Impact of the Cyclooxygenase System on Doxorubicin-lnduced Functional Multidrug Resistance 1 Overexpression and Doxorubicin Sensitivity in Acute Myeloid Leukemic HL-60 Cells

摘要

Multidrug resistance(MDR),a challenge in treating childhood acute myeloid leukemia(AML),is frequently associated with decreased drug accumulation caused by multidrug transporter MDR1.Doxorubicin,an important anti-AML drug,is a known MDR1 substrate and inducer.Its cytostatic efficacy is thus limited by MDR1 overexpres-sion.A recent study demonstrated cyclooxygenase-2-dependent,prostaglandin E_2(PGE_2)-mediated regulation of mdrl b expression in primary rat hepatocyte cultures.Cyclooxygenase-2 expression is increased in several malignancies and considered a negative prognostic factor.Our study focused on cyclooxygenase system's impact on drug-induced MDR1 overexpression in AML cells.As a prerequisite,coexpression of MDR1 and cyclooxygenase-2 mRNA in HL-60 cells and primary AML blasts was demonstrated by Northern blot.Interestingly,incubation of AML cells with doxorubicin not only induced functionally active MDR1 overexpression but also mediated increased cyclooxygenase-2 mRNA and protein expressions with subsequent PGE_3 release(determined by flow cytometry,rhoda--minel 23 efflux assay,reverse transcription-polymerase chain reaction,and enzyme-linked immunosorbent assay).After preincubation and subsequent parallel treatment with the cyclooxygenase-2-pref-erential inhibitor meloxicam,doxorubicin-induced MDR1 overexpression and function were reduced(maximally at 0.1-0.5 muM meloxicam),whereas cytostatic efficacy of doxorubicin in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assays was significantly increased by up to 78(HL-60)and 30%(AML blasts)after 72 h of doxorubicin treatment.In HL-60 cells,meioxicam-de-pendent effect on doxorubicin cytotoxicity was neutralized by PGE_2 preincubation.In conclusion,the cyclooxygenase system,especially the cyclooxygenase-2 isoform,might be involved in regulating doxorubicin-induced MDR1 overexpression in AML cells,with PGE2 seeming to be a mediating factor.Cyclooxygenase inhibitors thus bear promise to overcome MDR in AML and improve therapy.