A Pfs48/45-based vaccine to block Plasmodium falciparum transmission: phase 1, open-label, clinical trial

BACKGROUND

The stalling global progress in malaria control highlights the need for novel tools for malaria elimination, including transmission-blocking vaccines. Transmission-blocking vaccines aim to induce human antibodies that block parasite development in the mosquito and mosquitoes becoming infectious. The Pfs48/45 protein is a leading Plasmodium falciparum transmission-blocking vaccine candidate. The R0.6C fusion protein, consisting of Pfs48/45 domain 3 (6C) and the N-terminal region of P. falciparum glutamate-rich protein (R0), has previously been produced in Lactococcus lactis and elicited functional antibodies in rodents. Here, we assess the safety and transmission-reducing efficacy of R0.6C adsorbed to aluminium hydroxide with and without Matrix-M™ adjuvant in humans.

METHODS

In this first-in-human, open-label clinical trial, malaria-naïve adults, aged 18-55 years, were recruited at the Radboudumc in Nijmegen, the Netherlands. Participants received four intramuscular vaccinations on days 0, 28, 56 and 168 with either 30 µg or 100 µg of R0.6C and were randomised for the allocation of one of the two different adjuvant combinations: aluminium hydroxide alone, or aluminium hydroxide combined with Matrix-M1™ adjuvant. Adverse events were recorded from inclusion until 84 days after the fourth vaccination. Anti-R0.6C and anti-6C IgG titres were measured by enzyme-linked immunosorbent assay. Transmission-reducing activity of participants' serum and purified vaccine-specific immunoglobulin G was assessed by standard membrane feeding assays using laboratory-reared Anopheles stephensi mosquitoes and cultured P. falciparum gametocytes.

RESULTS

Thirty-one participants completed four vaccinations and were included in the analysis. Administration of all doses was safe and well-tolerated, with one related grade 3 adverse event (transient fever) and no serious adverse events occurring. Anti-R0.6C and anti-6C IgG titres were similar between the 30 and 100 µg R0.6C arms, but higher in Matrix-M1™ arms. Neat participant sera did not induce significant transmission-reducing activity in mosquito feeding experiments, but concentrated vaccine-specific IgGs purified from sera collected two weeks after the fourth vaccination achieved up to 99% transmission-reducing activity.

CONCLUSIONS

R0.6C/aluminium hydroxide with or without Matrix-M1™ is safe, immunogenic and induces functional Pfs48/45-specific transmission-blocking antibodies, albeit at insufficient serum concentrations to result in transmission reduction by neat serum. Future work should focus on identifying alternative vaccine formulations or regimens that enhance functional antibody responses.

TRIAL REGISTRATION

The trial is registered with ClinicalTrials.gov under identifier NCT04862416.

Career development in fragment-based drug discovery

The pharmaceutical industry is highly reliant on researchers who not only possess the technical knowledge but also the professional skills to collaborate in drug development. To prepare future practitioners to thrive in this interdisciplinary environment, Innovative Training Networks (ITNs) have become increasingly important in doctoral training. In this piece, we explore the benefits of these ITNs in training future practitioners in drug discovery. Through a bibliometric review, we find that the top researchers in fragment-based drug discovery have a high degree of collaboration and mobility across institutes. We then investigate which aspects of the ITN training program enable PhD students to gain these skills. We find that secondments, the short-term stays that students have in partner research institutes, are useful in preparing students to have both broad knowledge of drug discovery and specialization in their field of interest. Aside from imparting technical skills, we find that the collaborative environment in ITNs enables students to communicate better and to work effectively in teams. Doctoral students benefit by being exposed to relevant experiences that they can later apply as they navigate through the complex web of relationships and competencies in the industry. We conclude by recommending best practices to further improve ITNs in the training of future practitioners.

[Clinical characteristics of sexually abused individuals with borderline intellectual functioning or mild intellectual disability: an overview of the literature]

Sexual abuse in individuals with (above) average iq is associated with a wide range of behavioural and psychological clinical characteristics, including characteristics regarding body experience. However, research on the clinical characteristics of sexually abused individuals with borderline intellectual functioning or mild intellectual disability (bif-mid) is scarce. OBJECTIVE To provide an overview of the literature on the clinical characteristics of sexually abused individuals with bif-mid.<br/> METHOD: PubMed, Embase, PsycInfo, cinahl, Cochrane Library and Web of Science were searched for relevant publications using terms related to 'intellectual disability' and 'sexual abuse'. <br/> RESULTS: Seven studies were included. The studies in question mostly reported behavioural and psychological characteristics such as challenging behaviour, sexualised behaviour or posttraumatic stress, anxiety or depressive symptoms associated with sexual abuse in individuals with bif-mid. None of the studies reported problems regarding body experience. CONCLUSIONS Sexual abuse in individuals with bif-mid is associated with a broad range of behavioural and psychological characteristics similar to that of individuals with (above) average iq. Whether sexually abused individuals with bif-mid have similar problems in body experience as sexually abused individuals with (higher than) average iq needs to be investigated.

Structure-based exploration and pharmacological evaluation of N-substituted piperidin-4-yl-methanamine CXCR4 chemokine receptor antagonists

Using the available structural information of the chemokine receptor CXCR4, we present hit finding and hit exploration studies that make use of virtual fragment screening, design, synthesis and structure-activity relationship (SAR) studies. Fragment 2 was identified as virtual screening hit and used as a starting point for the exploration of 31 N-substituted piperidin-4-yl-methanamine derivatives to investigate and improve the interactions with the CXCR4 binding site. Additionally, subtle structural ligand changes lead to distinct interactions with CXCR4 resulting in a full to partial displacement of CXCL12 binding and competitive and/or non-competitive antagonism. Three-dimensional quantitative structure-activity relationship (3D-QSAR) and binding model studies were used to identify important hydrophobic interactions that determine binding affinity and indicate key ligand-receptor interactions.

G Protein-Coupled Receptor Signaling Networks from a Systems Perspective

The signal-transduction network of a mammalian cell integrates internal and external cues to initiate adaptive responses. Among the cell-surface receptors are the G protein-coupled receptors (GPCRs), which have remarkable signal-integrating capabilities. Binding of extracellular signals stabilizes intracellular-domain conformations that selectively activate intracellular proteins. Hereby, multiple signaling routes are activated simultaneously to degrees that are signal-combination dependent. Systems-biology studies indicate that signaling networks have emergent processing capabilities that go far beyond those of single proteins. Such networks are spatiotemporally organized and capable of gradual, oscillatory, all-or-none, and subpopulation-generating responses. Protein-protein interactions, generating feedback and feedforward circuitry, are generally required for these spatiotemporal phenomena. Understanding of information processing by signaling networks therefore requires network theories in addition to biochemical and biophysical concepts. Here we review some of the key signaling systems behaviors that have been discovered recurrently across signaling networks. We emphasize the role of GPCRs, so far underappreciated receptors in systems-biology research.

