In vitro response of blasts to IL-3, GM-CSF, and G-CSF is different for individual AML patients: factors that stimulate leukemic clonogenic cells also enhance Ara-C cytotoxicity

Mathematical modeling of the impact of cytokine response of acute myeloid leukemia cells on patient prognosis

Acute myeloid leukemia (AML) is a heterogeneous disease. One reason for the heterogeneity may originate from inter-individual differences in the responses of leukemic cells to endogenous cytokines. On the basis of mathematical modeling, computer simulations and patient data, we have provided evidence that cytokine-independent leukemic cell proliferation may be linked to early relapses and poor overall survival. Depending whether the model of cytokine-dependent or cytokine-independent leukemic cell proliferation fits to the clinical data, patients can be assigned to two groups that differ significantly with respect to overall survival. The modeling approach further enables us to identify parameter constellations that can explain unexpected responses of some patients to external cytokines such as blast crisis or remission without chemotherapy.

Effect of granulocyte colony-stimulating factor on outcomes in patients with non-M3 acute myelogenous leukemia treated with anthracycline-based induction (7+3 regimen) chemotherapies

We analyzed the effects of granulocyte colony-stimulating factor (G-CSF) on outcomes in 315 anthracycline-based induction chemotherapy-treated patients with non-M3 acute myelogenous leukemia (AML). Patients were classified as follows: no G-CSF administration during induction (no G-CSF group; 112 patients); administration immediately upon neutropenia onset (absolute neutrophil counts (ANC)<1000/μL), but before febrile neutropenia (preemptive group; 74 patients); and administration following febrile neutropenia development (therapeutic group; 129 patients). G-CSF users had a shorter time to ANC recovery than the no G-CSF group (p<0.001). The chemotherapy-induced febrile neutropenia (CIFN) duration was significantly shorter in the preemptive group than in other groups (p<0.001). The incidence of CIFN was not significantly different between preemptive and non-G-CSF users (84.8% versus 82.4%). Preemptive G-CSF administration modestly improved treatment-related mortality (TRM), compared with no G-CSF administration (p=0.076 in multivariate analysis). G-CSF administration did not affect relapse-free or overall survivals or the cumulative relapse incidence among the groups. In conclusion, preemptive G-CSF administration reduced CIFN duration and modestly improved TRM without affecting chemotherapy outcomes. These effects were not observed in the therapeutic group; therefore, initiation of G-CSF during induction therapy before the development of febrile neutropenia may be desirable.

Clonogenic growth patterns correlate with chemotherapy response in acute myeloid leukaemia

Cytosine arabinoside and anthracycline-containing regimens induce remission in upwards of 60% of previously untreated patients with adult acute myeloid leukaemia (AML). Despite this, in addition to primary drug resistance, the majority of these patients relapse. Reliable methods for uniformly recognising these two subgroups at presentation do not exist and therefore a further attempt has been made to relate in vitro toxicity, using a clonogenic assay, to clinical outcome. In 10 normal controls and 12 chemotherapy naïve cases, mononuclear cells harvested by density gradient separation were re-suspended at a concentration of 2 x 10(5)/ml and quadruplicates of 250 microl per well cultured in methycellulose containing foetal calf serum and phytohaemagglutinin stimulated leucocyte conditioned medium. Cell kill was determined for cytosine arabinoside, daunorubicin and etoposide either singly or in combination using both a pulsed and continuous exposure. Aggregates were scored after seven days and three distinct patterns recognised. The patients all received the same drugs in a standard protocol and achievement of complete remission correlated with growth pattern. The survival of normal marrow colony-forming cells or GM-CFUc and the leukemic equivalent designated L-CFUc were assessed and a sensitivity index (SI) determined as a ratio of these two values in which more reproducible results were found when the drug was continuously present. It is concluded that the microculture technique is feasible and clearly demonstrates chemotherapy effect but no correlation was demonstrated with clinical outcome. This is a negative pilot study and, as a means of recognising drug sensitivity or resistance, should be discarded in favour of currently available molecular techniques.

