcar-5) and pancreatic cancer (Miapaca2 and Panc-1). Additionally, the invasiveness of cancer cells was also significantly decreased upon such treatment. We then investigated pro-oncogenic signaling characteristics of cells upon mesothelin-silencing which revealed a significant decrease in phospho-ERK1 and PI3K/AKT activity. The molecular mechanism of reduced invasiveness was connected to the reduced expression of β-Catenin, an important marker of EMT (epithelial-mesenchymal transition). Ero1, a protein involved in clearing unfolded proteins and a member of the ER-Stress (endoplasmic reticulum-stress) pathway was also markedly reduced. Furthermore, Mesothelin silencing caused a significant increase in fraction of cancer cells in S-phase. In next step, treatment of ovarian cancer cells (OVca429) with a lentivirus expressing anti-mesothelin microRNA resulted in significant loss of viability, invasiveness, and morphological alterations. Therefore, we propose the inhibition of Mesothelin as a potential novel strategy for targeting human malignancies.

Synergistic antitumor activity of anti-CD25 recombinant immunotoxin LMB-2 with chemotherapy

PURPOSE

Although anti-CD25 recombinant immunotoxin LMB-2 is effective against CD25(+) hairy cell leukemia, activity against more aggressive diseases such as adult T-cell leukemia (ATL) is limited by rapid disease progression between treatment cycles. Our goal was to determine in vivo whether rapid growth of CD25(+) tumor is associated with high levels of tumor interstitial soluble CD25 (sCD25) and whether chemotherapy can reduce tumor sCD25 and synergize with LMB-2.

EXPERIMENTAL DESIGN

Tumor xenografts expressing human CD25 were grown in mice, which were then treated with LMB-2 and chemotherapy either alone or in combination, and sCD25 level and antitumor activity were measured.

RESULTS

CD25(+) human xenografts growing rapidly in nude mice had intratumoral sCD25 at levels that were between 21- and 2,200 (median 118)-fold higher than in serum, indicating that interstitial sCD25 interacts with LMB-2 in tumors. Intratumoral sCD25 levels were in the range 21 to 157 (median 54) ng/mL without treatment and 0.95 to 6.1 (median 2.6) ng/mL (P < 0.0001) 1 day after gemcitabine administration. CD25(+) xenografts that were too large to regress with LMB-2 alone were minimally responsive to gemcitabine alone but completely regressed with the combination. Ex vivo, different ratios of gemcitabine and LMB-2 were cytotoxic to the CD25(+) tumor cells in an additive, but not synergistic, manner.

CONCLUSIONS

Gemcitabine is synergistic with LMB-2 in vivo unrelated to improved cytotoxicity. Synergism, therefore, appears to be related to improved distribution of LMB-2 to CD25(+) tumors, and is preceded by decreased sCD25 within the tumor because of chemotherapy. To test the concept of combined treatment clinically, patients with relapsed/refractory ATL are being treated with fludarabine plus cyclophosphamide before LMB-2.

Development and evaluation of a dual-modality (MRI/SPECT) molecular imaging bioprobe

Specific bioprobes for single photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI) have enormous potential for use in cancer imaging in near-future clinical settings. The authors describe the development of dual modality molecular imaging bioprobes, in the form of magnetic nanoparticles (NPs) conjugated to antibodies, for SPECT and MRI of mesothelin-expressing cancers. The bioprobes were developed by conjugating (111)In labeled antimesothelin antibody mAbMB to superparamagnetic iron oxide NPs. Our experimental findings provide evidence that such bioprobes retain their magnetic properties as well as the ability to specifically localize in mesothelin-expressing tumors. It is anticipated that combining SPECT with MR will help obtain both functional and anatomical imaging information with high signal sensitivity and contrast, thereby providing a powerful diagnostic tool for early diagnosis and treatment planning of mesothelin-expressing cancers.

Mesothelin inhibits paclitaxel-induced apoptosis through the PI3K pathway

Mesothelin, a secreted protein, is overexpressed in some cancers, but its exact function remains unclear. The aim of the present study was to evaluate the possible function of mesothelin. Real-time PCR, RT (reverse transcription)-PCR, cytotoxicity assays, proliferative assays, apoptotic assays by Hoechst staining, detection of active caspases 3 and 7 by flow cytometric analysis, and immunoprecipitation and immunoblotting were performed. Cancer tissues in paclitaxel-resistant ovarian cancer patients expressed higher levels of mesothelin as assessed using real-time PCR than paclitaxel-sensitive ovarian cancer patients (the mean crossing point value change of mesothelin was 26.9+/-0.4 in the resistant group and 34.3+/-0.7 for the sensitive group; P<0.001). Mesothelin also protected cells from paclitaxel-induced apoptosis. The protein expression of Bcl-2 family members, such as Bcl-2 and Mcl-1, was significantly increased regardless of whether cells were treated with exogenous mesothelin or were mesothelin-transfectants. Furthermore, mesothelin-treated cells revealed rapid tyrosine phosphorylation of the p85 subunit of PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) 1/2 for enhancing MAPK (mitogen-activated protein kinase) activity. The anti-apoptotic ability was suppressed and the expression of Bcl-2 family in response to mesothelin was altered by inhibiting PI3K activity, but not by inhibiting MAPK activity. Thus mesothelin can inhibit paclitaxel-induced cell death mainly by involving PI3K signalling in the regulation of Bcl-2 family expression. Mesothelin is a potential target in reducing resistance to cytotoxic drugs.

