Respiratory Syncytial Virus Fusion Inhibitors Research Articles

A new mechanism of respiratory syncytial virus entry inhibition by small-molecule to overcome K394R-associated resistance.

Respiratory syncytial virus (RSV) infection is a major public health concern, and many small-molecule candidates targeting the viral fusion (F) protein are associated with a considerable risk of inducing drug-resistant mutations. This study investigated virological features of the K394R variant, a mutant strain conferring resistance to multiple RSV fusion inhibitors. Our results demonstrated that the K394R variant is highly fusogenic in cell cultures and more pathogenic than the parental strain in mice. The small-molecule inhibitor CL-A3-7 substantially reduced in vitro and in vivo infections of both wild-type RSV and the K394R variant by blocking the interaction of viral F protein with its cellular receptor, showing a new mechanism of action for small-molecules to inhibit RSV infection and overcome K394R-associated resistance.

Extensive Multiple 2D-/3D-QSAR Modeling, Molecular Docking and Pharmacophoric Approaches for Piperazinylquinoline Derivatives as Respiratory Syncytial Virus Fusion Inhibitors.

The human respiratory syncytial virus (RSV) is responsible for causing upper and lower respiratory tract infections in young children. RSV Fusion (F) protein is a surface glycoprotein that facilitates virus entry into host cells. Thus, newer designing of RSV Fusion (F) protein inhibitors is required on an urgent basis. In the present study, we have developed statistically robust. Quantitative structure-activity relationship (QSAR) models for the effective designing of newer analogues of piperazinylquinoline derivatives (H1-H12). Our developed models were retained with high statistical parameters (R2 > 0.6 and Q2 > 0.5). Our developed pharmacophore, model (AADHRR_2) (indicating that two hydrogen bond acceptors, one hydrogen bond donor, one hydrophobic group, and two aromatic rings) is crucial for retaining the activities of piperazinylquinoline derivatives against RSV. Moreover, docking analysis of 12 new analogues on RSV pre-F in complex with 5C4 Fab (PDB ID: 5W23) and post-F trimeric protein (PDB ID: 3RRR) suggested higher affinities of these molecules against studied targets with good docking scores. Thus, one can implement developed QSAR models, docking analogy and Pharmacophore models for identifications of potent leads for designed molecules as RSV Fusion (F) protein inhibitors.

A pilot phase 2a, randomized, double-blind, placebo-controlled study to explore the antiviral activity, clinical outcomes, safety, and tolerability of rilematovir at two dose levels in non-hospitalized adults with respiratory syncytial virus infection

ObjectivesTo assess the antiviral effect, clinical outcomes, and safety of the respiratory syncytial virus (RSV) fusion inhibitor rilematovir in non-hospitalized RSV-infected adults. MethodsThis phase 2a, double-blind, multicentre study randomly assigned RSV-positive adult outpatients ≤5 days from symptom onset 1:1:1 to receive rilematovir 500 mg, 80 mg, or placebo once-daily for 7 days. Antiviral effect was assessed by RSV RNA viral load (VL), measured by quantitative RT-PCR, and Kaplan-Meier (KM) estimates of time to undetectable VL. Clinical course was assessed by KM estimates of median time to resolution of key RSV symptoms assessed through patient-reported outcomes. ResultsRSV-positive patients (n = 72) were randomly assigned; 66 had confirmed RSV infection and received rilematovir 500 mg (n = 23), 80 mg (n = 21) or placebo (n = 22). Differences versus placebo in mean RSV RNA VL area under the curve (90% CI) through days 3, 5 and 8, respectively, were 0.09 (−0.837; 1.011), −0.10 (−2.171; 1.963), and −1.03 (−4.746; 2.682) log10 copies.day/mL for rilematovir 500 mg, and 1.25 (0.291; 2.204), 2.53 (0.430; 4.634), and 3.85 (0.097; 7.599) log10 copies.day/mL for rilematovir 80 mg. KM estimates of median (90% CI) time-to-first confirmed undetectable VL were 5.9 (3.85; 6.90), 8.0 (6.86; 12.80) and 7.0 (6.62; 10.88) days and 5.7 (2.93; 7.01), 8.1 (6.74; 12.80) and 7.9 (6.62; 11.74) days in patients with symptom onset ≤3 days, for rilematovir 500 mg, 80 mg, and placebo, respectively. KM estimates of median (90% CI) time to resolution of key RSV symptoms were 7.1 (5.03; 11.43), 7.6 (5.93; 8.32), and 9.6 (5.95; 14.00) days for rilematovir 500 mg, 80 mg, and placebo, respectively; and in patients with symptom onset ≤3 days, median 8.0, 7.6, and 11.8 days, respectively. DiscussionRilematovir use, initiated early, suggests a potential clinical benefit in RSV-infected adults, with data supporting development of RSV therapeutic options. Trial registrationThis study is registered with clinicaltrials.gov (NCT03379675).