Effects of TNFalpha on the growth and sensitivity to cytosine arabinoside of blast progenitors in acute myelogenous leukemia with special reference to the role of NF-kappaB

Leukemic blasts in acute myelogenous leukemia (AML) are derived from a minor population of cells called blast progenitors. Hematopoietic growth factors (HGFs) stimulate their growth and simultaneously sensitize them to cytosine arabinoside (Ara-C), a cell-cycle-specific cytotoxic drug. Since tumor necrosis factor alpha (TNFalpha) modifies HGF activities, we examined the effects of TNFalpha in combination with HGFs on in vitro growth and Ara-C sensitivity of AML blast progenitors in patient samples. TNFalpha variably affected HGF-supported colony formation and the self-renewal of blast progenitors. However, the combination of TNFalpha with IL-3 uniformly rendered blast progenitors more resistant to Ara-C irrespective of whether TNFalpha suppressed or augmented IL-3-supported growth, indicating that TNFalpha regulates the Ara-C sensitivity of leukemic progenitors independently of their cell cycle status. Since nuclear factor-kappaB (NF-kappaB) is activated by TNFalpha and induces expression of prosurvival genes, effects of the antisense oligodeoxynucleotides to NF-kappaB subunits, p65 and p50, were examined. Antisense oligodeoxynucleotides sensitized HL60 cells to Ara-C but rendered leukemic progenitors in patient samples even more resistant to Ara-C in the presence of TNFalpha and IL-3 in combination, indicating that NF-kappaB is involved in the Ara-C sensitivity of leukemic blast progenitors but may exert opposite dual functions, namely protection from and induction of apoptosis, under different conditions.

Purine nucleoside analogues in the treatment of myleoid leukemias

The purine nucleoside analogues (PNA), fludarabine (FA), cladribine (2-chlorodeoxyadenosine, 2-CdA) and 2'-deoxycoformycin (DCF), represent a novel group of cytotoxic agents with high activity in low-grade lymphoid malignancies. However, several investigations have revealed that these agents are active also in acute myeloid leukemia (AML) and chronic myelogenous leukemia (CML). Synergistic interaction between FA or 2-CdA with cytarabine (Ara-C) have been demonstrated in both preclinical and clinical studies. PNA enhance the cell concentration of Ara-CTP, which is active metabolite of Ara-C. It is likely that the addition of granulocyte colony stimulating factor (G-CSF) may further improve the effects of FA (FLAG) or 2-CdA (CLAG). The addition of anthracyclines to induction therapy does not appear to result in a substantial advantage in terms of CR achievement and duration. An alternative approach to increase FLAG activity might be the addition of investigational drugs with novel mechanism of action, such as topoiromerase I inhibitors. The addition of anthracyclines to induction therapy does not appear to result in a substantial advantage in terms of CR achievement and duration. Clinical studies have confirmed the efficacy of PNA alone or in combination protocols in the treatment of AML. These regimens seem to produce superior results with acceptable toxicities in previously treated and relapsed, poor risk AML. However, early relapses remain a significant problem in a majority of refractory or relapsed patients in CR after treatment with PNA based regimens. To prolong remission duration or even cure AML, auto--or allo stem cell transplantation should be considered. However, FAMP or 2-CdA containing regimens may impair mobilization and collection of stem cells from peripheral blood for autotransplantation. Few studies have analyzed the role of PNA in CML. 2-CdA, FAMP and DCF can induce hematologic response in chronic phase of CML but cytogenetic responses have not been observed. Preliminary results suggest, that PNA used alone or in combination may be used as palliation in blast phase of the disease. However, currently, the role of these agents in CML is insignificant because of the high activity of Glivec in this disease. Finally, PNA, especially FA play an important role in non-myeloablative conditioning regimens for allogenic stem cell transplantation in high-risk patients, possibly also with myeloid malignancies.

