Antiviral activity and ocular kinetics of antisense oligonucleotides designed to inhibit CMV replication.

PURPOSE To compare the antiviral activity and ocular distribution of first- and second-generation antisense oligonucleotides intended for the treatment of cytomegalovirus (CMV) retinitis. METHODS The antiviral activity of ISIS 13312 and ISIS 2922 (Isis Pharmaceuticals, Inc., Carlsbad, CA) against 10 clinical CMV isolates was compared with a plaque-reduction assay. The ocular pharmacokinetics were compared after intravitreal injection in rabbits (36-90 microg) and monkeys (125-500 microg). Vitreous and/or retina were collected after single and multiple injections to characterize ocular distribution, clearance, and accumulation. Oligonucleotide concentrations were measured by capillary gel electrophoresis and immunohistochemical techniques. RESULTS ISIS 13312 and ISIS 2922 demonstrated comparable antiviral activity that was consistent among the 10 clinical isolates examined (50% inhibitory concentration [IC(50)], <1 microM). Activity was independent of the resistance of CMV isolates to DNA polymerase inhibitors. After intravitreal injection, the kinetics of ISIS 2922 and ISIS 13312 were characterized by clearance from vitreous and distribution to the retina; however, ISIS 2922 was cleared more quickly from the retina than ISIS 13312. The half-life of ISIS 13312 in the monkey retina was approximately 2 months. Retinal concentrations of ISIS 13312 were dose dependent, with approximately a twofold increase in concentration after once-monthly doses compared with single-dose concentrations. Immunohistochemical analysis indicated that both oligonucleotides were efficiently distributed to numerous ocular tissues, including retina, ciliary body, and optic nerve. CONCLUSIONS ISIS 13312 possesses antiviral activity and pharmacokinetic properties that favor its use as a therapeutic agent in treatment of CMV retinitis. The half-life of ISIS 13312 in retina is longer than that of ISIS 2922, potentially allowing for less frequent administration.