Efficacy, but not antibody titer or affinity, of a heroin hapten conjugate vaccine correlates with increasing hapten densities on tetanus toxoid, but not on CRM197 carriers.

Vaccines against drugs of abuse have induced antibodies in animals that blocked the biological effects of the drug by sequestering the drug in the blood and preventing it from crossing the blood-brain barrier. Drugs of abuse are too small to induce antibodies and, therefore, require conjugation of drug hapten analogs to a carrier protein. The efficacy of these conjugate vaccines depends on several factors including hapten design, coupling strategy, hapten density, carrier protein selection, and vaccine adjuvant. Previously, we have shown that 1 (MorHap), a heroin/morphine hapten, conjugated to tetanus toxoid (TT) and mixed with liposomes containing monophosphoryl lipid A [L(MPLA)] as adjuvant, partially blocked the antinociceptive effects of heroin in mice. Herein, we extended those findings, demonstrating greatly improved vaccine induced antinociceptive effects up to 3% mean maximal potential effect (%MPE). This was obtained by evaluating the effects of vaccine efficacy of hapten 1 vaccine conjugates with varying hapten densities using two different commonly used carrier proteins, TT and cross-reactive material 197 (CRM197). Immunization of mice with these conjugates mixed with L(MPLA) induced very high anti-1 IgG peak levels of 400-1500 µg/mL that bound to both heroin and its metabolites, 6-acetylmorphine and morphine. Except for the lowest hapten density for each carrier, the antibody titers and affinity were independent of hapten density. The TT carrier based vaccines induced long-lived inhibition of heroin-induced antinociception that correlated with increasing hapten density. The best formulation contained TT with the highest hapten density of ≥30 haptens/TT molecule and induced %MPE of approximately 3% after heroin challenge. In contrast, the best formulation using CRM197 was with intermediate 1 densities (10-15 haptens/CRM197 molecule), but the %MPE was approximately 13%. In addition, the chemical synthesis of 1, the optimization of the conjugation method, and the methods for the accurate quantification of hapten density are described.

Oligoclonal antibody targeting ghrelin increases energy expenditure and reduces food intake in fasted mice.

Ghrelin, an enteric peptide hormone linked to the pathophysiology of obesity has been a therapeutic target of great interest over the past decade. Many research efforts have focused on the antagonism of ghrelin's endogenous receptor GHSR1a, which is found along ascending vagal afferent fibers, as well as in the arcuate nucleus of the hypothalamus. Additionally, peptidic inhibitors of ghrelin O-acyltransferase, the enzyme responsible for the paracrine activation of ghrelin, have recently been studied. Our research has taken an alternative immunological approach, studying both active and passive vaccination as a means to sequester ghrelin in the periphery, with the original discovery in rat of decreased feed efficiency and adiposity, as well as increased metabolic activity. Using our previous hapten designs as a stepping-stone, three monoclonal antibodies (JG2, JG3, and JG4) were procured against ghrelin and tested in vivo. While mAb JG4 had the highest affinity for ghrelin, it failed to attenuate the orexigenic effects of food deprivation on energy metabolism or food intake in mice. However, animals that were administered a combination of JG3:JG4 (termed a doublet) or JG2:JG3:JG4 (termed a triplet) demonstrated higher heat dispersion and rate of respiration (higher CO(2) emission and O(2) consumption) during a 24 h fast refeed. Mice administered the triplet cocktail of JG2:JG3:JG4 also demonstrated decreased food intake upon refeeding as compared to control animals. Recently, Lu and colleagues reported that a passive approach using a single, high affinity N-terminally directed monoclonal antibody did not abrogate the effects of endogenous ghrelin. Our current report corroborates this finding, yet, refutes that a monoclonal antibody approach cannot be efficacious. Rather, we find that a multiple monoclonal antibody (oligoclonal) approach can reproduce the underlying logic to previously reported efficacies using active vaccinations.

Impact of distinct chemical structures for the development of a methamphetamine vaccine.

(+)-Methamphetamine (METH) use and addiction has grown at alarming rates over the past two decades, while no approved pharmacotherapy exists for its treatment. Immunopharmacotherapy has the potential to offer relief through producing highly specific antibodies that prevent drug penetration across the blood-brain barrier thus decreasing reinforcement of the behavior. Current immunotherapy efforts against methamphetamine have focused on a single hapten structure, namely linker attachment at the aromatic ring of the METH molecule. Hapten design is largely responsible for immune recognition, as it affects presentation of the target antigen and thus the quality of the response. In the current paper we report the systematic generation of a series of haptens designed to target the most stable conformations of methamphetamine as determined by molecular modeling. On the basis of our previous studies with nicotine, we show that introduction of strategic molecular constraint is able to maximize immune recognition of the target structure as evidenced by higher antibody affinity. Vaccination of GIX(+) mice with six unique METH immunoconjugates resulted in high antibody titers for three particularly promising formulations (45-108 µg/mL, after the second immunization) and high affinity (82, 130, and 169 nM for MH2, MH6, and MH7 hapten-based vaccines, respectively). These findings represent a unique approach to the design of new vaccines against methamphetamine abuse.

