A vaccine strategy that induces protective immunity against heroin

Polymer-based vaccines for substance use disorders: Targeting ketamine and methamphetamine with protein-free hyperbranched polyethyleneimine carriers

Substance use disorders (SUDs) present a critical global health challenge, as current treatment options often prove insufficient, particularly for substances like ketamine and methamphetamine. In this study, we developed a novel immunotherapeutic strategy utilizing protein-free, polymer-based vaccines, with hyperbranched polyethylenimine (Hb-PEI) as a carrier to enhance immune specificity and remove the production of non-specific antibodies. Haptens for ketamine and methamphetamine were covalently conjugated to the Hb-PEI carrier, along with the Toll-like receptor (TLR) 7/8 agonist 1V209, to stimulate targeted humoral immune responses. Our results demonstrated that vaccines produced specific antibodies capable of effectively neutralizing ketamine- and methamphetamine-induced effects, such as conditioned place preference (CPP) and ketamine-induced analgesia. Notably, the immune response persisted for 95-112 days, demonstrating the vaccines' long-lasting efficacy. In contrast, no antibodies were generated when the adjuvant 1V209 was physically combined with the hapten, underscoring the importance of synergistic vaccine components. Additionally, the polymer-based approach exhibited excellent biocompatibility, without generating non-specific antibodies or causing adverse health effects. These findings highlight the potential of Hb-PEI-based vaccines as a promising platform for treating SUDs, offering a new pathway for clinical applications in combating drug addiction.

Opioid-Based Haptens: Development of Immunotherapy

Over the past decades, extensive preclinical research has been conducted to develop vaccinations to protect against substance use disorder caused by opioids, nicotine, cocaine, and designer drugs. Morphine or fentanyl derivatives are small molecules, and these compounds are not immunogenic, but when conjugated as haptens to a carrier protein will elicit the production of antibodies capable of reacting specifically with the unconjugated hapten or its parent compound. The position of the attachment in opioid haptens to the carrier protein will influence the specificity of the antiserum produced in immunized animals with the hapten-carrier conjugate. Immunoassays for the determination of opioid drugs are based on the ability of drugs to inhibit the reaction between drug-specific antibodies and the corresponding drug-carrier conjugate or the corresponding labelled hapten. Pharmacological studies of the hapten-carrier conjugates resulted in the development of vaccines for treating opioid use disorders (OUDs). Immunotherapy for opioid addiction includes the induction of anti-drug vaccines which are composed of a hapten, a carrier protein, and adjuvants. In this review we survey the design of opioid haptens, the development of the opioid radioimmunoassay, and the results of immunotherapy for OUDs.

A conjugate vaccine strategy that induces protective immunity against arecoline

Betel-quid chewing addiction is the leading cause of oral submucous fibrosis and oral cancer, resulting in significant socio-economic burdens. Vaccination may serve as a promising potential remedy to mitigate the abuse and combat accidental overdose of betel nut. Hapten design is the crucial factor to the development of arecoline vaccine that determines the efficacy of a candidate vaccine. Herein, we reported that two kinds of novel arecoline-based haptens were synthesized and conjugated to Bovine Serum Albumin (BSA) to generate immunogens, which generated antibodies with high affinity for arecoline but reduced binding for guvacoline and no affinity for arecaidine or guvacine. Notably, vaccination with Arec-N-BSA, which via the N-position on the tetrahydropyridine ring (tertiary amine group), led to a higher antibody affinity compared to Arec-CONH-BSA, blunted analgesia and attenuated hypothermia for arecoline.

Enhancing Protective Antibodies against Opioids through Antigen Display on Virus-like Particles

Opioid use disorder (OUD) has become a public health crisis, with recent significant increases in the number of deaths due to overdose. Vaccination can provide an attractive complementary strategy to combat OUD. A key for high vaccine efficacy is the induction of high levels of antibodies specific to the drug of abuse. Herein, a powerful immunogenic carrier, virus-like particle mutant bacteriophage Qβ (mQβ), has been investigated as a carrier of a small molecule hapten 6-AmHap mimicking heroin. The mQβ-6-AmHap conjugate was able to induce significantly higher levels of IgG antibodies against 6-AmHap than mice immunized with the corresponding tetanus toxoid-6-AmHap conjugate in head-to-head comparison studies in multiple strains of mice. The IgG antibody responses were persistent with high anti-6-AmHap titers 600 days after being immunized with mQβ-6-AmHap. The antibodies induced exhibited strong binding toward multiple heroin/morphine derivatives that have the potential to be abused, while binding weakly to medications used for OUD treatment and pain relief. Furthermore, vaccination effectively reduced the impacts of morphine on mice in both ambulation and antinociception assays, highlighting the translational potential of the mQβ-6-AmHap conjugate to mitigate the harmful effects of drugs of abuse.

Vaccines to Treat Substance Use Disorders: Current Status and Future Directions

Addiction, particularly in relation to psychostimulants and opioids, persists as a global health crisis with profound social and economic ramifications. Traditional interventions, including medications and behavioral therapies, often encounter limited success due to the chronic and relapsing nature of addictive disorders. Consequently, there is significant interest in the development of innovative therapeutics to counteract the effects of abused substances. In recent years, vaccines have emerged as a novel and promising strategy to tackle addiction. Anti-drug vaccines are designed to stimulate the immune system to produce antibodies that bind to addictive compounds, such as nicotine, cocaine, morphine, methamphetamine, and heroin. These antibodies effectively neutralize the target molecules, preventing them from reaching the brain and eliciting their rewarding effects. By obstructing the rewarding sensations associated with substance use, vaccines aim to reduce cravings and the motivation to engage in drug use. Although anti-drug vaccines hold significant potential, challenges remain in their development and implementation. The reversibility of vaccination and the potential for combining vaccines with other addiction treatments offer promise for improving addiction outcomes. This review provides an overview of anti-drug vaccines, their mechanisms of action, and their potential impact on treatment for substance use disorders. Furthermore, this review summarizes recent advancements in vaccine development for each specific drug, offering insights for the development of more effective and personalized treatments capable of addressing the distinct challenges posed by various abused substances.

Heroin metabolism in human blood and its impact for the design of an immunotherapeutic approach against heroin effects

Immunotherapeutic interventions that block drug effects by binding drug molecules to specific antibodies in the bloodstream have shown promising effects in animal studies. For heroin, which effects are mainly mediated by the metabolites 6-acetylmorphine (6-AM; also known as 6-monoacetylmorphine or 6-MAM) and morphine, the optimal antibody specificity has been discussed. In rodents, 6-AM specific antibodies have been recommended based on the rapid metabolism of heroin to 6-AM in the bloodstream. Since the metabolic rate of heroin in blood is unsettled in humans, we examined heroin metabolism with state-of-the-art analytical methodology (UHPLC-MS/MS) in freshly drawn human whole blood incubated with a wide range of heroin concentrations (1-500 μM). The half-life of heroin was highly concentration dependent, ranging from 1.2-1.7 min for concentrations at or above 25 μM, and gradually increasing to approximately 20 min for 1 μM heroin. At concentrations that can be attained in the bloodstream shortly after an i.v. injection, approximately 70% was transformed into 6-AM within 3 min, similar to previous observations in vivo. Our results indicate that blood enzymes play a more important role for the rapid metabolism of heroin in humans than previously assumed. This points to 6-AM as an important target for an efficient immunotherapeutic approach to block heroin effects in humans.

