An animal model of preclinical diagnosis of pancreatic ductal adenocarcinomas

Challenges of Anti-Mesothelin CAR-T-Cell Therapy

Chimeric antigen receptor (CAR)-T-cell therapy is a kind of adoptive T-cell therapy (ACT) that has developed rapidly in recent years. Mesothelin (MSLN) is a tumor-associated antigen (TAA) that is highly expressed in various solid tumors and is an important target antigen for the development of new immunotherapies for solid tumors. This article reviews the clinical research status, obstacles, advancements and challenges of anti-MSLN CAR-T-cell therapy. Clinical trials on anti-MSLN CAR-T cells show that they have a high safety profile but limited efficacy. At present, local administration and introduction of new modifications are being used to enhance proliferation and persistence and to improve the efficacy and safety of anti-MSLN CAR-T cells. A number of clinical and basic studies have shown that the curative effect of combining this therapy with standard therapy is significantly better than that of monotherapy.

Radiolabeled Human Monoclonal Antibody 067-213 has the Potential for Noninvasive Quantification of CD73 Expression

BACKGROUND

CD73 is an ectonucleotidase regulating extracellular adenosine concentration and plays an important role in adenosine-mediated immunosuppressive pathways. The efficacy of CD73-targeted therapy depends on the expression levels of CD73; therefore, monitoring CD73 status in cancer patients would provide helpful information for selection of patients who would benefit from CD73-targeted therapy. Here, we evaluated the ability of 111In-labeled antibody 067-213, which has high affinity for human CD73, to act as a noninvasive imaging probe.

METHODS

Cell binding and competitive inhibition assays for 111In-labeled 067-213 were conducted using MIAPaCa-2 (high CD73 expression) and A431 (low CD73 expression) cells. For in vivo assessments, biodistribution and SPECT/CT studies were conducted in MIAPaCa-2 and A431 tumor-bearing mice. To estimate the absorbed dose in humans, biodistribution and SPECT/CT studies were conducted in healthy rats.

RESULTS

111In-labeled 067-213 bound to MIAPaCa-2 and A431 cells in a CD73-dependent manner and the affinity loss after 111In-labeling was limited. Biodistribution and SPECT/CT studies with 111In-labeled 067-213 in mice showed high uptake in MIAPaCa-2 tumors and lower uptake in A431 tumors. In rats, the probe did not show high uptake in normal organs, including endogenously CD73-expressing organs. The estimated absorbed doses in humans were reasonably low.

CONCLUSIONS

111In-labeled 067-213 showed CD73-expression-dependent tumor uptake and low uptake in normal organs and tissues. Radiolabeled 067-213 holds promise as an imaging probe for noninvasive evaluation of CD73 expression levels in patients. Our data encourage further clinical studies to clarify a role for CD73 monitoring in patients receiving CD73-targeted immune therapy.

The Role of Mesothelin as a Diagnostic and Therapeutic Target in Pancreatic Ductal Adenocarcinoma: A Comprehensive Review

Mesothelin is a tumor differentiation antigen, which is highly expressed in several solid neoplasms, including pancreatic cancer. Its selective expression on malignant cells and on only a limited number of healthy tissues has made it an interesting candidate for investigation as a diagnostic and prognostic biomarker and as a therapeutic target. Based on a strong preclinical rationale, a number of therapeutic agents targeting mesothelin have entered clinical trials, including immunotoxins, monoclonal antibodies, antibody-drug conjugates, cancer vaccines, and adoptive T cell therapies with chimeric antigen receptors. In pancreatic cancer, mesothelin has been investigated mainly to address two unmet issues: the urgent need for new laboratory techniques for early tumor detection and the lack of successfully targetable oncogenic alterations for patients' treatment. In this review, we describe the clinicopathological significance of mesothelin expression in pancreatic cancer initiation and progression, we summarize available studies evaluating mesothelin as a potential diagnostic and prognostic biomarker in this disease, and we discuss current evidence and future perspectives of preclinical and clinical studies testing mesothelin as a molecular target for pancreatic cancer treatment.

