Predictive value of intracellular ATP level for cell viability after heating in malignant cells

An adenosine triphosphate (ATP) assay is known to be a useful chemosensitivity test, which correctly reflects cell viability. We investigated the usefulness of ATP assay as a thermosensitivity test by comparing two world-wide accepted assays which included a succinate dehydrogenase (SD) assay and a colony assay. We exposed KSE-1 and KSE-2 cell lines to various degrees of hyperthermia at 42, 43 and 44 degrees C for 0.5, 1, 2, 3 and 4 h, respectively. The ATP activity for the KSE-1 and KSE-2 cell lines was 2.0 and 0.7% in change of cell viability after heating at 44 degrees C for 4 h, respectively. Colony formation rates in the KSE-1 and KSE-2 cell lines were 0.9 and 0%, respectively, whereas the SD activity of each cell line was 24.1 and 22.8%. As a whole, the ATP assay showed a closer correlation to the colony assay than the SD assay because the latter revealed a more than 20% pseudo-viability due to the response between the base and residual enzyme even after the cells had died. Thus, the ATP assay was judged to be more sensitive than the SD assay; it was also quicker than the colony assay in evaluating cell viability after heating. We propose that the ATP assay should be included as another useful thermosensitivity test for malignant cells.