Differential metastasis inhibition by clinically relevant levels of heparins--correlation with selectin inhibition, not antithrombotic activity.
OBJECTIVE
Unfractionated heparin reduces metastasis in many murine models. Multiple mechanisms are proposed, particularly anticoagulation and/or inhibition of P-selectin and L-selectin. However, the doses used are not clinically tolerable and other heparins are now commonly used. We studied metastasis inhibition by clinically relevant levels of various heparins and investigated the structural basis for selectin inhibition differences.


METHODS
Five clinically approved heparins were evaluated for inhibition of P-selectin and L-selectin binding to carcinoma cells. Pharmacokinetic studies determined optimal dosing for clinically relevant anticoagulant levels in mice. Experimental metastasis assays using carcinoma and melanoma cells investigated effects of a single injection of various heparins. Heparins were compared for structural relationships to selectin inhibition.


RESULTS
One (Tinzaparin) of three low molecular weight heparins showed increased selectin inhibitory activity, and the synthetic pentasaccharide, Fondaparinux, showed none when normalized to anticoagulant activity. Experimental metastasis models showed attenuation with unfractionated heparin and Tinzaparin, but not Fondaparinux, at clinically relevant anticoagulation levels. Tinzaparin has a small population of high molecular weight fragments not present in other low molecular weight heparins, enriched for selectin inhibitory activity.


CONCLUSIONS
Heparin can attenuate metastasis at clinically relevant doses, likely by inhibiting selectins. Equivalent anticoagulation alone with Fondaparinux is ineffective. Clinically approved heparins have differing abilities to inhibit selectins, likely explained by size distribution. It should be possible to size fractionate heparins and inhibit selectins at concentrations that do not have a large effect on coagulation. Caution is also raised about the current preference for smaller heparins. Despite equivalent anticoagulation, hitherto unsuspected benefits of selectin inhibition in various clinical circumstances may be unwittingly discarded.
Stevenson
Jennifer L
JL
Glycobiology Research and Training Center, Department of Medicine, Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, California 92093-0687, USA.
Choi
Sharon H
SH
Varki
Ajit
A
D000818:Animals; D000925:Anticoagulants / Q000737:chemistry; D045744:Cell Line, Tumor; D004187:Disaccharides / Q000737:chemistry; D015951:Factor Xa / Q000737:chemistry; D005343:Fibrinolytic Agents / Q000494:pharmacology*; D000077425:Fondaparinux; D006493:Heparin / Q000737:chemistry / Q000494:pharmacology*; D006495:Heparin, Low-Molecular-Weight / Q000494:pharmacology; D007700:Kinetics; D019041:L-Selectin / Q000378:metabolism; D008545:Melanoma / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D009362:Neoplasm Metastasis; D009844:Oligosaccharides / Q000737:chemistry; D019007:P-Selectin / Q000378:metabolism; D011134:Polysaccharides / Q000494:pharmacology; D011485:Protein Binding; D019087:Selectins / Q000378:metabolism; D000080506:Sialyl Lewis X Antigen; D013696:Temperature; D013927:Thrombosis / Q000188:drug therapy*; D013997:Time Factors; D000078222:Tinzaparin
D000925:Anticoagulants; D004187:Disaccharides; D005343:Fibrinolytic Agents; D006495:Heparin, Low-Molecular-Weight; D009844:Oligosaccharides; D019007:P-Selectin; D011134:Polysaccharides; D019087:Selectins; D000080506:Sialyl Lewis X Antigen; D019041:L-Selectin; D000078222:Tinzaparin; D006493:Heparin; D015951:Factor Xa; D000077425:Fondaparinux