Alexander Birkmann

Helicase-primase inhibitor pritelivir for HSV-2 infection

BACKGROUND Pritelivir, an inhibitor of the viral helicase-primase complex, exhibits antiviral activity in vitro and in animal models of herpes simplex virus (HSV) infection. We tested the efficacy and safety of pritelivir in otherwise healthy persons with genital HSV-2 infection. METHODS We randomly assigned 156 HSV-2-positive persons with a history of genital herpes to receive one of four doses of oral pritelivir (5, 25, or 75 mg daily, or 400 mg weekly) or placebo for 28 days. Participants obtained daily swabs from the genital area for HSV-2 testing, which was performed with a polymerase-chain-reaction assay. Participants also maintained a diary of genital signs and symptoms. The primary end point was the rate of genital HSV shedding. RESULTS HSV shedding among placebo recipients was detected on 16.6% of days; shedding among pritelivir recipients was detected on 18.2% of days among those receiving 5 mg daily, 9.3% of days among those receiving 25 mg daily, 2.1% of days among those receiving 75 mg daily, and 5.3% of days among those receiving 400 mg weekly. The relative risk of viral shedding with pritelivir, as compared with placebo, was 1.11 (95% confidence interval [CI], 0.65 to 1.87) with the 5-mg daily dose, 0.57 (95% CI, 0.31 to 1.03) with the 25-mg daily dose, 0.13 (95% CI, 0.04 to 0.38) with the 75-mg daily dose, and 0.32 (95% CI, 0.17 to 0.59) with the 400-mg weekly dose. The percentage of days with genital lesions was also significantly reduced, from 9.0% in the placebo group to 1.2% in both the group receiving 75 mg of pritelivir daily (relative risk, 0.13; 95% CI, 0.02 to 0.70) and the group receiving 400 mg weekly (relative risk, 0.13; 95% CI, 0.03 to 0.52). The rate of adverse events was similar in all groups. CONCLUSIONS Pritelivir reduced the rates of genital HSV shedding and days with lesions in a dose-dependent manner in otherwise healthy men and women with genital herpes. (Funded by AiCuris; ClinicalTrials.gov number, NCT01047540.).

Mismatch primer-based PCR reveals that helicase–primase inhibitor resistance mutations pre-exist in herpes simplex virus type 1 clinical isolates and are not induced during incubation with the inhibitor

OBJECTIVES Previous studies suggested that helicase-primase inhibitor (HPI) resistance mutations can be selected at relatively high frequency from some isolates of herpes simplex virus type 1 (HSV-1). An intentional mismatch primer (IMP) PCR was developed to detect three known HPI resistance mutations well above the expected background frequency. The objective of this study was to provide proof that HPI resistance mutations pre-exist at relatively high frequency in some clinical isolates obtained from individuals naive to HPIs. METHODS Three different IMP PCRs were standardized to detect critical HPI resistance mutations (K356N or K356T in UL5, or A899T in UL52) at 10-100 times the expected background frequency (<10(-6)). Thirty HSV-1 clinical isolates were then screened for the resistance mutations in the absence of the inhibitor using IMP PCR. RESULTS Among 30 clinical isolates that were all susceptible to the HPI, BAY 57-1293, 5 were shown to contain UL5 mutations at 10-100 times higher than the expected frequency. No UL52 resistance mutations were encountered in this study. CONCLUSIONS The detection of HPI-resistant mutations in some clinical isolates by means of IMP PCR proved that the mutations pre-exist and showed that they are not induced during incubation with the inhibitor.

