Verapamil metabolites: potential P-glycoprotein-mediated multidrug resistance reversal agents

2003 ◽  
Vol 81 (8) ◽  
pp. 800-805 ◽  
Author(s):  
Cindy Woodland ◽  
Gideon Koren ◽  
Irving W Wainer ◽  
Gerry Batist ◽  
Shinya Ito
Keyword(s):  
Multidrug Resistance ◽  
Drug Transport ◽  
Mdck Cells ◽  
Parent Compound ◽  
Tubular Secretion ◽  
Dependent Manner ◽  
Reversal Agents ◽  
P Glycoprotein ◽  
Renal Tubular ◽  
Apical Membranes

Multidrug resistance in cancer chemotherapy frequently correlates with overexpression of the P-glycoprotein drug transporter. Attempts to reverse P-glycoprotein-mediated multidrug resistance with racemic verapamil or its less toxic (R)-enantiomer have been complicated by cardiotoxicity. The objective of this study was to investigate the effects of the major verapamil metabolite, norverapamil, as well as the PR-22 and D-620 metabolites, on P-glycoprotein-mediated drug transport. We measured the basolateral-to-apical fluxes of the P-glycoprotein substrates digoxin and vinblastine in the presence and absence of verapamil, (R)-norverapamil, (S)-norverapamil, racemic norverapamil, PR-22, or D-620 across confluent monolayers of Madin–Darby canine kidney (MDCK) cells that express P-glycoprotein on their apical membranes. Verapamil and norverapamil nonstereospecifically inhibited the renal tubular secretion of digoxin and vinblastine similarly in a dose-dependent manner. However, there was no decrease in the cellular accumulation of digoxin and vinblastine, suggesting that neither verapamil nor norverapamil prevent the substrates from entering the MDCK cells. Furthermore, the norverapamil metabolite P-22 also inhibited the secretion of these P-glycoprotein substrates. Our results suggest that the verapamil metabolites norverapamil and PR-22, which are less cardiotoxic than the parent compound, have comparable inhibitory abilities to verapamil (norverapamil greater than PR-22) and may be useful in reversing resistance to P-glycoprotein substrates.Key words: verapamil, norverapamil, PR-22, kidney, P-glycoprotein.

Modeling of P-glycoprotein-involved epithelial drug transport in MDCK cells

1999 ◽  
Vol 277 (1) ◽  
pp. F84-F96 ◽  
Author(s):  
Shinya Ito ◽  
Cindy Woodland ◽  
Balázs Sarkadi ◽  
Guido Hockmann ◽  
Scott E. Walker ◽  
...  
Keyword(s):  
Drug Transport ◽  
Diffusion Processes ◽  
Efflux Pump ◽  
Mdck Cells ◽  
Basolateral Membrane ◽  
Drug Efflux ◽  
Drug Transfer ◽  
P Glycoprotein ◽  
Drug Efflux Pump ◽  
Apical Membranes

P-glycoprotein (P-gp) on the apical membranes of epithelial cells is known as a drug efflux pump. However, unclear is its integral quantitative role in the overall epithelial drug transfer, which also involves distinct diffusion processes in parallel and sequence. We used a simple three-compartment model to obtain kinetic parameters of each drug transfer mechanism, which can quantitatively describe the transport time courses of P-gp substrates, digoxin and vinblastine, across P-gp-expressing MDCK cell monolayers grown on permeable filters. Our results show that the model, which assumes a functionally single drug efflux pump in the apical membrane with diffusion across two membranes and intercellular junctions, is the least complex model with which to quantitatively reproduce the characteristics of the data. Interestingly, the model predicts that the MDCK apical membranes are less diffusion permeable than the basolateral membrane for both drugs and that the distribution volume of vinblastine is 10-fold higher than that of digoxin. Additional experiments verified these model predictions. The modeling approach is feasible to quantitatively describe overall kinetic picture of epithelial drug transport. Further model refinement is necessary to incorporate other modes of drug transport such as transcytosis. Also, whether P-gp solely accounts for the pump function in this model awaits more studies.

scholarly journals Possible Involvement of the Drug Transporters P Glycoprotein and Multidrug Resistance-Associated Protein Mrp2 in Disposition of Azithromycin

2004 ◽  
Vol 48 (3) ◽  
pp. 809-814 ◽  
Author(s):  
Masami Sugie ◽  
Emiko Asakura ◽  
Ying Lan Zhao ◽  
Shoko Torita ◽  
Masayuki Nadai ◽  
...  
Keyword(s):  
Multidrug Resistance ◽  
Drug Transporters ◽  
Tubular Secretion ◽  
Intestinal Excretion ◽  
Normal Tissues ◽  
P Glycoprotein ◽  
Plasma Concentration Ratio ◽  
Erythromycin A ◽  
Renal Tubular

