Hyperthermic potentiation of cisplatin cytotoxicity on solid Ehrlich carcinoma.

Background: Hyperthermia produces marked effects on many biochemical parameters of tumor cells and has been reported to potentiate the effect of many drugs. We therefore evaluated the possible synergistic effect between hyperthermia and cisplatin against solid Ehrlich carcinoma. The study was based on the measurement of some biologic characteristics in tumor tissues, namely: DNA, RNA, and protein content and their rate of synthesis as parameters for nuclear damage; total lipids and cholesterol as parameters for membrane damage; acid-phosphatase and acid-ribonuclease as parameters for lysosomal damage; and tumor volume as a direct parameter for tumor growth.

Methods: Treatment of solid Ehrlich carcinoma by hyperthermia at 43 degrees C for 30 min for 3 successive days produced a 41.5% decrease in tumor volume, as well as a significant decrease in nucleic acids, protein contents and their rate of synthesis, in total lipids and cholesterol, and in acid-phosphatase and acid-ribonuclease. Chemotherapeutic management of the tumor by 5 mg/kg x 3 of cisplatin alone showed a continuous increase in tumor volume but at a lower rate than that of the untreated control. However, when cisplatin was given 1 h prior to hyperthermia, the tumor volume was significantly decreased by 82.6%.

Results: The effects observed on all the investigated parameter were intensified when cisplatin was combined with hyperthermia. The results obtained suggest that hyperthermia may enhance the penetration of cisplatin to its target site inside the tumor cells due to a membrane-damaging effect. The enhanced lethality of cisplatin on tumor cells may also be due to the inhibition of DNA repair processes by hyperthermia.