Purging of acute myeloid leukaemia cells from stem cell grafts by hyperthermia: enhancement of the therapeutic index by the tetrapeptide AcSDKP and the alkyl-lysophospholipid ET-18-OCH3

Hyperthermia has been shown to be a potential purging modality in autologou s stem cell transplantation settings owing to its selective toxicity toward s leukaemic cells, We describe two approaches to further increase the thera peutic index of the hyperthermic purging modality by using normal murine bo ne marrow cells and a murine model for acute myeloid leukaemia. First, the tetrapeptide AcSDKP was used to protect the normal haematopoietic progenito r cells against hyperthermic damage, Pretreatment for 8 h at 37 degreesC wi th 1 x 10(-9) mol/l AcSDKP resulted in a decrease in hyperthermic sensitivi ty of only normal haematopoietic progenitor cells, This combined treatment protocol revealed a therapeutic index (ratio of surviving fractions of norm al vs, leukaemic cells) of > 500, which was considered to be sufficient fur purging. This was confirmed in vivo by the survival of lethally irradiated recipients transplanted with purged simulated remission bone marrow (1 x 1 0(6) normal bone marrow cells and 5 x 10(4) leukaemic cells). A further inc rease of the therapeutic index cells was achieved by the alkyl-lysophosphol ipid ET-18-OCH3. An incubation for 4 h at 37 degreesC with 25 mug/ml in the presence of 5% fetal calf serum preferentially enhanced the cytotoxic effe ct towards the leukaemic stem cell. The combination of AcSDKP and ET-18-OCH 3 with hyperthermia resulted in a therapeutic index of > 5000. This enabled a reduction of the hyperthermic treatment and will further minimize the to xicity to normal haematopoietic stem cell subsets, while a therapeutic inde x far above the required Value is achieved. This tripartite purging treatme nt therefore offers a safe and East purging protocol for the elimination of residual leukaemic cells in autografts.