Abstract

Opioid conjugate vaccines have shown promise in attenuating the behavioral effects of heroin or morphine in animals. The goal of this study was to extend this approach to oxycodone (OXY), a commonly abused prescription opioid. Haptens were generated by adding tetraglycine (Gly)₄ or hemisuccinate (HS) linkers at the 6-position of OXY. Immunization of rats with OXY(Gly)₄ conjugated to the carrier proteins bovine serum albumin (BSA) or keyhole limpet hemocyanin (KLH) produced high-titer antibodies to OXY and its metabolite oxymorphone with substantially lower affinities for other structurally related opioid agonists and antagonists. There was no measurable binding of antibody by the (Gly)₄ linker alone or off-target opioids methadone and buprenorphine. OXY(HS) conjugates were less immunogenic despite achieving protein haptenation ratios comparable to OXY(Gly)₄-BSA. In rats given a single intravenous dose of OXY, immunization with OXY(Gly)₄-KLH increased OXY protein binding and retention in serum while decreasing its unbound (free) concentration in plasma and distribution to brain. Vaccine efficacy correlated with serum antibody titers, and it was greatest in rats given the lowest OXY dose (0.05 mg/kg) but was significant even after a larger OXY dose (0.5 mg/kg), equivalent to the high end of the therapeutic range in humans. These effects of OXY(Gly)₄-KLH on drug disposition were comparable to those of nicotine or cocaine vaccines that are in clinical trials as addiction treatments. Immunization with OXY(Gly)₄-KLH also reduced OXY analgesia in a thermal nociception test. These data support further study of vaccination with the OXY(Gly)₄-KLH immunogen as a potential treatment option for OXY abuse or addiction.