A randomized controlled trial of presatovir for respiratory syncytial virus after lung transplant

Respiratory syncytial virus (RSV) infection in lung transplant recipients is associated with high morbidity. This study evaluated the RSV fusion inhibitor presatovir in RSV-infected lung transplant recipients. In this international Phase 2b, randomized, double-blind, placebo-controlled trial (NCT02534350), adult lung transplant recipients with symptomatic confirmed RSV infection for ≤7 days received oral presatovir 200 mg on day 1 and 100 mg daily on days 2 to 14, or placebo (2:1), with follow-up through day 28. There were 2 coprimary endpoints: time-weighted average change in nasal RSV load from day 1 to 7, calculated from nasal swabs, in the full analysis set ([FAS]; all patients who received study drug and had quantifiable baseline nasal RSV load) and time-weighted average change in nasal RSV load from day 1 to 7 in the subset of patients with pretreatment symptom duration at the median or shorter of the FAS. Secondary endpoints were changes in respiratory infection symptoms assessed using the Influenza Patient-Reported Outcomes questionnaire and lung function measured by spirometry. Sixty-one patients were randomized, 40 received presatovir, 20 placebo, and 54 were included in efficacy analyses. Presatovir did not significantly improve the primary endpoint in the FAS (treatment difference [95% CI], 0.10 [-0.43, 0.63] log10 copies/ml; p=0.72) or the shorter symptom-duration subgroup (-0.12 [-0.94, 0.69] log10 copies/ml; p=0.76). Secondary endpoints were not different between presatovir and placebo groups. Presatovir was generally well tolerated. Presatovir treatment did not significantly improve change in nasal RSV load, symptoms, or lung function in lung transplant recipients.

Discovery of N-Containing (-)-Borneol Esters as Respiratory Syncytial Virus Fusion Inhibitors.

Respiratory syncytial virus (RSV) causes acute respiratory infections, thus, posing a serious threat to the health of infants, children, and elderly people. In this study, we have discovered a series of potent RSV entry inhibitors with the (-)-borneol scaffold. The active compounds 3b, 5a, 5c, 7b, 9c, 10b, 10c, and 14b were found to exhibit activity against RSV A strain A2 in HEp-2 cells. The most active substances, 3b (IC50 = 8.9 μM, SI = 111) and 5a (IC50 = 5.0 μM, SI = 83), displayed more potency than the known antiviral agent Ribavirin (IC50 = 80.0 μM, SI = 50). Time-of-addition assay and temperature shift studies demonstrated that compounds 3b, 5a, and 6b inhibited RSV entry, probably by interacting with the viral F protein that mediated membrane fusion, while they neither bound to G protein nor inhibited RSV attachment to the target cells. Appling procedures of molecular modeling and molecular dynamics, the binding mode of compounds 3b and 5a was proposed. Taken together, the results of this study suggest (-)-borneol esters to be promising lead compounds for developing new anti-RSV agents.

Mechanism of Cross-Resistance to Fusion Inhibitors Conferred by the K394R Mutation in Respiratory Syncytial Virus Fusion Protein.

