The in vitro pharmacology of GS-5759, a novel bifunctional phosphodiesterase 4 inhibitor and long acting ß2-adrenoceptor agonist.

Inhaled long-acting ß(2)-adrenoceptor agonists (LABA) that act as bronchodilators and the oral anti-inflammatory phosphodiesterase 4 (PDE4) inhibitor roflumilast are both approved therapies for chronic obstructive pulmonary disease (COPD). Here we describe the activity of a novel, inhaled, bifunctional, small molecule (R)-6-[(3-{[4-(5-{[2-hydroxy-2-(8-hydroxy-2-oxo-1,2-dihydroquinolin-5-yl)ethyl]amino}pent-1-yn-1-yl)phenyl]carbamoyl}phenyl)sulfonyl]-4-[(3-methoxyphenyl)amino]-8-methylquinoline-3-carboxamide (GS-5759), which has specific ß(2) agonist and PDE4 inhibitory activity. GS-5759 demonstrated potent and full agonist activity at ß(2) adrenoceptors (EC(50) = 8 ± 4 nM) and is a potent inhibitor of the PDE4 enzyme (IC(50) = 5 ± 3 nM). In cell assays, GS-5759 inhibited lipopolysaccharide (LPS)-induced tumor necrosis factor α (TNFα) production in human peripheral mononuclear cells (PBMC) with an IC(50) = 0.3 nM [confidence interval (CI) 0.1-0.6] and in human neutrophils formyl-methionyl-leucyl-phenylalanine (fMLP)-induced super oxide anion production with an IC(50) = 3 nM (CI 0.8-8). The addition of the ß(2) antagonist ICI 118551 shifted the IC(50) in these cell assays to 4 and 38 nM, respectively, demonstrating the contribution of both ß(2) agonist and PDE4 inhibitory activity to GS-5759. GS-5759 was also a potent inhibitor of profibrotic and proinflammatory mediator release from human lung fibroblasts. GS-5759 relaxed guinea pig airway smooth muscle strips precontracted with carbachol in a concentration-dependent manner with an EC(50) = 0.5 µM (CI 0.2-2) and had slow dissociation kinetics with an Off T(1/2) > 720 minutes at an EC(80) concentration of 3 µM. GS-5759 is a novel bifunctional molecule with both potent ß(2) agonist and PDE4 inhibitor activity that could provide inhaled bronchodilator and anti-inflammatory therapy for COPD.

Nonantibiotic macrolides prevent human neutrophil elastase-induced mucus stasis and airway surface liquid volume depletion.

Mucus clearance is an important component of the lung's innate defense system. A failure of this system brought on by mucus dehydration is common to both cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). Mucus clearance rates are regulated by the volume of airway surface liquid (ASL) and by ciliary beat frequency (CBF). Chronic treatment with macrolide antibiotics is known to be beneficial to both CF and COPD patients. However, chronic macrolide usage may induce bacterial resistance. We have developed a novel macrolide, 2'-desoxy-9-(S)-erythromycylamine (GS-459755), that has significantly diminished antibiotic activity against Staphylococcus aureus, Streptococcus pneumonia, Moraxella catarrhalis, and Haemophilus influenzae. Since neutrophilia frequently occurs in chronic lung disease and human neutrophil elastase (HNE) induces mucus stasis by activating the epithelial sodium channel (ENaC), we tested the ability of GS-459755 to protect against HNE-induced mucus stasis. GS-459755 had no effect on HNE activity. However, GS-459755 pretreatment protected against HNE-induced ASL volume depletion in human bronchial epithelial cells (HBECs). The effect of GS-459755 on ASL volume was dose dependent (IC50 ~3.9 µM) and comparable to the antibacterial macrolide azithromycin (IC50 ~2.4 µM). Macrolides had no significant effect on CBF or on transepithelial water permeability. However, the amiloride-sensitive transepithelial voltage, a marker of ENaC activity, was diminished by macrolide pretreatment. We conclude that GS-459755 may limit HNE-induced activation of ENaC and may be useful for the treatment of mucus dehydration in CF and COPD without inducing bacterial resistance.

Fosfomycin enhances the active transport of tobramycin in Pseudomonas aeruginosa.

Elevated levels of mucins present in bronchiectatic airways predispose patients to bacterial infections and reduce the effectiveness of antibiotic therapies by directly inactivating antibiotics. Consequently, new antibiotics that are not inhibited by mucins are needed to treat chronic respiratory infections caused by Pseudomonas aeruginosa and Staphylococcus aureus. In these studies, we demonstrate that fosfomycin synergistically enhances the activity of tobramycin in the presence of mucin. The bactericidal killing of a novel 4:1 (wt/wt) combination of fosfomycin-tobramycin (FTI) is superior (>9 log(10) CFU/ml) relative to its individual components fosfomycin and tobramycin. Additionally, FTI has a mutation frequency resulting in an antibiotic resistance >3 log(10) lower than for fosfomycin and 4 log(10) lower than for tobramycin for P. aeruginosa. Mechanistic studies revealed that chemical adducts are not formed, suggesting that the beneficial effects of the combination are not due to molecular modification of the components. FTI displayed time-kill kinetics similar to tobramycin and killed in a concentration-dependent fashion. The bactericidal effect resulted from inhibition of protein biosynthesis rather than cell wall biosynthesis. Studies using radiolabeled antibiotics demonstrated that tobramycin uptake was energy dependent and that fosfomycin enhanced the uptake of tobramycin in P. aeruginosa in a dose-dependent manner. Lastly, mutants resistant to fosfomycin and tobramycin were auxotrophic for specific carbohydrates and amino acids, suggesting that the resistance arises from mutations in specific active transport mechanisms. Overall, these data demonstrate that fosfomycin enhances the uptake of tobramycin, resulting in increased inhibition of protein synthesis and ultimately bacterial killing.

