[CANCER RESEARCH
45,1308-1313,
March 1985]
Differences in Cell Cycle Kinetics during Induced Granulocytic versus
Monocytic Maturation of HL-60 Leukemia Cells1
Dennis W. Ross2
Department of Pathology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27514
with a doubling time of 34 hr up to a density of 3 x 106 cells/ml.
ABSTRACT
Leukemia cells (HL-60) were induced to mature towards granulocytic and monocytic phenotypes using 1.1% dimethyl sulfoxide and 5 x 10~7 M 1-0-D-arabinofuranosylcytosine, respectively.
Granulocytic maturation was accompanied by a slight decrease
in cell volume and in total cell protein, but with an increase in
acid phosphatase. DNA histograms showed that after 7 days
there was a decrease in the number of cells with S or G2 DNA
content. Autoradiography revealed that most of the cells had
stopped in cycle with only 3% of the cells synthesizing DNA. The
rate of synthesis for these few cells, morphologically identified
as immature blast forms, was not diminished. Monocytic matu
ration was accompanied by an increase in cell volume and of anaphthyl acetate esterase. DNA histograms showed no change
over 7 days. Autoradiography revealed a large fraction of the
cells to be in cycle and synthesizing DNA, but at a markedly
reduced rate. Induced granulocytic and monocytic maturation
are characterized by a very different perturbation of the cell DNA-
The generation time is 24 hr with Gì,S, and G2 of 4,15, and 5
hr, respectively; this gives a growth fraction of 0.85. Several
scientists working under conditions similar to this investigation
already have well described the change in phenotypic expression
of morphology, cytochemical reactivity, function, and surface
immunotype accompanying induced granulocytic maturation, (7)
and monocytic maturation (11) using DMSO and ara-C. In this
study, morphology plus cytochemical changes are used to mon
itor the induction of maturation during the measurement of cell
cycle kinetic events.
MATERIALS AND METHODS
Culture of HL-60 Cells. The HL-60 cell line (a gift from Robert Gallo
of the National Cancer Institute) was maintained in RPMI Medium 1640
supplemented with fetal calf serum, penicillin, and streptomycin at 37°,
5% COa, and 100% humidity. The 10-ml cultures were grown in 50-ml
flasks subcultured to a density of 5 x 105/ml twice per week. The
doubling time of log-phase cultures was 33 plus 3 hr. The fetal calf serum
division cycle.
INTRODUCTION
The HL-60 promyelocytic leukemia, as described by Collins et
al. (2), may be induced towards either granulocytic or monocytic
maturation using a variety of chemical agents. A number of
studies have revealed the various functional qualities of these
cells (14) demonstrating that, although the mature cells are not
equivalent to their nonneoplastic counterparts, they possess
many of the morphological, cytochemical, immunological, and
functional characteristics of mature granulocytes or monocytes.
The earliest changes which accompany induced maturation,
including an increase of protein kinases in the cell membrane
(12) and a decrease in c-myc oncogene expression (3, 17) are
being studied. The mechanism of maturation induction promises
to be at least partially understood in the near future.
The purpose of this investigation is to compare the changes
in cell cycle kinetics which accompany granulocytic and mono
cytic maturation. These data are considered with respect to how
therapy designed to induce maturation in vivo might be expected
to alter cell cycle kinetics. This experience helps define what
types of studies are necessary to monitor maturation in vivo for
therapeutic trials with low-dose ara-C.3
The cell cycle kinetics of the HL-60 promyelocytic cell line have
been established by Foa ef al. (9) for the standard culture
conditions used in this investigation. Proliferation is exponential
used in these experiments came from a large common lot that was
frozen at liquid nitrogen temperature until just prior to use. The possible
growth and differentiation factors present in fetal calf serum were held
constant by using a single lot and a constant 17% supplement in all
experiments.
Cells were counted and sized with an electronic impedance aperture
system (19). Cell volumes were calibrated using 10-^m-diameter latex
beads.
Cytocentrifuge (Shandon, Cheshire, United Kingdom) smears were
stained with Wright's stain as well as for acid phosphatase and NSE
activity, according to the standard methods. Cellular MPO was measured
by automated flow cytochemistry using a Technicon (Tarrytown, NY) H6000 differential cell counter. Light scatter and absorption of cells in
suspension, stained for MPO using the 4-chloro-1 -naphthol substrate
reaction, were detected and recorded as an x-y scattergram reflecting
cell size and MPO content, respectively (13).
