Studies on sensitivity of human GM-CFU and L-CFU to hyperthermic killing in vitro

Heat shock proteins and Bcl-2 expression and function in relation to the differential hyperthermic sensitivity between leukemic and normal hematopoietic cells

A major problem in autologous stem cell transplantation is the occurrence of relapse by residual neoplastic cells from the graft. The selective toxicity of hyperthermia toward malignant hematopoietic progenitors compared with normal bone marrow cells has been utilized in purging protocols. The underlying mechanism for this selective toxicity has remained unclear. By using normal and leukemic cell line models, we searched for molecular mechanisms underlying this selective toxicity. We found that the differential heat sensitivity could not be explained by differences in the expression or inducibility of Hsp and also not by the overall chaperone capacity of the cells. Despite an apparent similarity in initial heat-induced damage, the leukemic cells underwent heat-induced apoptosis more readily than normal hematopoietic cells. The differences in apoptosis initiation were found at or upstream of cytochrome c release from the mitochondria. Sensitivity to staurosporine-induced apoptosis was similar in all cell lines tested, indicating that the apoptotic pathways were equally functional. The higher sensitivity to heat-induced apoptosis correlated with the level of Bcl-2 protein expression. Moreover, stable overexpression of Bcl-2 protected the most heat sensitive leukemic cells against heat-induced apoptosis. Our data indicate that leukemic cells have a specifically lower threshold for heat damage to initiate and execute apoptosis, which is due to an imbalance in the expression of the Bcl-2 family proteins in favor of the proapoptotic family members.

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-OCH(3)

Hyperthermia has been shown to be a potential purging modality in autologous stem cell transplantation settings owing to its selective toxicity towards leukaemic cells. We describe two approaches to further increase the therapeutic index of the hyperthermic purging modality by using normal murine bone marrow cells and a murine model for acute myeloid leukaemia. First, the tetrapeptide AcSDKP was used to protect the normal haematopoietic progenitor cells against hyperthermic damage. Pretreatment for 8 h at 37 degrees C with 1 x 10(-9) mol/l AcSDKP resulted in a decrease in hyperthermic sensitivity of only normal haematopoietic progenitor cells. This combined treatment protocol revealed a therapeutic index (ratio of surviving fractions of normal vs. leukaemic cells) of > 500, which was considered to be sufficient for purging. This was confirmed in vivo by the survival of lethally irradiated recipients transplanted with purged simulated remission bone marrow (1 x 10(6) normal bone marrow cells and 5 x 10(4) leukaemic cells). A further increase of the therapeutic index cells was achieved by the alkyl-lysophospholipid ET-18-OCH(3). An incubation for 4 h at 37 degrees C with 25 microg/ml in the presence of 5% fetal calf serum preferentially enhanced the cytotoxic effect 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 toxicity to normal haematopoietic stem cell subsets, while a therapeutic index far above the required value is achieved. This tripartite purging treatment therefore offers a safe and fast purging protocol for the elimination of residual leukaemic cells in autografts.

Synergistic cytotoxic effect of quercetin and heat treatment in a lymphoid cell line (OZ) with low HSP70 expression

Heat shock protein 70 (HSP70) protects cells from various injurious stimuli and is important in cell growth and differentiation. However, its expression in leukemia cells has not been analyzed systematically. We, therefore, investigated the expression of HSP70 in various types of leukemia cells and hematopoietic cell lines. Immunoblot analysis revealed that HSP72/73 were expressed at low levels in the acute lymphocytic leukemia cells and lymphoid cell lines examined. However, heat (43 C for 2 h) preferentially augmented HSP72/73 expression in lymphoid cells. This induction was partially blocked by the treatment with quercetin (10 microM for 24 h). Finally, heat shock following quercetin treatment synergistically induced apoptosis in a lymphoid cell line (OZ). These observations suggest the possibility of selective purging of lymphocytic leukemia cells by combination with quercetin and heat.

