Proteasome inhibition and mechanism of resistance to a synthetic, library-based hexapeptide

Background The hexapeptide 4A6 (Ac-Thr(tBu)-His(Bzl)-Thr(Bzl)-Nle-Glu(OtBu)-Gly-Bza) was isolated from a peptide library constructed to identify peptide-based transport inhibitors of multidrug resistance (MDR) efflux pumps including P-glycoprotein and Multidrug Resistance-associated Protein 1. 4A6 proved to be a substrate but not an inhibitor of these MDR efflux transporters. In fact, 4A6 and related peptides displayed potent cytotoxic activity via an unknown mechanism. Objective To decipher the mode of cytotoxic activity of 4A6. Methods Screening of 4A6 activity was performed against the NCI60 panel of cancer cell lines. Possible interactions of 4A6 with the 26S proteasome were assessed via proteasome activity and affinity labeling, and cell growth inhibition studies with leukemic cells resistant to the proteasome inhibitor bortezomib (BTZ). Results The NCI60 panel COMPARE analysis revealed that 4A6 had an activity profile overlapping with BTZ. Consistently, 4A6 proved to be a selective and reversible inhibitor of β5 subunit (PSMB5)-associated chymotrypsin-like activity of the 26S proteasome. This conclusion is supported by several lines of evidence: (i) inhibition of chymotrypsin-like proteasome activity by 4A6 and related peptides correlated with their cell growth inhibition potencies; (ii) 4A6 reversibly inhibited functional β5 active site labeling with the affinity probe BodipyFL-Ahx₃L₃VS; and (iii) human myeloid THP1 cells with acquired BTZ resistance due to mutated PSMB5 were highly (up to 287-fold) cross-resistant to 4A6 and its related peptides. Conclusion 4A6 is a novel specific inhibitor of the β5 subunit-associated chymotrypsin-like proteasome activity. Further exploration of 4A6 as a lead compound for development as a novel proteasome-targeted drug is warranted.

Pharmacological and toxicological assessment of a potential GnRH vaccine in young-adult male pigs

Active immunization against gonadotrophin-releasing hormone (GnRH) is successfully applied to prevent boar taint in pork. In men, GnRH immunization could be an alternative to hormone therapy in patients with prostate cancer. In this study, a new GnRH vaccine formulation (a modified GnRH peptide conjugate formulated with CoVaccine adjuvant) was investigated for its pharmacological efficacy and safety in young-adult male pigs. Immunization resulted in castrate-like plasma testosterone levels in all treated pigs from week 8 until the end of the study, 30 weeks after the first immunization. Testosterone depletion retarded testes growth, reduced the relative weight of the testes and accessory sex organs, and reduced sperm counts and motility. There was no clinically relevant toxicity. Typical vaccination-related adverse reactions, such as swelling at the injection site and fever, were considered acceptable. We conclude that this GnRH vaccine efficiently and rapidly reduced serum testosterone levels, without inducing chronic toxic effects, and therefore could be applicable in both veterinary and human medicine.

A combinatorial approach for the design of complementarity-determining region-derived peptidomimetics with in vitro anti-tumoral activity

The great success of therapeutic monoclonal antibodies has fueled research toward mimicry of their binding sites and the development of new strategies for peptide-based mimetics production. Here, we describe a new combinatorial approach for the production of peptidomimetics using the complementarity-determining regions (CDRs) from gastrin17 (pyroEGPWLEEEEEAYGWMDF-NH(2)) antibodies as starting material for cyclic peptide synthesis in a microarray format. Gastrin17 is a trophic factor in gastrointestinal tumors, including pancreatic cancer, which makes it an interesting target for development of therapeutic antibodies. Screening of microarrays containing bicyclic peptidomimetics identified a high number of gastrin binders. A strong correlation was observed between gastrin binding and overall charge of the peptidomimetic. Most of the best gastrin binders proceeded from CDRs containing charged residues. In contrast, CDRs from high affinity antibodies containing mostly neutral residues failed to yield good binders. Our experiments revealed essential differences in the mode of antigen binding between CDR-derived peptidomimetics (K(d) values in micromolar range) and the parental monoclonal antibodies (K(d) values in nanomolar range). However, chemically derived peptidomimetics from gastrin binders were very effective in gastrin neutralization studies using cell-based assays, yielding a neutralizing activity in pancreatic tumoral cell lines comparable with that of gastrin-specific monoclonal antibodies. These data support the use of combinatorial CDR-peptide microarrays as a tool for the development of a new generation of chemically synthesized cyclic peptidomimetics with functional activity.

Heterologous stacking of prion protein peptides reveals structural details of fibrils and facilitates complete inhibition of fibril growth

Fibrils play an important role in the pathogenesis of amyloidosis; however, the underlying mechanisms of the growth process and the structural details of fibrils are poorly understood. Crucial in the fibril formation of prion proteins is the stacking of PrP monomers. We previously proposed that the structure of the prion protein fibril may be similar as a parallel left-handed beta-helix. The beta-helix is composed of spiraling rungs of parallel beta-strands, and in the PrP model residues 105-143 of each PrP monomer can contribute two beta-helical rungs to the growing fibril. Here we report data to support this model. We show that two cyclized human PrP peptides corresponding to residues 105-124 and 125-143, based on two single rungs of the left-handed beta-helical core of the human PrP(Sc) fibril, show spontaneous cooperative fibril growth in vitro by heterologous stacking. Because the structural model must have predictive value, peptides were designed based on the structure rules of the left-handed beta-helical fold that could stack with prion protein peptides to stimulate or to block fibril growth. The stimulator peptide was designed as an optimal left-handed beta-helical fold that can serve as a template for fibril growth initiation. The inhibiting peptide was designed to bind to the exposed rung but frustrate the propagation of the fibril growth. The single inhibitory peptide hardly shows inhibition, but the combination of the inhibitory with the stimulatory peptide showed complete inhibition of the fibril growth of peptide huPrP-(106-126). Moreover, the unique strategy based on stimulatory and inhibitory peptides seems a powerful new approach to study amyloidogenic fibril structures in general and could prove useful for the development of therapeutics.

Functional reconstruction and synthetic mimicry of a conformational epitope using CLIPS technology

This paper describes immunization studies with CLIPS-constrained peptides covering only the major part (beta3-loop) of a structurally complex antigenic site on human Follicle Stimulating Hormone beta-subunit (FSH-beta). In cases where linear and SS-constrained peptides fail, the CLIPS-constrained peptides generate polyclonal antibodies with high neutralizing activity for hFSH. The sera were shown to be specific for hFSH over human Luteinizing Hormone (hLH) and human Chorionic Gonadotropin (hCG). ELISA-competition studies and circular dichroism (CD)-measurements illustrate clearly that activity of the peptides in antibody binding and generation relates directly to precise and appropriate fixation of the peptide conformation. Design of the CLIPS-peptides was entirely based on epitope mapping studies with two neutralizing anti-hFSH mAbs. Both mAbs were shown to bind to a conformational epitope located at the top of the beta1-beta3-loop covering the amino acid sequences Y58-P77 (beta3-loop). The results described in this paper show that CLIPS-constrained peptides covering the Y58-P77 sequence provide the minimally required structural entity necessary to generate reproducibly sera with high hFSH-neutralizing activity.

SUMO assay with peptide arrays on solid support: insights into SUMO target sites

The modification of proteins by SUMO (small ubiquitin-like modifier) regulates various cellular processes. Sumoylation often occurs on a specific lysine residue within the consensus motif psiKxE/D. However, little is known about the specificity and selectivity of SUMO target sites. We describe here a SUMO assay with peptide array on solid support for the simultaneous characterization of hundreds of different SUMO target sites. This approach was used to characterize known SUMO substrates. The position of the motif within the peptide and the amino acids flanking the acceptor site affected the efficiency of SUMO modification. Interestingly, a sequence of only four amino acids, corresponding to the SUMO consensus motif without flanking amino acids, was a bona fide target site. Analysis of a peptide library for all variants of the psiKxE/D consensus motif revealed that the first and third positions in the tetrapeptide preferably contain aromatic amino acid residues. Furthermore, by adding the SUMO E3 ligase PIAS1 to the reaction mixture, we show specific enhancement of the modification of a PIAS1-dependent SUMO substrate in this system. Overall, our results demonstrate that the sumoylation assay with peptide array on solid support can be used for the high-throughput characterization of SUMO target sites, and provide new insights into the composition, selectivity and specificity of SUMO target sites.

