Purpose: The aim of this study was to investigate intraocular properties and determine the highest nontoxic dose of hexadecyloxypropyl-cyclic-HPMPA (HDP-cHPMPA), a novel, potent, intravitreally injectable, slow-releasing crystalline drug for long-acting treatment of cytomegalovirus (CMV) retinitis.
Methods: Various concentrations of HDP-cHPMPA were first studied in vitro in a human foreskin fibroblast (HFF) cell line infected with human cytomegalovirus (HCMV) to determine the EC50. In vivo, 9 pigmented rabbits and 3 doses (55, 100, and 550 μg/eye) were tested in triplicate in 1 eye of each animal. The eyes were monitored with slit lamp, tonopen, indirect ophthalmoscopy, electroretinography (ERG), and histology. A confirmation toxicity study with the dose equivalent to the highest nontoxic dose in rabbit was performed in 9 guinea pig eyes (a second species) to study the potential adverse effect on intraocular pressure (IOP).
Results: In vitro testing in HFF cells showed an EC50 against HCMV of 0.02 μM, which is 75- and 60-fold greater than that of ganciclovir and cidofovir, respectively. All eyes injected with 550 μg/eye and 1 eye injected with 100 μg/eye of HDP-cHPMPA showed toxicity clinically (e.g., vitreous cells, disc edema, and retinal inflammation) as well as histologically (e.g., inflammatory cells in iris, vitreous, and retinal layers with disorganization). None of the eyes injected with 55 μg/eye of HDP-cHPMPA showed toxicity clinically (including ERG) and histologically. The equivalent dose (9.2 μg/eye) in the guinea pig eyes did not show toxicity either, including IOP evaluation (P > 0.05 at all time points after injection).
Conclusions: Intravitreal injection of the highest nontoxic dose of 55 μg/eye of HDP-cHPMPA in rabbit eyes yields a calculated intravitreal concentration of 65 μM, which is 3250-fold greater than the EC50 against HCMV (0.02 μM). Also, it does not cause hypotony in rabbit and guinea pig eyes and has a vitreous residence time of over 4 months.