Identification and profiling of CXCR3-CXCR4 chemokine receptor heteromer complexes

BACKGROUND AND PURPOSE

The C-X-C chemokine receptors 3 (CXCR3) and C-X-C chemokine receptors 4 (CXCR4) are involved in various autoimmune diseases and cancers. Small antagonists have previously been shown to cross-inhibit chemokine binding to CXCR4, CC chemokine receptors 2 (CCR2) and 5 (CCR5) heteromers. We investigated whether CXCR3 and CXCR4 can form heteromeric complexes and the binding characteristics of chemokines and small ligand compounds to these chemokine receptor heteromers.

EXPERIMENTAL APPROACH

CXCR3-CXCR4 heteromers were identified in HEK293T cells using co-immunoprecipitation, time-resolved fluorescence resonance energy transfer, saturation BRET and the GPCR-heteromer identification technology (HIT) approach. Equilibrium competition binding and dissociation experiments were performed to detect negative binding cooperativity.

KEY RESULTS

We provide evidence that chemokine receptors CXCR3 and CXCR4 form heteromeric complexes in HEK293T cells. Chemokine binding was mutually exclusive on membranes co-expressing CXCR3 and CXCR4 as revealed by equilibrium competition binding and dissociation experiments. The small CXCR3 agonist VUF10661 impaired binding of CXCL12 to CXCR4, whereas small antagonists were unable to cross-inhibit chemokine binding to the other chemokine receptor. In contrast, negative binding cooperativity between CXCR3 and CXCR4 chemokines was not observed in intact cells. However, using the GPCR-HIT approach, we have evidence for specific β-arrestin2 recruitment to CXCR3-CXCR4 heteromers in response to agonist stimulation.

CONCLUSIONS AND IMPLICATIONS

This study indicates that heteromeric CXCR3-CXCR4 complexes may act as functional units in living cells, which potentially open up novel therapeutic opportunities.

Inhibition of CXCR3-mediated chemotaxis by the human chemokine receptor-like protein CCX-CKR

BACKGROUND AND PURPOSE

Induction of cellular migration is the primary effect of chemokine receptor activation. However, several chemokine receptor-like proteins bind chemokines without subsequent induction of intracellular signalling and chemotaxis. It has been suggested that they act as chemokine scavengers, which may control local chemokine levels and contribute to the function of chemokines during inflammation. This has been verified for the chemokine-like receptor proteins D6 and DARC as well as CCX-CKR. Here, we provide evidence for an additional biological function of human (h)CCX-CKR.

EXPERIMENTAL APPROACH

We used transfection strategies in HEK293 and human T cells.

KEY RESULTS

Co-expression of hCCX-CKR completely inhibits hCXCR3-induced chemotaxis. We found that hCCX-CKR forms complexes with hCXCR3, suggesting a relationship between CCX-CKR heteromerization and inhibition of chemotaxis. Moreover, negative binding cooperativity induced by ligands both for hCXCR3 and hCCX-CKR was observed in cells expressing both receptors. This negative cooperativity may also explain the hCCX-CKR-induced inhibition of chemotaxis.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that hCCX-CKR prevents hCXCR3-induced chemotaxis by heteromerization thus representing a novel mechanism of regulation of immune cell migration.

Pharmacological characterization of a small-molecule agonist for the chemokine receptor CXCR3

BACKGROUND AND PURPOSE

The chemokine receptor CXCR3 is a GPCR found predominantly on activated T cells. CXCR3 is activated by three endogenous peptides; CXCL9, CXCL10 and CXCL11. Recently, a small-molecule agonist, VUF10661, has been reported in the literature and synthesized in our laboratory. The aim of the present study was to provide a detailed pharmacological characterization of VUF10661 by comparing its effects with those of CXCL11.

EXPERIMENTAL APPROACH

Agonistic properties of VUF10661 were assessed in a chemotaxis assay with murine L1.2 cells transiently transfected with cDNA encoding the human CXCR3 receptor and in binding studies, with [(125)I]-CXCL10 and [(125)I]-CXCL11, on membrane preparations from HEK293 cells stably expressing CXCR3. [(35)S]-GTPγS binding was used to determine its potency to induce CXCR3-mediated G protein activation and BRET-based assays to investigate its effects on intracellular cAMP levels and β-arrestin recruitment.

KEY RESULTS

VUF10661 acted as a partial agonist in CXCR3-mediated chemotaxis, bound to CXCR3 in an allosteric fashion in ligand binding assays and activated G(i) proteins with the same efficacy as CXCL11 in the [(35)S]-GTPγS binding and cAMP assay, while it recruited more β-arrestin1 and β-arrestin2 to CXCR3 receptors than the chemokine.

CONCLUSIONS AND IMPLICATIONS

VUF10661, like CXCL11, activates both G protein-dependent and -independent signalling via the CXCR3 receptor, but probably exerts its effects from an allosteric binding site that is different from that for CXCL11. It could stabilize different receptor and/or β-arrestin conformations leading to differences in functional output. Such ligand-biased signalling might offer interesting options for the therapeutic use of CXCR3 agonists.

Pharmacological modulation of chemokine receptor function

G protein-coupled chemokine receptors and their peptidergic ligands are interesting therapeutic targets due to their involvement in various immune-related diseases, including rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, chronic obstructive pulmonary disease, HIV-1 infection and cancer. To tackle these diseases, a lot of effort has been focused on discovery and development of small-molecule chemokine receptor antagonists. This has been rewarded by the market approval of two novel chemokine receptor inhibitors, AMD3100 (CXCR4) and Maraviroc (CCR5) for stem cell mobilization and treatment of HIV-1 infection respectively. The recent GPCR crystal structures together with mutagenesis and pharmacological studies have aided in understanding how small-molecule ligands interact with chemokine receptors. Many of these ligands display behaviour deviating from simple competition and do not interact with the chemokine binding site, providing evidence for an allosteric mode of action. This review aims to give an overview of the evidence supporting modulation of this intriguing receptor family by a range of ligands, including small molecules, peptides and antibodies. Moreover, the computer-assisted modelling of chemokine receptor-ligand interactions is discussed in view of GPCR crystal structures. Finally, the implications of concepts such as functional selectivity and chemokine receptor dimerization are considered.

Quantitative expression profiling of G-protein-coupled receptors (GPCRs) in metastatic melanoma: the constitutively active orphan GPCR GPR18 as novel drug target

G-protein-coupled receptors (GPCRs) have been implicated in the tumorigenesis and metastasis of human cancers and are considered amongst the most desirable targets for drug development. Utilizing a robust quantitative PCR array, we quantified expression of 94 human GPCRs, including 75 orphan GPCRs and 19 chemokine receptors, and 36 chemokine ligands, in 40 melanoma metastases from different individuals and benign nevi. Inter-metastatic site comparison revealed that orphan GPR174 and CCL28 are statistically significantly overexpressed in subcutaneous metastases, while P2RY5 is overexpressed in brain metastases. Comparison between metastases (all three metastatic sites) and benign nevi revealed that 16 genes, including six orphan receptors (GPR18, GPR34, GPR119, GPR160, GPR183 and P2RY10) and chemokine receptors CCR5, CXCR4, and CXCR6, were statistically significantly differentially expressed. Subsequent functional experiments in yeast and melanoma cells indicate that GPR18, the most abundantly overexpressed orphan GPCR in all melanoma metastases, is constitutively active and inhibits apoptosis, indicating an important role for GPR18 in tumor cell survival. GPR18 and five other orphan GPCRs with yet unknown biological function may be considered potential novel anticancer targets in metastatic melanoma.

