GB2353797A

GB2353797A - Stabilisation of peroxidases

Info

Publication number: GB2353797A
Application number: GB9920670A
Authority: GB
Inventors: Graham De Lisle Yearwood; Veronika Zsuzsanna Mann; Patrick Kilmartin; Adrian Charles Dawkes; Paul Hourd; John Edwards
Original assignee: Ortho Clinical Diagnostics Ltd
Current assignee: Ortho Clinical Diagnostics Ltd
Priority date: 1999-09-01
Filing date: 1999-09-01
Publication date: 2001-03-07
Also published as: GB9920670D0

Abstract

The present invention relates to a process for stabilising immunologically active compounds having peroxidase activity by adding to them an effective amount of at least one aryl boronic acid compound. The present invention also relates to stabilised reagents comprising an immunologically active compound having peroxidase activity and at least one aryl boronic acid compound. The immunologically active compounds are preferably horseradish peroxidase or myoglobin.

Description

1 2353797 1 Stabilisation of Pero xidases

Field of Invention

The present invention relates to a process for stabilising peroxidases and peroxidases conjugated to other molecules such as biologically active molecules, for use in analytical procedures.

Background of the Invention

Peroxidases, in particular horseradish peroxidase (HRP), are enzymes that are commonly used in analytical procedures including immunoassays. Many formats are known and used widely for the measurement of antigens, antibodies, haptens, and other analytes. Some examples are competitive and immunometric assays. In competitive immunoassays, a labelled analyte competes with the analyte in a sample for binding to an immobilised analyte binding species. Thus, increasing the concentration of the analyte in the sample reduces the labelled analyte which becomes immobili.sed. In immunometric assays, a labelled analyte binder complexes with analyte in the sample and an immobilised analyte binder. In this type of assay, increasing the concentration of the analyte in the sample results in an 25 increase in the labelled analyte binder which becomes immobilised. In both types of immunoassay, the immobilised labelled analyte is separated from the CDS- 180 1 unbound labelled analyte, and either the immobilised or unbound HRP activity is measured.

Reagents for use in analytical procedures, such as immunoassays, must remain active after manufacture, shipping, and periods of storage. During these periods they may be subject to relatively high or low temperatures which affect the activity. Therefore, it is a commercial advantage to provide a stable reagent containing the peroxidase-labelled material or other active biological components.

This is not readily achieved for many biological materials. For example, enzyme-labelled molecules and other complex biomolecules are widely used in immunoassays, and it has been observed that the activity of the enzyme or of the active biomolecule can decrease with time, especially at the low concentrations used in immunoassay procedures. Biological activity is found to decrease more rapidly as the storage temperature increases. one way to slow down or prevent a decrease in the activity of an enzyme or enzyme conjugated to an active molecule is to add a stabilising agent to the enzyme in solution in an amount sufficient to achieve stabilisation.

Methods for stabilisation of peroxidases or HRP include the addition of polyethylene glycol and calcium salts (US Patent 4, 728, 023); the addition of 8-anilino l-naphthalene sulfonic acid (FRG Patent 3,100,076); the addition of phenol and substituted phenols with one or CDS-180 3 more substituents from Cl-C3 lower alkyl, chlorine and bromine(US Patent 4,764,468); the addition of 4 aminoantipyrine (European Patent 070,992); the addition of polyvalent ions of Group III and IV (US Patent 4,169,012) and the addition of a 4-hydroxy or 4 alkoxyarylacetamide (US Patent 5, 372, 932).

Stabilisation of both HRP and other biomolecules has been achieved by the addition of a compound having a benzene ring substituted with at least one hydroxyl group and one group of Hammett sigma value (ap) -0.20:5 x t + 0. 2 4 or an amide (US Patent 5, 516, 672) Although the currently known additives improve the stability of peroxidase and other biological molecules, there is still a need for further improvement. In particular, reagent formulations which have improved stability at room temperature and the elevated temperatures experienced during transport of reagents are desired. Some of the known additives can interact with proteins and other components which are frequently used in analytical reagent formulations and in some cases can affect the immunological reactions which are utilized in immunoassays. Additives which stabilise the active components of the formulations and which have no deleterious effects on other components are also desired.

Organoboron compounds in aqueous solutions interact strongly with many molecules. The interaction, which can be by a number of different mechanisms, has been CDS-180 exploited in the purification of various materials. For example, 3- aminophenylboronic acid attached to a solid support is used in the fractionation of glycoproteins. Organoborates can inhibit many enzymes, affect animal metabolism and are recognised bacteriostats (see Boronate Ligands in Biochemical Separations, Amicon Corporation, Danvers, Publication 507, 1981, for a comprehensive review). Organoboron compounds have also been found to increase the light output from chemiluminescent reactions catalysed by HRP (PCT Publication No. WO 93/16195) alone or in combination with a phenolic or aromatic amine enhancer (PCT Publication No. WO 94/23060).

