| [ Background ] Multiple myeloma is a human B cell maliganancy confined to bone marrow. Despite initial response to chemotherapy, myeloma patients ultimately develop drug resistance. Myeloma cells predominantly localize in bone marrow and rarely occur in peripheral blood and never invade to other organs, which is closely associated with the bone marrow microenvironment (BMM). Recently, more attention is paid to the effects of bone marrow stromal cells (BMSCs) on myeloma cells. BMSCs are the main elements of microenvironment and express several adhesion molecules, which mediate adhesion to myeloma cells via ligand-receptor binding. Myeloma cells localize in bone marrow by adhesion to BMSCs and initiate IL-6 product by BMSCs, which contribute to growth, survival and drug resistance of myeloma cells. Presently, many researches mainly focus on the effect of IL-6 secreted by BMSCs on myeloma cells adhered toBMSCs. That direct or/and indirect effect of BMSCs on the proliferation and sensitivity to chemotherapy of multiple myeloma cells is undefined, so other pathways and mechanisms need to be further investigated.We established coculture system of normal human bone marrow fibroblastoid stromal cell line HFCL with multiple myeloma cell line RPMI8226 (non-IL-6 dependent cells) and investigated the effects of HFCL cells on the proliferation and response to chemotherapeutic agents of RPMI8226 cells in the coculture. Furthermore, we adopt Transwell coculture system to further get insight into the pathways of interaction in between.[ Objectives ] To investigate the effects of normal human bone marrow fibroblastoid stromal cell line HFCL on the proliferation and sensitivity to chemotherapy of multiple myeloma cells RPMI8226 in the coculture.[ Methods ] Setting up direct and indirect (Transwell) coculture systems of RPMI8226 cells with HFCL, respectively, RPMI8226 cells in suspension as control group. The adhesion ratio was determined by MTT colorimetric assay; growth curves was detected by trypan blue exclusion; the mitotic indices (Mis) of RPMI8226 cells were observed by Wright-Giemsa staining; Flow cytometer and Western Blot were used to study the changes of cell cycle and expression of proliferating cell nuclear antigen (PCNA), respectively. In cytotoxicity assays, cell viability was determined by MTT.[Results] In coculture experiment, the adhesion ratio of RPMI8226 cells after 1 hour was 29.4%; Growth curves showed the proliferation of RPMI8226 cells in direct contact with HFCL cells was inhibited as compared with control, no obvious changes wereobserved in RPMI8226 cells separated by Transwell inserts. Flow cytometer indicated that after 72h in culture, the percentage of G1, S phase cells of RPMI8226 in control group were 33.6% , 52.1%; the percentage of Gl, S phase cells of RPMI8226 cells in direct contact group was 40.4%, 40.8% , the percentage of Gl, S phase cells of RPMI8226 cells in Transwell was 30.6%, 49.1%. the percentage of Gl phase cells of RPMI8226 cells in direct contact group was higher and the percentage of S phase cells was lower (P<0.01 )as compared with RPMI8226 in control group. Moreover, the Mis of RPMI8226 cells in control group (1.4%, 3.4%, 3%, 1.8%, 1.6%) were higher than that of RPMI8226 cells(l.2%, 2.6%, 2%, 0.8%, 0.4%) in direct contact group. The expression of PCNA in RPMI8226 cells in control group was higher than RPMI8226 cells in direct contact group after 72h in culture. At the same time, dose-effect curves showed that HFCL diminished RPMI8226 cells death during exposure to mitoxantrone, vincristine, doxorubicin, topotecan,respectively.[ Conclusion] The normal human bone marrow fibroblastoid stromal cell line HFCL could inhibit the proliferation and progression of cell cycle of multiple myeloma cell line RPMI8226 cells in cell-cell contact culture, but no changes were observed in the proliferation when RPMI8226 cells were placed in Transwell inserts and cultured with HFCL. HFCL could diminish the effects of chemotherapeutic agents on RPMI8226 cells by cell to cell...
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