The Primary Syudy Of Biologicla Characteristics Of Tumor Stem Cells-derived From Bone Marrow Of Patients With Chronic Myelogenous Leukemia

The t(9;22)(q34;q 11) reciprocal chromosomal translocation occurs in nearly all patients with chronic myelogenous leukemia (CML). This translocation gives rise to the Philadelphia (Ph) chromosome and produces an abnormal Bcr-AbI fusion protein with a constitutively active tyrosine kinase. The Bcr-Abi kinase activates a number of signal transduction molecules involved in cell proliferation and apoptosis, and plays a central role in leukemogenesis. Consequently, the inhibition of the tyrosine kinase function of Bcr-Ab1 with the specific ST1571 compound leads to apoptosis in t(9;22)-positive cells. Clinical trials indicate that ST1571 is a highly active substance in CML with few side effects and is therefore used in all stages of the disease. However, the efficacy of the drug declines with its use in more advanced stages of the disease and most patients treated with ST1571 in accelerated or blast phase develop resistance.Recent data are beginning to shed light on mechanisms responsible for clinical resistance to STI571. For example, Bcr/Ab gene amplification or mutations may weaken the antitumor effects of ST1571. In addition, MDR1 overexpression was considered as an important clinical mechanism in the diversity of resistance development to ST1571 treatment. However, these genetic mechanisms of resistance may be responsible for only a fraction of the failures of STI571 therapy. CML arises at the level of stem cells, and like their normal counterparts, CML stem cells undergo orderly differentiation. Differentiated cells constitute the bulk of the leukemic cell mass in CML, whereas the stem cells responsible for disease maintenance may be poor targets for STI571. Several investigators have now provided evidence that ST1571 may have differential effects on CML cellsdepending on their state of differentiation; whereas STI571 is highly toxic to differentiated CML progenitors, CML stem cells may be relatively or even completely resistant to the the drug. The mechanisms involved in CML stem cell resistance to STI571 are unknown. Unfortunately, because of the difficulty of identifying and manipulating individual stem cells, up to data, we still could not isolate and identify CML stem cell, not to study their basic biology.The purpose of the first part of this paper is to further elucidate the mechanisms involved in some CML cell lines overexpressing exclusively P-glycoprotein (P-gp) resistance to ST1571. Firstly, resistant K562 cell line (K562/VP16) that overexpressed P-gp was achieved after exposure of the K562 cells to stepwise increase of concentrations of VP16. Then a small side population (SP) being capable of efflux Hoechst 33342 in K562/VP16 cell line was isolated by flow cytometry and the mechanisms involved in this K562/VP16 SP cells resistance to STI571 were studied. Our results showed that the levels of BCR-ABL and ABL proteins in K.562 cells were similar to those in non-SP K562/VP16 and K.562/VP16 SP cells. The 170 kDa P-gp was detected in K562/VP16 and K562/VP16 SP cells but not in K562 cells, and the expression levels of P-gp in these two cell lines were similar. Compared with non-SP K562/VP16, K562/VP16 SP cells were more resistant to STI571, and many multidrug resistance inhibitors could hardly reverse this resistance. In addition, in vivo study showed that the malignancy of K562/VP16 cells in vivo is largely dependent on the SP cells. So that BCR-ABL gene amplification and multidrug-resistant gene 1 (MDR1) overexpression might not be important clinical mechanism in the diversity of resistance development to STI571 treatment, and drug sensitivity as well as the development of drug resistance by keukemic cells may be at least partly due to a rare SP of tumor stem-like cells which drives leukemia.Overwhelming evidence in leukemia has shown that the clonal population of neoplastic cells exhibits marked heterogeneity with respect to proliferation and differentiation. Rare stem cells within the leukemic population possess extensive proliferation and self-renewal capacity that is not found in the majority of the leukemi...