The effect of hyperthermia alone or in combination with actinomycin D on the RNA metabolism of solid tumors in children.

The incorporation of 3H-uridine into the RNA was studied under normothermia 37 degrees C/120 min, hyperthermia 42.5 degrees/120 min, and both in combination with Actinomycin D by an autoradiographic in vitro method in 19 solid tumors of children: 6 Wilms' tumors, 5 neuroblastomas, 4 osteogenic sarcomas, and 4 different tumors. Hyperthermia invariably reduces the 3H-uridine incorporation into RNA by 11.7--86.4%, with an average of 47.5%. Actinomycin D consistently inhibits the 3H-uridine incorporation between 27.7 and 99.8%, with the average inhibition of 62.0% being far greater than that recorded for hyperthermia. The highest degree of 3H-uridine incorporation inhibition is obtained using hyperthermia in combination with Actinomycin D. The inhibition varies from 45.5--99.8%, with an average of 81.4%. In spite of the general regularity, the effect of hyperthermia and Actinomycin D are characterized by individual patterns. Obviously, they are dependent on proliferative activity rather than upon the particular type of tumor. The use of supranormal temperatures for the treatment of malignant tumors in man, also in combination with radiation or cytostatic drugs, is a possible and promising method of therapy.