GB2265459A - Chemiluminescent enhancers comprising organoboron compounds - Google Patents

Abstract

A method of increasing the light output and/or signal: background ratio of light output from a chemiluminescent reaction of a dihydrophthalazinedione (DPD), a peroxidase enzyme catalyst and an oxidant, by carrying out this reaction in the presence of an enhancer, "signal" being in the presence of the peroxidase, "background" in its absence, characterised in that the enhancer includes compounds of formula (I> <IMAGE> in which R, W, X, Y and Z have the following meanings; R is selected from hydrogen, n-butyl, O,O-propylene (a cyclic ether), 4'-chlorophenyl and 3',5'-dichlorophenyl, W is selected from hydrogen, hydroxy, methyl, methoxy and chloro, X is selected from hydrogen, methyl, chloro, amino and nitro, Y is selected from hydrogen, methyl, carboxy, chloro, bromo, iodo, phenyl, phenoxy, 4'-chloroanilino, 4'-boronylphenyl, 4'- bromophenyl, 2'-carboxyethenyl and trimethylsily, Z is selected from hydrogen, 5-chloro, 5-bromo, 5-(3'- trifluoromethyl)phenylazo, or 6-chloro, W and X together may represent a fused benzene ring and X and Y together may represent a fused benzene ring substituted by hydroxy in the 6 position of the naphthalene ring numbering, provided that when R is hydrogen, W, X, Y, Z are each separately hydrogen; when R W, X and Z are each hydrogen Y is selected from iodo, bromo, chloro, trimethylsily, phenoxy, phenyl, 4- chloroanilino, methyl, 4'-boronylphenyl, 2'-carboxyethenyl; when Y is hydrogen and the Rs together represent O,O-propylene (a cyclic ether), X is hydrogen; when R, W and Z are each hydrogen, X and Y together represent a fused benzene ring substituted by hydroxy in the 6-position of the naphthalene ring numbering; when W, X and Z are each hydrogen, R is n-butyl and Y is bromo or 4'-bromophenyl; when W, X and Z are each hydrogen, R is 4'-chlorophenyl and Y is chloro; when W and Y are each hydrogen, R is 3',5'-dichlorophenyl, Y is chloro and Z is 5-chloro; when W is methoxy, Z is 5-bromo; when W is hydroxy, Z is 5-(3'-trifluoromethyl)phenylazo; when W is chloro, X is chloro; when Y is chloro, X is nitro or chloro; when Y is carboxy, X is nitro; when W and Y are each chloro and X is amino, Z is 6-chloro; and the compounds bis(catechol)borate, boroglycine, pentaerythritol borate, 4-(3'-borono-4'-hydroxyphenylazo)benzoic acid, diphenylisobutoxyborane, diphenylboronic anhydride, dimethylphenylboronic acid (substitution pattern not established) and the sodium salt of 3-nitrophenylboronic acid.

Description

CHEMILUMINESCENT ENHANCERS Background of the invention 1. Field of the invention The present invention relates to an enhanced chemiluminescent reaction especially for use in a diagnostic assay, particularly immunoassay, and to a diagnostic kit for use in the assay. A chemiluminescent reaction is a chemical reaction which results in the emission of light. The luminescent emission is generally of sufficient duration to enable the light emitted to be detected or measured, and thereby to allow the detection or quantification of an analyte. The chemiluminescent reaction with which this invention is concerned is that between a 2,3-dihydro-1,4-phthalazinedione (DPD), especially luminol, with an oxidant, especially hydrogen peroxide, and a peroxidase enzyme, especially horseradish peroxidase, which catalyses the oxidation of the DPD by the oxidant.The oxidation is accompanied by emission of light.

2. Description of the prior art Luminescent assays making use of the above-mentioned peroxidase-catalysed oxidation of a DPD include several types.

This invention is concerned primarily with those in which the presence or amount of peroxidase is determined. It includes predominantly assays wherein horseradish peroxidase is conjugated to a ligand in order to label it and a luminescent reaction is used to detect or quantitate the label. This category includes ELISAs, competitive EIAs and nucleic acid hybridization assays, based on peroxidase labels. However, assays for measurement of free peroxidase, e.g. for analytical purposes, are also included.

A review of luminescent assays has been published by L. J. Kricka, Clinical Chemistry 37, 1472-1481 (1991).