Characterization of gastrin-cholecystokinin 2 receptor interaction in relation to c-fos induction

The interaction of gastrin with the cholecystokinin 2 (CCK2)/gastrin receptor has been studied extensively in relation to gastric acid secretion. However, not much is known about the contribution of individual amino acids of gastrin interacting with the CCK2 receptor, when gastrin is acting as a tumor growth factor. The purpose of the present study was to determine the significance of each individual amino acid residue of human gastrin-17 with respect to CCK2 receptor-mediated cell proliferation. Activation of this receptor was assessed using an in vitro bioassay based on gastrin-induced expression of a c-fos-luciferase reporter, transfected in AR42JB13 and Colo 320 cells, a rat pancreatic and human colorectal cell line respectively. Gastrin-17 dose dependently increased c-fos induction in both cancer cell lines. L365,260, a known CCK2 receptor antagonist, completely blocked the gastrin signal, demonstrating the specificity of this assay. We demonstrated for the first time that four carboxy-terminal amino acids of gastrin-17 are essential for activation of the CCK2 receptor with respect to c-fos induction. Also other residues of gastrin-17, notably glycine-2 for the rat CCK2 receptor and glutamic acid 8-10 and tyrosine-12 for the human receptor, were found to be important, although to a lesser extent. Alanine-substitution variants of each of the four carboxy-terminal amino acids of gastrin-17 showed strongly reduced receptor activation but did not act as competitive inhibitors of gastrin-17. Identification of the essential role of the carboxy-terminal tetrapeptide of gastrin-17 in CCK2 receptor-mediated c-fos induction indicates that gastrin inhibitory therapeutic strategies should mainly be targeted toward this region of gastrin.

Polyanion induced fibril growth enables the development of a reproducible assay in solution for the screening of fibril interfering compounds, and the investigation of the prion nucleation site

The misfolded conformer of the prion protein (PrP) that aggregates into fibrils is believed to be the pathogenic agent in transmissible spongiform encephalopathies. In order to find fibril interfering compounds a screening assay in solution would be the preferred format to approximate more closely to physical conditions and enable the performance of kinetic studies. However, such an assay is hampered by the high irreproducibility because of the stochastic nature of the fibril formation process. According to published fibril models, the fibrillar core may be composed of stacked parallel beta-strands. In these models positive charge repulsion may reduce the chance of favorable stacking and cause the irreproducibility in the fibril formation. This study shows that the charge compensation by polyanions induced a very strong fibril growth which made it possible to develop a highly reproducible fibril interference assay. The stimulating effect of the polyanions depended on the presence of the basic residues Lys(106), Lys(110) and His(111). The assay was validated by comparison of the 50% fibril inhibition levels of peptide huPrP106-126 by six tetracyclic compounds. With this new assay, the fibrillogenic core (GAAAAGAVVG) of peptide huPrP106-126 was determined and for the first time it was possible to test the inhibition potentials of peptide analogues. Also it was found that variants of peptide huPrP106-126 with proline substitutions at positions Ala(115), Ala(120), or Val(122) inhibited the fibril formation of huPrP106-126.

Monitoring health by values of acute phase proteins

A systemic acute phase reaction may develop during infection and inflammation, due to the action of peripherally liberated proinflammatory cytokines. Hepatic metabolism changes, and negative and positive acute phase proteins (APPs) can be measured in the blood: the APPs therefore represent appropriate analytes to assess health. While they are non-specific markers, their levels change with biological effects and this can be used to assess nutritional deficits and reactive processes, especially when positive and negative acute phase variables are combined in an index. Unfortunately, at present, no comprehensive, easy-to-use and cheap system is available to assess various acute phase proteins in serum or blood samples. Protein micro-array technology may satisfy this need; it will permit simultaneous analysis of numerous analytes in the same small volume sample and enable integration of information derived from systemic reactivity and nutrition with disease-specific variables. Applying such technology may help to address health problems in many countries.

GnRH tandem peptides for inducing an immunogenic response to GnRH-I without cross-reactivity to other GnRH isoforms

Gonadotropin releasing hormone (GnRH) occurs in various isoforms in mammals, i.e. GnRH-I (mammalian GnRH), GnRH-II (chicken GnRH-II), GnRH-III (salmon GnRH) and two forms of lamprey GnRH. The function of the latter four molecules have only been partially investigated. Also not much is known about the physiological effects of GnRH-I immunization on the function of these GnRH isoforms. In order to avoid possible harmful side-effects due to undesired neutralization of GnRH isoforms, GnRH-I specificity of antibodies raised against a panel of alternative GnRH antigens was determined. The results show that GnRH antigens can be designed which generate antibodies that specifically bind GnRH-I, without cross-reacting with other GnRH isoforms.

Novel rabies virus-neutralizing epitope recognized by human monoclonal antibody: fine mapping and escape mutant analysis

Anti-rabies virus immunoglobulin combined with rabies vaccine protects humans from lethal rabies infections. For cost and safety reasons, replacement of the human or equine polyclonal immunoglobulin is advocated, and the use of rabies virus-specific monoclonal antibodies (MAbs) is recommended. We produced two previously described potent rabies virus-neutralizing human MAbs, CR57 and CRJB, in human PER.C6 cells. The two MAbs competed for binding to rabies virus glycoprotein. Using CR57 and a set of 15-mer overlapping peptides covering the glycoprotein ectodomain, a neutralization domain was identified between amino acids (aa) 218 and 240. The minimal binding region was identified as KLCGVL (aa 226 to 231), with key residues K-CGV- identified by alanine replacement scanning. The critical binding region of this novel nonconformational rabies virus epitope is highly conserved within rabies viruses of genotype 1. Subsequently, we generated six rabies virus variants escaping neutralization by CR57 and six variants escaping CRJB. The CR57 escape mutants were only partially covered by CRJB, and all CRJB-resistant variants completely escaped neutralization by CR57. Without exception, the CR57-resistant variants showed a mutation at key residues within the defined minimal binding region, while the CRJB escape viruses showed a single mutation distant from the CR57 epitope (N182D) combined with mutations in the CR57 epitope. The competition between CR57 and CRJB, the in vitro escape profile, and the apparent overlap between the recognized epitopes argues against including both CR57 and CRJB in a MAb cocktail aimed at replacing classical immunoglobulin preparations.

Fast track selection of immunogens for novel vaccines through visualisation of the early onset of the B-cell response

A most essential step in vaccine research and development, ie vaccine studies in animals, seriously suffer from long timespans needed to arrive at effective immunogens. In this report we show how almost immediately after vaccination the antibody inducing potential of low immunogenic 'self' antigens can be accurately assessed. (We expect that this timespan can be reduced even more when 'non self' antigens are used, since such responses should be stronger.) The method takes advantage of the immediate onset after vaccination of the immune response in the spleen. This novel method allows detection of antigen-specific B cells of the spleen as early as 7 days after immunization and at frequencies as low as 10 in 1,000,000 cells. The method depends on sequential staining with PE- and APC-conjugated tetramers, made with the same biotinylated peptide. The antigenic peptides are biotinylated and tetramerized with either PE neutravidin or APC streptavidin. We expect that this method can be generally applied to visualize B cell responses, irrespective of the way they are induced. In addition to the fast selection and development of novel immunogens, this procedure can be used to delineate the kinetics of the B cell response, to phenotypically characterize and to isolate antigen-specific B cells, and, perhaps most importantly, to count them at the clonal level before any circulating antibodies can be detected.

Effects of GnRH immunization in sexually mature pony stallions

Immunization against gonadotrophin releasing hormone (GnRH) was studied as an alternative for the commonly used surgical castration in stallions. Two GnRH vaccines comprising non-mineral oil adjuvants were evaluated for their potential to induce high antibody titers directed against GnRH and subsequent effects on reproductive characteristics. Twelve sexually mature male hemicastrated Shetland ponies were assigned to three groups. Group 1 and 2 were injected with 1mg peptide equivalent of G6k-GnRH-tandem-dimer conjugated to ovalbumin (OVA) in CoVaccine HT adjuvant (GnRH/CoVaccine) and in Carbopol (GnRH/Carbopol), respectively, and group 3 was injected with CoVaccine HT adjuvant without antigen (controls). After immunization no adverse effects were observed with respect to the injections sites or general health. Two weeks after the second vaccination antibody titers against GnRH increased rapidly in all animals of the GnRH/CoVaccine group, at the same time reducing serum testosterone levels maximally for the further duration of the experiment. In the GnRH/Carbopol group antibody responses and effects on testosterone levels were intermediate in two stallions and not apparent in the remaining stallions of this group. Semen evaluation showed that from 2 weeks after the second immunization onwards, sperm motility was affected in all stallions treated with GnRH/CoVaccine and one stallion treated with GnRH/Carbopol. Seven weeks after the second immunization, no semen could be collected from two stallions, one of each group, due to suppressed libido. Histological examination of the testes, 15 weeks after the initial immunization, demonstrated reduction in seminiferous tubuli diameters in all stallions of the GnRH/CoVaccine group and one stallion of the GnRH/Carbopol group. Furthermore, spermatogenesis was extremely disorganized in these stallions, as indicated by absence of the lumen in the seminiferous tubules, the absence of spermatozoa and spermatids in the tubular cross-sections and the impossibility to determine the stage of the tubular cross-sections. Testis size was also substantially reduced in three out of four stallions treated with GnRH/CoVaccine. The results demonstrate that two immunizations with G6k-GnRH-tandem-dimer-OVA conjugate in a suitable adjuvant such as CoVaccine HT caused a rapid and complete reduction of serum testosterone levels in sexually mature stallions, subsequently leading to reduced sperm motility and affected testis function, while no adverse reactions were observed after immunizations.

