Isolation and characterization of an adriamycin-resistant breast tumor cell line.

An adriamycin-resistant human breast tumor cell line MDA-A1R was generated by step-wise selection in increasing concentrations of drug from the parent cell line MDA-MB-231. MDA-A1R cells grow as loosely attached cell aggregates with a doubling time of 28-32 h; the MDA-MB-231 parent cell line grows as a standard monolayer culture with a 20-h doubling time. The MDA-A1R cell line is highly resistant to adriamycin compared to the parent cell line, and is cross-resistant to velban and colchicine suggestive of a multidrug resistance (MDR) phenotype. MDA-A1R cells exhibit reduced net adriamycin content as compared to the parent cell line. The MDR-associated P-glycoprotein gene is amplified approximately 10- to 30-fold in MDA-A1R cells. P-glycoprotein sequences are overexpressed in the resistant cells and are stable for up to 13 wk after drug removal. Moreover, MDA-A1R cells show the presence of very high levels of P-glycoprotein. MDA-A1R is thus an in vitro model system to study the mechanism of MDR in human breast cancer.