The sensitivity of the peroxidase-catalysed chemiluminescent oxidation of DPDs can be enhanced by including in the reagents an enhancer, namely a 6-hydroxybenzothiazole (European Patent No. 87959B), a phenol selected from a narrowly defined-class (European Patent No. 1164548 or U.S. Patent No. 4,598,044), or an aromatic amine selected from a narrowly defined class (U.K. Patent No. 21629468 or U.S. Patent No. 4,729,950).

A further class of substituted phenols that enhance chemiluminescent reactions of this type are phenols substituted in ortho and/or para positions by imidazolyl or benzimidazolyl (U.K. Patent No. 2205945B, European Patent No. 2967528). These patents are owned by National Research Development Corporation.

European Patent Application Publication No. 219352A (Minnesota Mining and Mfg. Co.) describes various aromatic amines, including some of those previously mentioned in U.K. Application 2162946A, as enhancers. It is an object of the invention to extend the range of effective enhancers. This is a difficult task because no theory or mechanism has been published to explain how one should attempt to -select candidate compounds to try as enhancers. For the purposes of the present application the term "enhancer" and related terms will be used to include compounds that increase the total light output and/or the signal:background ratio of a chemiluminescent assay,. at at least one concentration of compound.

Summarv of the invention It has now been found that certain organoboron compounds are effective enhancers of chemiluminescence in a reaction between a dihydrophthalazinedione (DPD), a peroxidase enzyme catalyst and an oxidant. The enhancers of the present invention include compounds of formula (I)

in which R, W, X, Y and Z have the following meanings;; R is selected from hydrogen, n-butyl, 0,0-propylene (a cyclic ether), 4'-chlorophenyl and 3',5'-dichlorophenyl, W is selected from hydrogen, hydroxy, methyl, methoxy and chloro, X is selected from hydrogen, methyl, chloro, amino and nitro, Y is selected from hydrogen, methyl, carboxy, chloro, bromo, iodo, phenyl, phenoxy, 4'-chloroanilino, 4'-boronylphenyl, 4'-bromophenyl, 2'-carboxyethenyl and trimethylsilyl, Z is selected from hydrogen, 5-chloro, 5-bromo, 5-(3'-trifluoromethyl)phenylazo, or 6-chloro, W and X together may represent a fused benzene ring and X and Y together may represent a fused benzene ring substituted by hydroxy in the 6 position of the naphthalene ring numbering, provided that when R is hydrogen, W, X, Y, Z are each separately hydrogen; when R, W, X and Z are each hydrogen Y is selected from iodo, bromo, chloro, trimethylsilyl, phenoxy, phenyl, 4'-chloroanilino, methyl, 4'-boronylphenyl, 2'-carboxyethenyl; when Y is hydrogen and the Rs together represent 0,0-propylene (a cyclic ether), X is hydrogen; when R, W and Z are each hydrogen, X and Y together represent a fused benzene ring substituted by hydroxy in the 6-position of the naphthalene ring numbering; when W, X and Z are each hydrogen, R is n-butyl and Y is bromo or 4'-bromophenyl; when W, X and Z are each hydrogen, R is 4'-chlorophenyl and Y is chloro; when W and Y are each hydrogen, R is 3',5'-dichlorophenyl, Y is chloro and Z is 5-chloro; when W is methoxy, Z is 5-bromo; when W is hydroxy, Z is 5-(3'-trifluoromethyl)phenylazo; when W is chloro, X is chloro; when Y is chloro, X is nitro or chloro; when Y is carboxy, X is nitro; when W and Y are each chloro and X is amino, Z is 6-chloro; and the compounds bis(catechol)borate, boroglycine, pentaerythritol borate, 4-(3'-borono-4'-hydroxyphenylazo)benzoic acid, diphenylisobutoxyborane, diphenylboronic anhydride, dimethylphenylboronic acid (substitution pattern not established).

Of the compounds listed above those with 0-alkyl groups may undergo spontaneous hydrolysis, e.g. diphenylisobutoxyborane, 4-(4'-bromophenyl)phenyl-di-n-butoxyborane or 4-bromophenyl-din-butoxyborane. Others containing the structure (Aryl-0)2-B- Aryl may also undergo spontaneous hydrolysis, e.g. di(3',5'-dichlorophenoxy)-3,5-dichlorophenylborane or 4-chlorophenyl-di (4'-chlorophenoxy)borane.

The enhancers of the present invention that fall into formula (I) may be easily looked at by means of the table below in which H is hydrogen and the key to the compound reference numbers is present in the Examples.

