WO2005098451A1

WO2005098451A1 - Compounds that cause or prevent the removal of receptors from cell membranes, and methods of detecting them

Info

Publication number: WO2005098451A1
Application number: PCT/EP2005/003356
Authority: WO
Inventors: Martin Vey; Wiegand Lang; Joachim Röder
Original assignee: Zlb Behring Gmbh
Priority date: 2004-04-05
Filing date: 2005-03-31
Publication date: 2005-10-20
Also published as: DE102004017295A1

Abstract

Compounds are described that induce or prevent the removal of receptors that are present on a cell membrane and methods for finding the said compounds are described, in which first a marker molecule that binds to the receptors is allowed to act upon the cell membrane, then the test compound is added and after a sufficient incubation time it is checked whether the marker molecule is still adhering to the cell membrane or whether the splitting-off of the receptor in the presence of a suitable compound can be prevented, if a suitable further substance is added.

Description

ZLB BEHRING GMBH 2004/M003-A86 Pfe/vm

Compounds that cause or prevent the removal of receptors from cell membranes, and methods of detecting them

The invention relates to compounds and cellular molecules that can induce or prevent the removal of receptors (receptor molecules) that are present on a cell membrane, and methods for the detection of compounds and cellular molecules with these properties.

It is known that many physiological and pathophysiological processes in macro- and microorganisms are triggered by compounds that bind to receptors present on the cell membrane. This triggers reactions that affect the interior of the cell. For example, the binding of a thrombocyte (blood platelet) to collagen in the wall of a blood vessel is mediated by glycoproteins, which are located on the surface of the thrombocyte. After successful binding, secondary reactions are initiated in the thrombocyte, leading to its activation (1 , 2). As a consequence of binding, the shape of the thrombocyte changes, and it releases biologically active substances that initiate blood clotting at this point. Thrombocyte activation is a vital process, as it prevents an individual bleeding to death following an injury to blood vessels. On the other hand, in the case of chronically inflamed blood vessels, especially arteries, so-called arteriosclerosis develops, in which collagen can be released and then thrombocytes can be activated in intact arteries. This can lead to formation of a clot in the blood vessels, and the arteries can become obstructed, so that the organs supplied by these arteries can be severely damaged by the ensuing lack of oxygen. The most frequent cause of death in the industrially developed countries can in fact be attributed to the occlusion of arteries, for example in cardiac infarction or stroke.

Receptors for collagen binding and platelet activation have been identified in recent times. In particular, platelet activation by collagen is mediated by the thrombocyte molecule glycoprotein VI (GPVI). Furthermore, it has been shown in the mouse model that this receptor can be removed from the platelet surface permanently by binding the monoclonal antibody JAQ1 (3, 4). The processes that cause this receptor removal after antibody binding have not been elucidated precisely, but the aforesaid antibody, which induces receptor removal, is believed to have considerable therapeutic potential, primarily because it can also bind to human GPVI (4). Removal of the collagen receptor by means of this antibody has so far only been demonstrated in live mice, but not yet in vitro, therefore removal of the GPVI receptor from human platelets by means of JAQ1 has also not yet been demonstrated.

Since not only antibodies, but also other substances with the aforementioned property might display great therapeutic potential, e.g. for the treatment of arteriosclerotic pathologies, it is necessary to find such antibodies or other substances with specific effects on receptor removal from the cell membrane. However, appropriate screening methods are not yet available.

Another reason why it has not yet been possible to find a molecule with effects on the receptors of a cell membrane is that measurement of receptor removal involves very expensive experiments and is very time-consuming. Thus, until now, the test substance in the case of the collagen receptor GPVI, for example an antibody, has had to be injected into a mouse, then after some time the platelets are removed and tested for presence of the GPVI receptor. The number of molecules to be tested has therefore been very small to date, and selection of such molecules on a larger scale or even in the "high throughput system" has not been possible at all. As mentioned above, so far it has not been possible at all to detect the removal of GPVI receptors from human platelets, as there are no suitable in vitro methods.

