We investigated the role of apoptosis in
chemotherapy for
hematologic malignancies. Twelve consecutive patients with
acute myelogenous leukemia (AML) or
refractory anemia with excess of blasts in transformation (
RAEB-t) who were not tolerable for standard-dose
chemotherapy were treated with
CAG regimen (low-dose
cytosine arabinoside [
Ara-C] plus
aclarubicin with concurrent administration of
granulocyte colony-stimulating factor [
G-CSF]). Bone marrow mononuclear cells obtained before the commencement of the
chemotherapy were cultured with various concentrations (0-10(-5) M) of
Ara-C in the presence or absence of 10 ng/mL of
G-CSF, and the resultant cell proliferation/cytotoxicity was assayed. In all but one patient, half killing concentration (LC50) of
Ara-C was significantly reduced in the presence of
G-CSF (by 400- and 1.45-fold, median: 21-fold). Furthermore, LC(50) values in responders assayed in the presence of 10 ng/mL of
G-CSF were significantly lower than those in nonresponders (p = 0.02). In vitro killing tests using a
G-CSF-dependent leukemic cell line suggested that addition of
G-CSF potentiates
Ara-C-induced cytotoxicity through the mechanism of apoptosis. We thus assayed apoptosis in peripheral blood leukemic cells during CAG
chemotherapy by flow cytometry using
7-amino-actinomycin D. Peak percentages of apoptosis in responders were significantly higher than those in nonresponders (p = 0.02). These results collectively suggest that apoptosis plays an important role for eradicating leukemic cells by CAG chemo-
therapy.