New transport peptides broaden the horizon of applications for peptidic pharmaceuticals

Protein transduction domains (PTDs) have proven to be an invaluable tool to transduce a wide variety of cargo's including peptides across the plasma membrane and into intact tissue. The PTDs are able to deliver biologically active molecules both in vitro and in vivo. This study describes many new polybasic PTDs of which some are just as potent as the PTDs derived from extracellular RNAses or other published PTDs. Large differences in potency became apparent when the PTDs are coupled to particular cargoes. Therefore, the unique characteristic of a PTD may only become apparent when it is selected for a particular application. Rules for optimization of PTDs for particular applications are now emerging and open the way for a new generation of drug delivery agents. Because fixation artifacts and irreversible membrane binding may cause misinterpretation of the amount of internalization of polybasic peptides, we have developed an enzyme transduction assay based on the intracellular loading of a cell permeable substrate. In this assay, a fluorescent signal is generated by internalized enzyme in intact cells and not by membrane-bound or extracellular enzyme.

An in vitro screening assay based on synthetic prion protein peptides for identification of fibril-interfering compounds

Transmissible spongiform encephalopathies are neurodegenerative diseases and are considered to be caused by malformed prion proteins accumulated into fibrillar structures that can then aggregate to form larger deposits or amyloid plaques. The identification of fibril-interfering compounds is of therapeutic and prophylactic interest. A robust and easy-to-perform, high-throughput, in vitro fluorescence assay was developed for the detection of such compounds. The assay was based on staining with the fluorescent probe thioflavin S in polystyrene microtiter plates to determine the amyloid state of synthetic peptides, representing a putative transmembrane domain of human and mouse prion protein. In determining optimal test conditions, it was found that drying peptides from phosphate buffer prior to staining resulted in good reproducibility with an interassay variation coefficient of 8%. Effects of thioflavin S concentration and staining time were established. At optimal thioflavin S concentration of 0.2mg/ml, the fluorescence signals of thioflavin S with five different prion protein-based fibrillogenic peptides, as well as peptide Abeta((1-42)), were found to show a peptide-dependent linear correlation within a peptide concentration range of 10-400 microM. The ability of the assay to identify compounds that interfere with fibril formation and/or dissociate preformed fibrils was demonstrated for tetracyclic compounds by preceding coincubation with human prion protein peptide huPrP106-126.

Identification of an Interleukin-15α Receptor-binding Site on Human Interleukin-15

To identify the epitopes in human interleukin-15 (IL-15) that are responsible for binding to the interleukin-15 receptor alpha chain, antibody and receptor mapping by peptide scanning and site-directed mutagenesis was used. By using peptide scanning, we identified four regions in IL-15. The first region ((85)CKECEELEEKN(95)) is located in the C-D loop and is recognized by a set of non-inhibitory antibodies. The second region ((102)SFVHIVQMFIN(112)) is located in helix D and is recognized by two antibodies that are inhibitory of IL-15 bio-activity but not of IL-15 binding to IL-15Ralpha. The two remaining regions react with a recombinant soluble form of the IL-15Ralpha; the first ((44)LLELQVISL(52), peptide 1) corresponds to a sequence located in the B-helix and the second ((64)ENLII(68), peptide 2) to a sequence located in helix C. The latter is also contained in the epitope recognized by an antibody (monoclonal antibody B-E29) that prevents IL-15 binding to IL-15Ralpha. By site-directed mutagenesis, we confirmed that residues present in peptide 1 (Leu-45, Glu-46, Val-49, Ser-51, and Leu-52) and peptide 2 (Leu-66 and Ile-67) are involved in the binding of IL-15 to IL-15Ralpha. Furthermore, the results presented indicate that residues in the second peptide (Glu-64, Asn-65, and Ile-68) participate in IL-2Rbeta recruitment. This finding could have implications for the dynamics of receptor assembly. These results also indicate that the modes of interaction of IL-15 and IL-2 with their respective alpha chains are not completely analogous. Finally, some of the IL-15 mutants generated in this study displayed agonist or antagonist properties and may be useful as therapeutic agents.

Mapping of a discontinuous and highly conformational binding site on follicle stimulating hormone subunit-β (FSH- ) using domain Scan™ and Matrix Scan™ technology

This paper describes the application of two novel screening technologies, i.e. Domain Scan (24- and 30-mer peptides) and Matrix Scan (24-mer peptides) technology, in the mapping of a discontinuous epitope on FSH-beta for a series of 20 monoclonal antibodies. 11 out of 20 mAb's, mapping of which was not successful by conventional Pepscan technology (12-mer peptides), showed selective binding to peptide-constructs corresponding to the beta3-loop of FSH in the Domain and/or Matrix Scan. Systematic replacement analysis studies with peptide-construct 57VYETVRVPGCAC-SAc-ADSLYTYPVATQ81 revealed that for most mAb's the amino acids R62, A70, D71, and L73 form the core of the epitope. A Domain Scan performed in the C-O format showed highly selective binding for mAb's 1 and 2 with only three beta1-beta3 peptide-constructs covering the residues 60TVRVPGCAHHADSLY74 in combination with 10IAIEKEECRFAI21, while for mAb 10 binding was observed with peptide-constructs containing the C-terminal residues 97RGLGPSYCSFGEMKE114 in combination with the residues 10IAIEKEECRFAI21. A Matrix Scan of mAb 17 showed that peptides from four different regions on FSH (1st strand beta3-loop, alpha 1-loop, long alpha2-loop, det. loop) showed enhanced binding in combination with several 70ADSL73-containing peptides. BIACORE measurements with mAb's 1, 2, 13, and 17 using a set of 21 different peptide(-construct)s partially confirmed the Domain and Matrix Scan screening results. Only 24- and 33-mer peptides covering both the 1st and 2nd strand of the beta3-loop showed measurable binding. Cyclic beta3-loop peptide mimics were found to bind significantly stronger (Kd approximately 5 microM) than the lineair analogues, in agreement with the fact that the discontinuous epitope is part of a loop structure. Coupling of the lineair beta1-peptide 1oIAIEKEECRFAI21 to the linear beta3-peptide *52TFKELVYETVRVPGCAHHADSLYTYPVATQAH83# via disulfide bond formation showed a 2-3 fold increase in Kd, thus conforming participation of the beta 1-loop in antibody binding for these mAb's.

Multidrug-resistant tumor cells remain sensitive to a recombinant interleukin-4-Pseudomonas exotoxin, except when overexpressing the multidrug resistance protein MRP1

Tumor cells may become resistant to conventional anticancer drugs through the occurrence of transmembrane transporter proteins such as P-glycoprotein (ABCB1), breast cancer resistance protein (ABCG2), or members of the multidrug resistance-associated protein family (MRP1-MRP5; ABCC1-ABCC5). In this report, we studied whether tumor cells that are cytostatic drug resistant because of overexpression of one of the above mentioned proteins are sensitive to a new anticancer agent, interleukin-4 toxin (IL-4 toxin). IL-4 toxin is a fusion protein composed of circularly permuted IL-4 and a truncated form of Pseudomonas exotoxin (PE) [IL-4(38-37)-PE38KDEL]. Ninety-six-h cytotoxicity assays and 10-day clonogenic assays showed that drug-selected multidrug resistant (MDR) tumor cells that overexpress P-glycoprotein or breast cancer resistance proteins are still sensitive to IL-4 toxin. Also, tumor cells transfected with cDNA for MRP2-5 showed no resistance, or marginal resistance, only to the toxin as compared with the parent cells. In contrast, MRP1-overexpressing cells, both drug selected and MRP1 transfected, are clearly resistant to IL-4 toxin with resistance factors of 4.3 to 8.4. MRP1-overexpressing cells were not resistant to PE itself. IL-4 toxin resistance in MRP1-overexpressing cells could be reversed by the MRP1 inhibitors probenecid or MK571 and were not affected by glutathione depletion by DL-buthionine-S,R-sulfoximine. In a transport assay using plasma membrane vesicles prepared from MRP1-overexpressing cells, IL-4 toxin and IL-4, but not PE, inhibited the translocation of the known MRP1 substrate 17beta-estradiol 17-(beta-D-glucuronide) (E(2)17betaG). These data suggest that MRP1-overexpressing cells are resistant to IL-4 toxin because of extrusion of this agent by MRP1. Still, the results of this study demonstrate that IL-4 toxin effectively kills most MDR tumor cells and, therefore, represents a promising anticancer drug.

