cross-resistance to vincristin and etoposide in a sub line of the human breast cancer t47d cells selected for adriamycin-resistance

breast cancer is one of the most common malignancies among women. although chemotherapy remains a major therapeutic approach to treat cancers, drug therapy often fails for several reasons, particularly the drug resistance. resistance to multiple chemotherapeutic agents is one of the most important problems in the treatment of different types of cancers. therefore, in this study a resistant sub line of the human breast cancer t47d cells was isolated in vitro by stepwise exposure to increasing concentrations of adriamycin (adr) to compare the characteristics of parent and resistant cells. we also evaluated the phenomenon of cross-resistance to some other chemotherapeutic drugs. a significant increase in doubling time of resistant cells, named t47d/adr, (94 h) was observed when compared to the parental t47d cells (50 h) that indicates a relatively slow growth rate pattern of these cells. t47d/adr cells were 4 fold resistant to adriamycin and also showed cross-resistance to vincristin (vcr, 3.5 fold) and to etoposide (vp-16, 5.5 fold) when compared to parent cells. therefore, our results indicate that t47d/adr cells are also cross-resistant to structurally and functionally different chemotherapeutic agents and can be used as a model for studying molecular changes of drug resistance.