SPONTANEOUS PREMATURE CHROMOSOME CONDENSATION, MICRONUCLEUS FORMATION, AND NON-APOPTOTIC CELL-DEATH IN HEATED HELA S3 CELLS - ULTRASTRUCTURAL OBSERVATIONS

Hyperthermia is an efficient means of inducing cell death in vivo and in vitro Among human neoplastic cells, HeLa S3 cells are susceptible t o heat injury when exposed to long duration moderate hyperthermia (41. 5 C), conditions that are reproducible and sustainable in the clinical setting, Hence, HeLa S3 cells are a useful substrate for evaluation o f hyperthermic injury in human neoplasia. Previous studies have demons trated a consistent response of HeLa S3 cells to moderate hyperthermia : spontaneous premature condensation of chromosomes during heat exposu re in S phase followed by apparent nuclear fragmentation and, inevitab ly, cell death. To further characterize the morphological features of this process, HeLa S3 cells grown in suspension at 37 C were heated fo r 4, 8, 12, or 16 hours at 41.5 C and harvested in glutaraldehyde for electron microscopic evaluation. Compared with untreated controls, hea ted samples exhibited a characteristic pattern of chromosome condensat ion that mimicked mitotic prophase but was followed by haphazard asymm etric segregation of chromatid clusters in abnormal metaphase/anaphase and premature reformation of nuclear membrane, resulting not in nucle ar fragmentation, but in multiple micronuclei. This pattern of nuclear morphology was not observed in controls, The fraction of cells with m icronuclear morphology increased with time in heated samples (from 3.6 % at 4 hours to 16.6% at 16 hours), consistent with previous light mic roscopic analyses of nuclear fragmentation. Cells with multiple micron uclei subsequently exhibited features similar to necrotic cell death. Apoptosis was never observed Moderate hyperthermia appears to induce a novel morphological pattern of cell injury and death in HeLa S3 cell lines that may be useful as a means of screening cell fines for nonmor phological analyses of hyperthermic injury.