Mechanism of resistance of Yoshida sarcoma to nitrogen mustard. II. Further evidence for suppressed transport of nitrogen mustard

Sensitivity of Yoshida sarcoma lines resistant to nitrogen mustard (HN²) was not enhanced by pretreatment in vitro with SH-blocking agents such as 2,2′-dithiodi-pyridine. This fact seems to indicate that content of cellular sulfhydryl groups did not play a great role in acquisition of resistance to HN². No difference was observed between the sensitive and resistant lines in retention rate of HN² bound to DNA of the cells during incubation of the cells in an HN-free medium. These results suggested no considerable difference in the ability to repair DNA in both lines. Further evidence was added for suppressed transport through the cell membranes of the resistant lines. Damage to cell membranes was proved by vital staining when a concentration of SH-blocking agents in the pretreatment reached a certain level, and the binding rate of HN² to DNA of the resistant lines was recovered almost to the same level of the sensitive line by this pretreatment. However, the binding rate of the sensitive line was not changed by pretreatment with the blocking agents at any concentrations.