MDR-related properties of K 562 cells grown in two different culture media

Using a synthetic substitute, Ultroser HY, for fetal bovine serum to supplement a classical RPMI 1640 culture medium produced changes in the properties of sensitive and of multidrug-resistant K 562 cells. Though no morphological changes were found, a statistically significant decrease in doubling-time was noted. Plasma membranes were more rigid, as reflected by an increase in the order parameter values. Adriamycin cytotoxicity was decreased, as shown by an increase in IC 50 values. The THP-adriamycin uptake, monitored by fluorimetry, was diminished even when the revertant agent verapamil was added. Moreover, the apparent number of Pgp 170 molecules per cell was lower for resistant cells grown with Ultroser HY. Thus Pgp 170 was not involved in the MDR increase induced by Ultroser HY. In conclusion, it must be kept in mind that environmental factors such as media chemical composition influence the MDR phenomenon and that environmental factors may also influence the MDR phenomenon in clinical situations.