De novo acute myeloid leukemia with multilineage dysplasia: treatment results and prognostic evaluation from a series of 44 patients treated with fludarabine, cytarabine and G-CSF (FLAG)

OBJECTIVES

To evaluate therapeutic results and prognostic factors from a series of 44 patients affected by de novo acute myeloid leukemia with multilineage dysplasia (MD-AML), treated with the combination of fludarabine, cytarabine and G-CSF (FLAG).

METHODS

Forty-four patients with de novo MD-AML were treated with the FLAG regimen. The median age was 61 yr (range 31-75 yr). Induction therapy consisted of the FLAG regimen; consolidation included idarubicin plus cytarabine. Patients with a compatible donor and aged less than 55 yr were programmed to receive allogeneic bone marrow transplantation (BMT), while in those without a donor and aged less than 65 yr autologous transplantation with peripheral blood stem cells mobilized by a consolidation regimen plus G-CSF was planned. Bone marrow harvest was performed in poor mobilizers.

RESULTS

Complete remission (CR) was achieved in 28 out of 44 patients (64%). Death in induction occurred in four patients (9%), while 12 patients (27%) were resistant to FLAG. Toxicity of consolidation was negligible. Most patients aged less than 60 yr and achieving CR were eligible for transplantation procedures, the main reason of exclusion being early relapse. Median overall survival and disease free survival were 16 and 22 months, respectively. Unfavorable cytogenetics was the only parameter significantly related to inferior clinical outcome following multivariate analysis.

CONCLUSION

Multilineage dysplasia per se is not an adverse prognostic factor in AML patients treated with the FLAG regimen. Favorable results are obtained in patients with intermediate karyotype, while in those with adverse cytogenetics new approaches are clearly needed. The toxicity of the regimen is also acceptable in the elderly, and following induction/consolidation, most patients may be submitted to transplantation procedures.

Intra-arterial infusion of 5-fluorouracil plus granulocyte-macrophage colony-stimulating factor (GM-CSF) and chemoembolization with melphalan in the treatment of disseminated colorectal liver metastases

AIMS

We compared two prospective trials of intra-arterial cytokine/chemotherapeutic infusion plus chemoembolization in the treatment of inoperable colorectal liver metastases.

MATERIALS AND METHODS

One hundred and three patients with disseminated inoperable colorectal liver metastases received intra-arterial chemotherapy with 5-FU and granulocyte-macrophage colony-stimulating factor (GM-CSF) plus chemoembolization via an angiographically positioned hepatic artery catheter. Two different regimens were used in two consecutive studies. Group A: short-term i.a. infusion of 550 mg/m(2)5-FU (days 1-4) plus 80 microg/m(2)GM-CSF (day 1+2) combined with chemoembolization with 25 mg/m(2)melphalan plus Lipiodol and Gelfoam (day 5). Group B: continuous circadian intra-arterially administered 1400 mg/m(2)5-FU infusion plus 60 mg/m(2)i.v. leucovorin and 80 microg/m(2)GM-CSF (day 1+2) combined with chemoembolization with 25 mg/m(2)melphalan plus Lipiodol and Gelfoam (day 3).

RESULTS

One hundred and three patients (62 male/41 female) with a median age of 59.9 and a median Karnofsky index of 88.5 were treated with 447 cycles of immuno-chemoembolization (group A 299, group B 148 cycles). Fifty-seven percent of these patients had received prior systemic chemotherapy. Side-effects were seen in all patients, mainly upper abdominal pain lasting 1-4 days and grade 1 or 2 vomiting. Systemic side-effects were mild and transient with a very low rate of leukopenia. Using World Health Organization response criteria, the following responses could be demonstrated: group A: CR 2.7%, PR 32.4%, MR 21.6%, SD 12.7%, NR 16.2%; group B: CR 1.0%, PR 42.4%, MR 24.2%, SD 18.2%, NR 12.1%. Time to progression was 7 as compared to 8 months. Median survival was 17 months in group A, whereas it has not been reached after 28 months (P=0.0095) in group B. There was no statistically significant difference between chemo-naive patients and patients who had received prior systemic therapy.

