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Treatment of
Hypoxia-Resistant Astrocytoma Cell Migration with Glucose Inhibitors
Marie E. Beckner and Ian F. Pollack
University of Pittsburgh School of Medicine, Pittsburgh,
PA, USA
Hypothesis.
Interference with anaerobic metabolism is proposed as a means to inhibit the
invasive behavior of malignant astrocytoma cells.
Lack of stable vascular contacts by migrating tumor cells implies their reliance
on anaerobic, glycolytic metabolism during tissue invasion, despite lactic acid
production.
Gluconeogenic, PTEN-mutated U87 astrocytoma cells with loss of negative PI3K/Akt
pathway regulation, allowing unregulated glycogen synthesis (putatively removes
intracellular lactate), have the potential for hypoxic invasion.
Inhibitors of gluconeogenesis and glycogenesis should therefore suppress hypoxic
U87 cell migration.
Methods. U87 cell tolerance of hypoxia was tested
in Boyden migration assays under 1% oxygen, with and
without further suppression of mitochondrial ATP production using sodium azide
(10–50 mM).
Metabolic inhibitors (metformin and artemisinin) were added to migration assays
under chemical hypoxia to study their effects on glycolytic energy needed during
cell migration through porous (8-μm),
gelatin-coated filters.
Metformin (dimethylbiguanide)
inhibits gluconeogenesis (Argaud et al., Eur. J. Biochem. 213:1341–8, 1993;
Radziuk et al., Diabetes 46:1406–13, 1997).
Artemisinin affects glycolytic flux (Xiao et al., Zhongguo Yao Li Xue Bao
18:363–7, 1997; 20:750–4, 1999; Shuhua et al., SE Asian J. Trop. Med. Pub. Health
31:724–32, 2000).
Migrated cells (nuclei and pseudopods) exposed to various metabolic agents and
conditions were scanned and digitized.
Results. U87 cells showed comparably high levels of
spontaneous motility under either routine tissue culture conditions (normoxia)
or 1% oxygen (hypoxia) in 7 assays.
Also, dose curves of azide (10–50 mM) in the same assays for both conditions
showed either increased U87 cell migration (4 P-values
_0.035) up to 133.3% of control (normal oxygen, no azide) or remained
similar to control migration.
Metformin, 1 and 3 mM, present during the assays, suppressed
glycolytic-dependent U87 cell migration (27–50 mM azide) slightly to 86.7% ±
10.8% SD and 86.1%± 17.3% SD, respectively, of migration levels with no
metformin present.
However, U87 cells exposed to 1 mM metformin overnight, prior to assays, and
either at 1 and 3 mM levels during the assays, migrated at 66.2% ± 8.4%SD and
70.7% ± 11.9% SD, respectively, of migration levels for cells with no drug
exposure.
Also, artemisinin, 300 nM, present during assays, suppressed hypoxic U87
migration to 66.4% ± 5.2% SD of migration for cells with no drug exposure.
Conclusions.
U87 cells demonstrated robust hypoxic migration as shown by a lack of
suppression with 1% oxygen, even with additional azide suppression of
mitochondria.
However, anaerobic, glycolytic cell migration showed modest susceptibility to
clinically useful drugs that interfere with glucose metabolism.
Enhancing present and future therapies by inhibiting glycolytic cell migration
provides a new direction for counteracting treatment resistance in malignant
astrocytomas.
Combining a therapeutic strategy that inhibits anaerobic cell function with
therapies that inhibit normoxic cells may improve treatment outcomes.
This work was supported by The Nick Eric Wichman Foundation, Ellicott City, MD.
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