Phase I trial of continuous infusion anti-mesothelin recombinant immunotoxin SS1P

PURPOSE

To conduct a phase I trial of recombinant immunotoxin SS1P given by continuous infusion in chemoresistant solid tumors expressing mesothelin.

EXPERIMENTAL DESIGN

Eligible patients had mesothelioma, ovarian, or pancreatic cancer, which was recurrent or unresectable despite standard therapy, and were mesothelin positive by immunohistochemistry. SS1P was given by continuous infusion for 10 days, and cycles could be repeated at 4-week intervals in the absence of neutralizing antibodies or progressive disease.

RESULTS

Twenty-four patients, five with peritoneal mesothelioma, nine with pleural mesothelioma, two with pleural-peritoneal mesothelioma, seven with ovarian carcinoma, and one with pancreatic carcinoma, received 4, 8, 12, 18, and 25 microg/kg/d x10. The maximum tolerated dose was 25 microg/kg/d x10, where one of six patients had dose-limiting toxicity due to reversible vascular leak syndrome. Immunogenicity was observed in 18 (75%) of 24 patients, and five (21%) received a second cycle. Constant plasma levels of SS1P were maintained for most of the 10-day infusion time, with median peak levels of up to 153 ng/mL. One patient had a partial response. Nonmajor responses included cessation of ascites and independence from paracentesis, resolution of masses by positron emission tomography, and improved pain and range of motion.

CONCLUSIONS

As a single agent by continuous infusion, recombinant immunotoxin SS1P was well tolerated up to 25 microg/kg/d x10 and showed evidence of modest clinical activity. Continuous infusion showed no significant advantage over bolus dosing, and further clinical development of SS1P is proceeding by bolus dosing in combination with chemotherapy.

Beyond CA125: the coming of age of ovarian cancer biomarkers. Are we there yet?

Ovarian cancer (OC) is the fourth leading cause of cancer deaths among women in the United States, despite its relatively low incidence of 50 per 100,000. Even though advances in therapy have been made, the OC fatality-to-case ratio remains exceedingly high, due to the lack of accurate tools to diagnose early-stage disease when cure is still possible. The most studied marker for OC, CA125, is only expressed by 50-60% of patients with early stage disease. Large efforts have been deployed to identify novel serum markers, yet no single marker has emerged as a serious competitor for CA125. Various groups are investing in combination approaches to increase the diagnostic value of existing markers, but many markers may still lie in under-explored areas of ovarian cancer biology, such as tumor vasculature environment and post-translational modifications (glycomics).

Nanoparticulate delivery of diphtheria toxin DNA effectively kills Mesothelin expressing pancreatic cancer cells

Pancreatic cancer is the fourth leading cause of cancer-related deaths in this country, and there is currently no effective targeted treatment for this deadly disease. A dire need exists to rapidly translate our molecular understanding of this devastating disease into effective, novel therapeutic options. Mesothelin is a candidate target protein shown by a number of laboratories to be specifically overexpressed in pancreatic cancers and not in the adjacent normal tissue. Translational investigations have shown promising results using this molecule as a therapeutic target (e.g., vaccine strategies). In addition, the mesothelin promoter has been cloned and dissected and can therefore be used as a vehicle for regulating expression of DNA sequences. Using a novel, proven, biodegradable nanoparticulate system, we sought to target mesothelin-expressing pancreatic cancer cells with a potent suicide gene, diphtheria toxin-A (DT-A). We first confirmed reports that a majority of pancreatic cancer cell lines and resected pancreatic ductal adenocarcinoma specimens overexpressed mesothelin at the mRNA and protein levels. High mesothelin-expressing pancreatic cancer cell lines produced more luciferase than cell lines with undetectable mesothelin expression when transfected with a luciferase sequence under the regulation of the mesothelin promoter. We achieved dramatic inhibition of protein translation (>95%) in mesothelin-expressing pancreatic cancer cell lines when DT-A DNA, driven by the mesothelin promoter, was delivered to pancreatic cancer cells. We show that this inhibition effectively targets the death of pancreatic cancer cells that overexpress mesothelin. The work presented here provides evidence that this strategy will work in pre-clinical mouse pancreatic cancer models, and suggests that such a strategy will work in the clinical setting against the majority of pancreatic tumors, most of which overexpress mesothelin.

Mesothelin is a specific biomarker of invasive cancer in the Barrett-associated adenocarcinoma progression model: translational implications for diagnosis and therapy

Esophageal adenocarcinoma arises in the backdrop of Barrett metaplasia-dysplasia sequence, with the vast majority of patients presenting with late-stage malignancy. Mesothelin, a glycophosphatidylinositol-anchored protein, is aberrantly overexpressed on the surface of many solid cancers. Mesothelin expression was assessed in esophageal tissue microarrays encompassing the entire histological spectrum of Barrett-associated dysplasia and adenocarcinoma. Mesothelin expression was observed in 24/84 (29%) of invasive adenocarcinomas and in 5/34 (15%) lymph node metastases. In contrast, normal squamous and cardiac mucosa, as well as noninvasive Barrett lesions, failed to label with mesothelin. Mesothelin was expressed in the esophageal adenocarcinoma cell line JH-EsoAd1 but not in primary human esophageal epithelial cells. Anti-mesothelin antibody-conjugated CdSe/CDS/ZnS quantum rods were synthesized, and confocal bioimaging confirmed robust binding to JH-EsoAd1 cells. Anti-mesothelin antibody-conjugated nanoparticles can be useful for the diagnosis and therapy of mesothelin-overexpressing esophageal adenocarcinomas.

