A main pathological feature of inflammatory and autoimmune diseases resides in accumulation of activated leukocytes on a damaged tissue (inflammated tissue). A process of leukocytes from migration out of the circulatory system to transmigration on the inflammatory site involves four-step cascade reactions which interact each other: (1) adhesion and rolling, (2) activation, (3) firm adhesion and (4) transmigration (Springer, T., Ann. Rev. Physiol., 57: 827(1995)).
First, leukocytes adhere to the vascular endothelium to a slight degree and roll on its surface. Then, activation of cells mediated by soluble chemoattractants occurs, which starts formation of firmer bonding between leukocytes to vascular endothelial cells. This firm bonding successively causes adhesion and transmigration of leukocytes across the space between the vascular endothelial cells. These steps occur continuously and each step is indispensable for occurrence of leukocyte transmigration. This also suggests that leukocyte transmigration is controlled at each step. This fact provides many interesting themes from the viewpoint of pharmaceutics.
A number of receptors in vivo are known. Among them, receptors taking part in leukocyte transmigration are characterized in that they belong to the cell adhesion molecule family (Carlos and Harlan, Blood, 82: 2068(1994)). The initial adhesion and rolling are mediated by an adhesion receptor called “selectin”. Firm adhesion is mediated by mutual action between integrins on the leukocyte surface and immunoglobulin superfamily molecules expressed on the vascular endothelial surface. Both of these integrins and immunoglobulin type adhesion molecules mainly participate in leukocyte transmigration. Whether leukocytes pass through the extracellular matrix or stop at the inflammatory site after transmigration depends on integrins.
Integrins are a large family of heterodimeric glycoproteins in each of which two non-equivalent αand β-subunits are associated (Heynes, R., Cell, 69: 11(1992)). There exist at least 16 α-subunits (α-1 to α-9, αL, αM, αD, αX, αE, AIIb, αV) which are different each other and at least 9 β-subunits (β-1 to β9) which are different each other. Integrins are classified into subfamilies based on β-subunits. Leukocytes express many different integrins including α4β1, α5β1, α6β1, α4β7, αLβ2, αXβ2 and αVβ3.
The integrin α4β1 is known as a very late antigen (very late antigen-4; VLA-4) or CD49d/CD29. It is expressed by monocytes, lymphocytes, eosinophils and basocytes and serves as a modification factor to be a key in various inflammatory deficiencies (Helmer, M. Ann. Rev. Immunol., 8: 365(1990)). The integrin α4β1 functions as a receptor for vascular cell adhesion molecule-1 (VCAM-1) and also as a receptor for fibronectin (FN) of extracellular protein (Elices, et al., Cell, 60: 577(1990)).
In recent years, it has been proved by the below-described studies that selective inhibition against adhesion mediated by α4β1/VCAM-1 will become a solving means for the treatment of autoimmune and allergic inflammatory diseases.
Described specifically, an in vivo experiment has proved that a monoclonal antibody which blocks the pathway of α4β1/ VCAM-1 has anti-inflammatory effects and retards the progress of the diseases (Lobb et al., J. Clin., Invest., 94: 1722–28(1944)). In addition, reported are suppression, by an anti-α4 antibody, of both antigen-induced airway hypersensitivity and accumulation of leukocytes in airway alveolar secretion in guinea pigs used a pulmonary inflammation model (Pretolani, et al., J. Exp. Med., 180: 795(1994); suppression, by α4 or VCAM-1 antibody, of eosinophil transmigration on the airway of mice used as an antigen-induced model (Nakajima et al., J. Exp. Med., 179: 1145(1994)), retardation or suppression, by α4 or VCAM-1 monoclonal antibody treatment, of onset of delayed dermal hypersensitivity in mice and monkeys (Chisholm et al., Eur. J. Immunol., 179: 1145(1994), Silber et al., J. Clin., Invest., 93: 1554(1993)); a model of cardiac transplantation rejection due to (incidental to) specific immunosuppressive action (Isobe et al., J. Immunol., 153: 5810(1994)); graft versus host disease after bone marrow transplantation in mice (Yang et al., Proc. Natl. Acad. Sci. USA, 90; 10494(1993)); and experimental autoimmune encephalomyelitis in rats and mice (Yednock, et al., Nature., 356: 63(1992), Baron, et al., J. Exp. Med., 177: 57(1993)).
In addition, there is a report on significant retardation of the onset of diabetes by administration, to nonobese diabetic mice used as an in vivo model, of soluble VCAM-immunoglobulin (Ig) fusion protein prepared by fusing two human N-terminal regions to the common portion of human IgG1 in accordance with Rational Drug Design (Significant delays the onset of adoptively transferred autoimmune diabetes in nonobese mice (Jakubowski et al., J. Immunmol., 155: 938(1995)). Another report is that as a result of synthesis of a cyclic peptide antagonist by using the three-dimensional crystal structure of a VCAM-1 fragment for mimicking the binding loop portion of α4 integrin at the domain-1 of VCAM-1, CQIDSPC of the synthesized VCAM-1 peptide succeeded in inhibiting adhesion of VLA-4 expressed cells to purified VCAM-1 (Wang et al., Proc. Natl. Acad. Sci. USA, 92: 5714(1995)).
Reported as another strategy are blocking of adhesion of α4β1 to either one of binding sites of its corresponding receptor, that is, fibronectin including connecting segment-1 (CS-1) domain (E. A. Wayner, J. Cell. Biol., 116; 489(1992)); and in vitro inhibition, by synthetic CS-1 tetrapeptide (phenylacetic acid-Leu-Asp-Phe-d-Pro-amide), of leukocyte adhesion mediated by VLA-4 and amelioration of advance of coronary arterial diseases in cardiac transplantation of rabbits (Molossi et al., J. Clin. Invest., 95: 2601(1995)).
In addition, there are several reports on compounds exhibiting in vitro VLA-4 inhibitory activity (U.S. Pat. No. 5,821,231, WO96/22966, WO97/03094, WO98/04247 and WO98/04913)
Medicaments exhibiting sufficient effectiveness in oral administration and having clinical utility however have not yet been found.
An object of the present invention is therefore to provide a medicament which serves a selective inhibitor against VLA-4, exhibits effectiveness by oral administration and is administrable for a long period of time.