Flow Cytof luorometric Quantitäten of Cellular DNA. Flow cytometry
using quantitative measurement of fluorescence from propidium iodidestained DNA was used to generate a DNA histogram from which the
percentage of cells in G1/0 and (S+G2) could be calculated. The cells
were stained in suspension with propidium iodide, and fluorescence
proportional to DNA content was determined with a fluorescence-acti
vated cell sorter analyzer (Becton-Dickinson Co., Mountain View, CA)
(21).
Autoradiography and Liquid Scintillation Counting. The percentage
of cells in S phase and the relative rates of DNA synthesis were measured
by autoradiography. [3H]dThd with specific activity of 49 Ci/mw (Amersham radionuclides) was added to the cell culture medium at a final
concentration of 10 /iCi/ml for 60 min. The cells were then washed with
cold nonradioactive medium, and cytocentrifuge slide preparations were
made. The slides were fixed in acetic acid:methanol (1:3) for 15 min and
then 70% ethanol for 30 min and stored desiccated at 4°.At the end of
1This study was supported in part by the Blood Cell Fund.
2 To whom requests for reprints should be addressed.
3 The abbreviations used are: ara-C, 1-/3-o-arabinofuranosylcytosine; DMSO,
dimethyl sulfoxide; MPO, myetoperoxidase; NSE, nonspecific esterase or a-naphthyl acetate esterase; [3H]dThd, tritiated thymidine.
Received May 25, 1984; accepted November 29, 1984.
CANCER RESEARCH
an experiment, all slides were dipped in NTB3 nuclear track emulsion
(Kodak, Rochester, NY) that had been diluted with distilled water (1:1)
and kept liquid in a 44° water bath. The slides were exposed at 4°
VOL. 45 MARCH
1985
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KINETICS OF INDUCED MATURATION
continuous exposure as a function of a dose of ara-C. Cells,
even in untreated cultures, did not reach plateau phase in this
time period; thus, density-dependent inhibition was not a factor.
There was a dose-dependent decrease in cell number and in
(desiccated chamber) for 48 hr and then developed and counterstained
through the emulsion. The slides were scored for the percentage of
labeled cells (more than 4 silver grains overlying a cell). Relative rates of
DNA synthesis were determined by counting grains per cell. Alternatively,
an 8-ml aliquot of the labeled cell culture was taken and centrifugea,
crease in cell volume relative to control. The magnitude of these
perturbations, when plotted as percentage of change per hr
relative to control, was greatest ¡nthe first 24 hr. After 24 hr, the
difference between treated and control cultures became pro
gressively less at any dose as the cells recovered from the initial
unbalancing of cell growth. Cell viability, as measured by trypan
blue exclusion, was not affected by up to a 72-hr exposure with
IO"6 M ara-C or less. At 5 x 10~7 M, ara-C (midpoint of an
effective dose range from 1CT7to 10"6 M for maturation induction)
then washed twice with cold nonradioactive medium, followed by a cell
count. The cells were resuspended in 10% trichloroacetic acid, and the
precipitated material was collected on 47-mm-diameter, 0.2-Mm pore size
filters (Millipore) which were dried and placed in 20-ml glass vials.
Scintiverse (Fisher) was added, and the activity was counted (Packard,
liquid scintillation counter) and expressed as cpm/106 cells.
Protein Studies. Total cell protein was measured by the biuret reaction
in cell suspensions of known cellular concentration which had been
washed twice with NaCI solution (0.9 g/dl) to remove extracellular
proteins. The results were expressed as pg of protein per cell. Acid
phosphatase was measured in aliquots of the same cell suspensions
using the p-nitrophenyl phosphate reaction; results were expressed as
units of activity/mg of protein. Both methods used microdetermination
kits which contained calibration materials (Sigma).
The 2-dimensional protein electrophoresis studies were performed by
Dr. Jesse Edwards of the Department of Pathology, University of North
Carolina at Chapel Hill, according to methods published previously (4,
10).
RESULTS
Cell Number and Volume. The influence of dose for both
DMSO and ara-C on Å“il number, volume, and maturation was
studied. The purpose of these dose-response curve experiments
was to find an optimal concentration at which maturation is
induced with minimal perturbation of cell growth; ara-C produces
an unbalanced cell growth at low and intermediate doses, such
that cell division is impeded but synthesis of protein is not (18).
