Kinetic rationale for cytokine-induced recruitment of myeloblastic leukemia followed by cycle-specific chemotherapy in vitro.

In patients with acute myeloblastic leukemia incomplete response to induction chemotherapy and short disease-free survival may be related to cell kinetic quiescence of leukemic cells. In this in vitro study, we tested the hypothesis that treatment with cytokines and subsequent chemotherapy (ARA-C, daunorubicin) can increase proliferation and enhance leukemic cell kill. We evaluated the effects of recombinant human interleukin-3 (rh-IL-3), granulocyte-macrophage colony stimulating factor (rhGM-CSF) and granulocyte colony stimulating factor (rhG-CSF) alone and in combination on AML (N = 11) and blastic phase CML (N = 3) samples. Cellular DNA and RNA, incorporation of bromodeoxyuridine (BrdU), cell growth fraction, cell viability, and differentiation markers were evaluated in vitro. A decrease of the quiescent cell population (p = 0.003) and an increase in S-phase cells (p = 0.001) was observed in 8/11 AML samples treated with cytokine combinations. Pronounced heterogeneity or proliferative response was seen between individual cases and different cytokines, but in the majority of the samples IL-3 was most effective. Significantly increased Ki67 expression (p = 0.009) and BrdU incorporation (p = 0.01) were also found after exposure to cytokines indicating an increase in growth fraction. DNA synthesis time was unaffected. Eight samples of AML were treated for 24 hr with ara-C following 2 days of in vitro cytokine incubation. Evaluation of leukemic cell kill showed increased cytotoxicity in three of those five samples which had significant depletions of G0 cells and increases in S-phase. None of the leukemic samples without recruitment from G0 had an increase in ARA-C cytotoxicity. This study provides detailed cell kinetic analysis of cytokine effects on AML blasts and provides a rationale for a novel approach to the treatment of AML.