Intracavitary radioimmunotherapy to treat solid tumors

Radioimmunotherapy (RIT) potentially is an attractive treatment for radiosensitive early-stage solid tumors and as an adjuvant to cytoreductive surgery. Topical administration of RIT may improve the efficacy because higher local concentrations are achieved. We reviewed the results of locally applied radiolabeled monoclonal antibodies for the treatment of solid tumors. Intracavitary RIT in patients with ovarian cancer and glioma showed improved targeting after local administration, as compared to the intravenous administration. In addition, various studies showed the feasibility of locally applied RIT in these patients. In studies that included patients with small-volume disease, adjuvant RIT in ovarian cancer and glioma showed to be at least as effective as standard therapy. The information about RIT for peritoneal carcinomatosis of colorectal origin is scarce, while results from preclinical data are promising. RIT may be applied for other, relatively unexplored indications. Studies on the application of radiolabeled antibodies in early urothelial cell cancer have been performed, showing that intracavitary RIT may hold a promise. Moreover, in patients with malignant pleural mesothelioma or malignant pleural effusion, RIT may play a role in the palliative treatment. Intracavitary RIT limits toxicity and improves tumor targeting. RIT is more effective in patients with small-volume disease of solid cancers. RIT may have potential for palliation in patients with malignant pleural mesothelioma or malignant pleural effusion. The future of RIT may, therefore, not only be in the inclusion in contemporary multimodality treatment, but also in the expansion to palliative treatment.

Anti-mesothelin immunotoxin SS1P in combination with gemcitabine results in increased activity against mesothelin-expressing tumor xenografts

PURPOSE

To determine the antitumor activity of the anti-mesothelin immunotoxin SS1P in combination with gemcitabine against mesothelin-expressing tumor xenografts.

EXPERIMENTAL DESIGN

The in vitro activity of SS1P in combination with gemcitabine against the mesothelin-expressing cell line A431/K5 was evaluated using cytotoxicity and apoptosis assays. The antitumor activity of this combination was evaluated in nude mice bearing A431/K5 tumor xenografts. Tumor-bearing mice were treated with different doses and schedules of gemcitabine alone, SS1P alone (0.2 mg/kg i.v. every other day x three doses), or with both agents together, and tumor volumes were measured over time.

RESULTS

In vitro studies failed to show the synergy of SS1P plus gemcitabine against the mesothelin-expressing A431/K5 cells. In contrast, in the in vivo setting, there was a marked synergy when SS1P was combined with gemcitabine for the treatment of mesothelin-expressing tumor xenografts. This synergy was present using different doses and schedules of gemcitabine administration. In mice treated with fractionated doses of gemcitabine in combination with SS1P, complete tumor regression was observed in all mice and was long-lasting in 60% of the animals. Also, this antitumor activity was specific to SS1P because HA22, an immunotoxin targeting CD22 not expressed on A431/K5 cells, did not increase the efficacy of gemcitabine.

CONCLUSIONS

SS1P in combination with gemcitabine results in marked antitumor activity against mesothelin-expressing tumors. This combination could be potentially useful for the treatment of human cancers that express mesothelin and are responsive to gemcitabine therapy.

Releasable PEGylation of proteins with customized linkers

Releasable PEGylation employs customized linkers that reversibly tether a therapeutic moiety with polyethylene glycol polymers. The choice of releasable PEG linkers may have numerous applications that are insufficiently addressed by stable polymer attachment. Releasable PEGylation provides regeneration of authentic and fully active drug and allows tailored design of critical pharmacological parameters such as the maximal drug concentration and total drug exposure. This provides a prodrug format that combines beneficial attributes of PEGylation with controlled release. The linker release mechanisms are shown to be kinetically controlled by the design of a hydrolytically labile center and side chains for the steric modulation of the intramolecular elimination reactions and linker self-immolation. Recent reports have described both aromatic and aliphatic based customized linkers that release the unaltered original drug under physiological conditions and at therapeutically useful release rates. These studies have examined bioconjugates of cytokines, peptide hormones, immunotoxins, enzymes, and reporter proteins.

Releasable PEGylation of Mesothelin Targeted Immunotoxin SS1P Achieves Single Dosage Complete Regression of a Human Carcinoma in Mice