Design of Synthetic Peptides for Diagnostics

Due to the advantageous properties of synthetic molecules compared to biological ones biological molecules in diagnostic tests are replaced increasingly by synthetic ones, usually synthetic peptides or related molecules. The replacement of biological antigens by synthetic peptides is most advanced at present, as well as the use of site-specific antibodies induced with synthetic peptides. Moreover recent results indicate that synthetic molecules may also replace antibodies. Ultimately this will lead to diagnostic assays built of synthetic molecules only.

Discovery and in vivo evaluation of new melanocortin-4 receptor-selective peptides

The melanocortin-4 receptor (MC4R) is involved in several physiological processes, including body weight regulation and grooming behaviour in rats. It has also been suggested that the MC4R mediates the effects of melanocortin ligands on neuropathic pain. Selective compounds are needed to study the exact role of the MC4R in these different processes. We describe here the development and evaluation of new melanocortin compounds that are selective for the MC4R as compared with the other centrally expressed receptors, MC3R and MC5R. First, a library of 18 peptides, in which a melanocortin-based sequence was systematically point-mutated, was screened for binding to and activity on the MC3R, MC4R and MC5R. Compound Ac-Nle-Gly-Lys-D-Phe-Arg-Trp-Gly-NH(2) (JK1) appeared to be the most selective MC4R compound, based on affinity. This compound is 90- and 110-fold selective for the MC4R as compared to the MC3R and MC5R, respectively. Subsequent modification of JK1 yielded compound Ac-Nle-Gly-Lys-D-Nal(2)-Arg-Trp-Gly-NH(2) (JK7)(,) a selective MC4R antagonist with 34-fold MC4R/MC3R and 109-fold MC4R/MC5R selectivity. The compounds were active in vivo as determined in a grooming assay and a model for neuropathic pain in rats. Intravenous (i.v.) injections suggested that they were able to pass the blood-brain barrier.The compounds identified here will be useful in further research on the physiological roles of the MC4R.

Performance of male pigs immunized against GnRH is related to the time of onset of biological response

In this study, the performance of male pigs immunized against GnRH was determined in relation to the onset of their biological response to the immunization. Pigs were immunized at 9 and 17 wk of age and were housed in a pen together with both a surgically castrated and an intact boar littermate. Feed intake was restricted to 2.8 to 3.2 times maintenance requirement for energy. Animals were weighed weekly and slaughtered at 108 kg BW. Depending on the time of onset of the response after immunization in terms of biological effects, immunized pigs were retrospectively grouped into two categories. One category consisted of the immunized pigs, which had undetectable or low levels of LH and testosterone at the time of booster immunization-known as "early" responding immunocastrates (E-IM, n = 8), whereas the "late" responding immunocastrates (L-IM, n = 7) had substantial LH and testosterone levels at that time. This dichotomy of the response to immunization also was reflected in testis weight, with 17 g and 40 g for E-IM and L-IM pigs, respectively. At slaughter, testis size and weight were reduced (P < 0.001) in the immunocastrated pigs as compared to the intact boars. Androstenone concentrations in backfat of all immunocastrated pigs were undetectable. Growth performance (i.e., ADG and feed efficiency [FE, g gain/kg feed]), was better in boars and L-IM pigs than in surgical castrates and E-IM pigs (P < 0.05). Average daily gain and FE did not differ between E-IM pigs and the surgical castrates, but intact boars performed better than L-IM (P < 0.02). There were no significant differences in carcass quality (backfat thickness and meat percentage) between boars and surgical castrates at slaughter. However, for both characteristics L-IM pigs and intact boars performed better (P < 0.03) than E-IM pigs. Thus, growth performance in L-IM is better than in either E-IM or surgical castrates.

Functional analysis of synthetic insectatachykinin analogs on recombinant neurokinin receptor expressing cell lines

The activity of a series of synthetic tachykinin-like peptide analogs was studied by means of microscopic calcium imaging on recombinant neurokinin receptor expressing cell lines. A C-terminal pentapeptide (FTGMRa) is sufficient for activation of the stomoxytachykinin receptor (STKR) expressed in Schneider 2 cells. Replacement of amino acid residues at the position of the conserved phenylalanine (F) or arginine (R) residues by alanine (A) results in inactive peptides (when tested at 1microM), whereas A-replacements at other positions do not abolish the biological activity of the resulting insectatachykinin-like analogs. Calcium imaging was also employed to compare the activity of C-terminally substituted tachykinin analogs on three different neurokinin receptors. The results indicate that the major pharmacological and evolutionary difference between tachykinin-related agonists for insect (STKR) and human (NK1 and NK2) receptors resides in the C-terminal amino acid residues (R versus M). A single C-terminal amino acid change can turn an STKR-agonist into an NK-agonist and vice versa.

Effects of active immunization against GnRH on serum LH, inhibin A, sexual development and growth rate in Chinese female pigs

Surgical castration of young female pigs is common practice in Chinese pig farming today. The purpose of the present study is to investigate anti-GnRH immunization as a practical alternative to surgical castration for female pigs. Thirty-six Chinese female crossbred pigs (Chinese Yanan x Yorkshire) were selected from 12 litters, three pigs from each litter, at the age of 10-13 weeks. One pig from each litter was immunized with 62.5 microg D-Lys6-GnRH-tandem-dimer peptide conjugated to ovalbumin in Specol adjuvant at Week 0 (0 week post-vaccination, wpv), and a booster vaccination was given 8 weeks later (8 wpv). Its intact and castrate littermates (surgically castrated at the time of weaning, i.e. at 6 weeks of age) were administered the vehicle and served as controls. Antibody titers, serum LH and inhibin A were determined at the day of first vaccination, every 4 weeks thereafter and at the day of slaughter (18 wpv). At slaughter, ovaries were inspected for the presence of follicles and corpora lutea, and ovarian and uterine weights were recorded. Ten of twelve immunized pigs responded well to the immunization (immunocastrated animals), while the remaining two pigs responded poorly (nonresponders). Antibody titres in immunocastrated animals steadily increased after immunization, became maximal at 12 wpv and remained high until slaughter. Serum LH levels were reduced (P < 0.05) in immunocastrated pigs as compared to intact controls and surgical castrates. Serum inhibin A levels decreased after vaccination, and equaled surgical castrate levels from 8 wpv until the end of the experiment. Ovarian and uterine weights (1.3 +/- 0.2 and 43.9 +/- 11.4 g, respectively; mean +/- S.E.M.) were significantly lower (P < 0.05) in immunocastrates than in intact controls (9.4 +/- 1.1 and 390.9 +/- 67.2 g, respectively). Antibody titers were significantly lower (P < 0.05) in nonresponders than in immunocastrated pigs from 12 wpv to slaughter. Ovarian and uterine weights were similar in nonresponders and in intact controls. Macroscopically, no follicular structures were found in ovaries of immunocastrated pigs, while large follicles or corpora lutea were observed in the ovaries of both nonresponders and intact controls. Although not significant, immunocastrates had a numerically higher average daily gain than surgical castrates and intact controls (0.74 +/- 0.04 versus 0.66 +/- 0.04 versus 0.66 +/- 0.03 kg per day, respectively; mean +/- S.E.M., P = 0.09). Results obtained in the present study demonstrate that anti-GnRH immunization can be an attractive alternative to surgical castration for Chinese crossbred female pigs. Our results also question the beneficial effect of surgical castration on growth as compared to intact controls.

A structural model of pestivirus E(rns) based on disulfide bond connectivity and homology modeling reveals an extremely rare vicinal disulfide

E(rns) is a pestivirus envelope glycoprotein and is the only known viral surface protein with RNase activity. E(rns) is a disulfide-linked homodimer of 100 kDa; it is found on the surface of pestivirus-infected cells and is secreted into the medium. In this study, the disulfide arrangement of the nine cysteines present in the mature dimer was established by analysis of the proteolytically cleaved protein. Fragments were obtained after digestion with multiple proteolytic enzymes and subsequently analyzed by liquid chromatography-electrospray ionization mass spectrometry. The analysis demonstrates which cysteine is involved in dimerization and reveals an extremely rare vicinal disulfide bridge of unknown function. With the assistance of the disulfide arrangement, a three-dimensional model was built by homology modeling based on the alignment with members of the Rh/T2/S RNase family. Compared to these other RNase family members, E(rns) shows an N-terminal truncation, a large insertion of a cystine-rich region, and a C-terminal extension responsible for membrane translocation. The homology to mammalian RNase 6 supports a possible role of E(rns) in B-cell depletion.

