A pleiotropic defect reducing drug accumulation in cisplatin-resistant cells

The resistance of tumors to cisplatin remains a major cause of treatment failure in cancer patients. Multiple, simultaneous alterations are frequently encountered in cancer cells selected for cisplatin resistance. To determine whether the complex phenotype results from many different cellular alterations, single-step variants were isolated based on one-step selection in cisplatin. Reduced drug accumulation is a common feature of cisplatin-resistant (CP-r) cancer cells, which is probably caused by one or more dominant genes. Pulse-chase labeling and pulse-chase biotinylation of cell surface proteins suggest that membrane protein mislocalization occurs in CP-r cells, caused mainly by a defect in plasma membrane protein recycling, manifested also as a defect in acidification of lysosomes. This membrane protein mislocalization is presumed to reduce cell surface expression of a putative cisplatin carrier or carriers. In cells selected in several steps, decreased expression of folate-binding protein and arsenic-binding proteins, and reduced endocytosis were detected in CP-r cells, contributing to the reduced uptake of cisplatin, methotrexate and other related compounds. Multiple mechanisms in CP-r cells keep cytotoxic platinum compounds out of cells through defective expression of cell surface proteins such as transporters and carriers, and decreased expression of proteins involved in endocytosis.