In vitro Efficacy of Ganciclovir, Foscarnet, Cidofovir and Idoxuridine Against Feline Herpesvirus (FHV-1)

Abstract

Abstract: : Purpose: Feline herpesvirus type 1 (FHV-1) - an alphaherpesvirus with biological behavior very similar to herpes simplex virus type 1 (HSV-1) - is a common cause of ocular disease in cats worldwide. Currently no drugs are licensed for treatment of FHV-1, however some drugs developed for HSV-1 have been tested in vitro and used clinically for this purpose. Efficacy against HSV-1 does not guarantee efficacy against FHV-1. The purpose of this work was to establish the in vitro efficacy of 4 antiviral drugs against FHV-1. Methods: Idoxuridine (IDU), ganciclovir (GCV), cidofovir (HPMPC), and foscarnet (PFA) were purchased from (IDU, PFA) or donated by (GCV, HPMPC) commercial manufacturers. Standard plaque reduction assays were performed in 12-well culture plates. Briefly, a plaque-purified field isolate of FHV-1 was adsorbed onto 75-90% confluent Crandell-Reese feline kidney (CRFK) cells. Plain carboxymethylcellulose and 1% fetal bovine serum (CMC/FBS) or one of 5 drug concentrations dissolved in CMC/FBS was placed into duplicate wells and incubated at 37C for 2-3 days. For each drug concentration, plaque numbers from duplicate wells were averaged and the percentage reduction relative to non-treated control wells was calculated. Trials were performed 3-5 times for each drug. Effective dose 50 (ED₅₀) was defined as the drug concentration at which plaque numbers were reduced by 50% relative to non-treated control wells. Cytotoxicity assays were performed once to assess drug toxicity to CRFK cells. CRFK cells were added to Dulbecco's modified Eagle medium (DMEM) with 10% FBS and one of three drug concentrations to approximate 1x, 2x or 10x ED₅₀ for each antiviral drug. Cells were observed for morphologic changes, harvested, and counted using a hemacytometer at 24, 48, and 72 hours. Cell numbers for each drug concentration were expressed as the percentage reduction relative to control flasks containing DMEM/FBS only. Results: Mean (+/- SD) ED₅₀ for IDU, GCV, HPMPC, and PFA was 4.4 (+/-0.8), 5.1 (+/- 0.3), 10.9 (+/- 0.6), and 224.4 (+/- 35.1) µM, respectively. At 10x ED₅₀, CRFK cell numbers at 72 hours were reduced by 50-75% for all drugs. However, at 1x ED₅₀, cell numbers at all time points were reduced by < 25% for GCV, HPMPC, and PFA, and 50% for IDU. Obvious changes in CRFK cell morphology were not observed for any drug. Conclusion: These data suggest that IDU, GCV, and HPMPC have approximately equivalent in vitro efficacy against FHV-1, while PFA appears relatively ineffective. Given the known clinical efficacy of IDU in cats infected with FHV-1, clinical trials of GCV and HPMPC are warranted.

Keywords: 322 antiviral drugs • 390 drug toxicity/drug effects • 514 pharmacology