A viral conspiracy: hijacking the chemokine system through virally encoded pirated chemokine receptors

Several herpesviruses and poxviruses contain genes encoding for G protein-coupled receptor (GPCR) proteins that are expressed on the surface of infected host cells and/or the viral envelope. Most of these membrane-associated proteins display highest homology to the subfamily of chemokine receptors known to play a key role in the immune system. Virally encoded chemokine receptors have been modified through evolutionary selection both in chemokine binding profile and signaling capacity, ultimately resulting in immune evasion and cellular reprogramming in favor of viral survival and replication. Insight in the role of virally encoded GPCRs during the viral lifecycle may reveal their potential as future drug targets.

Virus-encoded G-protein-coupled receptors: constitutively active (dys)regulators of cell function and their potential as drug target

G-protein-coupled receptors encoded by herpesviruses such as EBV, HCMV and KSHV are very interesting illustrations of the (patho)physiological importance of constitutive GPCR activity. These viral proteins are expressed on the cell surface of infected cells and often constitutively activate a variety of G-proteins. For some virus-encoded GPCRs, the constitutive activity has been shown to occur in vivo, i.e., in infected cells. In this paper, we will review the occurrence of virus-encoded GPCRs and describe their known signaling properties. Moreover, we will also review the efforts, directed towards the discovery of small molecule antagonist, that so far have been mainly focused on the HCMV-encoded GPCR US28. This virus-encoded receptor might be involved in cardiovascular diseases and cancer and seems an interesting target for drug intervention.

Human cell-derived microparticles promote thrombus formation in vivo in a tissue factor-dependent manner

BACKGROUND

Circulating microparticles of various cell types are present in healthy individuals and, in varying numbers and antigenic composition, in various disease states. To what extent these microparticles contribute to coagulation in vivo is unknown.

OBJECTIVES

To examine the in vivo thrombogenicity of human microparticles.

METHODS

Microparticles were isolated from pericardial blood of cardiac surgery patients and venous blood of healthy individuals. Their numbers, cellular source, and tissue factor (TF) exposure were determined using flow cytometry. Their in vitro procoagulant properties were studied in a fibrin generation test, and their in vivo thrombogenicity in a rat model.

RESULTS

The total number of microparticles did not differ between pericardial samples and samples from healthy individuals (P = 0.786). In both groups, microparticles from platelets, erythrocytes, and granulocytes exposed TF. Microparticle-exposed TF antigen levels were higher in pericardial compared with healthy individual samples (P = 0.036). Pericardial microparticles were strongly procoagulant in vitro and highly thrombogenic in a venous stasis thrombosis model in rats, whereas microparticles from healthy individuals were not [thrombus weights 24.8 (12.2-41.3) mg vs. 0 (0-24.3) mg median and range; P < 0.001]. Preincubation of pericardial microparticles with an inhibitory antibody against human TF abolished their thrombogenicity [0 (0-4.4) mg; P < 0.01], while a control antibody had no effect [19.6 (12.6-53.7) mg; P > 0.05]. The thrombogenicity of the microparticles correlated strongly with their TF exposure (r = 0.9524, P = 0.001).

CONCLUSIONS

Human cell-derived microparticles promote thrombus formation in vivo in a TF-dependent manner. They might be the direct cause of an increased thromboembolic tendency in various patient groups.

Antithrombotic properties of a direct thrombin inhibitor with a prolonged half-life and AT-mediated factor Xa inhibitory activity

Rebound thrombin generation after successful thrombolysis might be related to (i) too short-term anticoagulant therapy and to (ii) the inability of heparin derivatives to inhibit clot-bound thrombin. To meet these shortcomings, a compound was synthesized, which consists of a pentasaccharide conjugated to a direct thrombin inhibitor. This compound (Org 42675) has a 10 times longer half-life compared with the original half-life of the direct thrombin inhibitor, while the thrombin inhibitory activity is maintained. An extra advantage of this product is the inhibitory activity on thrombin generation via antithrombin III (AT)-mediated factor (F)Xa inhibition. Org 42675 inhibited in vitro clot-bound thrombin with similar activity to the direct thrombin inhibitor argatroban. In experimental models in rats, Org 42675 showed on a molar base similar antithrombotic activity to unfractionated heparin, was more active than argatroban and was more active than fondaparinux sodium (AT-mediated FXa inhibitor) in arterial thrombosis. Finally, Org 42675 was far more active than the three reference compounds in an experimental thrombolysis model in rabbits. These properties of Org 42675, with its FXa and (clot-bound) thrombin inhibitory activity in combination with its long half-life, make this compound a powerful drug that is likely to be effective in the prevention of re-occlusion after successful thrombolysis in man.

Virally encoded G protein-coupled receptors: targets for potentially innovative anti-viral drug development

Various herpes- and poxviruses contain DNA sequences encoding proteins with homology to cellular chemokine receptors, which belong to the family of G protein-coupled receptors (GPCRs). Since GPCRs play a crucial role in cellular communication and chemokine receptors play a prominent role in the immune system, the virally encoded GPCRs may be crucial determinants of viral action. The Kaposi's sarcoma-associated herpesvirus (KSHV, or human herpesvirus 8), implicated in the pathogenesis of Kaposi's sarcoma (KS), a highly vascularized tumor, encodes a GPCR, referred to as ORF74. This virally encoded receptor was found to induce tumorigenesis and transgenic expression of ORF74 induces an angioproliferative disease resembling KS. Cytomegalovirus (CMV), suggested to play a role in atherosclerosis, encodes four GPCRs, among which US28. This virally encoded GPCR is able to induce migration of smooth muscle cells, a feature essential for the development of atherosclerosis. Remarkably, the KSHV and some CMV-encoded GPCRs display constitutive activity, while their cellular homologs do not. It remains to be determined whether this phenomenon contributes to the pathogenesis of viral action. Also, the family of poxviruses encodes GPCRs of which the function is not clear yet. In this review we will give an overview of the different virally encoded GPCRs, and discuss their putative role in viral action and potential as drug target.

Sensitive and rapid liquid chromatography-tandem mass spectrometry method for the determination of stavudine in human plasma

A sensitive method for the determination of stavudine in plasma was developed, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. The samples were extracted from plasma with Waters, Sep-Pak Vac, 100 mg, tC(18) solid-phase extraction (SPE) columns. Chromatography was performed on a Supelco Discovery C(18), 5 microm, 150 x 2 mm column with a mobile phase consisting of ammonium acetate (0.01 M)-acetonitrile-methanol (800:100:100, v/v/v) at a flow-rate of 0.3 ml/min. Detection was achieved by an Applied Biosystems API 2000 mass spectrometer (LC-MS-MS) set at unit resolution in the multiple reaction monitoring mode (MRM). Atmospheric pressure chemical ionization (APCI) was used for ion production. The mean recovery for stavudine was 94% with a lower limit of quantification set at 4 ng/ml. This assay method makes use of the increased sensitivity and selectivity of mass spectrometric (MS-MS) detection to allow for a more rapid (extraction and chromatography) and selective method for the determination of stavudine in human plasma than has previously been described.

