PET study of intravitreal adalimumab pharmacokinetics in a uveitis rat model

Adalimumab is an anti-TNFα drug approved for uveitis treatment by subcutaneous injection. This administration route exposes patients to systemic adverse effects and makes difficult to obtain therapeutic drug concentrations in the site of action due to the anatomical and physiological barriers of the eye. These inconveniences could be avoided by intravitreal injection. The aim of this study is to evaluate the pharmacokinetic profile and the biodistribution of the intravitreal administration of ⁸⁹Zr-adalimumab in a uveitis rat model using PET imaging. Adalimumab was radiolabelled to ⁸⁹Zr with a maximum specific activity of 10 MBq/mg. Four μL containing ≃1.74 MBq of ⁸⁹Zr-labelled adalimumab were injected into the vitreous. A microPET acquisition was carried out immediately after the injection and at different time points through a 10-day study and blood samples were obtained through the tail vein. Radiolabelling was successfully performed with a radiochemical purity after ultrafiltration of 99.69 %. The antibody ocular pharmacokinetics followed a one-compartment model, showing an intraocular elimination half-life of 15.57 h for healthy rats and  33.64 h for rats with uveitis, implying that ⁸⁹Zr-adalimumab remains around two times longer in rats with the disease compared to healthy ones. However, blood concentration half-life had similar values in both groups. In conclusion, this study shows for the first time the ocular and blood pharmacokinetic analysis of adalimumab in a uveitis model in rats.