Development of an Effective Monoclonal Antibody against Heroin and Its Metabolites Reveals Therapies Have Mistargeted 6-Monoacetylmorphine and Morphine over Heroin

The opioid epidemic is a global public health crisis that has failed to abate with current pharmaceutical treatments. Moreover, these FDA-approved drugs possess numerous problems such as adverse side effects, short half-lives, abuse potential, and recidivism after discontinued use. An alternative treatment model for opioid use disorders is immunopharmacotherapy, where antibodies are produced to inhibit illicit substances by sequestering the drug in the periphery. Immunopharmacotherapeutics against heroin have engaged both active and passive vaccines targeting heroin's metabolites, 6-monoacetylmorphine (6-AM) and morphine, since decades of research have stated that heroin's psychoactive and lethal effects are mainly attributed to these compounds. However, concerted efforts to develop effective immunopharmacotherapies against heroin abuse have faced little clinical advancement, suggesting a need for reassessing drug target selection. To address this issue, four unique monoclonal antibodies were procured with distinct affinity to either heroin, 6-AM, or morphine. Examination of these antibodies through in vitro and in vivo tests revealed monoclonal antibody 11D12 as the optimal therapeutic and provided crucial insights into the key chemical species to target for blunting heroin's psychoactive and lethal effects. These findings offer clarification into the problematic attempts of therapeutics targeting heroin's metabolites and provide a path forward for future heroin immunopharmacotherapy development.

Immunotherapies for the Treatment of Drug Addiction

Substance use disorders (SUD) are a serious public health concern globally. Existing treatment platforms suffer from a lack of effectiveness. The development of immunotherapies against these substances of abuse for both prophylactic and therapeutic use has gained tremendous importance as an alternative and/or supplementary to existing therapies. Significant development has been made in this area over the last few decades. Herein, we highlight the vaccine and other biologics development strategies, preclinical, clinical updates along with challenges and future directions. Articles were searched in PubMed, ClinicalTrial.gov, and google electronic databases relevant to development, preclinical, clinical trials of nicotine, cocaine, methamphetamine, and opioid vaccines. Various new emerging vaccine development strategies for SUD were also identified through this search and discussed. A good number of vaccine candidates demonstrated promising results in preclinical and clinical phases and support the concept of developing a vaccine for SUD. However, there have been no ultimate success as yet, and there remain some challenges with a massive push to take more candidates to clinical trials for further evaluation to break the bottleneck.

A Rapid Method for Direct Quantification of Antibody Binding-Site Concentration in Serum

The quantitation of the available antibody binding-site concentration of polyclonal antibodies in serum is critical in defining the efficacy of vaccines against substances of abuse. We have conceptualized an equilibrium dialysis (ED)-based approach coupled with fluorimetry (ED-fluorimetry) to measure the antibody binding-site concentration to the ligand in an aqueous environment. The measured binding-site concentrations in monoclonal antibody (mAb) and sera samples from TT-6-AmHap-immunized rats by ED-fluorimetry are in agreement with those determined by a more established equilibrium dialysis coupled with ultraperformance liquid chromatography tandem mass spectrometry (ED-UPLC-MS/MS). Importantly, we have shown that the measured antibody binding-site concentrations to the ligand by ED-fluorimetry were not influenced by the sample serum matrix; thus, this method is valid for determining the binding-site concentration of polyclonal antibodies in sera samples. Further, we have demonstrated that under appropriate analytical conditions, this method resolved the total binding-site concentrations on a nanomolar scale with good accuracy and repeatability within the microliter sample volumes. This simple, rapid, and sample preparation-free approach has the potential to reliably perform quantitative antibody binding-site screening in serum and other more complex biological fluids.

Calix[n]arene-based immunogens: A new non-proteic strategy for anti-cocaine vaccine

Introduction

Cocaine use disorder is a significant public health issue without a current specific approved treatment. Among different approaches to this disorder, it is possible to highlight a promising immunologic strategy in which an immunogenic agent may reduce the reinforcing effects of the drug if they are able to yield sufficient specific antibodies capable to bind cocaine and/or its psychoactive metabolites before entering into the brain. Several carriers have been investigated in the anti-cocaine vaccine development; however, they generally present a very complex chemical structure, which potentially hampers the proper assessment of the coupling efficiency between the hapten units and the protein structure.

Objectives

The present study reports the design, synthesis and preclinical evaluation of two novel calix[n]arene-based anti-cocaine immunogens (herein named as V4N2 and V8N2) by the tethering of the hydrolysis-tolerant hapten GNE (15) on calix[4]arene and calix[8]arene moieties.

Methods

The preclinical assessment corresponded to the immunogenicity and dose-response evaluation of V4N2 and V8N2. The potential of the produced antibodies to reduce the passage of cocaine analogue through the blood-brain-barrier (BBB), modifying its biodistribution was also investigated.

Results

Both calix[n]arene-based immunogens elicited high titers of cocaine antibodies that modified the biodistribution of a cocaine radiolabeled analogue (99mTc-TRODAT-1) and decreased cocaine-induced behavior, according to an animal model.

Conclusion

The present results demonstrate the potential of V4N2 and V8N2 as immunogens for the treatment of cocaine use disorder.

Housing conditions and microbial environment do not affect the efficacy of vaccines for treatment of opioid use disorders in mice and rats

Vaccines offer a promising prophylactic and therapeutic intervention to counteract opioid use disorders (OUD) and fatal overdoses. Vaccines generate opioid-specific antibodies that bind the target opioid, reducing drug distribution to the brain and preventing drug-induced behavioral and pharmacological effects. Due to their selectivity, anti-opioid vaccines can be administered in combination with FDA-approved medications. Because patients with OUD or other substance use disorders may be affected by other multifactorial co-morbidities, such as infection or depression, it is important to test whether vaccine efficacy is modified by factors that may impact individual innate or adaptive immunity. To that end, this study tested whether housing conditions would affect the efficacy of two lead vaccine formulations targeting oxycodone and fentanyl in male mice and rats, and further analyzed whether differences in the gastrointestinal (GI) microbiome would be correlated with either vaccine efficacy or housing conditions. Results showed that housing mice and rats in either conventional (non-controlled) or specific pathogen-free (SPF, sterile barrier maintained) environment did not affect vaccine-induced antibody responses against oxycodone and fentanyl, nor their efficacy against oxycodone- and fentanyl-induced antinociception, respiratory depression, and bradycardia. Differences in the GI microbiome detected via 16S rRNA gene sequencing were related to the housing environment. This study supports use of anti-opioid vaccines in clinical populations that may display deficits in microbiome function.

Synergistic immune and antinociceptive effects induced from the combination of two different vaccines against morphine/heroin in mouse

Animal studies have reported the use of different opioid-vaccine formulations with relative success These studies have suggested that new opioid-vaccine formulations are required, which are capable of triggering a robust humoral response. One strategy that has been used is the co-administration of two or more vaccines with different but complementary properties, which are capable of generating a robust immune response. We have developed two formulations of opioid-vaccine, the M6-TT, and M3-TT, which generate a robust immune response capable of recognizing heroin and morphine. In this work, we evaluate the combination of two vaccine formulations, which we call the M3/6-TT vaccine, to elicit a robust immune response and protection against heroin and morphine. Balb/c mice were immunized simultaneously with M6-TT vaccine and with M3-TT vaccine. A solid-phase antibody-capture ELISA was used for monitoring antibody titer responses after each booster dose in vaccinated animals. The study used tail-flick and hot-plate testing to evaluate the antinociceptive effects induced by heroin or morphine. Immunization with M3-TT and M6-TT vaccine elicits a robust immune response with an antibody titer of 1: 590 000 able to recognize heroin and morphine. These antibodies are capable of reducing the antinociceptive effects induced by doses of up to 40 mg/Kg. of morphine or 10 mg/kg of heroin. This suggests that the combination of two vaccine formulations that generate antibodies with different but complementary characteristics would be a new therapeutic strategy aimed at reducing drug relapses.