ABSTRACTThe fusion glycoprotein (F) is essential for respiratory syncytial virus (RSV) entry and has become an attractive target for anti-RSV drug development. Despite the promising prospect of RSV F inhibitors, issues of drug resistance remain challenging. In this study, we established a dual-luciferase protocol for RSV fusion inhibitor discovery. A small-molecule inhibitor, salvianolic acid R (LF-6), was identified to inhibit virus-cell and cell-cell fusion mediated by the RSV F protein. Sequence analysis of the resultant resistant viruses identified a K394R mutation in the viral F protein. The K394R mutant virus also conferred cross-resistance to multiple RSV fusion inhibitors, including several inhibitors undergoing clinical trials. Our study further showed that K394R mutation not only increased the triggering rate of F protein in prefusion conformation but also enhanced the fusion activity of F protein, both of which were positively correlated with resistance to fusion inhibitors. Moreover, the K394R mutation also showed cooperative effects with other escape mutations to increase the fusion activity of F protein. By substitution of K394 into different amino acids, we found that K394R or K394H substitution resulted in hyperfusiogenic F proteins, whereas F variants with other substitutions exhibited less fusion activity. Both K394R and K394H in F protein exhibited cross-resistance to RSV fusion inhibitors. Collectively, these findings reveal a positive correlation between the membrane fusion activity of F protein and the resistance of corresponding inhibitors. All of the results demonstrate that K394R in F protein confers cross-resistance to fusion inhibitors through destabilizing F protein and increasing its membrane fusion activity.IMPORTANCE Respiratory syncytial virus (RSV) causes serious respiratory tract disease in children and the elderly. Therapeutics against RSV infection are urgently needed. This study reports the discovery of a small-molecule inhibitor of RSV fusion glycoprotein by using a dual-luciferase protocol. The escape mutation (K394R) of this compound also confers cross-resistance to multiple RSV fusion inhibitors that have been reported previously, including two candidates currently in clinical development. The combination of K394R with other escape mutations can increase the resistance of F protein to these inhibitors through destabilizing F protein and enhancing the membrane fusion activity of F protein. By amino acid deletion or substitution, we found that a positively charged residue at the 394th site is crucial for the fusion ability of F protein, as well as for the cross-resistance against RSV fusion inhibitors. These results reveal the mechanism of cross-resistance conferred by the K394R mutation and the possible cross-resistance risk of RSV fusion inhibitors.

Pharmacological Characterization of TP0591816, a Novel Macrocyclic Respiratory Syncytial Virus Fusion Inhibitor with Antiviral Activity against F Protein Mutants.

Human respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in early childhood. However, no vaccines have yet been approved for prevention of RSV infection, and the treatment options are limited. Therefore, development of effective and safe anti-RSV drugs is needed. In this study, we evaluated the antiviral activity and mechanism of action of a novel macrocyclic anti-RSV compound, TP0591816. TP0591816 showed significant antiviral activities against both subgroup A and subgroup B RSV, while exerting no cytotoxicity. Notably, the antiviral activity of TP0591816 was maintained against a known fusion inhibitor-resistant RSV strain with a mutation in the cysteine-rich region or in heptad repeat B. Results of a time-of-addition assay and a temperature shift assay indicated that TP0591816 inhibited fusion of RSV with the cell membrane during viral entry. In addition, TP0591816 added after cell infection also inhibited cell-cell fusion. A TP0591816-resistant virus strain selected by serial passage had an L141F mutation, but no mutation in the cysteine-rich region or in heptad repeat B in the fusion (F) protein. Treatment with TP0591816 reduced lung virus titers in a dose-dependent manner in a mouse model of RSV infection. Furthermore, the estimated effective dose of TP0591816 for use against F protein mutants was thought to be clinically realistic and potentially tolerable. Taken together, these findings suggest that TP0591816 is a promising novel candidate for the treatment of resistant RSV infection.

Drug Resistance Assessment Following Administration of Respiratory Syncytial Virus (RSV) Fusion Inhibitor Presatovir to Participants Experimentally Infected With RSV.

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.