As a result, this unbalanced cell growth is manifested as an
increase in cell volume. Chart 1 shows results of an experiment
measuring the change ¡ncell number and volume over 3 days of
icr
IO
IN HL-60 CELLS
recovery from unbalanced cell growth was still possible, and
there was little change in cell number relative to control after 5
days (Chart 2). At this dose, monocytic maturation was induced
as measured by the percentage of NSE-positive cells (Table 1).
Similar experiments using DMSO demonstrated that 1.1% (v/v)
was the optimal dose for minimal perturbation of increase in cell
number, yet with good maturation induction as measured by the
percentage of morphologically mature granulocytes (Table 1).
These 2 concentrations, 5 x 10~7 M ara-C and 1.1% DMSO,
chosen to produce the minimal inhibition of increase in cell
number, are the same as found by other investigators as being
the minimal doses which induce maturation (6, 11). Chart 2
shows growth curves of cell number versus time in control and
treated cultures at these doses. Note in Table 1 that, although
the perturbation ¡ncell number after 7 days is minimal, ara-C
caused an increase in cell volume while DMSO caused a de
crease. These 2 differences were noted after 7 days. The small
increase in cell volume after 7-day exposure to ara-C might be
either a residual of the initial unbalanced cell growth or a result
of monocytoid maturation. The decrease in cell volume after 7day exposure to DMSO was observed morphologically as a
decrease in whole cell and nuclear area accompanying granulocytic maturation. After 5-day exposure to DMSO, a progressive
increase in dead cells and debris was noted. In cell counting and
cell volume measurements, these could be separated by a vol
ume threshold, set between the distinct debris and intact cell
peaks. In measurements involving morphological studies, only
intact cells are analyzed.
Protein. The changes in cell volume, which were noted in the
initial dose-response curve experiments, stimulated the studies
on cell protein. The objective was to locate specific phenotypic
changes which would permit quantitation of induced maturation.
Total cell protein, acid phosphatase, MPO, and high-resolution
Õ
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72
IO""
IO"
IO"'
IO""
IO"0
ARA-C,M
Chart 1. Change ¡ncell number (W„)
and volume (V0) versus M concentration of
ara-C for cultures of HL-60 human promyelocytic leukemia cells. The decrease in
cell number (top) and the increase ¡ncell volume (bottom) relative to control
(unexposed) cultures are plotted as a percentage of change per hr of exposure
after 24, 48, and 72 hr for 5 logs of concentration of ara-C.
CANCER
I
2
3
DAYS
4
S
Chart 2. Growth curve showing number versus time for HL-60 cell cultures
induced with no drug (control); 1.1% DMSO; or 5 x 10~7 M ara-C.
RESEARCH VOL. 45 MARCH 1985
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KINETICS OF INDUCED MATURATION
IN HL-60 CELLS
2-dimensional protein electrophoresis
in in CO
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+1 +1
00 OJ 5
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to ^r in
phoretograms showed many small changes in the overall classes
of proteins present in induced cells (Fig. 1b) relative to control
cells (Fig. 1a). No single protein or class of proteins showed a
very large increase in the induced cells; thus, none was suitable
as a quantitative marker of maturation. MPO was measured by
flow cytochemistry using the Technicon H-6000 automated cell
counter. Following 7-day exposure to DMSO, a decrease of 30%
coco
W ci
in the mean for cellular MPO was noted relative to control (Chart
3).
DNA Synthesis. The percentage of cells with S or G2 DNA
content decreased to 50% of control values after 5 days, and
33% of control after 7-day exposure to DMSO, but was constant
over 7 days for cultures treated with ara-C (Chart 4). The uptake
and incorporation of [3H]dThd into trichloroacetic acid-precipi
81
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,f
c\i
evi
were assayed ¡nHL-60
cells induced to granulocytic maturation with DMSO. Table 1
summarizes the results. Total cell protein, like cell volume, was
decreased by 30%. However, acid phosphatase activity was
increased by 60% (units/mg protein). The 2-dimensional electro-
o>
o
tated macromolecules were decreased in induced cultures after
5 and 7 days (39 and 6% for DMSO-treated, and 25 and 26%
for ara-C-treated cultures, respectively, relative to control values
of logarithmically growing untreated cultures at 3 days). Autoradiography revealed that, although both DMSO- and ara-C-treated
cultures showed decrease uptake of [3H]dThd, the patterns of
DNA synthesis were very different for the 2 conditions. Chart 4
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41
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co
S ig
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in
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CO
i-
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Chart 3. Cell size (y axis) and myeloperoxidasecontent (x axis) for HL-60 cells
untreated (top) and exposed to 1.1% DMSO for 7 days (bottom).Dots, paired cell
size and myeloperoxidase content measurement on a single cell as performed
using automated flow cytochemistry (TechniconInstruments Model H-6000).