Highly specific and sensitive liquid chromatography-tandem mass spectrometry method for the determination of 3-desmethylthiocolchicine in human plasma as analyte for the assessment of bioequivalence after oral administration of thiocolchicoside

A sensitive method for the determination of 3-desmethylthiocolchicine in plasma was developed, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. The plasma samples were extracted with ethyl acetate and separated on a Phenomenex Luna C18(2) 5 microm, 150x2 mm column with a mobile phase consisting of acetonitrile-0.005% formic acid (350:650, v/v) at a flow rate of 0.35 ml/min. Detection was achieved by an Applied Biosystems API 2000 mass spectrometer (LC-MS-MS) set at unit resolution in the multiple reaction monitoring mode. TurbolonSpray ionisation was used for ion production. The mean recovery for 3-desmethylthiocolchicine was 70%, with a lower limit of quantification set at 0.39 ng/ml. The increased selectivity of mass spectrometric (MS-MS) detection allowed us to distinguish between thiocolchicoside and its primary metabolite 3-desmethylthiocolchicine in human plasma, thereby giving more insight about the pharmacokinetics of the drug in humans.

Rapid and sensitive liquid chromatography-tandem mass spectrometry method for the quantitation of domperidone in human plasma

A rapid and sensitive method for the determination of domperidone in plasma was developed, using high-performance liquid chromatographic separation with tandem mass spectrometry detection. The samples were rendered basic with 1 M Na2CO3 and the domperidone extracted using tert.-butyl methyl ether, followed by back-extraction into formic acid (2% in water). Chromatography was performed on a Phenomenex Luna C8 (2), 5 microm, 150x2 mm column with a mobile phase consisting of acetonitrile-0.02% formic acid (300:700, v/v), delivered at 0.2 ml/min. Detection was performed using an Applied Biosystems Sciex API 2000 mass spectrometer set at unit resolution in the multiple reaction monitoring mode. TurbolonSpray ionisation was used for ion production. The mean recovery of domperidone was +/- 100%, with a lower limit of quantification set at 0.189 ng/ml. This assay method makes use of the increased sensitivity and selectivity of tandem mass spectrometric detection resulting in a rapid (extraction and chromatography) and sensitive method for the determination of domperidone in human plasma, which is more sensitive than previously described methods.

Sensitive liquid chromatography-tandem mass spectrometry method for the determination of clarithromycin in human plasma

A sensitive method for the determination of clarithromycin in plasma is described, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. Samples were prepared using liquid-liquid extraction and separated on a Supelco Discovery C18 column with a mobile phase consisting of acetonitrile, methanol and acetic acid. Detection was performed by a PE SCIEX API 2000 mass spectrometer in the multiple reaction monitoring (MRM) mode (LC-MS-MS) using TurbolonSpray ionization and monitoring the transition of the protonated molecular ion for clarithromycin at m/z 748.5 (M+1) to the predominant product ion of m/z 158.2. The mean recovery of clarithromycin was 87.3%, with a lower limit of quantification of 2.95 ng/ml when using 0.3-ml plasma. This high-throughput method was used to quantify 230 samples per day, and is sufficiently sensitive to be employed in pharmacokinetic studies.

The role of cytomegalovirus-encoded homologs of G protein-coupled receptors and chemokines in manipulation of and evasion from the immune system

Cytomegaloviruses (CMVs) have the ability to persist lifelong within the infected host. This ability implies that these viruses are highly adapted to their hosts. Most importantly, they will have to employ strategies to remain hidden from the host's immune system. Virus genes predicted to be involved in these strategies include genes encoding homologs of cellular immune effector or regulatory proteins, such as chemokine (CK) receptor-like G protein-coupled receptors (GPCRs), CKs and MHC class I molecules. These genes may have been pirated by the virus during the long co-evolution of pathogen and host. In light of the crucial roles that GPCRs, CKs and MHC class I molecules play in the normal physiology of the host, it is to be expected that the CMV homologs of these proteins may have a profound impact on this physiology and, at the same time, serve vital functions in maintenance as well as replication of the virus within the infected host. As a consequence, these viral homologs can be envisaged as attractive targets for novel anti-viral strategies. The aim of this report is to present an overview of the current state of knowledge on the (putative) functions of the CMV homologs of GPCRs and CKs.

Histamine H(1)-receptor activation of nuclear factor-kappa B: roles for G beta gamma- and G alpha(q/11)-subunits in constitutive and agonist-mediated signaling

Nuclear factor kappa B (NF-kappa B) is an important transcription factor in inflammation that has obtained a great interest as a drug target for the treatment of various allergic conditions. In this study, we show that the histamine H(1) receptor, which is also an important player in allergic and inflammatory conditions, activates NF-kappa B in both a constitutive and agonist-dependent manner. Moreover, the observed constitutive NF-kappa B activation is inhibited by various H(1)-receptor antagonists, suggesting that inverse agonism may account, at least in part, for their ascribed antiallergic properties. Investigation of the H(1) receptor-mediated NF-kappa B activation in transfected COS-7 cells indicates that the level of the observed constitutive activity of the H(1) receptor can be modulated by the expression levels of either G alpha-proteins or G beta gamma-heterodimers. Members of the G alpha(q/11)-family of G alpha-proteins are most effective in increasing H(1) constitutive activity. Also, coexpression of G beta(2) in combination with either G gamma(1) or G gamma(2) results in an increased constitutive activity of the H(1) receptor, whereas scavenging of G beta gamma-subunits by coexpression of G alpha(t) completely neutralizes the constitutive, but not the agonist-induced, NF-kappa B activity. Our data suggest that both G alpha(q/11)- and G beta gamma-subunits play a role in the agonist-induced, H(1) receptor-mediated NF-kappa B activation, but that constitutive NF-kappa B activation by the H(1) receptor is primarily mediated through G beta gamma-subunits.

Comparison of the antiatherosclerotic effect of tibolone with that of estradiol and ethinyl estradiol in cholesterol-fed, ovariectomized rabbits

OBJECTIVE

Tibolone is a synthetic steroid with tissue-specific estrogenic, progestogenic, and androgenic properties. The drug relieves climacteric symptoms and prevents osteoporosis but does not stimulate the endometrium. We have previously shown that in laboratory animals tibolone inhibits the atherogenesis induced by a high-cholesterol diet. Therefore, we compared the antiatherosclerotic effect of oral tibolone at different dose levels with that of oral 17beta-estradiol (E2) and ethinyl estradiol (EE).