CONCLUSION

Immuno-chemoembolization combined with 2-day circadian administration of 5-FU is an effective tool in the treatment of disseminated colorectal liver metastases. This regimen is also effective as second-line treatment.

Cyclosporin increases cellular idarubicin and idarubicinol concentrations in relapsed or refractory AML mainly due to reduced systemic clearance

The feasibility of adding both the multidrug resistance modulator cyclosporin (CsA) and granulocyte colony-stimulating factor (G-CSF) to a standard salvage regimen of idarubicin (IDA) and cytarabine was evaluated in patients with resistant or relapsed acute myeloid leukemia and myelodysplastic syndrome. Three patients received IDA 12 mg/m2/day, the next four patients 9 mg/m2/day. The dose of CsA was 16 mg/kg/day. Six patients showed Pgp expression and none MRP1 expression. Grade III or IV toxicity (CTC-NCIC criteria) was registered in six patients for gastrointestinal, two patients for cardiovascular and one patient for neurological complications. Three patients died in hypoplasia and three patients showed leukemic regrowth. Three control patients were treated with IDA 12 mg/m2/day and cytarabine, but no CsA and G-CSF. The plasma IDA and idarubicinol (ida-ol) area under the curve's of patients treated with IDA 12 mg/m2 plus CsA were higher (P< 0.05) than in controls. Cellular IDA concentrations were almost similar, but cellular ida-ol concentrations were significantly higher (P < 0.05) in the presence of CsA than in controls. We conclude that the toxicity either with IDA 12 or 9 mg/m2/day was too high. The modulating effect of CsA was mainly based on changes in plasma kinetics of IDA and ida-ol, although ida-ol cellular clearance was delayed in the presence of CsA.

Triggering Noncycling Hematopoietic Progenitors and Leukemic Blasts to Proliferate Increases Anthracycline Retention and Toxicity by Downregulating Multidrug Resistance

Expression of the multidrug resistance (MDR) mechanisms P-glycoprotein (Pgp) and MDR-related protein (MRP) decrease cellular retention and consequently cytotoxicity of anthracyclines. MDR is expressed on normal human hematopoietic progenitors and leukemic blasts. Normal CD34+ progenitors showed rhodamine efflux in 20% to 30% of the cells, which could be blocked by verapamil. These cells appeared noncycling, in contrast to the proliferating rhodamine bright (RhoB) cells. We postulated that MDR expression can be downregulated by proliferation induction. Triggering rhodamine dull (RhoD) CD34+ cells to proliferate indeed resulted in a higher rhodamine retention and significantly decreased efflux modulation by verapamil (P = .04). Also in acute myeloid leukemia (AML), the proliferation rate (percentage S/G2+M and Iododeoxyuridine labelings index) was significantly less in the RhoD blasts (P ≤ .008) and proliferation induction of RhoD blasts resulted in increased rhodamine retention. Anthracycline cytotoxicity was less for RhoD than RhoB cells in both normal progenitors and leukemic blasts. Proliferation induction of the RhoD cells resulted in increased anthracycline sensitivity. We conclude that noncycling progenitors, both normal and leukemic, have a relatively high MDR expression. Triggering these cells into proliferation downregulates MDR expression. These findings can be exploited to overcome MDR in the treatment of AML patients.

