Time-dependent inhibition

Flurbiprofen and indomethacin, which comprise the third class of inhibitors, cause a slow, time-dependent inhibition of COX-1 and COX-2, apparently via formation of a salt bridge between a carboxylate on the drug and Arg , which lies in the tunnel. 

IFN-)il exhibits dose- and time-dependent inhibition of HCV rephcation in various models, independently of type I and IIIFN receptors and induced pathways (Marcello et al. 2006). A pegylated form of IFN-A, will soon enter clinical evaluation. 

K. J. (1990). Time-dependent inhibition of oxygen radical induced lung injury. Inflammation 14, 509-522. 

If the inhibitor potency is such that the concentration of inhibitor required to affect significant, time-dependent inhibition is similar to the concentration of enzyme, then one must account for the tight binding nature of the inhibition (discussed further in Chapter 7). In this case Equation (6.1) is modified as follows ... 

The KA values reported by Williams et al. can be used to calculate the relative change in free energy for the enzyme-ligand complexes as described in Chapter 3, fixing the AG ng for the free enzyme at zero (Table 6.3). These data allow us to construct an energy level diagram for the process of time-dependent inhibition of... 

Methotrexate is a valuable drug that is commonly used in the treatment of inflammatory diseases, autoimmune diseases, and proliferative dieases. Its true potency can only be realized by the proper, quantitative analysis of the time-dependent inhibition of DHFR by this compound. 

D. H. Rich, and E. T. Sun, Mechanism of inhibition of pepsin by pepstatin. Effect of inhibitor structure on dissociation constant and time-dependent inhibition, Biochem. Pharmacol. 29 2205 (1980). 

Figure 9.11 Time-dependent inhibition of CYP3A4 by troglitazone [176],...

Atkinson, A., Kenny, J.R. and Grime, K. (2005) Automated assessment of time-dependent inhibition of human cytochrome P450 enzymes using liquid chromatography-tandem mass spectrometry analysis. Drug Metabolism and Disposition, 33 (11), 1637—1647. 

Assays are set up containing enzyme and inhibitor (or water for controls) in the initial volumes shown. Inhibitor concentrations listed are initial concentrations. Enzyme and inhibitor should be preincubated together if time-dependent inhibition is suspected. The assay is started by transfer of 20 pL of the contents of each well in groups 1 and 3 to a corresponding well in groups 2 and 4, respectively. Thereafter, 100 pL of substrate at an initial concentration of 30 pM (3 x K ) is added to all wells. The reaction wells then contain components at the concentrations listed in O Table 4-4. 

CYP3A5 inhibition Time-dependent inhibition CYP3A4 (half-life)... 

Yamamoto, T., Suzuki, A. and Kohno, Y. (2004) High-throughput screening for the assessment of time-dependent inhibitions of new drug candidates on... 

Figure 2. Time-dependent inhibition of ganglioside synthesis in N4TG1 cells by morphine and [d-A la1, D-Leu5 exkephalin under conditions described in text...

Time-dependent inhibition should be examined. A 30-minute preincubation (i.e., with nicotinamide adenine dinucleotide phosphate (NADPH) enzyme, and drug candidate prior to addition of the probe substrate) is recommended. 

It is recommended that time-dependent inhibition be examined when deemed appropriate. Time-dependent inhibition should be examined with and without NADPH over an inhibitor concentration range of 1- to 10-fold the clinically relevant plasma concentrations. Various preincubation time points, such as 0, 15, 30, 45, and 60 minutes, should be utilized along with at least a 10-fold dilution step prior to the substrate incubation. 

An in vitro examination of time-dependent inhibition of the major drug-metabolizing CYP enzymes should be considered essential for drug candidates. Time-dependent inhibition occurs when the inhibitory potential of a drug candidate increases as the enzyme is exposed to the inhibitor over time. This type of inhibition may occur by several potential mechanisms, including the following ... 

As is the case for direct inhibition, the FDA takes a conservative stance on interpreting time-dependent inhibition. The FDA states that any time-dependent and concentration-dependent loss of initial product formation rate indicates mechanism-based inhibition and that this finding should be followed up with human in vivo studies (1,2). 

Human CYP2E1 is one of the most efficient P450s to catalyze the oxidation of acetaminophen to NAPQI (157-159). Ethanol and isoniazid cause a time-dependent inhibition and induction of acetaminophen oxidation to NAPQI in humans (160,161) that can decrease risk for hepatotoxicity over the interval of concurrent administration and increase risk for hepatotoxicity a few hours after removal of ethanol or isoniazid. The latter induction phase of CYP2E1 may, in part, be responsible for cases of acetaminophen hepatotoxicity associated with the use of ethanol (162-165) or isoniazid (166-168). However, the induction is modest (2- to 3-fold) therefore, other susceptibility factors, genetic and others such as decreased glutathione stores and nutritional status, are likely to play an important role in some individuals (169-174). 

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