Recombinant immunotoxins exhibit targeting and cytotoxic functions needed for cell-specific destruction. However, antitumor efficacy, safety, and pharmacokinetics of these therapeutics might be improved by further macromolecular engineering. SS1P is a recombinant anti-mesothelin immunotoxin in clinical trials in patients with mesothelin-expressing tumors. We have modified this immunotoxin using several PEGylation strategies employing releasable linkages between the protein and the PEG polymers, and observed superior performance of these bioconjugates when compared to similar PEG derivatives bearing permanent linkages to the polymers. PEGylated derivatives displayed markedly diminished cytotoxicity on cultured mesothelin-overexpressing A431-K5 cells; however, the releasable PEGylated immunotoxins exhibited increased antitumor activity in A431-K5 xenografts in mice, with a diminished animal toxicity. Most significantly, complete tumor regressions were achievable with single dose administration of the bioconjugates but not the native immunotoxin. Pharmacokinetic analysis of the releasable PEGylated derivatives in mice demonstrated an over 80-fold expansion of the area under the curve exposure of bioactive protein when compared to native immunotoxin. A correlation in degree of derivatization, release kinetics, and polymer size with potency was observed in vivo, whereas in vitro cytotoxicity was not predictive of efficacy in animal models. The potent antitumor efficacy of the releasable PEGylated mesothelin-targeted immunotoxins was not exhibited by similar untargeted PEG immunotoxins in this model. Since the bioconjugates can also exhibit the attributes of passive targeting via enhanced permeability and retention, this is the first demonstration of a pivotal role of active targeting for immunotoxin bioconjugate efficacy.

Immunocytochemical study of the expression of mesothelin in fine-needle aspiration biopsy specimens of pancreatic adenocarcinoma

Mesothelin is a potential marker of pancreatic adenocarcinoma that was recently identified by serial analysis of gene expression. We evaluated the sensitivity and specificity of mesothelin as a marker of pancreatic adenocarcinoma on destained Papanicolaou (Pap) smears and unstained cellblocks from 28 patients using a monoclonal antibody to mesothelin. Intensity and proportion of staining was semiquantitatively graded on a scale of 1-3, and as 0%, 1 to <10%, 10-50%, or >50%. Positive staining for mesothelin was seen in 64% of the direct smears and in 36% of cell block sections. Focal positivity for mesothelin was noted in benign pancreatic tissue in one of 10 cases. Staining was most often focal (<50% of cells) in both direct smears and cell block sections. The overall sensitivity and specificity of mesothelin as a marker for pancreatic adenocarcinoma were 68% and 90%, respectively. Sensitivity was higher in Pap smears than in cell block sections (64% versus 36%). The presence of occasional mesothelin expression in benign tissue, its very focal expression in malignant tissue may limit the utility of mesothelin as a marker of pancreatic adenocarcinomas in fine-needle aspiration (FNA) specimens.

Antibody internalization studied using a novel IgG binding toxin fusion

Targeted therapy encompasses a wide variety of different strategies, which can be divided into direct or indirect approaches. Direct approaches target tumor-associated antigens by monoclonal antibodies (mAbs) binding to the relevant antigens or by small-molecule drugs that interfere with these proteins. Indirect approaches rely on tumor-associated antigens expressed on the cell surface with antibody-drug conjugates or antibody-based fusion proteins containing different kinds of effector molecules. To deliver a lethal cargo into tumor cells, the targeting antibodies should efficiently internalize into the cells. Similarly, to qualify as targets for such drugs newly-discovered cell-surface molecules should facilitate the internalization of antibodies that bind to them. Internalization can be studied be several biochemical and microscopy approaches. An undisputed proof of internalization can be provided by the ability of an antibody to specifically deliver a drug into the target cells and kill it. We present a novel IgG binding toxin fusion, ZZ-PE38, in which the Fc-binding ZZ domain, derived from Streptococcal protein A, is linked to a truncated Pseudomonas exotoxin A, the preparation of complexes between ZZ-PE38 and IgGs that bind tumor cells and the specific cytotoxicity of such immunocomplexes is reported. Our results suggest that ZZ-PE38 could prove to be an invaluable tool for the evaluation of the suitability potential of antibodies and their cognate cell-surface antigens to be targeted by immunotherapeutics based on armed antibodies that require internalization.

Overexpression of folate binding protein and mesothelin are associated with uterine serous carcinoma

PURPOSE

Folate receptor alpha (FOLR1) is a membrane bound receptor involved in the transport of folate as well as other regulatory cellular processes. The purpose of this study was to examine the expression of FOLR1 in uterine cancers and to identify changes in gene expression that are associated with overexpression of FOLR1.

EXPERIMENTAL DESIGN

Fifty-eight frozen uterine cancer specimens were stained for FOLR1 using immunohistochemistry and results were correlated with transcript expression noted on quantitative PCR. Total RNA from 16 cases of uterine serous carcinoma (USC) was analyzed for gene expression using the Affymetrix HG-U133A and HG-U133B GeneChip set. USCs overexpressing FOLR1 were compared to cancers with an absence of FOLR1 using binary comparison and template matching of data was used to identify genes that correlate with FOLR1 expression. Selected targets from this analysis were evaluated by quantitative PCR as well as in an independent set of USC represented in quadruplicate on a tissue microarray (TMA).

RESULTS

Overexpression of FOLR1 was observed in 11/16 (69%) of USC and 0/10 normal endometrium cases using frozen tissue specimens. Binary comparison between FOLR1 positive and negative cases identified 121 genes altered by 2-fold at p<0.01 of which 45 are well correlated with FOLR1 expression pattern. Using quantitative PCR, both mesothelin (MSLN) and PTGS1 (COX1) were significantly increased in FOLR1 overexpressing tumors (p=0.014 and p=0.006 respectively). TMA confirmed that overexpression of FOLR1 and MSLN respectively occurred in 23/48 (48%) and 17/54 (32%) of pure USC.

