Multidrug resistance-1 and P-glycoprotein in human chondrosarcoma cell lines:: Expression correlates with decreased intracellular doxorubicin and in vitro chemoresistance

We report on two chondrosarcoma cell lines, FS and AQ, that may be used as models of multidrug resistance in chondrosarcoma. Multidrug resistance-1 expression was assayed with reverse transcription-polymerase chain reaction. Immunostaining for the multidrug resistance-1 product, P-glycoprotein, was performed with the monoclonal antibody C494. Intracellular levels of doxorubicin were measured by fluorescent emission at 590 nm after 1 hour of incubation with the agent and again after 1, 2, and 4-hour washout periods. Chemosensitivity was assayed by staining micropellet cultures of AQ and FS cells with fluorescein acetate before and after the cells were exposed to varying doses of doxorubicin for 45 hours. Cytotoxicity was assessed by comparison of computer-processed images before and after treatment. The FS cell line was positive for multidrug resistance-1 expression, stained heavily for P-glycoprotein, and had significantly lower intracellular levels of doxorubicin than the AQ cell line, which was negative for multidrug resistance-1 and P-glycoprotein. Chemosensitivity testing showed that the FS cell Line was significantly more resistant to doxorubicin than was the AQ cell line at all doses tested. Our results show that multidrug resistance-1 expression in a human chondrosarcoma cell line results in resistance to doxorubicin in vitro.