Pharmacokinetics of a potential human cytomegalovirus therapeutic, a phosphorothioate oligonucleotide, after intravitreal injection in the rabbit

The disposition of ISIS 2922, a phosphorothioate oligonucleotide for treatment of cytomegalovirus associated retinitis, was evaluated in rabbits. Vitreous humor and retina samples were collected from rabbits that received a single intravitreal injection of 66 mu g [C-14]-labeled ISIS 2922 and were analyzed using anion exchange HPLC, Four hr postdosing, the concentration of ISIS 2922 in vitreous humor was 3.3 mu M. The elimination of ISIS 2922 from the vitreous humor exhibited first-order kinetics with a t(1/2) of 62 hr, By 10 days postdosing, the mean concentration of ISIS 2922 in rabbit vitreous humor had decreased to 0.17 mu M, which represented 22% of the total radioactivity remaining in the vitreous, The remaining 78% coeluted on anion exchange HPLC with shorter oligonucleotides, In retina, ISIS 2922 accumulated over the first 5 days postdosing, reaching a maximum concentration of 3.5 mu M, and then declined thereafter with an estimated t(1/2) of 79 hr. By 10 days postdosing when only 24% of the total radioactivity in the retina was parent compound, the concentration of ISIS 2922 remained at 1.6 mu M, which was 10 times higher than the concentration in the vitreous humor, Whereas the elimination of full-length ISIS 2922 and total radioactivity from the vitreous humor occurred at nearly equal rates, ISIS 2922 disappeared more rapidly than did total radioactivity from the retina, suggesting a greater role for metabolism in the clearance process from retina than the vitreous, Alternatively, the results are consistent with metabolites being cleared from the vitreous at approximately the same rate as parent compound while in the retina metabolites may be cleared more slowly, The data were analyzed with a user-defined pharmacokinetic model, which was then used to predict the potential for accumulation of ISIS 2922 during clinical dosing.