CONCLUSION

Both FOLR1 and MSLN are cell surface targets that are co-expressed at high levels in USC and are appealing targets for biologic therapy.

Diffuse mesothelin expression correlates with prolonged patient survival in ovarian serous carcinoma

PURPOSE

Mesothelin is an emerging marker for cancer diagnosis and target-based therapy, yet relatively little is known about the clinical significance of mesothelin expression in tumors. In this study, we correlate mesothelin immunoreactivity to clinicopathologic features in ovarian serous carcinoma.

EXPERIMENTAL DESIGN

Mesothelin expression levels were compared among 81 publicly available serial analysis of gene expression (SAGE) libraries of various carcinoma and normal tissue types. Immunohistochemistry using a well-characterized mesothelin monoclonal antibody (5B2) was done to evaluate mesothelin expression in 167 high-grade and 31 low-grade ovarian serous carcinomas. Immunohistochemistry staining scores were correlated with patient survival, tumor site, tumor grade, in vitro drug resistance, and differentiation status of tumor cells.

RESULTS

SAGE analysis showed that mesothelin was overexpressed in 50% of ovarian and pancreatic carcinomas but rarely in other cancer types, including liver, colon, kidney, prostate, and breast. Mesothelin immunoreactivity (>5% of tumor cells) was present in 55% of ovarian serous carcinomas with no difference in expression between high-grade and low-grade serous tumors (P = 0.82). Based on Kaplan-Meier analysis, we found that a diffuse mesothelin staining (>50% of tumor cells) in primary high-grade ovarian carcinomas correlated significantly with prolonged survival in patients who had advanced-stage disease and had received optimal debulking surgery followed by chemotherapy (P = 0.023). Mesothelin expression did not correlate significantly with patient age, tumor site, in vitro drug resistance, or tumor differentiation status (P > 0.10).

CONCLUSION

Our results provided new evidence that mesothelin expression is associated with prolonged survival in patients with high-grade ovarian serous carcinoma.

Molecular pathogenesis of pancreatic cancer

Pancreatic cancer is fundamentally a disease of inherited and acquired mutations in cancer-related genes. The genes targeted in pancreatic cancer include tumor-suppressor genes (p16/CDKN2A, TP53 and SMAD4), oncogenes (KRAS, BRAF, AKT2, MYB, and AIB1), and genome-maintenance genes (MLH1, MSH2, BRAC2 and other Fanconi anemia genes). An understanding of the cancer-related genes that are altered in pancreatic cancer has a number of clinical applications including genetic counseling for individuals with a family history of cancer, early detection of pancreatic neoplasia, and mechanism-based therapies for patients with advanced disease. This chapter will provide an overview of the molecular pathogenesis of pancreatic cancer with emphasis on clinical applications.

Identification of novel human CTL epitopes and their agonist epitopes of mesothelin

PURPOSE

Mesothelin is overexpressed in many pancreatic and ovarian cancers, mesotheliomas, and other tumor types. Clinical trials are ongoing using immunotoxins to target mesothelin, and patients immunized with allogeneic pancreatic tumor cell lines have shown immune responses to previously defined mesothelin epitopes. The purpose of this study was to define novel mesothelin CTL epitopes and, more importantly, agonist epitopes that would more efficiently activate human T cells to more efficiently lyse human tumors.

EXPERIMENTAL DESIGN AND RESULTS

Two novel mesothelin HLA-A2 epitopes were defined. T-cell lines generated from one of these epitopes were shown to lyse pancreatic and ovarian tumor cells. Several agonist epitopes were defined and were shown to (a) have higher affinity and avidity for HLA-A2, (b) activate mesothelin-specific T cells from normal individuals or cancer patients to a greater degree than the native epitope in terms of induction of higher levels of IFN-gamma and the chemokine lymphotactin, and (c) lyse several mesothelin-expressing tumor types in a MHC-restricted manner more effectively than T cells generated using the native peptide. External beam radiation of tumor cells at nontoxic levels was shown to enhance the expression of mesothelin and other accessory molecules, resulting in a modest but statistically significant increase in tumor cell lysis by mesothelin-specific T cells.

CONCLUSIONS

The identification of novel CTL agonist epitopes supports and extends observations that mesothelin is a potential target for immunotherapy of pancreatic and ovarian cancers, as well as mesotheliomas.

Effectiveness of anti-folate receptor beta antibody conjugated with truncated Pseudomonas exotoxin in the targeting of rheumatoid arthritis synovial macrophages

OBJECTIVE

To define the distribution of folate receptor beta (FRbeta)-expressing cells in various tissues, including rheumatoid arthritis (RA) synovial tissues, and to verify the effects of an immunotoxin composed of an anti-FRbeta monoclonal antibody (mAb) and truncated Pseudomonas exotoxin A (PEA) on apoptosis and tumor necrosis factor alpha (TNFalpha) production by adherent synovial mononuclear cells from RA patients.

METHODS

Anti-FRbeta mAb were produced by immunizing mice with FRbeta-transfected murine pre-B cells. The distribution of the FRbeta antigen was examined by immunohistochemical analysis using anti-FRbeta mAb and macrophage-specific anti-CD163 mAb. Anti-FRbeta mAb was chemically crosslinked with truncated PEA. FRbeta-expressing macrophages were produced by the transfection of adenovirus vector containing the FRbeta gene. Apoptotic cells were detected by staining with propidium iodide. TNFalpha was measured by enzyme-linked immunosorbent assay.