Synthetic peptides derived from the β2−β3 loop ofRaphanus sativusantifungal protein 2 that mimic the active site

Rs-AFPs are antifungal proteins, isolated from radish (Raphanus sativus) seed or leaves, which consist of 50 or 51 amino acids and belong to the plant defensin family of proteins. Four highly homologous Rs-AFPs have been isolated (Rs-AFP1-4). The structure of Rs-AFP1 consists of three beta-strands and an alpha-helix, and is stabilized by four cystine bridges. Small peptides deduced from the native sequence, still having biological activity, are not only important tools to study structure-function relationships, but may also constitute a commercially interesting target. In an earlier study, we showed that the antifungal activity of Rs-AFP2 is concentrated mainly in the beta2-beta3 loop. In this study, we synthesized linear 19-mer peptides, spanning the entire beta2-beta3 loop, that were found to be almost as potent as Rs-AFP2. Cysteines, highly conserved in the native protein, are essential for maintaining the secondary structure of the protein. Surprisingly, in the 19-mer loop peptides, cysteines can be replaced by alpha-aminobutyric acid, which even improves the antifungal potency of the peptides. Analogous cyclic 19-mer peptides, forced to adopt a hairpin structure by the introduction of one or two non-native disulfide bridges, were also found to possess high antifungal activity. The synthetic 19-mer peptides, like Rs-AFP2 itself, cause increased Ca2+ influx in pregerminated fungal hyphae.

Active immunization against gonadotrophin-releasing hormone in Chinese male pigs: effects of dose on antibody titer, hormone levels and sexual development

The objective of this study was to determine the optimal dose of a GnRH vaccine for immunocastration of Chinese male pigs, based on immune, endocrine and testicular responses. Forty-two crossbred (Chinese Yanan x Large White) male pigs were randomly assigned to one of the five treatments as follows: (I) 0 microg (control, n=8); (II) 10 microg (n=8); (III) 62.5 microg (n=8); (IV) 125 microg (n=8); (V) 250 microg (n=10), D-Lys6-GnRH tandem dimer (TDK) peptide equivalent of conjugate (TDK-OVA), using Specol as the adjuvant. Pigs were immunized at 13 and 21 weeks of age and were slaughtered at 31 weeks of age. Blood samples for antibody titer and hormone assays were collected at 13, 21, 24 and 31 weeks of age. At these time-points, testis size was also measured. At slaughter, testis weight was recorded and fat samples were collected for androstenone assay. Four animals, one out of each immunized group, responded poorly to the immunization (non-responders). At slaughter, serum testosterone and LH levels, fat androstenone levels and testis size/weight of these non-responders were similar to those in control animals. Antibody titers of non-responders were substantially lower (P<0.05) than in other immunized pigs. For the animals that responded well to the immunization (immunocastrated pigs), serum testosterone and LH levels, fat androstenone levels and testis size or weight were reduced (P<0.05) as compared to either controls or non-responders, at all doses tested. There was a significant effect of dose of TDK-OVA on antibody titers. The overall mean antibody titers in the 62.5 or 125 microg dose group (53.6 and 50.5% binding, respectively) were significantly higher than in the 10 or 250 microg group (39.2 and 40.24% binding, respectively). At slaughter, there was a significant dose effect on testis size or weight and on serum testosterone levels, but there was no dose effect on serum LH levels and fat androstenone levels. Testis size or weight in the 10 microg group was reduced to a lesser extent (P<0.05) than in the three higher dose groups. At slaughter, in comparison to controls, mean testis size of immunocastrated pigs in treatments II-V was reduced to 55, 21, 33 and 25%, respectively, whereas testis weight was reduced to 39, 12, 18 and 14%, respectively. Reduction of testis size and/or weight is important for visual assessment of castration at the slaughterline, therefore, it is concluded that a dose of 10 microg peptide is not suitable. We conclude that, within the dose-range studied, the 62.5 microg dose is optimal for future GnRH immunization studies or future practical use in immunocastration of Chinese male pigs.

Functional mimicry of a discontinuous antigenic site by a designed synthetic peptide

Functional reproduction of the discontinuous antigenic site D of foot-and-mouth disease virus (FMDV) has been achieved by means of synthetic peptide constructions that integrate each of the three protein loops that define the antigenic site into a single molecule. The site D mimics were designed on the basis of the X-ray structure of FMDV type C-S8c1 with the aid of molecular dynamics, so that the five residues assumed to be involved in antigenic recognition are located on the same face of the molecule, exposed to solvent and defining a set of native-like distances and angles. The designed site D mimics are disulfide-linked heterodimers that consist of a larger unit containing VP2(71-84), followed by a polyproline module and by VP3(52-62), and a smaller unit corresponding to VP1(188-194) (VP=viral protein). Guinea pig antisera to the peptides recognized the viral particle and competed with site D-specific monoclonal antibodies, while inoculation with a simple (not covalently joined to one another) admixture of the three VP1-VP3 sequences yielded no detectable virus-specific serum conversion. Similar results have been reproduced in two bovines. Antisera to the peptides also moderately neutralize FMDV in cell cultures and partially protect guinea pigs against challenge with the virus. These results demonstrate functional mimicry of the discontinuous site D by the peptides, which are therefore obvious candidates for a multicomponent, peptide-based vaccine against FMDV.

The role of the individual amino acids of a GnRH-tandem-dimer peptide used as an antigen for immunocastration of male piglets determined with systematic alanine replacements

Immunocastration targeting gonadotropin releasing hormone (GnRH) can be obtained in male piglets using native GnRH conjugates. However, due to insufficient efficacy of these conjugates, improved GnRH antigens, like peptides existing of repeats of the GnRH amino acid sequence, have been designed. We previously reported about a dimerised GnRH-tandem peptide with a D-Lys at position 6 of the native GnRH sequence (G6k-TD) being highly effective. To evaluate the contribution of each individual amino acid of the GnRH decapeptide to the efficacy of the G6k-TD peptide, each amino acid was replaced consecutively by alanine (Ala-scan). The G6k-TD peptides were conjugated to ovalbumin, used for immunisation and tested for their ability to elicit GnRH antibodies and to immunocastrate male piglets. The results show that four out of nine amino acids (pGlu-1, Ser-4, Arg-8 and Gly-10) can be replaced by alanine without negatively affecting immunocastration efficacy. Replacement of amino acids in other positions (Tyr-5, Leu-7 and Pro-9) gave partial decrease of efficacy, respectively, five, six and six out of seven piglets were immunocastrated. Replacements at two other positions (His-2 and Trp-3) completely negated immunocastration activity. Thus, seven out of nine amino acid positions in the basic unit of G6k-TD can be substituted by alanine without affecting immunocastration efficacy.

Definition of neutralizing sites on African horse sickness virus serotype 4 VP2 at the level of peptides

The antigenic structure of African horse sickness virus (AHSV) serotype 4 capsid protein VP2 has been determined at the peptide level by PEPSCAN analysis in combination with a large collection of polyclonal antisera and monoclonal antibodies. VP2, the determinant for the virus serotype and an important target in virus neutralization, was found to contain 15 antigenic sites. A major antigenic region containing 12 of the 15 sites was identified in the region between residues 223 and 400. A second domain between residues 568 and 681 contained the three remaining sites. These sites were used for the synthesis of peptides, which were later tested in rabbits. Of the 15 synthetic peptides, three were able to induce neutralizing antibodies for AHSV-4, defining two neutralizing epitopes, 'a' and 'b', between residues 321 and 339, and 377 and 400, respectively. A combination of peptides representing both sites induced a more effective neutralizing response. Still, the relatively low neutralization titres make the possibility of producing a synthetic vaccine for AHSV unlikely. The complex protein-protein interaction of the outer shell of the viral capsid would probably require the presence of either synthetic peptides in the correct conformation or peptide segments from the different proteins VP2, VP5 and VP7.

Pharmacological characterization of STKR, an insect G protein-coupled receptor for tachykinin-like peptides

STKR is a G protein-coupled receptor that was cloned from the stable fly, Stomoxys calcitrans. Multiple sequence comparisons show that the amino acid sequence of this insect receptor displays several features that are typical for tachykinin (or neurokinin, NK) receptors. Insect tachykinin-related peptides, also referred to as "insectatachykinins," produce dose-dependent calcium responses in Drosophila melanogaster Schneider 2 cells, which are stably transfected with this receptor (S2-STKR). These responses do not depend on the presence of extracellular Ca(2+)-ions. A rapid agonist-induced increase of inositol 1,4,5-trisphosphate (IP(3)) is observed. This indicates that the agonist-induced cytosolic Ca(2+)-rise is caused by a release of Ca(2+) ions from intracellular calcium stores. The pharmacology of STKR is analyzed by studying the effects of the most important antagonists for mammalian NK-receptors on STKR-expressing insect cells. The results show that spantide II, a potent substance P antagonist, is a real antagonist of insectatachykinins on STKR. We have also tested the activity of a variety of natural insectatachykinin analogs by microscopic image analysis of calcium responses in S2-STKR cells. At a concentration of 1 microM, almost all natural analogs produce a significant calcium rise in stable S2-STKR cells. Interestingly, Stc-TK, an insectatachykinin that was recently discovered in the stable fly (S. calcitrans), also proved to be an STKR-agonist. Stc-TK, a potential physiological ligand for STKR, contains an Ala-residue (or A) instead of a highly conserved Gly-residue (or G). Arch.