Modulation of in vitro chemosensitivity in acute myelogenous leukemia cell line by GM-CSF: opposing effects observed with different cytotoxic drugs and time exposure

In some studies the GM-CSF (granulocyte-macrophage colony-stimulating factor) increased the in vitro sensitivity of acute myeloid leukemia (AML) cells to cytosine arabinoside (Ara-C), however, in clinical trials no favorable effects were shown. We used a GM-CSF responsive AML cell line (AML 193) to test the effects of growth stimulation on in vitro efficacy of Ara-C and methotrexate (MTX). In 6 days continuous exposure, dose dependent Ara-C cytotoxicity was counteracted by GM-CSF. Conversely, MTX cytotoxicity was increased significantly. However, in a short term treatment (24 h, high doses) the GM-CSF increased both MTX and Ara-C cytotoxicity. These effects might depend on different drug regimens and cell features.

Proliferative reaction of myelogenous leukemia cells with cytokines G-CSF, GM-CSF, M-CSF, SCF and TPO

In recent years, many cytokines have been defined and some of them used clinically. In hematological malignancies, cytokines, including granulocyte colony-stimulating factor (G-CSF), have been widely used for leukopenia after chemotherapy. However, in acute myelogenous leukemia (AML), some leukemic cells may be induced to proliferate by these cytokines and they must be used with care. In this study, we have investigated cell reactivity and proliferation with G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CMF), macrophage colony-stimulating factor (M-CSF), stem cell factor (SCF) and thrombopoietin (TPO) in cases of AML. We have also investigated the reactivity of some myeloid leukemia cell lines to TPO. G-CSF, GM-CSF, M-CSF, SCF and TPO caused proliferation of leukemic cells in 25%, 58.3%, 8.3%, 21.1% and 0% of cases, respectively. Because of this result, the use of G-CSF in AML should be regarded as potentially hazardous. TPO did not cause proliferation of leukemic cells in any case of AML, or in cell lines except MO7E, which is a megakaryocytic cell line. This result suggests that TPO might cause proliferation of some megakaryocytic leukemia cells. We cannot conclude that TPO does not cause proliferation of other AML cells, as the number of cases was small and it has been reported elsewhere that leukemia cells may proliferate when exposed to TPO in 50% of AML cases. Reactivity of AM L cells to TPO is an important factor when deciding the indications of TPO in AML and myelodysplastic syndrome.

Fludarabine, cytarabine, and G-CSF (FLAG) for the treatment of poor risk acute myeloid leukemia

Thirty-eight patients with primary resistant or relapsing acute myeloid leukemia (AML) were treated with fludarabine, cytarabine and granulocyte colony-stimulating factor (FLAG). Median age was 41 (range 11-70). Sixteen patients had AML that was primary resistant to induction treatment, while 22 were relapsed, 11 after autologous bone marrow transplant (AuBMT), 8 less than 6 months from complete remission (CR) achievement, and 3 were second relapse from chemotherapy alone. Overall, 21 of 38 patients (55%) obtained CR. Age, sex, length of CR, and interval between autoBMT and FLAG administration did not significantly influence the CR rate. On the contrary, a normal karyotype at diagnosis was significantly related to a better outcome. There were 4 induction deaths (10%), due to fungal infection in 2 patients and hemorrhagic complications in the remaining two. All patients experienced profound cytopenia. Median time to neutrophil (>500/microl) recovery was 21 days, while a platelet count >20,000/microl was reached after 23 days. The median period of hospitalization was 31 days. The nonhematological toxicity was mild, mainly consisting of mucositis. There were 17 documented infections and 17 episodes of fever of unknown origin. Following CR achievement, 6 patients received autoBMT, 3 alloBMT, 2 high-dose arabinosil-cytosine, and 2 are on a waiting list for transplantation procedure. We conclude that FLAG is an effective and well-tolerated regimen for refractory or recurrent AML, mainly useful for patients to be admitted to bone marrow transplantation.

