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

Biologic Approaches to Treat Substance-Use Disorders

In contrast to traditional pharmacodynamic approaches to treat substance-use disorders (SUDs), the use of biologics (vaccines, monoclonal antibodies, and genetically modified enzymes) is based on a pharmacokinetic principle: reduce the amount of (and, ideally, eliminate) abused drug entering the central nervous system (CNS). Preclinical studies indicate that biologics are effective in both facilitating abstinence and preventing relapse to abused substances ranging from nicotine to heroin. While data are still emerging, the results from multiple clinical trials can best be described as mixed. Nonetheless, these clinical studies have already provided important insights using 'first-generation' tools that may inform the development of effective and commercially viable biologics to treat tobacco-, cocaine-, and methamphetamine-use disorders.

Animal Models and the Development of Vaccines to Treat Substance Use Disorders

The development of pharmacotherapies for substance use disorders (SUDs) is a high priority in addiction research. At present, there are no approved pharmacotherapies for cocaine and methamphetamine use disorders, while treatments for nicotine and opioid use are moderately effective. Indeed, many of these treatments can cause adverse drug side effects and have poor medication compliance, which often results in increased drug relapse rates. An alternative to these traditional pharmacological interventions is immunotherapy or vaccines that can target substances associated with SUDs. In this chapter, we discuss the current knowledge on the efficacy of preclinical vaccines, particularly immunogens that target methamphetamine, cocaine, nicotine, or opioids to attenuate drug-induced behaviors in animal models of SUDs. We also review vaccines (and antibodies) against cocaine, nicotine, and methamphetamine that have been assessed in human clinical trials. While preclinical studies indicate that several vaccines show promise, these findings have not necessarily translated to the clinical population. Thus, continued effort to design more effective vaccine immunogens using SUD animal models is necessary in order to support the use of immunotherapy as a viable option for individuals with SUDs.

Synthesis of Hapten-Protein Conjugate Vaccines with Reproducible Hapten Densities

The ability to prepare hapten-carrier conjugates reproducibly with consistent lot-to-lot hapten densities and protein yields is a critical component of hapten vaccine development. This entails the development of appropriate coupling chemistries that do not cause protein precipitation and the development of methods to quantify hapten density. Recently, extensive efforts have been devoted to design vaccines against drugs of abuse. We describe, herein, a method for conjugation of a morphine-like hapten (MorHap) to tetanus toxoid (TT), which involves conjugation of MorHap to the surface lysines of TT through the N-hydroxysuccinimide portion of a heterobifunctional linker and the subsequent attachment of the thiol on MorHap to the maleimide portion of the cross-linker. Methods are described for the analytical quantification of the hapten density of the conjugates using modified Ellman's test, trinitrobenzenesulfonic acid (TNBS) assay, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS).

A simple nonradioactive method for the determination of the binding affinities of antibodies induced by hapten bioconjugates for drugs of abuse

The accurate analytical measurement of binding affinities of polyclonal antibody in sera to heroin, 6-acetylmorphine (6-AM), and morphine has been a challenging task. A simple nonradioactive method that uses deuterium-labeled drug tracers and equilibrium dialysis (ED) combined with ultra performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) to measure the apparent dissociation constant (K d) of antibodies to 6-AM and morphine is described. The method can readily detect antibodies with K d in the low nanomolar range. Since heroin is rapidly degraded in sera, esterase inhibitors were included in the assay, greatly reducing heroin hydrolysis. MS/MS detection directly measured the heroin in the assay after overnight ED, thereby allowing the quantitation of % bound heroin in lieu of K d as an alternative measurement to assess heroin binding to polyclonal antibody sera. This is the first report that utilizes a solution-based assay to quantify heroin-antibody binding without being confounded by the presence of 6-AM and morphine and to measure K d of polyclonal antibody to 6-AM. Hapten surrogates 6-AcMorHap, 6-PrOxyHap, MorHap, DiAmHap, and DiPrOxyHap coupled to tetanus toxoid (TT) were used to generate high affinity antibodies to heroin, 6-AM, and morphine. In comparison to competition ED-UPLC/MS/MS which gave K d values in the nanomolar range, the commonly used competition enzyme-linked immunosorbent assay (ELISA) measured the 50% inhibition concentration (IC50) values in the micromolar range. Despite the differences in K d and IC50 values, similar trends in affinities of hapten antibodies to heroin, 6-AM, and morphine were observed by both methods. Competition ED-UPLC/MS/MS revealed that among the five TT-hapten bioconjugates, TT-6-AcMorHap and TT-6-PrOxyHap induced antibodies that bound heroin, 6-AM, and morphine. In contrast, TT-MorHap induced antibodies that poorly bound heroin, while TT-DiAmHap and TT-DiPrOxyHap induced antibodies either did not bind or poorly bound to heroin, 6-AM, and morphine. This simple and nonradioactive method can be extended to other platforms, such as oxycodone, cocaine, nicotine, and methamphetamine for the selection of the lead hapten design during substance abuse vaccine development.

