Co-expression Of MDR1 Research Articles

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

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 overexpression. A recent study demonstrated cyclooxygenase-2-dependent, prostaglandin E(2) (PGE(2))-mediated regulation of mdr1b 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(2) release (determined by flow cytometry, rhodamine123 efflux assay, reverse transcription-polymerase chain reaction, and enzyme-linked immunosorbent assay). After preincubation and subsequent parallel treatment with the cyclooxygenase-2-preferential inhibitor meloxicam, doxorubicin-induced MDR1 overexpression and function were reduced (maximally at 0.1-0.5 microM 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, meloxicam-dependent 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 PGE(2) seeming to be a mediating factor. Cyclooxygenase inhibitors thus bear promise to overcome MDR in AML and improve therapy.

MM-TRAG (MGC4175), a novel intracellular mitochondrial protein, is associated with the taxol- and doxorubicin-resistant phenotype in human cancer cell lines

In the search for novel genes involved in the taxol resistance phenotype, prior studies of gene expression in taxol-resistant cell lines and their paired drug-sensitive parental lines using high-density Affymetrix microarrays identified MGC4175 as an overexpressed transcript. In this report, we characterize MGC4175 and demonstrate that seven of eight taxol- and doxorubicin-resistant cell lines overexpressed MGC4175 as compared to their chemotherapy naive parent lines. Sequence analyses of MGC4175 cDNA and the predicted amino acid sequence did not show significant homology to any known sequence or protein domain, with an open reading frame of 356 bp that is predicted to encode a protein product of 118 amino acids. Both the MGC4175 and MDR1 genes are located at chromosome position 7q21. Southern blot analysis demonstrated that a single copy of MGC4175 is present in the human genome, and MGC4175 overexpression is not caused by genomic amplification or gene arrangement. Human MGC4175 fused to the carboxy terminus of enhanced green fluorescent protein (EGFP) and expressed in U-2OS cells localized the protein to the perinuclear region with further studies colocalizing this protein to the mitochondria. The Cancer Profiling Arrays and the Cancer Cell Line Profiling Array demonstrated that MGC4175 is broadly expressed in various tissues with no significant difference of MGC4175 expression between chemotherapy naive tumor cells and normal cells. However, MGC4175 is overexpressed 1.2- to 12.3-fold after 48 h of taxol induction and 0.65- to 6.5-fold after doxorubicin induction in various human cancer cell lines. In light of the overexpression of MGC4175 in association with taxol exposure, drug resistance, the coexpression of MDR1 and the mitochondrial localization of its protein, we propose to name this transcript MDR1 and Mitochondrial Taxol Resistance Associated Gene ( MM-TRAG) and suggest that MM-TRAG may play a role in the development of taxol resistance in human cancer.

A new PCR MIMIC strategy to quantify low mdr1 mRNA levels in drug resistant cell lines and AML blast samples

Determination of the MDR-phenotype in patients suffering from AML is an important hallmark of treatment outcome but is often complicated by technical problems in P-gp assessment. A PCR-MIMIC strategy was employed to construct PCR-fragments for a competitive and quantitative mdr1 reverse transcription-PCR-assay. Using K562 cells, which had been selected for drug resistance to the epipodophyllotoxin VP16, a stepwise increase of mdr1 levels depending on the concentration of VP 16 was shown with the MIMIC technique. Comparison of mdr1 levels in drug selected K562 cells with the corresponding levels for P-gp and functional data indicated a mRNA threshold that has to be exceeded for the full expression of the MDR-phenotype. Subsequently mdr1 levels of 34 samples of de novo acute myeloid leukemia were determined with the PCR-MIMIC strategy. Ten patient samples could be identified with elevated mdr1 levels which were substantially lower than the levels observed in the MDR-cell line K 562 0.7 μM VP16. Outcome analysis revealed that eight of the ten patients had an unfavourable prognosis and did not achieve CR after induction chemotherapy. Coexpression of mdr1 and CD 34 was not associated with CR in all examined cases. Moreover all these patients had unfavourable cytogenetic aberrations. These data indicate a sensitive technique with applicability in patient material.