The problem then was to find substances that can induce or prevent the removal of receptors from cell membranes and to develop screening methods that are suitable for finding the said substances.

Now it was found that a compound that can induce the removal of receptors that are present on a cell membrane is found if we first allow a marker molecule that binds to the receptors to act upon the cell membrane, then add the test compound and, after a sufficient incubation time in suitable conditions, check whether the marker molecule is still adhering to the cell membrane. As a rule, a method is used in which the marker molecule that binds to the receptors does not also itself induce the removal of the receptor at the same time, but merely marks the receptor as a neutral agent by its binding, without altering its properties adversely for the detection being described.

When, in a sub-case, a marker molecule is used that leads to removal of the relevant receptor, a marker molecule that is active to that extent can be used for detecting compounds, substances and cellular molecules for the inhibition of receptor removal.

The compound suitable for removal of the receptors can be an endogenous compound, an enzyme, an antibody, another protein or peptide, a polysaccharide, lipid or a low-molecular compound.

The receptor present on the cell membrane can be any receptor at all, but especially a collagen receptor. In this case the marker molecule is preferably an antibody to the collagen receptor. An especially preferred marker molecule is the labelled antibody JAQ1 that is described in detail in EP 1228768A1 and has also been deposited. The JAQ1 labelled antibody belongs to the group of antibodies which, after binding to the collagen receptor, also break it down. However, after proteolytic pretreatment (removal of the F_c portion), the properties of the JAQ1 antibody can be altered so that it is still labelled but no longer breaks down the collagen receptor. The JAQ1 antibody is then in the F(ab')₂ format and can be used for the method of detection described in Example 2.

Basically the neutral marker molecule can be selected from the groups of low- molecular substances provided with detectable substituents, the peptide or protein ligands or in particular from the parts of monoclonal antibodies that still bind antigens. It can be detected by physical, chemical or biochemical methods, because it has fluorescence, radioactivity or enzymatic properties, which can be utilized for dye reactions. When the marker molecule reacts with a receptor present on the cell membrane, the receptor and hence also the cell are specifically labelled and detectable. The unbound marker molecules must be removed by washing the cells or membranes.

The membranes or cells labelled in this way can then be brought into contact with test substances and incubated in suitable conditions. After that, the effect on removal of the receptor can be demonstrated by determining the marker substance still bound on the membranes or cells or alternatively after separating the cells or membranes from the residues. If the membranes or cells still contain the marker molecules, the receptor has not been removed. If, however, the marker molecule can no longer be detected on the membranes, the test substance has caused the receptor to be detached.

It is also possible to investigate the residues after separating the membranes: if they still contain marker molecules, the test substance was active in removal of the receptors. If, however, the residues do not contain any marker molecules, the test substance did not cause the removal of the receptors.

In the case of an active marker molecule, test substances would mutatis mutandis be identified correspondingly, which prevent detachment of the receptor.

Among the compounds that are suitable for the removal of receptors from a cell membrane, the removal of collagen receptors from the thrombocyte membrane has been investigated particularly thoroughly.

It is also possible, however, to find compounds that prevent the removal of the receptors that are present on a cell membrane. This is possible by a method in which we first allow a neutral marker molecule, which binds to the receptors, to act upon the cell membrane, and then allow a compound that is suitable by itself for the removal of receptors from a cell membrane to act on the cell membrane together with or after the test compound and then check, after a sufficient incubation time in suitable conditions, whether the marker molecule is still adhering to the cell membrane. As a rule, marker molecules are employed that do not already prevent the removal of the receptor by themselves, and designated as "neutral" above.

The said compound can be an enzyme, an antibody, another protein or peptide, a polysaccharide, lipid or alternatively a low-molecular compound. The receptor present on the cell membrane can be a collagen receptor, for example. In this case the marker molecule is preferably an antibody to the collagen receptor.