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.

Lipid tucaresol as an adjuvant for methamphetamine vaccine development

The immunopotentiator tucaresol was modified for incorporation into liposomes, where it was found to be a superior adjuvant to MPLA for vaccination against methamphetamine.

Synthesis and immunological effects of heroin vaccines

Three haptens have been synthesized with linkers for attachment to carrier macromolecules at either the piperidino-nitrogen or via an introduced 3-amino group. Two of the haptens, with a 2-oxopropyl functionality at either C6, or at both the C3 and C6 positions on the 4,5-epoxymorphinan framework, as well as the third hapten (DiAmHap) with diamido moieties at both the C3 and C6 positions, should be much more stable in solution, or in vivo in a vaccine, than a hapten with an ester in one of those positions, as found in many heroin-based haptens. A "classical" opioid synthetic scheme enabled the formation of a 3-amino-4,5-epoxymorphinan which could not be obtained using palladium chemistry. Our vaccines are aimed at the reduction of the abuse of heroin and, as well, at the reduction of the effects of its predominant metabolites, 6-acetylmorphine and morphine. One of the haptens, DiAmHap, has given interesting results in a heroin vaccine and is clearly more suited for the purpose than the other two haptens.

Characterization and optimization of heroin hapten-BSA conjugates: method development for the synthesis of reproducible hapten-based vaccines

A potential new treatment for drug addiction is immunization with vaccines that induce antibodies that can abrogate the addictive effects of the drug of abuse. One of the challenges in the development of a vaccine against drugs of abuse is the availability of an optimum procedure that gives reproducible and high yielding hapten-protein conjugates. In this study, a heroin/morphine surrogate hapten (MorHap) was coupled to bovine serum albumin (BSA) using maleimide-thiol chemistry. MorHap-BSA conjugates with 3, 5, 10, 15, 22, 28, and 34 haptens were obtained using different linker and hapten ratios. Using this optimized procedure, MorHap-BSA conjugates were synthesized with highly reproducible results and in high yields. The number of haptens attached to BSA was compared by 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay, modified Ellman's test and matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Among the three methods, MALDI-TOF MS discriminated subtle differences in hapten density. The effect of hapten density on enzyme-linked immunosorbent assay (ELISA) performance was evaluated with seven MorHap-BSA conjugates of varying hapten densities, which were used as coating antigens. The highest antibody binding was obtained with MorHap-BSA conjugates containing 3-5 haptens. This is the first report that rigorously analyzes, optimizes and characterizes the conjugation of haptens to proteins that can be used for vaccines against drugs of abuse. The effect of hapten density on the ELISA detection of antibodies against haptens demonstrates the importance of careful characterization of the hapten density by the analytical techniques described.

Adjuvants for vaccines to drugs of abuse and addiction

Immunotherapeutic vaccines to drugs of abuse, including nicotine, cocaine, heroin, oxycodone, methamphetamine, and others are being developed. The theoretical basis of such vaccines is to induce antibodies that sequester the drug in the blood in the form of antibody-bound drug that cannot cross the blood brain barrier, thereby preventing psychoactive effects. Because the drugs are haptens a successful vaccine relies on development of appropriate hapten-protein carrier conjugates. However, because induction of high and prolonged levels of antibodies is required for an effective vaccine, and because injection of T-independent haptenic drugs of abuse does not induce memory recall responses, the role of adjuvants during immunization plays a critical role. As reviewed herein, preclinical studies often use strong adjuvants such as complete and incomplete Freund's adjuvant and others that cannot be, or in the case of many newer adjuvants, have never been, employed in humans. Balanced against this, the only adjuvant that has been included in candidate vaccines in human clinical trials to nicotine and cocaine has been aluminum hydroxide gel. While aluminum salts have been widely utilized worldwide in numerous licensed vaccines, the experience with human responses to aluminum salt-adjuvanted vaccines to haptenic drugs of abuse has suggested that the immune responses are too weak to allow development of a successful vaccine. What is needed is an adjuvant or combination of adjuvants that are safe, potent, widely available, easily manufactured, and cost-effective. Based on our review of the field we recommend the following adjuvant combinations either for research or for product development for human use: aluminum salt with adsorbed monophosphoryl lipid A (MPLA); liposomes containing MPLA [L(MPLA)]; L(MPLA) adsorbed to aluminum salt; oil-in-water emulsion; or oil-in-water emulsion containing MPLA.