Cyclic lactam hybrid α-MSH/Agouti-related protein (AGRP) analogues with nanomolar range binding affinities at the human melanocortin receptors.

A novel hybrid melanocortin pharmacophore was designed based on the topographical similarities between the pharmacophores of Agouti related protein (AGRP) an endogenous melanocortin antagonist, and α-melanocyte-stimulating hormone (α-MSH), an endogenous melanocortin agonist. When employed in two different 23-membered macrocyclic lactam peptide templates, the designed hybrid AGRP/MSH pharmacophore yielded non-competitive ligands with nanomolar range binding affinities. The topography-based pharmacophore hybridization strategy will prove useful in development of unique non-competitive melanocortin receptor modulators.

Synthesis of 'clickable' acylhomoserine lactone quorum sensing probes: unanticipated effects on mammalian cell activation.

Alkynyl- and azido-tagged 3-oxo-C(12)-acylhomoserine lactone probes have been synthesized to examine their potential utility as probes for discovering the mammalian protein target of the Pseudomonas aeruginosa autoinducer, 3-oxo-C(12)-acylhomoserine lactone. Although such substitutions are commonly believed to be quite conservative, from these studies, we have uncovered a drastic difference in activity between the alkynyl- and azido-modified compounds, and provide an example where such structural modification has proved to be much less than conservative.

Catalytic antibody degradation of ghrelin increases whole-body metabolic rate and reduces refeeding in fasting mice.

Obesity is a chronic, costly, and globally prevalent condition, with excess caloric intake a suspected etiologic factor. Nonsurgical treatments are modestly efficacious, and weight loss maintenance is hampered by anti-famine homeostatic mechanisms. Ghrelin, a gastric hormone linked to meal initiation, energy expenditure, and fuel partitioning, is hypothesized to facilitate weight gain and impede weight loss. Unique among known animal peptides, the serine-3 residue of ghrelin is posttranslationally acylated with an n-octanoic acid, a modification important for the peptide's active blood-brain transport and growth hormone secretagogue receptor-1 agonist activity. Pharmacological degradation of ghrelin would be hypothesized to reduce ghrelin's biological effects. To study endogenous ghrelin's role in appetite and energy expenditure, we generated antibodies that hydrolyze the octanoyl moiety of ghrelin to form des-acyl ghrelin. The most proficient antibody catalyst, GHR-11E11, was found to display a second-order rate constant of 18 M(-1) x s(-1) for the hydrolysis of ghrelin to des-acyl ghrelin. I.v. administration of GHR-11E11 (50 mg/kg) maintained a greater metabolic rate in fasting C57BL/6J mice as compared with mice receiving a control antibody and suppressed 6-h refeeding after 24 h of food deprivation. Indirect respiratory measures of metabolism after refeeding and relative fuel substrate utilization were unaffected. The results support the hypothesis that acylated ghrelin stimulates appetite and curbs energy expenditure during deficient energy intake, whereas des-acyl ghrelin does not potently share these functions. Catalytic anti-ghrelin antibodies might thereby adjunctively aid consolidation of caloric restriction-induced weight loss and might also be therapeutically relevant to Prader-Willi syndrome, characterized after infancy by hyperghrelinemia, hyperphagia, and obesity.

Structure-activity relationships of cyclic lactam analogues of alpha-melanocyte-stimulating hormone (alpha-MSH) targeting the human melanocortin-3 receptor.