Synthetic peptide vaccines: unexpected fulfillment of discarded hope?

In the early eighties it was realized that the ultimate vaccine would be a synthetic peptide. Major efforts were put into the development of a synthetic vaccine for foot-and-mouth disease virus (FMDV) for which even today no alternative exists besides the classical vaccine based on inactivated virus. Despite impressive progress, a peptide vaccine that could match the classical vaccine with respect to efficacy (i.e. full protection of all animals after a single vaccination) has not materialized. This has led to the belief that synthetic vaccines were not possible. However, in the early nineties we developed a synthetic peptide vaccine for canine parvovirus that did match the classical vaccine based on inactivated virus (i.e. protected all animals). Based on the difference of FMDV (an RNA virus) and canine parvovirus (a DNA virus), we suggested that in the case of FMDV, more than one antigenic site should be used, instead of the single one used previously. In our opinion multiple sites are necessary to prevent the development of escape mutants of FMDV. Unfortunately, the additional sites of FMDV are highly discontinuous. Until recently it was impossible to reconstruct these sites in the form of synthetic peptides. In the past few years, new methods have been developed that allow recombination of such sites into synthetic molecules. If successfully applied to FMDV, synthetic peptide vaccines and many others may become feasible in the near future. Moreover, the ability to mimic complex discontinuous sites by synthetic peptides will have a major impact on the rapidly developing area of therapeutic vaccines.

Synthetic peptides as functional mimics of a viral discontinuous antigenic site

Functional reproduction of discontinuous antigenic site D of foot-and-mouth disease virus (FMDV) has been achieved by means of synthetic peptide constructions that integrate into a single molecule each of the three protein loops that define the antigenic site. The site D mimics are designed on the basis of the X-ray structure of FMDV type C-S8c1 with the aid of molecular dynamics, so that the five residues assumed to be involved in antigenic recognition are located on the same face of the molecule, exposed to solvent and defining a set of native-like distances and angles. The designed site D mimics are disulphide-linked heterodimers that consist of a larger unit containing VP2(71-84), followed by a polyproline module and by VP3(52-62), and a smaller unit corresponding to VP1(188-194). Guinea pig antisera to the peptides recognize the viral particle and compete with site D-specific monoclonal antibodies, while inoculation with a simple (non-covalently bound) admixture of the three VP1-VP3 sequences yields no detectable virus-specific serum conversion. Similar results have been reproduced in two cattle. Antisera to the peptides are also moderately neutralizing of FMDV in cell culture and partially protective of guinea pigs against challenge with the virus. These results demonstrate functional mimicry of the discontinuous site D by the peptides, which are therefore obvious candidates for a multicomponent peptide-based vaccine against FMDV.

The nature of the bond between peptide and carrier molecule determines the immunogenicity of the construct

The influence of the nature of the bond between a peptide and a (lipidic) carrier molecule on the immunogenicity of that construct was investigated. As types of bonds a thioester-, a disulfide-, an amide- and a thioether bond were investigated. As carrier molecules a peptide, an N-palmitoylated peptide or a C(16)-hydrocarbon chain were used. The biostability of the bond between peptide and carrier molecule is thioether > amide > disulfide >> thioester. However, the immunogenic potency of the constructs used was found to be thioester > disulfide > amide > thioether. In conclusion, a construct with a bond between peptide and (lipidic) carrier molecule that is more susceptible to biological degradation is more immunogenic when used in a peptide-based vaccine than a bond that is less susceptible to biological degradation.

Inactivated recombinant plant virus protects dogs from a lethal challenge with canine parvovirus

A vaccine based upon a recombinant plant virus (CPMV-PARVO1), displaying a peptide derived from the VP2 capsid protein of canine parvovirus (CPV), has previously been described. To date, studies with the vaccine have utilized viable plant chimaeric particles (CVPs). In this study, CPMV-PARVO1 was inactivated by UV treatment to remove the possibility of replication of the recombinant plant virus in a plant host after manufacture of the vaccine. We show that the inactivated CVP is able to protect dogs from a lethal challenge with CPV following parenteral immunization with the vaccine. Dogs immunized with the inactivated CPMV-PARVO1 in adjuvant displayed no clinical signs of disease and shedding of CPV in faeces was limited following CPV challenge. All immunized dogs elicited high titres of peptide-specific antibody, which neutralized CPV in vitro. Levels of protection, virus shedding and VP2-specific antibody were comparable to those seen in dogs immunized with the same VP2- peptide coupled to keyhole limpet hemocyanin (KLH). Since plant virus-derived vaccines have the potential for cost-effective manufacture and are not known to replicate in mammalian cells, they represent a viable alternative to current replicating vaccine vectors for development of both human and veterinary vaccines.

Active immunization against gonadotrophin-releasing hormone in Chinese male pigs

We have investigated, under the normal conditions of local Chinese pig farming, castration of young male pigs by vaccination with a newly developed vaccine against gonadotrophin releasing hormone (GnRH). Because of the very early onset of puberty, long fattening period and relatively harsh circumstances in Chinese pig production, an investigation of the endocrine response of Chinese breeds to this type of vaccination was of particular interest. Fifteen crossbred boars (Yorkshire x Yanan) from three different litters were randomly assigned to three groups of five animals each. The first group was immunized at 13 weeks of age with a GnRH tandem dimer OVA-conjugate in Specol and received a booster immunization 8 weeks later. The second group was injected with Specol alone and served as untreated controls. The remaining group was surgically castrated at the time of weaning (at 6 weeks of age). Pigs were fed ad libitum from weaning onwards. All animals were slaughtered at 31 weeks of age. Immunized boars had undetectable or low serum testosterone (0.09 +/- 0.12 ng/ml), low fat androstenone (0.05 +/- 0.01 microg/g) levels and very low testes weights (19.1 +/- 4.3 g). Intact controls had much higher serum levels of testosterone (9.76 +/- 4.81 ng/ml), fat androstenone levels (2.26 +/- 0.87 microg/g) and testes weights (114.3 +/- 29.41 g) at slaughter. Both the immunized and castrated group grew significantly faster than intact boars (p < 0.01). Average daily gains in immunized, castrated and intact animals were 0.69 +/- 0.08, 0.63 +/- 0.05 and 0.42 +/- 0.07 kg (mean +/- SD), respectively. The present data demonstrate for the first time that the newly developed anti-GnRH vaccine works very well under practical Chinese pig farming conditions, and can be an attractive alternative to surgical castration.

Characterisation of a protective linear B cell epitope against feline parvoviruses

Monoclonal antibody 3C9 was the starting material in the definition of the epitope that led to the synthesis of the first efficient peptide vaccine against a viral disease (canine parvovirus) in the natural host (dog). In this report, we have analysed the specificity of the antibody at the single amino acid level and the contribution of each residue to the binding, using multiple length analysis. Moreover, a replacement analysis allowed determining those critical residues for the binding. Finally, in an attempt to optimise the production cost of the vaccine, we have determined that the minimal dose required for induction of protective antibodies can be as low as 0.5 microg of peptide. Also, KLH can be replaced as a carrier for a much cheaper alternative such as ovalbumine. All these findings implicate a substantial reduction in the cost of the vaccinal dose.

Peptide transport by the multidrug resistance protein MRP1

Small hydrophobic peptides were studied as possible substrates of the multidrug resistance protein (MRP)-1 (ABCC1) transmembrane transporter molecule. As observed earlier for P-glycoprotein- (Pgp; ABCB1) overexpressing cells, MRP1-overexpressing cells, including cells stably transfected with the MRP1 cDNA, showed distinct resistance to the cytotoxic peptide N-acetyl-Leu-Leu-norleucinal (ALLN). Resistance to this peptide and another toxic peptide derivative, which is based on a Thr-His-Thr-Nle-Glu-Gly backbone conjugated to butyl and benzyl groups (4A6), could be reversed by MRP1 inhibitors. The reduced toxicity of 4A6 in MRP1-overexpressing cells was found to be associated with lower accumulation of a fluorescein-labeled derivative of this peptide. Glutathione (GSH) depletion had a clear effect on resistance to ALLN but hardly affected 4A6 resistance. In a limited structure-activity study using peptides that are analogous to 4A6, MRP1-overexpressing cells were found to be resistant to these peptides as well. Remarkably, when selecting A2780 ovarian cancer cells for resistance to ALLN, even in the absence of Pgp blockers, resulting cell lines had up-regulated MRP1, rather than any of the other currently known multidrug resistance transporter molecules including Pgp, MRP2 (ABCC2), MRP3 (ABCC3), MRP5 (ABCCS), and the breast cancer resistance protein ABCG2. ALLN-resistant, MRP1-overexpressing cells were found to be cross-resistant to 4A6 and the classical multidrug resistance drugs doxorubicin, vincristine, and etoposide. This establishes MRP1 as a transporter for small hydrophobic peptides. More extensive structure-activity relationship studies should allow the identification of clinically useful peptide antagonists of MRP1.