DESIGN

Atherosclerotic lesion formation (increase in vessel wall cholesterol deposition and fatty streak formation) was measured in ovariectomized rabbits after 20 weeks on an atherogenic diet (fed daily 80 g of a rabbit chow containing 0.4% cholesterol, 3.75% peanut oil, and 3.75% coconut oil) in eight groups: group 1, placebo (n = 35); group 2, control (n = 34) received normal rabbit chow; group 3, E2 group (E2 4 mg, n = 12); group 4, EE group (EE 60 microg, n = 10); and groups 5-8, tibolone (6 mg, n = 12; 2 mg, n = 13; 0.6 mg, n = 25; and 0.15 mg, n = 11, respectively). During the study, blood samples were obtained for the evaluation of plasma triglycerides, cholesterol, lipoproteins, and glutamate pyruvate transaminase. After 20 weeks, the animals were killed, and cholesterol concentration and the formation of fatty streaks in the wall of the aortic arch were evaluated.

RESULTS

In the placebo group, the atherogenic diet induced a mean increase in total plasma cholesterol concentration from 1.1+/-0.1 mmol/L (control group) to 34.1+/-1.8 mmol/L (mean +/- SE). This resulted in an accumulation of cholesterol in the aortic arch from 48+/-4 (control group) to 608+/-44 nmol/mg protein and in the formation of fatty streaks (41.8+/-3.2% of the surface of the aortic arch was covered with fatty streaks). Tibolone had strong dose-dependent antiatherosclerotic effects. It reduced the accumulation of cholesterol in the aortic arch at doses of 6 to 0.15 mg by 99, 97, 87, and 57% and the formation of fatty streaks by 98, 97, 81, and 38%, respectively. E2 had only a marginal antiatherosclerotic effect, whereas EE showed an effect comparable to that of tibolone at doses of 2 to 0.6 mg. With EE, the accumulation of cholesterol in the vessel wall was reduced by 93% and the formation of fatty streaks by 73%. Mean plasma cholesterol concentrations were also reduced by tibolone (64, 70, 61, and 47%) and EE (57%). This reduction was mainly mediated via a reduction in beta-very-low-density lipoprotein cholesterol. Analysis, however, indicated that the observed antiatherosclerotic effects of tibolone and EE, at least partly, are due to a direct effect on the vessel wall and independent of the changes in plasma cholesterol. At equipotent antiatherosclerotic doses, EE showed a stronger uterotropic effect (measured as the increase in uterine weight) than tibolone. EE increased uterine weight from 0.57 g/kg body weight (BW) (control group) to 3.5 g/kg BW; tibolone at doses of 6, 2, 0.6, and 0.15 mg increased uterine weight to 2.5, 2.8, 2.2, and 1.3 g/kg BW, respectively.

CONCLUSION

Tibolone can protect the arterial vessel wall against atherosclerotic lesions induced by a hypercholesterolemic diet. However, it has much less estrogenic effects on the uterus compared with EE at equipotent doses, indicating tissue selectivity for tibolone. The clinical implications of these findings require investigation.

Constitutive signaling of the human cytomegalovirus-encoded chemokine receptor US28

Previously it was shown that the HHV-8-encoded chemokine receptor ORF74 shows considerable agonist-independent, constitutive activity giving rise to oncogenic transformation (Arvanitakis, L., Geras-Raaka, E., Varma, A., Gershengorn, M. C., and Cesarman, E. (1997) Nature 385, 347-350). In this study we report that a second viral-encoded chemokine receptor, the human cytomegalovirus-encoded US28, also efficiently signals in an agonist-independent manner. Transient expression of US28 in COS-7 cells leads to the constitutive activation of phospholipase C and NF-kappaB signaling via G(q/11) protein-dependent pathways. Whereas phospholipase C activation is mediated via Galpha(q/11) subunits, the activation of NF-kappaB strongly depends on betagamma subunits with a preference for the beta(2)gamma(1) dimer. The CC chemokines RANTES (regulated on activation, normal T cell expressed and secreted) and MCP-1 (monocyte chemotactic protein-1) act as neutral antagonists at US28, whereas the CX(3)C chemokine fractalkine acts as a partial inverse agonist with IC(50) values of 1-5 nm. Our data suggest that a high level of constitutive activity might be a more general characteristic of viral G protein-coupled receptors and that human cytomegalovirus might exploit this G protein-coupled receptor property to modulate the homeostasis of infected cells via the early gene product US28.

Identification of rat H3 receptor isoforms with different brain expression and signaling properties

We identified the cDNAs of three functional rat H3 receptor isoforms (H3A, H3B, and H3C) and one nonfunctional truncated H3 receptor (H3T). The H3A, H3B, and H3C receptor isoforms vary in the length of their third intracellular loop; the H3B and H3C receptor lack 32 and 48 amino acids, respectively. Transient expression of the H3A, H3B, and H3C receptors in COS-7 cells results in high affinity binding for the H3 antagonist [125I]iodophenpropit, which is displaced by selective H3 agonists and antagonists. The three isoforms differentially couple to the Gi protein-dependent inhibition of adenylate cyclase or stimulation of p44/p42 mitogen activated protein kinase (MAPK), a new signaling pathway for the H3 receptor. Whereas the H3A receptor was less effective in inhibiting forskolin-induced cAMP production compared with the H3B or H3C receptor, this isoform was more effective in the stimulation of p44/p42 MAPK. The H3 receptor isoforms also displayed differential CNS expression in key areas involved in regulation of sensory, endocrine, and cognitive functions. A differential H3 receptor isoform expression was seen in, for example, hippocampus, where a characteristic dorsoventral distribution was revealed. Differential H3 receptor expression was also characteristic for the cerebellum, indicating possible histaminergic regulation of motor functions. The identification of these new H3 receptor isoforms and their specific signaling properties adds a new level of complexity to our understanding of the role of histamine, and the H3 receptor in brain function. The heterogeneous distribution of the isoforms suggests that H3 receptor isoform-specific regulation is important in several brain functions.

The effect of mutations in the DRY motif on the constitutive activity and structural instability of the histamine H(2) receptor

In previous studies we showed that the wild-type histamine H(2) receptor stably expressed in Chinese hamster ovary cells is constitutively active. Because constitutive activity of the H(2) receptor is already found at low expression levels (300 fmol/mg protein) this receptor is a relatively unique member of the G-protein-coupled receptor (GPCR) family and a useful tool for studying GPCR activation. In this study the role of the highly conserved DRY motif in activation of the H(2) receptor was investigated. Mutation of the aspartate 115 residue in this motif resulted in H(2) receptors with high constitutive activity, increased agonist affinity, and increased signaling properties. In addition, the mutant receptors were shown to be highly structurally instable. Mutation of the arginine 116 residue in the DRY motif resulted also in a highly structurally instable receptor; expression of the receptor could only be detected after stabilization with either an agonist or inverse agonist. Moreover, the agonist affinity at the Arg-116 mutant receptors was increased, whereas the signal transduction properties of these receptors were decreased. We conclude that the Arg-116 mutant receptors can adopt an active conformation but have a decreased ability to couple to or activate the G(s)-protein. This study examines the pivotal role of the aspartate and arginine residues of the DRY motif in GPCR function. Disruption of receptor stabilizing constraints by mutation in the DRY motif leads to the formation of active GPCR conformations, but concomitantly to GPCR instability.