A variety of dicarboxylic acid linkers introduced between the alpha-amino group of Pro(6) and the -amino group of Lys(10) of the cyclic lactam alpha-melanocyte-stimulating hormone (alpha-MSH)-derived Pro(6)-D-Phe(7)/D-Nal(2')(7)-Arg(8)-Trp(9)-Lys(10)-NH2 pentapeptide template lead to nanomolar range and selective hMC3R agonists and antagonists. Replacement of the Pro(6) residue and the dicarboxylic acid linker with 2,3-pyrazine-dicarboxylic acid furnished a highly selective nanomolar range hMC3R partial agonist (analogue 12, c[CO-2,3-pyrazine-CO-D-Phe-Arg-Trp-Lys]-NH2, EC50 = 27 nM, 70% max cAMP) and an hMC3R antagonist (analogue 13, c[CO-2,3-pyrazine-CO-D-Nal(2')-Arg-Trp-Lys]-NH2, IC50 = 23 nM). Modeling experiments suggest that 2,3-pyrazinedicarboxylic acid stabilizes a beta-turn-like structure with the D-Phe/D-Nal(2') residues, which explains the high potency of the corresponding peptides. Placement of a Nle residue in position 6 produced a hMC3R/hMC5R antagonist (analogue 15, c[CO-(CH 2)2-CO-Nle-D-Nal(2')-Arg-Trp-Lys]-NH2, IC50 = 12 and 17 nM, respectively), similarly to the previously described cyclic gamma-melanocyte-stimulating hormone (gamma-MSH)-derived hMC3R/hMC5R antagonists. These newly developed melanotropins will serve as critical biochemical tools for elucidating the full spectrum of functions performed by the physiologically important melanocortin-3 receptor.

Development of cyclic gamma-MSH analogues with selective hMC3R agonist and hMC3R/hMC5R antagonist activities.

A series of cyclic lactam analogues of gamma-MSH (H-Tyr1-Val2-Met3-Gly4-His5-Phe6-Arg7-Trp8-Asp9-Arg10-Phe11-Gly12-OH) with a bulky hydrophobic residue in the direct proximity to the pharmacophore (Xaa-D-Phe/D-Nal(2')-Arg-Trp) were designed and synthesized by solid-phase methods. A variety of amino acids with a broad range of hydrophobic/hydrophilic properties was introduced in position 5 to further explore their complementary role in receptor selectivity. Biological evaluation of these peptides revealed several analogues with potent hMC3R agonist and hMC3R/hMC5R antagonist activities, and good receptor selectivity. Analogue 4, c[Nle-Arg-D-Phe-Arg-Trp-Glu]-NH2, was found to be a very potent and selective hMC3R agonist (EC50=1.2 nM, 112% act). In addition, analogue 13, c[Nle-Val-D-Nal(2')-Arg-Trp-Glu]-NH2, was identified as an hMC3R/hMC5R antagonist with the best selectivity against the hMC4R in this series (pA2(hMC3R)=8.4; pA2(hMC5R)=8.7). These results indicate the significance of steric factors in melanocortin receptor selectivity and suggest that introduction of bulky residues in the direct proximity to the melanocortin pharmacophore is an effective approach to design of novel hMC3R and hMC5R selective ligands.

Structure-activity studies of new melanocortin peptides containing an aromatic amino acid at the N-terminal position.

Cyclic melanotropin peptides, designed with an aromatic amino acid substitution at the N-terminal position of the MT-II-type scaffold, were prepared by solid-phase peptide synthesis and evaluated for their ability to bind to and activate human melanocortin-1, -3, -4, and -5 receptors. The structure-activity studies of these MT-II analogues have identified a selective antagonist at the hMC4R (H-Phe-c[Asp-Pro-d-Nal(2')-Arg-Trp-Gly-Lys]-NH(2), pA(2)=8.7), a selective partial agonist at the hMC4R (H-d-Nal(2')-c[Asp-Pro-d-Phe-Arg-Trp-Gly-Lys]-NH(2), IC(50)=11nM, EC(50)=56nM), and a selective partial agonist at the hMC3R (H-d-Phe-c[Asp-Pro-d-Phe-Arg-Trp-Lys]-NH(2), IC(50)=3.7nM, EC(50)=4.9nM). Aromatic amino acid substitution at the N-terminus in conjuction with the expansion of the 23-membered cyclic lactam MT-II scaffold to a 26-membered scaffold by addition of a Gly residue in position 10 leads to melanotropin peptides with enhanced receptor selectivity.

Novel 3D pharmacophore of alpha-MSH/gamma-MSH hybrids leads to selective human MC1R and MC3R analogues.