Freesia Study Design: JNJ-53718678 in Hematopoietic Cell Transplant Recipients with Respiratory Syncytial Virus Infection of the Upper Respiratory Tract

Background Although Respiratory Syncytial Virus (RSV) is a commonly recognized respiratory pathogen that can cause upper respiratory tract infections (URTI) and severe lower respiratory tract infections (LRTI) in infants and young children, it can also affect immunocompromised (IC) patients. Hematopoietic cell transplantation (HCT) recipients are at high risk for severe disease caused by RSV. The progression of RSV from URTI to LRTI can cause significant morbidity, often leading to hospitalization, intensive care unit admissions for supportive care and results in mortality in 2-5% of RSV infected HCT recipients. At some clinical centers oral or intravenous ribavirin, intravenous immunoglobulin or anti-RSV-enriched antibody preparations are used to treat RSV infection. However, there are currently no approved direct-acting antiviral agents indicated for the prevention or treatment of RSV infection in IC adult patients. A recently conducted trial evaluating another RSV fusion inhibitor in HCT recipients demonstrated strong trends toward clinical benefit among patients who were early in their disease course and were severely immunocompromised. JNJ-53718678 (JNJ-8678) is a fusion protein inhibitor that was well tolerated and showed antiviral activity in a Phase 1b study of RSV-infected infants, and was well tolerated and demonstrated antiviral efficacy in healthy adult volunteers in a human viral challenge study. FREESIA will evaluate the clinical outcomes, antiviral activity, safety, tolerability, pharmacokinetics (PK), and PK/pharmacodynamics (PD) of JNJ-8678 in HCT recipients with RSV URTI who are at the highest risk for progression to LRTI. Study Design and Methods This is a randomized, double-blind, placebo-controlled, multi-center study to evaluate JNJ-8678 in adult and adolescent HCT recipients with RSV URTI. In the adult cohort, a sample size of approximately 249 patients is targeted. (Figure 1). Adult and adolescent HSCT recipients will be enrolled if they present for medical care with an absolute lymphocyte count <1,000 cells/μL, a PCR-based diagnosis of RSV infection, new onset of at least one respiratory symptom (nasal congestion, rhinorrhea, cough or pharyngitis) and/or worsening of one of these symptoms, if chronic due to an existing diagnosis, within 4 days prior to the anticipated start of dosing and no evidence of abnormalities consistent with LRTI on a chest X-ray. Eligible patients will be randomized 2:1 to receive orally either 500 mg JNJ-8678 once-daily (qd) or placebo qd for 21 days. The follow-up period will be 28 days in duration. The primary endpoint is the proportion of patients developing RSV LRTI, by external adjudication. Clinical course of RSV infection, antiviral activity, health-related quality of life, RSV viral sequencing and RSV viral kinetics will also be assessed. The PK/PD relationship of JNJ-8678 exposure with selected efficacy and safety parameters will be explored. Safety and tolerability, including AEs, laboratory assessments, ECGs, vital signs, and physical examination will be assessed. This study will begin recruitment globally in the northern hemisphere in November 2019. This study will clarify the role JNJ-8678 may play in the treatment of RSV in a broader IC population, potentially addressing a substantial unmet medical need. Disclosures Chemaly: Gilead: Research Funding; Gilead: Other: Personal fees; Chimerix: Research Funding; ReViral: Other: Personal fees; Oxford Immunotec: Other: Personal fees; Ansun: Other: Personal fees; Chimerix: Other: Personal fees; Oxford Immunotec: Research Funding; Merck: Research Funding; Ansun Pharmaceuticals: Research Funding; Janssen: Other: Personal fees; ADMA Biologics: Other: Personal fees; Merck: Other: Personal fees; Clinigen: Other: Personal fees; Ablynx: Other: Personal fees. Boeckh:Chimerix: Research Funding; GSK: Other: Personal fees; Merck: Research Funding; GSK: Research Funding; Clinigen: Other: Personal fees; Merck: Other: Personal fees. Weber:Janssen Pharmaceuticals: Employment; Johnson & Johnson: Equity Ownership. Fleischhackl:Johnson & Johnson: Equity Ownership; Janssen Pharmaceuticals: Employment. Stevens:Johnson & Johnson: Equity Ownership; Janssen Pharmaceuticals: Employment. Michiels:Johnson & Johnson: Equity Ownership; Janssen Pharmaceuticals: Employment. Rivas:Janssen Pharmaceuticals: Employment; Johnson & Johnson: Equity Ownership. Chien:Johnson & Johnson: Equity Ownership; Janssen Pharmaceuticals: Employment. Witek:Johnson & Johnson: Equity Ownership; Janssen Pharmaceuticals: Employment.