Mutational analysis of the antagonist-binding site of the histamine H(1) receptor

We combined in a previously derived three-dimensional model of the histamine H(1) receptor (Ter Laak, A. M., Timmerman, H., Leurs, H., Nederkoorn, P. H. J., Smit, M. J., and Donne-Op den Kelder, G. M. (1995) J. Comp. Aid. Mol. Design. 9, 319-330) a pharmacophore for the H(1) antagonist binding site (Ter Laak, A. M., Venhorst, J., Timmerman, H., and Donné-Op de Kelder, G. M. (1994) J. Med. Chem. 38, 3351-3360) with the known interacting amino acid residue Asp(116) (in transmembrane domain III) of the H(1) receptor and verified the predicted receptor-ligand interactions by site-directed mutagenesis. This resulted in the identification of the aromatic amino acids Trp(167), Phe(433), and Phe(436) in transmembrane domains IV and VI of the H(1) receptor as probable interaction points for the trans-aromatic ring of the H(1) antagonists. Subsequently, a specific interaction of carboxylate moieties of two therapeutically important, zwitterionic H(1) antagonists with Lys(200) in transmembrane domain V was predicted. A Lys(200) --> Ala mutation results in a 50- (acrivastine) to 8-fold (d-cetirizine) loss of affinity of these zwitterionic antagonists. In contrast, the affinities of structural analogs of acrivastine and cetirizine lacking the carboxylate group, triprolidine and meclozine, respectively, are unaffected by the Lys(200) --> Ala mutation. These data strongly suggest that Lys(200), unique for the H(1) receptor, acts as a specific anchor point for these "second generation" H(1) antagonists.

Design, synthesis and testing of amino-bicycloaryl based orally bioavailable thrombin inhibitors

Replacement of the highly basic benzamidine moiety with moderate basic amino-bicycloaryl moieties in a series of thrombin inhibitors related to NAPAMP provided potent enzyme inhibition and significant improvements in membrane transport and oral bioavailability.

Molecular properties and signalling pathways of the histamine H1 receptor

With cloning of the gene encoding the histamine H1 receptor, a new area of histamine research has become reality. Finally, it seems feasible to study the target of the therapeutically important clans of antihistamine. Expression of the genes in mammalian cells allows detailed investigations of the various signal transduction routes of the histamine H1 receptor. Moreover, using molecular biological techniques, it is now possible to investigate ligand receptor interaction at the molecular level. Studies with mutant H1 receptors have shown that H1 antagonists bind to a specific amino acid residues in TM3 and 5. It is expected that these new developments will provide much fundamental knowledge on the ligand interaction with the H1 receptor.

Identity of adenylyl cyclase isoform determines the rate of cell cycle progression in NIH 3T3 cells

Cell cycle progression is regulated by cAMP in several cell types. Cellular cAMP levels depend on the activity of different adenylyl cyclases (ACs), which have varied signal-receiving capabilities. The role of individual ACs in regulating proliferative responses was investigated. Native NIH 3T3 cells contain AC6, an isoform that is inhibited by a variety of signals. Proliferation of exogenous AC6-expressing cells was the same as in control cells. In contrast, expression of AC2, an isoform stimulated by protein kinase C (PKC), resulted in inhibition of cell cycle progression and increased doubling time. In AC2-expressing cells, platelet-derived growth factor (PDGF) elevated cAMP levels in a PKC-dependent manner. PDGF stimulation of mitogen-activated protein kinases 1 and 2 (MAPK 1,2), DNA synthesis, and cyclin D1 expression was reduced in AC2-expressing cells as compared with control cells. Dominant negative protein kinase A relieved the AC2 inhibition of PDGF-induced DNA synthesis. Expression of AC2 also blocked H-ras-induced transformation of NIH 3T3 cells. These observations indicate that, because AC2 is stimulated by PKC, it can be activated by PDGF concurrently with the stimulation of MAPK 1,2. The elevation in cAMP results in inhibition of signal flow from the PDGF receptor to MAPK 1,2 and a significant reduction in the proliferative response to PDGF. Thus, the molecular identity and signal receiving capability of the AC isoforms in a cell could be important for proliferative homeostasis.

Tibolone prevents atherosclerotic lesion formation in cholesterol-fed, ovariectomized rabbits

Tibolone (Org OD14), a synthetic steroid with estrogenic and progestogenic/androgenic properties, is clinically effective for the treatment of climacteric symptoms and the prevention and treatment of osteoporosis in postmenopausal women. The effect on atherogenesis, however, is not known. In the current study, we investigated the effect of tibolone in comparison with that of estradiol and norethisterone acetate on atherogenesis in 140 ovariectomized New Zealand White rabbits that had been induced by an atherogenic diet (0.4% cholesterol, 20 weeks). Tibolone at 18, 6, or 2 mg/d orally completely prevented cholesterol accumulation and fatty streak formation in the aorta; the impairment of endothelium-dependent smooth muscle relaxation of the aorta; and complex lesion formation after endothelial denudation in the carotid artery. Tibolone also reduced the increased postovariectomy plasma lipid concentrations. Analysis of the results, however, indicated that a substantial part of the strong, beneficial effects were plasma lipid independent. Compared with subcutaneous estradiol decanoate (150 microgram once weekly) and oral 17beta-estradiol (4 mg/d), the effects of tibolone were more pronounced at equipotent uterotropic activity. Norethisterone acetate (1 mg/d) did not affect atherosclerotic lesion formation. There are no indications that the progestogenic/androgenic properties of tibolone counteracted its atheroprotective effect on the vessel wall. Therefore, tibolone has the intrinsic potential to be a compound that protects the arterial vessel wall against atherosclerotic processes.

Agonist-independent regulation of constitutively active G-protein-coupled receptors

G-protein-coupled receptors constitute one of the largest protein super-families in mammals. Since the cloning of the encoding genes, these important drug targets have been subjected to thorough biochemical and pharmacological studies. It has become clear that G-protein-coupled receptors not only transmit signals after stimulation by agonists but can also spontaneously couple to signal-transduction pathways. Recent findings show that constitutively active G-protein-coupled receptors can also be regulated in an agonist-independent manner, which has important implications for the interpretation of the actions of (inverse) agonists and the results of site-directed-mutagenesis studies.

Constitutive activity and structural instability of the wild-type human H2 receptor

Stable expression of the human H2 receptor in Chinese hamster ovary cells resulted in an increase in basal cyclic AMP (cAMP) production, which was inhibited by the inverse agonists cimetidine, famotidine, and ranitidine with potencies similar to those found for the rat H2 receptor. Burimamide, a neutral antagonist at the rat H2 receptor, behaved as a weak partial agonist at the human H2 receptor. Burimamide competitively antagonized both the histamine-induced increase in cAMP and the cimetidine-induced reduction of the basal cAMP level with apparent K(B) values that were similar to its H2 receptor affinity. Investigation of the modulation of receptor expression after long-term drug treatment revealed that at low concentrations histamine induced a significant reduction in H2 receptor expression, whereas at high concentrations receptor expression was slightly increased. The partial agonist burimamide induced, like inverse agonists, an up-regulation of the human H2 receptor after prolonged treatment. These findings suggest a structural instability of the constitutively active human H2 receptor in transfected Chinese hamster ovary cells. Occupation of the H2 receptor by any ligand reduces the instability, thus resulting in higher cellular expression levels.

