Identification of broad-spectrum antiviral compounds and assessment of the druggability of their target for efficacy against respiratory syncytial virus (RSV).

The search for novel therapeutic interventions for viral disease is a challenging pursuit, hallmarked by the paucity of antiviral agents currently prescribed. Targeting of viral proteins has the inextricable challenge of rise of resistance. Safe and effective vaccines are not possible for many viral pathogens. New approaches are required to address the unmet medical need in this area. We undertook a cell-based high-throughput screen to identify leads for development of drugs to treat respiratory syncytial virus (RSV), a serious pediatric pathogen. We identified compounds that are potent (nanomolar) inhibitors of RSV in vitro in HEp-2 cells and in primary human bronchial epithelial cells and were shown to act postentry. Interestingly, two scaffolds exhibited broad-spectrum activity among multiple RNA viruses. Using the chemical matter as a probe, we identified the targets and identified a common cellular pathway: the de novo pyrimidine biosynthesis pathway. Both targets were validated in vitro and showed no significant cell cytotoxicity except for activity against proliferative B- and T-type lymphoid cells. Corollary to this finding was to understand the consequences of inhibition of the target to the host. An in vivo assessment for antiviral efficacy failed to demonstrate reduced viral load, but revealed microscopic changes and a trend toward reduced pyrimidine pools and findings in histopathology. We present here a discovery program that includes screen, target identification, validation, and druggability that can be broadly applied to identify and interrogate other host factors for antiviral effect starting from chemical matter of unknown target/mechanism of action.

Discovery of LFF571: an investigational agent for Clostridium difficile infection.

Clostridium difficile (C. difficile) is a Gram positive, anaerobic bacterium that infects the lumen of the large intestine and produces toxins. This results in a range of syndromes from mild diarrhea to severe toxic megacolon and death. Alarmingly, the prevalence and severity of C. difficile infection are increasing; thus, associated morbidity and mortality rates are rising. 4-Aminothiazolyl analogues of the antibiotic natural product GE2270 A (1) were designed, synthesized, and optimized for the treatment of C. difficile infection. The medicinal chemistry effort focused on enhancing aqueous solubility relative to that of the natural product and previous development candidates (2, 3) and improving antibacterial activity. Structure-activity relationships, cocrystallographic interactions, pharmacokinetics, and efficacy in animal models of infection were characterized. These studies identified a series of dicarboxylic acid derivatives, which enhanced solubility/efficacy profile by several orders of magnitude compared to previously studied compounds and led to the selection of LFF571 (4) as an investigational new drug for treating C. difficile infection.

Atomic-scale characterization of conformational changes in the preQ1 riboswitch aptamer upon ligand binding.

Riboswitches are mRNA structural elements that act as intracellular sensors of small-molecule metabolites. By undergoing conformational changes capable of modulating translation or terminating transcription, riboswitches are able to play a role in regulating the concentration of essential metabolites in the cell. Computer-guided fluorescence experiments were carried out to interrogate molecular dynamics and conformational changes in the minimal riboswitch aptamer that binds 7-aminomethyl-7-deazaguanine (preQ1). Our combined experimental results and computational analysis suggest that the preQ1 riboswitch apo form is structured but shows no evidence of a ligand-binding pocket. Simulations of the apo and bound forms indicate a large conformational change is triggered by the breaking of the Watson-Crick base pairing of nucleotides G11 and C31 upon preQ1 removal, followed by collapse of the pocket due to interfering π-stacking. Computational predictions of local aptamer dynamics were validated by fluorescence experiments employing 2-aminopurine substitutions. In-line probing reactions confirmed that fluorophore-labeled riboswitches retain similar higher-order structural features as the unlabeled aptamer upon ligand binding, although their affinity for the ligand is reduced by the introduction of the fluorescent reporter.

Antibacterial optimization of 4-aminothiazolyl analogues of the natural product GE2270 A: identification of the cycloalkylcarboxylic acids.

4-Aminothiazolyl analogues of the antibiotic natural product GE2270 A (1) were designed, synthesized, and optimized for their activity against Gram positive bacterial infections. Optimization efforts focused on improving the physicochemical properties (e.g., aqueous solubility and chemical stability) of the 4-aminothiazolyl natural product template while improving the in vitro and in vivo antibacterial activity. Structure-activity relationships were defined, and the solubility and efficacy profiles were improved over those of previous analogues and 1. These studies identified novel, potent, soluble, and efficacious elongation factor-Tu inhibitors, which bear cycloalkylcarboxylic acid side chains, and culminated in the selection of development candidates amide 48 and urethane 58.