36. Translation of an Adenovirus-Based Cocaine Vaccine dAd5GNE to a Clinical Trial

Abstract

dAd5GNE, an anti-cocaine vaccine based on a disrupted serotype 5 adenovirus gene transfer vector covalently conjugated to the cocaine analog GNE, evokes high titers of high affinity anti-cocaine antibodies that prevent cocaine from reaching its cognate receptor in the CNS. dAd5GNE has been shown to be effective in preclinical efficacy studies in mice, rats and nonhuman primates. In order to translate dAd5GNE to the clinic, this study focused on optimizing the choice of adjuvant, timing of vaccination regimen and dose. Adjuvant. To evaluate vaccine formulation, the adjuvants Adjuplex and Alum were assessed at a fixed dose to identify the formulation that evoked the fastest and highest titer response. BALB/c mice vaccinated with dAd5GNE/Adjuplex demonstrated high serum anti-cocaine antibody titers (>5×105) after a single administration while animals vaccinated with dAd5GNE/Alum required multiple injections to achieve high titers, and mice vaccinated with dAd5GNE/PBS plateaued at a lower titer. Therefore, a formulation based on the Adjuplex adjuvant was chosen for the clinical protocol. Timing. The measurement of titer half-life in nonhuman primates following individual vaccinations at variable intervals was used to inform the timing between vaccine boosts. The anti-cocaine antibody titer half-life in 8 dAd5GNE/Adjuplex vaccinated nonhuman primates was assayed regularly over the course of 1 yr and the titer half-life was calculated following each administration. The average half-life for all animals was 4.0 ± 0.2 wk. Continued cocaine use did not impact the titer half-life. These results indicate that a 4 wk interval for vaccinations is necessary to maintain the high titer anti-cocaine antibody levels. Dose. We measured the dose response in mice to provide the baseline for a phase I/II clinical trial and identified the range of doses that bracket the anticipated minimum effective dose and maximum tolerated dose. Doses from 0.04-40 μg of the vaccine were evaluated in BALB/c for the capacity to evoke antibody titers and to minimize access of radiolabelled cocaine to the CNS. Doses at and above 4 µg produced high anti-cocaine antibody titers above the threshold for efficacy (>5×105) which substantially reduced cocaine levels in the brain (p<0.0001 vs PBS). Using a modified weight adjusted dose from these results, the vaccine doses to be evaluated in the clinical trial were determined to be 100 to 1000 µg. The results of these studies combine to provide the specifications for critical vaccine design parameters required to translate the anti-cocaine vaccine to evaluation in a clinical trial. Based on these specifications the FDA has allowed the Adjuplex-formulated dAd5GNE vaccine to proceed to clinical study with a monthly vaccination regimen in recovering cocaine addicts.