The invention further relates to a method for finding a compound that can remove the receptors that are present on a cell membrane, in which a neutral marker molecule that binds to the receptors is first allowed to act upon the cell membrane, then the test compound is added and, after a sufficient incubation time in suitable conditions, we test whether the marker molecule is still adhering to the cell membrane. Then if necessary we can check, by adding the marker molecule again, whether the receptors have really been removed completely.

A method of this kind is preferred in which a marker molecule is used which does not itself induce the removal of the receptors that are present on a cell membrane.

Preferably the method is carried out for removing the collagen receptor GPVI in the presence of an antibody to the said collagen receptor. The labelled, monoclonal antibody JAQ1 in the F(ab')₂ format is especially suitable as the antibody.

The method according to the invention can also be used for finding a compound which can prevent the removal of the receptors that are present on a cell membrane. First, a neutral marker molecule that binds to the receptors is allowed to act upon the cell membrane, then a compound that is known to be suitable in itself for the removal of receptors from the cell membrane is added to the test compound together with or after a suitable period of time and it is checked, after a sufficient incubation time under suitable conditions, to determine whether the marker molecule is still adhering to the cell membrane. Preferably a marker molecule is used for this that does not itself already prevent the removal of the receptors that are present on the cell membrane.

Preferably this method is carried out for detecting the hampered removal of collagen receptors that are present on a cell membrane, especially the collagen receptor GPVI in the presence of an antibody to the said collagen receptor. The use of the labelled monoclonal antibody JAQ1 is especially preferred.

Detection for the removal of a receptor under in vitro conditions, here the removal of the collagen receptor GPVI from thrombocytes, is described in Example 1. A method for finding compounds that induce the removal of collagen receptors from thrombocytes is described in Example 2. In this case the JAQ1 monoclonal antibody was converted proteolytically to its F(ab')₂ fragment and therefore the induction of receptor removal, but not receptor binding, was stopped. This fragment in fluorescence-labelled form is ideally suitable for labelling the GPVI molecule and for the subsequent search for receptor-removing substances. These methods greatly reduce the cost in financial terms and in terms of time and experiments for finding the said molecules, and animal experiments are no longer required at all. The method according to the invention can be carried out particularly advantageously with antibodies that are directed against the receptors, but is also suitable for low-molecular substances that cause the removal or inhibition of membrane receptors. Low-molecular substances have the advantage, among other things, that they can be produced in a simplified dosage form, for example for oral application. Therefore patient compliance is greatly increased, self-medication becomes possible, the cost of treatment is lowered and even long-term treatment, for example for prophylaxis against recurrence of thrombosis, is organizationally and financially affordable.

The removal of collagen receptors from human thrombocytes has been described here just as one example of application of the method according to the invention, which is of general application. The aforesaid method of labelling the receptors and subsequently detecting their removal from the membrane after incubation with the test substance can therefore be applied to all detection reactions in which receptors are to be removed from the cell membrane. Thus, activators and inhibitors of processes that remove protein receptors, lipid receptors or carbohydrate receptors can be found. These substances can then be used for treating physiological conditions or diseases that are associated with receptors and with the molecules that mediate their removal. Furthermore, with the method according to the invention it is possible to identify as yet unknown molecules that cause the removal of molecules from membranes, and thus a manipulation is made accessible, i.e. either the specific detection or the modulation of activity for the purpose of a therapeutic application.

As an example of how such a method can be carried out in vitro, detection of the removal of the collagen receptor GPVI from the human thrombocyte surface by the JAQ1 monoclonal antibody is described below and is illustrated in Figs. 1-3.

They show the detection of removal of the collagen receptor GPVI from thrombocytes in vitro. In this set-up, the marker molecule is at the same time the molecule that causes removal of the receptor. Human platelets (1x10⁷) were incubated with fluorescence-labelled monoclonal antibody JAQ1 (2 g/ml) and then their fluorescence was analysed in a cytofluorometer. In Fig. 1 the thrombocytes were incubated with the antibody for 10 min.

