The effect of high-dose thiotepa, alone or in combination with other chemotherapeutic agents, on a murine B-cell leukemia model simulating autologous stem cell transplantation.

The use of thiotepa (TH) is increasing, especially in stem cell transplantation, mainly due to its safety and blood-brain barrier penetration. We evaluated the use of TH in a murine model simulating autologous stem cell transplantation, with or without additional agents. Between 1 and 11 days following inoculation of BALB/c mice with 10(5)-10(8) B-cell leukemia (BCL1) cells (simulating pre-transplant leukemia loads), each group received an 'induction-like' irradiation and/or cytotoxic regimen. Animals were either followed without treatment, or an adoptive transfer (AT) was performed to untreated BALB/c mice. Administered alone without AT, high-dose TH did not change the time to appearance of leukemia. Nevertheless, in the AT experiments, TH as a single agent showed better antileukemic activity than busulfan (BU). Cyclophosphamide (CY)-containing regimens were the most effective, and the TH-CY combination was as effective as the commonly used BU-CY combination, and more effective than the BU-TH combination. Moreover, a synergistic effect was seen in the TH-CY combination (none of the animals developed leukemia, whereas 4/10 animals in the CY-TBI group developed leukemia (P=0.029)). In conclusion, although TH produced only a moderate effect against BCL1 leukemia when used alone, its combination with CY is promising and should be tested further in allogeneic murine models and clinical studies.