Morphine alkaloids: History, biology, and synthesis

This chapter provides a short overview of the history of morphine since it's isolation by Sertürner in 1805. The biosynthesis of the title alkaloid as well as all total and formal syntheses of morphine and codeine published after 1996 are discussed in detail. The last section of this chapter provides a detailed overview of medicinally relevant derivatives of the title alkaloid.

Improvements on a chemically contiguous hapten for a vaccine to address fentanyl-contaminated heroin

Unintentional overdose deaths related to opioids and psychostimulants have increased in prevalence due to the adulteration of these drugs with fentanyl. Synergistic effects between illicit compounds and fentanyl cause aggravated respiratory depression, leading to inadvertent fatalities. Traditional small-molecule therapies implemented in the expanding opioid epidemic present numerous problems since they interact with the same opioid receptors in the brain as the abused drugs. In this study, we report an optimized dual hapten for use as an immunopharmacotherapeutic tool in order to develop antibodies capable of binding to fentanyl-contaminated heroin in the periphery, thus impeding the drugs' psychoactive effects on the central nervous system. This vaccine produced antibodies with nanomolar affinities and effectively blocked opioid analgesic effects elicited by adulterated heroin. These findings provide further insight into the development of chemically contiguous haptens for broad-spectrum immunopharmacotherapies against opioid use disorders.

The morphine/heroin vaccine decreased the heroin-induced antinociceptive and reinforcing effects in three inbred strains mouse

Clinical trials have indicated that a vaccine must be immunogenic in genetically diverse human populations and that immunogenicity and protective efficacy in animal models are two key indices required for the approval of a new vaccine. Additionally, the immune response (immunogenicity) and immunoprotection are dependent on the mouse strain. Therefore, the objective of the present study was to determine the immune response (immunogenicity) and the protective efficacy (behavioral response) in three inbred mouse strains immunized with the M₆TT vaccine. Female BALB/c, C57Bl/6, and DBA/2 inbred mice were immunized with the M₆-TT vaccine. A solid-phase antibody-capture ELISA was used to monitor antibody titer responses after each booster dose in vaccinated animals. The study used tail-flick testing to evaluate the antinociceptive effects induced by heroin. Additionally, heroin-induced locomotor activity and place preference were evaluated. The M₆-TT vaccine was able to generate a specific antibody titer in the three inbred mouse strains evaluated. The antibodies reduced the antinociceptive effect of different doses of heroin. In addition, they decreased the heroin-induced locomotor activity and place preference. These findings suggest that the M₆-TT vaccine generates a powerful immunogenic response capable of reducing the antinociceptive and reinforcing effects of heroin in different inbred mouse strains, which supports its possible future use in clinical trials in genetically diverse human populations.

Pharmacological mechanisms underlying the efficacy of antibodies generated by a vaccine to treat oxycodone use disorder

Therapeutic vaccines offer a viable strategy to treat opioid use disorders (OUD) complementary to current pharmacotherapies. The candidate Oxy(Gly)₄-sKLH vaccine targeting oxycodone displayed pre-clinical proof of efficacy, selectivity and safety, and it is now undergoing clinical evaluation. To further support its implementation in the clinic, this study tested critical in vivo neuropsychopharmacological properties of the Oxy(Gly)₄-sKLH vaccine in rats. While repeated immunizations with Oxy(Gly)₄-sKLH were necessary to maintain the antibody response overtime, exposure to free oxycodone did not boost oxycodone-specific antibody levels in vaccinated rats, limiting concerns of immune-related side effects. Immunization with Oxy(Gly)₄-sKLH achieved sustained antibody titers over a period of five months following initial vaccination, supporting its potential for providing long-lasting protection. In vivo studies of selectivity showed that vaccination prevented oxycodone-induced but not methadone-induced antinociception, while still preserving the opioid antagonist naloxone's pharmacological effects. Vaccination did not interfere with fentanyl-induced antinociception or fentanyl distribution to the brain. These in vivo data confirm the previously reported in vitro selectivity profile of Oxy(Gly)₄-sKLH. Vaccination extended oxycodone's half-life up to 25 h compared to control. While vaccination reduced the reinforcing efficacy of oxycodone in an intravenous self-administration model, signs of toxicity were not observed. These rodent studies confirm that active immunization with Oxy(Gly)₄-sKLH induces highly specific and long-lasting antibodies which are effective in decreasing the reinforcing effects of oxycodone while preserving the efficacy of medications used to treat OUD and overdose.

Synthesis and immunological effects of C14-linked 4,5-epoxymorphinan analogues as novel heroin vaccine haptens

Active immunization is being explored as a potential therapeutic to combat accidental overdose and to mitigate the abuse potential of opioids. Hapten design is one of the crucial factors that determines the efficacy of a candidate vaccine to substance abuse and remains one of the most active areas of research in vaccine development. Herein we report for the first time the synthesis of three novel opiate surrogates with the linker attachment site at C14, 1 (6,14-AmidoHap), 2 (14-AmidoMorHap), and 3 (14-AmidoHerHap) as novel heroin haptens. The compounds 1, 2, and 3 are analogues with different substituents at C6: an acetamide, a hydroxyl moiety, and an acetate, respectively. All three haptens had a phenolic hydroxyl group at C3. The haptens were conjugated to the tetanus toxoid carrier protein, adjuvanted with liposomal monophosphoryl lipid A/aluminum hydroxide and were tested in mice in terms of immunogenicity and efficacy. Immunization of mice resulted in antibody endpoint titers of >10⁵ against all the haptens. Neither of the conjugates of 1, 2, and 3 had induced antibodies with selectivity broad enough to recognize and bind heroin, 6-AM, and morphine resulting in little to no protection against the antinociceptive effects of heroin in vivo. Only the mice immunized with conjugate 3 were partially protected against heroin-induced antinociception. These results contribute to the growing body of knowledge that the linker position and the subtle structural differences in the hapten scaffold impact the selectivity of the induced antibodies. Together, these highlight the importance of rational hapten design for heroin vaccine development.

Three novel opiate surrogates with the linker at C14, 1 (6,14-AmidoHap), 2 (14-AmidoMorHap), and 3 (14-AmidoHerHap) were conjugated to tetanus toxoid (TT) and tested as heroin vaccines. The C3 and C6 moieties are crucial in antibody selectivity.