ABSTRACT P glycoprotein and multidrug resistance-associated protein 2 (Mrp2), ATP-dependent membrane transporters, exist in a variety of normal tissues and play important roles in the disposition of various drugs. The present study seeks to clarify the contribution of P glycoprotein and/or Mrp2 to the disposition of azithromycin in rats. The disappearance of azithromycin from plasma after intravenous administration was significantly delayed in rats treated with intravenous injection of cyclosporine, a P-glycoprotein inhibitor, but was normal in rats pretreated with intraperitoneal injection erythromycin, a CYP3A4 inhibitor. When rats received an infusion of azithromycin, cyclosporine and probenecid, a validated Mrp2 inhibitor, significantly decreased the steady-state biliary clearance of azithromycin to 5 and 40% of the corresponding control values, respectively. However, both inhibitors did not alter the renal clearance of azithromycin, suggesting the lack of renal tubular secretion of azithromycin. Tissue distribution experiments showed that azithromycin is distributed largely into the liver, kidney, and lung, whereas both inhibitors did not alter the tissue-to-plasma concentration ratio of azithromycin. Significant reduction in the biliary excretion of azithromycin was observed in Eisai hyperbilirubinemic rats, which have a hereditary deficiency in Mrp2. An in situ closed-loop experiment showed that azithromycin was excreted from the blood into the gut lumen, and the intestinal clearance of azithromycin was significantly decreased by the presence of cyclosporine in the loop. These results suggest that azithromycin is a substrate for both P glycoprotein and Mrp2 and that the biliary and intestinal excretion of azithromycin is mediated via these two drug transporters.

scholarly journals The Fluorescent Probe Bodipy-FL-Verapamil Is a Substrate for Both P-glycoprotein and Multidrug Resistance-related Protein (MRP)-1

2002 ◽  
Vol 50 (5) ◽  
pp. 731-734 ◽  
Author(s):  
Enrico Crivellato ◽  
Luigi Candussio ◽  
Anna M. Rosati ◽  
Fiora Bartoli-Klugmann ◽  
Franco Mallardi ◽  
...  
Keyword(s):  
Multidrug Resistance ◽  
Drug Transport ◽  
Mrna Level ◽  
Fluorescent Microscopy ◽  
Flow Cytometric Analysis ◽  
Cell Types ◽  
Multidrug Resistant ◽  
Related Protein ◽  
P Glycoprotein ◽  
Multidrug Resistance Related Protein

Several fluorescent probes have been used in functional studies to analyze drug transport in multidrug-resistant cells by fluorescent microscopy. Because many of these molecules have some drawbacks, such as toxicity, nonspecific background, or accumulation in mitochondria, new fluorescent compounds have been proposed as more useful tools. Among these substances, Bodipy-FL-Verapamil, a fluorescent conjugate of the drug efflux blocker verapamil, has been used to study P-glycoprotein activity in different cell types. In this study we tested by fluorescent microscopy the accumulation of Bodipy-FL- Verapamil in cell lines that overexpress either P-glycoprotein (P-gp) or multidrug resistance-related protein 1 (MRP1). Expression of P-gp and MRP1 was evaluated at the mRNA level by RT-PCR technique and at the protein level by flow cytometric analysis using C219 and MRP-m6 monoclonal antibodies. Results indicate that Bodipy-FL-Verapamil is actually a substrate for both proteins. As a consequence, any conclusion about P-gp activity obtained by the use of Bodipy-FL-Verapamil as fluorescent tracer should be interpreted with caution.

scholarly journals ATP-dependent thermostabilization of human P-glycoprotein (ABCB1) is blocked by modulators

2019 ◽  
Vol 476 (24) ◽  
pp. 3737-3750 ◽  
Author(s):  
Sabrina Lusvarghi ◽  
Suresh V. Ambudkar
Keyword(s):  
Conformational Changes ◽  
Drug Transport ◽  
Atp Hydrolysis ◽  
Atp Binding ◽  
Dependent Manner ◽  
Deficient Mutant ◽  
Concentration Dependent Manner ◽  
Glycoprotein P ◽  
Binding Domains ◽  
P Glycoprotein