Organoboron compounds also have been used in electron transfer electrodes (PCT Publication No. WO 85/02861).

Aryl boronic acids are a family of compounds within the organoboron group. Aryl boronic acids have been used in formulations of liquid detergents which contain proteolytic enzymes (PCT Publication No WO 92/19707).

At high concentrations of aryl boronic a cid, the proteolytic enzymes are prevented from degrading other protein components of the detergent formulation. on subsequent dilution in wash water the protbolytic enzymes become re-active.

Surprisingly, we have found that aryl boronic acid compounds can be added as a stablilising agent to slow down or prevent a decrease in the activity of peroxidase CDS-180 or peroxidase that has been conjugated to another molecule (hereinafter peroxidase labelled conjugate or conjugate), particularly HRP or HRP- conjugate intended for use in an immunoassay.

Summary of the Invention

Therefore, an object of the present invention is to provide a stable peroxidase composition comprising at least one aryl boronic acid compound. A second object of the present invention is to provide a method for stabilising peroxidases, particularly HRP, comprising adding at least one aryl boronic acid compound to the enzyme. A third object of the invention is to provide a method for stabilising a peroxidase labelled conjugate by adding at least one aryl boronic acid compound to the conjugate reagent. The stabilised compositions are useful in analytical procedures. They are particularly useful in enzyme immunoassays.

One embodiment of the present invention is a stabilised peroxidase reagent, comprising: a peroxidase and at least one aryl boronic acid compound that is either unsubstituted or is substituted with one or more substituents selected from the group consisting of:

alkyl, substituted alkyl, aryl, substituted aryl excluding substitution with hydroxyl, ether, amine, substituted amine, azo, amide, halogen, nitro, thiol, thiol derivative, aldehyde, acid, acid salt, ester, sulfonate, phosphonate, trimethyl silyl.

CDS-180 6 Another embodiment of the present invention is a method for stabilising peroxidase activity, comprising:

adding to a peroxidase an amount effective for stabilising the peroxidase of at least one aryl boronic acid compound that is either unsubstituted or is substituted with one or more substituents selected from the group consisting of: alkyl, substituted alkyl, aryl, substituted aryl excluding substitution with hydroxyl, ether, amine, substituted amine, azo, amide, halogen, nitro, thiol, thiol derivative, aldehyde, acid, acid salt, ester, sulfonate, phosphonate, trimethyl silyl.

A preferred embodiment is either the composition or method above wherein the peroxidase is horseradish is peroxidase.

DETAILED DESCRIPTION

The present invention relates to the use of aryl boronic acid compounds as stabilisers of HRP. The stabiliser is an aryl boronic acid of the formula ArB (OH) 2 where Ar is phenyl or naphthyl.

The aryl structure can be either unsubstituted or substituted with one or more substituents selected from the group consisting of: alkyl, substituted alkyl, aryl, substituted aryl excluding substitution with hydroxyl, ether, amine, substituted amine, azo, amide, halogen, nitro, thiol, thiol derivative, aldehyde, acid, WS180 7 acid salt, ester, sulfonate, phosphonate, trimethyl silyl. Some examples of substituted and unsubstituted compounds are:

H n ---,<H PHENYLBORONIC ACID O:H 4 - BROMOPHENYLBORONIC ACID 0 o' <H H- p C=0 CH3 3 - ACETAMIDOPHENYLBORONIC ACID CDS-180 HO \ / OH B U0:9 1-NAPHTYL BORONIC ACID Preferred compounds for use in the present invention are 4-bromophenylboronic acid, 3 acetamidophenylboronic acid, and phenylboronic acid, which are shown above. A preferred embodiment of the present invention is a stabilised HRP composition comprising bromophenylboronic acid or a method of stabilising HRP using bromophenylboronic acid. In particular, 4-bromophenylboronic acid showed desirable solubility and suitable stability effects. However, one skilled in the art will know how to choose an aryl boronic acid compound that is suitable for a particular situation.

The aryl boronic acid stabiliser can be added at any desired point of time to the peroxidase or peroxidase conjugate. The reagent ingredients, the stabiliser itself and the peroxidase or peroxidase conjugate, as well as the various other parts of the assay reagent may be present in solid or dissolved form.

The stabiliser should be added in amount sufficient to CDS-180 1 achieve stabilisation. Preferably, the stabiliser is added in an amount that is 0.01% to 0.1% weight per volume (% w/v).