Effect of the morphine/heroin vaccine on opioid and non-opioid drug-induced antinociception in mice

Pain is a common symptom in patients with opioid use disorder (OUD), which increases synthetic and illicit synthetic opioid abuse and even fatalities due to opioid overdose. Many FDA-approved drugs are available for the treatment of OUD, however, the use of these medications is limited, mainly due to the development of various side effects. Active vaccination is a new therapeutic approach but the resulting antibodies may compromise the use and efficiency of opioid and non-opioid drugs. In this study, we evaluated whether the antibodies produced by the morphine/heroin vaccine (M-TT) would alter the antinociceptive effects of opioid and non-opioid drugs. Female Balb-c mice were immunized with the M-TT vaccine. A solid-phase antibody-capture ELISA was used for monitoring antibody titer responses after each booster dose in vaccinated animals, followed by tail-flick testing. This study found that the M-TT vaccine did not affect the antinociception induced by different doses of morphine or the ability of non-opioid and synthetic opioid drugs to decrease thermal pain. Moreover, the combination of vaccination and naloxone increased the time-course of morphine antagonism relative to either vaccination or naloxone alone. These results suggest that the antibody titers generated by the M-TT vaccine 1) are capable of reducing morphine-induced antinociception and 2) are selective enough not to alter antinociception induced by non-opioid or synthetic drugs. These characteristics support its potential as a treatment agent for patients with symptoms of pain comorbid to OUD.

A synthetic opioid vaccine attenuates fentanyl-vs-food choice in male and female rhesus monkeys

AIM

Opioid-targeted vaccines are under consideration as candidate Opioid Use Disorder medications. We recently reported that a fentanyl-targeted vaccine produced a robust and long-lasting attenuation of fentanyl-vs-food choice in rats. In the current study, we evaluated an optimized fentanyl-targeted vaccine in rhesus monkeys to determine whether vaccine effectiveness to attenuate fentanyl choice translated to a species with greater phylogenetic similarity to humans.

METHODS

Adult male (2) and female (3) rhesus monkeys were trained to respond under a concurrent schedule of food (1 g pellets) and intravenous fentanyl (0, 0.032-1 μg/kg/injection) reinforcement during daily 2 h sessions. Fentanyl choice dose-effect functions were determined daily and 7-day buprenorphine treatments (0.0032-0.032 mg/kg/h IV; n = 4-5) were determined for comparison to vaccine effects. Subsequently, a fentanyl-CRM₁₉₇ conjugate vaccine was administered at week 0, 3, 8, 15 over a 29-week experimental period during which fentanyl choice dose-effect functions continued to be determined daily.

RESULTS

Buprenorphine significantly decreased fentanyl choice and reciprocally increased food choice. Vaccination eliminated fentanyl choice and increased food choice in four-of-the-five monkeys. A transient and less robust vaccine effect was observed in the fifth monkey. Fentanyl-specific antibody concentrations peaked after the third vaccination to approximately 50 μg/mL while anti-fentanyl antibody affinity increased to a sustained low nanomolar level.

CONCLUSION

These results translate fentanyl vaccine effectiveness from rats to rhesus monkeys to decrease fentanyl-vs-food choice, albeit with greater individual differences observed in monkeys. These results support the potential and further clinical evaluation of this fentanyl-targeted vaccine as a candidate Opioid Use Disorder medication.

Therapeutic and Prophylactic Vaccines to Counteract Fentanyl Use Disorders and Toxicity

The incidence of fatal overdoses has increased worldwide due to the widespread access to illicit fentanyl and its potent analogues. Vaccines offer a promising strategy to reduce the prevalence of opioid use disorders (OUDs) and to prevent toxicity from accidental and deliberate exposure to fentanyl and its derivatives. This study describes the development and characterization of vaccine formulations consisting of novel fentanyl-based haptens conjugated to carrier proteins. Vaccine efficacy was tested against opioid-induced behavior and toxicity in mice and rats challenged with fentanyl and its analogues. Prophylactic vaccination reduced fentanyl- and sufentanil-induced antinociception, respiratory depression, and bradycardia in mice and rats. Therapeutic vaccination also reduced fentanyl intravenous self-administration in rats. Because of their selectivity, vaccines did not interfere with the pharmacological effects of commonly used anesthetics nor with methadone, naloxone, oxycodone, or heroin. These preclinical data support the translation of vaccines as a viable strategy to counteract fentanyl use disorders and toxicity.

Emerging Concepts and Technologies in Vaccine Development

Despite the success of vaccination to greatly mitigate or eliminate threat of diseases caused by pathogens, there are still known diseases and emerging pathogens for which the development of successful vaccines against them is inherently difficult. In addition, vaccine development for people with compromised immunity and other pre-existing medical conditions has remained a major challenge. Besides the traditional inactivated or live attenuated, virus-vectored and subunit vaccines, emerging non-viral vaccine technologies, such as viral-like particle and nanoparticle vaccines, DNA/RNA vaccines, and rational vaccine design, offer innovative approaches to address existing challenges of vaccine development. They have also significantly advanced our understanding of vaccine immunology and can guide future vaccine development for many diseases, including rapidly emerging infectious diseases, such as COVID-19, and diseases that have not traditionally been addressed by vaccination, such as cancers and substance abuse. This review provides an integrative discussion of new non-viral vaccine development technologies and their use to address the most fundamental and ongoing challenges of vaccine development.

Synthesis of Potential Haptens with Morphine Skeleton and Determination of Protonation Constants

Vaccination could be a promising alternative warfare against drug addiction and abuse. For this purpose, so-called haptens can be used. These molecules alone do not induce the activation of the immune system, this occurs only when they are attached to an immunogenic carrier protein. Hence obtaining a free amino or carboxylic group during the structural transformation is an important part of the synthesis. Namely, these groups can be used to form the requisite peptide bond between the hapten and the carrier protein. Focusing on this basic principle, six nor-morphine compounds were treated with ethyl acrylate and ethyl bromoacetate, while the prepared esters were hydrolyzed to obtain the N-carboxymethyl- and N-carboxyethyl-normorphine derivatives which are considered as potential haptens. The next step was the coupling phase with glycine ethyl ester, but the reactions did not work or the work-up process was not accomplishable. As an alternative route, the normorphine-compounds were N-alkylated with N-(chloroacetyl)glycine ethyl ester. These products were hydrolyzed in alkaline media and after the work-up process all of the derivatives contained the free carboxylic group of the glycine side chain. The acid-base properties of these molecules are characterized in detail. In the N-carboxyalkyl derivatives, the basicity of the amino and phenolate site is within an order of magnitude. In the glycine derivatives the basicity of the amino group is significantly decreased compared to the parent compounds (i.e., morphine, oxymorphone) because of the electron withdrawing amide group. The protonation state of the carboxylate group significantly influences the basicity of the amino group. All of the glycine ester and the glycine carboxylic acid derivatives are currently under biological tests.

Sulfonate-isosteric replacement examined within heroin-hapten vaccine design

Heroin overdose and addiction remain significant health and economic burdens in the world today costing billions of dollars annually. Moreover, only limited pharmacotherapeutic options are available for treatment of heroin addiction. In our efforts to combat the public health threat posed by heroin addiction, we have developed vaccines against heroin. To expand upon our existing heroin-vaccine arsenal, we synthesized new aryl and alkyl sulfonate ester haptens; namely aryl-mono-sulfonate (HMsAc) and Aryl/alkyl-di-sulfonate (H(Ds)2) as carboxyl-isosteres of heroin then compared them to our model heroin-hapten (HAc) through vaccination studies. Heroin haptens were conjugated to the carrier protein CRM197 and the resulting CRM-immunoconjugates were used to vaccinate Swiss Webster mice following an established immunization protocol. Binding studies revealed that the highest affinity anti-heroin antibodies were generated by the HMsAc vaccine followed by the HAc and H(Ds)2 vaccines, respectively (HMsAc > HAc≫HDs2). However, neither the HMsAc nor H(Ds)2 vaccines were able to generate high affinity antibodies to the psychoactive metabolite 6-acetyl morphine (6-AM), in comparison to the HAc vaccine. Blood brain bio-distribution studies supported these binding results with vaccine efficiency following the trend HAc > HMsAc ≫ H(Ds)2 The work described herein provides insight into the use of hapten-isosteric replacement in vaccine drug design.

