The potency-insolubility conundrum in pharmaceuticals: Mechanism and solution for hepatitis C protease inhibitors.

As compounds are optimized for greater potency during pharmaceutical discovery, their aqueous solubility often decreases, making them less viable as orally-administered drugs. To investigate whether potency and insolubility share a common origin, we examined the structural and thermodynamic properties of telaprevir, a sparingly soluble inhibitor of hepatitis C virus protease. Comparison of the hydrogen bond motifs in crystalline telaprevir with those present in the protease-telaprevir complex revealed striking similarities. Additionally, the thermodynamics of telaprevir dissolution closely resembles those of protein-ligand dissociation. Together, these findings point to a common origin of potency and insolubility rooted in particular amide-amide hydrogen bond patterns. The insolubility of telaprevir is shown by computational analysis to be caused by interactions in the crystal, not unfavorable hydrophobic hydration. Accordingly, competing out the particular amide-amide hydrogen bond motifs in crystalline telaprevir with 4-hydroxybenzoic acid yielded a co-crystalline solid with excellent aqueous dissolution and oral absorption. The analysis suggests a generalizable approach for identifying drug candidate compounds that either can or cannot be rendered orally bioavailable by alteration of their crystalline solid phases, in an approach that provides a pragmatic way to attain substantial enhancements in the success rate of drug discovery and development.

Protein Z Plasma Levels are Not Elevated in Patients with Non-Arteritic Anterior Ischemic Optic Neuropathy.

BACKGROUND: Protein Z is a glycoprotein that acts as a co-factor for the inhibition of activated coagulation factor X. Protein Z circulating in abnormal levels has been associated with increased risk for acute ischemic events. Non-arteritic Anterior Ischemic Optic Neuropathy (N-AION) is caused by acute ischemic infarction of the optic nerve head, supplied by the posterior ciliary arteries. OBJECTIVES: The aim was to investigate whether there is an association between N-AION and plasma protein Z levels. PATIENTS AND METHODS: Twenty-six cases of confirmed N-AION and fifty-two controls were included in the study group. Protein Z was estimated in thawed citrate plasma on both N-AION cases and controls by an enzyme immunoassay. The imprecision of the estimation was satisfactory (CV = 4, 6%). RESULTS: The controls' protein Z values distributed within a range 340 to 4200 ng/ml (median = 1420, mean = 1673, SD = 1040 ng/ml). Patients' protein Z values distributed within a range 420 to 3600 ng/ml (median = 1030, mean = 1520, SD = 939 ng/ml). There was no statistical difference between the two distributions (Independent t-test, p=0.529). CONCLUSION: In our study, protein Z levels are not implicated in the pathogenesis of non-arteritic anterior ischemic optic neuropathy (N-AION).

Genetic risk factors associated with thrombosis in children with congenital neurologic disorders.

Thromboembolic events during the perinatal period are responsible for irreversible brain damage owing to cerebral hypoxia and neuronal necrosis. We investigated the presence of thrombophilia risk factors in children with congenital neurologic disorders. Nineteen children (9 males and 10 females), aged 1 to 14 years (median 4.5 years), who had presented with symptoms and signs of congenital neurologic disorders were studied. Thirty-five age-matched healthy children recruited from the same geographic area served as controls. Three patients of 19 (15.8%) were carrying the factor V Leiden mutation compared with 2 children among the controls (5.7%). One patient was heterozygous for the prothrombin G20210A variant (5.2%) compared with one child who was heterozygous among the controls. Three patients were homozygous (15.8%) and 11 were heterozygous (57.9%) for the C677T 5,10-methylenetetrahydrofolate reductase gene mutation compared with 4 (11.5%) and 18 (51.4%), respectively, among the controls. Three patients of 19 (15.8%) were carrying more than one mutation. We found 18 mutations in 79% (15/19) of the patients and 25 mutations in 69% (24/35) of the healthy children. Among the individuals carrying the homozygous 677TT 5,10-methylenetetrahydrofolate reductase genotype, we found 7 mutations in 32% (6/19) of the patients and 7 mutations in 20% (7/35) of the healthy children (P > .05). In one patient, lupus anticoagulant and antiphospholipid antibodies of IgG isotype were detected. Reduced activities of protein C, protein S, or antithrombin III were not observed in either the patient or the control group. Although, among our cases, we found some well-known risk factors associated with thrombosis in adults, the pathogenesis of these clinical entities remains obscure.

Genetic background of osteonecrosis: associated with thrombophilic mutations?

Intravascular coagulation is considered a major pathogenetic mechanism for nontraumatic osteonecrosis. The aim of our study was to evaluate the association of thrombophilic factor V G1691A mutation (factor V Leiden) and G20210A prothrombin mutation with the disease. Mutation presence was investigated by polymerase chain reaction techniques in a study population of 72 adult Caucasian patients with osteonecrosis of the femoral head and 300 healthy Caucasian control subjects. The disease was considered idiopathic in 23 patients and secondary in 49. The factor V Leiden mutation was present in 18% of patients, compared with 4.6% of control subjects, resulting in a statistically significant odds ratio of 4.5. The prothrombin mutation was not significantly increased in the idiopathic osteonecrosis subgroup (8.7% versus 2.6%) with an odds ratio of 3.5. Overall, either of these coagulation disorders was present in 22.2% of patients and in 7.3% of control subjects resulting in a significant odds ratio of 3.6. Factor V Leiden, a genetic risk factor for venous thrombosis, is associated with nontraumatic osteonecrosis of the femoral head, supporting the hypothesis that intravascular coagulation is a major pathogenetic mechanism of the disease.

Effect of Gravity on Colloidal Deposition Studied by Atomic Force Microscopy.

Atomic force microscopy (AFM) was used to study the effect of gravitational forces on the deposition of submicrometer colloidal particles onto solid surfaces to test the usual assumption that the contribution of gravity to the behavior of particles with diameters <1 &mgr;m is negligible. The effects of both particle size and density were examined using polystyrene sulfate latex, silica, and colloidal gold particles of several sizes ranging from 10 nm to 1 &mgr;m. The results show that significant differences are observed in the deposition of colloidal particles onto horizontal and vertical surfaces, under identical suspension conditions and exposure times, showing that gravitational forces can have a considerable effect. This effect was quantified by analysis of the AFM images. The experimental results are compared to calculations of the expected coverage and particle surface concentration assuming diffusion-limited adsorption and deposition by sedimentation. Gravity can be negligible for low-density particles with diameters considerably smaller than 1 &mgr;m. However, if the density of the colloidal particles is high, as in the case of colloidal gold, gravity can become a significant driving force for particle transport to the surface, even for particles with diameters much smaller than 100 nm. Copyright 2001 Academic Press.