In one embodiment of the invention, the stabiliser can be added to a liquid reagent which is subsequently dried since a more uniform distribution of the stabiliser and thus a better action in the case of additions close to the lower limit of the effective range is hereby achieved. For example the aryl. boronic acid compound can be added to the peroxidase or conjugate solution before lyophilisation or after reconstitution of the lyophilisate with an aqueous solvent. In the latter case, the solvent can, of course, first also be mixed with the stabiliser and then added is to the lyophilisate for dissolving it. If, for example, the peroxidase or peroxidase conjugate is a component in a dry analytical assay element, e.g., thin-film or slide elements, the stabiliser would preferably be added to a coating solution prior to the coating process. It is however, contemplated that the stabiliser could be added after the coating process is completed. For example, by spraying it on.

The peroxidase may be conjugated to another molecule that is biologically active or imm unologically effective. Such a molecule is referred to herein as an "active molecule". An active molecule is one which can be used in an analytical procedure. Preferably said active molecule would be an antibody or a fragment CDS180 1 thereof, an antigen or a hapten, protein, glycoprotein, peptide, protein mimetic, nucleic acid sequence (s), steroid, hormone or derivatives of any of the foregoing or a compound made of more than one or a combination of the foregoing.

When practicing the present invention, it may be desirable to add also a preserving agent. Common preserving agents include, for example, 2 hydroxpyridine-N-oxide, chloroacetamide, N,N-methylene bis (N-1-hydroxymethyl)-2,5-dioxo-4-imidazolidinyl)- urea, 5 bromo-S-nitro-1,3-dioxan.

In solutions which have a pH close to or below 7.0, boronates are uncharged and hydrophobic interactions and charge transfer interactions cause tight binding to many molecules, particularly proteins. Surprisingly we have found that this interaction gives a stabilising effect on biologically active molecules.

Several assays were performed wherein aryl boronic acid was added to the reagents containing a peroxidase label. Assays can be carried out using an enzyme label which can be attached to the ligand to form a labelled ligand or to the ligand binder to form a labelled li-gand binder. Enzymes such as peroxidases, e.g. horseradish peroxidase (HRP), are preferred labels. A preferred embodiment is where the enzyme is a peroxidase. There is a variety of types of this enzyme. Horseradish peroxidase is the most preferred type and it is readily available.

CDS-180 It is within the skill of the ordinary artisan to determine a suitable substrate for a given enzyme label.

The substrate can be a material which is directly acted upon by the enzyme label or a material that is involved in a series of reactions which involve enzymatic reaction of the label.

The effectiveness and advantages of the invention are further illustrated by the following examples.

Examples

Example 1: Stabilisation of an HRP-antibody conjugate A monoclonal antibody (raised against human follicle stimulating hormone) was conjugated to HRP using succinimidyl-4-(N-maleiraidomethyl) cyclohexane-1 carboxylate (SMCC) and N-succinimidyl S acetylthioacetate (SATA) obtained from Pierce and Warriner, Chester, U.K. The HRP-antibody conjugate was then biotinylated using BIOTIN-XX-NHS (Calbiochem, Beeston, U.K.) The biotinylated HRP-antibody was desalted on a PD710 column (Pharmacia B i'otech, St.Albans, U.K.) following the manufacturer's recommended protocol using 100mM potassium phosphate buffer pH 6.0 containing 300mM sodium chloride as an eluting buffer. The conjugate was quantified by UV adsorption, diluted in test reagents with various additives and then stored at 2-8 degrees C or 37 degrees C. The activity of the conjugate in the reagents was CDS-180 1 then tested by incubating 100 microlitres of the reagent in a VITROS ECi streptavidin coated microwell (Ortho Clinical Diagnostics, U.K.) for 15 minutes at 37 degrees C. During the incubation the biotinylated HRP-antibody conjugate becomes immobilised on the surface of the microwell by the reaction of the biotin with streptavidin. After washing the microwells, the activity of the immobilised HRP-antibody complex was measured using an enhanced luminescence reaction (US Patent 5, 372, 931). VITROS ECi Signal Reagent, containing luminogenic substrates (a luminol derivative and a peracid salt) and an electron transfer agent, was added to the microwells. The HRP in the bound conjugate catalyzes the oxidation of the luminol derivative, is producing light. The electron transfer agent (a substituted acetanilide) increases the level of light produced and prolongs its emission. The light signals from the microwells were measured using an AMERLITE Analyzer (Ortho-Clinical Diagnostics, U.K.).

The biotinylated HRP-antibody conjugate described above was diluted in 0.1 M potassium phosphate buffer pH 7.0 to give a concentration of 10 ng/mL. Magnesium depleted KATHON (Rohm and Haas, U.K.) was added as a preservative (1% w/v) and bovine serum albumin (1% w/v) was added to prevent non-specific adsorption of the conjugate to the surface of the microwells. Each aryl boronic acid stabilising agent was formulated as a 200 mg/mL solution in dimethylformamide WMF) and added to CDS-180 13 - the conjugate solution to give the desired molarity of stabiliser. The conjugate solutions were stored at 2-8 degrees C or 37 degrees C for 2 hours, 24 hours, 96 hours and 9 weeks. The activity of the HRP in the conjugate was then measured as described above. The results are shown in Table 1.

