Biological optimization of hyperthermia: modification of tumor membrane lipids.

The sensitivity of the solid mammary adenocarcinomas CA755 and MtGB, grown in the medial aspect of the hind legs of host mice, to local hyperthermia (43.5 +/- 0.1 degrees C for 1 hr) was increased by feeding the host mice a diet enriched in linoleic acid. The enhanced sensitivity was expressed only when the diet was fed for 15 days prior to the tumor transfer. Infusion of lidocaine into the tumor immediately before the hyperthermic exposure enhanced the thermal sensitivity of the controls but not of the linoleic acid-enriched tumors. Sensitivity was analyzed by tumor growth rates and growth delay following exposure. The fatty acid patterns revealed that the proportion of polyunsaturated fatty acids (20:4 and 22:6) decreased reciprocally with increased linoleic acid in the liver phospholipids, whereas in the tumor all polyunsaturated fatty acids increased at the expense of monounsaturated fatty acids. These studies suggest that dietary lipids affected tumor cell sensitivity to hyperthermia.