Development of thermotolerance in HMV-I human malignant melanoma cells grown in vitro as multicellular spheroids.

Abstract

The development and decay of thermotolerance were studied in spheroids of HMV-I human malignant melanoma cells and exponentially growing monolayer cells. Thermotolerance was induced by an initial heat treatment at 44° for 15 min. At varying times after preheating, spheroids and monolayer cells were subjected to graded doses of second heating at 44°, and cell survival was assayed by colony formation. The thermosensitivity of monolayer cells rapidly decreased after preheating, reaching a maximum decrease at 3 and 6 hr. However, more marked thermotolerance developed in spheroids at 1 and 6 hrs compared to that of monolayer cells. Thereafter, the thermotolerance decayed gradually in an exponential manner for a few days. It appears that the kinetics of tolerance decay was almost the same in the spheroids and monolayer cells, in contrast to the difference in development of thermotolerance in the two.