Kappa opioid agonists in the treatment of itch: just scratching the surface?

Chronic pruritus is a debilitating condition affecting 23-44 million Americans. Recently, kappa opioid agonists (KOAs) have emerged as a novel class of potent antipruritic agents. In 2021, the Food and Drug Administration approved difelikefalin (Korsuva) for the treatment of moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis. Difelikefalin is a potent, peripherally restricted KOA that is intravenously available. Although promising, difelikefalin is currently available as an intravenous composition only, limiting the scope of use. Oral formulations of difelikefalin did not meet the primary endpoint criteria in recent phase 2 clinical trials; however, additional clinical studies are ongoing. The future for KOAs in the treatment of pruritus is encouraging. Orally active pathway-biased KOAs, such as triazole 1.1, may serve as viable alternatives with broader applications. Extended-release compositions, such as the TP-2021 ProNeura subdermal implant, may circumvent the pharmacokinetic issues associated with peptide-based KOAs. Lastly, dual-acting kappa opioid receptor agonist/mu opioid receptor antagonists are orally bioavailable and may be useful in the treatment of various forms of chronic itch. In this review, we summarize the results of KOAs in clinical and preclinical trials and discuss future directions of drug development.

Immunoglobulin G4-Related Disease-Associated Dermatitis with Pruritus: A Positive Response to Dupilumab

Immunoglobulin G4-related disease (IgG4-RD) is a rare fibro-inflammatory condition characterized by IgG4-expressing plasma cell infiltration of the skin and other organs, leading to profound itchiness. Oral corticosteroids are the first-line therapy for IgG4-RD but relapses and potential side effects are common. In this case, we discuss a patient with a hyperpigmented, scaling dermatitis on his arms, back, and chest with lichen amyloidosis (LA) that incompletely responded to corticosteroids. He had reduced quality of life secondary to chronic pruritus. Dupilumab, an IL-4 and IL-13 inhibitor, was initiated. He experienced a transient worsening, followed by complete resolution of his itch with remission of his rash. While the pathogenesis of IgG4-RD is not entirely understood, a T-helper 2 (Th2) immune response has been implicated, with interleukins (IL) 4, 5, 10, and 13 playing a role in IgG4 class switch, resulting in eosinophilia and elevated IgE. The strong response of dupilumab in this case may provide evidence in favor of the involvement of IL-4 and IL-13 in the pathogenesis of cutaneous IgG4-RD. Future clinical studies involving larger patient populations may be warranted.

Diet, sleep, and exercise in inflammatory skin diseases

Inflammatory skin conditions are significantly impacted by lifestyle habits, particularly those related to diet, exercise, and sleep. Although ancient cultures emphasized the importance of lifestyle behaviors as both etiology and therapy in disease, modern medicine often overlooks nonpharmacological therapy. However, recent studies show that diet can have a significant impact on inflammatory skin diseases such as psoriasis, hidradenitis suppurativa, and atopic dermatitis. Foods high in glycemic index, advanced glycation end-products, and omega-6 polyunsaturated fatty acids are associated with obesity and systemic inflammation, which can exacerbate inflammatory skin diseases. In addition, lifestyle behaviors such as exercise and sleep have been shown to have positive effects on inflammatory skin diseases. This review aims to highlight the importance of lifestyle behaviors in the context of inflammation and inflammatory dermatoses.

Cellular and Molecular Mechanisms of MEK1 Inhibitor-Induced Cardiotoxicity

Background

Trametinib is a MEK1 (mitogen-activated extracellular signal-related kinase kinase 1) inhibitor used in the treatment of BRAF (rapid accelerated fibrosarcoma B-type)-mutated metastatic melanoma. Roughly 11% of patients develop cardiomyopathy following long-term trametinib exposure. Although described clinically, the molecular landscape of trametinib cardiotoxicity has not been characterized.

Objectives

The aim of this study was to test the hypothesis that trametinib promotes widespread transcriptomic and cellular changes consistent with oxidative stress and impairs cardiac function.

Methods

Mice were treated with trametinib (1 mg/kg/d). Echocardiography was performed pre- and post-treatment. Gross, histopathologic, and biochemical assessments were performed to probe for molecular and cellular changes. Human cardiac organoids were used as an in vitro measurement of cardiotoxicity and recovery.

