CG5/Dx human breast cancer cell line: characterization of a new doxorubicin-resistant variant.

By continuous exposure of CG5 human breast cancer cell line to increasing doxorubicin (Dx) concentrations, a multidrug-resistant (MDR) subline (CG5/Dx) was obtained. The resistant variant showed P-glycoprotein (P-gp) expression and a lower intracellular doxorubicin level than the parental cells. CG5/Dx cells were 19.4 fold more resistant to Dx than CG5 cells and showed a cross-resistance to some structurally related and unrelated compounds. Differences in kinetics, biological and ultrastructural features between the two cell lines were investigated. The CG5/Dx cells grew more slowly, produced higher CEA levels and showed a reduced progesterone receptor (PgR) content than the parental cells. Ultrastructural studies revealed differences involving, polyribosomes, rough endoplasmic reticulum, [mitochondria] and cytoskeleton.