Enhancement of a Heroin Vaccine through Hapten Deuteration

The United States is in the midst of an unprecedented epidemic of opioid substance use disorder, and while pharmacotherapies including opioid agonists and antagonists have shown success, they can be inadequate and frequently result in high recidivism. With these challenges facing opioid use disorder treatments immunopharmacotherapy is being explored as an alternative therapy option and is based upon antibody-opioid sequestering to block brain entry. Development of a heroin vaccine has become a major research focal point; however, producing an efficient vaccine against heroin has been particularly challenging because of the need to generate not only a potent immune response but one against heroin and its multiple psychoactive molecules. In this study, we explored the consequence of regioselective deuteration of a heroin hapten and its impact upon the immune response against heroin and its psychoactive metabolites. Deuterium (H_dAc) and cognate protium heroin (H_Ac) haptens were compared head to head in an inclusive vaccine study. Strikingly the H_dAc vaccine granted greater efficacy in blunting heroin analgesia in murine behavioral models compared to the H_Ac vaccine. Binding studies confirmed that the H_dAc vaccine elicited both greater quantities and equivalent or higher affinity antibodies toward heroin and 6-AM. Blood-brain biodistribution experiments corroborated these affinity tests. These findings suggest that regioselective hapten deuteration could be useful for the resurrection of previous drug of abuse vaccines that have met limited success in the past.

Combining a Candidate Vaccine for Opioid Use Disorders with Extended-Release Naltrexone Increases Protection against Oxycodone-Induced Behavioral Effects and Toxicity

Opioid use disorders (OUDs) and opioid-related fatal overdoses are a significant public health concern in the United States and worldwide. To offer more effective medical interventions to treat or prevent OUD, antiopioid vaccines are in development that reduce the distribution of the targeted opioids to brain and subsequently reduce the associated behavioral and toxic effects. It is of critical importance that antiopioid vaccines do not interfere with medications that treat OUD. Hence, this study tested the preclinical proof of concept of combining a candidate oxycodone vaccine [oxycodone-keyhole limpet hemocyanin (OXY-KLH)] with an FDA-approved extended-release naltrexone (XR-NTX) depot formulation in rats. The effects of XR-NTX on oxycodone-induced motor activity and antinociception were first assessed in nonvaccinated naïve rats to establish a baseline for subsequent studies. Next, OXY-KLH and XR-NTX were coadministered to determine whether the combination would affect the efficacy of each individual treatment, and it was found that the combination of OXY-KLH and XR-NTX offered greater efficacy in reducing oxycodone-induced motor activity, thigmotaxis, antinociception, and respiratory depression over a range of repeated or escalating oxycodone doses in rats. These data support the feasibility of combining antibody-based therapies with opioid receptor antagonists to provide greater or prolonged protection against opioid-related toxicity or overdose. Combining antiopioid vaccines with XR-NTX may provide prophylactic measures to subjects at risk of relapse and accidental or deliberate exposure. Combination therapy may extend to other biologics (e.g., monoclonal antibodies) and medications against substance use disorders. SIGNIFICANCE STATEMENT: Opioid use disorders (OUDs) remain a major problem worldwide, and new therapies are needed. This study reports on the combination of an oxycodone vaccine [oxycodone-keyhole limpet hemocyanin (OXY-KLH)] with a currently approved OUD therapy, extended-release naltrexone (XR-NTX). Results demonstrated that XR-NTX did not interfere with OXY-KLH efficacy, and combination of low doses of XR-NTX with vaccine was more effective than each individual treatment alone to reduce behavioral and toxic effects of oxycodone, suggesting that combining OXY-KLH with XR-NTX may improve OUD outcomes.

Polymer-mediated delivery of vaccines to treat opioid use disorders and to reduce opioid-induced toxicity

Vaccines offer a potential strategy to treat opioid use disorders (OUD) and to reduce the incidence of opioid-related overdoses. Vaccines induce opioid-specific polyclonal antibodies that selectively and effectively bind the target opioid and prevent its distribution across the blood-brain barrier. Because antibody-mediated reduction of drug distribution to the brain reduces drug-induced behavior and toxicity, vaccine efficacy depends on the quantity and quality of the antibody response. This study tested whether polymer-mediated delivery could improve vaccine efficacy against opioids as well as eliminate the need for booster injections normally required for a successful immunization. A series of novel biodegradable biocompatible thermogelling pentablock co-polymers were used to formulate a candidate vaccine against oxycodone in mice and rats. Polymer-based delivery of the anti-oxycodone vaccine was equally or more effective than administration in aluminum adjuvant in generating oxycodone-specific antibodies and in reducing oxycodone-induced effects and oxycodone distribution to the brain in mice and rats. The composition and release kinetics of the polymer formulations determined vaccine efficacy. Specifically, a formulation consisting of three simultaneous injections of the anti-oxycodone vaccine formulated in three different polymers with slow, intermediate, and fast release kinetics was more effective than an immunization regimen consisting of three sequential injections with the vaccine adsorbed on aluminum. The novel three-phased polymer vaccine formulation was effective in blocking oxycodone-induced antinociception, respiratory depression and bradycardia in rats.

Evaluation of a Dual Fentanyl/Heroin Vaccine on the Antinociceptive and Reinforcing Effects of a Fentanyl/Heroin Mixture in Male and Female Rats

Opioid-targeted vaccines represent an emerging treatment strategy for opioid use disorder. To determine whether concurrent vaccination against two commonly abused opioids (fentanyl and heroin) would confer broader spectrum opioid coverage, the current study evaluated dual fentanyl/heroin conjugate vaccine effectiveness using a warm water tail-withdrawal and a fentanyl/heroin-vs-food choice procedure in male and female rats across a 105-day observation period. Vaccine administration generated titers of high-affinity antibodies to both fentanyl and heroin sufficient to decrease the antinociceptive potency of fentanyl (25-fold), heroin (4.6-fold), and a 1:27 fentanyl/heroin mixture (7.5-fold). Vaccination did not alter the antinociceptive potency of the structurally dissimilar opioid agonist methadone. For comparison, continuous treatment with a naltrexone dose (0.032 mg/kg/h) shown previously to produce clinically relevant plasma-naltrexone levels decreased the antinociceptive potency of fentanyl, heroin, and the 1:27 fentanyl/heroin mixture by approximately 20-fold. Naltrexone treatment also shifted the potency of 1:27 fentanyl/heroin mixture in a drug-vs-food choice self-administration procedure 4.3-fold. In contrast, vaccination did not attenuate 1:27 fentanyl/heroin mixture self-administration in the drug-vs-food choice procedure. These data demonstrate that a vaccine can simultaneously attenuate the thermal antinociceptive effects of two structurally dissimilar opioids. However, the vaccine did not attenuate fentanyl/heroin mixture self-administration, suggesting a greater magnitude of vaccine responsiveness is required to decrease opioid reinforcement relative to antinociception.

Preclinical Evaluation of Vaccines to Treat Opioid Use Disorders: How Close are We to a Clinically Viable Therapeutic?