Results

Long-term administration of trametinib was associated with significant reductions in survival and left ventricular ejection fraction. Histologic analyses of the heart revealed myocardial vacuolization and calcification in 28% of animals. Bulk RNA sequencing identified 435 differentially expressed genes and 116 differential signaling pathways following trametinib treatment. Upstream gene analysis predicted interleukin-6 as a regulator of 17 relevant differentially expressed genes, suggestive of PI3K/AKT and JAK/STAT activation, which was subsequently validated. Trametinib hearts displayed elevated markers of oxidative stress, myofibrillar degeneration, an 11-fold down-regulation of the apelin receptor, and connexin-43 mislocalization. To confirm the direct cardiotoxic effects of trametinib, human cardiac organoids were treated for 6 days, followed by a 6-day media-only recovery. Trametinib-treated organoids exhibited reductions in diameter and contractility, followed by partial recovery with removal of treatment.

Conclusions

These data describe pathologic changes observed in trametinib cardiotoxicity, supporting the exploration of drug holidays and alternative pharmacologic strategies for disease prevention.

Application of Pharmacokinetic Prediction Platforms in the Design of Optimized Anti-Cancer Drugs

Cancer is the second most common cause of death in the United States, accounting for 602,350 deaths in 2020. Cancer-related death rates have declined by 27% over the past two decades, partially due to the identification of novel anti-cancer drugs. Despite improvements in cancer treatment, newly approved oncology drugs are associated with increased toxicity risk. These toxicities may be mitigated by pharmacokinetic optimization and reductions in off-target interactions. As such, there is a need for early-stage implementation of pharmacokinetic (PK) prediction tools. Several PK prediction platforms exist, including pkCSM, SuperCypsPred, Pred-hERG, Similarity Ensemble Approach (SEA), and SwissADME. These tools can be used in screening hits, allowing for the selection of compounds were reduced toxicity and/or risk of attrition. In this short commentary, we used PK prediction tools in the optimization of mitogen activated extracellular signal-related kinase kinase 1 (MEK1) inhibitors. In doing so, we identified MEK1 inhibitors with retained activity and optimized predictive PK properties, devoid of hERG inhibition. These data support the use of publicly available PK prediction platforms in early-stage drug discovery to design safer drugs.

DCHS1, Lix1L, and the Septin Cytoskeleton: Molecular and Developmental Etiology of Mitral Valve Prolapse

Mitral valve prolapse (MVP) is a common cardiac valve disease that often progresses to serious secondary complications requiring surgery. MVP manifests as extracellular matrix disorganization and biomechanically incompetent tissues in the adult setting. However, MVP has recently been shown to have a developmental basis, as multiple causal genes expressed during embryonic development have been identified. Disease phenotypes have been observed in mouse models with human MVP mutations as early as birth. This study focuses on the developmental function of DCHS1, one of the first genes to be shown as causal in multiple families with non-syndromic MVP. By using various biochemical techniques as well as mouse and cell culture models, we demonstrate a unique link between DCHS1-based cell adhesions and the septin-actin cytoskeleton through interactions with cytoplasmic protein Lix1-Like (LIX1L). This DCHS1-LIX1L-SEPT9 axis interacts with and promotes filamentous actin organization to direct cell-ECM alignment and valve tissue shape.

Mitral Valve Prolapse Induces Regionalized Myocardial Fibrosis

Background Mitral valve prolapse (MVP) is one of the most common forms of cardiac valve disease and affects 2% to 3% of the population. Previous imaging reports have indicated that myocardial fibrosis is common in MVP and described its association with sudden cardiac death. These data combined with evidence for postrepair ventricular dysfunction in surgical patients with MVP support a link between fibrosis and MVP. Methods and Results We performed histopathologic analysis of left ventricular (LV) biopsies from peripapillary regions, inferobasal LV wall and apex on surgical patients with MVP, as well as in a mouse model of human MVP (Dzip1S14R/+). Tension-dependent molecular pathways were subsequently assessed using both computational modeling and cyclical stretch of primary human cardiac fibroblasts in vitro. Histopathology of LV biopsies revealed regionalized fibrosis in the peripapillary myocardium that correlated with increased macrophages and myofibroblasts. The MVP mouse model exhibited similar regional increases in collagen deposition that progress over time. As observed in the patient biopsies, increased macrophages and myofibroblasts were observed in fibrotic areas within the murine heart. Computational modeling revealed tension-dependent profibrotic cellular and molecular responses consistent with fibrosis locations related to valve-induced stress. These simulations also identified mechanosensing primary cilia as involved in profibrotic pathways, which was validated in vitro and in human biopsies. Finally, in vitro stretching of primary human cardiac fibroblasts showed that stretch directly activates profibrotic pathways and increases extracellular matrix protein production. Conclusions The presence of prominent regional LV fibrosis in patients and mice with MVP supports a relationship between MVP and progressive damaging effects on LV structure before overt alterations in cardiac function. The regionalized molecular and cellular changes suggest a reactive response of the papillary and inferobasal myocardium to increased chordal tension from a prolapsing valve. These studies raise the question whether surgical intervention on patients with MVP should occur earlier than indicated by current guidelines to prevent advanced LV fibrosis and potentially reduce residual risk of LV dysfunction and sudden cardiac death.