Discovery of (aza)indole derivatives as novel respiratory syncytial virus fusion inhibitors.

A new class of indole derivatives (3) have been identified as potent RSV fusion inhibitors. SAR exploration revealed that 5-Cl and the sulfonyl side chain of the indole scaffold are crucial for anti-RSV activity. Further optimization led to the discovery of a cyclic sulfone (8i) with 2 nM anti-RSV activity and a much improved PK profile compared to the non-cyclic sulfone counterpart.

1646. Combined Resistance Analyses From Phase 2b Studies of Presatovir Treatment in RSV-Infected Adults

BackgroundPresatovir is an oral respiratory syncytial virus (RSV) fusion inhibitor in development for the treatment of RSV infection. Results from a healthy volunteer challenge study show that presatovir significantly reduced RSV viral load and clinical signs and symptoms. Here we present combined resistance analyses from 4 phase 2b studies in naturally RSV-infected adults.MethodsRSV RNA was isolated from nasal swabs collected at baseline and postbaseline in studies GS-US-218-0108, GS-US-218–1502, GS-US-218–1227, and GS-US-218–1797. Full-length RSV fusion (F) gene was PCR amplified and population sequencing was performed.ResultsOf 233 presatovir-treated adults in the efficacy analyses, post-baseline resistance-associated substitutions were detected in 18 (7.7%) subjects. Frequencies of resistance development varied by study (Table 1). Resistance substitutions known to confer high-level (>200 fold) reduced susceptibility to presatovir detected in >1 subject were: T400I (n = 6), S398L (n = 3), L141F (n = 2), and F140I (n = 2) in F. Subjects with resistant virus had less viral load reduction than presatovir-treated subjects without resistant virus. Resistance development did not impact clinical outcomes. In study GS-US-218-0108, subjects with lymphopenia (<200 cells/μL) at baseline were significantly more likely to develop resistance substitutions.Table 1:Resistance Development Frequencies in Phase 2b StudiesStudySubject PopulationPresatovir DosePresatovir-Treated Subjects in Efficacy Analysis, nSubjects with Resistance- Associated Substitutions, n (%)GS-US-218-0108Hematopoietic cell transplant (HCT) recipients with upper respiratory tract infectionDays 1, 5, 9, 13, and 17: 200 mg8910 (11.2%)GS-US-218-1502HCT recipients with lower respiratory tract infectionDays 1, 5, 9, 13, and 17: 200 mg296 (20.7%)GS-US-218-1227Hospitalized adultsDay 1: 200 mg801 (1.3%)GS-US-218-1797Lung transplant recipientsDay 1: 200 mg Days 2–14: 100 mg351 (2.9%)ConclusionPresatovir treatment resulted in varying rates of resistance development across 4 phase 2b studies. Resistance development impacted virologic response without affecting clinical outcomes. Differences among study populations and dosing regimens may have influenced rates of resistance development.Disclosures D. Porter, Gilead Sciences, Inc.: Employee and Shareholder, Salary and stocks. Y. Guo, Gilead Sciences, Inc.: Employee and Shareholder, Salary and stocks. J. Perry, Gilead Sciences, Inc.: Employee and Shareholder, Salary and stocks. D. Gossage, Gilead Sciences, Inc.: Employee and Shareholder, Salary and stocks. T. Watkins, Gilead Sciences, Inc.: Employee and Shareholder, Salary and stocks. J. Chien, Gilead Sciences, Inc.: Employee and Shareholder, Salary and stocks. R. Jordan, Gilead Sciences, Inc.: Employee and Shareholder, Salary and stocks.

Discovery of Benzoazepinequinoline (BAQ) Derivatives as Novel, Potent, Orally Bioavailable Respiratory Syncytial Virus Fusion Inhibitors.

