Mechanism of resistance of Yoshida sarcoma to nitrogen mustard

Uptake and binding of methyl-bis(2-chloroethyl)amine hydrochloride (HN₂) to the cells of Yoshida sarcoma during their acquisition of resistance to this drug was investigated. With the increase of resistance index, drug uptake by the cells decreased. A good parallelism was found between resistance index and binding rate of the drug with cellular constituents when the intact cells were kept contacted in vitro with the drug in an incubation medium. When the cells were homogenized before contact with the drug, there was no difference in binding rate of the drug between sensitive and resistant cell lines. Suppression of cell membrane transport seemed to play a role in the acquisition of resistance by the cells.