The ongoing opioid crisis, now into its second decade, represents a global public health challenge. Moreover, the opioid crisis has manifested despite clinical access to three approved opioid use disorder medications: the full opioid agonist methadone, the partial opioid agonist buprenorphine, and the opioid antagonist naltrexone. Although current opioid use disorder medications are underutilized, the ongoing opioid crisis has also identified the need for basic research to develop both safer and more effective opioid use disorder medications. Emerging preclinical evidence suggests that opioid-targeted vaccines or immunopharmacotherapies may be promising opioid use disorder therapeutics. One premise for this article is to critically examine whether vaccine effectiveness evaluated using preclinical antinociceptive endpoints is predictive of vaccine effectiveness on abuse-related endpoints such as drug self-administration, drug discrimination, and conditioned place preference. A second premise is to apply decades of knowledge in the preclinical evaluation of candidate small-molecule therapeutics for opioid use disorder to the preclinical evaluation of candidate opioid use disorder immunopharmacotherapies. We conclude with preclinical experimental design attributes to enhance preclinical-to-clinical translatability and potential future directions for immunopharmacotherapies to address the dynamic illicit opioid environment.

Effectiveness and selectivity of a heroin conjugate vaccine to attenuate heroin, 6-acetylmorphine, and morphine antinociception in rats: Comparison with naltrexone

BACKGROUND

One emerging strategy to address the opioid crisis includes opioid-targeted immunopharmacotherapies. This study compared effectiveness of a heroin-tetanus toxoid (TT) conjugate vaccine to antagonize heroin, 6-acetylmorphine (6-AM), morphine, and fentanyl antinociception in rats.

METHODS

Adult male and female Sprague Dawley rats received three doses of active or control vaccine at weeks 0, 2, and 4. Vaccine pharmacological selectivity was assessed by comparing opioid dose-effect curves in 50 °C  warm-water tail-withdrawal procedure before and after active or control heroin-TT vaccine. Route of heroin administration [subcutaneous (SC) vs. intravenous [IV)] was also examined as a determinant of vaccine effectiveness. Continuous naltrexone treatment (0.0032-0.032 mg/kg/h) effects on heroin, 6-AM, and morphine antinociceptive potency were also determined as a benchmark for minimal vaccine effectiveness.

RESULTS

The heroin-TT vaccine decreased potency of SC heroin (5-fold), IV heroin (3-fold), and IV 6-AM (3-fold) for several weeks without affecting IV morphine or SC and IV fentanyl potency. The control vaccine did not alter potency of any opioid. Naltrexone dose-dependently decreased antinociceptive potency of SC heroin, and treatment with 0.01 mg/kg/h naltrexone produced similar, approximate 8-fold decreases in potencies of SC and IV heroin, IV 6-AM, and IV morphine. The combination of naltrexone and active vaccine was more effective than naltrexone alone to antagonize SC heroin but not IV heroin.

CONCLUSIONS

The heroin-TT vaccine formulation examined is less effective, but more selective, than chronic naltrexone to attenuate heroin antinociception in rats. Furthermore, these results provide an empirical framework for future preclinical opioid vaccine research to benchmark effectiveness against naltrexone.

Conjugate vaccine produces long-lasting attenuation of fentanyl vs. food choice and blocks expression of opioid withdrawal-induced increases in fentanyl choice in rats

The current opioid crisis remains a significant public health issue and there is a critical need for biomedical research to develop effective and easily deployable candidate treatments. One emerging treatment strategy for opioid use disorder includes immunopharmacotherapies or opioid-targeted vaccines. The present study determined the effectiveness of a fentanyl-tetanus toxoid conjugate vaccine to alter fentanyl self-administration using a fentanyl-vs.-food choice procedure in male and female rats under three experimental conditions. For comparison, continuous 7-day naltrexone (0.01-0.1 mg/kg/h) and 7-day clonidine (3.2-10 μg/kg/h) treatment effects were also determined on fentanyl-vs.-food choice. Male and female rats responded for concurrently available 18% diluted Ensure® (liquid food) and fentanyl (0-10 μg/kg/infusion) infusions during daily sessions. Under baseline and saline treatment conditions, fentanyl maintained a dose-dependent increase in fentanyl-vs.-food choice. First, fentanyl vaccine administration significantly blunted fentanyl reinforcement and increased food reinforcement for 15 weeks in non-opioid dependent rats. Second, surmountability experiments by increasing the unit fentanyl dose available during the self-administration session 10-fold empirically determined that the fentanyl vaccine produced an approximate 22-fold potency shift in fentanyl-vs.-food choice that was as effective as the clinically approved treatment naltrexone. Clonidine treatment significantly increased fentanyl-vs.-food choice. Lastly, fentanyl vaccine administration prevented the expression of withdrawal-associated increases in fentanyl-vs.-food choice following introduction of extended 12 h fentanyl access sessions. Overall, these results support the potential and further consideration of immunopharmacotherapies as candidate treatments to address the current opioid crisis.

The continuing search for an addiction vaccine

Inspired by advances in immunology, in the 1970s scientists began to study the possibilities of mobilizing the human immune system against intruders other than pathogenic viruses and bacteria. In 1972 the suggestion was first made that it might be possible to provoke immunity to narcotic dependence. Because molecules of narcotics such as heroin and cocaine are too small to stimulate an immune response, researchers sought ways of coupling them to immunogenic proteins. The substances they developed soon became known as addiction vaccines. However, despite fifty years of research, and despite the growing problem of addiction, no vaccine against heroin, cocaine, methamphetamine or nicotine addiction has yet been licensed for clinical use. This paper reviews the history of addiction vaccinology, seeks to explain the unique appeal of a vaccinological approach to addiction, and argues for broad discussion of how such vaccines should ultimately be used.

Development of vaccines to treat opioid use disorders and reduce incidence of overdose

Vaccines offer a promising therapeutic strategy to treat substance use disorders (SUD). Vaccines have shown extensive preclinical proof of selectivity, safety, and efficacy against opioids, nicotine, cocaine, methamphetamine, and designer drugs. Despite clinical evaluation of vaccines targeting nicotine and cocaine showing proof of concept for this approach, no vaccine for SUD has yet reached the market. This review first discusses how vaccines for treatment of opioid use disorders (OUD) and reduction of opioid-induced fatal overdoses fit within the current medication assisted treatment (MAT) portfolio, and then summarizes ongoing efforts toward translation of vaccines targeting heroin, oxycodone, fentanyl, and other opioids. This article is part of the Special Issue entitled 'New Vistas in Opioid Pharmacology'.

A chemically contiguous hapten approach for a heroin-fentanyl vaccine

Background: Increased death due to the opioid epidemic in the United States has necessitated the development of new strategies to treat addiction. Monoclonal antibodies and antidrug vaccines provide a tool that both aids addiction management and reduces the potential for overdose. Dual drug vaccines formulated by successive conjugation or by mixture have certain drawbacks. The current study examines an approach for combatting the dangers of fentanyl-laced heroin, by using a hapten with one epitope that has domains for both fentanyl and heroin. Results: We evaluated a series of nine vaccines developed from chemically contiguous haptens composed of both heroin- and fentanyl-like domains. Analysis of the results obtained by SPR and ELISA revealed trends in antibody affinity and titers for heroin and fentanyl based on epitope size and linker location. In antinociception studies, the best performing vaccines offered comparable protection against heroin as our benchmark heroin vaccine, but exhibited attenuated protection against fentanyl compared to our fentanyl vaccine. Conclusion: After thorough investigation of this strategy, we have identified key considerations for the development of a chemically contiguous heroin-fentanyl vaccine. Importantly, this is the first report of such a strategy in the opioid-drug-vaccine field.

