A novel approach to cyclin-dependent kinase 5/p25 inhibitors: A potential treatment for Alzheimer's disease

Based on the earlier results of our in-house database and compound library, a series of novel clubbed thienyl triazoles was designed which may emerge as potential cdk5/p25 inhibitors, for the treatment of Alzheimer's disease. A benign synthesis was planned so as to take an advantage of MAOS (Microwave Assisted Organic Synthesis) method. Evaluation of the SAR of this series has allowed the identification of compounds 4, 5, 7 and 8 from series I while 13, 14, 16 and 17 from series II as significant cdk5/p25 inhibitors and thus have potential as possible treatments for Alzheimer's disease.

Opposite behaviors of reactive metabolites of tienilic acid and its isomer toward liver proteins: use of specific anti-tienilic acid-protein adduct antibodies and the possible relationship with different hepatotoxic effects of the two compounds

Tienilic acid (TA) is responsible for an immune-mediated drug-induced hepatitis in humans, while its isomer (TAI) triggers a direct hepatitis in rats. In this study, we describe an immunological approach developed for studying the specificity of the covalent binding of these two compounds. For this purpose, two different coupling strategies were used to obtain TA-carrier protein conjugates. In the first strategy, the drug was linked through its carboxylic acid function to amine residues of carrier proteins (BSA-N-TA and casein-N-TA), while in the second strategy, the thiophene ring of TA was attached to proteins through a short 3-thiopropanoyl linker, the corresponding conjugates (BSA-S-5-TA and betaLG-S-5-TA) thus preferentially presenting the 2, 3-dichlorophenoxyacetic moiety of the drug for antibody recognition. The BSA-S-5-TA conjugate proved to be 30 times more immunogenic than BSA-N-TA. Anti-TA-protein adduct antibodies were obtained after immunization of rabbits with BSA-S-5-TA (1/35000 titer against betaLG-S-5-TA in ELISA). These antibodies strongly recognized the 2, 3-dichlorophenoxyacetic moiety of TA but poorly the part of the drug engaged in the covalent binding with the proteins. This powerful tool was used in immunoblots to compare TA or TAI adduct formation in human liver microsomes as well as on microsomes from yeast expressing human liver cytochrome P450 2C9. TA displayed a highly specific covalent binding focused on P450 2C9 which is the main cytochrome P450 responsible for its hepatic activation in humans. On the contrary, TAI showed a nonspecific alkylation pattern, targeting many proteins upon metabolic activation. Nevertheless, this nonspecific covalent binding could be completely shifted to a thiol trapping agent like GSH. The difference in alkylation patterns for these two compounds is discussed with regard to their distinct toxicities. A relationship between the specific covalent binding of P450 2C9 by TA and the appearance of the highly specific anti-LKM2 autoantibodies (known to specifically recognize P450 2C9) in patients affected with TA-induced hepatitis is strongly suggested.

Electrospray ionization mass spectrometric analysis of intact cytochrome P450: identification of tienilic acid adducts to P450 2C9

A general scheme for the purification of baculovirus-expressed cytochrome P450s (P450s) from the crude insect cell pastes has been designed which renders the P450s suitable for analysis by high-performance liquid chromatography (HPLC) electrospray ionization mass spectrometry (ESI-MS). An HPLC/ESI-MS procedure has been developed to analyze small amounts of intact purified P450 (P450s cam-HT, 1A1, 1A2, 2A6, 2B1, 2C9, 2C9 C175R, 3A4, 3A4-HT) and rat NADPH cytochrome P450 reductase (P450 reductase). The experimentally determined and predicted (based on the amino acid sequences) molecular masses (MMs) of the various proteins had identical rank orders. For each individual protein, the difference between the experimentally determined (+/-SD, based on experiments performed on at least 3 different days) and predicted MMs ranged from 0.002 to 0.035%. Each experimentally determined MM had a standard deviation of less than 0.09% (based on the charge state distribution). Application of this HPLC/ESI-MS technique made the detection of the covalent modification to P450 2C9 following mechanism-based inactivation by tienilic acid possible. In the absence of glutathione, three P450 2C9 species were detected that produced ESI mass spectra corresponding to native P450 2C9 and both a monoadduct and a diadduct of tienilic acid to P450 2C9. In the presence of glutathione, only native P450 2C9 and the monoadduct were detected. Based on the observed mass shifts for the P450 2C9/tienilic acid adducts, a mechanism for the inactivation of P450 2C9 by tienilic acid is proposed.