To further evaluate elements that could contribute to the 3D topographical structure of gamma-MSH, we have systematically designed a group of linear gamma-MSH analogues and evaluated their biological activities: without a N-terminal acetyl, with and without a C-terminal amide, with Nle(3), with l- or d-Phe(6) or d-Nal(2')(6), and with d-Trp(8) or d-Nal(2')(8). It was found that changing the C-terminal acid in gamma-MSH to an amide and replacing Met with Nle leads to increased binding affinities at all four subtypes of melanocortin receptors (10-100 fold). Substitution of Trp(8) with d-Nal(2')(8) and Phe(6) with d-Phe(6) in gamma-MSH-NH(2) forms a selective antagonist for the hMC3R, whereas, substitution of Phe(6) with d-Nal(2')(6) and replacing Trp(8) with d-Trp(8) at gamma-MSH-NH(2) yields a selective partial agonist for the hMC1R. Finally, substitution of His(5) with Pro(5) and Trp(8) with d-Nal(2')(8) in gamma-MSH-NH(2) leads to a highly potent and selective agonist for the hMC1R. Molecular modeling showed that, at the C-terminal of Nle(3)-gamma-MSH-NH(2), there is a reverse-turn-like structure, suggesting that there might be a secondary binding site involved in ligand-receptor interaction for gamma-MSH analogues that may explain the enhanced binding affinities of the Nle(3)-gamma-MSH-NH(2) analogues. Our results indicate that increasing the hydrophobicity and replacing Phe(6) and Trp(8) with bulkier aromatic amino acid residues is very important for selectivity of alpha-MSH/gamma-MSH hybrids for hMCRs.

Design of novel melanotropin agonists and antagonists with high potency and selectivity for human melanocortin receptors.

alpha-MSH and gamma-MSH are the natural endogenous hormones for the human melanocortin-1, 3, 4 and 5 receptors (hMC1R, hMC3R, hMC4R and hMC5R). These and more potent, stable and prolonged acting analogues such as NDP-alpha-MSH, MT-II and SHU-9119 are not very receptor selective. To develop potent and selective agonist and antagonist ligands for the melanocortin receptors we have used state-of-the-art biophysical studies, computational chemistry, and design of conformational and topographical constraints with novel templates.

Thalidomide metabolites and analogues. 3. Synthesis and antiangiogenic activity of the teratogenic and TNFalpha-modulatory thalidomide analogue 2-(2,6-dioxopiperidine-3-yl)phthalimidine.

Versatile synthesis of the teratogenic, TNFalpha-modulatory, and antiangiogenic thalidomide analogue 2-(2,6-dioxopiperidine-3-yl)phthalimidine (1) and its direct antiangiogenic properties are described. With thalidomide or thalidomide derivatives as precursors, the synthesis involved either carbonyl reduction/thiation-desulfurization or carbonyl reduction/acyliminium ion reduction protocols. Compared to earlier studies with thalidomide, which was only active with microsomal treatment, 1 exhibited marginal inhibitory activity in the rat aortic ring assay, thereby demonstrating the requirement for metabolic activation.

Facial recognition of heroin vaccine opiates: type 1 cross-reactivities of antibodies induced by hydrolytically stable haptenic surrogates of heroin, 6-acetylmorphine, and morphine.

Novel synthetic compounds similar to heroin and its major active metabolites, 6-acetylmorphine and morphine, were examined as potential surrogate haptens for the ability to interface with the immune system for a heroin vaccine. Recent studies have suggested that heroin-like haptens must degrade hydrolytically to induce independent immune responses both to heroin and to the metabolites, resulting in antisera containing mixtures of antibodies (type 2 cross-reactivity). To test this concept, two unique hydrolytically stable haptens were created based on presumed structural facial similarities to heroin or to its active metabolites. After conjugation of a heroin-like hapten (DiAmHap) to tetanus toxoid and mixing with liposomes containing monophosphoryl lipid A, high titers of antibodies after two injections in mice had complementary binding sites that exhibited strong type 1 ("true") specific cross-reactivity with heroin and with both of its physiologically active metabolites. Mice immunized with each surrogate hapten exhibited reduced antinociceptive effects caused by injection of heroin. This approach obviates the need to create hydrolytically unstable synthetic heroin-like compounds to induce independent immune responses to heroin and its active metabolites for vaccine development. Facial recognition of hydrolytically stable surrogate haptens by antibodies together with type 1 cross-reactivities with heroin and its metabolites can help to guide synthetic chemical strategies for efficient development of a heroin vaccine.

Liposomes containing monophosphoryl lipid A: a potent adjuvant system for inducing antibodies to heroin hapten analogs.

