Study On The Mechanism Of N - Cadherin - Positive Leukemia Cells Drug Insensitivity

Acute myeloid leukemia (AML) is a type of cancer in which the bone marrow makes abnormal myeloblasts. Leukemia stem cells (LSC) play a key role in leukogenesis. Self-renewal and drug resistance are key features of leukemic stem cells, which results in relapse of leukemia. Our previouse studies have found that N-cadherin-positive leukemia cells is not sensitive to chemotherapy, which suggested that N-cadherin take an important role in maintaining the drug resisitance properties of LSC.To explore the mechanism of the chemotherapy resistance of N-cadherin positive leukemia cells, we determined the quiescent state of N-cadherin positive leukemia cells and analyzed the relationship of proportion of GO phase cells with the chemotherapy resistance. The quiescent state of N-cadherin positive and negative leukemia cells was determined by flow cytometry. After KG la cells were induce to enter cell cycle, the proportion of GO phase cells and the sensitivity to VP16was determined. Then we transplanted sorted leukemia cells into NOD/SCID mice by tail vein injection and the localization and the homing site of human leukemia cell was analyzed. Additionally, the expression levels of cell-cycle related protein P21and P27in N-cadherin positive and negative cells were further detected by real-time RT-PCR. Finally we determined the quiescent state and drug resisitance properties of leukemia cells after inhibiting the N-cadherin mediated cell-cell interaction by EGTA treatment.The results showed that the proportion of GO phase cells in N-cadherin positive leukemia cells was higher than that in negative cells. After KG1a cells were induced to enter cell cycle, the proportion of GO phase cells was decreased significantly and the sensitivity to VP16was increased, especially in AS2O3treated group. In vivo assay indicated that N-cadherin positive cells localized preferentially at the endosteal surface abutting murine osteoblasts and remained quiescent state. The results also showed that the expression levels of cell-cycle related protein P21and P27in N-cadherin negative were higher than that in N-cadherin positive cells. Following EGTA treatment for48hours, the proportion of GO phase cells was decreased and the drug-sensitivity was enhanced significantly.Taken together, these data strongly support that N-cadherin-mediated adhesion keeps N-cadherin positive leukemia cells in quiescent state, and thus protect these leukemia cells from chemotherapy.