P-glycoprotein (P-gp), an ATP-binding cassette transporter associated with multidrug resistance in cancer cells, is capable of effluxing a number of xenobiotics as well as anticancer drugs. The transport of molecules through the transmembrane (TM) region of P-gp involves orchestrated conformational changes between inward-open and inward-closed forms, the details of which are still being worked out. Here, we assessed how the binding of transport substrates or modulators in the TM region and the binding of ATP to the nucleotide-binding domains (NBDs) affect the thermostability of P-gp in a membrane environment. P-gp stability after exposure at high temperatures (37–80°C) was assessed by measuring ATPase activity and loss of monomeric P-gp. Our results show that P-gp is significantly thermostabilized (>22°C higher IT50) by the binding of ATP under non-hydrolyzing conditions (in the absence of Mg2+). By using an ATP-binding-deficient mutant (Y401A) and a hydrolysis-deficient mutant (E556Q/E1201Q), we show that thermostabilization of P-gp requires binding of ATP to both NBDs and their dimerization. Additionally, we found that transport substrates do not affect the thermal stability of P-gp either in the absence or presence of ATP; in contrast, inhibitors of P-gp including tariquidar and zosuquidar prevent ATP-dependent thermostabilization in a concentration-dependent manner, by stabilizing the inward-open conformation. Altogether, our data suggest that modulators, which bind in the TM regions, inhibit ATP hydrolysis and drug transport by preventing the ATP-dependent dimerization of the NBDs of P-gp.

Drug efflux mediated by the human multidrug resistance P-glycoprotein is inhibited by cell swelling

1994 ◽  
Vol 107 (12) ◽  
pp. 3281-3290
Author(s):  
A. Sardini ◽  
G.M. Mintenig ◽  
M.A. Valverde ◽  
F.V. Sepulveda ◽  
D.R. Gill ◽  
...  
Keyword(s):  
Multidrug Resistance ◽  
Chloride Channels ◽  
Drug Transport ◽  
Atp Hydrolysis ◽  
Cell Swelling ◽  
Drug Efflux ◽  
Fluorescent Substrate ◽  
Membrane Stretch ◽  
P Glycoprotein ◽  
In Cells

P-glycoprotein (P-gp), the product of the human multidrug resistance (MDR1) gene, confers multidrug resistance on cells by acting as an ATP-dependent drug transporter. A method using confocal microscopy was developed to measure the transport activity of P-gp from the rate of movement of doxorubicin, a fluorescent substrate of P-gp, across the membrane of a single cell. Recent work has shown that expression of P-gp enhances the activation of chloride channels in response to cell swelling, suggesting that membrane stretch might switch P-gp from a drug-transporting mode to a mode in which it activates chloride channels. In agreement with this idea, we find that cell swelling inhibits drug efflux in cells expressing P-gp but is without effect on the slower background efflux in cells not expressing P-gp and in cells transiently transfected with a mutated MDR1 in which the ATP hydrolysis sites had been inactivated. The identification of a novel means for inhibiting P-gp-mediated drug transport may have implications for the reversal of multidrug resistance during chemotherapy.

Identification of the synthetic surfactant nonylphenol ethoxylate: a P-glycoprotein substrate in human urine

1998 ◽  
Vol 274 (6) ◽  
pp. F1127-F1139 ◽  
Author(s):  
Jeffrey H. M. Charuk ◽  
Arthur A. Grey ◽  
Reinhart A. F. Reithmeier
Keyword(s):  
Cyclosporin A ◽  
Drug Transport ◽  
Mdck Cells ◽  
Chinese Hamster ◽  
Multidrug Resistant ◽  
The Body ◽  
Transepithelial Transport ◽  
Synthetic Surfactant ◽  
Nonylphenol Ethoxylate ◽  
P Glycoprotein

P-glycoprotein (Mdr1p) is an ATP-dependent drug efflux pump that is overexpressed in multidrug-resistant cells and some cancers. Mdr1p is also expressed in normal tissues like the kidney, where it can mediate transepithelial drug transport. A human urinary compound that reverses multidrug resistance and blocks [3H]azidopine photolabeling of P-glycoprotein was purified to homogeneity and identified by 1H-NMR and mass spectrometry as the synthetic surfactant nonylphenol ethoxylate (NPE). Multidrug-resistant Chinese hamster ovary (CHO) C5 cells accumulated less [3H]NPE than parental drug-sensitive Aux-B1 cells, and Mdr1p substrates, verapamil and cyclosporin A, increased this surfactant’s accumulation in C5 cells. NPE blocked the net transepithelial transport (basolateral to apical) of [3H]cyclosporin A in epithelia formed by Madin-Darby canine kidney (MDCK) cells. Net transepithelial transport (basal to apical) of [3H]NPE was demonstrated in MDCK cells and was inhibited by cyclosporin A. These findings show NPE is a Mdr1p substrate excreted into urine by kidney P-glycoprotein. NPE is a widely used surfactant and a known hormone disrupter that is readily absorbed orally or topically. The current findings indicate the function of kidney Mdr1p may be to eliminate exogenous compounds from the body.

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