- Multistep Binding of the Non-Steroidal Inhibitors Orteronel and Seviteronel to Human Cytochrome P450 17A1 and Relevance to Inhibition of Enzyme Activity
-
Orteronel (TAK-700) is a substituted imidazole that was developed for the treatment of castration-resistant prostate cancer but was dropped in phase III clinical trials. Both enantiomers of this inhibitor of cytochrome P450 (P450) 17A1 show some selectivity in differentially blocking the 17α-hydroxylation and lyase activities of the enzyme. Although both enantiomers of this compound have sub-micromolar IC50 values and bind to the enzyme with a type II spectral change (indicative of nitrogen-iron bonding) and reported Kd values of 56 and 40 nM (R and S, respectively), the rates of binding to P450 17A1 were relatively slow. We considered the possibility that the drug is a slow, tight-binding inhibitor. Analysis of the kinetics of binding revealed rapid formation of an initial complex, presumably in the substrate binding site, followed by a slower change to the spectrum of a final iron complex. Similar kinetics were observed in the interaction of another inhibitor, the triazole (S)-seviteronel (VT-464), with P450 17A1. Kinetic tests and modeling indicate that the further change to the iron-complexed form of the orteronel- or seviteronel-P450 complex is not a prerequisite for enzyme inhibition. Accordingly, the inclusion of heme-binding heterocyclic nitrogen moieties in P450 17A1 inhibitors may not be necessary to achieve inhibition but may nevertheless augment the process.
- Child, Stella A.,Guengerich, F. Peter
-
-
Read Online
- Kinetic processivity of the two-step oxidations of progesterone and pregnenolone to androgens by human cytochrome P450 17A1
-
Cytochrome P450 (P450, CYP) 17A1 plays a critical role in steroid metabolism, catalyzing both the 17-hydroxyla-tion of pregnenolone and progesterone and the subsequent 17,20-lyase reactions to form dehydroepiandrosterone (DHEA) and androstenedione (Andro), respectively, critical for generating glucocorticoids and androgens. Human P450 17A1 reaction rates examined are enhanced by the accessory protein cytochrome b5 (b5), but the exact role of b5 in P450 17A1-catalyzed reactions is unclear as are several details of these reactions. Here, we examined in detail the processivity of the 17-hydroxylation and lyase steps. b5 did not enhance reaction rates by decreasing the koff rates of any of the steroids. Steroid binding to P450 17A1 was more complex than a simple two-state system. Pre-steady-state experiments indicated lag phases for Andro production from progesterone and for DHEA from pregnenolone, indicating a distributive character of the enzyme. However, we observed processivity in pregnenolone/DHEA pulse– chase experiments. (S)-Orteronel was three times more inhibitory toward the conversion of 17-hydroxypregnenolone to DHEA than toward the 17-hydrox-ylation of pregnenolone. IC50 values for (S)-orteronel were identical for blocking DHEA formation from pregnenolone and for 17-hydroxylation, suggestive of processivity. Global kinetic modeling helped assign sets of rate constants for individual or groups of reactions, indicating that human P450 17A1 is an inherently distributive enzyme but that some processivity is present, i.e. some of the 17-OH pregnenolone formed from pregnenolone did not dissociate from P450 17A1 before conversion to DHEA. Our results also suggest multiple conformations of P450 17A1, as previously proposed on the basis of NMR spectroscopy and X-ray crystallography.
- Gonzalez, Eric,Guengerich, F. Peter
-
-
Read Online
- PRODUCTION METHOD OF IMIDAZOLE DERIVATIVES
-
The present invention provides an advantageous production method of an imidazole derivative, which is suitable for industrial production. Compound (VI) is produced by reacting compound (I) with a Grignard reagent or a magnesium reagent, and a lithium reagent, and then reacting the resulting compound with compound (V).
- -
-
-
- 1,1-Diarylalkenes as anticancer agents: Dual inhibitors of tubulin polymerization and phosphodiesterase 4
-
A series of 1,1-diarylalkene derivatives were prepared to optimize the properties of CC-5079 (1), a dual inhibitor of tubulin polymerization and phosphodiesterase 4 (PDE4). By using the 3-ethoxy-4-methoxyphenyl PDE4 pharmacophore as one of the aromatic ri
- Ruchelman, Alexander L.,Man, Hon-Wah,Chen, Roger,Liu, Wei,Lu, Ling,Cedzik, Dorota,Zhang, Ling,Leisten, Jim,Collette, Alice,Narla, Rama Krishna,Raymon, Heather K.,Muller, George W.
-
p. 6356 - 6374
(2011/12/02)
-
