Physical observations on rapid freezing of tumour cells to -40 degrees C using differential scanning calorimetry

Cryoablation is now an established modality in treating liver tumours although local recurrence of liver tumours after cryosurgery, remains a problem. Thus, the optimal, final subzero temperature for cryoablation was investigated using an in vitro, model cell system, comprising rat colonic carcinoma cell line DHD/K12/TRb and a programmable freezer. Freezing to -40 degrees C was lethal to these tumour cells and Differential Scanning Calorimetry revealed ice nucleation peaks in the thermal scans. With slow freezing at -10 degrees C.min(-1) to -40 degrees C or lower, ice nucleation occurred at -20 degrees C+/-3 degrees C. In contrast to rapid freezing at -100 degrees C.min(-1), ice nucleation peaks were observed at -45 degrees C+/-5 degrees C. Viable, frozen tumour cells exhibited a single peak of ice nucleation at -20 degrees C; thermal scans of non-viable, tumour cells destroyed by freezing to -40 degrees C showed four ice nucleation peaks at higher temperatures. Freezing to -40 degrees C was essential for complete growth inhibition and thermal analysis confirmed that death is most likely due to intracellular ice crystal formation.