Mutations close to functional motif IV in HSV-1 UL5 helicase that confer resistance to HSV helicase–primase inhibitors, variously affect virus growth rate and pathogenicity

Herpes simplex virus (HSV) helicase-primase (HP) is the target for a novel class of antiviral compounds, the helicase-primase inhibitors (HPIs), e.g. BAY 57-1293. Although mutations in herpesviruses conferring resistance to nucleoside analogues are commonly associated with attenuation in vivo, to date, this is not necessarily true for HPIs. HPI-resistant HSV mutants selected in tissue culture are reported to be equally pathogenic compared to parental virus in animal models. Here we demonstrate that a slow-growing HSV-1 mutant, with the BAY 57-1293-resistance mutation Gly352Arg in UL5 helicase, is clearly less virulent than its wild-type parent in a murine zosteriform infection model. This contrasts with published results obtained for a mutant containing a different HPI-resistance substitution (Gly352Val) at the same location, since this mutant was reported to be fully pathogenic. We believe our report to be the first to describe an HPI-resistant HSV-1 mutant, that is markedly less virulent in vivo and slowly growing in tissue culture compared to the parental strain. Another BAY 57-1293-resistant UL5 mutant (Lys356Gln), which showed faster growth characteristics in cell culture, however, was at least equally virulent compared to the parent strain.

Effects of therapy using a helicase-primase inhibitor (HPI) in mice infected with deliberate mixtures of wild-type HSV-1 and an HPI-resistant UL5 mutant.

Point mutations in the HSV-1 UL5 (helicase) gene confer resistance to helicase-primase inhibitors (HPIs), e.g. BAY 57-1293. Such mutations normally occur at a frequency of < or =10(-6)PFU. However, individual HSV-1 laboratory strains and some clinical isolates contained resistance mutations (e.g. UL5: Lys356Asn) at 10(-4)PFU. To address the possibility that pre-existing mutants at high frequency might have an impact on therapy using HPIs, deliberate mixtures were prepared to contain the SC16 UL5: Lys356Asn mutant in SC16 wild-type in the proportion of 1/500 or 1/50PFU. Mice were infected in the neck-skin with 5x10(4)PFU/mouse of wt alone, mutant alone, or the respective mixture. The mutant could not be detected in infectious virus yields from mice inoculated with the 1/500 mixture. However, resistant mutant was recovered from some treated mice inoculated with the 1/50 mixture. All mice inoculated with mixtures remained responsive to BAY 57-1293-therapy with no increase in clinical signs compared to treatment of wt-infected mice.

Effect of Pritelivir Compared With Valacyclovir on Genital HSV-2 Shedding in Patients With Frequent Recurrences: A Randomized Clinical Trial

Importance Current therapy of herpes infections relies on nucleoside analogues. Pritelivir is a well-tolerated novel herpes simplex virus (HSV) helicase-primase inhibitor that reduced genital shedding and lesions. Objective To compare the efficacy of pritelivir with valacyclovir for suppression of genital HSV-2 infection. Design, Setting, and Participants A phase 2, randomized, double-blind, crossover clinical trial at clinical research centers in 4 US cities (October 2012-July 2013) compared daily oral doses of 100 mg of pritelivir with 500 mg of valacyclovir. The planned sample size was 98 adults, allowing for detection of a 50% reduction in viral shedding between the study treatments. Healthy adults with 4 to 9 annual genital HSV-2 recurrences were eligible. 45 participants were randomized to receive pritelivir [corrected] and 46 to receive valacyclovir first when the US Food and Drug Administration placed the trial on clinical hold based on findings in a concurrent nonclinical toxicity study, and the sponsor terminated the study. Interventions Participants took the first drug for 28 days followed by 28 days of washout before taking the second drug for 28 days. Throughout treatment, the participants collected genital swabs 4 times daily for testing by HSV polymerase chain reaction assays. Main Outcomes and Measures The primary end point was within-participant genital HSV shedding while receiving pritelivir compared with valacyclovir. Secondary end points included the quantity of HSV in positive swabs and the frequency of genital lesions and shedding episodes. Results Of the 91 randomized participants (median age, 48 years; 57 women [63%]), 56 had completed both treatment periods at the time of the studys termination. In intent-to-treat analyses, HSV shedding was detected in 2.4% (173 of 7276 ) of swabs during pritelivir treatment compared with 5.3% (392 of 7453) during valacyclovir treatment (relative risk [RR], 0.42 [corrected]; 95% CI, 0.21 to 0.82; P = .01). In swabs with HSV, the mean quantity of HSV was 3.2 log10 copies/mL during pritelivir treatment vs 3.7 log10 copies/mL during valacyclovir treatment (difference, -0.1; 95% CI, -0.6 to 0.5; P = .83). Genital lesions were present on 1.9% of days in the pritelivir group vs 3.9% in the valacyclovir group (RR, 0.40; 95% CI, 0.17-0.96; P = .04). The frequency of shedding episodes did not differ by group, with 1.3 per person-month for pritelivir and 1.6 per person-month for valacyclovir (RR, 0.80; 95% CI, 0.52 to 1.22; P = .29). Treatment-emergent adverse events occurred in 62.3% of participants in the pritelivir group and 69.2% of participants in the valacyclovir group. Conclusions and Relevance Among adults with frequently recurring genital HSV-2, the use of pritelivir compared with valacyclovir resulted in a lower percentage of swabs with HSV detection over 28 days. Further research is needed to assess longer-term efficacy and safety. Trial Registration clinicaltrials.gov Identifier: NCT01658826.

