Heat- and 4-hydroperoxy-ifosfamide-induced apoptosis in B cell precursor leukaemias

In the group of high risk childhood acute lymphoblastic leukaemia (ALL), very early and early relapses have a very poor prognosis with conventional chemotherapy alone. Remission induction in these patients is often hindered by drug resistance. Thus, intensifying chemotherapy strategies are required. Application of hyperthermia enhances efficacy of certain anti-neoplastic drugs such as ifosfamide. In this study, effects and molecular mechanisms of ifosfamide - and hyperthermia-induced apoptosis are investigated in a B cell precursor leukaemia cell line (REH) and in primary patient-derived B cell progenitor leukaemic blasts. Both 4OOH-IFA and hyperthermia are able to induce cell death in leukaemic cells, mainly by induction of caspase-dependent apoptosis. However, completely different kinetics of caspase-3, -8 and -9 activation are found for both stimuli. In addition, activation of caspase-1 is only observed following stimulation with hyperthermia. Combined application of ifosfamide and hyperthermia reveals increased cytotoxicity in both the leukaemia cell line and in 5/8 of the patient-derived leukaemic blast samples. In conclusion, hyperthermia and ifosfamide mediate cytotoxicity in B precursor leukaemic blasts by different kinetics of caspase activation. This might explain the additive effects of 4OOH-IFA and heat on leukaemic cell death. Therefore, whole body thermochemotherapy could be considered as a treatment option in relapsed leukaemic patients.