Retinal toxicity of ISIS 2922 and ISIS 4015, phosphorothioate oligonucleotides complementary to human cytomegalovirus (CMV) and herpes simplex virus (HSV) RNA, were evaluated. The intravitreal concentration of ISIS 2922 found not to cause permanent toxic changes in the rabbit retina was 10 microM and in the pig retina, 5 microM. The 3 microM concentration was associated with a transient inflammatory response, and 1 microM caused no retinal toxicity or inflammation. ISIS 4015 showed very mild toxicity with no permanent retinal changes and very mild inflammation at doses of 10 microM; this dose was effective in ameliorating or preventing HSV-1 retinitis when injected 1 day and 1 week prior to virus inoculation. These oligonucleotides have a low intraocular therapeutic index. Attempts to improve the therapeutic index of these compounds are indicated. Only a clinical trial can determine the toxicity profile of ISIS 2922 for the treatment of CMV retinitis.

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The effect of liposome-encapsulated (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC; cidofovir) was evaluated as prophylaxis in a rabbit model of experimentally induced retinitis caused by preretinal inoculation of herpes simplex virus type 1 (HSV-1). Cidofovir (100 micrograms) in liposomes (0.1 mL) was injected intravitreally 10-120 days before retinal inoculation with HSV-1. Twenty-two of 26 eyes pretreated with liposome-encapsulated cidofovir 10-60 days before HSV-1 inoculation were protected from experimentally induced retinitis, and 2 of 5 eyes pretreated 120 days before inoculation were protected. Intravitreal levels of cidofovir were low (0.7 microgram/mL) but detectable 120 days after injection. One 100-micrograms intravitreal injection of liposome-encapsulated cidofovir appears to have a remarkably potent and prolonged (up to 4 months) antiviral effect in this experimental model of HSV-1 retinitis. Since HPMPC is even more potent against cytomegalovirus than HSV-1, liposome-encapsulated cidofovir may prove to be effective local therapy for AIDS patients with cytomegalovirus retinitis.

Acyclovir diphosphate dimyristoylglycerol (ACVDP-DG) is a lipid prodrug which is active against ACVresistant strains of herpes simplex virus because of its intracellular metabolism to ACV monophosphate. In human cytomegalovirus (HCMV)-infected MRC-5 cells, ACVDP-DG was ninefold more active than ACV. When liposomal [8-3 H]ACVDP-DG was injected intravitreally at the maximum nontoxic dose of 1 mol in rabbits, the drug remained above its estimated 90% HCMV-inhibitory concentration for 18 days. Intravitreal ganciclovir persists above its 90% inhibitory concentration for only 1 to 2 days. ACVDP-DG may be useful as a local treatment for HCMV retinitis.Human cytomegalovirus (HCMV) retinitis occurs in 15 to 42% of patients with AIDS (9,10,12,14,17). Two antiviral drugs currently available for the treatment of HCMV retinitis are ganciclovir (GCV) and foscarnet, both of which are associated with significant toxicities (5) and the emergence of resistance (4, 16). Intravitreal injections with GCV have been used in patients not tolerating systemic therapy (11,23). The main disadvantage of this local therapy is the need for four to six injections per eye per month (1,8,13,21).Acyclovir diphosphate dimyristoylglycerol (ACVDP-DG) is an analog of CDP diacylglycerol and is very active in herpes simplex virus type 1-and type 2-infected cells in vitro (15). ACVDP-DG is metabolized to ACV monophosphate intracellularly and retains substantial in vitro antiviral activity in ACVresistant thymidine kinase-deficient mutants of herpes simplex virus type 1 and type 2 because of its unique metabolism (15). In this paper, we report the antiviral activity of ACVDP-DG in HCMV-infected MCR-5 cells and the ocular toxicity and pharmacokinetics after intravitreal injections of liposomal ACVDP-DG in rabbit eyes.Human embryonic lung fibroblast cells (MRC-5) and HCMV (strain AD169) were obtained from the American Type Culture Collection (Rockville, Md.). Virus stocks were prepared by infecting subconfluent MRC-5 cells; the titers of HCMV in the cell-free supernatant were determined, and aliquots were stored in liquid nitrogen. Subconfluent MRC-5 cells in 24-well culture dishes were pretreated for 24 h with drugs in minimal essential medium containing 2% fetal bovine serum and antibiotics. The medium was removed, and virus was added, absorbed for 1 h at 37ЊC, aspirated, and replaced with the drug dilutions. After 5 days of incubation, HCMV DNA was quantified in triplicate by nucleic acid hybridization with an HCMV antiviral susceptibility test kit from Diagnostic Hybrids, Inc. (Athens, Ohio). Results are expressed as percentages of the amount of HCMV-specific DNA in untreated HCMV-infected control cells.The concentration of ACVDP-DG which inhibited the replication of the AD169 strain of HCMV in MRC-5 cells by 50% (IC 50 ) was at 2.4 M, compared with IC 50 s of 22 and 1.1 M for ACV and GCV, respectively (Fig. 1). The concentration of GCV required to reduce HCMV DNA by 90% was 28 M, compared with 36 M for ACVDP-DG and 316 M for ACV. The 50% toxic dose of...