Chemical Interventions for the Opioid Crisis: Key Advances and Remaining Challenges

The present United States opioid crisis requires urgent and innovative scientific intervention. This perspective highlights a role for the chemical sciences by expounding upon three key research areas identified as priorities by the National Institute on Drug Abuse (NIDA). Specifically, important advances in chemical interventions for overdose reversal, strategies for opioid use disorder (OUD) treatment, including immunopharmacotherapies, and next-generation alternatives for pain management will be discussed. Ultimately, progress made will be presented in light of remaining challenges for the field.

A Fentanyl Vaccine Alters Fentanyl Distribution and Protects against Fentanyl-Induced Effects in Mice and Rats

Fentanyl is an extremely potent synthetic opioid that has been increasingly used to adulterate heroin, cocaine, and counterfeit prescription pills, leading to an increase in opioid-induced fatal overdoses in the United States, Canada, and Europe. A vaccine targeting fentanyl could offer protection against the toxic effects of fentanyl in both recreational drug users and others in professions at risk of accidental exposure. This study focuses on the development of a vaccine consisting of a fentanyl-based hapten (F) conjugated to keyhole limpet hemocyanin (KLH) carrier protein or to GMP-grade subunit KLH (sKLH). Immunization with F-KLH in mice and rats reduced fentanyl-induced hotplate antinociception, and in rats reduced fentanyl distribution to the brain compared with controls. F-KLH did not reduce the antinociceptive effects of equianalgesic doses of heroin or oxycodone in rats. To assess the vaccine effect on fentanyl toxicity, rats immunized with F-sKLH or unconjugated sKLH were exposed to increasing subcutaneous doses of fentanyl. Vaccination with F-sKLH shifted the dose-response curves to the right for both fentanyl-induced antinociception and respiratory depression. Naloxone reversed fentanyl effects in both groups, showing that its ability to reverse respiratory depression was preserved. These data demonstrate preclinical selectivity and efficacy of a fentanyl vaccine and suggest that vaccines may offer a therapeutic option in reducing fentanyl-induced side effects.

Heat shock proteins: A dual carrier-adjuvant for an anti-drug vaccine against heroin

Heroin is a highly abused opioid that has reached epidemic status within the United States. Yet, existing therapies to treat addiction are inadequate and frequently result into rates of high recidivism. Vaccination against heroin offers a promising alternative therapeutic option but requires further development to enhance the vaccine's performance. Hsp70 is a conserved protein with known immunomodulatory properties and is considered an excellent immunodominant antigen. Within an antidrug vaccine context, we envisioned Hsp70 as a potential dual carrier-adjuvant, wherein immunogenicity would be increased by co-localization of adjuvant and antigenic drug hapten. Recombinant Mycobacterium tuberculosis Hsp70 was appended with heroin haptens and the resulting immunoconjugate granted anti-heroin antibody production and blunted heroin-induced antinociception. Moreover, Hsp70 as a carrier protein surpassed our benchmark Her-KLH cocktail through antibody-mediated blockade of 6-acetylmorphine, the main mediator of heroin's psychoactivity. The work presents a new avenue for exploration in the use of hapten-Hsp70 conjugates to elicit anti-drug immune responses.

Improved Admixture Vaccine of Fentanyl and Heroin Hapten Immunoconjugates: Antinociceptive Evaluation of Fentanyl-Contaminated Heroin

Fentanyl and its derivatives have become pervasive contaminants in the U.S. heroin supply. Previously, we reported a proof-of-concept vaccine designed to combat against heroin contaminated with fentanyl. Herein, we optimized the admixture vaccine and found that it surpassed the individual vaccines in every antinociceptive test, including a 10% fentanyl to heroin formulation. It is anticipated that other co-occurring drug abuse disorders may also be examined with admixture vaccines.

Prophylactic vaccination protects against the development of oxycodone self-administration

Abuse of prescription opioids is a growing public health crisis in the United States, with drug overdose deaths increasing dramatically over the past 15 years. Few preclinical studies exist on the reinforcing effects of oxycodone or on the development of therapies for oxycodone abuse. This study was conducted to determine if immunopharmacotherapy directed against oxycodone would be capable of altering oxycodone-induced antinociception and intravenous self-administration. Male Wistar rats were administered a small-molecule immunoconjugate vaccine (Oxy-TT) or the control carrier protein, tetanus toxoid (TT), and trained to intravenously self-administer oxycodone (0.06 or 0.15 mg/kg/infusion). Brain oxycodone concentrations were 50% lower in Oxy-TT rats compared to TT rats 30 min after injection (1 mg/kg, s.c.) whereas plasma oxycodone was 15-fold higher from drug sequestration by circulating antibodies. Oxy-TT rats were also less sensitive to 1-2 mg/kg, s.c. oxycodone on a hot water nociception assay. Half of the Oxy-TT rats failed to acquire intravenous self-administration under the 0.06 mg/kg/infusion training dose. Oxycodone self-administration of Oxy-TT rats trained on 0.15 mg/kg/infusion was higher than controls; however under progressive ratio (PR) conditions the Oxy-TT rats decreased their oxycodone intake, unlike TT controls. These data demonstrate that active vaccination provides protection against the reinforcing effects of oxycodone. Anti-oxycodone vaccines may entirely prevent repeated use in some individuals who otherwise would become addicted. Vaccination may also reduce dependence in those who become addicted and therefore facilitate the effects of other therapeutic interventions which either increase the difficulty of drug use or incentivize other behaviors.

A rapid solution-based method for determining the affinity of heroin hapten-induced antibodies to heroin, its metabolites, and other opioids

We describe for the first time a method that utilizes microscale thermophoresis (MST) technology to determine polyclonal antibody affinities to small molecules. Using a novel type of heterologous MST, we have accurately measured a solution-based binding affinity of serum antibodies to heroin which was previously impossible with other currently available methods. Moreover, this mismatch approach (i.e., using a cross-reactive hapten tracer) has never been reported in the literature. When compared with equilibrium dialysis combined with ultra-performance liquid chromatography/tandem mass spectrometry (ED-UPLC/MS/MS), this novel MST method yields similar binding affinity values for polyclonal antibodies to the major heroin metabolites 6-AM and morphine. Additionally, we herein report the method of synthesis of this novel cross-reactive hapten, MorHap-acetamide—a useful analog for the study of heroin hapten–antibody interactions. Using heterologous MST, we were able to determine the affinities, down to nanomolar accuracies, of polyclonal antibodies to various abused opioids. While optimizing this method, we further discovered that heroin is protected from serum esterase degradation by the presence of these antibodies in a concentration-dependent manner. Lastly, using affinity data for a number of structurally different opioids, we were able to dissect the moieties that are crucial to antibody binding. The novel MST method that is presented herein can be extended to the analysis of any ligand that is prone to degradation and can be applied not only to the development of vaccines to substances of abuse but also to the analysis of small molecule/protein interactions in the presence of serum.