TABLE R W X Y Z 5001 H H H bromo H 5003 H H amino H H 5004 H H H H H 5006 H H H iodo H 5007 H H H 2'-carboxyethenyl H 1001 H H H trimethylsilyl H 1003 H methoxy H H 5-bromo 1005 H hydroxy H H 5-(3'trifluoro methyl )phenylazo 1009 H methyl H H H 1010 H H H phenoxy H 1011 H H H phenyl H 1012 O,O-propylene H H H H 1013 1015, 1017, 1018, 1019 and 1048 named compounds

R W X Y Z 1021 H H nitro chloro H 1022 H chloro chloro H H 1024 H H chloro chloro H 1026 H chloro amino chloro 6-chloro 1028 H H chloro H H 1029 H H H chloro H 1030 H H nitro H H 1033 H H H 4'-chloroanilino H 1034 H H H methyl H 1037 H H H 4'-boronyl- H phenyl 1038 n-butyl H H 4'-bromo H phenyl 1040 3',5'-dichloro- H chloro H 5-chloro phenyl 1041 4'-chlorophenyl H H chloro H 1044 n-butyl H H bromo H 1045 H H nitro carboxy H . ~ . 1006 fused benzene, hydroxy substituted in 6 position of naphthalene ring 1002 fused benzen'e

While the invention applies to increasing the light output and/or the signal:background ratio from any chemiluminescent reaction involving the above-stated reaction partners, for any purpose, it is primarily of interest in connection with an assay.

The term "assay" herein covers detection, semi- quantitation and quantitation. Typically, the assay is carried out so that the light output is relatable to the amount of peroxidase employed, the peroxidase then being the substance directly determined. The ratio of light output when peroxidase is present in the sample to light output when it is absent becomes important in assuring the sensitivity of the assay. This is conveniently termed a "signal to background" ratio. Similarly, if the substance to be determined is another of the reaction partners, the "signal" denotes the presence of the- substance to be determined, the "background" its absence.

Although the invention is usable to determine the presence or amount of any one of the four above-stated reaction partners, such a reaction partner is not necessarily itself the substance to be assayed. Thus, the oxidant can be produced as a result of an earlier reaction or cascade of earlier reactions carried out on a sample. The peroxidase or the luminol can be in the form of a conjugate to, say, an antibody which is used in an immunoassay to determine an antigen.The invention is accordingly applicable to any method of diagnostic assay of a substance, the presence or amount of which is relatable to the presence or amount of a reaction partner selected from the group consisting of a DPD, a peroxidase enzyme an oxidant and an enhancer which together are reactable in -a chemiluminescent reaction and wherein the reaction is carried out, the light output is detected or measured and thence the presence or amount of the substance to be assayed is related to the light output.

The invention also includes a kit for use in the assay comprising the DPD, the peroxidase and the enhancer. -The oxidant could be supplied separately or included in the kit.

Brief description of the drawings The Figure shows the structure of some of the enhancers of the present invention.

Description of the preferred embodiments The enhancers of the present invention include 4-iodophenylboronic acid (PIBA), 4-bromophenylboronic acid (PBBA), 4-chlorophenylboronic acid, 3-chlorophenylboronic acid, 3,4-dichlorophenylboronic acid, 2,3-dichlorophenylboronic acid, 5-bromo-2methoxybenzeneboronic acid, 3-nitrophenylboronic acid, 4-chloro 3-nitrophenylboronic acid, 3-aminophenylboronic acid, 3-amino2,4,6-trichlorophenylboronic acid, 4-(2'-carboxyethenyl)phenylboronic acid, l-naphthaleneboronic acid, 6-hydroxy-2-naphthaleneboronic acid, phenylboronic acid, 2-methylphenylboronic acid, 4-methylphenylboronic acid, dimethyl-phenylboronic acid, 4-bromophenyl-di-n-butoxyborane, 4-carboxy-3-nitrophenylboronic acid, 4-(trimethylsilyl)benzeneboronic acid, 4-biphenylboronic acid, 4-(phenoxy)benzeneboronic acid, 4-(3'-borono-4'-hydroxyphenylazo)benzoic acid, diphenylisobutoxyborane, 4-(4'chloroanilino)phenylboronic acid, 4,4'-bis(phenylboronic acid), 4-(4'-bromophenyl)phenyl-di-n-butoxyborane, di(3',5'-dichloro phenoxy)-3,5-di chlorophenyl borane, 4-chlorophenyl-di-(4'-chlorophenoxy)borane, pentaerythritol borate, boroglycine, 2-phenyl1,3,2-dioxaborinane, bis(catechol)borate and 2-hydroxy-5-(3' trifluoromethyl)-phenylazo)benzene boronic acid and diphenylboronic anhydri de.

