Summary
Low-molecular-weight heparins (LMWH) exhibit potent anticoagulant efficacy via their plasmatic effects on thrombin and factor Xa. These agents are also effective
in releasing endothelial tissue factor pathway inhibitor (TFPI),the natural inhibitor
of tissue factor, and exhibit significant anti-metastatic effects in experimental
animal models. However, the potential for bleeding complications has slowed down the
more widespread adoption of LMWH therapy in cancer patients. In this study, the effect
of a non-anticoagulant form of LMWH (NA-LMWH) on experimental lung metastasis and
tumor cell-induced platelet aggregation in vivo was compared to the LMWH enoxaparin. Using the B16 melanoma mouse model of metastasis,
subcutaneous (s.c.) injection of NA-LMWH or enoxaparin (10 mg/kg), three hours before
intravenous (i.v.) injection of metastatic melanoma cells, followed by daily doses
for 14 days, reduced lung tumor formation by 70% (P<0.001). I.v. injection of tumor
cells resulted in a significant (50–62%, P<0.01) fall in platelet counts. Pre-injection
(i.v.) of enoxaparin completely abolished the tumor cell-induced thrombocytopenia,
whereas NA-LMWH had no effect. Four hours after a single s.c. dose, enoxaparin but
not NALMWH prolonged the clotting time three-fold and delayed the time to clot initiation
more than 10-fold as measured by a Sonoclot analyzer and by thromboelastography, respectively.
Enoxaparin but not NA-LMWH demonstrated a significant anticoagulant effect in mice.
Both NA-LMWH and enoxaparin caused similar TFPI release from endothelial cells in vitro.These data provide evidence to support the potential of NA-LMWH as an anti-metastatic
agent without any significant impact on coagulation.
Keywords
Heparin - low-molecular-weight heparin - metastasis - anticoagulant