A novel benzoazepinequnoline (BAQ) series was discovered as RSV fusion inhibitors. BAQ series originated from compound 2, a hit from similarity-based virtual screening. In SAR exploration, benzoazepine allowed modifications in the head moiety. Benzylic sulfonyl on benzoazepine and 6-Me on quinoline were crucial for good anti-RSV activity. Although the basic amine in the head portion was crucial for anti-RSV activity, the attenuated basicity was required to reduce Vss. Introducing oxetane to the head portion led to discovery of compound 1, which demonstrated single-digit nM anti-RSV activity against different RSV strains, reasonable oral exposure in plasma, and 78-fold higher exposure in lung. Compound 1 also displayed 1 log viral reduction in a female BALB/c mice RSV model by b.i.d. oral dosing at 12.5 mg/kg. A single resistant mutant at L138F in fusion protein proved compound 1 to be a RSV fusion inhibitor.

A Phase 2b Randomized Controlled Trial of Presatovir, an Oral RSV Fusion Inhibitor, for the Treatment of Respiratory Syncytial Virus (RSV) in Lung Transplant (LT) Recipients

A Phase 2b Randomized Controlled Trial of Presatovir, an Oral RSV Fusion Inhibitor, for the Treatment of Respiratory Syncytial Virus (RSV) in Lung Transplant (LT) Recipients

Differential antiviral activities of respiratory syncytial virus (RSV) inhibitors in human airway epithelium

ObjectivesWe report the use of reconstituted 3D human airway epithelium cells (HuAECs) of bronchial origin in an air–liquid interface to study respiratory syncytial virus (RSV) infection and to assess the efficacy of RSV inhibitors in (pre-)clinical development.MethodsHuAECs were infected with RSV-A Long strain (0.01 CCID50/cell, where CCID50 represents 50% cell culture infectious dose in HEp2 cells) on the apical compartment of the culture. At the time of infection or at 1 or 3 days post-infection, selected inhibitors were added and refreshed daily on the basal compartment of the culture. Viral shedding was followed up by apical washes collected daily and quantifying viral RNA by RT-qPCR.ResultsRSV-A replicates efficiently in HuAECs and viral RNA is shed for weeks after infection. RSV infection reduces the ciliary beat frequency of the ciliated cells as of 4 days post-infection, with complete ciliary dyskinesia observed by day 10. Treatment with RSV fusion inhibitors resulted in an antiviral effect only when added at the time of infection. In contrast, the use of replication inhibitors (both nucleoside and non-nucleoside) elicited a marked antiviral effect even when the start of treatment was delayed until 1 day or even 3 days after infection. Levels of the inflammation marker RANTES (mRNA) increased ∼200-fold in infected, untreated cultures (at 3 weeks post-infection), but levels were comparable to those of uninfected cultures in the presence of PC786, an RSV replication inhibitor, suggesting that an efficient antiviral treatment might inhibit virus-induced inflammation in this model.ConclusionsOverall, HuAECs offer a robust and physiologically relevant model to study RSV replication and to assess the efficacy of antiviral compounds.

3D-QSAR Studies of 1,2,3,9b-tetrahydro-5H-imidazo[2,1-a]isoindol-5-ones Derivatives as RSV Fusion Inhibitors

Background: Respiratory syncytial virus (RSV) is a major cause of acute lower respiratory- tract infections (ALRI) in young children, elderly and high-risk adults and results in considerable hospitalizations. The fusions of RSV were proved to be a potent target in combating virus. Methods: A series of newly reported isoindol-5-ones derivatives as RSV fusion inhibitors was studied via in silico methodologies 3D-QSAR (CoMFA and CoMSIA) to explore compounds with better activity. Internal and external cross-validation techniques were investigated. Results: Satisfactory CoMFA model (q2=0.542, r2=0.908) and CoMSIA model (q2=0.563, r2=0.874) were obtained. The external validation indicated that CoMFA and CoMSIA models possessed high predictive powers with Q2 F2 values of 0.734 and 0.701, respectively. The contour maps shows the bulky, and hydrogen bond acceptor groups at R2 position are essential to improve the antivirus activity. The minor and hydrophobic groups such as ether bond at para-position or metaposition of substituent group R1 may increase their activities. Conclusion: The plots of CoMFA and CoMISA provided information of the structure–activity relationship and revealed the chemical features affecting the antivirus activity. These results expand our understanding of RSV fusion inhibitors and could be helpful in rationally designing of new analogs with more potent inhibitory activities. Keywords: RSV fusion inhibitors, QSAR, Isoindol-5-ones, ALRI, pneumonia, respiratory diseases.

