Cycloheximide-induced apoptosis in melanoma cells derived from regressing cutaneous tumours of Sinclair swine

The role of apoptosis in the spontaneous regression of Sinclair swine melanoma was investigated in vitro with swine melanoma cell lines. Growth characteristics and sensitivity to cycloheximide-induced apoptosis were determined in melanoma cell lines derived from tumours that were progressing or undergoing regression in vivo. In contrast to cell lines derived from progressing tumours, those derived from regressing tumours showed induction of apoptosis; this phenomenon was dependent on dose but independent of cell growth stage in culture. Chromatin condensation, cell shrinkage, and fragmentation into apoptotic bodies, as well as DNA fragmentation into large kilobase fragments, occurred in cell lines from regressing tumours but not from progressing tumours. These findings suggest that swine melanoma cells are inherently more sensitive to cell death during tumour regression. The apoptosis-sensitive and resistant cell lines will be important for further studies of the roles of cell signalling pathways and gene expression in tumour regression.