gs-5806 and Respiratory-Syncytial-Virus-Infections

Respiratory syncytial virus (RSV) infection is the leading cause of hospitalisation for children under 5 years of age and causes excess mortality in the elderly. There is still no approved vaccine available, although the disease can be curtailed by RSV-specific monoclonal antibody. The only antiviral drug approved for the treatment of RSV infection is ribavirin aerosol, but this treatment is cumbersome and its efficacy is questionable. A new antiviral, GS-5806, which interferes with virus-cell fusion, has proven efficacious in experimental RSV infections in adults.

Topics: Administration, Inhalation; Antiviral Agents; Humans; Indazoles; Pyrazoles; Respiratory Syncytial Virus Infections; Ribavirin; Sulfonamides; Treatment Outcome

Presatovir is an oral respiratory syncytial virus (RSV) fusion inhibitor targeting RSV F protein. In a double-blind, placebo-controlled study in healthy adults experimentally infected with RSV (Memphis-37b), presatovir significantly reduced viral load and clinical disease severity in a dose-dependent manner.. Viral RNA from nasal wash samples was amplified and the F gene sequenced to monitor presatovir resistance. Effects of identified amino acid substitutions on in vitro susceptibility to presatovir, viral fitness, and clinical outcome were assessed.. Twenty-eight treatment-emergent F substitutions were identified. Of these, 26 were tested in vitro; 2 were not due to lack of recombinant virus recovery. Ten substitutions did not affect presatovir susceptibility, and 16 substitutions reduced RSV susceptibility to presatovir (2.9- to 410-fold). No substitutions altered RSV susceptibility to palivizumab or ribavirin. Frequency of phenotypically resistant substitutions was higher with regimens containing lower presatovir dose and shorter treatment duration. Participants with phenotypic presatovir resistance had significantly higher nasal viral load area under the curve relative to those without, but substitutions did not significantly affect peak viral load or clinical manifestations of RSV disease.. Emergence of presatovir-resistant RSV occurred during therapy but did not significantly affect clinical efficacy in participants with experimental RSV infection.

Topics: Adolescent; Adult; Amino Acid Substitution; Dose-Response Relationship, Drug; Double-Blind Method; Drug Resistance, Viral; Humans; Indazoles; Middle Aged; Respiratory Syncytial Virus Infections; Respiratory Syncytial Viruses; Sulfonamides; Viral Fusion Protein Inhibitors; Viral Load; Young Adult

GS-5806 is a novel, orally bioavailable RSV fusion inhibitor discovered following a lead optimization campaign on a screening hit. The oral absorption properties were optimized by converting to the pyrazolo[1,5-a]-pyrimidine heterocycle, while potency, metabolic, and physicochemical properties were optimized by introducing the para-chloro and aminopyrrolidine groups. A mean EC50 = 0.43 nM was found toward a panel of 75 RSV A and B clinical isolates and dose-dependent antiviral efficacy in the cotton rat model of RSV infection. Oral bioavailability in preclinical species ranged from 46 to 100%, with evidence of efficient penetration into lung tissue. In healthy human volunteers experimentally infected with RSV, a potent antiviral effect was observed with a mean 4.2 log10 reduction in peak viral load and a significant reduction in disease severity compared to placebo. In conclusion, a potent, once daily, oral RSV fusion inhibitor with the potential to treat RSV infection in infants and adults is reported.

Topics: Administration, Oral; Animals; Antiviral Agents; Dogs; Dose-Response Relationship, Drug; Drug Discovery; Humans; Indazoles; Macaca fascicularis; Microbial Sensitivity Tests; Molecular Structure; Pyrazoles; Rats; Respiratory Syncytial Virus Infections; Respiratory Syncytial Viruses; Structure-Activity Relationship; Sulfonamides; Virus Internalization

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and pneumonia in infants. Effective treatment for RSV infection is a significant unmet medical need. While new RSV therapeutics are now in development, there are very few animal models that mimic the pathogenesis of human RSV, making it difficult to evaluate new disease interventions. Experimental infection of Holstein calves with bovine RSV (bRSV) causes a severe respiratory infection that is similar to human RSV infection, providing a relevant model for testing novel therapeutic agents. In this model, viral load is readily detected in nasal secretions by quantitative real-time PCR (qRT-PCR), and cumulative symptom scoring together with histopathology evaluations of infected tissue allow for the assessment of disease severity. The bovine RSV model was used to evaluate the antiviral activity of an RSV fusion inhibitor, GS1, which blocks virus entry by inhibiting the fusion of the viral envelope with the host cell membrane. The efficacy of GS1, a close structural analog of GS-5806 that is being developed to treat RSV infection in humans was evaluated in two randomized, blind, placebo-controlled studies in bRSV-infected calves. Intravenous administration of GS1 at 4 mg/kg of body weight/day for 7 days starting 24 h or 72 h postinoculation provided clear therapeutic benefit by reducing the viral load, disease symptom score, respiration rate, and lung pathology associated with bRSV infection. These data support the use of the bovine RSV model for evaluation of experimental therapeutics for treatment of RSV.

