Discovery of a 2'-fluoro-2'-C-methyl C-nucleotide HCV polymerase inhibitor and a phosphoramidate prodrug with favorable properties

A series of 2'-fluorinated C-nucleosides were prepared and tested for anti-HCV activity. Among them, the triphosphate of 2'-fluoro-2'-C-methyl adenosine C-nucleoside (15) was a potent and selective inhibitor of the NS5B polymerase and maintained activity against the S282T resistance mutant. A number of phosphoramidate prodrugs were then prepared and evaluated leading to the identification of the 1-aminocyclobutane-1-carboxylic acid isopropyl ester variant (53) with favorable pharmacokinetic properties including efficient liver delivery in animals.

Highly potent HCV NS4B inhibitors with activity against multiple genotypes

The exploration of novel inhibitors of the HCV NS4B protein that are based on a 2-oxadiazoloquinoline scaffold is described. Optimization to incorporate activity across genotypes led to a potent new series with broad activity, of which inhibitor 1 displayed the following EC50 values: 1a, 0.08 nM; 1b, 0.10 nM; 2a, 3 nM; 2b, 0.6 nM, 3a, 3.7 nM; 4a, 0.9 nM; 6a, 3.1 nM.

Structural and regulatory elements of HCV NS5B polymerase--β-loop and C-terminal tail--are required for activity of allosteric thumb site II inhibitors

Elucidation of the mechanism of action of the HCV NS5B polymerase thumb site II inhibitors has presented a challenge. Current opinion holds that these allosteric inhibitors stabilize the closed, inactive enzyme conformation, but how this inhibition is accomplished mechanistically is not well understood. Here, using a panel of NS5B proteins with mutations in key regulatory motifs of NS5B – the C-terminal tail and β-loop – in conjunction with a diverse set of NS5B allosteric inhibitors, we show that thumb site II inhibitors possess a distinct mechanism of action. A combination of enzyme activity studies and direct binding assays reveals that these inhibitors require both regulatory elements to maintain the polymerase inhibitory activity. Removal of either element has little impact on the binding affinity of thumb site II inhibitors, but significantly reduces their potency. NS5B in complex with a thumb site II inhibitor displays a characteristic melting profile that suggests stabilization not only of the thumb domain but also the whole polymerase. Successive truncations of the C-terminal tail and/or removal of the β-loop lead to progressive destabilization of the protein. Furthermore, the thermal unfolding transitions characteristic for thumb site II inhibitor – NS5B complex are absent in the inhibitor – bound constructs in which interactions between C-terminal tail and β-loop are abolished, pointing to the pivotal role of both regulatory elements in communication between domains. Taken together, a comprehensive picture of inhibition by compounds binding to thumb site II emerges: inhibitor binding provides stabilization of the entire polymerase in an inactive, closed conformation, propagated via coupled interactions between the C-terminal tail and β-loop.

Optimization of Pharmacokinetics through Manipulation of Physicochemical Properties in a Series of HCV Inhibitors

A novel series of HCV replication inhibitors based on a pyrido[3,2-d]pyrimidine core were optimized for pharmacokinetics (PK) in rats. Several associations between physicochemical properties and PK were identified and exploited to guide the design of compounds. In addition, a simple new metric that may aid in the prediction of bioavailability for compounds with higher polar surface area is described (3*HBD-cLogP).

Relative contributions of collagen and elastin to elasticity of the vocal fold under tension

This study examined the contributions of collagen and elastin to the tensile elastic properties of the vocal fold lamina propria. Uniaxial stress-strain responses of vocal fold cover and vocal ligament specimens from 20 human larynges (12 males, 8 females) were quantified with sinusoidal stretch-release deformation in vitro. Mid-coronal sections of 12 specimens were examined histologically with Masson's trichrome and elastin van Gieson stain to quantify the relative densities of collagen and elastin fibers. Results showed that significantly higher levels of collagen were found in the male vocal fold than female, for both the cover and the ligament. For male there was a significantly higher level of elastin in the cover than in the ligament. On average, the elastic modulus of the male cover was about twice that of the female at high-tensile strain (35-40%), whereas the male ligament was 3-5 times stiffer than the female in the same range. The ligament was stiffer than the cover for male, but the opposite was observed for female. These findings suggested that collagen and elastin could contribute differentially to elasticity of the cover and the ligament. The data may provide guidance for surgical reconstruction and tissue engineering of different lamina propria layers.

A Biodegradable, Acellular Xenogeneic Scaffold for Regeneration of the Vocal Fold Lamina Propria

A novel method for preparing an acellular xenogeneic extracellular matrix scaffold for tissue engineering was developed. Bovine vocal fold lamina propria specimens were treated with high-concentration sodium chloride, nucleic acid digestion, and ethanol dehydration for decellularization and removal of immunogenic foreign epitopes. Human vocal fold fibroblasts from primary culture were seeded onto the acellular scaffolds and cultured for 21 days. The decellularized and the recellularized scaffolds were examined by light microscopy, fluorescent microscopy, and scanning electron microscopy. Collagen synthesis and release by fibroblasts were quantified by the Sircol assay, whereas the synthesis and release of hyaluronic acid, decorin, and fibronectin were assessed by enzyme-linked immunosorbent assays. Viscoelastic shear properties of the scaffolds were quantified by a simple-shear rheometer at frequencies of up to 250 Hz. Preliminary results showed that a biodegradable, acellular extracellular matrix scaffold with an intact basement membrane and 3-dimensional structure of the matrix proteins was engineered. Vocal fold fibroblasts readily attached to and infiltrated the scaffold with high viability and active protein synthesis, demonstrating the biocompatibility. The elastic shear modulus and dynamic viscosity of the acellular scaffold and the fibroblast-repopulated scaffold were comparable to those of the human vocal fold cover. These findings support the potential of the scaffold as a xenograft for vocal fold reconstruction and regeneration.

Elasticity of the human false vocal fold

OBJECTIVES

Very little is known about the elasticity of the human ventricular fold (false vocal fold). To better understand the potential role of the false fold in the fluid dynamics and aeroacoustics of phonation, we made some measurements on the elastic properties of human ventricular fold tissues in vitro.

METHODS

Uniaxial tensile stress-strain characteristics of 6 male and 6 female false fold specimens were quantified with sinusoidal stretch-release deformation. Midcoronal sections of 3 specimens were examined to quantify the relative densities of collagen, elastin, seromucous glandular tissue, and adipose tissue by digital image analysis.

RESULTS

Nonlinear stress-strain curves with hysteresis (viscous energy loss) were observed, with large interindividual differences. A hybrid linear-exponential model was used to determine the elastic modulus (tangent Young's modulus) of the false fold. On average, the male false fold was twice as stiff as the female at a tensile strain of 20% to 30%.

CONCLUSIONS

This preliminary gender-related difference in elasticity could be attributed to a higher proportion of glandular tissue in the female false fold, due to the lower elastic modulus of glands. The present data allow one to develop a more comprehensive biomechanical model of phonation, for optimizing postoperative voice production following laryngeal reconstruction procedures.