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M9650529.TXT
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1996-03-09
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Document 0529
DOCN M9650529
TI Decreased potency of MDR-modulators under serum conditions determined by
a functional assay.
DT 9605
AU Ludescher C; Eisterer W; Hilbe W; Hofmann J; Thaler J; Department of
Internal Medicine, University of Innsbruck,; Austria.
SO Br J Haematol. 1995 Nov;91(3):652-7. Unique Identifier : AIDSLINE
MED/96048907
AB A variety of agents are capable of overcoming P-glycoprotein-mediated
multidrug resistance (MDR) in vitro. However, the clinical potential of
these compounds is often limited due to high plasma protein binding. We
compared the efficacy of several MDR-reversing compounds in serum-free
culture medium and under serum conditions by means of a functional
assay. Using flow cytometry the efflux of the fluorescent dye rhodamine
123 (Rh123) was measured from normal peripheral blood CD8+ T-lymphocytes
which express low levels of P-glycoprotein. Inhibition of Rh123 efflux
by R-verapamil, dexnigludipine-HCl, cyclosporin A, SDZ PSC833 and the
protein kinase C (PKC) inhibitor CGP 41251 was determined in serum-free
medium and in serum at concentrations from 0.1 to 50 mumol/l. With the
exception of SDZ PSC833 all MDR modulators showed an insufficient or
suboptimal modulation of P-glycoprotein under serum conditions at
concentrations achievable in vivo. The highest potency under serum
conditions demonstrated SDZ PSC833: even at a concentration of 0.5
mumol/l a sufficient inhibitory effect was observed. Subsequently this
approach was applied to patients suffering from B-cell chronic
lymphocytic leukaemia (B-CLL; n = 3) and acute myeloid leukaemia (AML; n
= 2) which were positive in the Rh123 efflux assay. As for normal CD8+
T-lymphocytes, much higher drug concentrations were required under serum
conditions to effectively inhibit Rh123 efflux from the leukaemic cells.
Thus the interpretation of results of clinical 'modulator' trials should
consider the decreased bioavailability of MDR-reversing agents.
DE Acute Disease Antimetabolites, Antineoplastic/*METABOLISM
Antineoplastic Agents/PHARMACOLOGY Cyclosporine/PHARMACOLOGY
CD8-Positive T-Lymphocytes/*METABOLISM Dihydropyridines/PHARMACOLOGY
Dose-Response Relationship, Drug *Drug Resistance, Multiple Flow
Cytometry Human Leukemia, B-Cell, Chronic/METABOLISM Leukemia,
Myeloid/METABOLISM P-Glycoprotein/PHARMACOLOGY Rhodamines/*METABOLISM
Verapamil/PHARMACOLOGY JOURNAL ARTICLE
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).