CANCER
RESEARCH
VOL. 45 MARCH
1985
1310
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KINETICS
60
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OF
INDUCED
MATURATION
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,
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cells are larger with increased NSE, but they do not adhere to
tissue culture dishes or to glass slides. The cells are distributed
around the cell cycle and are synthesizing DNA, but at a much
reduced rate. This difference in the perturbation of cell cycle
events between induced granulocytic and monocytic maturation
is important for several reasons. Maturation arrest and induced
maturation represent 2 phenomena in the behavior of leukemic
cells which show proliferation is somehow abnormally uncoupled
from maturation in these cells. The difference between the cells
piling up in Gìfollowing DMSO and arresting throughout the
whole cycle following ara-C demonstrates that induced matura
DMSO_i
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tion is not a simple or direct consequence of slowed proliferation.
Other investigations of changes following induced maturation
in cell cycle kinetics for both DMSO (8) and leukocyte-conditioned
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246
DAYS
CELLS
in cell cycle kinetics. For granulocytic maturation induced by
DMSO, the cells are smaller with less protein but an increased
acid phosphatase. Most of the cells have stopped synthesizing
DNA at points distributed around the cell cycle. A few cells are
resistant to maturation induction. These cells are seen on autoradiographs as undifferentiated cells synthesizing DNA at a
normal rate. For monocytic maturation induced by ara-C, the
4020604020604020
50;
IN HL-60
DAYS
Chart 4. Change ¡nDNA kinetics for HL-60 cell cultures untreated or induced
with 1.1% DMSO or 5 x 10"' M ara-C. Left panels, percentage of cells with S or
G, DNA content from Days 1 to 7 as determined by flow cytofluorometry. The
percentage of mitotic cells at 3 and 6 days counted on stained cytocentrifuge
smears is also indicated. Right panels, incorporation of ['HjdThd; striped bars.
amount of label incorporated into macromolecules as determined by liquid scintil
lation counting; open bars, percentage of cells taking up a pulse label as determined
by autoradiography; stippled bars, rate of uptake of label as determined by grain
counts in autoradiography. All values in the right panels are given as percentage
of control values for 3-day cultures.
displays, ¡nthe right panels, total uptake (striped bars), percent
age of labeled cells (open oars), and rate of synthesis in labeled
cells measured by grain counts (stippled bars). For DMSO,
uptake and the percentage of labeled cells were decreased, but
the few labeled cells synthesized DNA at a rate equal to control.
Morphologically, these labeled cells were identified on autoradiographs as consisting only of immature blast forms. Induced
mature cells, past the myelocyte stage, were not seen as labeled
with [3H]dThd. For ara-C, [3H]dThd uptake was also decreased,
but the percentage of labeled cells was equivalent to control.
The disparity between decreased uptake but normal numbers of
labeled cells was explained by the grain count data which
showed that these labeled cells were synthesizing DNA at a
much reduced rate. These contrasting patterns of DNA synthesis
were seen in the photomicrographs of [3H]dThd pulse-labeled
cells 7 days after exposure to DMSO (Fig. 2a) or ara-C (Fig. 2b).
The DMSO-induced cultures showed a few heavily labeled cells;
ara-C-induced cultures showed many lightly labeled cells.
DISCUSSION
Induced maturation in the HL-60 leukemia is accompanied by
morphological and phenotypic changes as well as an alteration
medium (5) in DNA synthesis show an initial increase at 24 to 72
hr, followed by a subsequent inhibitor after 72 hr. Ferrerò ef al.