The preferred enhancers are PIBA, PBBA, 4-biphenylboronic acid, 4-(trimethylsilyl)-benzeneboronic acid, boroglycine, 2-hydroxy-5-(3'-(trifluoromethyl)phenylazo)benzeneboronic acid, 4-chloro-3-nitrophenylboronic acid, 4-chlorophenylboronic acid, 4-(2'-carboxyethenyl)phenylboronic acid, 4-(4'-bromophenyl)phenyldi-n-butoxyborane, 4-chlorophenyl-di-(4'-chlorophenoxy)borane, 4-4'-bis(phenylboronic acid), diphenylboronic anhydride, 4-chloro ani linophenylboronic acid and - 4-bromophenyl-di-n-butoxyborane as they increase light output as well as reducing the background luminescence. The remaining enhancers exert their effect primarily by reducing the background luminescence, and thereby improving the signal:background ratio.

The structure of some of these compounds are shown in the accompanying Figure. The reference numbers are explained in the Examples.

The improvement in signal:background ratio is of importance in controlling the sensitivity of chemiluminescent assays. The enhancers of the present invention are therefore of particular use in those situations where a high degree of sensitivity is required, for example in blotting assays. Thus the present invention is of especial use in blotting assays including Western, Southern and Northern blotting assays, as well as dot blots and other nucleic acid hybridisation assays.

The best results are obtained at higher pH. Preferably the pH is in the range 7.5 to 9 at the time of mixing all the reagents.

Any chemiluminescent DPD can be used in the invention, that is to say any DPD which is oxidisable in the presence of a peroxidase catalyst by an added oxidant to give chemiluminescence can be used. Examples are luminol, isoluminol, ABEI and AHEI, and 7-dimethylaminonaphthalene-l ,2-dicarboxylic acid hydrazide, of which luminol is normally preferred. The DPD can be free or conjugated to a ligand to provide a direct label. Such luminophore-labelled assays are known in the art.

The oxidant can be any added substance (not oxygen itself) which oxidises the DPD in a light-emitting reaction; hydrogen peroxide is usual, but a perborate, such as the sodium salt, is an alternative.

The peroxidase enzyme will normally be HRP and of a grade appropriate to use in luminescent assays. Preferably the HRP is a basic isoenzyme, for example of Sigma Type VIA or IX. It can be free or conjugated to a ligand.

The concentrations of the reaction partners of the chemiluminescent reaction wil-l depend on the nature of the assay being carried out and particularly on which of them is being assayed. Generally stated, the light output is greater, the greater the concentration of DPD. Thus, when peroxidase or oxidant is being assayed, the use of excess DPD is recommended.

Generally stated, the DPD concentration is desirably from 0.5 micromole to 200 millimoles per litre, preferably 0.5 to 100 mi cromol es/litre. Generally stated, the oxidant concentration is desirably in the range 0.5 micromoles to 300 millimoles/ litre, preferably 10 to 200 millimoles/litre.

The concentration of peroxidase is of interest if peroxidase is not the reaction partner being assayed. Excess peroxidase does not normally have a marked effect on light intensity, the peroxidase being a catalyst which is recycled. Where luminol or the oxidant is being assayed, therefore, the peroxidase need only be present in a modest concentration, such as 0.01 microgram to 5000 mg./litre, preferably not more than 50 mg./litre, but depending on the activity of the peroxidase per gram.

The concentration of the enhancer will usually be in the range 0.01 micromole to 4 moles/litre, preferably 10 micromoles to 100 millimoles/litre. It is believed that the enhancer or a species or derivative thereof competes with the DPD in the reaction and it is therefore desirable to use a considerable excess of DPD relative to the enhancer, preferably between 2 and 20 times the molar concentration of the enhancer.

In brief, all conditions and features of the chemiluminescent reactions, the reaction partners thereof, applications of the assay and so on (except where inconsistent with the above description) can be as set forth in European Patent No. 116454B, the disclosure of which in relation thereto is herein incorporated by reference.