The C-C Chemokine Receptor Type 4 Is an Immunomodulatory Target of Hydroxychloroquine

The emergence of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; COVID-19) in China, reported to the World Health Organization on December 31, 2019, has led to a large global pandemic and is a major public health issue. As a result, there are more than 200 clinical trials of COVID-19 treatments or vaccines that are either ongoing or recruiting patients. One potential therapy that has garnered international attention is hydroxychloroquine; a potent immunomodulatory agent FDA-approved for the treatment of numerous inflammatory and autoimmune conditions, including malaria, lupus, and rheumatoid arthritis. Hydroxychloroquine has demonstrated promise in vitro and is currently under investigation in clinical trials for the treatment of COVID-19. Despite an abundance of empirical data, the mechanism(s) involved in the immunomodulatory activity of hydroxychloroquine have not been characterized. Using the unbiased chemical similarity ensemble approach (SEA), we identified C-C chemokine receptor type 4 (CCR4) as an immunomodulatory target of hydroxychloroquine. The crystal structure of CCR4 was selected for molecular docking studies using the SwissDock modeling software. In silico, hydroxychloroquine interacts with Thr-189 within the CCR4 active site, presumably blocking endogenous ligand binding. However, the CCR4 antagonists compound 18a and K777 outperformed hydroxychloroquine in silico, demonstrating energetically favorable binding characteristics. Hydroxychloroquine may subject COVID-19 patients to QT-prolongation, increasing the risk of sudden cardiac death. The FDA-approved CCR4 antagonist mogalizumab is not known to increase the risk of QT prolongation and may serve as a viable alternative to hydroxychloroquine. Results from this report introduce additional FDA-approved drugs that warrant investigation for therapeutic use in the treatment of COVID-19.

Non-addictive orally-active kappa opioid agonists for the treatment of peripheral pain in rats

Addiction to conventional opioid pain analgesics is a major societal problem that is increasing at an alarming rate. New drugs to combat the effects of opioid abuse are desperately needed. Kappa-opioid agonists are efficacious in peripheral pain models but suffer from centrally-mediated effects. In this article, we discuss our efforts in developing peripheral kappa-based opioid receptor agonists that have the potential analgesic activity of opioids but do not manifest the negative side-effects of opioid use and abuse. Further, derivatives of the tetra-peptide D-Phe-D-Phe-D-Nle-D-Arg-NH2, such as CR665, exhibit high peripheral to central selectivity in analgesic models when administered intravenously (i.v.); however, they are inactive when administered orally. Application of our laboratory's proprietary non-natural amino acid technology to CR665 produced derivatives that exhibit peripheral analgesic activity when dosed orally but do not promote CNS-based effects. Lead compound JT09 activates the kappa-opioid receptor with EC50s in the low nM range, while agonist selectivity for kappa over other peripheral opioid receptors was >33,400 fold. Results indicate that JT09 is approximately as efficacious as morphine in alleviating peripheral pain, while failing to produce undesired CNS-mediated activity. Additionally, JT09 did not promote other CNS-mediated effects associated with morphine (addiction, sedation, dysphoria, tolerance, addiction). Thus, we propose that JT09 has potential for development as a novel analgesic. PERSPECTIVE: This article presents data supporting the analgesic properties of an orally available, peripherally-restricted, kappa-opioid agonist for peripheral pain. A potential out-patient pharmaceutical that acts as efficacious as morphine in alleviating peripheral pain, while failing to produce undesired CNS-mediated effects, could help reduce the current health care burden associated with prescription opioids.