HSV antivirals - current and future treatment options.

Herpes simplex virus (HSV) types 1 and 2 can cause infections with clinical manifestations ranging from benign and generally self-limiting blisters or sores as seen in labial and genital herpes through to severe and in rare cases even life-threatening infections. At present, approved treatments for herpes simplex virus are almost all nucleoside analogs. Novel antiviral approaches include therapeutic vaccines, with the most advanced having successfully completed Phase 2 clinical development. Moreover, several small molecules approaches are being developed for the treatment of genital or labial HSV infections. Of particular interest are two novel compounds (amenamevir and pritelivir) belonging to the new class of helicase-primase inhibitors with promising Phase 2 data.

Baseline sensitivity of HSV-1 and HSV-2 clinical isolates and defined acyclovir-resistant strains to the helicase–primase inhibitor pritelivir

Fifty-nine US isolates of HSV-1 and HSV-2 obtained between 1998 and 2004 were tested for sensitivity to the helicase-primase inhibitor, pritelivir (AIC316, BAY 57-1293) by plaque-reduction assay. All isolates, which were collected prior to any clinical use of primase-helicase inhibitors, were sensitive and showed mean EC50 values of 0.026 and 0.029μM for HSV-1 and HSV-2, respectively. Furthermore, several laboratory-selected acyclovir-resistant HSV mutants were also sensitive to pritelivir. These data provide a baseline for HSV sensitivity to pritelivir in general population before it is introduced and broadly used to treat HSV infection. The data also validate pritelivir as an appropriate therapy for nucleoside-resistant HSV infections.

Mathematical modeling of herpes simplex virus-2 suppression with pritelivir predicts trial outcomes

