Fluorescent substrates of sister-P-glycoprotein (BSEP) evaluated as markers of active transport and inhibition: evidence for contingent unequal binding sites.

Article Details

Citation

Wang EJ, Casciano CN, Clement RP, Johnson WW

Fluorescent substrates of sister-P-glycoprotein (BSEP) evaluated as markers of active transport and inhibition: evidence for contingent unequal binding sites.

Pharm Res. 2003 Apr;20(4):537-44.

PubMed ID
12739759 [ View in PubMed
]
Abstract

PURPOSE: Although sister-P-glycoprotein (SPGP, BSEP) is closely related to P-glycoprotein, it is much more selective in distribution and substrate recognition. Moreover, because inhibition or lack of BSEP function has severe consequences including cholestasis, hepatotoxicity, exposure to toxic xenobiotics, and drug interactions, in vitro methods are necessary for quantifying and characterizing specific inhibition of BSEP. Therefore, the objective is to discern a method and quantitatively characterize several example BSEP inhibitors. METHODS: With fluorescent markers having been used successfully to evaluate and quantify inhibition of P-gp-mediated transport, this study evaluates several compounds for specific cell retention caused by BSEP inhibitors. In addition to the several compounds asserted to be BSEP inhibitors, the compounds suggested to be BSEP substrates might also inhibit BSEP competitively. Retained fluorescence of possible BSEP substrates was measured by a flow cell cytometer using transfected cells presenting the BSEP transporter specifically and abundantly. RESULTS: Several compounds were shown to inhibit BSEP active transport of the fluorescent substrates dihydrofluorescein and bodipy. The inhibition potency was quantified (i.e., cyclosporin A IC50 approximately 7 microM), revealing incongruent relative sensitivities among the substrate markers, with H2FDA generally the most sensitive of the series of substrate markers evaluated. CONCLUSIONS: The inconsistent sensitivities of the transport markers (H2FDA and bodipy) were reminiscent of the apparent multiple binding site behaviors observed for P-gp and could indicate opposing and unequal yet interacting binding sites akin to those of P-gp. Nonetheless, notable differences between P-gp and BSEP in marker substrate recognition/transport were apparent despite the observed overlap in xenobiotic recognition and transport. Thus far the most potent inhibitors seem to be cyclosporin, tamoxifen, and valinomycin. There are likely to be much more potent inhibitors, and other substrates also may be more sensitive to inhibition of transport.

DrugBank Data that Cites this Article

Drug Transporters
DrugTransporterKindOrganismPharmacological ActionActions
DoxorubicinBile salt export pumpProteinHumans
Unknown
Substrate
Details
FluoresceinBile salt export pumpProteinHumans
Unknown
Substrate
Details
GlyburideBile salt export pumpProteinHumans
Unknown
Substrate
Inhibitor
Details
KetoconazoleBile salt export pumpProteinHumans
Unknown
Inhibitor
Details
PaclitaxelBile salt export pumpProteinHumans
No
Substrate
Inhibitor
Details
ProgesteroneBile salt export pumpProteinHumans
Unknown
Inhibitor
Details
ReserpineBile salt export pumpProteinHumans
Unknown
Inhibitor
Details
TroglitazoneBile salt export pumpProteinHumans
Unknown
Inhibitor
Details
VinblastineBile salt export pumpProteinHumans
No
Substrate
Inhibitor
Details
Binding Properties
DrugTargetPropertyMeasurementpHTemperature (°C)
CyclosporineBile salt export pumpIC 50 (nM)7500N/AN/ADetails
CyclosporineBile salt export pumpIC 50 (nM)7800N/AN/ADetails
GlyburideBile salt export pumpIC 50 (nM)146500N/AN/ADetails
GlyburideBile salt export pumpIC 50 (nM)260100N/AN/ADetails
KetoconazoleBile salt export pumpIC 50 (nM)65400N/AN/ADetails
PaclitaxelBile salt export pumpIC 50 (nM)26800N/AN/ADetails
PaclitaxelBile salt export pumpIC 50 (nM)28900N/AN/ADetails
ProgesteroneBile salt export pumpIC 50 (nM)17300N/AN/ADetails
ProgesteroneBile salt export pumpIC 50 (nM)224600N/AN/ADetails
ReserpineBile salt export pumpIC 50 (nM)10200N/AN/ADetails
TroglitazoneBile salt export pumpIC 50 (nM)66400N/AN/ADetails
VinblastineBile salt export pumpIC 50 (nM)114700N/AN/ADetails
VinblastineBile salt export pumpIC 50 (nM)62000N/AN/ADetails
Drug Interactions
DrugsInteraction
Astemizole
Glimepiride
Glimepiride may decrease the excretion rate of Astemizole which could result in a higher serum level.
Astemizole
Diclofenac
Diclofenac may decrease the excretion rate of Astemizole which could result in a higher serum level.
Astemizole
Pravastatin
Pravastatin may decrease the excretion rate of Astemizole which could result in a higher serum level.
Astemizole
Indomethacin
Indomethacin may decrease the excretion rate of Astemizole which could result in a higher serum level.
Astemizole
Rosiglitazone
Rosiglitazone may decrease the excretion rate of Astemizole which could result in a higher serum level.