Therapeutic efficacy of a respiratory syncytial virus fusion inhibitor

Respiratory syncytial virus is a major cause of acute lower respiratory tract infection in young children, immunocompromised adults, and the elderly. Intervention with small-molecule antivirals specific for respiratory syncytial virus presents an important therapeutic opportunity, but no such compounds are approved today. Here we report the structure of JNJ-53718678 bound to respiratory syncytial virus fusion (F) protein in its prefusion conformation, and we show that the potent nanomolar activity of JNJ-53718678, as well as the preliminary structure–activity relationship and the pharmaceutical optimization strategy of the series, are consistent with the binding mode of JNJ-53718678 and other respiratory syncytial virus fusion inhibitors. Oral treatment of neonatal lambs with JNJ-53718678, or with an equally active close analog, efficiently inhibits established acute lower respiratory tract infection in the animals, even when treatment is delayed until external signs of respiratory syncytial virus illness have become visible. Together, these data suggest that JNJ-53718678 is a promising candidate for further development as a potential therapeutic in patients at risk to develop respiratory syncytial virus acute lower respiratory tract infection.

Discovery of methylsulfonyl indazoles as potent and orally active respiratory syncytial Virus(RSV) fusion inhibitors

Recently we described a novel class of imidazopyridine compounds that showed exceptional anti-RSV potency in cell culture. However, unfavorable pharmacokinetic (PK) properties and glutathione (GSH) adduct liabilities impeded their further development. In a bid to address the PK and early safety concerns, a small compound library consisting of dozens of scaffold-hopping analogues was designed and synthesized for RSV CPE assay screening, which led to the identification of a new chemical starting point: methylsulfonyl indole compound 8. In this paper, we report the discovery and optimization of a series of methylsulfonyl indazoles as potent RSV fusion inhibitors. In particular, compound 47 was orally efficacious in a RSV mouse model, with 1.6 log unit viral load reduction at 25 mg/kg BID upon oral dosing. The results may have broad implications for the design of new RSV fusion inhibitors, and demonstrate the potential for developing novel therapies for RSV infection.

Discovery of Piperazinylquinoline Derivatives as Novel Respiratory Syncytial Virus Fusion Inhibitors.

A novel series of piperazinylquinoline derivatives were discovered as respiratory syncytial virus (RSV) fusion inhibitors by the ligand-based screening approach. Among 3,000 hits, 1-amino-3-[[2-(4-phenyl-1-piperidyl)-4-quinolyl]amino]propan-2-ol (7) was proven to be active against the RSV long (A) strain. The anti-RSV activity was improved by converting piperidine to benzylcarbonyl substituted piperazine. The basic side chain was also found to be crucial for anti-RSV activity. The selected analogues, 45 and 50, demonstrated anti-RSV activities up to EC50 = 0.028 μM and 0.033 μM, respectively. A direct anti-RSV effect was confirmed by a plaque reduction assay and a fusion inhibition assay. Both 45 and 50 showed promising DMPK properties with good oral bioavailability, and could potentially lead to novel therapeutic agents targeting the RSV fusion process.

GS-5806 Inhibits a Broad Range of Respiratory Syncytial Virus Clinical Isolates by Blocking the Virus-Cell Fusion Process.

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.

Molecular mechanism of respiratory syncytial virus fusion inhibitors.

Respiratory syncytial virus (RSV) is a leading cause of pneumonia and bronchiolitis in young children and the elderly. Therapeutic small molecules have been developed that bind the RSV F glycoprotein and inhibit membrane fusion, yet their binding sites and molecular mechanisms of action remain largely unknown. Here we show that these inhibitors bind to a three-fold-symmetric pocket within the central cavity of the metastable prefusion conformation of RSV F. Inhibitor binding stabilizes this conformation by tethering two regions that must undergo a structural rearrangement to facilitate membrane fusion. Inhibitor-escape mutations occur in residues that directly contact the inhibitors or are involved in the conformational rearrangements required to accommodate inhibitor binding. Resistant viruses do not propagate as well as wild-type RSV in vitro, indicating a fitness cost for inhibitor escape. Collectively, these findings provide new insight into class I viral fusion proteins and should facilitate development of optimal RSV fusion inhibitors.