Design and synthesis of peptidomimetic factor VIIa inhibitors.

Selective factor VIIa-tissue factor complex (FVIIa/TF) inhibition is regarded as a promising target for developing new anticoagulant drugs. In previous reports, we described a S3 subsite found in the X-ray crystal structure of compound 2 that bound to FVIIa/soluble tissue factor (sTF). Based on the X-ray crystal structure information and with the aim of improving the inhibition activity for FVIIa/TF and selectivity against other serine proteases, we synthesized derivatives by introducing substituents at position 5 of the indole ring of compound 2. Among them, compound 16 showed high selectivity against other serine proteases. Contrary to our expectations, compound 16 did not occupy the S3-subsite; X-ray structure analysis revealed that compound 16 improved selectivity by forming hydrogen bonds with Gln217, Thr99 and Asn100.

Factor VIIa inhibitors: target hopping in the serine protease family using X-ray structure determination.

Selective factor VIIa-tissue factor complex (FVIIa/TF) inhibition is regarded as a promising target for developing new anticoagulant drugs. Compound 1 was discovered from focused screening of serine protease-directed compounds from our internal collection. Using parallel synthesis supported by structure-based drug design, we identified peptidemimetic FVIIa/TF inhibitors (compounds 4-11) containing L-Gln or L-Met as the P2 moiety. However, these compounds lacked the selectivity of other serine proteases in the coagulation cascade, especially thrombin. Further optimization of these compounds was carried out with a focus on the P4 moiety. Among the optimized compounds, 12b-f showed improved selectivity.

Structure of human factor VIIa/tissue factor in complex with a peptide-mimetic inhibitor: high selectivity against thrombin by introducing two charged groups in P2 and P4.

The crystal structure of human factor VIIa/soluble tissue factor (FVIIa/sTF) in complex with a highly selective peptide-mimetic FVIIa inhibitor which shows 1670-fold selectivity against thrombin inhibition has been solved at 2.6 A resolution. The inhibitor is bound to FVIIa/sTF at the S1, S2 and S3 sites and at the additional S1 subsite. Two charged groups, the amidino group in P2 and the carboxylate group in P4, form ionic interactions with Asp60 and Lys192 of FVIIa, respectively. Structural comparisons between factor VIIa and thrombin show that thrombin has oppositely charged residues, Lys60F and Glu192, in the S2 site and the S1 subsites, respectively. These data suggest that the utilization of the differences of charge distribution in the S2 site and the S1 subsites between FVIIa and thrombin is critical for achieving high selectivity against thrombin inhibition. These results will provide valuable information for the structure-based drug design of specific inhibitors for FVIIa/TF.

Utilisation of human pharmacology studies with biomarkers for new drug applications in Japan.

OBJECTIVE: This study evaluated the utilisation of human pharmacology studies with biomarkers for either efficacy or safety estimation conducted for new drug applications (NDAs) submitted to the Japanese regulatory authority, the Ministry of Health, Labour and Welfare (MHLW). METHODS: A total of 50 new chemical entities (NCEs) posted on the Websites, which were approved from June 2000 to November 2001, were evaluated by investigating their approval information. The utilisation of human pharmacology studies with biomarkers was evaluated by focusing on the classification referred to biomarkers for either efficacy or safety estimation and timing of studies. RESULTS: The human pharmacology studies with biomarkers for either efficacy or safety estimation were conducted in 20 compounds classified by utilising measures of either efficacy (17 compounds) or safety (seven compounds). In 4 of 17 NCEs, some of the biomarkers in human pharmacology studies were similar to the clinical endpoints for efficacy assessment in therapeutic exploratory and/or therapeutic confirmatory studies. For safety assessment in therapeutic exploratory and/or therapeutic confirmatory studies, clinical endpoints rather than biomarkers in human pharmacology studies were used in all seven NCEs. The timing of each type of clinical study could only be obtained for 15 NCEs. Of these 15 NCEs, human pharmacology studies with biomarkers for either efficacy or safety estimation were conducted on six compounds. There were only two compounds for which human pharmacology studies with biomarkers for efficacy estimation were conducted before pivotal studies such as a therapeutic exploratory study or a bridging study. CONCLUSION: Our survey suggests that with Japanese NDAs, human pharmacology studies with biomarkers for either efficacy or safety estimation do not play a key role in accelerating drug development and maximising the knowledge gained from confirmatory trials. The relationship between a biomarker and a clinical endpoint should be investigated appropriately for accelerating drug development. We think that the utilisation of human pharmacology studies with biomarkers for either efficacy or safety estimation in the regulatory review process for NDAs should be encouraged with the advancements of drug evaluation research using an appropriate biomarker based on clinical pharmacology.

Evaluation of Binding Equation Method for Unbound Serum Concentration Prediction of Valproic Acid in Polytherapy Pediatric Patients with Epilepsy.