RESULTS

FRbeta-expressing cells were not present in peripheral blood leukocytes and their activated cells. In all of the tissues examined, most FRbeta-expressing cells were CD163+. The immunotoxin significantly induced the apoptosis of FRbeta-transfected macrophages and adherent RA synovial mononuclear cells and inhibited TNFalpha production by adherent RA synovial mononuclear cells.

CONCLUSION

We demonstrated the limited distribution of FRbeta-expressing cells in various tissues. The immunotoxin targeting FRbeta-expressing cells will provide a therapeutic tool for rheumatoid synovitis.

Gene overexpression in pancreatic adenocarcinoma: diagnostic and therapeutic implications

Pancreatic cancer is the deadliest of cancers, and effective diagnostic and therapeutic strategies are lacking. Global gene expression profiling holds promise for improved diagnosis and treatment. Knowledge of the location and timing of gene overexpression and the function of these genes, including their effects on signaling pathways, is important. These data may be used to develop histologic and serum biomarkers as well as to develop immunotherapeutic, molecular targeting, and gene therapy strategies. We have compiled a list of overexpressed genes in pancreatic cancer for which overexpression was confirmed by reverse transcriptase polymerase chain reaction, immunohistochemistry, and/or in situ hybridization following initial identification by global gene expression profiling. The techniques used in the determination of overexpression, problems encountered in global gene expression profiling, and the diagnostic and therapeutic implications of overexpression are discussed. The S100 gene family, mesothelin, prostate stem cell antigen, and 14-3-3 sigma, may have important clinical implications in pancreatic cancer diagnosis and treatment.

Expression of novel markers of pancreatic ductal adenocarcinoma in pancreatic nonductal neoplasms: additional evidence of different genetic pathways

Solid pseudopapillary tumor, pancreatoblastoma, undifferentiated carcinoma with osteoclastic-like giant cells, and acinar cell carcinomas are rare pancreatic nonductal neoplasms. Compared to the significant advances in our understanding of the pathogenesis of pancreatic ductal adenocarcinomas in the last decades, the molecular mechanisms underlying pancreatic nonductal neoplasms are poorly understood. In order to elucidate their molecular pathogenesis, we constructed tissue microarrays to study the expression of some novel pancreatic ductal adenocarcinoma-associated tumor markers in these nonductal pancreatic neoplasms. We analyzed nine markers including tumor suppressor gene (14-3-3 sigma), proliferation marker (topoisomerase II alpha), epithelial markers (prostate stem cell antigen, mesothelin and cytokeratin 19), stromal markers (fascin, hsp47 and fibronectin), and gamma-synuclein whose function is not delineated. In addition, we included tumor suppressor gene DPC4 and oncogene Beta-catenin to further confirm their expression in pancreatic nonductal tumors. Our results showed that in contrast to pancreatic ductal adenocarcinomas that show loss of Dpc4 protein in 55% of cases, loss of Dpc4 expression is absent in pancreatic nonductal neoplasms. Expression of 14-3-3 sigma is frequently seen in both pancreatic nonductal neoplasms (25-100%) and ductal adenocarcinomas (89%). Aberrant nuclear expression of beta-catenin is common in pancreatic nonductal neoplasms, specifically in solid pseudopapillary tumors (88%) and pancreatoblastomas (100%) but is rarely seen in pancreatic ductal adenocarcinomas (<5%). Expression of topoisomerase II alpha is not seen in solid pseudopapillary tumors and undifferentiated carcinomas with osteoclastic-like giant cells but is focally seen in pancreatoblastomas (50%) and acinar cell carcinomas (85%). Expression of PSCA and mesothelin was observed in pancreatic nonductal neoplasms but their expression was seen less frequently (0-50%) and weaker than that in pancreatic ductal adenocarcinomas (60-100%). CK19, a marker of pancreatic ductal adenocarcinomas, is not expressed in pancreatic nonductal neoplasms. Expression of gamma-synuclein as well as stromal markers (fascin, hsp47 and fibronectin) is frequently seen in both. Our findings indicate pancreatic nonductal neoplasms have distinctive patterns of protein expression relative to pancreatic ductal adenocarcinomas and suggest that pancreatic nonductal neoplasms have different genetic pathways from the more common pancreatic ductal adenocarcinomas.

Mesothelin: a new target for immunotherapy

Mesothelin is a differentiation antigen present on normal mesothelial cells and overexpressed in several human tumors, including mesothelioma and ovarian and pancreatic adenocarcinoma. The mesothelin gene encodes a precursor protein that is processed to yield the 40-kDa protein, mesothelin, attached to the cell membrane by a glycosylphosphatidyl inositol linkage and a 31-kDa shed fragment named megakaryocyte-potentiating factor. The biological function of mesothelin is not known. Mesothelin is a promising candidate for tumor-specific therapy, given its limited expression in normal tissues and high expression in several cancers. SS1(dsFv)PE38 is a recombinant anti-mesothelin immunotoxin that is undergoing clinical evaluation in patients with mesothelin-expressing tumors. There is evidence that mesothelin is an immunogenic protein and could be exploited as a therapeutic cancer vaccine. A soluble mesothelin variant has been identified and could be a useful tumor marker for malignant mesotheliomas.

