Peptides 23 (2002) 999–1010
Role of SA–Le
a
and E-selectin in metastasis assessed
with peptide antagonist
Insug O.
a
, Laszlo Otvos, Jr.
a
, Thomas Kieber-Emmons
b
,
Magdalena Blaszczyk-Thurin
a,∗
a
The Wistar Institute, 3601 Spruce Street, Philadelphia, PA 19104, USA
b
Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
Received 10 August 2001; accepted 10 December 2001
Abstract
E-selectin ligand Sialyl–Lewis a (SA–Le
a
) carbohydrate is expressed on many carcinomas. Peptide mimicking SA–Le
a
(DLWD-
WVVGKPAG) was previously selected from a recombinant library by screening with monoclonal antibody (MAb) NS19-9. In this study,
the residues critical for interaction with the NS19-9 were mapped using peptide array generated by substitution of various amino acid
residues. The replacement of Trp 5 with Phe resulted in a change of peptide’s secondary structure and increased binding with MAb and
E-selectin, suggesting improved carbohydrate mimicry. Colonization of tumor cells expressing SA–Le
a
was blocked by the peptide and was
completely abolished in E-selectin knock out mice. The data suggest the critical role of carbohydrate antigens and E-selectin in metastasis
and that peptides mimicking carbohydrate antigens can function as antagonists of this process. © 2002 Published by Elsevier Science Inc.
Keywords: Carbohydrate structure; Sialyl–Lewis a; Peptide mimics; E-selectin; Tumor metastasis
1. Introduction
Tumor metastasis is a multistep process requiring
detachment of malignant cells from the primary tumor,
penetration of blood or lymph vessels and attachment to en-
dothelium of distant organs and formation of a new tumor
[44]. E-selectin is a tumor necrosis factor- (TNF-) and
interleukin-1 (IL-1)-inducible, calcium-dependent adhe-
sion molecule, that is expressed on vascular endothelium
and it is postulated to mediate the initial interaction with
tumor cells [9,27,34,60]. E-selectin was also demonstrated
to mediate leukocytes rolling along the vessel wall in the
leukocyte endothelial cascade involved in the inflammatory
response [55].
E-selectin binds to glycoconjugates carrying the terminal
tetrasaccharide sialyl–LeX (SA–LeX), NeuAc2,3Gal1,
4(Fuc1,3)GlcNAc1,3Gal1,4Glc1-R [2] and its po-
sitional isomer, SA–Le
a
, NeuAc2,3Gal1,3(Fuc1,4)
GlcNAc1,3Gal1,4Glc1-R [1] that are expressed on
most of carcinoma cells (SA–LeX and/or SA–Le
a
) and
leukocytes (SA–LeX). Although adhesion pathways utilized
by different tumors show considerable diversity, recent re-
ports suggest that E-selectin and SA–Le
a
and/or SA–LeX
∗
Corresponding author. Tel.: +1-215-898-3855; fax: +1-215-898-3868.
E-mail address: mthurin@wistar.upenn.edu (M. Blaszczyk-Thurin).
carbohydrate ligands, might be involved in tumor metas-
tasis [60,65]. Cancer cells that express both SA–Le
a
and
SA–LeX undergo SA–Le
a
-mediated adhesion almost ex-
clusively, possibly due to the higher affinity of E-selectin
for the SA–Le
a
structure [1].
The expression of ligands for E-selectin by both neu-
trophils and cancer cells raises the possibility that the
basic mechanism that underlie initial step of metastases
formation, i.e. interaction of endothelial selectins with
the tumor-associated carbohydrate ligands SA–LeX and/or
SA–Le
a
is equivalent to that mediating rolling step in the in-
flammatory process. The crucial role of selectin-dependent
neutrophil adhesion and carcinoma cell adhesion implies
that in vivo blockage of selectin-dependent interactions
can decrease leukocyte mobilization and the incidence
of metastases, respectively. Various selectin inhibitors of
selectin-dependent interaction including peptidic inhibitors
have been considered as an anti-inflammatory approach by
many laboratories [6,18,36,38,39,41,47,51,56].
Although there is no direct evidence of involvement of
E-selectin in naturally occurring tumor metastases in hu-
mans, several studies demonstrate the selectin mediated ad-
hesion of tumor cells is a key event in metastasis process
in vivo. The administration of E-selectin specific antibody
and soluble E-selectin was shown to abrogate the formation
of hepatic metastasis and lung colony formation in vivo in
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