Efficacy of ASP2151, a helicase-primase inhibitor, against thymidine kinase-deficient herpes simplex virus type 2 infection in vitro and in vivo

Department of Virology, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan.
Antiviral research (Impact Factor: 3.94). 12/2011; 93(2):301-4. DOI: 10.1016/j.antiviral.2011.11.015
Source: PubMed


ASP2151 was developed as a novel inhibitor of herpes simplex virus (HSV) and varicella-zoster virus helicase-primase. The anti-HSV activity of ASP2151 toward a clinical HSV isolate with acyclovir (ACV)-resistant/thymidine kinase (TK)-deficiency was characterized in vitro and in vivo using a plaque reduction assay and the ear pinna infection in mice. The IC(50) ranged from 0.018 to 0.024 μg/ml, indicating the susceptibility of TK-deficient HSV-2 was similar to that of wild-type HSV-2 strains. Anti-HSV activity of ASP2151 in vivo was evaluated in mice infected with wild-type HSV-2 and TK-deficient HSV-2. ASP2151 significantly reduced the copy numbers of wild-type HSV-2 and TK-deficient HSV-2 at the inoculation ear pinna, while valacyclovir significantly reduced the copy number of wild type HSV-2 but not that of TK-deficient HSV-2 in the inoculated ear pinna. Thus, ASP 2151 showed therapeutic efficacy in mice infected with both wild-type and TK-deficient HSV-2. In conclusion, ASP2151 is a promising novel herpes helicase-primase inhibitor that indicates the feasibility of ASP2151 for clinical application for the treatment of HSV infections, including ACV-resistant/TK-deficient HSV infection.

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    ABSTRACT: ASP2151 is an antiherpes agent targeting the helicase-primase complex of herpes simplex virus (HSV)-1, HSV-2, and varicella-zoster virus (VZV). We characterized the ASP2151-resistant HSV-1 and HSV-2 variants or mutants based on findings from sequencing analysis, growth, pathogenicity, and susceptibility testing, identifying several single base-pair substitutions resulting in amino acid changes in the helicase and primase subunit of ASP2151-resistant mutants. Amino acid alterations in the helicase subunit were clustered near helicase motif IV in the UL5 helicase gene of both HSV-1 and HSV-2, while the primase subunit substitution associated with reduced susceptibility, R367H, was found in ASP2151-resistant HSV-1 mutants. However, while susceptibility in the ASP2151-resistant HSV mutants to existing antiherpes agents was equivalent to that in wild-type HSV strains, ASP2151-resistant HSV mutants showed attenuated in vitro growth capability and in vivo pathogenicity compared with the parent strains. Taken together, our present findings demonstrated that important amino acid substitutions associated with reduced susceptibilities of HSV-1 and HSV-2 to ASP2151 exist in both the helicase and primase subunits of the helicase-primase complex, and that mutations in this complex against ASP2151 might confer defects in viral replication and pathogenicity.
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    ABSTRACT: ASP2151 (amenamevir) is a helicase-primase inhibitor against herpes simplex virus type 1 (HSV-1), HSV-2, and varicella zoster virus. Here, to determine and analyze the correlation between the pharmacodynamic (PD) and pharmacokinetic (PK) parameters of ASP2151, we examined the PD profile of ASP2151 using in vitro plaque reduction assay and a murine model of HSV-1 infection. ASP2151 inhibited the in vitro replication of HSV-1 with a mean EC(50) value of 14 ng/mL. In the cutaneously HSV-1-infected mouse model, ASP2151 dose-dependently suppressed intradermal HSV-1 growth, with the effect reaching a plateau at a dose of 30 mg/kg/day. The dose-fractionation study showed that intradermal HSV-1 titers were below the detection limit in mice treated with ASP2151 at 100 mg/kg/day divided into two daily doses and at 30 or 100 mg/kg/day divided into three daily doses. The intradermal HSV-1 titer correlated with the C(max), AUC(24h), and time above 100 ng/mL of ASP2151 plasma concentration (T>100). The continuous infusion of ASP2151 effectively decreased intradermal HSV-1 titers below the limit of detection in mice in which the plasma ASP2151 concentration reached 79-145 ng/mL. Our findings suggest that the antiviral efficacy of ASP2151 is most closely associated with the PK parameter T>100 in HSV-1-infected mice. Based on these results, we propose that a plasma ASP2151 concentration exceeding 100 ng/mL for 21-24 h per day provides the maximum efficacy in HSV-1-infected mice.
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Koji Chono