A mathematical model for antiviral clinical trials improves dose selection and understanding of drug-virus interaction. Dosing HSV Choosing the correct drug dose can be the difference between the success or the failure of a clinical trial, yet this decision is frequently stochastic. Current models aim to improve this process by predicting the pharmacokinetics and pharmacodynamics of an antiviral agent. Schiffer et al. expand these models to include viral and immunological factors that influence the course of infection. They model herpes simplex virus shedding during dose trials of pritelivir, a DNA helicase-primase inhibitor. They find that not only does pritelivir decrease viral shedding by inhibiting replication in epithelial cells at appropriate doses but also it limits downstream viral spread to additional sites. Their model successfully predicts outcome in a subsequent trial and may serve as a tool to improve dosing decisions in the clinic. Pharmacokinetic and pharmacodynamic models estimate the potency of antiviral agents but do not capture viral and immunologic factors that drive the natural dynamics of infection. We designed a mathematical model that synthesizes pharmacokinetics, pharmacodynamics, and viral pathogenesis concepts to simulate the activity of pritelivir, a DNA helicase-primase inhibitor that targets herpes simplex virus. Our simulations recapitulate detailed viral kinetic shedding features in five dosage arms of a phase 2 clinical trial. We identify that in vitro estimates of median effective concentration (EC50) are lower than in vivo values for the drug. Nevertheless, pritelivir potently decreases shedding at appropriate doses based on its mode of action and long half-life. Although pritelivir directly inhibits replication in epithelial cells, our model indicates that pritelivir also indirectly limits downstream viral spread from neurons to genital keratinocytes, within genital ulcers, and from ulcer to new mucosal sites of infection. We validate our model based on its ability to predict outcomes in a subsequent trial with a higher dose. The model can therefore be used to optimize dose selection in clinical practice.

Lead Development of Thiazolylsulfonamides with Carbonic Anhydrase Inhibitory Action

A series of congeners structurally related to pritelivir, N-[5-(aminosulfonyl)-4-methyl-1,3-thiazol-2-yl]-N-methyl-2-[4-(2-pyridinyl)phenyl]acetamide, a helicase-primase inhibitor for the treatment of herpes simplex virus infections, was prepared. The synthesized primary and secondary sulfonamides were investigated as inhibitors of six physiologically and pharmacologically relevant human (h) carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, the cytosolic enzymes hCA I and II, the mitochondrial ones hCA VA and VB, and the transmembrane, tumor associated hCA IX and XII. Low nanomolar inhibition KI values were detected for all of them, with a very interesting and well-defined structure-activity relationship. As many CAs are involved in serious pathologies, among which are cancer, obesity, epilepsy, glaucoma, etc., sulfonamide inhibitors as those reported here may be of interest as drug candidates. Furthermore, pritelivir itself is an effective inhibitor of some CAs, also inhibiting whole blood enzymes from several mammalian species, which may be a favorable pharmacokinetic feature of the drug which can be transported throughout the body bound to blood CA I and II.

Pharmacokinetics-Pharmacodynamics of the Helicase-Primase Inhibitor Pritelivir following Treatment of Wild-Type or Pritelivir-Resistant Virus Infection in a Murine Herpes Simplex Virus 1 Infection Model

ABSTRACT Herpes simplex virus (HSV) infections can cause considerable morbidity. Transmission of HSV-2 has become a major health concern, since it has been shown to promote transmission of other sexually transmitted diseases. Pritelivir (AIC316, BAY 57-1293) belongs to a new class of HSV antiviral compounds, the helicase-primase inhibitors, which have a mode of action that is distinct from that of antiviral nucleoside analogues currently in clinical use. Analysis of pharmacokinetic-pharmacodynamic parameters is a useful tool for the selection of appropriate doses in clinical trials, especially for compounds belonging to new classes for which no or only limited data on therapeutic profiles are available. For this purpose, the effective dose of pritelivir was determined in a comprehensive mouse model of HSV infection. Corresponding plasma concentrations were measured, and exposures were compared with efficacious concentrations derived from cell cultures. The administration of pritelivir at 10 mg/kg of body weight once daily for 4 days completely suppressed any signs of HSV infection in the animals. Associated plasma concentrations adjusted for protein binding stayed above the cell culture 90% effective concentration (EC90) for HSV-1 for almost the entire dosing interval. Interestingly, by increasing the dose 6-fold and prolonging the treatment duration to 8 days, it was possible to treat mice infected with an approximately 30-fold pritelivir-resistant but fully pathogenic HSV-1 virus. Corresponding plasma concentrations exceeded the EC90 of this mutant for <8 h, indicating that even suboptimal exposure to pritelivir is sufficient to achieve antiviral efficacy, possibly augmented by other factors such as the immune system.