Evaluation of a biomarker for the diagnosis of pancreas cancer using an animal model

Many approaches have been taken to identify new biomarkers of pancreatic ductal carcinoma (PDC). Since animal models can be sampled under controlled conditions, better standardization is possible compared with heterogeneous human studies. Transgenic rats with conditional activation of oncogenic RAS in pancreatic tissue develop PDC that closely resembles the biological and histopathological features of human PDC. Using this model, we evaluated the usefulness of leucine-rich α2-glycoprotein-1 (LRG-1) as a serum marker. In this study, we found that LRG-1 was overexpressed in rat PDC compared with normal pancreas tissue of the control rats. Serum levels of LRG-1 were also significantly higher in rats bearing PDC than in controls. Importantly, chronic pancreatitis in male Wistar Bonn/Kobori rats, which is a widely accepted as a model of chronic pancreatitis, did not cause serum levels of LRG-1 to become elevated. These results strongly support serum LRG-1 as a candidate biomarker for noninvasive diagnosis of PDC. Our models of pancreas cancer provide a useful strategy for evaluation of candidate markers applicable to human cancer.

Transgenic rat models for mutagenesis and carcinogenesis

Rats are a standard experimental animal for cancer bioassay and toxicological research for chemicals. Although the genetic analyses were behind mice, rats have been more frequently used for toxicological research than mice. This is partly because they live longer than mice and induce a wider variety of tumors, which are morphologically similar to those in humans. The body mass is larger than mice, which enables to take samples from organs for studies on pharmacokinetics or toxicokinetics. In addition, there are a number of chemicals that exhibit marked species differences in the carcinogenicity. These compounds are carcinogenic in rats but not in mice. Such examples are aflatoxin B1 and tamoxifen, both are carcinogenic to humans. Therefore, negative mutagenic/carcinogenic responses in mice do not guarantee that the chemical is not mutagenic/carcinogenic to rats or perhaps to humans. To facilitate research on in vivo mutagenesis and carcinogenesis, several transgenic rat models have been established. In general, the transgenic rats for mutagenesis are treated with chemicals longer than transgenic mice for more exact examination of the relationship between mutagenesis and carcinogenesis. Transgenic rat models for carcinogenesis are engineered mostly to understand mechanisms underlying chemical carcinogenesis. Here, we review papers dealing with the transgenic rat models for mutagenesis and carcinogenesis, and discuss the future perspective.

In vivo18F-fluorodeoxyglucose-positron emission tomography/computed tomography imaging of pancreatic tumors in a transgenic rat model carrying the human KRASG12V oncogene

A novel KRAS-mediated transgenic rat model has previously been demonstrated, in which animals develop multiple pancreatic ductal adenocarcinoma (PDAC) that is histologically similar to human PDAC within two weeks. Positron emission tomography (PET)/computed tomography (CT) is commonly used for the diagnosis and staging of PDAC in humans, and can be adopted for optimal use in animal experiments. The aim of the present study was to evaluate the carcinogenic process in a rat pancreatic carcinoma model using small-animal multimodality imaging systems. The utility of fluorodeoxyglucose (FDG)-PET/CT in detecting the location and size of PDAC during tumor development in the present transgenic rat model was assessed. A small animal multimodality PET/CT system and contrast-enhanced CT (CECT) system were used for the imaging analysis of KRAS^G12V male transgenic rats (n=6), which developed pancreatic tumors following the administration of an injection of Cre recombinase (Cre)-carrying adenovirus. Laparotomies performed at six weeks post-treatment revealed that all three (100%) Cre-expressing rats developed pancreatic tumors that were <2 mm in diameter, none of which were detected by ¹⁸F-FDG PET/CT or CECT. At eight weeks post-treatment, the pancreatic tumors were heterogeneously visualized by ¹⁸F-FDG-PET/CT and CECT in two of the three rats. Furthermore, the autopsies confirmed that all three rats had developed pancreatic tumors. These novel findings provide evidence that the FDG-PET/CT imaging system is a valuable tool for the evaluation of the carcinogenic process, and one which may aid in treatment and preventive methods for pancreatic tumors in mammalian models. A limitation associated with the early detection of PDACs warrants further investigation.

