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I Department of Clinical Science and Immunology
2 Department of Haematology, University of Cape Town Medical School,
Observatory 7925, South Africa
3 Henry Kaplan Award for the best poster Clinical Session
A.Introduction
The plasminogen-plasmin system is involved in many physiological
processes such as fibrinolysis, tissue remodelling, destruction
of intercellular matrix and cell migration [1 ]. Human cells release
plasminogen activators of two distinct immunochemical types -urokinase
and tissue plasminogen activator [2-4]. The activity of these enzymes
in biological systems is regulated by a variety of agents such as
hormones, retinoids and tumour promoters [5-11]. It is also regulated
by protease inhibitors such as protease nexins [12] and by receptors
for the enzyme on the surface of human fibroblasts [ 13]. Leukaemic
cells secrete both species of plasminogen activator and patients
with acute myeloid leukaemia whose cells release only tissue p1asminogen
do not respond to combination chemotherapy [14].
B.Methods
Heparinized blood samples were obtained from 117 patients with
acute myeloid leukaemia (AML), from 31 patients with chronic myeloid
leukaemia (CML), and from 89 patients with other myeloproliferative
disorders. Cells were isolated by centritugation on Ficoll-Hypaque
and resuspended in RPMI containing 3% foetal calfserum to give 4
Mio. cells/ml [14]. The medium was harvested by centrifugation 24
h later and stored at -80 °C for analysis of enzyme activity. Plasminogen
activators were assayed by measuring the plasminogen-dependent re1ease
ofso1uble radioactive fibrin degradation peptides from insoluble
125I-Iabelled fibrin-coated multiwell dishes
as previously described [15]. Molecular species of plasminogen activators
were identified by electrophoretic and immunochemical procedures
as previously described [2].
C.Results and Discussion
Immunochemical analysis showed that granulocytes from 23 normal
individuals released urokinase exclusively. Cells from 24/117 patients
with AML secreted tissue plasminogen activator, cells from 67/117
patients secreted urokinase, cells from 14/ 117 patients secreted
a mixture of both enzymes and cells from 12/117 patients secreted
too little enzyme for identification (Table 1). The molecular species
of enzyme appeared to have prognostic significance since none of
the patients whose cells secreted tissue plasminogen activator entered
remission with chemotherapy whereas remission was induced in 80%
of patients whose cells secreted urokinase. There was a significant
difference in median survival between those patients whose cells
secreted tissue plasminogen activator (5 weeks) and those individuals
whose cells secreted
Table I. Correlation between clinical outcome and molecular
species of plasminogen
activator released by cultured cells from 117 patients with AML
urokinase (32 weeks). No significant differences in age or white
blood cell count at the time of presentation were found between
those patients whose cells secreted tissue plasminogen activator
and urokinase. Cells from approximately 20% of patients with AML
secreted tissue plasminogen activator. Cells from 31 patients with
CML were examined for ,5pecies of plasminogen activator produced.
Cells from 15/31 patients secreted tissue plasminogen activator,
cells from only 7/31 secreted urokinase and cells from 9/31 secreted
both species of enzyme. Thus, the proportion of patients with CML
whose cells secreted tissue plasminogen activator was much higher
than in the AML group and cells from only 23% of these individuals
secreted urokinase. Cells isolated from 89 patients with other myeloproliferative
and preleukaernic disorders have also been investigated. Cells from
47/89 patients secreted tissue plasminogen activator, celI5 from
16/89 patients secreted urokinase and cells from the remainder secreted
both enzyme species. Thus, the myeloproliferative disorders contain
a far higher percentage of individuals whose cells secrete tissue
plasminogen activator the enzyme which is associated with a failure
to respond to chemotherapy in patients with AML. This is of interest
as it is well known that when patients with CML or myelodysplastic
states transform, they have a poor prognosis and do not respond
to chemotherapy. We are investigating the plasminogen activator
status of our patients with myeloproliferative disorders at regular
intervals in order to ascertain whether those patients with tissue
plasminogen activator have a worse prognosis than those patients
whose cells secrete urokinase. It appears as if the type of plasminogen
activator secreted by leukaemic cells cultured in vitro will serve
as a useful aid to prognosis for patients with AML and possibly
also for patients with other myeloproliferative disorders.
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