Enzyme-linked immunosorbent assay using a virus type-specific peptide based on a subdomain of envelope protein E(rns) for serologic diagnosis of pestivirus infections in swine

Peptides deduced from the C-terminal end (residues 191 to 227) of pestivirus envelope protein E(rns) were used to develop enzyme-linked immunosorbent assays (ELISAs) to measure specifically antibodies against different types of pestiviruses. The choice of the peptide was based on the modular structure of the E(rns) protein, and the peptide was selected for its probable independent folding and good exposure, which would make it a good candidate for an antigenic peptide to be used in a diagnostic test. A solid-phase peptide ELISA which was cross-reactive for several types of pestivirus antibodies and which can be used for the general detection of pestivirus antibodies was developed. To identify type-specific pestivirus antibodies, a liquid-phase peptide ELISA, with a labeled, specific classical swine fever virus (CSFV) peptide and an unlabeled bovine viral diarrhea virus peptide to block cross-reactivity, was developed. Specificity and sensitivity of the liquid-phase peptide ELISA for CSFV were 98 and 100%, respectively. Because the peptide is a fragment of the E(rns) protein, it can be used to differentiate between infected and vaccinated animals when a vaccine based on the E2 protein, which is another pestivirus envelope protein, is used.

Mimotopes: realization of an unlikely concept

Theoretically it seems highly unlikely that relatively small peptides could mimic functionally discontinuous epitopes of antigens. Nevertheless various recent reports show this to be the case. Peptide mimics of protein-, polysaccharide- and DNA-epitopes have been shown to be able to replace the native epitope. Moreover, some of them are able to induce, when used in a vaccine, antibodies with the same activity as that of the antibody used as a template. These mimics, called mimotopes, can be used in vaccines and diagnostics and can be developed more or less systematically using solely antibodies and random, semi-random and dedicated peptide arrays or libraries. Furthermore, the mimotope concept which seems to have proven itself for antibody and antigen interaction can be applied equally well to many receptor ligand interactions and thus may form a new generic approach to the development of drugs. Ltd.

Epitopes on glycoprotein E and on the glycoprotein E/glycoprotein I complex of bovine herpesvirus 1 are expressed by all of 222 isolates and 11 vaccine strains

Glycoprotein E (gE) of bovine herpesvirus 1 (BHV1) forms a complex with glycoprotein I (gI) and plays an important role in cell-to-cell spread mechanisms of the virus, but is not essential for propagation of the virus. To study the antigenic variability of BHV1 glycoprotein E, a set of six well characterised monoclonal antibodies (MAbs) was established using BHV1 gE and gI deletion mutants, eukaryotically expressed gE and gI and pepscan analysis. Two of these MAbs reacted with a linear gE epitope (MAbs 3 and 52), two reacted with a more conformation dependent gE epitope (MAbs 61 and 81) and two reacted with epitopes formed by a complex formed between gE and glycoprotein I (MAbs 67 and 75). With these six MAbs the gE expression of 222 BHV1 isolates and 11 BHV1 modified-live vaccine strains was studied in vitro, using an immunoperoxidase monolayer assay. All 222 BHV1 isolates and 11 vaccine strains were found to react with MAbs 61, 81 and 75. Three of the 222 isolates failed to react with MAb 67 and two of the vaccines reacted very weakly with MAbs 3 and 52. Analysis of the gE genes of these five aberrant isolates and the gE glycoproteins they expressed, did not show obvious size differences compared to wild-type BHV1. We conclude that the tested gE epitopes are highly conserved, including the epitopes formed by the gI/gE complex.

Applicability of three anti-PrP peptide sera including staining of tonsils and brainstem of sheep with scrapie

Three rabbit antibodies (R521, R505, R524) were produced, and raised to synthetic peptides corresponding to residues 94-105, 100-111, and 223-234, respectively, of the sheep prion protein (PrP). Epitope mapping analysis revealed the monospecific character of antisera R505 and R524. In addition to the amino acid sequence against which it was raised, R521 also recognized other small epitopes. ELISA and radio-immunoprecipitation were used to assess the relative immunoreactivities of the antisera to the normal sheep prion protein (PrP(c)). Highest reactivity was found for R521, followed by R505 and R524. According to Western blot analysis, all three sera specifically reacted with the prion proteins PrP(Sc) and PrP27-30, extracted from the brain stem of a scrapie-affected sheep. Yet, with R505 not all of the lower molecular weight deglycosylated forms could be detected. Contrary to the immunoreactivities found with the PrP(Sc) and PrP27-30 isoforms, only R521 recognised PrP(c) from a healthy sheep. The usefulness of all three anti-peptide sera in the immunohistochemical detection of PrP(Sc) in brain stem and tonsils of scrapie-affected sheep was demonstrated and compared with an established rabbit anti-PrP serum.

Extending the CD4(+) T-cell epitope specificity of the Th1 immune response to an antigen using a Salmonella enterica serovar typhimurium delivery vehicle

We analyzed the CD4 T-cell immunodominance of the response to a model antigen (Ag), MalE, when delivered by an attenuated strain of Salmonella enterica serovar Typhimurium (SL3261*pMalE). Compared to purified MalE Ag administered with adjuvant, the mapping of the peptide-specific proliferative responses showed qualitative differences when we used the Salmonella vehicle. We observed the disappearance of one out of eight MalE peptides' T-cell reactivity upon SL3261*pMalE immunization, but this phenomenon was probably due to a low level of T-cell priming, since it could be overcome by further immunization. The most striking effect of SL3261*pMalE administration was the activation and stimulation of new MalE peptide-specific T-cell responses that were silent after administration of purified Ag with adjuvant. Ag presentation assays performed with MalE-specific T-cell hybridomas showed that infection of Ag-presenting cells by this intracellular attenuated bacterium did not affect the processing and presentation of the different MalE peptides by major histocompatibility complex (MHC) class II molecules and therefore did not account for immunodominance modulation. Thus, immunodominance of the T-cell response to microorganisms is governed not only by the frequency of the available T-cell repertoire or the processing steps in Ag-presenting cells that lead to MHC presentation but also by other parameters probably related to the infectious process and to the bacterial products. Our results indicate that, upon infection by a microorganism, the specificity of the T-cell response induced against its Ags can be much more effective than with purified Ags and that it cannot completely be mimicked by purified Ags administered with adjuvant.

Cross-reactive epitopes and HLA-restriction elements in human T cell recognition of the Mycobacterium leprae 18-kD heat shock protein

We have previously demonstrated that the Mycobacterium leprae 18-kD heat shock protein (HSP18) is represented among the antigenic targets of human T cell responses induced by M. leprae immunization and that the peptide 38-50 serves as an immunodominant epitope recognized by CD4+ T cell clones. By using peripheral blood mononuclear cells and T cell lines from the same donor group, we have in this study shown that the M. leprae HSP18 and peptide 38-50 were recognized by memory T cells 8 years after immunization with M. leprae. The finding that M. bovis BCG-induced T cell lines responded to M. leprae HSP18, but not to the peptide 38-50, suggested the existence of additional T cell epitopes of a cross-reactive nature. Consistent with this, testing of the T cell lines for proliferative responses to the complete HSP18 molecule, truncated HSP18 (amino acid (aa) residues 38-148) and overlapping synthetic peptides, made it possible to identify two cross-reactive epitope regions defined by aa residues 1-38 and 41-55. While peptide 38-50-reactive T cell clones showed limited cross-reactivity by responding to M. leprae, M. avium and M. scrofulaceum, the T cell lines specific to the epitopes 1-38 and 41-55 were broadly cross-reactive, as demonstrated by their response to M. leprae, M. tuberculosis complex, M. avium and other mycobacteria. MHC restriction analysis of the HSP18-responding T cell lines showed that the epitopes 1-38 and 38-50 were presented by one of the two HLA-DR molecules expressed from self HLA-DRB1 genes, whereas the epitope 41-55 was recognized in the presence of autologous as well as HLA-DR and HLA-DQ mismatched allogeneic antigen-presenting cells. The results obtained in this study made it possible to identify cross-reactive T cell epitopes of the M. leprae HSP18, and provide an explanation for T cell recognition of this antigen in individuals infected with species of the M. tuberculosis complex or environmental mycobacteria.