Expression of Q227L-galphas in MCF-7 human breast cancer cells inhibits tumorigenesis

The effects of expression of mutant (Q227L)-activated Galphas and elevation of cAMP on mitogen-activating protein kinase (MAPK) activity and the transformed phenotype were studied in the MCF-7 human mammary epithelial cell line. Elevation of cAMP partially inhibited the epidermal growth factor-stimulated DNA synthesis and the intrinsic MAPK (ERK-1 and ERK-2) of serum-starved MCF-7 cells. Addition of 8Br-cAMP or expression of mutant (Q227L)-activated Galphas in MCF-7 cells blocked the ability of these cells to grow in an anchorage-independent manner, as assessed by colony formation in soft agar. 8Br-cAMP in the culture medium also blocked estrogen stimulation of MCF-7 cell proliferation in vitro. MCF-7 cells expressing Q227L-Galphas grew very slowly in vitro, and when these cells were injected s.c. into athymic mice implanted with estrogen pellets, the frequency of tumor formation was reduced greatly and the sizes of the tumors formed were much smaller than those in mice injected with MCF-7 cells that had been transfected with the empty vector. These results indicate that the intracellular levels of cAMP in transformed mammary epithelial cells can be a crucial factor in determining the expression of the transformed phenotype. Interactions between the Gs/adenylyl cyclase and MAPK-1,2 signaling pathways could be one mechanism by which expression of the transformed phenotype in mammary epithelial cells are regulated.

Sensitization of the histamine H1 receptor by increased ligand affinity

Histamine regulates a variety of physiological processes including inflammation, gastric acid secretion, and neurotransmission. The cellular response to histamine is subject to dynamic control, and exaggerated histamine reactivity in response to cysteinyl leukotrienes and other stimuli is important in a variety of different pathological conditions. The molecular mechanisms controlling histamine responsiveness are still unresolved. In investigating histamine responses in embryonic stem (ES5) and F9 embryonic carcinoma cells, we encountered a novel mechanism controlling the cellular reaction to histamine. Unstimulated cells displayed neither [3H]pyrilamine binding nor histamine-induced increases in cytosolic Ca2+ levels. Pretreatment of these cells, however, with leukotriene D4, leukotriene E4, serotonin, or fetal calf serum induced an immediate and transient ability of these cells to respond to histamine with an increase in cytosolic Ca2+ levels. This effect could be inhibited by pertussis toxin and was mimicked by GTP analogues. Importantly, the latter compounds also provoked immediate high affinity [3H]pyrilamine binding. We conclude that in these cells histamine responsiveness is directly controlled by pertussis toxin-sensitive G protein-coupled receptors, whose activation enables the H1 receptor to bind its ligand. These findings define a novel mechanism for regulating histamine H1 receptor activity and provide for the first time molecular insight into the mechanism by which cysteinyl leukotrienes and other external stimuli can increase histamine responsiveness.

Modulation of forskolin-mediated adenylyl cyclase activation by constitutively active G(S)-coupled receptors

In transfected CHO cells constitutively active histamine H2 receptors not only increase the basal cAMP level, but also enhance forskolin-induced cAMP production. The increased forskolin response was inhibited by inverse H2 agonists with potencies similar to those determined at basal levels. The modulation of the forskolin response was also observed after H2 receptor expression in HEK-293 and Sf9 cells or TSH receptor expression in COS-7 cells. The enhancement of forskolin-induced cAMP production seems to be a general characteristic of constitutively active G(S)-coupled receptors and can be very useful to study inverse agonism at wild-type receptors.

Adenylyl cyclase 6 is selectively regulated by protein kinase A phosphorylation in a region involved in Galphas stimulation

Receptors activate adenylyl cyclases through the Galphas subunit. Previous studies from our laboratory have shown in certain cell types that express adenylyl cyclase 6 (AC6), heterologous desensitization included reduction of the capability of adenylyl cyclases to be stimulated by Galphas. Here we further analyze protein kinase A (PKA) effects on adenylyl cyclases. PKA treatment of recombinant AC6 in insect cell membranes results in a selective loss of stimulation by high (>10 nM) concentrations of Galphas. Similar treatment of AC1 or AC2 did not affect Galphas stimulation. Conversion of Ser-674 in AC6 to an Ala blocks PKA phosphorylation and PKA-mediated loss of Galphas stimulation. A peptide encoding the region 660-682 of AC6 blocks stimulation of AC6 and AC2 by high concentrations of Galphas. Substitution of Ser-674 to Asp in the peptide renders the peptide ineffective, indicating that the region 660-682 of AC6 is involved in regulation of signal transfer from Galphas. This region contains a conserved motif present in most adenylyl cyclases; however, the PKA phosphorylation site is unique to members of the AC6 family. These observations suggest a mechanism of how isoform selective regulatory diversity can be obtained within conserved regions involved in signal communication.

The C terminal tail of the histamine H2 receptor contains positive and negative signals important for signal transduction and receptor down-regulation

To examine the role of the C terminal tail in H2 receptor regulation, three cDNAs, encoding truncated histamine H2 receptor mutants (H2T295, H2T307, and H2T341), were constructed and stably transfected in Chinese hamster ovary (CHO) cells. The amino acids before position 307 appear to be necessary for proper receptor transport or folding, as no detectable H2 receptor binding of the H2T295 was observed after transfection. Truncation of the C terminal tail by 51 amino acids (H2T307) did not affect the binding properties of H2 antagonists and histamine or histamine-induced signaling. Yet, removal of 17 amino acids generated a mutant receptor (H2T341), which was able to form a ternary complex but was unable to fully activate the Gs protein on histamine exposure. Agonist-induced but not the cyclic AMP-dependent H2 receptor down-regulation was more profound for the H2T307 receptor, indicating that different structural elements of the H2 receptor protein are involved in the cyclic AMP-dependent and independent pathways of H2 receptor down-regulation. Taken together, in this study we identified regions in the C terminal tail of the H2 receptor that act as positive and/or negative signals in H2 receptor signaling and down-regulation.

Immunological response in laparoscopic surgery

Immunological response to surgical trauma may be protected during laparoscopic surgery. A less surgical trauma, in comparison with conventional surgery, may explained these important advantages. Plasma and macrophages studies have demonstrated that laparoscopic cholecystectomy causes less depression of cell mediated immunity than open cholecystectomy. What will be the impact of this immunological protection in laparoscopic advanced and oncological surgery? Experimental studies have showed that laparoscopic techniques in advanced and oncological surgery may have important advantages concerning the "preservation of the immune status" of the patient. That will imply in the future a lower percentage of infections, local recurrence and even a lower percentage of distant metastases. On the other hand, the appearance of tumor implants in the port sites after laparoscopic resection for cancer is a significant drawback of this procedure. Proper investigations have to be carried out in order to find the cause and the solution of this dilemma.

