Abstract
The microltidrug resistant cell lines HL60/AR and GLC4/ADR show high overexpression of the gene encoding the microltidrug resistance associated protein MRP compared to their drug sensitive parental counterparts. This and the virtual absence of mdr1/P-glycoprotein gene expression was proven by a complementary DNA polymerase chain reaction (cDNA-PCR) approach. Applying a 72-hour tetrazolium based colorimetric MTT-assay we demonstrate on both MDR sublines a dose-dependent modulation of drug resistances by the leukotriene LTD 4 receptor antagonist MK571. A complete reversal of vincristine resistances was achieved at final MK571 concentrations of 30 μM (HL60/AR) or 50 μM (GLC4/ADR) which by itself did not disturb cellular proliferation. The drug resistance of a mdr1/P-gp overexpressing microltidrug-resistant HL60 subline, in contrast, was not significantly affected by MK571. Similar effects were seen using the glutathione (GSH) synthesis inhibitor buthionine sulfoximine (BSO). Our results point to a relationship between MRP and a conjugate transporter and identify MK571 as a new tool structure for developing modulators specific for a MRP associated microltidrug resistance.
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