Scott H. James

Antiviral therapy for herpesvirus central nervous system infections: neonatal herpes simplex virus infection, herpes simplex encephalitis, and congenital cytomegalovirus infection.

Herpesvirus infections of the central nervous system (CNS) are a significant cause of morbidity and mortality, including long-term neurologic sequelae. Among the family of herpesviruses, the most significant CNS infections are due to herpes simplex virus (HSV) and cytomegalovirus (CMV). The onset of HSV CNS infection can occur in neonates as well as older children and adults. CNS infection associated with CMV occurs predominantly in the perinatal period, but may also be seen rarely in children and adults, especially in immunocompromised individuals. Although advances in antiviral agents have led to improved outcomes, there is still a need for more effective treatments.

Current and future therapies for herpes simplex virus infections: mechanism of action and drug resistance

Forty years after the discovery of acyclovir (ACV), it remains the mainstay of therapy for herpes simplex virus (HSV) infections. Since then, other antiviral agents have also been added to the armamentarium for these infections but ACV remains the therapy of choice. As the efficacy of ACV is reassessed, however, it is apparent that a therapy with increased efficacy, reduced potential for resistance, and improved pharmacokinetics would improve clinical outcome, particularly in high risk patients. Inhibitors of viral targets other than the DNA polymerase, such as the helicase primase complex, are of particular interest and will be valuable as new therapeutic approaches are conceived. This review focuses on currently approved HSV therapies as well as new systemic therapies in development.

Neonatal Herpes Simplex Virus Infection: Epidemiology and Treatment

Herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) are highly prevalent viruses capable of establishing lifelong infection. Genital herpes in women of childbearing age represents a major risk for mother-to-child transmission (MTCT) of HSV infection, with primary and first-episode genital HSV infections posing the highest risk. The advent of antiviral therapy with parenteral acyclovir has led to significant improvement in neonatal HSV disease mortality. Further studies are needed to improve the clinicians ability to identify infants at increased risk for HSV infection and prevent MTCT, and to develop novel antiviral agents with increased efficacy in infants with HSV infection.

Neonatal Herpes Simplex Virus Infection.

Herpes simplex virus (HSV) 1 and HSV-2 infections are highly prevalent worldwide and are characterized by establishing lifelong infection with periods of latency interspersed with periodic episodes of reactivation. Acquisition of HSV by an infant during the peripartum or postpartum period results in neonatal HSV disease, a rare but significant infection that can be associated with severe morbidity and mortality, especially if there is dissemination or central nervous system involvement. Diagnostic and therapeutic advances have led to improvements in mortality and, to a lesser extent, neurodevelopmental outcomes, but room exists for further improvement.

Cyclopropavir Inhibits the Normal Function of the Human Cytomegalovirus UL97 Kinase

ABSTRACT Cyclopropavir (CPV) is active against human cytomegalovirus (CMV), as well as both variants of human herpesvirus 6 and human herpesvirus 8. The mechanism of action of CPV against CMV is similar to that of ganciclovir (GCV) in that it is phosphorylated initially by the CMV UL97 kinase, resulting in inhibition of viral DNA synthesis. Resistance to CPV maps to the UL97 kinase but is associated primarily with H520Q mutations and thus retains good antiviral activity against most GCV-resistant isolates. An examination of CMV-infected cultures treated with CPV revealed unusual cell morphology typically associated with the absence of UL97 kinase activity. A surrogate assay for UL97 kinase activity confirmed that CPV inhibited the activity of this enzyme and that its action was similar to the inhibition seen with maribavir (MBV) in this assay. Combination studies using real-time PCR indicated that, like MBV, CPV also antagonized the efficacy of GCV and were consistent with the observed inhibition of the UL97 kinase. Deep sequencing of CPV-resistant laboratory isolates identified a frameshift mutation in UL27, presumably to compensate for a loss of UL97 enzymatic activity. We conclude that the mechanism of action of CPV against CMV is complex and involves both the inhibition of DNA synthesis and the inhibition of the normal activity of the UL97 kinase.