Characterization of human mesothelin transcripts in ovarian and pancreatic cancer

Background

Mesothelin is an attractive target for cancer immunotherapy due to its restricted expression in normal tissues and high level expression in several tumor types including ovarian and pancreatic adenocarcinomas. Three mesothelin transcript variants have been reported, but their relative expression in normal tissues and tumors has been poorly characterized. The goal of the present study was to clarify which mesothelin transcript variants are commonly expressed in human tumors.

Methods

Human genomic and EST nucleotide sequences in the public databases were used to evaluate sequences reported for the three mesothelin transcript variants in silico. Subsequently, RNA samples from normal ovary, ovarian and pancreatic carcinoma cell lines, and primary ovarian tumors were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and nucleotide sequencing to directly identify expressed transcripts.

Results

In silico comparisons of genomic DNA sequences with available EST sequences supported expression of mesothelin transcript variants 1 and 3, but there were no sequence matches for transcript variant 2. Newly-derived nucleotide sequences of RT-PCR products from tissues and cell lines corresponded to mesothelin transcript variant 1. Mesothelin transcript variant 2 was not detected. Transcript variant 3 was observed as a small percentage of total mesothelin amplification products from all studied cell lines and tissues. Fractionation of nuclear and cytoplasmic RNA indicated that variant 3 was present primarily in the nuclear fraction. Thus, mesothelin transcript variant 3 may represent incompletely processed hnRNA.

Conclusion

Mesothelin transcript variant 1 represents the predominant mature mRNA species expressed by both normal and tumor cells. This conclusion should be important for future development of cancer immunotherapies, diagnostic tests, and gene microarray studies targeting mesothelin.

Novel markers of pancreatic adenocarcinoma in fine-needle aspiration: mesothelin and prostate stem cell antigen labeling increases accuracy in cytologically borderline cases

The interpretation of pancreas fine-needle aspiration (FNA) is extremely difficult given the cytologic overlap of neoplastic and reactive processes. Using serial analysis of gene expression, we have discovered 2 new markers of pancreatic adenocarcinoma, mesothelin and prostate stem cell antigen (PSCA), and confirmed their specificity by immunohistochemical labeling. Here we evaluate the potential contribution of immunohistochemical labeling of mesothelin and PSCA to the interpretation of pancreas FNAs. Thirty pancreas FNAs with follow-up data were reviewed. Unstained cell block sections from these aspirates labeled for mesothelin and PSCA using immunohistochemistry were compared with initial cytologic diagnoses and with follow-up diagnoses. On follow-up, 19 patients proved to have cancer, and 11 did not. Initial cytologic diagnosis of malignancy correlated with carcinoma on follow-up in 12 of 12 cases, and initial benign cytologic diagnosis correlated with benign follow-up in 8 of 9 cases (sensitivity, 92%; specificity, 100%). Six of the 9 patients with suspicious cytology were found to have a carcinoma on follow-up. PSCA labeling was present in 16 of the 19 patients who ultimately were proven to have carcinoma; PSCA labeling was absent in 10 of the 11 lesions proven to be benign (sensitivity, 84%; specificity, 91%). Mesothelin labeling was present in 13 of the 19 patients who ultimately were proven to have carcinoma; mesothelin labeling was absent in 10 of the 11 lesions proven to be benign (sensitivity, 68%; specificity, 91%). Five of the 6 cytologically suspicious cases with malignant follow-up labeled for either PSCA or mesothelin (83%), and 2 of the 6 cases labeled for both markers. None of the 3 suspicious cases with benign follow-up labeled for either PSCA or mesothelin. Increasingly, molecular techniques are identifying potential cancer markers that may have diagnostic utility. In this study, immunohistochemical labeling for 2 of these markers, PSCA and mesothelin, appears highly specific for pancreatic adenocarcinoma in FNA specimens and useful in categorizing cytologically suspicious lesions.

Large-scale molecular and tissue microarray analysis of mesothelin expression in common human carcinomas

The 40-kilodalton processed glycoprotein, mesothelin, is highly expressed in epithelial mesotheliomas and adenocarcinomas of the ovary (serous papillary) and pancreas, but its expression in a large series of other common carcinomas has not been completely explored. In the present study, we used oligonucleotide and tissue microarrays to profile the expression of the mesothelin gene (MSLN) and encoded protein, respectively. Among 150 carcinomas of multiple anatomic sites, we found the highest average expression of MSLN in serous carcinomas of the ovary and adenocarcinomas of the pancreas, consistent with previous reports, as well as measurable but less-striking expression in pulmonary, gastric/esophageal, and colorectal adenocarcinomas. On tissue microarrays containing 621 carcinomas derived from the same and additional sites as those profiled by gene expression, mesothelin immunoreactivity was highest in cancers of the ovary (serous papillary, endometrioid, and undifferentiated) and pancreas, with less frequent staining seen in adenocarcinomas of the endometrium, lung, and stomach/esophagus. Some immunopositivity was observed in 42% of pulmonary adenocarcinomas, including 18% that had >50% of tumor cells that were immunoreactive. Some 14% of breast and 30% of colorectal adenocarcinomas showed immunopositivity, but no case contained >50% tumor cells that were immunoreactive. Mesothelin was either entirely absent or present in <5% of carcinomas of the prostate, bladder/ureter, liver, kidney, and thyroid. Overall, we observed good concordance between the results obtained by oligonucleotide and tissue microarrays. This large study of the MSLN gene and protein expression in common carcinomas provides data for future investigations that evaluate the utility of mesothelin/megakaryocyte potentiating factor as a potential serum tumor marker or target of immunotoxin-based therapy in human cancers.