Impact of exogenous growth factors on proliferation and chemosensitivity of minimal residual acute myeloid leukemia

The biological heterogeneity of AML makes growth factor augmentation of cell cycle-dependent chemotherapy unlikely to be successful for all patients. Patients whose leukemic cells empirically demonstrate cytokine-induced chemosensitization in vitro might benefit from the concurrent administration of growth factors during consolidation chemotherapy. We have explored the growth factor-dependence and response of primary bone marrow samples from patients with AML at diagnosis, remission, and relapse to determine whether minimal residual leukemia remains growth factor-responsive. Most cases of AML studied at all phases of treatment were growth factor-responsive. Growth factor response of occult remission clonogenic leukemic precursors (CFU-L) was usually concordant with their response at diagnosis. Occult CFU-L were markedly resistant to cytosine arabinoside (median LD99% 20 microM); preincubation with IL-3 or GM-CSF did not significantly improve their ara-C sensitivity. While occult remission CFU-L appear to remain growth factor-responsive, it appears unlikely that growth factor augmentation of consolidation chemotherapy will overcome the important problem of drug resistance of residual leukemia.

Ara-C: cellular and molecular pharmacology

The antimetabolite cytosine arabinoside (ara-C) represents a prototype of the nucleoside analog class of antineoplastic agents and remains one of the most effective drugs used in the treatment of acute leukemia as well as other hematopoietic malignancies. The ability of ara-C to kill neoplastic cells is regulated at three distinct but interrelated levels. First, the activity of ara-C depends on conversion to its lethal triphosphate derivative, ara-CTP, a process that is influenced by multiple factors, including nucleoside transport, phosphorylation, deamination, and levels of competing metabolites, particularly dCTP. Second, the antiproliferative and lethal effects of ara-C are linked to the ability of ara-CTP to interfere with one or more DNA polymerases as well as the degree to which it is incorporated into elongating DNA strands, leading to DNA fragmentation and chain termination. Finally, the fate of the cell is ultimately determined by whether a threshold level of ara-C-mediated DNA damage is exceeded, thereby inducing apoptosis, or programmed cell death. The latter process is influenced by components of various signal transduction pathways (e.g., PKC) and expression of oncogenes (e.g., bcl-2, c-Jun), perturbations in which may significantly alter ara-C sensitivity. A better understanding of these factors could eventually lead to the development of novel therapeutic strategies capable of overcoming ara-C resistance and improving therapeutic efficacy.

In leukemic hematopoiesis CD34 antigen does not have the same significance as it does normal hematopoiesis

The aim of the present study was to analyze whether or not leukemic clonogenic cells are restricted to the CD34+ cell fraction and to investigate the effect of IL-3 and G-CSF on blast cell populations dissected according to their CD34 reactivity. For this purpose 34 patients were studied. Patients were classified into three groups according to CD34 antigen expression: (1) cases in which all blast cells (100%) were positive for the CD34 Ag (n = 9); (2) cases in which all blast cells lacked the expression of this antigen (n = 10); and (3) patients in whom both, CD34 positive and negative blast cell subsets coexisted (n = 15). In 15 cases immunomagnetic cell selection was performed and two subpopulations were separated: one, phenotypically more immature (CD34+), and another, theoretically more differentiated (CD34-/33+). In addition, in three cases both CD34+ and CD34- blast cell subpopulations were sorted using a FACStar flow cytometer. Blast colony assays were performed using 0.9% methylcellulose and two different recombinant human hematopoietic growth factors (HGFs), IL-3 and G-CSF, were used as growth stimulants. Either, a single or a combination of the growth factors was added to cultures. Colony formation was observed in both 100% positive or 100% negative cases for the CD34 antigen as well as in the CD34+ and CD34- cell fractions separated by immunomagnetic selection or flow cytometry. The effect of G-CSF and IL-3 on both cell fractions was as follows: cases with a uniform population according to CD34 expression (100% positive or negative) showed a better growth response with IL-3 especially for the CD34+ cases (87% vs 40% of CD34+ and CD34- cases, respectively). Within the CD34-/33+ selected fractions, IL-3 tended to induce a higher proliferative response than G-CSF while the opposite was found within the CD34+ cell selected fractions. In contrast it was observed that both IL-3 and G-CSF induced a higher PE on the CD34- blast cells (both selected and 100% negative), although the difference was not statistically significant. The existence of a possible synergistic effect (SE) between HGFs was also explored. Overall, a synergistic growth was observed in nine out of the 13 selected cases studied and this effect could be seen in both CD34- or CD34+ blast cell fractions. The analysis of the complete phenotypic characteristics of these cells revealed that cell fractions showing SE were more immature according to the expression of CD15 and HLA-DR antigens. We can conclude that in leukemic hematopoiesis, CD34 antigen expression does not have the same significance as it does in normal hematopoiesis since clonogenic cells are not restricted to the CD34+ acute myeloid leukemia (AML) blast cell fraction. Moreover, our study shows that the heterogeneous response to HGFs observed in AML patients may be associated with the existence of immunophenotypically different blast cell subsets.