Rat N-ERC/mesothelin as a marker for in vivo screening of drugs against pancreas cancer

Pancreatic ductal adenocarcinoma (PDA) is a highly lethal disease, which is usually diagnosed in an advanced stage. We have established transgenic rats carrying a mutated K-ras gene controlled by Cre/loxP activation. The animals develop PDA which is histopathologically similar to that in humans. Previously, we reported that serum levels of N-ERC/mesothelin were significantly higher in rats bearing PDA than in controls. In the present study, to determine whether serum levels of N-ERC/mesothelin correlated with tumor size, we measured N-ERC/mesothelin levels in rats bearing PDA. Increased serum levels of N-ERC/mesothelin correlated with increased tumor size. This result indicates an interrelationship between the serum level of N-ERC/mesothelin and tumor size. We next investigated the effect of chemotherapy on serum N-ERC/mesothelin levels. Rat pancreatic cancer cells were implanted subcutaneously into the flank of NOD-SCID mice. In the mice treated with 200 mg/kg gemcitabine, tumor weight and the serum level of N-ERC/mesothelin were significantly decreased compared to controls. These results suggest that serum N-ERC/mesothelin measurements might be useful for monitoring response to therapy.

Twenty-one proteins up-regulated in human H-ras oncogene transgenic rat pancreas cancers are up-regulated in human pancreas cancer

OBJECTIVES

We have established rat models of pancreatic ductal adenocarcinoma (PDAC) in which expression of a human H-ras(G12V) or K-ras(G12V) oncogene regulated by the Cre/lox system drives pancreatic carcinogenesis. Pancreatic ductal adenocarcinoma which develops in H-ras(G12V) and K-ras(G12V) transgenic rats is cytogenetically and histopathologically similar to human PDAC. The present study was designed to determine the feasibility of using the commercially available H-ras(G12V) transgenic rat to find diagnostic protein biomarkers for human pancreatic cancer.

METHODS

For an animal model to be useful for searching for protein biomarkers for a disease, it is essential that proteins that are up-regulated in the model are also up-regulated in humans. We used liquid chromatography-tandem mass spectrometry (LC-MS/MS) to compare H-ras(G12V) transgenic rat PDAC with surrounding normal pancreas tissue.

RESULTS

We identified 30 up-regulated proteins in the H-ras(G12V) transgenic rat PDAC lesions; importantly, 21 human homologs of these 30 rat proteins are up-regulated in human pancreatic cancer patients.

CONCLUSIONS

These results indicate that numerous proteins that are up-regulated in H-ras(G12V) transgenic rat PDAC are also up-regulated in human pancreatic cancer; therefore, this rat model can be used to search for diagnostic biomarkers for this disease.

A novel reporter rat strain that expresses LacZ upon Cre-mediated recombination

The recent widespread application of Cre/loxP technology has resulted in a new generation of conditional animal models that can better recapitulate many salient features of human disease. These models benefit from the ability to monitor the expression and functionality of Cre protein. We have generated a conditional (Cre/loxP dependent) LacZ reporter rat (termed the LacZ541 rat) to monitor Cre in transgenic rats. When LacZ541 rats were bred with another transgenic rat line expressing Cre recombinase under the control of the CAG promoter, LacZ/Cre double transgenic embryos displayed ubiquitous expression of LacZ, and when LacZ541 rats were bred with transgenic rats expressing Cre/loxP-dependent oncogenic H- or K-ras, LacZ was expressed in the lesions resulting from the activation of the oncogene. The LacZ541 rat enables evaluation of the performance of Cre-expressing systems which are based upon transgenic rats or somatic gene transfer vectors and provides efficient and simple lineage marking.

