Prognostic models for acute myeloid and
lymphoid leukemias are presented that demonstrate that cell kinetic quiescence in acute
leukemia is associated with poor response to
chemotherapy, short remission duration, and survival. Recruitment of cells into the cell cycle should therefore enhance cytotoxic effects of cell cycle - specific chemotherapeutic agents. We previously demonstrated recruitment of myeloid leukemic cells by
cytokines. We have now investigated whether recruitment can be used to increase cell killing by
cytosine arabinoside (
Ara-C). Blast cells from 16 acute
leukemias were stimulated with
cytokines as follows: 13
acute myeloid leukemias (AML) and 3
chronic myeloid leukemia (CML) in blastic phase (1 lymphoid, 2 myeloid) were treated with recombinant human
granulocyte colony stimulating factor (rhG-CSF),
recombinant human granulocyte-macrophage colony stimulating factor (rhG-CSF, AMGEN, 500 U/ml each), and recombinant human
interleukin-3 (rhIL-3, IMMUNEX, 20 ng/ml), alone and in combination. After 48 h, at the time of maximal
DNA synthesis,
Ara-C (10(-3) M) was added and cell counts, cytokinetics (
DNA/
RNA,
DNA/
bromodeoxyuridine and
DNA/Ki67 flow cytometry), and cell viability/clonogenicity (
fluorescein diacetate/
propidium iodide exclusion flow cytometry) were investigated. In all 13 cases of AML recruitment was found; in 6 of these cases over a three fold increase in S phase (P = 0.008) and a significant (P = 0.004) depletion of G0 was demonstrated. In 9 of 13 patients with AML, the effect of
Ara-C was investigated, and in 3 of 5 patients with over three fold increase in S phase,
Ara-C toxicity was enhanced. None of the patients with less than a three fold increase in S phase and no demonstrable recruitment from G0 had increased
Ara-C cytotoxicity.
Ara-C cytoreduction was paralled by reduction in clonogenicity as demonstrated by
fluorescein diacetate/
propidium iodide (FDA/PI) flow cytometry. Four samples of
acute lymphoblastic leukemia (ALL) were treated with
low molecular weight B-cell growth factor (15 kDa) and recruitment of
aneuploid cells from G0 to G1 was found in all patients (from 19.3% to 84.9%). These results indicate that recruitment of leukemic cells is inducible by
cytokines and that the cytotoxicity of cell cycle-specific drugs such as
Ara-C can be increased. This concept is presently being tested in vivo.