P-Glycoprotein-ATPase Modulation: The Molecular Mechanisms

Abstract

P-glycoprotein-ATPase is an efflux transporter of broad specificity that counteracts passive allocrit influx. Understanding the rate of allocrit transport therefore matters. Generally, the rates of allocrit transport and ATP hydrolysis decrease exponentially with increasing allocrit affinity to the transporter. Here we report unexpectedly strong down-modulation of the P-glycoprotein-ATPase by certain detergents. To elucidate the underlying mechanism, we chose 34 electrically neutral and cationic detergents with different hydrophobic and hydrophilic characteristics. Measurement of the P-glycoprotein-ATPase activity as a function of concentration showed that seven detergents activated the ATPase as expected, whereas 27 closely related detergents reduced it significantly. Assessment of the free energy of detergent partitioning into the lipid membrane and the free energy of detergent binding from the membrane to the transporter revealed that the ratio, q, of the two free energies of binding determined the rate of ATP hydrolysis. Neutral (cationic) detergents with a ratio of q = 2.7 ± 0.2 (q > 3) followed the aforementioned exponential dependence. Small deviations from the optimal ratio strongly reduced the rates of ATP hydrolysis and flopping, respectively, whereas larger deviations led to an absence of interaction with the transporter. P-glycoprotein-ATPase inhibition due to membrane disordering by detergents could be fully excluded using (2)H-NMR-spectroscopy. Similar principles apply to modulating drugs.

The DrrAB Efflux System of Streptomyces peucetius Is a Multidrug Transporter of Broad Substrate Specificity

“…3, panel D. Interestingly, of the three Hoechst dyes tested, only H 33342 was transported. Recent studies showed that a certain balance between the hydrophobic and hydrophilic forces in the structure of the target substrate is essential for optimum efflux by Pgp (39). Because H 33342 is the most amphiphilic of the three dyes, this may explain why DrrAB is able to preferentially transport H 33342 but not the other two dyes.…”

How Phosphorylation and ATPase Activity Regulate Anion Flux though the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)

“…The open state can also be prolonged by binding of potentiators that reduce the ATPase activity and slow down flopping and drug release (rate constant k 2 ). As shown for P-glycoprotein, drug release is rate-determining (88).…”

How to overcome ATP-binding cassette drug efflux transporter-mediated drug resistance?

“…Since overexpression of some of the ABC transporters was correlated with a poor chemotherapeutic response and prognosis of patients with specific cancer types, inhibition of ABC transporters appears a logical approach to circumvent MDR and improve patient's outcome [82,83] . However, other than in a preclinical setting where ABC transporters could reverse MDR, this promise has still not been fulfilled in clinical practice.…”

“…Competitive inhibitors exert their function by tightly binding and blocking the substrate binding pockets. Non-competitive inhibitors exert their function by binding to a non-substrate binding site thereby inhibiting the ATPase activity or modulating transporters' function allosterically [15,[83][84][85] . Another strategy to circumvent MDR that will be discussed further is the application of small interfering RNA (siRNA) [86][87][88] and microRNA (miRNA) [89,90] inoculation to down-regulate ABC transporter expression.…”