Intraocular properties of an alkoxyalkyl derivative of cyclic 9-(S)-(3-hydroxyl-2-phosphonomehoxypropyl) adenine, an intravitreally injectable anti-HCMV drug in rabbit and guinea pig.
OBJECTIVE
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 microg/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 microM, which is 75- and 60-fold greater than that of ganciclovir and cidofovir, respectively. All eyes injected with 550 microg/eye and 1 eye injected with 100 microg/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 microg/eye of HDP-cHPMPA showed toxicity clinically (including ERG) and histologically. The equivalent dose (9.2 microg/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 microg/eye of HDP-cHPMPA in rabbit eyes yields a calculated intravitreal concentration of 65 microM, which is 3250-fold greater than the EC50 against HCMV (0.02 microM). Also, it does not cause hypotony in rabbit and guinea pig eyes and has a vitreous residence time of over 4 months.
Tammewar
Ajay M
AM
Jacobs Retina Center at Shiley Eye Center, University of California-San Diego Department of Ophthalmology, La Jolla, San Diego, CA 92037, USA.
Cheng
Lingyun
L
Hostetler
Karl Y
KY
Falkenstein
Iryna
I
Beadle
James R
JR
Barron
Erin C
EC
Kozak
Igor
I
Freeman
William R
WR
D000225:Adenine / Q000031:analogs & derivatives* / Q000633:toxicity; D000818:Animals; D000998:Antiviral Agents / Q000633:toxicity*; D002460:Cell Line; D003587:Cytomegalovirus / Q000187:drug effects*; D017726:Cytomegalovirus Retinitis / Q000188:drug therapy; D003692:Delayed-Action Preparations; D004596:Electroretinography; D005123:Eye / Q000166:cytology / Q000187:drug effects*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000821:virology; D006168:Guinea Pigs; D007267:Injections; D007429:Intraocular Pressure / Q000187:drug effects; D009943:Organophosphorus Compounds / Q000633:toxicity*; D011817:Rabbits; D014822:Vitreous Body
D000998:Antiviral Agents; D003692:Delayed-Action Preparations; D009943:Organophosphorus Compounds; C072574:cyclic-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine; D000225:Adenine