Metabolomic and transcriptomic profiling of human K-ras oncogene transgenic rats with pancreatic ductal adenocarcinomas

Pancreatic ductal adenocarcinoma (PDAC) is one of the most debilitating malignancies in humans, and one of the reasons for this is the inability to diagnose this disease early in its development. To search for biomarkers that can be used for early diagnosis of PDAC, we established a rat model of human PDAC in which expression of a human K-ras(G12V) oncogene and induction of PDAC are regulated by the Cre/lox system. In the present study, transgenic rats bearing PDAC and control transgenic rats with normal pancreatic tissues were used for metabolomic analysis of serum and pancreatic tissue by non-targeted and targeted gas chromatography-mass spectrometry and transcriptomic analysis of pancreatic tissue by microarray. Comparison of the metabolic profiles of the serum and pancreatic tissue of PDAC-bearing and control rats identified palmitoleic acid as a metabolite, which was significantly decreased in the serum of PDAC-bearing animals. Transcriptomic analysis indicated that several transcripts involved in anaerobic glycolysis and nucleotide degradation were increased and transcripts involved in the trichloroacetic acid cycle were decreased. Other transcripts that were changed in PDAC-bearing rats were adenosine triphosphate citrate lyase (decreased: fatty acid biosynthesis), fatty acid synthase (increased: fatty acid biosynthesis) and arachidonate 5-lipoxygenase activating protein (increased: arachidonic acid metabolism). Overall, our results suggest that the decreased serum levels of palmitoleic acid in rats with PDAC was likely due to its decrease in pancreatic tissue and that palmitoleic acid should be investigated in human samples to assess its diagnostic significance as a serum biomarker for human PDAC.

Circulating microRNAs in serum of human K-ras oncogene transgenic rats with pancreatic ductal adenocarcinomas

OBJECTIVES

Novel biomarkers for pancreatic ductal adenocarcinoma (PDAC) are urgently needed because of its poor prognosis. We have previously established an animal model for human PDAC using transgenic rats in which expression of a human K-ras(G12V) oncogene is regulated by the Cre/lox system. Using this model, we searched for candidate circulating microRNAs (miRNAs) for use as novel clinical diagnostic biomarkers for PDAC.

METHODS

Rats bearing PDACs were generated using our model. MicroRNA expression in serum and pancreatic tissues of PDAC and control rats was compared by microarray analysis. Rat serum levels of 28 miRNAs identified by microarray analysis and 4 miRNAs previously reported to be high in plasma of PDAC patients were quantified by real-time quantitative reverse transcription polymerase chain reaction.

RESULTS

Quantification by real-time quantitative polymerase chain reaction revealed that miR-155, miR-21, and miR-210 were higher in serum of PDAC rats, similar to plasma of patients with PDAC. In addition, miR-18a, miR-203, miR-30b-5p, miR-31, miR-369-5p, miR-376a, and miR-541 were higher and miR-375 was lower in the serum of PDAC rats.

CONCLUSION

We identified 4 previously unreported miRNAs (miRNA-203, miRNA-369-5p, miRNA-376a, and miRNA-375) whose expression is significantly different in PDAC rats compared to control rats. These miRNAs need to be quantitated in humans as potential novel clinical diagnostic biomarkers for PDAC.

The bidirectional interation between pancreatic cancer and diabetes

The bidirectional interation between pancreatic cancer (PanCa) and diabetes has been confirmed by epidemiological studies, which provide evidence-based medical support for further research into the mechanisms involved in the interaction. We reviewed the literature regarding the role of diabetes in the generation and progression of PanCa and the mechanism by which PanCa induces diabetes for its malignant progression. The effect of antidiabetic drugs on the occurrence and prognosis of PanCa was also reviewed. Diabetes may directly promote the progression of PanCa by pancreatic duct enlargement and hypertension, as well as by enabling an increased tumor volume. Hyperinsulinemia, insulin resistance, cytokines, hyperglycemia and genotype change are also important factors in the progression of PanCa with diabetes. Hyperglycemia may be the first clinical manifestation and is helpful in the early diagnosis of PanCa. Furthermore, antidiabetic drugs can have different effects on the occurrence and prognosis of PanCa. The bidirectional interation between PanCa and diabetes is involved in the occurrence, proliferation, invasion, metastasis and prognosis of PanCa with diabetes. The discovery of biomarkers for the early diagnosis of PanCa, as well as the novel usage of metformin for its antitumor effects and determining the potential mechanisms of these effects, may be the next direction for PanCa research and treatment.

