Fibronectin Confer The Drug Resistance In Multiple Myeloma Cells

Background: Multi-drug resistance(MDR) is a major obstacle to the treatment of refractory and relapse multiple myeloma. Historically, most mechanisms of drug resistance that have been discovered were focused on the tumor cells only, and the cell-environmental interactions are not fully appreciated. Myeloma cells are known to express a number of diverse cell adhesion molecules(CAMs) mediating cell-cell as well as cell-extracellular matrix(ECM) contacts by its counterreceptors. Recently, it has been realized that this contacts can regulate apoptosis and cell survival in a wide variety of cell types. Fibronectin, a component of the ECM, is one of the counterreceptors to CAMs. For this reason, we took RPMI 8226 cells to probe into the effect of fibronectin on the drug resistance formation in the multiple myeloma and its mechanisms related. We hope for a new approaches to reverse MDR of myeloma in clinic.-3-Methods: The adhesion of RPMI 8226 human myeloma cells to fibronectin was observed by crystal violet staining; the cytotoxicity of chemotherapeutic drugs to RPMI 8226 cells was measured by methyl-thiazol-tetrazolium(MTT) assay after adhesion to fibronectin or not; the phosphatidylscrine exposure of RPMI 8226 cells was identified with the help of Annexin V FITC fluorescence binding assay; the aneuploid DNA and the concentration of intracellular doxorubicin(DOX) were analyzed through flow cytometry. The morphologic changes of target cells were observed by means of light and electronic microscope.Result: The adhesion function of RPMI 8226 human myeloma cells to fibronectin was higher than control(OD: 0.49 vs 0.03, P<0.01). Fibronectin was able to raise significantly the drug resistance of RPMI 8226 to chemotherapeutic agents, reduce the sensitivity of chemotherapy. The IC5o values of Doxorubicin, Topptecan and Vincristin were 323.3 + 20.9/1089.4 ?27.4, 98.6+ 8.5/512.7?12.4 and 564.9 + 15.4/1599.5 + 135.5 ng/mL, respectively, in nonadhered controls compared with FN-adhered cells. The resistance index was 3.4, 5.2 and 2.8, respectively. After treatment of RPMI 8226 cells with the drugs, the target cells were morphologically characterized by condensation of the nuclear chromatin, shrinkage and formation of apoptotic bodies; the phosphatidylserine exposure was decreased compared with control (P<0.05); the aneuploid DNA from target cells by flow cytometry was decreased as well. Meanwhile, with the help of flow cytometry, we found no difference of intracellular concentration of doxorubicin in RPMI 8226 cells between the nonadhered and FN-adhered cells.-4-Conclusion: (1) Fibronectin-mediated adhesion can enhance the tolerance of RPMI 8226 cells to chemotherapeutical agents and, moreover induce the drug resistance in myeloma cells. (2) Fibronectin seems to confer the drug resistance in myeloma cells through suppression of apoptosis, which differs from the classical revealed mechanisms such as overexpression of drug-transporters. The data presented here could be a new clue for reversing drug resistance of multiple myeloma in clinic.