Inverse agonism of histamine H2 antagonist accounts for upregulation of spontaneously active histamine H2 receptors

Histamine H2 receptors transfected in Chinese hamster ovary (CHO) cells are time- and dose-dependently upregulated upon exposure to the H2 antagonists cimetidine and ranitidine. This effect appears to be H2 receptor-mediated as no change in receptor density was observed after H1 or H3 antagonist treatment or after incubation with the structural analogue of cimetidine, VUF 8299, which has no H2 antagonistic effects. By using transfected CHO cells expressing different densities of wild-type H2 receptors or an uncoupled H2Leu124Ala receptor, the histamine H2 receptor was found to display considerable agonist-independent H2 receptor activity. Cimetidine and ranitidine, which both induce H2 receptor upregulation, actually functioned as inverse agonists in those cell lines displaying spontaneous agonist-independent H2 receptor activity. Burimamide, on the other hand, was shown to act as a neutral antagonist and did as expected not induce H2 receptor upregulation after long-term exposure. The displayed inverse agonism of H2 antagonists appears to be a mechanistic basis for the observed H2 antagonist-induced H2 receptor upregulation in transfected CHO cells. These observations shed new light on the pharmacological classification of the H2 antagonists and may offer a plausible explanation for the observed development of tolerance after prolonged clinical use.

Effect of intraperitoneal administration of granulocyte/macrophage-colony-stimulating factor in rats on omental milky-spot composition and tumoricidal activity in vivo and in vitro

Milky spots in the greater omentum are small accumulations of leucocytes that consist mainly of macrophages and have recently shown to be a selective dissemination site of intraperitoneal (i.p.) inoculated tumour cells. However, milky-spot macrophages show tumoricidal activity and may, therefore, be an excellent source of effector cells suited for local immunotherapy. In the present study we first examined whether granulocyte/macrophage-colony-stimulating factor (GM-CSF) treatment of isolated milky-spot macrophages affects the cytotoxicity against syngeneic colon carcinoma cells (CC531) in vitro. Secondly, we studied the influence of intraperitoneal GM-CSF administration on the number and antitumour activity of milky-spot and peritoneal macrophages. All studies were performed in Wag/Rij rats in which a syngeneic colon carcinoma cell line (CC531) is available. The results of the in vitro study showed that GM-CSF treatment of the omental macrophages led to an increased cytotoxicity against the tumour cell line. Intraperitoneal administration of 1000 U GM-CSF daily for 7 consecutive days demonstrated both an enhanced antitumour activity of the milky-spot macrophages and an increase in the milky-spot macrophage population. An increase in the proliferative capacity, according to bromodeoxyuridine incorporation, was shown in the milky-spot macrophages. Taking into account both the enhanced macrophage number and their enhanced activity upon i.p. GM-CSF treatment, the milky-spot macrophages may provide a rationale for local intraperitoneal immunotherapy in the prevention of intra-abdominal tumour growth.

Two distinct pathways for histamine H2 receptor down-regulation. H2 Leu124 --> Ala receptor mutant provides evidence for a cAMP-independent action of H2 agonists

Pretreatment of Chinese hamster ovary cells expressing the histamine H2 receptor (CHOrH2 cells) with histamine resulted in a time-dependent (t1/2 approximately 7 h) and dose-dependent (EC50=18 nM) H2 receptor down-regulation measured as [125I]iodoaminopotentidine binding (44+/-10% down-regulation). Pretreatment of CHOrH2 cells with cholera toxin or forskolin also led to H2 receptor down-regulation. Forskolin time-dependently (t1/2 approximately 7 h) and dose-dependently (EC50 = 0.3 microM) induced H2 receptor down-regulation. Both histamine and forskolin induced rapid down-regulation of H2 receptor mRNA levels, probably caused by mRNA destabilization. Recently, Moro et al. (Moro, O. Lameh, J., Hogger, P., and Sadée, W. (1993) J. Biol. Chem. 268, 22273-22276) showed that hydrophobic amino acids in a conserved G-protein-coupled receptor motif in the second intracellular loop are implicated in G-protein coupling. To uncouple the H2 receptor from the Gs-protein, we introduced the Leu124 --> Ala mutation in the second intracellular loop of the H2 receptor. The H2 Leu124 --> Ala mutant showed altered agonist-binding parameters, attenuated histamine-induced cAMP production, and was down-regulated by concentrations of histamine that did not give rise to cAMP production. Taken together, in CHOrH2 cells, H2 receptor down-regulation appears to be induced by two distinct pathways, a cAMP-dependent and cAMP-independent pathway.

Regulation of the human histamine H1 receptor stably expressed in Chinese hamster ovary cells

1. The human H1 receptor gene expressed in Chinese hamster ovary cells (CHOhumH1) encodes a classical histamine H1 receptor with a pharmacology similar to that of the H1 receptor found in guinea-pig cerebellum and the endogenously expressed human H1 receptor in 1321N1 astrocytoma cells as determined by [3H]-mepyramine binding studies. 2. In CHOhumH1 cells, histamine induced a concentration-dependent rise in inositol phosphates (EC50 2.23 +/- 0.97 microM) and a rapid increase of [Ca2+]i, followed by a sustained increase of [Ca2+]i upon addition of 100 microM histamine. 3. Short-term exposure of CHOhumH1 cells to histamine (100 microM) resulted in a decrease of subsequent histamine-induced Ca2+ responses. The histamine-induced desensitization appeared to be heterologous as the ATP-induced Ca2+ response was also found to be affected. 4. The process of heterologous histamine-induced desensitization of the Ca2+ response in CHOhumH1 cells can be ascribed to an alteration at the level of the intracellular Ca2+ pool, as the Ca2+ response of caffeine (10 mM), which releases Ca2+ from intracellular Ca2+ stores was also attenuated upon short-term histamine exposure. 5. In CHOhumH1 cells the PKC activator, PMA, was found to inhibit the histamine (100 microM)-induced Ca2+ response concentration-dependently (IC50 0.2 +/- 0.03 microM) as well as the ATP (100 microM)-induced Ca2+ response. However, this inhibition was only partial and less effective than histamine-pretreatment. Moreover, in CHOhumH1 cells PKC downregulation induced by long-term exposure to PMA (1 microM) did not affect the histamine-induced desensitization nor did pretreatment with the specific PKC inhibitor Ro-31-8220 (10 microM), indicating that in CHOhumH1 cells PKC is probably not involved in the heterologous desensitization. 6. Long-term treatment of CHOhumH1 cells with histamine or other H1 agonists resulted in a time- and concentration-dependent decrease in the number of H1 receptor binding sites (maximal reduction: 47 +/- 5%). 7. Long-term exposure of CHOhumH1 cells to ATP or PMA did not affect H1 receptor density. 8. Both histamine (100 microM)- and ATP (100 microM)-induced Ca2+ responses were affected upon long-term exposure of cells to histamine (100 microM), which might be explained by an alteration at a level distant from the receptor. 9. These results show that in CHOhumH1 cells the human histamine H1 receptor is susceptible to short-term and long-term receptor regulation in which PKC does not seem to play a role. The CHOhumH1 cells therefore provide an excellent model system for studying the mechanism(s) of PKC-independent H1 receptor regulation.