Characterization of multidrug-resistant pituitary tumor cells.
These studies were designed to investigate the role of P-glycoprotein in an endocrine cell line. Drug-resistant pituitary cells were obtained by growing GH4C1 cells in the presence of increasing concentrations of colchicine. Cells resistant to colchicine at 0.4 micrograms/ml, termed GH4C1/RC.4, exhibited the multidrug-resistance phenotype, as the LD50 values for colchicine, puromycin, actinomycin D, and doxorubicin were between 8 and 30 times greater than the corresponding values for the parental GH4C1 cells. Verapamil at 10 microM increased the sensitivity of GH4C1/RC.4 cells to colchicine, puromycin, and actinomycin D, almost completely reversing the drug resistance. Flow cytometry and fluorescence microscopy were used to demonstrate that GH4C1/RC.4 cells retained less rhodamine 123 than GH4C1 cells, and that the rate of efflux of rhodamine 123 was much faster for GH4C1/RC.4 cells. Immunocytochemical staining with a monoclonal antibody, C219, to the 170-kilodalton P-glycoprotein showed directly that GH4C1/RC.4 cells overexpress P-glycoprotein. We used drug-resistant pituitary cells to assess the possible role of P-glycoprotein in uptake and efflux of several hormones. At equilibrium, GH4C1 and GH4C1/RC.4 cells bound similar amounts of [125I]L-triiodothyronine and [125I]L-thyroxine, and verapamil did not alter either equilibrium binding or thyroid hormone efflux kinetics. Multidrug-resistant GH4C1/RC.4 cells retained less [3H]hydrocortisone than parental GH4C1 cells at equilibrium, and verapamil increased the equilibrium concentration of [3H]hydrocortisone 3.6-fold. The effect of verapamil was due to its ability to reverse multidrug resistance, since two other chemosensitizers, quinidine and vinblastine, increased [3H]hydrocortisone retention as effectively as verapamil but another calcium channel blocker, nifedipine, had no effect. The drug-resistant GH4C1/RC.4 line synthesized more GH (290%) and much less PRL (5%) than the parent. Hydrocortisone stimulated GH synthesis and inhibited PRL similarly in GH4C1 and GH4C1/RC.4 cells. The results show that the GH4C1/RC.4 line is multidrug-resistant and overexpresses the 170-kilodalton P-glycoprotein and suggest that the P-glycoprotein pump contributes to hydrocortisone kinetics.
Department of Pharmacology, University of Rochester School of Medicine and Dentistry, New York 14642.
E J
EJ
Nelson
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PM
Hinkle
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000818:Animals; D000911:Antibodies, Monoclonal; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003078:Colchicine / Q000494:pharmacology*; D003609:Dactinomycin / Q000494:pharmacology*; D004317:Doxorubicin / Q000494:pharmacology*; D004351:Drug Resistance / Q000502:physiology*; D005456:Fluorescent Dyes; D006854:Hydrocortisone / Q000378:metabolism; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000032:analysis / Q000502:physiology*; D010911:Pituitary Neoplasms; D011691:Puromycin / Q000494:pharmacology*; D020112:Rhodamine 123; D012235:Rhodamines; D013974:Thyroxine / Q000378:metabolism; D014284:Triiodothyronine / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000911:Antibodies, Monoclonal; D005456:Fluorescent Dyes; D008562:Membrane Glycoproteins; D012235:Rhodamines; D014284:Triiodothyronine; D003609:Dactinomycin; D020112:Rhodamine 123; D011691:Puromycin; D004317:Doxorubicin; D013974:Thyroxine; D003078:Colchicine; D006854:Hydrocortisone