Selection and Recombinant Phenotyping of a Novel CMX001 and Cidofovir Resistance Mutation in Human Cytomegalovirus

ABSTRACT CMX001 is an orally available lipid acyclic nucleotide phosphonate that delivers high intracellular levels of cidofovir (CDV)-diphosphate and exhibits enhanced in vitro antiviral activity against a wide range of double-stranded DNA viruses, including cytomegalovirus (CMV). Mutations in the DNA polymerase of CMV that impart resistance to CDV also render the virus resistant to CMX001. Here, we report a novel resistance mutation that arose under the selective pressure of CMX001. The wild-type CMV strain AD169 was propagated in human foreskin fibroblasts under increasing concentrations of CMX001 over 10 months, and the resulting strain (named CMX001R) was less susceptible to CDV and CMX001 in a plaque reduction assay. Genotypic analysis of virus strain CMX001R via conventional sequencing of the genes encoding the CMV DNA polymerase (UL54) and UL97 kinase (UL97) demonstrated one mutation that changed the wild-type aspartate to glutamate at position 542 in UL54. A recombinant virus with this novel D542E mutation was generated via bacterial artificial chromosome-mediated marker transfer experiments. Subsequent phenotypic resistance analysis of the D542E mutant demonstrated reductions in susceptibility of greater than 10-fold to CMX001 and CDV, but no resistance to foscarnet (FOS) or ganciclovir (GCV). Analysis of replicative fitness showed that both strain CMX001R and the D542E mutant viruses demonstrated a smaller plaque phenotype and slower replication kinetics than their respective parent viruses. These data describe the first resistance mutation generated under the selective pressure of CMX001 and suggest that CMX001 may have a unique resistance profile associated with reduced viral replication and maintenance of sensitivity to FOS and GCV.

Advances in the prevention and treatment of congenital cytomegalovirus infection.

Purpose of review Cytomegalovirus (CMV) is the most common cause of congenital infection in the world. Symptomatic infants are at increased risk of developing permanent sequelae, including sensorineural hearing loss and neurodevelopmental delay. Advances in the treatment and prevention of congenital CMV infection are a high priority nationally and globally. Recent findings In symptomatic infants, antiviral therapy with 6 months of oral valganciclovir improves hearing and neurodevelopmental outcomes. Strategies to prevent congenital or maternal CMV infections, including the use of CMV hyperimmune globulin and development of a maternal vaccine, have yet to yield positive results. Summary The clinical significance of congenital CMV infection, developments in antiviral therapy, and efforts to prevent congenital disease are herein reviewed.

Treatment of Herpes Simplex Virus Infections in Pediatric Patients: Current Status and Future Needs

Herpes simplex virus type 1 (HSV‐1) and type 2 (HSV‐2) are members of the Herpesviridae family and are characterized by their ability to establish latency after primary infection and subsequently reactivate. HSV infections in the neonatal and pediatric populations range from uncomplicated mucocutaneous diseases to severe, life‐threatening infections involving the central nervous system (CNS). The antiviral agent acyclovir has significantly improved treatment outcomes of HSV infections, including the frequency of mucocutaneous recurrences and mortality associated with CNS and disseminated infections.

Mother-to-Child Transmission of Herpes Simplex Virus

Infections with herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2), both alpha herpesviruses, are highly prevalent worldwide. Both HSV types commonly cause genital infection, which, when acquired or reactivated during pregnancy, carries with it the risk of transmission to the fetus or neonate. Women who acquire primary or first-episode genital herpes during pregnancy are at greater risk for transmitting the infection than are women with recurrent genital herpes. Because viral infection and reactivation are frequently asymptomatic, many affected women are unaware of their infection and risk of transmission to their infants. Neonatal HSV infection can have devastating long-term consequences, especially when the central nervous system (CNS) is involved. Treatment of affected neonates with intravenous acyclovir has improved outcomes but there is room for further improvement, especially in regard to CNS disease. Working with pregnant women to prevent mother-to-child transmission of HSV is an important component in reducing the overall disease burden of neonatal HSV infections.

Helicase‐Primase as a Target of New Therapies for Herpes Simplex Virus Infections

The seminal discovery of acyclovir 40 years ago heralded the modern era of truly selective antiviral therapies and this drug remains the therapy of choice for herpes simplex virus infections. Yet by modern standards, its antiviral activity is modest and new drugs against novel molecular targets such as the helicase‐primase have the potential to improve clinical outcome, particularly in high‐risk patients. A brief synopsis of current therapies for these infections and clinical need is provided to help provide an initial perspective. The function of the helicase‐primase complex is then summarized and the development of new inhibitors of the helicase‐primase complex, such as pritelivir and amenamevir, is discussed. We review their mechanism of action, propensity for drug resistance, and pharmacokinetic characteristics and discuss their potential to advance current therapeutic options. Strategies that include combinations of these inhibitors with acyclovir are also considered, as they will likely maximize clinical efficacy.