Evaluation of retinal toxicity and liposome encapsulation of the anti-CMV drug 2'-nor-cyclic GMP.

PURPOSE: Human cytomegalovirus (HCMV) is an important pathogen in the immunocompromised patient. CMV retinitis is a leading cause of blindness in patients with AIDS. Ganciclovir and foscarnet are currently the treatments being used for this retinitis, but they both have major toxicities when used systemically. Intravitreal therapy with ganciclovir has been used in some patients who cannot tolerate systemic treatment. The major problem with this modality is the necessity for administration of between 1 and 3 intravitreal injections per eye per week. 2'-nor-cyclic GMP is a nucleotide analog, a cyclic phosphate derivative of ganciclovir. Neutral salts of the compound are extremely water soluble, and the charged phosphate group at neutral pH make it an ideal candidate for encapsulation into a multivesicular liposome system. METHODS: The authors evaluated the retinal toxicity of the diethanolammonium salt 2'-nor-cyclic GMP by using electroretinographic, morphologic, and ophthalmoscopic techniques after intravitreal injections in rabbit eye. RESULTS: The intraocular therapeutic index for 2'-nor-cyclic GMP is 20. At the 10 micrograms dose, electroretinogram, ophthalmoscopic examination, and both light and electron microscopy revealed no abnormalities. Toxicity was evident at 50 micrograms and higher doses with ERG changes (loss of amplitude) and retinal pathology that varied from vacuolization of the retinal pigment epithelium and loss of height of the outer photoreceptor segment to loss of the entire outer retina. In addition, an in vitro drug release half-life of 1,000 hours (more than 75 times that of ganciclovir) was found for 2'-nor-cyclic GMP in liposome, which may be able to be exploited in the therapy of patients with CMV retinitis unable to tolerate toxic systemic therapy. CONCLUSION: The anti-CMV drug, 2'-nor-cyclic GMP, may be promising for intravitreal injection, particularly if encapsulated into liposomes.

An animal model of focal, subacute, viral retinitis.

To study local intravitreal therapies for retinitis due to herpes viruses, an animal model of focal, subacute, relatively nonlethal herpes family retinitis is needed. Herpes simplex virus type 1 (HSV-1) was injected into the subretinal space of 33 Dutch pigmented rabbit eyes. The animals were observed for up to 42 days after the inoculation. All inoculated eyes developed a focal, enlarging area of retinitis in a predictable manner, showing focal enlarging areas of retinal opacification and necrosis with variable retinal hemorrhage. In the inoculated eyes, retinal detachment developed in all animals within 21 days; 33% of the animals developed focal retinitis in the uninoculated eye. Histologic examination showed encephalitis to be present in 11 (73%) of the 15 animals studied after 1 week. This model may be used to evaluate the therapeutic efficacy of new antiviral agents and modalities in the treatment of herpes family viral retinitis. The model is most similar to herpes simplex or zoster retinitis in humans, but also shares some similarities (and differences) with cytomegalovirus (CMV) retinitis in humans.

Atypical healing of cytomegalovirus retinitis. Significance of persistent border opacification.

PURPOSE: To analyze a phenomenon seen in patients with acquired immune deficiency syndrome (AIDS) with cytomegalovirus (CMV) retinitis undergoing systemic antiviral treatment: a persistent white border opacification on the edge of healed CMV retinitis. PATIENTS AND METHODS: The authors prospectively evaluated a population of 137 patients with AIDS and CMV retinitis during a 44-month period. Eleven patients (12 eyes) who were undergoing maintenance antiviral treatment were identified with an atypical healing response--the persistence of a white flat border opacification that did not advance for many weeks to months. Patient records and photographs were reviewed. Results of one autopsy were analyzed with histopathology and special stains. RESULTS: The persistent white edge maintained (without advancement or smoldering) for an average of 11.6 weeks (range, 4 to 41 weeks). This border opacification was not affected by reinduction treatment in the six patients to whom reinduction was given. Results from histopathologic examination of one patient with a persistent white border are presented: these results show that dead cytomegalic cells formed stable structures within the retina, causing white opacification that could be confused with active lesions. Immunoperoxidase stains identified CMV antigens. CONCLUSION: This persistent white border opacification, which does not advance or smolder, represents an important clinical entity that should be recognized during antiviral treatment for CMV retinitis. It can often be observed. If it is not recognized as a stable configuration, patients may undergo unnecessary reinductions with potentially toxic doses of antiviral medications.