Evaluation of a θ-defensin in a murine model of herpes simplex virus type 1 keratitis

PURPOSE. To test the activity of a synthetic theta-defensin, retrocyclin ( RC)- 2, in a murine herpes simplex virus ( HSV)-1 keratitis model. METHODS. The in vitro antiviral activity of RC- 2 against HSV- 1 KOS was determined by yield reduction and viral inactivation assays. Efficacy in an experimental murine HSV- 1 keratitis model was tested using pre- or postinfection treatment with 0.1% peptide in PBS with or without 2% methylcellulose. Viral titers in the tear film were determined by plaque assay. RESULTS. RC- 2 inhibited HSV- 1 KOS in vitro with an EC50 of 10 mu M (similar to 20 mu g/mL) in yield- reduction assays, but was not directly virucidal. RC- 106 ( a less active analogue) did not inhibit HSV- 1 KOS in culture. Incubating the virus with RC- 2 or applying the peptide in 2% methylcellulose to the cornea before viral infection significantly reduced the severity of ocular disease, but postinfection treatment with 0.1% RC- 2 in PBS with or without 2% methylcellulose did not. Viral titers were significantly reduced on some days after infection in the preincubation and prophylaxis groups. CONCLUSIONS. RC- 2 was active against HSV- 1 KOS in cultures and showed protective activity in vivo when used in a prophylactic mode, but the peptide showed limited activity in a postinfection herpes keratitis model. These findings support data obtained from experiments with HIV-1, HSV-2, and influenza A, indicating that RCs inhibit the entry of viruses rather than their replication.