Therapeutic Potential of Kappa Opioid Agonists

Many original research articles have been published that describe findings and outline areas for the development of kappa-opioid agonists (KOAs) as novel drugs; however, a single review article that summarizes the broad potential for KOAs in drug development does not exist. It is well-established that KOAs demonstrate efficacy in pain attenuation; however, KOAs also have proven to be beneficial in treating a variety of novel but often overlapping conditions including cardiovascular disease, pruritus, nausea, inflammatory diseases, spinal anesthesia, stroke, hypoxic pulmonary hypertension, multiple sclerosis, addiction, and post-traumatic cartilage degeneration. This article summarizes key findings of KOAs and discusses the untapped therapeutic potential of KOAs in the treatment of many human diseases.

Targeting Peripheral Kappa Opioid Receptors for the Treatment of Chronic Pain: Review Article

Addiction to conventional opioid pain analgesics is a major societal problem that is increasing at an alarming rate. New drugs to combat the effects of opioid abuse are desperately needed. Kappa-opioid agonists are efficacious in peripheral pain models but suffer from centrally-mediated effects. In this review, we discuss our efforts, as well as other's efforts in developing peripheral kappa-based opioid receptor agonists that have the potential analgesic activity of opioids but do not manifest the negative side-effects of opioid use and abuse. Further, derivatives of the tetra peptide D-Phe-D-Phe-D-Nle-D-Arg-NH₂, such as CR665, exhibit high peripheral to central selectivity in analgesic models when administered intravenously (IV); however, they are inactive when administered orally. Application of the JT Pharmaceuticals non-natural amino acid technology to CR665 produced derivatives that exhibit peripheral analgesic activity when dosed orally but do not promote CNS-based effects. Lead compound JT09 activates the kappa-opioid receptor with EC50s in the low nM range, while agonist selectivity for kappa over other peripheral opioid receptors was >33,400 fold. Results indicate that JT09 acts as efficacious as morphine in alleviating peripheral pain, while failing to produce undesired CNS-mediated activity. Additionally, JT09 did not promote other CNS-mediated effects associated with morphine (addiction, sedation, dysphoria, tolerance). Thus, we propose that JT09 has potential for development as a novel analgesic.

A novel thermostable branching enzyme from an extremely thermophilic bacterial species, Rhodothermus obamensis

A branching enzyme (EC 2.4.1.18) gene was isolated from an extremely thermophilic bacterium, Rhodothermus obamensis. The predicted protein encodes a polypeptide of 621 amino acids with a predicted molecular mass of 72 kDa. The deduced amino acid sequence shares 42-50% similarity to known bacterial branching enzyme sequences. Similar to the Bacillus branching enzymes, the predicted protein has a shorter N-terminal amino acid extension than that of the Escherichia coli branching enzyme. The deduced amino acid sequence does not appear to contain a signal sequence, suggesting that it is an intracellular enzyme. The R. obamensis branching enzyme was successfully expressed both in E. coli and a filamentous fungus, Aspergillus oryzae. The enzyme showed optimum catalytic activity at pH 6.0-6.5 and 65 degrees C. The enzyme was stable after 30 min at 80 degrees C and retained 50% of activity at 80 degrees C after 16 h. Branching activity of the enzyme was higher toward amylose than toward amylopectin. This is the first thermostable branching enzyme isolated from an extreme thermophile.

An enzyme linked immunosorption assay for tissue factor pathway inhibitor

An assay for the quantification of full-length and carboxy-terminus truncated tissue factor pathway inhibitor (TFPI) has been developed. The assay is a classical two-antibody sandwich assay with a monoclonal capture antibody directed against the third Kunitz-type domain of human TFPI and a polyclonal rabbit peroxidase-labelled anti-human TFPI detecting antibody. The assay is sensitive to full-length and carboxy-terminus truncated TFPI with intact third Kunitz-type domain, but not to two-domain TFPI. TFPI associated with lipoproteins is not or only sparsely detected and TFPI in complex with factor Xa only partially measured. The assays gives linear reference curves in the dose range of 5 to 100 ng/ml in a double logarithmic plot. The normal range assessed from analyses on citrated plasma from 81 normal human donors is 7.8 to 26.0 ng/ml (average +/- 2 SD, log-normal distribution). There is no statistically significant difference between TFPI levels measured in 10 fasting and 10 non-fasting individuals. The reproducibility of the assay is about 5.6-5.9% (relative standard error) and the within-days and between-day reproducibilities are 4.7-5.1% and 5.9-8.5%, respectively. The assay is in very good agreement with a commercial ELISA assay recently marketed. A robust, reproducible and convenient ELISA assay for the determination of full-length and three-domain TFPI has been developed.