Mesothelin overexpression promotes mesothelioma cell invasion and MMP-9 secretion in an orthotopic mouse model and in epithelioid pleural mesothelioma patients

PURPOSE

Mesothelin (MSLN) is a tumor-associated antigen, being investigated as a biomarker and therapeutic target in malignant pleural mesothelioma (MPM). The biologic function of MSLN overexpression in MPM is unknown. We hypothesized that MSLN may promote tumor invasion in MPM, a tumor characterized primarily by regional aggressiveness and rare distant metastases.

EXPERIMENTAL DESIGN

Human and murine MPM cells with MSLN forced expression and short hairpin RNA knockdown were examined for proliferation, invasion, and matrix metalloproteinase (MMP) secretion. The influence of MSLN overexpression on MPM cell invasion was assessed in an orthotopic mouse model and in patient samples.

RESULTS

MSLN expression promotes MPM cell invasion and MMP secretion in both human and murine MPM cells. In an orthotopic MPM mouse model characterized by our laboratory, MPM cells with MSLN overexpression preferentially localized to the tumor invading edge, colocalized with MMP-9 expression, and promoted decreased survival without an increase in tumor burden progression. In a tissue microarray from epithelioid MPM patients (n = 139, 729 cores), MSLN overexpression correlated with higher MMP-9 expression at individual core level. Among stage III MPM patients (n = 72), high MSLN expression was observed in 26% of T2 tumors and 51% of T3 tumors.

CONCLUSIONS

Our data provide evidence elucidating a biologic role for MSLN as a factor promoting tumor invasion and MMP-9 expression in MSLN expressing MPM. As regional invasion is the characteristic feature in MSLN expressing solid cancers (MPM, pancreas, and ovarian), our observations add rationale to studies investigating MSLN as a therapeutic target.

RAS oncogenic signal upregulates EZH2 in pancreatic cancer

The neoplastic transformation by mutant RAS is thought to require remodeling of expression of an entire set of genes. However, the underlying mechanism for initiation of gene expression remodeling in tumorigenesis remains elusive. This study was aimed to define the oncogenic role of EZH2, a histone modifier protein that is induced by oncogenic mutant RAS, using pancreatic cancers of transgenic rats exogenously expressing human mutant RAS. Immunohistochemical observation of preneoplastic or cancerous lesions in the animal model suggested that upregulation of Ezh2 protein is an initiating event in pancreatic carcinogenesis. MEK-inhibition or Elk-1-knockdown downregulated EZH2, and MEK-inhibition or EZH2-knockdown restored expression of a tumor suppressor, RUNX3 in human and rat pancreatic cancer cells activated by the oncogenic RAS. Furthermore, Elk-1- or EZH2-knockdown inhibited growth of the cancer cells. These results strongly suggested that the oncogenic RAS upregulates EZH2 through MEK-ERK signaling, resulted in downregulation of tumor suppressors including RUNX3 in pancreatic carcinogenesis.

Mesothelin overexpression promotes autocrine IL-6/sIL-6R trans-signaling to stimulate pancreatic cancer cell proliferation

