OBJECTIVETo explore the role of autophagy in doxorubicin (DOX)-induced resistance of human myeloma cell line RPMI8226.

METHODSWe established doxorubicin induced resistant subline of myeloma cell line RPMI8226/DOX by drug concentration step-elevation method. Resistant index of DOX was measured by MTT assay. Autophagy of myeloma cell lines RPMI8226/s and RPMI8226/DOX was detected by transmission electron microscopy, immunofluorescence (LC3-FITC) and western blot respectively. Apoptosis of RPMI8226/DOX cells induced by DOX combined with autophagic inhibitor hydroxychloroquine or 3-MA was identified by AnnexinV-FITC/PI double fluorescence dyeing.

RESULTSResistant index of RPMI8226/DOX was approximately 10.8 fold of that of RPMI8226/S. Electron microscopic studies revealed that most of RPMI8226/DOX cells displayed viable attributes and contained numerous autophagic vacuoles. Fluorescent images of RPMI8226/DOX cells showed a punctuate distribution in LC3 protein. Increased LC3-II protein in RPMI8226/DOX cells was determined by immunoblotting. There were no differences among 8 μmol/L HCQ (3.24±1.08)%, 10 mmol/L 3-MA (2.81±0.80)% or control \[(2.12±1.24)%\] (P>0.05) in terms of AnnexinV-FITC/PI double fluorescence dyeing; Compared with apoptosis of (9.75±2.15)%, (24.36±2.16)% and (40.51±3.14)% of RPMI8226/DOX cells under 2, 4 and 6 μmol/L DOX, apoptosis increased significantly after 24 h incubation under 2, 4 and 6 μmol/L DOX combined with 8 μmol/L HCQ as of \[(16.56±1.89)%, (36.44±2.91)% and (62.68±3.75)%, respectively\], or under 2, 4 and 6 μmol/L DOX combined with 10 mmol/L 3-MA as of \[(15.47±1.85)%, (39.28±3.06)% and (55.46±4.07)%, respectively\] (P<0.05).

CONCLUSIONAutophagy was involved in doxorubicin-induced resistance of myeloma cell line RPMI8226, DOX resistance in myeloma cells was reversed partly by autophagy inhibitor hydroxychloroquine or 3-MA, and autophagy may be one of mechanisms for drug resistance.