Optimization of the screening hit 1 led to the identification of novel 1,5-naphthyridine aminothiazole and pyrazole derivatives, which are potent and selective inhibitors of the transforming growth factor-beta type I receptor, ALK5. Compounds 15 and 19, which inhibited ALK5 autophosphorylation with IC50 = 6 and 4 nM, respectively, showed potent activities in both binding and cellular assays and exhibited selectivity over p38 mitogen-activated protein kinase. The X-ray crystal structure of 19 in complex with human ALK5 is described, confirming the binding mode proposed from docking studies.

Inhibitors of transforming growth factor beta (TGF-beta) type I receptor (ALK5) offer a novel approach for the treatment of fibrotic diseases such as renal, hepatic, and pulmonary fibrosis. The optimization of a novel phenylpyridine pyrazole series (1a) led to the identification of potent, selective, and orally active ALK5 inhibitors. The cellular potency and pharmacokinetics profiles of these derivatives were improved and several compounds presented antifibrotic activity when orally administered to rats in an acute liver model of dimethylnitrosamine- (DMN-) induced expression of collagen IA1 mRNA, a major gene contributing to excessive extra cellular matrix deposit. One of the most potent ALK5 inhibitors identified in this chemical series, compound 13d (GW788388), reduced the expression of collagen IA1 by 80% at a dose of 1 mg/kg twice a day (b.i.d.). This compound significantly reduced the expression of collagen IA1 mRNA when administered orally at 10 mg/kg once a day (u.i.d.) in a model of puromycin aminonucleoside-induced renal fibrosis.

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.

Effective treatments for respiratory syncytial virus (RSV) infection are lacking. Here, we report a human proof-of-concept study for RV521, a small-molecule antiviral inhibitor of the RSV-F protein. In this randomized, double-blind, placebo-controlled trial, healthy adults were challenged with RSV-A Memphis-37b. After infection was confirmed (or 5 days after challenge virus inoculation), subjects received RV521 (350 mg or 200 mg) or placebo orally every 12 h for 5 days. The primary endpoint was area under the curve (AUC) for viral load, as assessed by reverse transcriptase quantitative PCR (RT-qPCR) of nasal wash samples. The primary efficacy analysis set included subjects successfully infected with RSV who received ≥1 dose of study drug. A total of 66 subjects were enrolled (n = 22 per group); 53 were included in the primary analysis set (RV521 350 mg: n = 16; 200 mg: n = 18; placebo: n = 19). The mean AUC of RT-qPCR-assessed RSV viral load (log10 PFU equivalents [PFUe]/ml · h) was significantly lower with RV521 350 mg (185.26; standard error [SE], 31.17; P = 0.002) and 200 mg (224.35; SE, 37.60; P = 0.007) versus placebo (501.39; SE, 86.57). Disease severity improved with RV521 350 mg and 200 mg versus placebo (P = 0.002 and P = 0.009, respectively, for AUC total symptom score [score × hours]). Daily nasal mucus weight was significantly reduced (P = 0.010 and P = 0.038 for RV521 350 mg and 200 mg, respectively, versus placebo). All treatment-emergent adverse events were grade 1 or 2. No subjects discontinued due to adverse events. There was no evidence of clinically significant viral resistance, and only three variants were detected. RV521 effectively reduced RSV viral load and disease severity in humans and was well tolerated. (This study has been registered at ClinicalTrials.gov under registration no. NCT03258502.)

RV521 is an orally bioavailable inhibitor of respiratory syncytial virus (RSV) fusion that was identified after a lead optimization process based upon hits that originated from a physical property directed hit profiling exercise at Reviral. This exercise encompassed collaborations with a number of contract organizations with collaborative medicinal chemistry and virology during the optimization phase in addition to those utilized as the compound proceeded through preclinical and clinical evaluation. RV521 exhibited a mean IC 50 of 1.2 nM against a panel of RSV A and B laboratory strains and clinical isolates with antiviral efficacy in the Balb/C mouse model of RSV infection. Oral bioavailability in preclinical species ranged from 42 to >100% with evidence of highly efficient penetration into lung tissue. In healthy adult human volunteers experimentally infected with RSV, a potent antiviral effect was observed with a significant reduction in viral load and symptoms compared to placebo.