CDS-180 14 - Table 1 - Activity of HRP after storage of an HRPantibody conjugate.

Additive HRP HRP HRP HRP activity activity activity activity after 2 after 24 after after 9 hours hours 96 hours weeks storage storage storage storage Control - no 100 105.2 96.8 81.8 additive, Stored at 2-8 degrees C No additive, 97.7 41.8 6.6 - Stored at 37 degrees C 4-bromophenyl- 104.3 113.4 100.0 60.1 boronic acid (0.1% W/V), stored at 37 degrees C 3-acetamino- 100.5 106.5 97.1 Insuffic phenylboronic ient acid (0.1% sample W/V), stored at 37 degrees C 4- 100.3 91.1 94.3 51.1 phenylboronic acid (0.1% W/V), stored at 37 degrees C DMF 98.2 64.4 8.5 (0.5% v/v), stored at 37 degrees C CDS-180 HRP activity is the light output expressed as a percentage of the control light output (no additive 2 hours storage at 2-8 degrees C).

It can be seen from Table 1 that the activity of HRP decreased markedly after storage at 37 degrees C in the absence of a stabiliser. HRP activity is retained during storage at 2-8 degrees C or in the presence of the aryl boronic acid compounds. Even after 9 weeks storage at 37 degrees C, the HRP activity is still over 50% of the starting activity in the presence of a stabiliser.

Example 2: Stabilisation of an HRPtestosterone conjugate HRP was chemically coupled to testosterone-3 carboxymethyloxime by reaction with dicyclohexylcarbodiimide and N-hydroxysuccinimide (Aldrich Chemical Co., Gillingham, U.K.). The purified conjugate was diluted to a concentration of 60 ng/mL in a 50mM phosphate buffer pH 7.0 containing 1.3% sodium chloride, 2% sucrose', 0.5% magnesium de pleted KATHON, 0.2% bovine serum albumin and 600 microgram/L DANAZOL as a steroid releasing agent. The conjugate. solution was stored at 25 degrees C in the presence of various concentrations of 4-bromophenylboronic: acid and the HRP conjugate activity was then measured using a competitive immunoassay procedure.

CDS-180 A monoclonal antibody to testosterone was biotinylated using NHS-LC-biotin (Pierce and Warriner, Chester, U.K.) and diluted to 10 mg/L in a SOmM potassium phosphate buffer pH 7.3 containing 1.3% sodium chloride, 70 mM EDTA, 0.5% magnesium depleted KATHON, 1% human plasma, 0. 05% normal mouse serum and 600 microgram/L of DANAZOL. Charcoal stripped human plasma (25 microlitres) was incubated with 50 microlitres of the HRP-testosterone conjugate solution and 100 microlitres of the biotinylated antibody solution in a VITROS ECI streptavidin coated microwell (Ortho-Clinical Diagnostics, U.K.) for 30 minutes at 87 degrees C.

During the incubation, the HRP-testosterone conjugate becomes bound to the biotinylated antibody and the complex is immobilised on the surface of the streptavidin coated microwell through the reaction of biotin with streptavidin. After washing the microwell, the HRP activity was measured using VITROS ECi Signal Reagent in a VITROS ECi Analyzer. The results are shown in Table 2.

CDS-180 Table 2 - Stabilisation of an HRP-testosterone conjugate Concentrati HRP HRP HRP HRP on of 4- activity activity activity activity bromophenyl at 0 at 7/8 at 21 days at 26/28 boronic days days storage days acid storage storage (%) storage (% W/V) (%) (%) (%) 0.0 100 89.3 83.4 77.1 0.01 100 96.3 88.0 - 0.02 100 92.8 - 86.4 0.03.100 94.7 89.0 0.04 100 98.1 - 91.0 0.05 100 95.3 92.2 92.1 0.1 100 98.7 99.9 - HRP activity is the light output expressed as a percentage of the 0 day storage light output.

