Effects of Hyperthermia on the Cycling, Noncycling, and Hypoxic Cells of Irradiated and Unirradiated Multicell Spheroids

Abstract

Chinese hamster [lung] V79 cells grown as multicell spheroids responded to hyperthermia [used as a method of cancer therapy] differently than cells grown as monolayers. Small spheroids exhibited an increased resistance to elevated temperatures, analogous to that previously observed with ionizing radiation. In larger spheroids, accumulation of noncycling G1-like cells resulted in an increase in thermal resistance. Large spheroids heated under hypoxic conditions showed a greater net sensitivity than under aerobic conditions. The thermosensitivity of single cells or small spheroids was not enhanced under similar hypoxic conditions, nor was the thermosensitivity of the chronically hypoxic cells of spheroids (selected by their resistance to radiation) modified by heating under hypoxic conditions. Any increased thermosensitivity of hypoxic cells may result from secondary changes accompanying O2 depletion, rather than from molecular O2 per se.