Thermal sensitivity and thermal tolerance of human B-lineage acute lymphoblastic leukemia (ALL) cells

The thermal sensitivities of four B-cell precursor acute lymphoblastic (ALL) cell lines (REH and KM-3 = pre pre B-ALL; NALM-6 and HPB-NULL = pre B-ALL), and 1 B-cell ALL (NAMALWA) cell line were studied and compared to the thermal sensitivity of the T-lineage ALL cell line MOLT-3 using an in vitro clonogenic assay system by limiting dilution. B-lineage ALL cells were as sensitive to hyperthermia as were T-lineage ALL cells. D0 values at 42 degrees C ranged from 44.9 min (NALM-6) to 85.6 min (NAMALWA), D0 values at 43 degrees C ranged from 15.3 min (NALM-6) to 35.7 min (KM-3), and D0 values at 44 degrees C ranged from 11.1 min (NALM-6) to 23.8 min (HPB-NULL). By comparison, the D0 values of MOLT-3 cells were 95.1 min at 42 degrees C, 23.8 min at 43 degrees C, and 14.7 min at 44 degrees C. The maximum log kill values which were observed ranged from 0.8 log (KM-3 and HPB-NULL) to 1.3 logs (NALM-6) at 42 degrees C, from 1.4 logs (KM-3) to 4.2 logs (NALM-6) at 43 degrees C, and from 3.8 logs (HPB-NULL) to 4.8 logs (NALM-6) at 44 degrees C. A thermal tolerant plateau was observed in the hyperthermia survival curves of REH, NALM-6, and HPB-NULL cells, providing circumstantial evidence that thermal tolerance may develop in some B-cell precursor ALL cells after 90-120 min of continuous heating. In contrast, no thermal tolerant plateau was observed in the hyperthermia survival curves of pre-pre-B-ALL/KM-3 B-cell ALL/NAMALWA or T-lineage ALL/MOLT-3 cells. The kinetics of development and decay of thermotolerance was studied for NALM-6 cells. Thermotolerance after a priming heat exposure to 42 degrees C for 30 min was maximum at 8 hr with a maximum thermotolerance ratio of 2.0, and it decayed by 24 hr. These findings extend previous studies on the thermal sensitivity of human leukemia cells and provide new information on the thermal sensitivity and thermotolerance of B-lineage ALL cells.