Pre-clinical safety and toxicology profile of a candidate vaccine to treat oxycodone use disorder

Opioid use disorders (OUD) and overdose represent a public health threat, resulting in thousands of deaths annually worldwide. Vaccines offer a promising treatment for OUD and potentially the prevention of fatal overdoses. The Oxy(Gly)₄-sKLH Conjugate Vaccine, Adsorbed (Oxy(Gly)₄-sKLH) has shown promising pre-clinical efficacy at reducing the behavioral and pharmacological effects of oxycodone. To support its clinical evaluation, a GLP toxicology study was performed to address the safety of Oxy(Gly)₄-sKLH. Sprague Dawley rats were vaccinated with either aluminum adjuvant (alum) or vaccine adsorbed on alum. Low and high doses of Oxy(Gly)₄-sKLH, equivalent to a 1X or 47X human dose, respectively, were administered every two weeks for a total of four vaccinations. Both vaccine doses induced high antibody titers. Vaccine-related toxicity was assessed postmortem in one experimental group after receiving the fourth immunization of the vaccine’s high dose. For the remaining experimental groups, rats were challenged with 1.5 mg/kg/day s.c. oxycodone for 7 days after the fourth vaccination to assess whether concurrent exposure to oxycodone in vaccinated animals resulted in toxicity. All rats, except a subset of the aluminum control and the high dose vaccine groups, were sacrificed following oxycodone exposure. These subsets were allowed a four weeks recovery period prior to euthanasia. In this study, no Oxy(Gly)₄-sKLH-related hematology, clinical chemistry, urinalysis, body weight, organ weight, or anatomic pathology toxicological findings were observed. These results demonstrate that the Oxy(Gly)₄-sKLH vaccine is well tolerated, is immunogenic even at low doses, and does not produce undesired side effects in rats.