In the absence of a stabiliser, the activity of the HRP-testosterone. conjugate had decreased to 83.4% after 21 days storage at 25 degrees C. With increasing amounts of bromophenylboronic acid the conjugat.e was more stable. After 26-28 days storage in the absence of a stabiliser, the activity of the HRP-testosterone conjugate had decreased to 77.1%. Again with increasing amounts of bromophenylboronic acid the conjugate was more stable.

is CDS-180 Example 3: Stabilisation of an HRP-antibody/antigen complex HRP was chemically coupled to a monoclonal antibody to hepatitis B core antigen (HBc) using succinimidyl-4 (N-maleimidomethyl) cyclohexane- I -carboxyl ate (SMCC) and N-succinimidyl S-acetylthioacetate (SATA). The purified HRP conjugate was diluted to a concentration of 0.057 microgram/mL in a 20mM sodium phosphate buffer pH 6.2 containing 2.0% sodium chloride, 2.0% magnesium depleted KATHON, 2.0% bovine serum albumin and 0.065 microgram/mL recombinant HBc (Chiron Corporation, Emeryville, California, U.S.A.). The HRP-labelled anti HBc antibody combines with the HBc antigen to form an HRP-labelled antibody/ antigen complex. The solution was stored at 25 degrees C or 37 degrees C in the presence or absence of 4-bromophenylboronic acid and the HRP antibody/ antigen complex activity was then measured using an immunoassay procedure.

A monoclonal antibody to human IgM was biotinylated using BIOTIN-X-NHS (Calbiochem, Beeston, U.K.) and diluted to 0.75 mg/L in a 2SmM potassium phosphate/lSmM sodium tetraborate buffer pH 8.2 containing 0.5% bovine serum albumin and 0.96% magnesium-depleted KATHON. Human plasma containing IgM antibodies to HBc was diluted 1 in in a 100mM potassium phosphate buffer containing 0.9% sodium chloride, 5% bovine serum albumin and 1% BRONIDOX (Henkel K.G., Germany). 25 microlitres of the diluted CDS-180 19 - plasma was incubated with 145 microlitres of the biotinylated anti-IgM antibody solution in a VITROS ECi streptavidin coated microwell (OrthoClinical Diagnostics, U.K.) for 15 minutes at 37 degrees C. During the incubation, any IgM antibodies in the plasma become immobilised on the surface of the streptavidin coated microwell by reaction with the biotinylated antiIgM and the reaction of biotin with streptavidin. After washing the microwell, 100 microlitres of the HRP- labelled antibody/antigen complex solution is added to the microwell and incubated for a further 15 minutes at 37 degrees C. During this reaction, the HBc in the complex reacts with any antibodies to HBc immobilised on the microwell. After washing the microwell the activity of HRP bound to the surface of the microwell was measured using VITROS ECi Signal Reagent in a VITROS ECi Analyzer. The results are shown in Table 3.

CDS-180 Table 3 - Stabilisation of an HRP-ant ibody/ antigen complex Concentrati HRP HRP HRP HRP on of 4- activity activity activity activity bromophenyl at 0 at 1 at 15 at 1 week boronic days week weeks storage at acid storage storage storage at 37 degrees (% W/V) at 25 25 degrees c degrees c (%) c (%) 0.0 100 1.0 0.9 0.5 0.01 100 38. 0 0.0 0.0 0.1 100 61.0 45.1 15.3 HRP activity is the light output expressed as a percentage of the 0 day storage light output.

In the absence of a stabiliser, the activity of the HRP conjugate had decreased to less than 1% after storage for 1 week. With 0.01% bromophenylboronic acid the conjugate retained 38% of its activity after 1'week storage at 25 degrees C, and with 0.1% bromophenylboronic acid 45% of the activity was retained after 15 weeks storage at 25 degrees C and 15% of the activity was retained after 1 week storage at 37 degrees C.

CDS-180 21 Example 4: HRP conjugate used in a dry, thinfilm format In addition to the working examples above, as was discussed previously, the present invention is contemplated to be useful in a dry immunoassay analytical element. Therefore, the following examples describe embodiments of the invention that should result in an enzyme conjugate having the beneficial properties of this invention.

Dry analytical elements comprising HRP for determining the presence or amount of an analyte, such as, but not limited to glucose, triglycerides, lipase, glycerol, cholesterol, cholesterol esters are well known. Dry immunoassay analytical elements comprising HRP-conjugates are also well known, such as immunoassay elements for determining C-Reactive Protein (CRP), digoxin, phenytoin and the like.

The stabiliser may be introduced into the element in any layer or zone including the spreading layer, subbing layers and/or reagent layers using well known methods, for example hopper and gravure coating techniques. In a preferred element HRP and stabiliser are present together.