Graphical abstract

Opioid Dose- and Route-Dependent Efficacy of Oxycodone and Heroin Vaccines in Rats

Heroin and oxycodone abuse occurs over a wide range of drug doses and by various routes of administration characterized by differing rates of drug absorption. The current study addressed the efficacy of a heroin vaccine [morphine hapten conjugated to keyhole limpet hemocyanin (M-KLH)] or oxycodone vaccine [oxycodone hapten conjugated to keyhole limpet hemocyanin (OXY-KLH)] for reducing drug distribution to brain after intravenous heroin or oxycodone, or subcutaneous oxycodone. Rats immunized with M-KLH or keyhole limpet hemocyanin (KLH) control received an intravenous bolus dose of 0.26 or 2.6 mg/kg heroin. Vaccination with M-KLH increased retention of heroin and its active metabolites 6-acetylmorphine (6-AM) and morphine in plasma compared with KLH controls, and reduced total opioid (heroin + 6-AM + morphine) distribution to brain but only at the lower heroin dose. Immunization also protected against respiratory depression at the lower heroin dose. Rats immunized with OXY-KLH or KLH control received 0.22 or 2.2 mg/kg oxycodone intravenously, the molar equivalent of the heroin doses. Immunization with OXY-KLH significantly reduced oxycodone distribution to brain after either oxycodone dose, although the magnitude of effect of immunization at the higher oxycodone dose was small (12%). By contrast, vaccination with OXY-KLH was more effective when oxycodone was administered subcutaneously rather than intravenously, reducing oxycodone distribution to brain by 44% after an oxycodone dose of 2.3 mg/kg. Vaccination also reduced oxycodone-induced antinociception. These data suggest that the efficacy of OXY-KLH and M-KLH opioid vaccines is highly dependent upon opioid dose and route of administration.

Enhancing Efficacy and Stability of an Antiheroin Vaccine: Examination of Antinociception, Opioid Binding Profile, and Lethality

In recent years, drug conjugate vaccines have shown promise as therapeutics for substance use disorder. As a means to improve the efficacy of a heroin conjugate vaccine, we systematically explored 20 vaccine formulations with varying combinations of carrier proteins and adjuvants. In regard to adjuvants, we explored a Toll-like receptor 9 (TLR9) agonist and a TLR3 agonist in the presence of alum. The TLR9 agonist was cytosine-guanine oligodeoxynucleotide 1826 (CpG ODN 1826), while the TLR3 agonist was virus-derived genomic doubled-stranded RNA (dsRNA). The vaccine formulations containing TLR3 or TLR9 agonist alone elicited strong antiheroin antibody titers and blockade of heroin-induced antinociception when formulated with alum; however, a combination of TLR3 and TLR9 adjuvants did not result in improved efficacy. Investigation of month-long stability of the two lead formulations revealed that the TLR9 but not the TLR3 formulation was stable when stored as a lyophilized solid or as a liquid over 30 days. Furthermore, mice immunized with the TLR9 + alum heroin vaccine gained significant protection from lethal heroin doses, suggesting that this vaccine formulation is suitable for mitigating the harmful effects of heroin, even following month-long storage at room temperature.

A Stable Heroin Analogue That Can Serve as a Vaccine Hapten to Induce Antibodies That Block the Effects of Heroin and Its Metabolites in Rodents and That Cross-React Immunologically with Related Drugs of Abuse

An improved synthesis of a haptenic heroin surrogate 1 (6-AmHap) is reported. The intermediate needed for the preparation of 1 was described in the route in the synthesis of 2 (DiAmHap). A scalable procedure was developed to install the C-3 amido group. Using the Boc protectng group in 18 allowed preparation of 1 in an overall yield of 53% from 4 and eliminated the necessity of preparing the diamide 13. Hapten 1 was conjugated to tetanus toxoid and mixed with liposomes containing monophosphoryl lipid A as an adjuvant. The 1 vaccine induced high anti-1 IgG levels that reduced heroin-induced antinociception and locomotive behavioral changes following repeated subcutaneous and intravenous heroin challenges in mice and rats. Vaccinated mice had reduced heroin-induced hyperlocomotion following a 50 mg/kg heroin challenge. The 1 vaccine-induced antibodies bound to heroin and other abused opioids, including hydrocodone, oxycodone, hydromorphone, oxymorphone, and codeine.

Conjugate Vaccine Immunotherapy for Substance Use Disorder

Substance use disorder, especially in relation to opioids such as heroin and fentanyl, is a significant public health issue and has intensified in recent years. As a result, substantial interest exists in developing therapeutics to counteract the effects of abused drugs. A promising universal strategy for antagonizing the pharmacology of virtually any drug involves the development of a conjugate vaccine, wherein a hapten structurally similar to the target drug is conjugated to an immunogenic carrier protein. When formulated with adjuvants and immunized, the immunoconjugate should elicit serum IgG antibodies with the ability to sequester the target drug to prevent its entry to the brain, thereby acting as an immunoantagonist. Despite the failures of first-generation conjugate vaccines against cocaine and nicotine in clinical trials, second-generation vaccines have shown dramatically improved performance in preclinical models, thus renewing the potential clinical utility of conjugate vaccines in curbing substance use disorder. This review explores the critical design elements of drug conjugate vaccines such as hapten structure, adjuvant formulation, bioconjugate chemistry, and carrier protein selection. Methods for evaluating these vaccines are discussed, and recent progress in vaccine development for each drug is summarized.

Current status and future prospects for the development of substance abuse vaccines

INTRODUCTION

Substance use disorders (SUD) are a significant threat to both individual and public health. To date, SUD pharmacotherapy has focused primarily on agonist medications (i.e. nicotine replacement therapy for tobacco use disorder; methadone and buprenorphine for opioid use disorder), antagonist medications (i.e. naltrexone for opioid use disorder), and aversive therapy (i.e. disulfiram for alcohol use disorder). Pharmacotherapeutic approaches utilizing an immunological framework for medication development represent an important focus of study for treatment of these illnesses. Areas covered: This review discusses vaccines for treatment of substance use disorders. Using PubMed ( https://www.ncbi.nlm.nih.gov/pubmed/ ), we searched both preclinical and human clinical trials of vaccines for treatment of nicotine, cocaine, methamphetamine, and opioid use disorders. In addition, we searched for recently developed strategies for enhancement of the immunologic response through alteration of conjugate molecules and adjuvants. Expert commentary: Despite challenges in human clinical trials of SUD vaccines, a number of strategies have been introduced which may ultimately improve efficacy. These challenges, as well as their implications for vaccine development, are discussed. Additionally, the optimal conditions for research study and treatment are considered.

Development of a Clinically Viable Heroin Vaccine

Heroin is a highly abused opioid and incurs a significant detriment to society worldwide. In an effort to expand the limited pharmacotherapy options for opioid use disorders, a heroin conjugate vaccine was developed through comprehensive evaluation of hapten structure, carrier protein, adjuvant and dosing. Immunization of mice with an optimized heroin-tetanus toxoid (TT) conjugate formulated with adjuvants alum and CpG oligodeoxynucleotide (ODN) generated heroin "immunoantagonism", reducing heroin potency by >15-fold. Moreover, the vaccine effects proved to be durable, persisting for over eight months. The lead vaccine was effective in rhesus monkeys, generating significant and sustained antidrug IgG titers in each subject. Characterization of both mouse and monkey antiheroin antibodies by surface plasmon resonance (SPR) revealed low nanomolar antiserum affinity for the key heroin metabolite, 6-acetylmorphine (6AM), with minimal cross reactivity to clinically used opioids. Following a series of heroin challenges over six months in vaccinated monkeys, drug-sequestering antibodies caused marked attenuation of heroin potency (>4-fold) in a schedule-controlled responding (SCR) behavioral assay. Overall, these preclinical results provide an empirical foundation supporting the further evaluation and potential clinical utility of an effective heroin vaccine in treating opioid use disorders.