(6) report that DNA synthesis and induced maturation may be
independent events that block DNA synthesis with either hydroxyurea or ara-C, and are still able to induce granulocytic
maturation with retinole acid. Long-term proliferation following
maturation induction with DMSO (as measured by colony-form
ing ability in methylcellulose) is lost very quickly (within 24 hr)
after exposure (8). Recent studies by Boyd and Metcalf (1) on
monocyte/macrophage
differentiation induced in HL-60 cells
after 4-day exposure to sodium butyrate show a different pattern
of alteration in cell cycle kinetics than that observed ¡nthis
investigation for monocytic maturation induced by ara-C. They
found that butyrate treatment arrests the differentiated cells in
Gì.They also measured a rapid loss in clonogenicity after ex
posure to butyrate as an inducing agent. There is a similarity in
phenotype between butyrate and ara-C-induced HL-60 cells
despite the different action of these 2 agents and the difference
in cell cycle kinetics. Maturation induction may be a consequence
of interference at any one of multiple points in the DNA metabolic
pathway resulting in many agents which can act as inducers
(20).
The results of maturation induction in HL-60 leukemia may be
modeled by a compartment representation as shown in Chart 5,
that is quite similar to standard representations of nonleukemic
hematopoiesis. A compartment of uncommitted, undifferentiated
stem cells capable of long-term proliferation occasionally pro
duces a committed progeny which enters an intermediate com
partment characterized by both cell division and maturation. This
compartment is shown schematically by a triangle (to emphasize
the amplification in cell number) leading into a final rectangular
compartment of nondividing cells. For uninduced HL-60 cells in
the logarithmic phase of growth, the stem cell compartment is
relatively large with only a few spontaneously committed cells
and minimal maturation. Cell death can occur as loss from any
compartment, but all nonstem cells in the committed and nondi
viding compartments eventually die. With induced maturation,
there is a large shift from the stem cell to the committed com
partment, measurable as a loss of clonogenicity (1, 8) with final
CANCER RESEARCH VOL. 45 MARCH 1985
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KINETICS OF INDUCED MATURATION
REFERENCES
UNTREATED
CELL
IN HL-60 CELLS
1. Boyd, A. W., and Metealf, D. Induction of differentiation in HL-60 teukaemic
cells: a cell cycle dependent all-or-noneevent. Leuk. Res., 8: 27-43,1984.
2. Collins, S. J., Gallo, R. C., and Gallagher, R. E. Continuous growth and
differentiation of human myeloid leukemic cells in suspension culture. Nature
(Lond.), 270: 347-349,1977.
3. Dalla Pavera,R., Westin, E., Gelmann, E. P., Martinotti, S., Bregni, M., WongStaal, F., and Gallo, R. C. The human oncogene c-myc: structure, expression,
and amplification in the human promyetocytic leukemia cell line HL-60. Haematol. Blood Transfus., 28: 247-254, 1983.
4. Edwards, J. J., Anderson, N. G., Nance, S. L., and Anderson, N. L. Red cell
proteins, I. Two-dimensional mapping of human erythrocyte lysate proteins.
Blood, 53:1121-1132,1979.
5. Elias, L., Wogenrich, F. J., Wallace,J. M., and Longmire,J. Altered pattern of
differentiation and proliferation of HL-60 promyelocytic leukemia cells in the
presence of leukocyte conditioned medium. Leuk. Res., 4: 301-307,1980.
6. Ferrerò,D., Tarella,C., Gallo, E., Ruscelli, F. W., and Breitman,T. R. Terminal
differentiation of the human promyelocytic leukemia cell line, HL-60, in the
absence of cell proliferation. Cancer Res., 42: 4421-4426,1982.
7. Fibach, E., Peled, T., Trêves,A., Komberg, A., and Rachmilewitz, E. A.
Modulation of the maturation of human leukemic promyelocytes (HL-60) to
granulocytes or macrophages. Leuk. Res., 6: 781-790,1982.
8. Fibach, E., Trêves,A., Peled, T., and Rachmilewitz, E. A. Changes in cell
kinetics associated with differentiation of a human promyelocytic cell line
(HL60).Cell Tissue Kinet., Õ5:425-429, 1982.
9. Foa, P., Maiolo, A. T., Lombardi, L., Toivonen, H., Rytomaa, T., and Polli, E.
E. Growth pattern of the human promyelocytic leukaemiacell line HL-60. Cell
Tissue Kinet., 75: 399-404, 1982.
10. Gemmell,M. A., and Anderson, N. L. Lymphocyte, monocyte and granulocyte
proteins compared by use of two-dimensional electrophoresis. Clin. Chem.,
28: 1062-1066,1982.
11. Griffin, J., Munroe, D., Major, P., and Kufe, D. Induction of differentiation of
human myeloid leukemia cells by inhibitors of DNA synthesis. Exp. HematoL.
JO:774-781, 1982.