An analytical element, comprising HRP and an aryl boronic acid stabiliser in the same layer, for the determination of cholesterol would have the following composition and format:

CDS-180 22 - Layer Component Range of Dry Coverage (g/ 2) Spreading Barium sulfate 70-140 Layer Cellulose Acetate 6-12 Polyurethane resin 0.5-1.5 Reagent Potassium phosphate 1-2 Layer buffer (pH 5.5 - 6.5) TRITON X-100 5-11 (surfactant) HRP 5,000-160,000 International Units (M Aryl boronic acid 0.01 - 10 - stabiliser Cholesterol oxidase 2, 000 IU - 4000 IU Cholesterol ester 1, 500 IU-12, 000 IU hydrolase 2-(3,5-Dimethyoxy-40.8-3 hydroxyphenyl-4,5 bis M dimethylaminophenyl) imidazole 5,5-Dimethyl-1,3- 0.2-0.8 cyclohexane dione Subbing Poly(N- 0.2-0.8 Layer isopropylacrylamide) Binder Layer Gelatin (hardened) 10-25 Potassium phosphate 0.1-2 buffer TRITON X200E 0.005 - 0.02 surfactant Support Poly(ethylene terephthalate) CDS-180 23 - The element can be mounted into slides, kept in strips or other suitable form and stored under conditions to be tested. The reflectance density measured using a relectance spectrometer obtained with cholesterol standards using a control element (for example, a fresh element) can be compared with elements stored under test conditions. The location of the stabiliser in the element and the amount of the stabiliser can be readily altered until the desired stability is obtained, as would be well known to the skilled artisan.

Example 5: Dry Immunoassay Element for the detection of Phenytoin is An immunoassay analytical element, comprising a phenytoin-HRP conjugate and aryl boronic acid stabiliser in the same layer, for the determination of phenytoin has the following composition and format:

CDS180 24 Layer Component Dry - Coverage (g/M1) Gravure Phenytoin-HRP 1.0 X 10-6 _ le)o conjugate X 10-6 Magenta dye 0.01 - 0.05 3-(N- 0.001-0.01 Morpholino) propanesul fonic acid buffer, pH 7.0 Bovine serum albumin 1.0 X 10-4 -5.0 X 10-4 Polyacrylamide 0.05 X 10-3 3.0 X 10-3 Trehalose 0.1 -0.4 Aryl boronic acid 0.0001 - 1.0 stabiliser Bead Spreading Poly (vinyl to luene- co- 100-160 Layer methylacrylic acid) beads (20- 40 microns) Poly(methyl acrylate- 1.8 - 3.5 co-sodium-2 acrylamido-2 methylpropane sulfonate-co-2 acetoacetoxyethyl methacrylate) Gylcerol 1.0 - 3.0 Bovine serum albumin 0.05 -3.0 Mannitol 0.05 - 3.0 Dimedone 0.1-1.0 N- 0.1 - 1.0 [TRIS (hydroxymethyl) m ethyl]-2- aminoethane sulfonic acid buffer, pH 7.0 Aryl boronic acid 0.01 - 10.0 stailiser Receptor Layer Poly(N- 0.1_ 1.0 CDS-180 Layer Component Dry Coverage (g/M,2) isopropylacrylamide comethacrylic acid co-N,N' methylenebisacrylamid e) 4,5-Bis-(4- 0.1- 2.0 dimethylaminophenyl) hydroxyphenyl) imidazole Dimedone 0.01-1.0 TETRONIC T908 0.01-0.04 surfactant OLIN 10G surfactant 0.005-0.02 TX 100 surfactant 0.01-0.03 N- 0.01-0.02 TRIS (hydroxymethyl) m ethyl]-2- aminoethane sulfonic acid buffer, pH 7.0 Poly[ styrene-co-p- (2- 0.05 - 0.3 chloroethylsulfonyl methyl)styrene] beads having a phenytoin antibody bound thereto Gelatin Layer Gelatin 5-20 N- 2.0-8.0 1 TRI S (hydroxymethyl) m ethyl]-2- aminoethane sulfonic pH 7.0 acid buffer, TX-100 surfactant 0.01-0.03 Dis (vinylsul f onylmeth -.0.05-0.30 yl)ether Support Poly (ethylene terephthalate) CDS-180 26 As above, the element can be mounted into slides, kept in strips or other suitable form and stored under conditions to be tested. The reflectance density obtained with phenytoin standards using a control element (for example, a fresh element) can be compared with elements stored under test conditions. The location of the stabiliser in the element and the amount of the stabilser can be readily altered until the desired stability is obtained, as would be well known to the skilled artisan.

The aryl boronic acid compounds will act to stabilise dry analytical elements comprising FRP directed to analytes, in addition to the cholesterol element described above and dry immunoassay analytical elements comprising I-T-RP-conjugates directed to immunassays in addition to that described above for phenytoin.

Example 6 - Stabilisation of myoglobin Myoglobin, hemoglobin and cytochrome C are proteins which have peroxidase activity. The enzymic activity of these proteins has been utilized in immunoassays in which they have been detected by their enzyme-catalysed luminescent reaction of luminol with peroxide (GB Patent No. 2,063,469).

Myoglobin has been shown to be a useful marker for acute myocardial infarction (US Patent No. 5,744,358). Standard reference solutions of myoglobin are used in the measurement of this analyte by immunological reactions, and the stability of these solutions can be improved by the addition of an aryl boronic acid compound.