The effects of hyperthermia in bone marrow purging of breast cancer

The number of autologous bone marrow transplants done for solid tumours, particularly breast cancer, has risen steadily over the last ten years. The role of bone marrow or peripheral blood progenitor cell purging in transplantation is incompletely understood. Theoretically, the reinfusion of untreated bone marrow containing tumour cells might result in relapse in some patients treated with high-dose chemotherapy and hematopoietic support. Therefore, safe and effective purging techniques may increase long-term, disease-free survivorship. In this study, hyperthermia was evaluated for its ability to purge CAMA-1 breast cancer cells from normal human bone marrow. Between two and nine trials of a range of temperatures (42-45 degrees C) and durations of treatment (1-4 h) were performed. The effect of hyperthermia on normal bone marrow alone and in mixes with breast cancer cells was also evaluated. Hyperthermia (45 degrees C, 4 h) produced > 5 logs of CAMA-1 cell kill. Exposures of 45 degrees C for 2 h and 44 degrees C for 4 h resulted in approximately three logs of cell kill, corresponding to < 1% survival of clonogenic cells. Normal bone marrow was considerably more vulnerable to heat treatments, however, with approximately 1% of progenitors remaining clonogenic after exposure of 43 degrees C for 2 h and 44 degrees C for 1 h. Therefore, although hyperthermia is able to achieve adequate CAMA-1 breast cancer cell kill, it remains more toxic to normal bone marrow as a purging method. To make hyperthermia useful in purging systems, mechanisms to selectively alter thermal sensitivity must be pursued.

The development and magnitude of thermotolerance during chronic hyperthermia in murine bone marrow granulocyte-macrophage progenitors: I

Murine bone marrow granulocyte-macrophage progenitors (CFU-GM) are capable of developing thermotolerance during exposure to temperatures < 42.5 degrees C. Bone marrow from the tibia and femora was heated to 40-42 degrees C (i.e. chronic hyperthermia), and challenged immediately with 15 min at 44 degrees C at regular intervals during treatment (step-up heating). CFU-GM were heated and cultured in McCoy's 5A medium + 15% FBS (fetal bovine serum) and lung-conditioned medium (source of colony stimulating factor) in semisolid agar. The kinetics of thermotolerance development and decay, and the magnitude of the thermotolerance during chronic heating with temperatures of 40-41.5 degrees C were similar. Survival increased rapidly to a maxima by approximately 120 min of hyperthermia (temperatures of 40-41.5 degrees C) and thereafter decreased with a slope similar to the controls. Normalization for cell killing by chronic hyperthermia that occurred during "step-up' heating permitted analysis of thermotolerance in the surviving cells. The surviving fraction after 15 min at 44 degrees C, during incubation at 40, 41 and 41.5 degrees C increased from 0.13 to maxima of 0.56 +/- 0.04, 0.71 +/- 0.03 and 0.82 +/- 0.03 respectively, by 150 min and did not decrease for up to 480 min during chronic hyperthermia. The surviving fraction after 15 min at 44 degrees C during incubation at 42 degrees C increased more slowly than during incubations at 40-41.5 degrees C. The survival of thermotolerant cells after exposure to 15 min at 44 degrees C during 42 degrees C chronic hyperthermia was maximal at 0.87 +/- 0.08 by 120 min and then decreased after approximately 150 min of exposure to 42 degrees C. The thermotolerance ratios (TTR's) were 4.0, 5.4, 6.7 and 6.9 for temperatures of 40, 41, 41.5 and 42 degrees C respectively. The results suggest that chronic hyperthermia temperatures (i.e. 40-42 degrees C) induce rapid thermotolerance development in CFU-GM during the thermal exposure and protect this normal marrow progenitor during whole body hyperthermia or ex vivo purging of leukaemic cells.

Total body hyperthermia in combination with etoposide and melphalan in a child with acute myelomonocytic leukemia

In vitro and clinical studies have shown antineoplastic effects of hyperthermia alone and in combination with other treatment modalities. Synergistic cytotoxic effects of chemotherapy and hyperthermia have been demonstrated on leukemic cell clones in vitro. It seems that hyperthermia is effective in overcoming chemotherapy resistance. Several groups treated solid tumors by using total body hyperthermia (TBHT). However, only a few studies have been reported investigating the clinical effects of TBHT in myeloproliferative disorders. We report the case of a 7-year-old boy with myelomonocytic leukemia treated with TBHT (2 hours, 42 degrees C) combined with etoposide (600 mg/m2), melphalan (30 mg/m2) and hyperglycemia (200-300 mg/dl). Within 24 hours after TBHT, the leukemic cells decreased after TBHT from 53,000/microliters to zero. Skin leukemic infiltrates, resistant to conventional treatment, also responded well. Although our patient relapsed 34 days after TBHT, these results indicate that TBHT in combination with cytotoxic treatment may be a useful treatment modality in refractory leukemia.