In a previous study, we determined the in vivo population binding parameters of valproic acid (VPA) to serum proteins at single dose in nine healthy young and defined a binding equation that was derived from the Scatchard equation. Schever et al. and Yu also determined the in vivo population binding parameters of VPA in patients with epilepsy receiving VPA monotherapy or polytherapy. In this study, we retrospectively evaluated the ability of a binding equation using each of population mean binding parameters of Kodama et al. (Method 1), Scheyer et al. (Method 2), or Yu (Method 3) to predict the unbound serum VPA concentration in 23 pediatric patients with epilepsy receiving polytherapy. Mean prediction error, mean absolute prediction error (MAE), and root mean squared error (RMSE) were separately calculated for each method and served as a measure of prediction bias and precision. All three methods were significantly biased, showing a bias to overpredict unbound serum VPA. The MAEs and RMSEs for Methods 1 and 2 were similar in magnitude (Method 1: MAE = 16.5, RMSE = 23.1; Method 2: MAE = 14.0, RMSE = 17.5). On the other hand, each value for Method 3 was extremely high (MAE = 32.8 and RMSE = 36.3). Method 3 is apparently inferior to other two methods in accuracy and precision. For Methods 1 and 2, similar tendency to overprediction was observed in total concentration above 400 &mgr;mol L(minus sign1). These two methods may be useful to patients with total VPA lower than 400 &mgr;mol L(minus sign1).

Protein binding of valproic acid in Japanese pediatric and adult patients with epilepsy.

The binding of valproic acid to serum proteins in pediatric and adult patients was studied. Serum samples were obtained from 48 Japanese pediatric patients with epilepsy (group A) and 48 Japanese adult patients with epilepsy (group B) receiving valproic acid monotherapy. The patients' age ranged from 1 to 15 years for the pediatric patients and from 18 to 44 years (group B--younger) and 45 to 63 years (group B--older) for the adult patients. The serum concentrations of total and unbound valproic acid were measured by fluorescence polarization immunoassay, and the unbound serum fraction of valproic acid was analyzed by ultrafiltration. The mean association constant, K, and total concentration of binding sites, n(P), were as follows: group A, K = 0.016 L/mumol, n(P) = 1077 microM; group B, K = 0.011 L/mumol, n(P) = 1365 microM; group B--younger, K = 0.013 L/mumol, n(P) = 1291 microM; and group B--older, K = 0.006 L/mumol, n(P) = 1827 microM. Significant differences between groups A and B were observed in the serum free fatty acid concentration and the serum concentration ratio of free fatty acids to albumin. However, no significant differences between the two groups were observed in the binding of valproic acid to serum proteins. Group A's serum concentration ratio of free fatty acids to albumin was significantly lower than in group B--older and was lower than in group B--younger. However, there were no significant differences in binding between group A and groups B--younger and B--older. The serum concentration of albumin was significantly higher in group B--younger than in group B--older. Consequently, there was a significant difference in binding between groups B--younger and B--older. The serum protein binding of valproic acid was similar in pediatric and adult patients with epilepsy, but binding characteristics differed between younger and older adults.

Inhibitory effects of amino-acid fluids on drug binding to site II of human serum albumin in vitro.

The effects of amino-acid fluids on ligand binding to human serum albumin (HSA) were investigated by fluorescence and ultrafiltration techniques. Warfarin and dansylsarcosine were used as the site marker fluorescence probes for site I and site II of HSA, respectively. Amino-acid fluids specifically decreased the fluorescence intensity induced by dansylsarcosine-HSA binding without any effects on that induced by warfarin-HSA binding. The ultrafiltration technique clarified that the free fraction of the site II drug, diazepam, in human serum was increased in the presence of amino-acid fluids, while no effect was observed in the free fraction of the site I drug, warfarin. The potencies of the effect on binding to site II, observed by fluorescence and ultrafiltration techniques, correlated well with the L-tryptophan contents in amino-acid fluids or with those in L-tryptophan solutions. Based on the comparison between the effects of amino-acid fluids and L-tryptophan solutions, we confirmed that L-tryptophan in amino-acid fluids specifically inhibits drug binding to site II of HSA.

Structure-based design of P3 moieties in the peptide mimetic factor VIIa inhibitor.

Selective factor VIIa-tissue factor complex (FVIIa/TF) inhibition is seen as a promising target for developing new anticoagulant drugs. Structure-based designs of the P3 moiety in the peptide mimetic factor VIIa inhibitor successfully lead to novel inhibitors with selectivity for FVIIa/TF and extrinsic coagulation the same as or even higher than those of previously reported peptide mimetic factor VIIa inhibitors. X-ray crystal structure analysis reveals that one of the novel inhibitors shows improved selectivity by forming interactions between the inhibitor and FVIIa as expected. Another of the novel inhibitors achieves improved selectivity through an unexpected hydrogen bond with Gln217, with a unique bent conformation in FVIIa/TF accompanied by conformational changes of the inhibitor and the protein.

