Variable interaction of heat and procaine in potentiation of radiation lethality in mammalian cells of neoplastic origin.

Abstract

Mild hyperthermia in conjunction with procaine HCl acts as a potentiator of radiation lethality in HeLa cells, with little toxicity for unirradiated cells. The majority of irradiated cells responds extensively within a four hour period of treatment with the two agents. Potentiation of radiation lethality by the combined treatment was also found in a line of human melanoma cells, and to a lesser extent in a line of human ovarian carcinoma cells. The interaction of heat and procaine in the process of potentiation of radiation lethality was assessed from a series of radiation survival curves, with temperatures ranging from 37 to 42 degrees C and procaine concentrations from 1 to 3 mM. The interactive factor was obtained from the ratio of the Dose Reduction Factor (DRF) due to procaine in heated cells, to the DRF due to procaine in unheated cells; a ratio larger than unity denotes interaction of heat and procaine. The largest interaction was observed when individual agents exerted only a minimal radiopotentiating effect, as if increased effectiveness of one agent pre-empted the effectiveness of the other agent.