[Drug resistance of doxorubicin-resistant CHO cell line]

Some characteristics of doxorubicin-resistant CHO cell line (RC1) were studied by means of cell biological methods and SDS-PAGE electrophoresis. The resistance factor was 16.5-fold, and RC1 revealed cross-resistances to colchicine, actinomycin and harringtonine. By indirect immunofluorescence assay, P-glycoprotein was not detected. Compared with CHO, the doxorubicin (Dox) uptake and accumulation of RC1 decreased, but the membrane fluidity of RC1 increased. The reduction in drug accumulation was correlated with increase in membrane fluidity. Dox was mainly distributed in the cell nucleus of CHO, but in both cytoplasm and nucleus of RC1. This suggested that Dox was transported more slowly in RC1 cytoplasm than in CHO cytoplasm, resulting in less Dox entrance into the cell nucleus of RC1 than into that of CHO. We also found that a 30-40 kDa nuclear protein which was expressed normally in CHO disappeared in RC1.