Effects of rGM-CSF on leukemia cell proliferation and on the incorporation of cytosine arabinoside into DNA

The effect of haemopoietic growth factors on the cell cycle of AML progenitors and their sensitivity to cytosine arabinoside in vitro

This study examines the effect of pretreatment in liquid culture of acute myeloid leukaemic (AML) progenitors with recombinant human IL-3 or G and GM-CSF. Prior to and following cytokine priming, the sensitivity of cells to cytosine arabinoside (Ara-C) at concentrations ranging from 10(-12) to 10(-4) M was assessed in clonogenic culture. In addition, the initial percentage of AML cells in S phase was assessed and their subsequent kinetic response to cytokine treatment evaluated by FACScan analysis. Light-density marrow cells (LDMCs) from 19 AML patients were initially T-cell and monocyte depleted in order to remove potential sources of endogenous cytokine production prior to in vitro investigation. LDMCs were incubated in liquid phase for 7 d in a chemically defined complete medium with or without cytokines. Clonogenic data from fresh AML LDMCs not pretreated with growth factors demonstrated a heterogenous response to Ara-C. In only 4/15 marrows tested clonogenically was there any improvement in sensitivity to Ara-C following cytokine priming. S-phase data on all 19 marrows were similarly variable either before or after cytokine preincubation. There was no discernible correlation between clonogenic and kinetic data, nor could any relationship be established between in vitro findings and the FAB subtypes of patients or clinical outcomes. In summary, it would appear that the cell-cycle status of AML cells is likely to be only one of many contributory factors governing the sensitivity of AML progenitors to Ara-C. The clinical response of AML patients to cytokine therapy in association with cell-cycle-specific cytotoxic agents may therefore be variable and unpredictable.

Poor prognosis acute myelogenous leukemia

Poor prognosis AML consists of 3 clinically definable groups of patients whose response to therapy is substantially worse than that of standard prognosis patients. The response rate is lowest for those patients who have more than a single risk factor and for the patients who have low platelet and serum albumin levels at diagnosis. The treatment associated mortality of the latter patients is quite high. Even if one avoids the high mortality rate by carefully selecting patients the likelihood that drug resistant disease is present is very high. Since the basis for resistance is multifactorial, a variety of strategies will have to be explored as means to improve treatment outcome. At the present time, the greatest chance for long term survival is found in relatively young patients whose AML is induced into complete remission and who then receive a matched allogeneic bone marrow transplant.