Antiviral effect in human cytomegalovirus-infected cells, pharmacokinetics, and intravitreal toxicology in rabbits of acyclovir diphosphate dimyristoylglycerol

Ganciclovir release rates in vitreous from different formulations of 1-O-hexadecylpropanediol-3-phospho-ganciclovir

PURPOSE

To determine the optimal formulation of lipid prodrug, 1-O-hexadecyloxypropyl-phospho-ganciclovir (HDP-P-GCV), for intravitreal delivery.

METHODS

Equal concentrations of crystalline or liposomal HDP-P-GCV were exposed to rabbit whole vitreous, core vitreous, peripheral vitreous, human plasma, and heat inactivated rabbit vitreous, and the samples were incubated at 37 degrees C for one week. Aliquots were taken at day 1, 2, 3, and 7 and subjected to HPLC analysis for conversion to GCV.

RESULTS

The resultant concentration of GCV from crystalline HDP-P-GCV in vitreous was 198 +/- 49 microM (n = 3) at day 1 and 1253 +/- 248 microM (n = 3) at day 7. The resultant concentration of GCV from the liposomal formulation of HDP-P-GCV in vitreous was much lower, yielding a concentration of 66 +/- 7 microM (n = 3) at day 1 and 243 +/- 39 microM (n = 3) at day 7 (P < 0.001, t Test). When the crystalline HDP-P-GCV was incubated with heat-inactivated vitreous, the detectable GCV concentrations were low (22 microM) and did not increase over time. The concentration of GCV detected from the crystalline HDP-P-GCV in the core vitreous was 19.69 +/- 3.84 microM (n = 3) at day 1 and 1537.36 +/- 177.14 microM (n = 3) at day 7. The concentration of GCV released from crystalline HDP-P-GCV in peripheral vitreous was 32.86 +/- 5.07 microM (n = 3) at day 1 and 1805.78 +/- 327.94 microM (n = 3) at day 7. Detectable GCV concentration from both core and peripheral vitreous samples increased over time, however, the magnitude of GCV release from peripheral vitreous samples was higher (P < 0.05, t Test).

CONCLUSION

In vitreous, HDP-P-GCV as a crystalline formulation was converted to GCV more rapidly than liposomal formulation of HDP-P-GCV. Vitreous cells may play an important role in the metabolism of either formulation of HDP-P-GCV delivered into vitreous.

Intravitreal toxicology and therapeutic efficacy of the carboxymethyl ester of the 1-O-octadecyl-sn-glycerol-3-phosphonoformate (ODG-PFA-O-Me), a novel lipid antiviral prodrug for intraocular drug delivery

This study was conducted to evaluate the vitreous clarity and intraocular therapeutic index of three preparations ofthe carboxymethyl ester of 1-O-octadecyl-sn-glycerol-3-phosphonoformate (ODG-PFA-O-Me), a long acting lipid derivative of foscarnet with potent anti-CMV activity. Twenty-six New Zealand white rabbits were intravitreally injected with one of three preparations of ODG-PFA-O-Me or control diluent. The vitreous clarity was graded after injection using indirect ophthalmoscopy and fundus photography. Drug intraocular toxicity was evaluated by electroretinography and by post-sacrifice tissue pathology using light and electron microscopy. Intravitreal injection of micellar ODG-PFA-O-Me showed variable local retinal toxicity and vitreal compound aggregates in eyes with the middle and high doses. The intraocular therapeutic index was lower than 465:1. Intravitreal injection of liposomal ODG-PFA-O-Me, either free acid or sodium salt, revealed clear vitreous for the 0.632 and 0.84 mM final intravitreal concentrations. No retinal toxicity was confirmed for the 1.12 mM final intravitreal concentration at the eight week observation following injection. The intraocular therapeutic index was between 585-1037:1. ODG-PFA-O-Me possesses better vitreous compatibility than ODG-PFA. Liposomal ODG-PFA-O-Me can be intravitreally injected with a resulting clear vitreous and high intraocular therapeutic index. Liposomal ODG-PFA-O-Me could be a long acting nontoxic intravitreous injectable drug for CMV retinitis.