Study Of Relationship Between Midkine Expression And Drug Efflux In Childhood Acute Lymphoblastic Leukemia Cells

Background:Midkine (MK) is a heparin-binding growth factor that was found rescent years as the product of a retinoic acid-responsive gene. It has45%sequence identity to pleiotrophin (PTN), and together PTN comprise a family of heparin-binding growth factors. In addition, it has been reported that MK exerts several cancer-related activities, including cell growth, survival, mitogenesis, transformation, angiogenesis, anti-apoptotosis, and fibrinolysis.In acute myeloid leukemia (AML) cell lines and AML patients’cell, the abnormal expression of MK was found. So, MK may involve in the occurrence and development of acute leukemia. However there are a few reports about clinic study of MK expression in childhood acute lymphoblastic leukemia patients (ALL) at home and abroad,multidrug resistance (MDR), ability of cancer cell to different chemotherapeutic drugs, is a major clinical obstacle in the treatment of hematological malignancies. And the main mechanism of MDR is the antineoplastic drug efflux induced by overexpression of drug transport proteins. Other mechanisms involved in MDR include alterations in the apoptotic response, activation of DNA repair or alterations in drug-target interactions. Numerous studies have been performed to confirm that MK promotes cancer cells to resistant to cytotoxic agents by anti-apoptotic, promoting cell growth, and anti-aging. However, it has never been reported that MK is associated with the ability of drug efflux of cancer cells.Objective:To investigate the expression of midkine gene in childhood acute lymphoblastic leukemia patients (ALL) and to explore the clinical significance of midkine. To explore the possible effects of midkine (MK) gene on the chemotherapeutic drugs efflux in leukemia cells by observing Rh123efflux in different individuals.Methods:A total of153children with ALL diagnosed in Blood Diseases Hospital, Institute of Hematology, Chinese Academy of Medical Sciences and Peking Union Medical College from December2006to February2009were enrolled in this study. Real-time quantitative PCR method was used to determine the expression of midkine and MDR1at mRNA level in patients and15control children. Meanwhile, laser scanning confocal microscope was used to observe the rhodamine123efflux from the leukemia cells in30new diagnosed B-lineage ALL patients and the mononuclear cells from15children with nonmalignant hematological diseases,(as control).Results:Significant statistic difference in midkine gene expression was found among the normal group, the complete remission group and the de novo group, and the midkine levels were increased in turns (P<0.01). In the rhodamine123efflux test, mean fluorescence intensity (MFI) in the leukemia cells was obviously lower than that in normal cells and mere was an evident inverse correlation between the MFI and MK mRNA expression. Otherwise, there was no significant correlation between the MFI and MDR1mRNA expression.Conclusions:MK expressed highly in new diagnosed B-lineage ALL patients, decreased in CR patients. MK gene level may be one of indexes to assess therapeutic effect. There was powerful efflux capability of rhodamine123in leukemia cells with high midkine gene expression.The midkine may participate in multidrug resistance. This study provided a new way to improve the sensitivity of chemotherapy in clinical treatment. But MDR1levels had no correlation with the degree of rhodamine123efflux, the futher experiments will be done to identify the other transportprotein contributing to MDR in children ALL.