Oral Bioavailability and In Vivo Efficacy of the Helicase-Primase Inhibitor BILS 45 BS against Acyclovir-Resistant Herpes Simplex Virus Type 1

Abstract

Nucleoside analogs such as acyclovir (ACV) and penciclovir and prodrugs thereof have been approved as drugs of choice for the treatment of herpes simplex virus (HSV) infections (1, 11). While nucleoside-based therapeutics are quite effective for the treatment of primary and recurrent mucocutaneous infections, present medications are not effective for the treatment of nucleoside-resistant herpesvirus infections in immunocompromised individuals (4,5,29). Moreover, nucleoside-based antiviral therapeutics have limited effects on the establishment of latent HSV infections (6,17,31). Therefore, significant improvements in therapy may be achievable with distinct inhibitors with improved efficacy and pharmacokinetic (PK) properties and a new mechanism of action. We have reported previously on the discovery of specific non-nucleoside-based inhibitors of the HSV type 1 (HSV-1) helicase-primase (10). This enzyme is composed of the virus-encoded UL5, UL8, and UL52 gene products, which are all essential for HSV DNA replication and growth (3,7,9,19,23). The most optimized aminothiazolyl-phenyl compounds exhibited potent antiviral activity against a series of HSV strains analyzed in vitro, including HSV-1 and HSV-2 strains that are ACV r . One of the inhibitors, BILS 179 BS, showed antiviral activity in murine models of wild-type HSV disease after oral administration (10), but its activity against ACV r HSV disease had not been evaluated. In the present report, we provide a detailed examination of the PK and pharmacodynamic properties of a helicase-primase inhibitor, BILS 45 BS, in a mouse model of ACV r HSV infection. PK studies were done with hairless mice, where BILS 45 BS demonstrated in vivo efficacy against wild-type HSV-1 infection with a 50% effective dose (ED 50 ) of 56 mg/kg. The athymic nude mouse model was chosen for the present study because ACV r HSV-1 fails to induce significant disease in normal mice (2, 14-16). In addition, since ACV r HSV infections cause significant disease mainly in the immunocompromised patient population, information obtained with these immunodeficient animals may have clinical relevance (14-16). Our results show that BILS 45 BS, an analog structurally related to BILS 179 BS, exhibited excellent oral efficacy against ACV r HSV-1 infections in nude mice, highlighting the potential of this novel class of antiherpetic agents for the treatment of ACV r HSV disease in humans. MATERIALS AND METHODSCell culture and viruses. All of the cell culture reagents and media used in this study were obtained from Gibco BRL (Burlington, Ontario, Canada). Cells were from the American Type Culture Collection (Manassas, Va.). Vero (African green monkey kidney) cells were grown in Dulbecco's modified Eagle's medium supplemented with 8% fetal bovine serum, 100 U of penicillin per ml, 100 g of streptomycin sulfate per ml, and 100 g of kanamycin sulfate per ml. Baby hamster kidney (BHK) 21/C13 (ATCC CCL10) cells were grown in ␣-MEM instead of Dulbecco's modified Eagle's medium. All cells were grown at 37°C in an ...

Understanding Helicases as a Means of Virus Control

“…HSV infected mice fed BILS 179 BS, or its derivative BILS 45 BS, have fewer and smaller cutaneous and genital lesions than mice fed a placebo. HSV viral titers also show a dose dependent reduction following administration of the BILS compounds [1,170]. Mice infected with acyclovir-resistant HSV also respond to oral administration of BILS 45 BS [170].…”

“…A later derivative called BILS 45 BS, which is absorbed more rapidly into the blood, differs only by the lack of a methyl group [170]. In the presence of the inhibitor, HSV primase activity is inhibited with an IC 50 of 0.15 µM, while the DNA unwinding activity of the HSV helicase is inhibited with an IC 50 of 1.3 µM.…”

“…HSV viral titers also show a dose dependent reduction following administration of the BILS compounds [1,170]. Mice infected with acyclovir-resistant HSV also respond to oral administration of BILS 45 BS [170]. Thus, these aminothiazolphenyl-based molecules are a promising class of compounds for the treatment of nucleoside-resistant HSV disease in humans.…”

Management of multidrug‐resistant viruses in the immunocompromised host

“…BILS 179-BS and BILS 45-BS have shown potent activity against HSV-1 and HSV-2, including ACV-resistant strains (Crute et al, 2002;Duan et al, 2003). In plaque reduction assays they were found to be nearly 5-10 times more potent than ACV against wild-type HSV virus.…”

“…More importantly, BILS 45-BS was up to 20 times more active against viral mutants with ACV resistance. The compounds have been taken forward into animal models with encouraging results (Crute et al, 2002;Duan et al, 2003) but have not yet made it into the clinic.…”