Immunometric assay of myoglobi Two mouse monoclonal antibodies to myoglobin were obtained from BiosPacific, USA. BRP was chemically coupled to one of the myoglobin monoclonal antibodies usingsulfosuccinimidyl-4-(N-maleimidomethyl) cyclohexane-l-carboxylate (sulfo-SMCC) and N- hydroxysuccinimidyl S-acetylthioacetate (NHS-SATA) obtained from Pierce and Warriner, U.K. The purified BRP conjugate was diluted to a concentration of 3 microgram/mL in a IOOmM potassium phosphate buffer pH 6.5 containing 1.0% magnesium-depleted KATHON and 0.5% bovine serum albumin.

27 The second myoglobin monoclonal antibody was biotinylated using biotin-LC- NHS (Pierce and Warriner, U.K.) and diluted to 3 microgram/mL in a I OOmM. potassium phosphate buffer pH 6.5 containing 5.0% bovine serum albumin and 1.0% magnesium-depleted KATHON.

Standard solutions of human cardiac myoglobin obtained from BiosPacific, Emeryville, USA were prepared in a IOOmM potassium phosphate buffer pH 7. 0 containing 1.0% magnesium depleted KATHON, 5. 0% bovine serum albumin, I OmM sodium chloride and I m.M EDTA.

10 microlitres of a standard myoglobin solution were incubated with 70 microlitres of the biotinylated monoclonal antibody solution and 70 microlitres of the BRP-labelled monoclonal antibody solution in a VITROS ECi streptavidin coated microwell (OrthoClinical Diagnostics, U.K.) for 8 minutes at 37 degrees C. During the incubation, the biotinylated antibody becomes immobilised on the surface of the streptavidin coated microwell by the reaction of biotin with streptavidin. At the same time, myoglobin in the standard solution becomes immobilised to the biotinylated antibody and also binds with the BRP-labelled monoclonal antibody. After washing the microwell the activity of ERP bound to the surface of the microwell was measured using VITROS ECi Signal Reagent in a VITROS ECi Analyzer. The activity of the BRP bound to the microwells, measured as the light output in the Analyzer, is proportional to the immunoreactivity of the myoglobin added in the assay. A response curve of light output against myoglobin immunoreactivity was constructed using a series of standard myoglobin solutions covering the range 0 to 1757 ng/ml.

Stability of myoglobin Human cardiac myoglobin was dissolved at a concentration of 350 ng/mI in 100mM potassium phosphate buffer pH 7.0 containing 1.0% magnesium depleted KATHON, 5.0% bovine serum albumin, I OmM sodium chloride and 1 mM EDTA. 4-bromophenylboronic acid and 3-acetamidophenylboronic acid were each formulated as a 100 mg/mL solution in ethanol and added to the myoglobin solution to give the desired concentration of stabiliser. The myoglobin solutions were then stored at 25 degrees C or 37 degrees C and after I week and 2 weeks the amount of immunoreactive myoglobin was measured using the immunometric 28 assay described above. The effect of 4-bromophenylboronic acid and 3acetamidophenylboronic acid on myoglobin stability is shown in Table 4, and the effect of varying the concentration of 4-brornophenylboronic acid is shown in Table 5.

Table 4 - Stabilisation of myoglobi Myoglobin Immunoreactivity Additive 0 days 1 week 2 weeks 1 -,yeek 2 weeks storage storage at 25 storage at 25 storage at 37 storage at 37 deg C deg C deg C deg C Control - 100 66 49 14 12 No additive 4-brorno, phenyl 100 79 79 33 25 boronic acid (0.12% W/v) 3 acetamido 100 84 80 53 42 phenyl boronic acid (0.12% W/V) Myoglobin immunoreactivity is expressed as a percentage of the 0 days storage immunoreactivity.

29 In the absence of a stabiliser, the immunoreactivity of the myoglobin decreased to 49% after storage for 2 weeks at 25 degrees C. With 0.12% 4bromophenylboronic acid the myoglobin immunoreactivity retained 79% of its activity after 2 weeks storage at 25 deg C, and with 0. 12% 3-acetarnidophenylboronic acid, 80% of the activity was retained after 2 weeks storage at 25 degrees C.

In the absence of a stabiliser, the immunoreactivity of the myoglobin decreased to 12% after storage for 2 weeks at 37 degrees C. With 0.12% 4bromophenylboronic acid the 10. myoglobin immunoreactivity retained 25% of its activity after 2 weeks storage at 3 7 deg C, and with 0. 12% 3-acetarnidophenylboronic acid, 42% of the activity was retained after 2 weeks storage at 37 degrees C.

Table 5 - Stabilisation of myoglobi Myoglobin immunoreactivity is expressed as a percentage of the 0 days storage immunoreactivity.