In Fig. 2 the thrombocytes were incubated with the antibody for 60 min.

In Fig. 3 the thrombocytes were first incubated with the antibody for 60 min, washed and then incubated with the antibody for a further 10 min.

Counts: number of events (thrombocytes) measured in the cytofluororneter; FL1 height: intensity of the fluorescence of the measured thrombocytes.

Example 1 : Detection of the removal of collagen receptors from human thrombocytes

Human thrombocytes are isolated and concentrated according to standard methods and washed four times in Hepes-Tyrode buffer. Then the thrombocytes are counted in the Cell-Analyzer-Systern of the company Scharfe and adjusted to a cell concentration of 1 x 10⁸/ml and 100 μ\ is pipetted into each sample tube, after the respective sample has been placed in it. It is then incubated with the JAQ1 (subtype) lgG2a monoclonal antibody, which has been labelled with a fluorescent dye (fluorescein isothiocyanate), once for 10 min (Fig. 1) and once for 60 min (Fig. 2) at room temperature and at a final antibody concentration (2 μg/ml in DMEM cell culture medium and 10% fetal calf serum, FCS). Then the platelets were washed. In a third test set-up (Fig. 3) the platelets were incubated with the antibody for 60 min, then washed and incubated once again with the fluorescence-labelled antibody at the same concentration. The platelets were finally washed in this set-up as well. The binding of the antibody to the platelets in all three situations was then analysed in a cytofluororneter (FACSCalibur, supplied by BD in San Jose, Ca, excitation wavelength 488 nm, emitted wavelength 535 nm ± 15 nm). In Fig. 1 , a fluorescence-labelled thrombocyte population after incubation with the antibody for 10 min can be identified from the peak of the graph at a fluorescence intensity (FL1) of 10², i.e. the thrombocytes are laden with fluorescence-labelled JAQ1 antibody bound to GPVI. After incubation with the antibody for 60 min (Fig. 2) the fluorescence intensity peak is now only 10¹, i.e. the platelets are no longer laden with the fluorescence-labelled antibody and the GPVI has been separated. Fig. 3 shows that after incubation with antibody for 60 min, then washing and incubation again for 10 min, no fluorescence-labelled platelets can be detected, since the peak of the graph is still at an intensity of 10¹. This means that the target molecule is in fact no longer present on the platelets, since neither the antibody from the 60-rnin incubation nor the antibody from the subsequent 10-min incubation was able to bind to the platelets. Hence it can be concluded that the GPVI, which was still present after antibody treatment for 10 min, was removed from the platelets in the course of the 60-min incubation and accordingly the labelled, bound antibody was also removed along with it.

Example 2: Method of detection for substances that mediate collagen receptor removal

Human platelets are incubated for 10 min with a fluorescence-labelled antibody (20 /g/ml in DMEM cell culture medium and 10% fetal calf serum, FCS) against the GPVI collagen receptor, which does not induce cleavage of the receptor (JAQ1 in F(ab')₂ format) and incubated with the test substance at room temperature for 60 min. Optionally, washing of the platelets can be carried out after the antibody treatment. At the end of the 60-min incubation with the test substance, the platelets are tested for fluorescence labelling. If fluorescence-labelled platelets are no longer found, the collagen receptor has been split off and the substance has thus tested positive. If, however, the platelets are still fluorescence-labelled by the antibody, the test substance did not cause scission of the receptor.

Example 3: Method of detection for substances that inhibit receptor removal

Human platelets are incubated with fluorescence-labelled JAQI IgG (2 μg/ml in DMEM cell culture medium and 10% fetal calf serum, FCS) at room temperature for 60 min. The test substance is either added to the JAQ1 -bound platelets simultaneously with the antibod/ or separately after 10-min incubation with fluorescence antibody followed by washing of the platelets, and incubated for 60 min at room temperature. Then the platelets are washed and analysed for fluorescence. If the human platelets still bear the fluorescence-labelled JAQ1 , the substance prevented removal of the collagen receptor. If the human platelets no longer bear the fluorescence-labelled antibody, removal of the receptor has occurred and the test substance was not suitable for inhibiting removal. Bibliography:

1 , Gibbins JM, Okuma M, Farndale R, Barnes M, Watson SP. Glycoprotein VI is the collagen receptor in platelets which underlies tyrosine phosphoryfatlon of the Fc receptor gamma-chain. FEBS Lett. 1997 Aug 18; 413(2):255-9.