Stromelysin-1 and mesothelin are differentially regulated by Wnt-5a and Wnt-1 in C57mg mouse mammary epithelial cells

BACKGROUND

The Wnt signal transduction pathway is important in a wide variety of developmental processes as well as in the genesis of human cancer. Vertebrate Wnt pathways can be functionally separated into two classes, the canonical Wnt/beta-catenin pathway and the non-canonical Wnt/Ca2+ pathway. Supporting differences in Wnt signaling, gain of function of Wnt-1 in C57mg mouse mammary epithelial cells leads to their morphological transformation while loss of function of Wnt-5a leads to the same transformation. Many downstream target genes of the Wnt/beta-catenin pathway have been identified. In contrast, little is known about the Wnt/Ca2+ pathway and whether it regulates gene expression.

RESULTS

To test the hypothesis that a specific cell line can respond to distinct Wnts with different patterns of gene expression, we over-expressed Wnt-5a and Rfz-2 in C57mg mammary epithelial cells and compared this cell line to C57mg cells over-expressing Wnt-1. These Wnts were chosen since previous studies suggest that C57mg cells respond differently to these Wnts, and since these Wnts can activate different signaling pathways in other systems. Using DNA microarray analysis, we identified several genes that are regulated by Wnt-5a and Rfz-2 as well as by Wnt-1. We then focused on two genes previously linked to various cancers, mesothelin and stromelysin-1, which are respectively up-regulated by Wnt-1 and Wnt-5a in C57mg cells.

CONCLUSION

Different Wnts have distinct effects on gene expression in a single cell line.

Exploration of global gene expression patterns in pancreatic adenocarcinoma using cDNA microarrays

Pancreatic cancer is the fifth leading cause of cancer death in the United States. We used cDNA microarrays to analyze global gene expression patterns in 14 pancreatic cancer cell lines, 17 resected infiltrating pancreatic cancer tissues, and 5 samples of normal pancreas to identify genes that are differentially expressed in pancreatic cancer. We found more than 400 cDNAs corresponding to genes that were differentially expressed in the pancreatic cancer tissues and cell lines as compared to normal pancreas. These genes that tended to be expressed at higher levels in pancreatic cancers were associated with a variety of processes, including cell-cell and cell-matrix interactions, cytoskeletal remodeling, proteolytic activity, and Ca(++) homeostasis. Two prominent clusters of genes were related to the high rates of cellular proliferation in pancreatic cancer cell lines and the host desmoplastic response in the resected pancreatic cancer tissues. Of 149 genes identified as more highly expressed in the pancreatic cancers compared with normal pancreas, 103 genes have not been previously reported in association with pancreatic cancer. The expression patterns of 14 of these highly expressed genes were validated by either immunohistochemistry or reverse transcriptase-polymerase chain reaction as being expressed in pancreatic cancer. The overexpression of one gene in particular, 14-3-3 sigma, was found to be associated with aberrant hypomethylation in the majority of pancreatic cancers analyzed. The genes and expressed sequence tags presented in this study provide clues to the pathobiology of pancreatic cancer and implicate a large number of potentially new molecular markers for the detection and treatment of pancreatic cancer.

An ELISA method for detection of human antibodies to an immunotoxin

INTRODUCTION

The use of biological molecules, such as immunotoxins, as pharmaceuticals is limited by the presence and development of human antibodies to these agents. This immune response can cause significant inflammatory-related toxicities and can interfere with the efficacy of the biological agent. Therefore, a clinically applicable method to detect these human antibodies is needed for screening patients prior to enrollment and for monitoring patients during treatment. The SS1(dsFv)-PE38 immunotoxin currently in clinical trials is a hybrid molecule targeted against mesothelin-expressing cancer cells via the Fv portion of a murine antibody linked to the Pseudomonas exotoxin (PE), which can inhibit protein synthesis leading to cell death. The objective of this study was to determine if an enzyme-linked immunosorbent assay (ELISA)-based method could be used to detect human anti-SS1(dsFv)-PE38 antibodies in patient serum.

METHODS

Human antibodies to the immunotoxin in serially diluted serum specimens were captured on immunotoxin-coated ELISA plates, and detected using a secondary goat antihuman antibody linked to biotin in combination with horseradish peroxidase linked to avidin D (HRP-Avidin). The color was developed with tetramethyl benzidine (TMB). Curves of optical density (OD(630)) versus dilution for 44 serum specimens were compared with positive and negative control serum specimens to classify the serum as positive or negative for anti-immunotoxin antibodies.

RESULTS

Ten out of the 40 patients screened were positive for anti-immunotoxin antibodies. Repeated testing of seven samples produced the same results in two independent experiments. The first two patients treated with the immunotoxin developed anti-immunotoxin antibodies during treatment. The results were in perfect concordance with a tissue culture-based neutralization assay performed by an independent laboratory.

DISCUSSION

An ELISA-based strategy using an immunotoxin to capture human anti-immunotoxin antibodies provides a consistently accurate technology for screening and monitoring patient serum specimens in clinical trials.