Scientific overview: 2013 BBC plenary symposium on tobacco addiction

Nicotine dependence plays a critical role in addiction to tobacco products, and thus contributes to a variety of devastating tobacco-related diseases (SGR 2014). Annual costs associated with smoking in the US are estimated to be between $289 and $333 billion. Effective interventions for nicotine dependence, especially in smokers, are a critical barrier to the eradication of tobacco-related diseases. This overview highlights research presented at the Plenary Symposium of Behavior, Biology and Chemistry: Translational Research in Addiction Conference (BBC), hosted by the UT Health Science Center San Antonio, on March 9-10, 2013. The Plenary Symposium focused on tobacco addiction, and covered topics ranging from basic science to national policy. As in previous years, the meeting brought together globally-renowned scientists, graduate student recruits, and young scientists from underrepresented populations in Texas and other states with the goal of fostering interest in drug addiction research in young generations.

Effect of currently approved carriers and adjuvants on the pre-clinical efficacy of a conjugate vaccine against oxycodone in mice and rats

Vaccination against the highly abused prescription opioid oxycodone has shown pre-clinical efficacy for blocking oxycodone effects. The current study further evaluated a candidate vaccine composed of oxycodone derivatized at the C6 position (6OXY) conjugated to the native keyhole limpet hemocyanin (nKLH) carrier protein. To provide an oxycodone vaccine formulation suitable for human studies, we studied the effect of alternative carriers and adjuvants on the generation of oxycodone-specific serum antibody and B cell responses, and the effect of immunization on oxycodone distribution and oxycodone-induced antinociception in mice and rats. 6OXY conjugated to tetanus toxoid (TT) or a GMP grade KLH dimer (dKLH) was as effective as 6OXY conjugated to the nKLH decamer in mice and rats, while the 6OXY hapten conjugated to a TT-derived peptide was not effective in preventing oxycodone-induced antinociception in mice. Immunization with 6OXY-TT s.c. absorbed on alum adjuvant provided similar protection to 6OXY-TT administered i.p. with Freund's adjuvant in rats. The toll-like receptor 4 (TLR4) agonist monophosphoryl lipid A (MPLA) adjuvant, alone or in combination with alum, offered no advantage over alum alone for generating oxycodone-specific serum antibodies or 6OXY-specific antibody secreting B cells in mice vaccinated with 6OXY-nKLH or 6OXY-TT. The immunogenicity of oxycodone vaccines may be modulated by TLR4 signaling since responses to 6OXY-nKLH in alum were decreased in TLR4-deficient mice. These data suggest that TT, nKLH and dKLH carriers provide consistent 6OXY conjugate vaccine immunogenicity across species, strains and via different routes of administration, while adjuvant formulations may need to be tailored to individual immunogens or patient populations.

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.

New directions in nicotine vaccine design and use

Clinical trials of nicotine vaccines suggest that they can enhance smoking cessation rates but do not reliably produce the consistently high serum antibody concentrations required. A wide array of next-generation strategies are being evaluated to enhance vaccine efficacy or provide antibody through other mechanisms. Protein conjugate vaccines may be improved by modifications of hapten or linker design or by optimizing hapten density. Conjugating hapten to viruslike particles or disrupted virus may allow exploitation of naturally occurring viral features associated with high immunogenicity. Conjugates that utilize different linker positions on nicotine can function as independent immunogens, so that using them in combination generates higher antibody concentrations than can be produced by a single immunogen. Nanoparticle vaccines, consisting of hapten, T cell help peptides, and adjuvants attached to a liposome or synthetic scaffold, are in the early stages of development. Nanoparticle vaccines offer the possibility of obtaining precise and consistent control of vaccine component stoichiometry and spacing and immunogen size and shape. Passive transfer of nicotine-specific monoclonal antibodies offers a greater control of antibody dose, the ability to give very high doses, and an immediate onset of action but is expensive and has a shorter duration of action than vaccines. Viral vector-mediated transfer of genes for antibody production can elicit high levels of antibody expression in animals and may present an alternative to vaccination or passive immunization if the long-term safety of this approach is confirmed. Next-generation immunotherapies are likely to be substantially more effective than first-generation vaccines.