In vitro and ex vivo evidence for modulation of P-glycoprotein activity by progestins
Section snippets
Materials and drugs
Culture media, FCS, medium supplements, antibiotics, and HBSS were purchased from Invitrogen, collagen-R was from Serva, DMSO and Triton X-100 were from AppliChem, doxorubicin hydrochloride from Sigma–Aldrich, calcein-AM from MoBiTec, rhodamine123 from Calbiochem, vincristine from Merck Biosciences, 96-well microtiter plates and culturing bottles were from Nunc. The PE labelled antibodies against human CD8+ and mouse IgG2a as well as the vacutainer®CPT™ were purchased from BD Biosciences.
Evaluation of the Pgp inhibitory potency of progestins with the calcein assay
Due to the low solubility of the progestins and the very high expression level of Pgp in L-MDR1 cells, none of the progestins revealed plateau effects in L-MDR1 cells and levonorgestrel and norethisterone even did not reach f2 values (Table 1; Fig. 1A–C). We therefore also tested all compounds in P388/dx cells, a murine cell line over-expressing Pgp as well, but to a lower extent than L-MDR1 cells. In this cell line some progestins showed plateau effects and only levonorgestrel did not reach f2
Discussion
The results of the present in vitro/ex vivo study revealed a potent Pgp inhibitor effect of several progestins, which are widely used for OC and HRT. The extent of Pgp inhibition in L-MDR1 cells by most progestins was comparable to that of the potent Pgp inhibitor quinidine and slightly weaker than that of verapamil. The rank order of inhibition was essentially confirmed in P388/dx cells with one notable exception. In contrast to other progestins whose f2 values were roughly one order of
Acknowledgements
The authors thank Mrs. Stephanie Fuchs for her excellent technical assistance and Mrs. Jennifer Lohr for conducting some of the calcein assays. Furthermore, we thank Janssen-Cilag GmbH, Eli Lilly and Co., and Grünenthal GmbH for kindly providing the test compounds, Dr. Dario Ballinari (Pharmacia and Upjohn) for providing the cell lines P388 and P388/dx, and Dr. Alfred H. Schinkel for providing the cell line L-MDR1. Moreover, we would like to thank Dr. Nina Wettschurek for her help with the flow
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