The following Examples illustrate the invention. In the Examples, compounds of series 5000 are obtainable from the stated sources, compounds of series 1000 are identified by means of their Chemical Abstracts Registry Number and others are obtainable from US Borax Research Corporation, 412 Crescent Nay, Anaheim, California 92901-9794.

EXAMPLE 1 This Example shows that para-bromophenylboronic acid (PBBA) enhances a chemiluminescent reaction between luminol (LU) horseradish peroxidase (HRP), and H202 giving a high signal: background ratio.

1. Effect of PBBA (Compound 5001) on the siqnal:backsround ratio of a chemiluminescent reaction PBBA was added in various concentrations (range 0.05pg to 0.5pug) to a luminol-H202 reaction in the presence and absence of HRP. The luminol-hydrogen peroxide reagent was prepared as follows: sodium luminol (12.5mg) was dissolved in 50ml of Tris buffer (O.lmol/l, pH 8.6), and 15.5}it of hydrogen peroxide (30% w/v) was mixed with 0.5m1 of Tris buffer (O.lmol/l, pH 8.6).

These two solutions were combined and protected from light. The luminol-hydrogen peroxide reagent (100p1 of a 1:10 dilution) was added to a cuvette together with either 10all1 of HRP Type VI A (HRP, Sigma Chemical Co., 1:50,000 dilution) or as a control 10p1 of Tris Buffer (O.lmol/l, pH 8.6), and various amounts of PBBA (Aldrich Chemical Co.), range 0.05pg-0.5pg in O.lmol/l Tris, pH 8.6). The reagents were mixed and the light emission recorded after 5 minutes on a Berthold Biolumat LB9500C.

This experiment was repeated, replacing the luminol with isoluminol. The measured light output and signal:background ratios are shown in Table 1. Column (a) shows that PBBA enhances the light emission in the luminol-HRP-peroxidase reaction. Column (b) shows that addition of PBBA reduces the background level of luminescence. Columns (d) and (e) show a similar effect with isoluminol.

TABLE 1 Lumi nol Isol umi nol (a) (b) (c) (d) (e) (f) Signal Signal Signal: Signal Signal Signal: PBBA (with (no Background (with (no Background (pig) HRP) HRP) ratio HRP) HRP) ratio 0 87,616 18,833 4.7 14,485 7927 1.8 0.05 101,227 16,556 6.1 15,772 7664 2.1 0.1 108,213 16,065 6.7 16,553 6114 2.7 0.2 112,644 13,890 8.1 68,282 5736 11.9 0.3 122,116 10,899 11.2 619,880 5613 110.4 0.4 133,401 10,706 12.5 775,965 5278 147.0 0.5 151,572 8,963 16.9 2. Effect of PBBA on the light output of a chemiluminescent reaction The above experiment was repeated this time keeping the amount of PBBA enhancer fixed and varying the amount of HRP.

The reagents used were 100p1 of luminol-hydrogen peroxide, either (a) 40p1 of PBBA (O.Olmg/ml in O.lmol/l Tris buffer, pH 8.6) or (b) as a control, 40p1 of Tris buffer (O.lmol/l, pH 8.6) and various amounts of HRP (range 5p1 to 40p1 of 1:50,000 dilution of a lmg/ml stock solution).

The reagents were mixed and light output recorded after 5 minutes on a Berthold Biolumat LB9500C. The measured signal (light output) and signal:background ratios are shown in Table 2. By comparing columns (a) and (b) it can be seen that PBBA increased the light output of the chemiluminescent reaction at all concentrations tested. An improved signal:background ratio is shown by comparing results with HRP present with the zero HRP results.

TABLE 2 (a) (b) Signal Signal: Signal Signal: HRP (with Background (no Background (pg) PBBA) Ratio PBBA) Ratio 0 9,125 13,405 100 15,861 1.7 15,148 1.1 200 22,895 2.5 19,384 1.4 400 38,495 4.2 25,968 1.9 600 61,491 6.7 33,964 2.5 800 105,972 11.6 34,790 2.6 EXAMPLE 2 Effect of organoboron compounds on a chemiluminescent reaction A solution of 2,4-dichlorophenylboronic acid (5002) (lmg/ml, Lancaster Synthesis Inc., Windham, NH) was prepared as follows: 5mg 2,4-dichlorophenylboronic acid was dissolved in 50p1 of DMSO, then added to 4950p1 of Tris buffer (O.lmol/l, pH 8.6).