In the absence of a stabiliser, the immunoreactivity of the myoglobin had decreased to 49% after storage for 2 weeks at 25 degrees C and to 12% after 2 weeks at 37 degrees C. With Myoglobin Immunoreactivity Concentration 0 days storage 1 week 2 weeks 1 week 2 weeks of 4-bromo storage at storage at storage at storage at phenylboronic 25 deg C 25 deg C 37 deg C 37 deg C acid (o/O) (%) C/0) (% W/V) 0 100 66 49 14 12 0.1 100 68 46 22 39 0.2 100 68 57 22 26 0.3 100 74 65 28 25 0.4 100 73 66 37 32 ------..:.

0.5 100 77 74 26 26 increasing amounts of 4-bromophenylboronic acid the myoglobin was more stable. In the presence of 0.5 % 4-bromophenylboronic acid, 74% of the myoglobin immunoreactivity was retained after 2 weeks at 25 degrees C and 26% was retained after 2 weeks at 37 degrees C. 5 All cited materials herein are hereby incorporated by reference. Furthermore, it should be noted that the present invention includes all modifications falling within the scope of the following claims. It is to be understood that numerous changes and modifications may be made therein without departing from the scope and intent of the invention.

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Claims

1. A method for stabilising an immunologically active compound having peroxidase activity, comprising: adding to the compound having peroxidase activity an amount effective for stabilising the immunologically active compound of at least one aryl boronic acid compound that is either unsubstituted or is substituted with one or more substituents selected from the group consisting of: alkyl, substituted alkyl, aryl, substituted aryl excluding substitution with hydroxyl, ether, amine, substituted arnine, azo, amide, halogen, nitro, thiol, thiol derivative, aldehyde, acid, acid salt, ester, sulfonate, phosphonate, and trimethyl silyl.

2. The method of claim 1, wherein the aryl boronic acid compound is 4bromophenylboronic acid.

3. The method of claim 1, wherein the aryl boronic. acid compound is 3acetamidophenylboronic acid.

4. The method of any one of claims I to 3, wherein the immunologically active compound is myoglobin.

5. The method of any one of claims I to 3, wherein the immunologically active compound is a peroxidase.

6. The method of claim 5, wherein the peroxidase is horseradish peroxidase.

7. The method of claim 5 or claim 6, wherein the peroxidase is conjugated to an active molecule.

8. The method of claim 7, wherein the active molecule is selected from the group consisting of.- an antibody or a fragment thereof, an antigen; a hapten; a protein; a glycoprotein; a protein mimetic; a nucleic acid sequence; a steroid; a hormone; 'or a derivative of any of the foregoing.

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9. The method of any one of claims 1 to 8, wherein the aryl boronic acid compound and the immunologically active compound having peroxidase activity are present together in an aqueous solution.

10. The method of claim 9, wherein the amount of aryl boronic acid compound added is from 0.0 1 percent to 0.5 percent, preferably about 0. 1 percent, by weight per volume.

11. A stabilised reagent comprising: an immunologically active compound having peroxidase activity and at least one aryl boronic acid compound that is either unsubstituted or is substituted with one or more substituents selected from a group consisting of.. alkyl, substituted alkyl, aryl, substituted aryl excluding substitution with hydroxyl, ether, amine, substituted amine, azo, amide, halogen, nitro, thiol, thiol derivative, aldehyde, acid, acid salt, ester, sulfonate, phosphonate, and trimethyl silyl.

12. The stabilised reagent of claim 11, wherein the aryl boronic acid compound is 4bromophenylboronic acid.

13. The stabilised reagent of claim 11, wherein the aryl boronic acid compound is 3- acetamidophenylboronic acid.

14. The stabilised reagent of any one of claims 11 to 13, wherein the reagent further comprises a preserving agent.

15. The stabilised reagent of any one of claims 11 to 14, wherein the immunologically active compound is myoglobin.

16. The stabilised reagent of any one of claims 11 to 14, wherein the immunologically active compound is a peroxidase. 30

17. The stabilised reagent of claim 16, wherein the peroxidase is horseradish peroxidase.

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18. The stabilised reagent of claim 16 or claim 17, wherein the peroxidase is conjugated to an active molecule.

19. The stabilised reagent of claim 18, wherein the active molecule is selected from the 5 group consisting of. an antibody or a fragment thereof, an antigen; a hapten; a protein; a glycoprotein; a protein mimetic; a nucleic acid sequence; a steroid; a hormone; or a derivative of any of the foregoing.

20. The stabilised reagent of any one of claims 11 to 19, wherein the aryl boronic acid compound and the immunologically active compound having peroxidase activity are present together in an aqueous solution.

21. The stabilised reagent of claim 20, wherein the aryl boronic acid compound is present in an amount that is from 0.0 1 percent to 0. 5 percent, preferably about 0. 1 percent, by weight per volume.