The Mr 193,000 vault protein is up-regulated in multidrug-resistant cancer cell lines

Vaults are 13 megadalton ribonucleoprotein particles composed largely of the major vault protein (MVP) and two high molecular weight proteins, p240 and p193, and a small vault RNA (vRNA). Increased levels of MVP expression, vault-associated vRNA, and vaults have been linked directly to multidrug resistance (MDR). To further define the putative role of vaults in MDR, we produced monoclonal antibodies against the Mr 193,000 vault protein and studied its expression levels in various multidrug-resistant cell lines. We find that, like MVP, p193 mRNA and protein levels are increased in various multidrug-resistant cell lines. Subcellular fractionation of vault particles revealed that vault-associated p193 levels are increased in multidrug-resistant cells as compared with the parental, drug-sensitive cells. Furthermore, protein analysis of postnuclear supernatants and co-immunoprecipitation studies show that drug-sensitive MVP-transfected tumor cells lack this up-regulation in vault-associated p193. Our observations indicate that vault formation is limited not only by the expression of the MVP but also by the expression or assembly of at least one of the other vault proteins.

Identification of promiscuous epitopes from the Mycobacterial 65-kilodalton heat shock protein recognized by human CD4(+) T cells of the Mycobacterium leprae memory repertoire

By using a synthetic peptide approach, we mapped epitopes from the mycobacterial 65-kDa heat shock protein (HSP65) recognized by human T cells belonging to the Mycobacterium leprae memory repertoire. A panel of HSP65 reactive CD4(+) T-cell lines and clones were established from healthy donors 8 years after immunization with heat-killed M. leprae and then tested for proliferative reactivity against overlapping peptides comprising both the M. leprae and Mycobacterium tuberculosis HSP65 sequences. The results showed that the antigen-specific T-cell lines and clones established responded to 12 mycobacterial HSP65 peptides, of which 9 peptides represented epitopes crossreactive between the M. tuberculosis and M. leprae HSP65 (amino acids [aa] 61 to 75, 141 to 155, 151 to 165, 331 to 345, 371 to 385, 411 to 425, 431 to 445, 441 to 455, and 501 to 515) and 3 peptides (aa 343 to 355, 417 to 429, and 522 to 534) represented M. leprae HSP65-specific epitopes. Major histocompatibility complex restriction analysis showed that presentation of 9 of the 12 peptides to T cells were restricted by one of the 2 HLA-DR molecules expressed from self HLA-DRB1 genes, whereas 3 peptides with sequences completely identical between the M. leprae and M. tuberculosis HSP65 were presented to T cells by multiple HLA-DR molecules: peptide (aa 61 to 75) was presented by HLA-DR1, -DR2, and -DR7, peptide (aa 141 to 155) was presented by HLA-DR2, -DR7, and -DR53, whereas both HLA-DR2 and -DR4 (Dw4 and Dw14) were able to present peptide (aa 501 to 515) to T cells. In addition, the T-cell lines responding to these peptides in proliferation assays showed cytotoxic activity against autologous monocytes/macrophages pulsed with the same HSP65 peptides. In conclusion, we demonstrated that promiscuous peptide epitopes from the mycobacterial HSP65 antigen can serve as targets for cytotoxic CD4(+) T cells which belong to the human memory T-cell repertoire against M. leprae. The results suggest that such epitopes might be used in the peptide-based design of subunit vaccines against mycobacterial diseases.

Naturally occurring mutations within 39 amino acids in the envelope glycoprotein of maedi-visna virus alter the neutralization phenotype

Infectious molecular clones have been isolated from two maedi-visna virus (MVV) strains, one of which (KV1772kv72/67) is an antigenic escape mutant of the other (LV1-1KS1). To map the type-specific neutralization epitope, we constructed viruses containing chimeric envelope genes by using KV1772kv72/67 as a backbone and replacing various parts of the envelope gene with equivalent sequences from LV1-1KS1. The neutralization phenotype was found to map to a region in the envelope gene containing two deletions and four amino acid changes within 39 amino acids (positions 559 to 597 of Env). Serum obtained from a lamb infected with a chimeric virus, VR1, containing only the 39 amino acids from LV1-1KS1 in the KV1772kv72/67 backbone neutralized LV1-1KS1 but not KV1772kv72/67. The region in the envelope gene that we had thus shown to be involved in escape from neutralization was cloned into pGEX-3X expression vectors, and the resulting fusion peptides from both molecular clones were tested in immunoblots for reactivity with the KV1772kv72/67 and VR1 type-specific antisera. The type-specific KV1772kv72/67 antiserum reacted only with the fusion peptide from KV1772kv72/67 and not with that from LV1-1KS1, and the type-specific VR1 antiserum reacted only with the fusion peptide from LV1-1KS1 and not with that from KV1772kv72/67. Pepscan analysis showed that the region contained two linear epitopes, one of which was specific to each of the molecularly cloned viruses. This linear epitope was not bound by all type-specific neutralizing antisera, however, which indicates that it is not by itself the neutralization epitope but may be a part of it. These findings show that mutations within amino acids 559 to 597 in the envelope gene of MVV virus result in escape from neutralization. Furthermore, the region contains one or more parts of a discontinuous neutralization epitope.

Characterization of melanocortin receptor ligands on cloned brain melanocortin receptors and on grooming behavior in the rat

Since the melanocortin MC3 and melanocortin MC4 receptors are the main melanocortin receptor subtypes expressed in rat brain, we characterized the activity and affinity of nine melanocortin receptor ligands using these receptors in vitro, as well as their activity in a well-defined melanocortin-induced behavior in the rat: grooming behavior. We report here that [D-Tyr4]melanotan-II and RMI-2001 (Ac-cyclo-[Cys4, Gly5, D-Phe7, Cys10]alpha-MSH-NH2) have significantly higher affinity and potency on the rat melanocortin MC4 receptor as compared to the rat melanocortin MC3 receptor. Nle-gamma-MSH (melanocyte-stimulating hormone) was the only ligand with higher affinity and potency on the rat melanocortin MC3 receptor. The potency order of melanocortin MC4 receptor agonists, but not that of melanocortin MC3 receptor agonists, fitted with the potency of these ligands to stimulate grooming behavior, when administered intracerebroventricularly. SHU9119 (Ac-cyclo-[Nle4, Asp5, D-Nal(2)7, Lys10]alpha-MSH-(4-10)-NH2) and RMI-2005 (Ac-cyclo-[Cys4, Gly5, D-Na](2)7, Nal(2)9, Cys10]alpha-MSH-(4-10)-NH2) were able to inhibit alpha-MSH-induced melanocortin receptor activity in vitro, as well as alpha-MSH-induced grooming behavior. Melanotan-II, [Nle4-D-Phe7]alpha-MSH and RMI-2001 were also effective in inducing grooming behavior when administered intravenously. In the absence of purely selective melanocortin MC(3/4) receptor ligands, we demonstrated that careful comparison of ligand potencies in vitro with ligand potencies in vivo, could identify which melanocortin receptor subtype mediated alpha-MSH-induced grooming behavior. Furthermore, blockade of novelty-induced grooming behavior by SHU9119 demonstrated that this physiological stress response is mediated via activation of the melanocortin system.

Conformation of the core sequence in melanocortin peptides directs selectivity for the melanocortin MC3 and MC4 receptors

Melanocortin peptides regulate a variety of physiological processes. Five melanocortin receptors (MC-R) have been cloned and the MC3R and MC4R are the main brain MC receptors. The aim of this study was to identify structural requirements in both ligand and receptor that determine gamma-melanocyte-stimulating hormone (MSH) selectivity for the MC3R versus the MC4R. Substitution of Asp10 in [Nle4]Lys-gamma2-MSH for Gly10 from [Nle4]alpha-MSH, increased both activity and affinity for the MC4R while the MC3R remained unaffected. Analysis of chimeric MC3R/MC4Rs and mutant MC4Rs showed that Tyr268 of the MC4R mainly determined the low affinity for [Nle4]Lys-gamma2-MSH. The data demonstrate that Asp10 determines selectivity for the MC3R, however, not through direct side chain interactions, but probably by influencing how the melanocortin core sequence is presented to the receptor-binding pocket. This is supported by mutagenesis of Tyr268 to Ile in the MC4R which increased affinity and activity for [Nle4]Lys-gamma2-MSH, but decreased affinity for two peptides with constrained cyclic structure of the melanocortin core sequence, MT-II and [D-Tyr4]MT-II, that also displayed lower affinity for the MC3R. This study provides a general concept for peptide receptor selectivity, in which the major determinant for a selective receptor interaction is the conformational presentation of the core sequence in related peptides to the receptor-binding pocket.