The C-terminus of tissue factor pathway inhibitor is essential to its anticoagulant activity

Tissue factor pathway inhibitor (TFPI) from different cell lines shows up to 15-fold differences in the ratio of anticoagulant to chromogenic activity. The anticoagulant activity was dependent on the purification procedure used and it was possible to isolate two fractions of recombinant TFPI. Only one of these fractions showed anticoagulant activity comparable with TFPI from normal human plasma, and Western blotting showed that the low-activity fraction did not react with an antibody raised against a peptide of TFPI located near the C-terminal. Analysis by mass spectroscopy of peptides from V8 protease digests showed that C-terminal amino acids could only be identified from the high-activity form, while heterologous fragmentation had taken place in the form with low anticoagulant activity. Previously published studies on TFPI have been performed using material of low anticoagulant activity compared with plasma TFPI, and we suggest that these studies have been performed with material degraded in the C-terminus.

Inhibition of extrinsic pathway inhibitor shortens the coagulation time of normal plasma and of hemophilia plasma

An increasing amount of evidence suggests that coagulation factors VIII and IX play a role not only in the intrinsic but also in the extrinsic pathway of coagulation. In this context the influence of the Extrinsic Pathway Inhibitor (EPI) on the coagulation time of hemophilia plasma lacking FVIII or FIX has been investigated. The coagulation time was measured in a dilute thromboplastin assay. Addition of recombinant EPI (rEPI) prolonged the coagulation time of normal plasma while the addition of an inhibitory antibody against EPI shortened the coagulation time. At low concentrations of thromboplastin the coagulation time of hemophilia plasma was prolonged and at all dilutions of thromboplastin, addition of anti-EPI IgG normalized the coagulation time of a hemophilia plasma. Analysis of 10 individual donor plasma samples and 8 individual hemophilia samples showed that addition of anti-EPI IgG shortened the coagulation time more in hemophilia plasma than in normal plasma. This illustrates the importance of a powerful extrinsic FVII dependent pathway to achieve hemostasis in the case of FVIII or FIX deficiency (hemophilia A and B).

Extrinsic pathway inhibitor (EPI) released to the blood by heparin is a more powerful coagulation inhibitor than is recombinant EPI

EPI released to the blood after injection of heparin, as well as recombinant EPI (r-EPI) added to normal plasma prolonged both the dilute Tissue Thromboplastin (TTP) time and the Activated Partial Thromboplastin Time (APTT). It is known that EPI inhibits both factor Xa and the factor VIIa-TTP complex. The prolongation of the APTT by EPI reflects only its inhibition of factor Xa. Addition of anti-EPI immunoglobulins (IgG) to normal plasma shortened the dilute TTP time 7.3 seconds (p less than 0.001) and the APTT by 0.7 seconds (p less than 0.001). In postheparin plasma, with polybrene added to neutralize the direct effect of heparin, the TTP was about 26 seconds longer and the APTT about 9 seconds longer than baseline values. These effects were completely abolished by anti-EPI IgG, as were the effects of r-EPI. The EPI activity (chromogenic substrate-assay) of this postheparin plasma was 1.7 U/ml. The EPI activity of the plasma spiked with r-EPI to obtain comparable effects on clotting were much higher; about 22 U/ml for the TTP effect and about 5 U/ml for the APTT effect. The findings indicate that r-EPI is considerably less potent than postheparin EPI as inhibitor of plasma coagulation. This is most striking when coagulation is initiated through the extrinsic pathway. Possibly, the anticoagulant effect of r-EPI mainly depends on its Xa inhibitory effect.