Solutions of 3-aminophenylboronic acid (5003) (lmg/ml, Sigma), 3-nitro-phenylboronic acid (lmg/ml, Aldrich), phenylboronic acid (5004) (lmg/ml, Aldrich) and butaneborinic acid (5005) (lmg/ml, Sigma) were prepared in Tris buffer (O.lmol/l, pH 8.6). The stock solution of HRP Type VIA (lmg/ml) and luminol-hydrogen peroxide reagent were prepared as described previously.

Luminol-hydrogen peroxide (100p1, 1:10 dilution) was mixed with either 10U1 of HRP (1:50,000 dilution) or, 10p1 of Tris buffer (O.lmol/l, pH 8.6). The light emission was measured in a Berthold Biolumat LB9500C, and then 5p1 of 2,4-dichlorophenylboronic acid was added and the light emission was remeasured. A control without any test compound was run in parallel.

The above experiment was repeated except that 2,4-dichlorophenylboronic acid was replaced by 3-aminophenylboronic acid (spy), 3-nitrophenylboronic acid (5111), , phenylboronic acid (5U1), or butaneborinic acid (40p1).

The measured light output and signal:background ratios are shown in Table 3 for each compound tested and its con-trol. The control consisted of buffer in place of the compound under test as an enhancer. None of the compounds tested increased the light emission from the HRP catalyzed oxidation of luminol.

However, the signal to background ratio was improved in the case of 3-nitrophenylboronic acid, phenylboronic acid, and 3-aminophenylboronic acid as compared to their control values. This was due to the reduction in the background light emission from the luminol-peroxide reagent caused by these compounds. Thus, these three compounds are of use in the--present invention. 2-4dichlorophenylboronic acid and butane boronic acid are not of use as they neither increased the light output or the signal: background ratio. The small increase in light output observed for butaneborinic acid is not significantly relevant to be of use in the present invention.

TABLE 3 Signal Signal Signal: (with (no Background HRP HRP Ratio 2,4-dichlorophenyl- control 271,566 20,990 12.9 boronic acid (5002) test 128,274 16,246 7.9 3-nitrophenyl- control 175,440 25,196 6.9 boronic acid test 132,887 16,400 8.1 phenylboronic acid control 156,658 26,564 5.9 (5004) test 54,554 5,601 9.7 3-aminophenyl- control 249,204 19,615 12.7 boronic acid (5003) test 60,222 1,038 58.0 butaneborinic acid control 64,652 39,640 1.6 (5005) test 65,197 54,389 1.2 EXAMPLE 3 Screening of further organoboron compounds The stock solution of HRP Type VIA (lmg/m1) and luminolhydrogen peroxide were prepared as described above. 101 test compound of varying concentration (O.Ol-lmg/ml) was added to luminol-hydrogen peroxide (100y 1: :10 dilution). 10U1 HRP Type VIA or as a control 10p1 Tris buffer was added. The light emission was measured on a Berthold Biolumat LB9500C.