Topics: Animals; Antiviral Agents; Bronchiolitis; Cattle; Cattle Diseases; Cell Line; Cell Membrane; Double-Blind Method; Humans; Indazoles; Lung; Male; Pyrazoles; Respiratory Syncytial Virus Infections; Respiratory Syncytial Virus, Bovine; Respiratory Syncytial Virus, Human; Sulfonamides; Viral Load

Respiratory syncytial virus (RSV) is a common cause of infant hospitalizations and is increasingly recognized as a cause of considerable morbidity and mortality. No accepted antiviral treatment exists.. We conducted a double-blind, placebo-controlled study of GS-5806, an oral RSV-entry inhibitor, in healthy adults who received a clinical challenge strain of RSV intranasally. Participants were monitored for 12 days. At the time of a positive test for RSV infection or 5 days after inoculation, whichever occurred first, participants were randomly assigned to receive GS-5806 or placebo in one of seven sequential cohorts. Cohorts 1 to 4 received a first dose of 50 mg of GS-5806 and then 25 mg daily for the next 4 days, cohort 5 received a first dose of 50 mg and then 25 mg daily for the next 2 days, cohort 6 received one 100-mg dose, and cohort 7 received a first dose of 10 mg and then 5 mg daily for the next 4 days. Dose selection for cohorts 5, 6, and 7 occurred after an interim analysis of data for cohorts 1 to 4. The primary end point was the area under the curve (AUC) for the viral load, which was assessed after administration of the first dose through the 12th day after inoculation. Secondary end points were mucus weight and symptom scores.. Among the 54 participants in cohorts 1 to 4 who were infected with RSV, active treatment was associated with a lower viral load (adjusted mean, 250.7 vs. 757.7 log10 plaque-forming-unit equivalents [PFUe] × hours per milliliter; P<0.001), lower total mucus weight (mean, 6.9 g vs. 15.1 g; P=0.03), and a lower AUC for the change from baseline in symptom scores (adjusted mean, -20.2 vs. 204.9 × hours; P=0.005). The results were similar in cohorts 5, 6, and 7. Adverse events, including low neutrophil counts and increased levels of alanine aminotransferase, were more common among participants receiving GS-5806.. Treatment with GS-5806 reduced the viral load and the severity of clinical disease in a challenge study of healthy adults. (Funded by Gilead Sciences; ClinicalTrials.gov number, NCT01756482.).

Topics: Administration, Oral; Adolescent; Adult; Antiviral Agents; Area Under Curve; Double-Blind Method; Female; Humans; Indazoles; Male; Pyrazoles; Respiratory Syncytial Virus Infections; Respiratory Syncytial Viruses; Severity of Illness Index; Sulfonamides; Viral Load; Young Adult

Respiratory syncytial virus (RSV) is a globally prevalent viral infection with limited treatment options which hospitalizes millions each year. Treatment options have been limited to palivizumab, a monoclonal antibody, approved for prophylaxis in high-risk infants and ribavirin with very limited efficacy and significant safety concerns. This Perspective surveys the range of direct acting antiviral agents (DAAs) that target key steps in the viral life cycle. A number of approaches to DAAs have produced landmark clinical studies over the past few years, notably in fusion and nucleoside inhibitors, and an update of the clinical status of these compounds is provided. Non-nucleoside inhibitors of replication are reviewed in addition to inhibitors of other mechanisms, notably the RSV N and G proteins. This article will provide an informative perspective of the current status of drug discovery targeted at providing an effective therapy for RSV infection.

Topics: Animals; Antiviral Agents; Drug Discovery; Humans; Nucleocapsid Proteins; Palivizumab; Respiratory Syncytial Virus Infections; Respiratory Syncytial Virus, Human; Small Molecule Libraries; Viral Fusion Proteins

GS-5806 is a small-molecule inhibitor of human respiratory syncytial virus fusion protein-mediated viral entry. During viral entry, the fusion protein undergoes major conformational changes, resulting in fusion of the viral envelope with the host cell membrane. This process is reproduced in vitro using a purified, truncated respiratory syncytial virus (RSV) fusion protein. GS-5806 blocked these conformational changes, suggesting a possible mechanism for antiviral activity.

Topics: Antiviral Agents; Indazoles; Protein Conformation; Pyrazoles; Respiratory Syncytial Virus Infections; Respiratory Syncytial Virus, Human; Sulfonamides; Viral Proteins

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections in infants and young children. In addition, RSV causes significant morbidity and mortality in hospitalized elderly and immunocompromised patients. Currently, only palivizumab, a monoclonal antibody against the RSV fusion (F) protein, and inhaled ribavirin are approved for the prophylactic and therapeutic treatment of RSV, respectively. Therefore, there is a clinical need for safe and effective therapeutic agents for RSV infections. GS-5806, discovered via chemical optimization of a hit from a high-throughput antiviral-screening campaign, selectively inhibits a diverse set of 75 RSV subtype A and B clinical isolates (mean 50% effective concentration [EC50] = 0.43 nM). The compound maintained potency in primary human airway epithelial cells and exhibited low cytotoxicity in human cell lines and primary cell cultures (selectivity > 23,000-fold). Time-of-addition and temperature shift studies demonstrated that GS-5806 does not block RSV attachment to cells but interferes with virus entry. Follow-up experiments showed potent inhibition of RSV F-mediated cell-to-cell fusion. RSV A and B variants resistant to GS-5806, due to mutations in F protein (RSV A, L138F or F140L/N517I, and RSV B, F488L or F488S), were isolated and showed cross-resistance to other RSV fusion inhibitors, such as VP-14637, but remained fully sensitive to palivizumab and ribavirin. In summary, GS-5806 is a potent and selective RSV fusion inhibitor with antiviral activity against a diverse set of RSV clinical isolates. The compound is currently under clinical investigation for the treatment of RSV infection in pediatric, immunocompromised, and elderly patients.

Topics: Antiviral Agents; Bronchi; Cell Fusion; Cell Line; Drug Evaluation, Preclinical; Drug Resistance, Viral; Humans; Indazoles; Pyrazoles; Respiratory Syncytial Virus Infections; Respiratory Syncytial Virus, Human; Sulfonamides; Virus Internalization

Topics: Antiviral Agents; Female; Humans; Indazoles; Male; Pyrazoles; Respiratory Syncytial Virus Infections; Respiratory Syncytial Viruses; Sulfonamides