12. Kraft, K. S., and Andersson, W. B. Phorbol esters increase the amount of
Ça" phospholipid dependent protein kinase associated with plasma mem
brane. Nature (Lond.), 301: 621-623,1983.
13. Mansberg, H. P., Saunders, A. M., and Groner, W. The Hemalog-Dwhite cell
differential system. J. Histochem. Cytochem., 22: 711-724,1974.
14. Newburger, P. E., Chovaniec, M. E., Greenberger, J. S., and Cohen, H. J.
Functional changes in human leukemic cell line HL-60. J. Cell Biol., 82: 315321,1979.
15. Ohta, M., Saito, M., Suda, K., Sakamoto, S., Kitagawa, S., Miura, Y., and
Takaku, F. Differentiationof humanleukemiacells and its usefulnessfor clinical
diagnosis. Leuk. Res., 7: 363-374,1983.
16. Olsson, I. Review article: is the maturation arrest in myeloid leukemia reversi
ble? Acta Med. Scand., 274: 261-272,1983.
17. Reitsma, P. H., Rothberg, P. G., Astrin, S. M., Trial, J., Bar-Shavit,Z., Hall, A.,
Teitelbaum, S. L., and Kahn, A. J. Regulation of myc gene expression in HL60 leukaemia cells by a vitamin D metabolite. Nature (Lond.), 306: 492-494,
1983.
18. Ross, D. W. The nature of unbalancedcell growth caused by cytotoxic agents.
Virchows Arch. Cell Pathol., 37: 225-235,1981.
19. Ross, D. W. Unbalancedcell growth and increased protein synthesis induced
by chemotherapeuticagents. Blood Cells, 9: 57-68,1983.
20. Ross, D. W. Leukemiccell maturation.Arch. Pathol. Lab. Med., in press, 1985.
21. Roti-Roti, J. L., Higashikubo,R., Blair, O. C., and Uygur, N. Cell cycle position
and nuclear protein content. Cytometry, 3: 91-96,1982.
DEATH
NON-DIVIDING********
COMMIT!INDUCED
UNCOMMITTED
.n
*r^1
^v.ÃtI
CELL
4^;ED
i M
DEATH
Chart 5. Model of kinetics for untreated and induced cultures of HL-60 human
promyelocytic leukemia cells.
progression to the nondividing mature cell compartment (Chart
5, bottom). Olsson (16) has reviewed leukemic cell maturation
using a similar representation with a probabilistic model for
commitment. Initially, there may be no change or even an in
crease in the number of cells measured in the DNA cell division
cycle.
The HL-60 cell line may be viewed as an in vitro model of one
person's leukemia. Much of the biological behavior it exhibits
would be common to any leukemia. However, cell cycle kinetics
and the potential for maturation induction have been shown to
be quite variable from one patient to the next (15). Attempts at
using maturation induction as a therapeutic maneuver in vivo
must be monitored by tests that will determine to what degree
the leukemic population is responding, by measuring both the
change in phenotype from immature to mature cells, and the
changes in cell cycle kinetics and long-term proliferation.
ACKNOWLEDGMENTS
The author is grateful to Phillip H. Davis, Jr., for providing excellent technical
assistance and to Karen E. Vance for editing and manuscript preparation.
CANCER
RESEARCH
VOL. 45 MARCH
1985
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KINETICS OF INDUCED MATURATION
y,*
•1.
IN HL-60 CELLS
feQÇ.
«'v
I
â€
«I.
.
2a
Fig. 1. Two-dimensional protein etectrophoretograms of HL-60 cells untreated (a) and exposed to 1.1% DMSO for 7 days (b). The pH gradient is along the x axis
spanning pH 7.5 (right) to pH 3.0 (left), and the molecular weight gradient is along the y axis spanning 8,000 dallons (bottom) to 45,000 daltons (top).
Fig. 2. Autoradtographs of HL-60 cells pulse labeled with [3H]dThd which have been exposed for 7 days to 1.1% DMSO (a) or 5 x 10~TM ara-C (b). The DMSOtreated culture shows only a few heavily labeledcells; the ara-C-treated culture shows many lightly labeledcells.
CANCER
RESEARCH
VOL. 45 MARCH
1985
1313
Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1985 American Association for Cancer Research.
Differences in Cell Cycle Kinetics during Induced Granulocytic
versus Monocytic Maturation of HL-60 Leukemia Cells
Dennis W. Ross
Cancer Res 1985;45:1308-1313.
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