Although innumerable reports have been published in which P-gp has been shown to confer MDR to malignant (including leukemia) cells, so far, large-scale studies in the clinical setting have not convincingly proven that MDR1 plays a major role in clinical drug resistance when the influence of other known prognostic factors in human leukemia are taken into account.
Expression dynamics of drug resistance genes, multidrug resistance 1 (MDR1) and lung resistance protein (LRP) during the evolution of overt leukemia in myelodysplastic syndromes.
In conclusion, these results suggested that the MDR1 TT genotype might influence risk of development of acute lympoblastic leukemia and the CC genotype might be linked to a poor prognosis of ALL.
In contrast, it had no effect on P-glycoprotein-mediated paclitaxel resistance in MDR1-transduced human leukemia K562 cells and multidrug resistance-related protein 1-mediated doxorubicin resistance in MRP1-transfected human epidermoid cancer KB-3-1 cells.
In the tumor-bearing nude mice, anti-tumor drugs vincristine, daunorubicin (DNR), STI571, and STI571 plus VCR for the treatment of mdr1 and bcr/abl double positive leukemia were studied respectively.
Increased expression and amplification of mdr1 sequences were also found in multidrug-resistant sublines of human leukemia and ovarian carcinoma cells.
P-glycoprotein (P-gp)/multi-drug resistance 1 (MDR1) gene is recognized to be, at least in part, responsible for the refractoriness to chemotherapy of leukemia.
Sequential emergence of MRP- and MDR1-gene over-expression as well as MDR1-gene translocation in homoharringtonine-selected K562 human leukemia cell lines.
Since mdr1 and mdr3 are frequently expressed in untreated as well as treated leukemia, such combination therapy should be considered for untreated patients as well as treated patients.
The MDR1 expression rate was significantly correlated with factors such as a history of preceding chemotherapy, elder age of the patient, and certain disease types (eg, leukemia progressed from myelodysplastic syndrome).
The cytotoxic studies have demonstrated a higher sensitivity of the leukemia lines to DOX-BNNPs compared with the carcinoma lines: IC<sub>50</sub>(DOX-BNNPs) is 1.13, 4.68, 0.025, and 0.14 μg/mL for the KB-3-1, MDR KB-8-5, K562, and MDR i-S9 cell lines, respectively.
These findings indicate that siRNA specifically and efficiently interferes with the expression of mdr1 and could be used as a molecularly defined therapeutic approach for MDR in the treatment of leukemia.