Treating laminitis: beyond the mechanics of trimming and shoeing.

Laminitis is typically classified into developmental or prodromal, acute, subacute, and chronic phases. Scientific evidence regarding the pathophysiology of laminitis does exist, but it is often conflicting and dependent on the clinician's interpretation/understanding of the study or the model used for inducing laminitis. The diagnosis of laminitis consists of obtaining an accurate history, performing a thorough physical examination, and taking good-quality radiographs. The use of radiographs for diagnosis and interpretation of laminitis is an absolute necessity for the clinician. Laminitis is one disease that requires the assembly of a team consisting of the veterinarian, the farrier, and the owner to be successfully treated.

Antibacterial activities of a fosfomycin/tobramycin combination: a novel inhaled antibiotic for bronchiectasis.

OBJECTIVES: To compare the in vitro and in vivo activities of a 4:1 (w/w) fosfomycin/tobramycin combination (FTI) with those of fosfomycin and tobramycin alone against cystic fibrosis (CF) and non-CF bronchiectasis pathogens. METHODS: Clinical isolates of CF Pseudomonas aeruginosa, Staphylococcus aureus, Haemophilus influenzae, Stenotrophomonas maltophilia, Burkholderia cepacia complex, Escherichia coli and Klebsiellia spp. were evaluated by MIC, MBC, post-antibiotic effect (PAE), synergy, time-kill, a rat pneumonia model and spontaneous mutation frequency (SMF). RESULTS: FTI showed high activity against E. coli, H. influenzae, S. aureus and Klebsiella spp. For the S. aureus strains, 75% of which were methicillin resistant (MRSA), FTI had a lower MIC(90) than tobramycin. For P. aeruginosa, FTI had a lower MIC(90) than fosfomycin, but tobramycin was more active than either. Synergy studies showed no antagonism between fosfomycin and tobramycin, and 93% of the isolates demonstrated no interaction. FTI was rapidly bactericidal and exhibited concentration-dependent killing in time-kill studies. In the rat pneumonia model, FTI and tobramycin demonstrated bactericidal killing of P. aeruginosa; both were more active than fosfomycin alone. The SMF for S. aureus resistance to FTI was 2-4 log(10) lower than that for tobramycin and 2-7 log(10) lower than that for fosfomycin. For P. aeruginosa, the FTI SMF was 2-3 log(10) lower than that for fosfomycin and 1-2 log(10) lower than that for tobramycin. CONCLUSIONS: FTI is a broad-spectrum antibiotic combination with high activity in vitro and in vivo. These data suggest FTI could be a potential treatment for respiratory infections caused by gram-positive and gram-negative aerobic bacteria.

A prodrug approach toward the development of water soluble fluoroquinolones and structure--activity relationships of quinoline-3-carboxylic acids.

A fluoroquinolone prodrug, PA2808, was prepared and shown to convert to the highly active parent drug PA2789. In vitro and in vivo activation of PA2808 by alkaline phosphatase was demonstrated using disk diffusion and rat lung infection models. The water solubility of PA2808 showed a marked increase compared to PA2789 over a pH range suitable for aerosol drug delivery. A total of 48 analogues based on PA2789 were prepared and screened against a panel of Gram-positive and Gram-negative pathogens. Incorporating a cyclopropane-fused pyrrolidine (amine) at C-7 resulted in some of the most active analogues.

The in vivo efficacy and side effect pharmacology of GS-5759, a novel bifunctional phosphodiesterase 4 inhibitor and long-acting ß 2-adrenoceptor agonist in preclinical animal species.

Bronchodilators are a central therapy for symptom relief in respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma, with inhaled ß 2-adrenoceptor agonists and anticholinergics being the primary treatments available. The present studies evaluated the in vivo pharmacology of (R)-6-[[3-[[4-[5-[[2-Hydroxy-2-(8-hydroxy-2-oxo-1,2-dihydroquinolin-5-yl)ethyl]amino]pent-1-ynyl]phenyl]carbamoyl]phenyl]sulfonyl]-4-[(3-methoxyphenyl)amino]-8-methylquinoline-3-carboxamide (GS-5759), a novel bifunctional compound with both phosphodiesterase 4 (PDE4) inhibitor and long-acting ß 2-adrenoceptor agonist (LABA) activity, which has been optimized for inhalation delivery. GS-5759 dose-dependently inhibited pulmonary neutrophilia in a lipopolysaccharide (LPS) aerosol challenge model of inflammation in rats with an ED50 ≤ 10 µg/kg. GS-5759 was also a potent bronchodilator with an ED50 of 0.09 µg/kg in guinea pigs and 3.4 µg/kg in dogs after methylcholine (MCh) and ragweed challenges respectively. In cynomolgus monkeys, GS-5759 was dosed as a fine-particle dry powder and was efficacious in the same dose range in both MCh and LPS challenge models, with an ED50 = 70 µg/kg for bronchodilation and ED50 = 4.9 µg/kg for inhibition of LPS-induced pulmonary neutrophilia. In models to determine therapeutic index (T.I.), efficacy for bronchodilation was evaluated against increased heart rate and GS-5759 had a T.I. of 700 in guinea pigs and >31 in dogs. In a ferret model of emesis, no emesis was seen at doses several orders of magnitude greater than the ED50 observed in the rat LPS inflammation model. GS-5759 is a bifunctional molecule developed for the treatment of COPD, which has both bronchodilator and anti-inflammatory activity and has the potential for combination as a triple therapy with a second compound, within a single inhalation device.