No abstract

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 M 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.

Selective cyclooxygenase-2 (COX-2) inhibitors, like coxibs, demonstrate efficacy in the treatment of pain and inflammation, comparable to unselective non-steroidal anti-inflammatory drugs (NSAIDs). COX-2 expression was, for a long time, linked only to pathophysiology, but ongoing research has also demonstrated constitutive COX-2 expression within normal tissues such as brain, kidney, pancreas, intestine and blood vessels. Irrespective of their tendency to reduce severe gastrointestinal (GI) events, strong debates have been ignited regarding new adverse effects of specific COX-2 inhibitors, most notably those of a cardiovascular (CV) nature, such as blood pressure elevation, myocardial infarction and stroke. This review evaluates the recent patent literature concerning new therapeutic options offered by selective COX-2 inhibitors, with emphasis on technological improvements and COX-2 inhibitors as components of drug combinations

Children with Down Syndrome (DS) are at an 150 fold increased risk to develop acute megakaryoblastic leukemia (AMKL) within the first 4 years of life. About 10% of newborns with trisomy 21 showed transient myeloproliferative disorder (TMD). Although mutations of the transcriptional factor GATA1, resulting in the shortened GATA1s have been shown in almost all blasts in DS-AMKL and TMD the predisposition to leukemiogenesis related to trisomy 21 is not clear. TMD occurred during embryonic stress hematopoiesis leading to the hepatic proliferation of the GATA1s positive blasts. Typically blasts disappeared within the first 3 month of live, however after a median time of 1.3years (0.6 to 3.7 years) 20% of the children suffered AMKL and required intensive cytostatic treatment. The expression of chromosome 21 encoded hematological transcription factors (TFs) such RUNX1, ETS-2 and ERG were analysed in leukemic blasts from DS- TMD(n=7), DS-AMKL (n=25), DS without hematological disorder (n=10), AMKL (n=10) and healthy controls (n=7) by qRT-PCR. Results: No increase of RUNX1, ETS-2 and ERG expression could be shown. By contrast, ERG was decrease in all leukemias and in DS without hematological disorder (p Anova.<0.002). GATA1s was significantly overexpressed in TMD and DS-AMKL (pAnova <0.02), whereas GATA1 expression in AMKL and controls was not changed. GATA2 was elevated (pAnova <0.01) in all megakaryoblastic leukemias, with or without DS (pAnova <0.0001). PU.1, typically associated with early lymphatic differentiation and granulopoiesis was down regulated in all megakaryoblastic leukemias and, surprisingly, in DS without hematological disorder. This confirmed previously reported results by gene-array analysis1. To get further insight in the predisposition caused by trisomy 21 we analysed regenerating hematopoiesis in DS (n=14) partly resembling embryonic stress hematopoiesis. Correlated to the amount of bone marrow activation (CD38 positivity) a myeloid cell population (CD13/CD33 positive); with the co-expression of CD56 (NCAM) and CD36 (thrombospondin-receptor) could be detected by immunophenotyping (median percentage all nucleated bone marrow cells: 73±10%). In children without DS but regenerating hematopoiesis (n=41) a similar population of 4.6±1.8% (p<0.00001) could be detected. For further analysis the CD33/CD56 positive cells were sorted (FACSVantage). The cells showed normal myeloid morphology and differentiation, lack of GATA1s mutation, but an aberrant TF expression pattern. RUNX1 was 10-fold and ETS-2 5-fold higher expressed compared to controls (p<0.012). Summarized, (1) DS-AMKL and TMD leukemic blasts showed no general gene-dosage effect. However, (2) in stimulated bone marrow (stress hematopoiesis) trisomy 21 led to an overexpression of chromosome 21 encoded TFs, which might contribute to leukemiogenesis.