2, Nies andt B, Watson SP. Platelet-collagen interaction: is GPVI the central receptor? Blood. 2003 July 15; 102(2):499-61.

3, European Patent application: EP 1 228768 A1.

4, Nieswandt B, Schulte V, Bergrneier W, Mokhtari-Nejad R, Rackebrandt K, Cazenave JP, Ohlmann P, Gachet C, Zimgibl H. Long-term antithrombotic protection by in vivo depletion of platelet glycoprotein VI in mice. J Exp Med. 2001 Feb 19; 193(4):459-69.

5, Schulte V, Rabie T, Prostredna M, Aktas B, G runner S, Nieswandt B. Targeting of the collagen-binding site on glycoprotein VI is not essential for in vivo depletion of the receptor. Blood 2003 May 15; 101 (10:3948-52.

Claims

1 Θ -ZLB BEHRING GMBH 2004/M003-A86 Pfe/vmClaims:

1. Compound that can induce the removal of receptors that are present on a cell membrane, characterized in that it is found by a method in which first a neutral marker molecule that binds to the receptors is allowed to act upon the cell membrane, then the test compound is added and, after a sufficient incubation time in suitable conditions, it is checked whether the marker molecule is still adhering to the cell membrane.

2. Compound according to claim 1 , characterized in that it is an endogenous substance, an enzyme, an antibody, another protein or peptide, a polysaccharide, lipid or a low-molecular compound.

3. Compound according to claims 1 or 2, characterized in that the receptor present on the cell membrane is a collagen receptor.

4. Compound according to claims 1 to 3, characterized in that the receptor present on the cell membrane is a collagen receptor and the marker molecule is an antibody to the collagen receptor.

5. Compound according to claims 1 to 4, characterized in that the receptor present on the cell membrane is a collagen receptor and the marker molecule is the labelled antibody fragment JAQ1 F(ab^*)₂.

6. Compound that can prevent the removal of the receptors present on a cell membrane, characterized in that it is found by a method in which first a neutral marker molecule that binds to the receptors is allowed to act upon the cell membrane, t en a compound that is in itself suitable for removing receptors from the cell membrane is allowed to act upon the cell membrane together with or after the test compound and, after a sufficient incubation time in suitable conditions, it is checked whether the marker molecule is still adhering to the cell membrane, or which is found by applying a method according to claim 10.

7. Compound according to claim 6, characterized in that it is an enzyme, an antibody, another protein or peptide, polysaccharide, lipid or a low-molecular substance.

8. Compound according to claims 6 or 7, characterized in that the receptor present on the cell membrane is a collagen receptor.

9. Compound according to claims 6 to 8, characterized in that the receptor present on the cell membrane is a collagen receptor and the marker molecule is an antibody to the collagen receptor.

10. Method of finding a compound according to claim 6, characterized in that a marker molecule that binds to the receptors and leads to removal of the receptors is allowed to act upon the cell membrane, simultaneously with or after addition of a test compound, and after a sufficient incubation time in suitable conditions, it is checked whether the marker molecule is still adhering to the cell membrane, and if necessary by adding the marker molecule again it is then checked whether the receptors have been removed completely.

11. Method according to claim 10, characterized in that it is carried out for detecting the removal of the GPVI collagen receptor in the presence of an antibody to the GPVI collagen receptor.

12. Method according to claims 10 or 11 , characterized in that it is carried out for detecting the removal of the GPVI collagen receptor in the presence of the labelled monoclonal antibody JAQ1.