Reduced antineoplastic activity in mice of cisplatin administered with high salt concentration in the vehicle.

The effect of high NaCl concentration in the vehicle on the toxic and antineoplastic activities of cisplatin [cis-dichloro-diammineplatinum(II)] (CDDP) was reinvestigated in mice. The toxicity, as measured by the survival of mice given CDDP iv, was reduced by 50-60% when the NaCl concentration in the vehicle was raised from 0.9 to 4%. In ascitic P388 leukemia the antineoplastic activity of CDDP given ip was not reduced significantly. However, in all other systems studied the antitumor activity was reduced when the CDDP was dissolved in high NaCl solution. The tumor models studied included systemic P388 and L1210 leukemias, Lewis lung carcinoma, and 5 human tumor xenografts. The human tumors were studied by the subrenal capsule assay. In the case of a malignant melanoma and a malignant fibrous histiocytoma, the effect also was demonstrated in the subcutaneous nude mouse model. In one of the malignant melanomas a 50% increase in the CDDP dose did not compensate for the reduced antitumor activity caused by the high NaCl concentration in the vehicle. These results, which stand in contrast to current views, question the experimental basis for the use of high-NaCl vehicles in the "high-dose" CDDP regimens.