Novel interactions of large P3 moiety and small P4 moiety in the binding of the peptide mimetic factor VIIa inhibitor.

Selective factor VIIa-tissue factor complex (FVIIa/TF) inhibition is seen as a promising target for developing new anticoagulant drugs. A novel peptide mimetic factor VIIa inhibitor, ethylsulfonamide-d-biphenylalanine-Gln-p-aminobenzamidine, shows 100-fold selectivity against thrombin in spite of its large P3 moiety, unlike previously reported FVIIa/TF selective inhibitors. X-ray crystal structure analysis reveals that the large P3 moiety, d-biphenylalanine, and the small P4 moiety, ethylsulfonamide, make novel interactions with the 170-loop and Lys192 of FVIIa/TF, respectively, accompanying ligand-induced conformational changes of the 170-loop, Gln217, and Lys192. Structural comparisons of FVIIa with thrombin and amino acid sequence comparisons among coagulation serine proteases suggest that these interactions play an important role in achieving selective inhibition for FVIIa/TF.

Potent inhibition by star fruit of human cytochrome P450 3A (CYP3A) activity.

There has been very limited information on the capacities of tropical fruits to inhibit human cytochrome P450 3A (CYP3A) activity. Thus, the inhibitory effects of tropical fruits on midazolam 1'-hydroxylase activity of CYP3A in human liver microsomes were evaluated. Eight tropical fruits such as common papaw, dragon fruit, kiwi fruit, mango, passion fruit, pomegranate, rambutan, and star fruit were tested. We also examined the inhibition of CYP3A activity by grapefruit (white) and Valencia orange as controls. The juice of star fruit showed the most potent inhibition of CYP3A. The addition of a star fruit juice (5.0%, v/v) resulted in the almost complete inhibition of midazolam 1'-hydroxylase activity (residual activity of 0.1%). In the case of grape-fruit, the residual activity was 14.7%. The inhibition depended on the amount of fruit juice added to the incubation mixture (0.2-6.0%, v/v). The elongation of the preincubation period of a juice from star fruit (1.25 or 2.5%, v/v) with the microsomal fraction did not alter the CYP3A inhibition, suggesting that the star fruit did not contain a mechanism-based inhibitor. Thus, we discovered filtered extracts of star fruit juice to be inhibitors of human CYP3A activity in vitro.

Inhibitory effects of citrus fruits on cytochrome P450 3A (CYP3A) activity in humans.

The capacities of citrus fruits to inhibit midazolam 1'-hydroxylase activity of cytochrome P450 3A (CYP3A) expressed in human liver microsomes were evaluated. Eight citrus fruits such as ama-natsu, banpeiyu, Dekopon, hassaku, hyuga-natsu, completely matured kinkan (Tamatama), takaoka-buntan and unshu-mikan were tested. We also examined the inhibition of CYP3A activity by grapefruit (white) and grapefruit juice (white, Tropicana-Kirin). The addition of a fruit juice prepared from banpeiyu, hassaku, takaoka-buntan or Tamatama caused the inhibition of the microsomal CYP3A activity. The inhibition depended on the amount of a fruit juice added to the incubation mixture (2.5 and 5.0%, v/v). The fruit juice from banpeiyu showed the most potent inhibition of CYP3A. The addition of a banpeiyu juice (5.0%, v/v) resulted in the inhibition of midazolam 1'-hydroxylase activity to about 20% of control without a fruit juice. The elongation of the preincubation period of a fruit juice from banpeiyu (5.0%, v/v) with the microsomal fraction (5 to 15 min) led to the enhancement of the CYP3A inhibition (5% of control). Thus, we discovered ingredients of banpeiyu to be inhibitor(s) or mechanism-based inhibitor(s) of human CYP3A activity, but the inhibitory effects of them were somewhat lower than those of grapefruit.

Crystal structure of human factor VIIa/tissue factor in complex with peptide mimetic inhibitor.

The 3D structure of human factor VIIa/soluble tissue factor in complex with a peptide mimetic inhibitor, propylsulfonamide-D-Thr-Met-p-aminobenzamidine, is determined by X-ray crystallography. As compared with the interactions between thrombin and thrombin inhibitors, the interactions at S2 and S3 sites characteristic of factor VIIa and factor VIIa inhibitors are revealed. The S2 site has a small pocket, which is filled by the hydrophobic methionine side chain in P2. The small S3 site fits the small size residue, D-threonine in P3. The structural data and SAR data of the peptide mimetic inhibitor show that these interactions in the S2 and S3 sites play an important role for the improvement of selectivity versus thrombin. The results will provide valuable information for the structure-based drug design of specific inhibitors for FVIIa/TF.