Cytokines, molecular biological abnormalities, and acute myelogenous leukemia

Leukemia cell proliferation is dependent upon cytokines produced by the leukemia cells or by the microenvironment under stimulation by leukemia cells. Abnormal expression of the p53, rb, and ras genes is associated with cytokine production, suggesting that abnormal expression can affect leukemia cells by affecting intracellular growth controls and by stimulating cytokine production. While these observations suggest that cytokines can be used to stimulate leukemia proliferation during cytotoxic therapy increasing the sensitivity to treatment, they also suggest that inhibition of cytokine affects could increase clinical responses by reducing leukemia cell regrowth between courses of therapy.

Hematopoietic Growth Factors and Blast Progenitors in Acute Leukemia

Leukemic cells are maintained by a minor subpopulation of cells called leukemic stem cells (LSC) with proliferative and self-renewal capacity, both of which are detected with leukemic colony assay, with the latter being an important prognositic factor. Drug sensitivity tests employing leukemic colony assay revealed the effects of cytotoxic drugs on LSC to be diverse and that cytosine arabinoside predominantly suppresses self-renewal, which probably accounts for its effectiveness in AML therapy. Hematopoietic growth factors (HGFs) regulate the growth of LSC and various in vitro effects of HGFs on acute leukemia cells have been reported. These effects appear to reflect physiological functions of each HGF and can be categorized into groups according to their distinct functions. Endogenously produced HGFs stimulate LSC in an autocrine or a paracrine fashion, resulting in autonomous growth of these cells, which also correlates with the patients' prognosis. HGFs can enhance the cytotoxicity of anti-leukemia drugs in vitro, possibly mainly through recruitment of LSC from the dormant state into active cell cycling. HGFs have been clinically tested in leukemia therapy. Although recovery of blood leukocyte counts can consistently be accelerated with HGF treatment, the effectiveness of HGFs in sensitizing leukemia cells to chemotherapeutic agents and/or improving patient prognosis has not been clearly demonstrated. Different strategies using HGFs and related molecules must be tested in future leukemia therapy.

Rationale for high-dose chemotherapy and application of haematopoietic growth factors in acute myeloid leukaemia

High-dose chemotherapy in acute myeloid leukaemia (AML) is more effective and not associated with a higher risk of lethal complications during the induction phase as compared with less intensive regimens. This seemingly paradoxical finding is explained by the more rapid reduction of the leukaemic cell mass and the faster restoration of normal haematopoesis. In the most recent study on double induction therapy by the German AML Cooperative Group involving 665 adult patients with AML the rate of complete remission was 66%-73%. Haematopoietic growth factors used as part of the anti-tumour regimen offer a number of advantages. These include acceleration of haematopoietic recovery and the potential to enhance the sensitivity of leukaemic blasts when given prior to and during cytostatic therapy. New perspectives to further enhance the intensity of antileukaemic therapy may emerge from the introduction of peripheral stem cell transplantation into the treatment strategy.