In order to create an effective immunization approach for a potential vaccine to heroin, liposomes containing monophosphoryl lipid A [L(MPLA)] were tested as an adjuvant system to induce antibodies to heroin hapten analogs. Four synthetic haptens and two immunization strategies were employed. In the first strategy, a hydrophobic 23 amino acid immunogenic peptide derived from the membrane proximal external region of gp41 from HIV-1 envelope protein was embedded as a carrier in the outer surface of L(MPLA), to which was conjugated a 15 amino acid universal T cell epitope and a terminal heroin hapten analog. In the second strategy, tetanus toxoid (TT) carrier protein was decorated with haptens by conjugation, and the hapten-conjugated protein was mixed with L(MPLA). After immunization of mice, each of the immunization strategies was effective for induction of IgG anti-hapten antibodies. The first immunization strategy induced a mean end-point IgG titer against one of two haptens tested of approximately 12,800; however, no detectable antibodies were induced against the liposome-associated HIV-1 carrier peptide. In the second immunization strategy, depending on the hapten used for decorating the TT, end-point IgG titers ranged from 100,000 to 6,500,000. In this strategy, in which hapten was conjugated to the TT, end-point IgG titers of 400,000 to the TT carrier were observed with each conjugate. However, upon mixing unconjugated TT with L(MPLA), anti-TT titers of 6,500,000 were observed. We conclude that L(MPLA) serves as a potent adjuvant for inducing antibodies to candidate heroin haptens. However, antibodies to the carrier peptide or protein were partly or completed inhibited by the presence of conjugated hapten.

Liposomes containing lipid A: an effective, safe, generic adjuvant system for synthetic vaccines.

Liposomes containing monophosphoryl lipid A (MPLA) have previously exhibited considerable potency and safety in human trials with a variety of candidate vaccines, including vaccines to malaria, HIV-1 and several different types of cancer. The long history of research and development of MPLA and liposomal MPLA as vaccine adjuvants reveals that there are numerous opportunities for creation and development of generic (nonproprietary) adjuvant system formulations with these materials that are not only highly potent and safe, but also readily available as native materials or as synthetic compounds. They are easily manufactured as potentially inexpensive and easy to use adjuvant systems and might be effective even with synthetic peptides as antigens.

Generation of quorum quenching antibodies.

The exchange of information within and among bacterial populations using small diffusible molecules has been termed "quorum sensing" (QS). Due to the extracellular distribution of the QS autoinducer molecules and the evolutionary highly conserved nature of signaling components, microbial QS systems represent an excellent target for anti-infective immunotherapy. Recently, we have described the generation of quorum quenching monoclonal antibodies (mAbs) against acyl homoserine lactones (AHL) used by Pseudomonas aeruginosa as well as Staphylococcal autoinducing peptides (AIP). These mAbs suppressed QS signaling in bacteria and neutralized AHL-mediated cytotoxic effects in vitro, as well as protected animals in Staphylococcus aureus infection models.

A vaccine strategy that induces protective immunity against heroin.

Heroin addiction is a wide-reaching problem with a spectrum of damaging social consequences. A vaccine capable of blocking heroin's effects could provide a long-lasting and sustainable adjunct to heroin addiction therapy. Heroin, however, presents a particularly challenging immunotherapeutic target, as it is metabolized to multiple psychoactive molecules. To reconcile this dilemma, we examined the idea of a singular vaccine with the potential to display multiple drug-like antigens; thus two haptens were synthesized, one heroin-like and another morphine-like in chemical structure. A key feature in this approach is that immunopresentation with the heroin-like hapten is thought to be immunochemically dynamic such that multiple haptens are simultaneously presented to the immune system. We demonstrate the significance of this approach through the extremely rapid generation of robust polyclonal antibody titers with remarkable specificity. Importantly, both the antinociceptive effects of heroin and acquisition of heroin self-administration were blocked in rats vaccinated using the heroin-like hapten.

Solid-phase peptide head-to-side chain cyclodimerization: discovery of C(2)-symmetric cyclic lactam hybrid α-melanocyte-stimulating hormone (MSH)/agouti-signaling protein (ASIP) analogues with potent activities at the human melanocortin receptors.

A novel hybrid melanocortin pharmacophore was designed based on the pharmacophores of the agouti-signaling protein (ASIP), an endogenous melanocortin antagonist, and α-melanocyte-stimulating hormone (α-MSH), an endogenous melanocortin agonist. The designed hybrid ASIP/MSH pharmacophore was explored in monomeric cyclic, and cyclodimeric templates. The monomeric cyclic disulfide series yielded peptides with hMC3R-selective non-competitive binding affinities. The direct on-resin peptide lactam cyclodimerization yielded nanomolar range (25-120 nM) hMC1R-selective full and partial agonists in the cyclodimeric lactam series which demonstrates an improvement over the previous attempts at hybridization of MSH and agouti protein sequences. The secondary structure-oriented pharmacophore hybridization strategy will prove useful in development of unique allosteric and orthosteric melanocortin receptor modulators. This report also illustrates the utility of peptide cyclodimerization for the development of novel GPCR peptide ligands.