Mesothelin (MSLN) overexpression in pancreatic cancer (PC) leads to enhanced cell survival/proliferation and tumor progression. After screening for a number of growth factors/cytokines, we found that the MSLN expression correlated closely with interleukin (IL)-6 in human PC specimens and cell lines. Stably overexpressing MSLN in different PC cell lines (MIA-MSLN and Panc1-MSLN) led to higher IL-6 production. Silencing MSLN by small interfering RNA (siRNA) significantly reduced IL-6 levels. Blocking the observed constitutive activation of nuclear factor-kappaB (NF-κB) with IKK inhibitor wedelolactone in MIA-MSLN cells also reduced IL-6. Silencing IL-6 by siRNA reduced cell proliferation, cell cycle progression and induced apoptosis with significant decrease of c-myc/bcl-2. Interestingly, recombinant IL-6-induced proliferation of MIA-MSLN cells but not MIA-V cells. Although messenger RNA/protein levels of IL-6R did not vary, soluble IL-6R (sIL-6R) was significantly elevated in MIA-MSLN and was reduced by treatment with the TACE/ADAM17 inhibitor TAPI-1, indicating intramembrane IL-6R cleavage and IL-6 trans-signaling may be operative in MIA-MSLN cells. Blocking the IL-6/sIL-6R axis using sIL-6R antibody abrogated basal proliferation/survival as well as recombinant human IL-6-induced cell proliferation. Our data suggest that MSLN-activated NF-κB induces elevated IL-6 expression, which acts as a growth factor to support PC cell survival/proliferation through a novel auto/paracrine IL-6/sIL-6R trans-signaling. In addition, using a panel of PC cells with varying MSLN/IL-6 expressions, we showed that MSLN/IL-6 axis is a major survival axis in PC supporting tumor cell growth under anchorage-dependent and independent conditions. The close correlation between MSLN and IL-6 provides a new rationale for combination therapy for effective control of MSLN-overexpressing PCs.

Experimental animal models of pancreatic carcinogenesis for prevention studies and their relevance to human disease

Pancreatic cancer is difficult to cure, so its prevention is very important. For this purpose, animal model studies are necessary to develop effective methods. Injection of N-nitrosobis(2-oxopropyl)amine (BOP) into Syrian golden hamsters is known to induce pancreatic ductal adenocarcinomas, the histology of which is similar to human tumors. Moreover, K-ras activation by point mutations and p16 inactivation by aberrant methylation of 5' CpG islands or by homozygous deletions have been frequently observed in common in both the hamster and humans. Thus, this chemical carcinogenesis model has an advantage of histopathological and genetic similarity to human pancreatic cancer, and it is useful to study promotive and suppressive factors. Syrian golden hamsters are in a hyperlipidemic state even under normal dietary conditions, and a ligand of peroxizome proliferator-activated receptor gamma was found to improve the hyperlipidemia and suppress pancreatic carcinogenesis. Chronic inflammation is a known important risk factor, and selective inhibitors of inducible nitric oxide synthase and cyclooxygenase-2 also have protective effects against pancreatic cancer development. Anti-inflammatory and anti-hyperlipidemic agents can thus be considered candidate chemopreventive agents deserving more attention.

Serum level of expressed in renal carcinoma (ERC)/ mesothelin in rats with mesothelial proliferative lesions induced by multi-wall carbon nanotube (MWCNT)

Expressed in renal carcinoma (ERC)/mesothelin is a good biomarker for human mesothelioma and has been investigated for its mechanistic rationale during the mesothelioma development. Studies are thus ongoing in our laboratories to assess expression of ERC/mesothelin in sera and normal/proliferative/neoplastic mesothelial tissues of animals untreated or given potentially mesothelioma-inducible xenobiotics, by an enzyme-linked immunosorbent assay (ELISA) for N- and C-(terminal fragments of) ERC/mesothelin and immunohistochemistry for C-ERC/mesothelin. In the present paper, we intend to communicate our preliminary data, because this is the first report to show how and from what stage the ERC/mesothelin expression changes during the chemical induction of mesothelial proliferative/neoplatic lesions. Serum N-ERC/mesothelin levels were 51.4 +/- 5.6 ng/ml in control male Fischer 344 rats, increased to 83.6 +/- 11.2 ng/ml in rats given a single intrascrotal administration of 1 mg/kg body weight of multi-wall carbon nanotube (MWCNT) and bearing mesothelial hyperplasia 52 weeks thereafter, and further elevated to 180 +/- 77 ng/ml in rats similarly treated and becoming moribund 40 weeks thereafter, or killed as scheduled at the end of week 52, bearing mesothelioma. While C-ERC/mesothelin was expressed in normal and hyperplastic mesothelia, the protein was detected only in epithelioid mesothelioma cells at the most superficial layer. It is thus suggested that ERC/mesothelin can be used as a biomarker of mesothelial proliferative lesions also in animals, and that the increase of levels may start from the early stage and be enhanced by the progression of the mesothelioma development.