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 – 1,500 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.

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.

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.