Acute and Long-Term Effects of Hyperthermia in B16-F10 Melanoma Cells

Objective: Hyperthermia uses exogenous heat induction as a cancer therapy. This work addresses the acute and long-term effects of hyperthermia in the highly metastatic melanoma cell line B16-F10. Materials and Methods: Melanoma cells were submitted to one heat treatment, 45 degrees C for 30 min, and thereafter were kept at 37 degrees C for an additional period of 14 days. Cultures maintained at 37 degrees C were used as control. Cultures were assessed for the heat shock reaction. Results: Immediately after the heat shock, cells began a process of fast degradation, and, in the first 24 h, cultures showed decreased viability, alterations in cell morphology and F-actin cytoskeleton organization, significant reduction in the number of adherent cells, most of them in a process of late apoptosis, and an altered gene expression profile. A follow-up of two weeks after heat exposure showed that viability and number of adherent cells remained very low, with a high percentage of early apoptotic cells. Still, heat-treated cultures maintained a low but relatively constant population of cells in S and G(2)/M phases for a long period after heat exposure, evidencing the presence of metabolically active cells. Conclusion: The melanoma cell line B16-F10 is susceptible to one hyperthermia treatment at 45 degrees C, with significant induced acute and long-term effects. However, a low but apparently stable percentage of metabolically active cells survived long after heat exposure.