Extrinsic pathway inhibitor (EPI) and the post-heparin anticoagulant effect in tissue thromboplastin induced coagulation

It is known that the anticoagulant effect of blood or plasma is greater when heparin is given in vivo than when added in similar heparin concentrations in vitro. In this study, we neutralized heparin in citrated blood with polybrene, and then triggered coagulation with dilute tissue thromboplastin (TTP) and CaCl2. The clotting time was longer and the release of fibrinopeptide A (FPA) was retarded in the post injection samples compared to samples spiked with heparin in vitro. We have earlier reported that the extrinsic pathway inhibitor (EPI) is released to the blood after heparin injection. This was demonstrated here also for LMW heparin Enoxaparine both after intravenous and subcutaneous administration. Polyclonal blocking antibodies to EPI were added to blood or plasma heparinized in vivo or in vitro, and the direct heparin effect was neutralized with polybrene. When TTP and CaCl2 now were added and clotting time and the release of FPA recorded, the postheparin effect was greatly reduced by the antibodies. Addition of EPI antibodies to post-heparin plasma samples from cancer patients caused a marked reduction in the thromboplastin clotting times. We conclude that the release of EPI to the blood contributes significantly to the anticoagulant effect of heparin ex vivo.

Recombinant human extrinsic pathway inhibitor. Production, isolation, and characterization of its inhibitory activity on tissue factor-initiated coagulation reactions

Previous studies have shown that extrinsic pathway inhibitor (EPI) is an effective inhibitor of factor Xa alone or factor VIIa-tissue factor complex in the presence of factor Xa. Since tissue factor exposure is implicated in thrombogenesis, we hypothesized that EPI may be valuable in the treatment of some thromboembolic episodes. Furthermore, EPI may be an important factor in bleeding complications in hemophiliacs. In the present study, human EPI was expressed in baby hamster kidney cells using a mammalian expression vector. Transfected cells expressed 1-2 micrograms/ml of recombinant EPI (rEPI) which was purified to homogeneity by heparin-Sepharose chromatography, ion-exchange chromatography, and reverse phase high performance liquid chromatography. Purified rEPI exhibited a specific activity of 30,000 units/mg and migrated as a single band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular weight of 42,000. In addition, the NH2-terminal sequence of rEPI was identical to that of HepG2 EPI and HeLa EPI. The ability of rEPI to inhibit factor X activation by a complex of factor VIIa-tissue factor was then examined in the presence and absence of plasma concentrations of human factors VIII and IX. Using relipidated human brain tissue factor apoprotein, rEPI inhibited the factor VIIa-mediated activation of factor X half-maximally at 2.5 and 1 nM in the presence and absence of factors VIII and IX, respectively. Using monolayers of a human bladder carcinoma cell line (J82) as the source of tissue factor, the activation of factor X by cell-bound factor VIIa was inhibited half-maximally by 5 nM rEPI in the presence of factors VIII and IX. The proteolytic activity of J82 cell-bound factor Xa toward prothrombin was inhibited half-maximally at approximately 5 nM rEPI, while the amidolytic activity of factor Xa in solution was inhibited by rEPI with a Ki of 130 pM. Recombinant EPI also inhibited the amidolytic activity of factor VIIa half-maximally at 10 nM rEPI in the presence of relipidated tissue factor apoprotein and calcium. These results indicate that, in the presence of plasma concentrations of factors VIII and IX, at least 10 times the plasma concentration of EPI is required to reduce factor VIIa-dependent factor X activation one order of magnitude in vitro. In the absence of functional factor VIII and IX, rEPI at plasma levels was a potent inhibitor of factor VIIa-mediated factor X activation, and this activity presumably accounts for the inability of hemophiliacs to initiate hemostasis via the extrinsic pathway.

Monoclonal antibodies as probes to the differentiated exocrine pancreas react to monoclonal islet tumor tissue

Pancreatic exocrine and ductal reacting monoclonal antibodies were derived from a mouse immunized with fixed pluripotent rat islet tumor cells (MSL) and boosted in vitro with fixed and concentrated tumor cell culture supernatant. Antibodies were obtained against duct cells, intercalated ducts, acinar cells and zymogen granules as well as against parietal cells. Unexpectedly, no monoclonal antibodies were directed against the endocrine pancreas, whereas six out of seven exocrine reacting antibodies stained total or subpopulations of cells in sections of monoclonal hypoglycemic MSL-tumors. These data may support the hypothesis of a common endodermal origin of the exocrine and endocrine pancreas.