Slow binding inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase

Abstract

The mechanism of slow binding inhibition of 3-hydroxy-3-methylglutaryl- coenzyme A reductase by lovastatin, fluindostatin, and related compounds was studied. Several of these compounds, including lovastatin, were found to be slow binding, while other less potent inhibitors were not. From a comparison of kinetic parameters obtained by steady-state measurements and progress curve analysis, it was concluded that the slow binding inhibitors bind by a mechanism which is more accurately described by biphasic binding than by single-step binding. The overall association rates of the slow binding inhibitors range from 1 x 10(6) to 4 x 10(-7) M-1 s-1, and the dissociation rates are in the range of 10(-3) s-1. The structures of slow binding and reversible inhibitors were compared by using molecular modeling methods. From these comparisons, it was proposed that the slow binding and very potent inhibition of, for instance, lovastatin, is not simply a result of binding of a transition state or reaction intermediate analogue. The various lipophilic groups of the inhibitors that do not seem to be related to structural features of the substrate may also play a crucial role in determining the mechanism of binding of HMGR inhibitors.

Molecular mechanism for inhibition of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase by rosuvastatin

“…Inhibition kinetics are competitive with respect to HMG-CoA and non-competitive when NADPH is varied. Similar slow binding kinetics have been reported for compactin [10], lovastatin, fluindostatin and analogues [11].…”

“…The forward and reverse rate constants for the equilibrium between E.I and E.I * may lead to changes in the degree of inhibition during the time scale of enzyme assays, but they are sufficiently rapid to be unlikely to influence the pharmacokinetics and biological activity of rosuvastatin. The magnitudes of the forward and reverse rate constants are similar for rosuvastatin (Figure 1), lovastatin, fluindostatin and analogues [11]. The increase in affinity in going from E.I to E.I * appears to be comparable in magnitude …”

“…Bottom panel: the structure of rosuvastatin and kinetic scheme for inhibition [9][10][11]. There is rapid formation of an initial E.I complex, with a dissociation constant, K i , of ≈ 1 nM, followed by a slow transition (forward rate constant k f = 0.019 s −1 ; reverse rate constant k r = 0.009 s −1 ) to give a more tightly bound complex, and an overall steady-state inhibition constant, K i * , of ≈ 0.1 nM.…”

“…Catalytic activity was determined by following A 340 as a measure of NADPH utilization[10,11]. Binding is competitive with HMG-CoA, so that the absolute values of K i and K i * are obtained by extrapolation to zero substrate.…”

Fluvastatin, HMG‐CoA Reductase Inhibitor: Antiatherogenic Profiles Through Its Lipid‐Lowering–Dependent and ‐Independent Actions

“…In rat liver microsomes, a cell free system, fluvastatin inhibited HMG-CoA reductase activity with an IC 50 of 7 nM (35,44). Kinetic studies demonstrated that the inhibitory effect of fluvastatin was competitive regarding HMG-CoA and that the potency of fluvastatin was related to a slow inhibition of HMG-CoA reductase due to biphasic binding steps (35,44).…”