MDR1 expression in poor-risk acute myeloid leukemia with partial or complete monosomy 7

Abstract

Expression of the multidrug resistance (MDR1) phenotype, encoded by the MDR1 gene, is an adverse prognostic factor for CR and survival in acute myeloid leukemia (AML). Other prognostic factors, such as specific cytogenetic abnormalities, have been identified in AML. We have investigated the expression of the MDR1 gene in untreated AML patients with monosomy 7 (n = 12), and partial deletions (n = 7) of the long arm of chromosome 7 (respectively −7/7q−), because of the extremely bad prognosis associated with these cytogenetic abnormalities and because of the fact that the MDR1 gene is located on chromosome 7q21.1.The findings were compared with the level of MDR1 expression in a group of 42 other AML patients, matched for age with favourable, neutral or complex cytogenetic abberations. MDR1 mRNA expression, as measured by the RNase protection assay was significantly higher in the −7/7q− group vs other AML patients (median 1.3 vs 0.1 arbitrary units, P = 0.02). Protein expression of MDR1 in the −7/7q− group, as determined with the monoclonal antibody MRK16, was found to be similar to the levels found in the control group. With a functional rhodamine retention assay using the modulator PSC833, increased MDR1 activity was observed in the −7/7q− group as compared to the control group of patients (P = 0.05). Considering the higher MDR1 mRNA expression and equal or slightly elevated level of protein expression of MDR1, we studied the presence of MDR1 genes in this group of −7/7q− patients. Fluorescence in situ hybridization (FISH) studies, using a specific MDR1 probe revealed no loss of an MDR1 allele in any of the deleted q− arms of the seven patients with 7q−, whereas all monosomy 7 patients lacked one MDR1 gene homologue. To determine whether there was selective loss of the MDR1 gene in the −7/7q− patients, the genetic polymorphism of the MDR1 gene was used. Both allelic variants (G and T) were represented in the −7/7q− and in the control group, showing a predominance for GT at position 2677 of the MDR1 gene in the control group. In the 12 monosomy 7 patients loss of the MDR1 allele was random. Methylation studies of the CpG island of the MDR1 gene revealed no hypermethylation in any of the −7/7q− patients. We conclude that MDR1 expression in −7/7q− AML patients is upregulated at transcriptional, but not at translational level, suggesting that mechanisms other than MDR1 are responsible for the poor prognosis in these patients. Leukemia (2001) 15, 398-405.

Prevalence and prognostic impact of allelic imbalances associated with leukemic transformation of Philadelphia chromosome–negative myeloproliferative neoplasms

“…However, as expected, blast phase patients with loss of chromosomal material on 7q showed poor survival, because this is known to be predictive for rapid progression and poor response in AML therapy. [35][36][37] MPN-blast phase patients with cytogenetically undetectable 7qCNN-LOH had comparable survival rates to those with Ϫ7/7qϪ in their leukemic cells, which is in accordance with previously published data. 44 In addition, 9pCNN-LOH with homozygous JAK2 mutation was also linked to an inferior outcome in MPN-blast crisis in comparison with patients with either heterozygous JAK2V617F or wild-type JAK2.…”

“…Abnormalities involving chromosome 7 are frequently detectable in de novo and secondary AML, [34][35][36][37] and preceding studies have found a critical breakpoint region involving a locus at centromeric band 7q22, whereas the telomeric breakpoint varies from q32 to q36. Interestingly, the minimal deleted region in our cohort was located at 7q22.1 encompassing only 2 promising target genes, SH2B2 (previously named APS) and CUTL1.…”

Drug Resistance in Childhood Acute Myeloid Leukemia

“…MDR1 did not correlate with a lower induction rate in relapsed or refractory childhood acute myeloid leukemia [110]. Mechanisms other than MDR1 are responsible for the poor prognosis in monosomy 7 patients [111].…”

Effect of CIK on multidrug-resistance reversal and increasing the sensitivity of ADR in K562/ADR cells

“…MDR is the major complication and a formidable obstacle in the therapy of AL (6). Certain previous studies that used cyclosporine and verapamil to reverse the MDR of AL were not practical in the clinic due to the side-effects.…”