The substrate binding site of human liver cytochrome P450 2C9: an approach using designed tienilic acid derivatives and molecular modeling

Biochemical experiments, using the well-defined human liver CYP2C9 expressed in yeast, and molecular modeling techniques were used to derive a predictive model for substrates of CYP2C9. The ability of 10 2-aroylthiophenes related to tienilic acid to act as substrates for CYP2C9 was studied. Four of them were original compounds that were synthesized and completely characterized by several spectroscopic techniques. In these 10 compounds various chemical functions, such as ester, amide, alcohol, phenol, ether or tetrazole functions, replaced the OCH2COOH function of tienilic acid. Among them, only the derivatives containing an acidic function (carboxylic acids, phenol, and tetrazole whose pKaS are 4.8, 6.3, and 3.8, respectively) underwent a 5-hydroxylation of their thiophene ring like tienilic acid. Despite their close structural analogy with tienilic acid, all of the other compounds not only did not undergo any 5-hydroxylation of their thiophene ring but also failed to act as inhibitors of CYP2C9. These results strongly suggested that the presence, at pH 7.4, of a negative charge on the substrate is a very important feature in its recognition by CYP2C9. In fact, the four new substrates of CYP2C9 described in this study, a carboxylic acid, phenol, and tetrazole derivative, each of which is related to tienilic acid, and the antiinflammatory drug, suprofen (with Km between 12 and 130 microM and kcat between 0.2 and 1.3 min-1), as well as almost all CYP2C9 substrates reported in the literature, exhibit a pKa below 7 (except phenytoin whose pKa is 8.1). They mainly exist as anions at physiological pH. By using molecular modeling techniques, 12 CYP2C9 substrates were superimposed with respect to their hydroxylation site and fitted onto templates, which were rigid molecules such as (S)-warfarin and phenytoin. It was thus possible to arrange them in order that all their anionic sites were at a distance around 4 A from a common point (a putative cationic site of the protein) in space. These results provide a model of the substrate binding site of CYP2C9, in which substrates interact through their anionic site A- with a cationic residue of the CYP2C9 protein C+. In that model, the distance between the hydroxylation site (Hy) and the anionic site (A-) is 7.8 +/- 1.6 A, and the <HyA-C+ angle is 82 +/- 15 degrees.

Studies on uricosuric diuretics. 4. Three-dimensional structure-activity relationships and receptor mapping of (aryloxy)acetic acid diuretics

Attempts to develop new (aryloxy)acetic acids with a better profile of diuretic and uricosuric activities as well as with fewer side effects have produced a series of compounds in which the ring system has been varied. Diuretic screening of these analogues in rats indicated that the great difference in the activity between these compounds might be ascribed to a difference in the ring system rather than that in the substituent effect and that the annulation hypothesis described before is not necessarily applicable to all of these compounds. This prompted us to study the relationship between the structure and the diuretic activity of the (aryloxy)acetic acids. An active model (receptor model) was created with the indanone moiety of R-(-)-3 and the dihydrobenzofuran-2-carboxylic acid moiety of S-(+)-4. The three-dimensional structure-activity study of known compounds 2-4, and 5a using the active model showed that the degree of fitting to the model is related to the diuretic activity of these compounds. This was also confirmed for compounds 6a, 6b, 9a, 10a, 11a, 12a, 13a, 14a, 15a, and 16a, and the relation between the structure and the diuretic activity was rationalized qualitatively. With these insights in mind, a modified receptor model was constructed. We believe that this model is useful for a prediction of the activity of compounds not yet synthesized as well as for designing new (aryloxy)acetic acid diuretics.