Inhibition of cell-cell binding by lipid assemblies

Details Inhibition of cell-cell binding by lipid assemblies Inhibition of cell-cell binding by lipid assemblies

1998-02-27

2001-05-22

Kishore, Gollamudi S. (Department: 1615)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Liposomes

C514S025000, C514S042000, C514S053000, C514S054000, C514S061000

Reexamination Certificate

active

06235309

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to the field of therapeutic compounds designed to interfere between the binding of ligands and their receptors on cell surface. More specifically, it provides products and methods for inhibiting cell migration and activation using lipid assemblies with surface recognition elements that are specific for the receptors involved in cell migration and activation.
BACKGROUND OF THE INVENTION
The adhesion of circulating neutrophils to endothelial cells is one of the important events occurring in the process of inflammation. Neutrophils recruitment to tissues is initiated by an adhesion cascade. Through this process, cells roll and eventually attach firmly to the endothelium. The factors that contribute to the high binding strength of this interaction are not fully understood, but is thought to involve interaction between selections on one cell with carbohydrate ligands on another cell. By interfering with the binding between these components, it may be possible to counter pathological conditions related to cell migration.
A number of adhesion molecules mediate the interaction of neutrophils and other leukocytes to the endothelium. Amongst them are the ICAMs, VCAM, CD11, CD18, the integrity &agr;4&bgr;1, and several receptors now known collectively as selections. Each of these molecules is part of a ligand-receptor pair, one of which is expressed on Bevilacqua (Ann. Rev. Immunol. 11:767, 1993). In various combinations, these and other molecules support leukocyte adhesion to the vessel wall and extravasation, and may also participate in activation of cell effector functions. Expression of many of these molecules is up-regulated by soluble factors such as cytokines, thereby acting to increase the recruitment of leukocytes to an affected area.
Amongst the plurality of adhesion molecules that have been described, three have been collected together in a category known as selecting. One was formerly known as ELAM-1, and was identified using inhibitory monoclonal antibodies against cytokine-activated endothelial cells, and is now known as E-selectin. Another was formerly designated as PADGEM, GMP-140, or CD61. It was originally identified on platelets, and is now known as P-selectin. A third identified on lymphocytes was formerly designated as mLHR, Leu8, TQ-1, gp90
MEL
, Lam-1, or Lecam-1, and is now known as L-selectin. The selections were grouped together on the basis of a structural similarity, before very much was known about their binding specificity. All are single chain polypeptides having a carbohydrate binding domain near the N-terminus, an EGF repeat, and anywhere between 2 to 9 modules of approximately 60 amino acids each sharing homology with complement binding proteins. For general reviews, the reader is referred to Lasky (Ann. Rev. Biochem. 64:113, 1995) and Kansas (Blood 88:3259, 1996).
The three selections differ from each other in a number of important respects. As depicted schematically in
FIG. 3
, the selections have different ligand counterparts in the adhesion process. Each selectin is regulated differently, and participates in a different manner in the process of inflammation or immunity. There is also an increasing appreciation for differences in the ligand binding requirements between the selecting.
E-selectin has garnered a significant amount of recent research interest because of its role in inflammation. The migration of inflammatory mediator cells to an inflammatory site is thought to be mediated in part by adhesion of the cells to vascular endothelial cells. Studies in vitro have suggested that E-selectin participates in the adhesion of not only neutrophils, but also eosinophils, monocytes and a subpopulation of memory T-cells to endothelium that has been activated by endotoxin, IL-1, or TNF. Expression of E-selectin by endothelial monolayer increases by about 10-fold and peaks at about 4 hours after stimulation with IL-1, subsiding to near basal levels within 24 hours. The biological role of E-selectin is thought to be a strong binding of cells bearing a suitable E-selectin ligand, over a time-course of 20 minutes to 1 hour, particularly during the course of local inflammation.
Phillips et al. (Science 250:1130, 1990) first identified the binding target of E-selectin as the oligosaccharide sialyl Lewis X (sLe
x
) (NeuAc&agr;2,3Gal&bgr;1,4(fuc&agr;1,3)GlcNac-), a terminal structure found on the cell surface glycoprotein of neutrophils. This has become the prototype carbohydrate ligand for the selectin class. This and related oligosaccharides are the subject of U.S. Pat. No. 5,576,305 and PCT application WO 92/07572.
The sLe
x
unit has been assembled into various polymeric structures in an attempt to improve its weak binding to selections. For example, U.S. Pat. No. 5,470,843 and DeFrees et al. (J. Am. Chem. Soc. 117:66, 1995) disclose bivalent sialyl X saccharides. U.S. Pat. No. 5,470,843 discloses a carbohydrate-containing polymer having a synthetic polymer backbone with 10-20 sLe
x
, sLe
&mgr;
, or GlcNac linked via a bifunctional spacer.
DeFrees et al. (J. Am. Chem. Soc. 118:6101, 1996) describe a sLex preparation made with conventional phospholipid liposome technology. The liposomes contain phosphatidylcholine, cholesterol, phospholipid conjugated with methoxypolyethylene glycol, and phospholipid conjugated with sLex through a polyethylene glycol spacer. Data is presented showing that this composition is 5×10
3
fold more potent than the sLe
x
monomer in inhibiting the binding of E-selectin to cells. Murohara et al. (Cardiovasc. Res. 30:965, 1995) tested sLe
x
phospholiposomes in a myocardial reperfusion model, and found that a dose of 400 &mgr;g/kg body weight reduced the proportional size of the area of risk and necrosis.
P-selectin is a transmembrane glycoprotein of approximately 140 kDa, substantially larger than E-selectin. It was originally described on platelets, in which it may be found in &agr;- and dense-granules. Upon activation of platelets with a mediator like thrombin, P-selectin is rapidly redistributed to the cell surface. In endothelial cells, it is found in granules known as Weibel-Palade bodies, from which it is redistributed to the surface upon activation with histamine. Shuttling of P-selectin to storage granules appears to be mediated by a sorting signal present in the cytoplasmic domain, and apparently unique in comparison with E-selectin.
Accordingly, P-selectin differs from E-selectin in that it may be rapidly expressed from storage granules rather than requiring de novo synthesis. P-selectin binds carbohydrate ligands present on neutrophils, monocytes, and memory T cells. Not only is P-selectin in a preformed state, its expression is stimulated by mediators such as histamine which in turn are preformed and stored in the granules of inflammatory cells. The adherence of leukocytes to P-selectin rather than E-selectin on endothelial cells is perhaps the initial event that occurs for recruitment of leukocyte cells to an injured site. Interference with P-selectin binding may be particularly important when it is desirable to limit leukocyte migration.
The presence of P-selectin on platelets suggests additional unique biological roles compared with the other selecting. In one hypothesis, sites of tissue injury may be acutely enriched with short-acting platelet activators, and active platelets expressing P-selectin may directly recruit other leukocytes. In another hypothesis, neutrophils or monocytes at an inflamed site may be able to catch platelets by way of the P-selectin, which in turn could lead to clot formation or additional mediator release. In an experimental thrombus model, it has been observed that platelets accumulate first at the injury site, followed by leukocyte adherence and fibrin deposition. Both of the latter two steps was inhibited by antibodies against P-selectin (Palabrica et al., Nature,
359:848, 1992).
L-selectin has a number of features that are different from the other known selectins. First, the tissue distribution pattern is opposite to that of

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