The following test compounds were all screened in this manner, Chemical Abstracts Registry Numbers are in brackets: 1001 4-(trimethylsilyl) benzeneboronic acid (17865-11-1) 1002 l-naphthaleneboronic acid (31093-44-4) 1003 5-bromo-2-methoxybenzeneboronic acid (84694-45-1) 1004 2-biphenylboronic acid (4688-76-0) 1005 2-hydroxy-5-(3'-(trifluoromethyl)-phenylazo)benzene boronic acid 1006 6-hydroxy-2-naphthalene boronic acid 1007 l-thianthreneboronic acid (108847-76-3) 1008 4-dibenzofuranboronic acid (100124-06-9) 1009 2-tolueneboronic acid (16419-60-6) 1010 4-(phenoxy)benzeneboronic acid (109412-50-2) 1011 4-biphenylboronic acid (5122-94-1) 1012 2-phenyl-1,3,2-dioxaborinane (4406-77-3) 1013 bis(catechol)borate 1014 boraxarophenanthrene 1015 boroglycine 1016 tetraphenylboron sodium (143-66-8) 1017 pentaerythritol borate 1018 4-(3'-borono-4'-hydroxyphenylazo)benzoic acid 1019 diphenyl isobutoxyborane (23147-97-9) 1020 2,4,6-trichlorophenylboronic acid (73852-18-3) 1021 4-chloro-3-nitrophenylboronic acid 1022 2,3-dichlorophenylboronic acid 1023 2,5-dichlorophenylboronic acid (135145-90-3) 1024 3,4-dichlorophenylboronic acid 1025 3,5-dichlorophenylboronic acid (67492-50-6) 1026 3-amino-2,4,6-trichlorophenylboronic acid 1027 2-chlorophenylboronic acid 1028 3-chlorophenylboronic acid (63503-60-6) 1029 4-chlorophenylboronic acid (1679-18-1) 1030 3-nitrophenylboronic acid (13331-27-6) 1031 3-chloroacetylaminophenylboronic acid 1032 3-(2'-methylbutylamino)phenylboronic acid 1033 4-(4'-chloroanilino)phenylboronic acid 1034 4-methylphenylboronic acid (5720-05-8) 1035 1,4-phenyldiboronic acid 1036 dimethylphenylboronic acid (position of methyl groups not established) 1037 4,4'-bis(phenylboronic acid) (4151-80-8) 1038 4-(4'-bromophenyl )phenyl-di-n-butoxyborane 1039 di-(3',4',6'-trichlorophenoxy)-3,4,6-trichlorophenyl- borane 1040 di-(3' ,5'-dichlorophenoxy)-3,5-dichlorophenylborane 1041 4-chlorophenyl-di-(4'-chlorophenoxy)borane 1042 3-nitrophenylboronic acid, sodium salt 1043 3-nitrophenylboronic acid, calcium salt 1044 4-bromophenyl-di-n-butoxyborane 1045 4-carboxy-3-ni trophenyl boroni c acid 1046 2-benzimidazolylphenylboronic acid (58534-74-0) 1047 di-(l-naphthoxy)-l-naphthylborane 1048 diphenylboronic anhydride 1049 2-boromethylphenyl-di-(2'-boromethylphenoxy)borane 1050 2-(methylthiomethyl)phenylboronic acid 1051 methyl-(2-tolylboronic acid)sulfoxide In Table 4, column (a) shows whether the test compound lowered the light output from the luminol-hydrogen peroxide solution (Y = yes, N = no). Column (b) shows whether the signal obtained after adding the HRP was greater in the presence of the test compound than in its absence, (Y = yes, N = no). A compound showing Y in column (b) is of preferred use in the present invention as it increases the light output of the reaction. Column (c) shows whether there was an increase in the signal:background ratio by over 25% of the control value (Y = yes, N = no), column (d) shows the actual calculated value of the signal:background ratio (value of column (b)/value of column (a)). Column (c) is a simplified representation of the results in column (d). Signal:background ratio is the ratio of light output in the presence and absence of HRP with the test compound being present.

All compounds increasing the signal:background ratio by over 25% of at least one concentration (Y in column (c)) are of use in the present invention. Those compounds that increase the light output (Y in column (b)) as well as increasing the signal:background ratio (Y in column (c)) are of especial use in the present invention. Thus, compounds 1001, 1002, 1003, 1005, 1006, 1009, 1010, 1011, 1012, 1013, 1015, 1017, 1018, 1019, 1021, 1022, 1024, 1026, 1028, 1029, 1030, 1033, 1034, 1036, 1037, 1038, 1040, 1041, 1044, 1045 and 1048 are of use in increasing the signal:background ratio of a chemiluminescent reaction. Of these, compounds 1001, 1005, 1011, 1015, 1021, 1029, 1033, 1037, 1038, 1041, 1044 and 1048 also increase the light output and are therefore of especial use in the present invention.

TABLE 4 (a) (b) (c) (d) Compound mg/ml Decrease in Increase Increase Signal: background in signal in signal: Background: (without HRP (with HRP, background ratio with test with test ratio (control = cpd.) cpd.) with no enhancer) 1001 1 Y N Y 10.9 (2.1) 0.1 Y Y Y 6.7 0.01 Y Y Y 3.2 1002 1 Y N N 0.7 (2.3) 0.1 Y N Y 3.4 0.01 Y N N 2.5 1003 1 Y N N 2.6 (2.3) 0.1 Y N Y 12.1 0.01 Y N Y 8.6 1004 1 Y N N 1.7 (2.3) 0.1 Y N N 2.2 0.01 Y N N 1.9 1005 1 Y N N 2.4 (2.1) 0.1 N Y Y 2.9 0.01 N Y Y 2.7 1006 1 Y N N 0.3 (1.8) 0.1 Y N N 1.5 0.01 Y N Y 5.8 1007 1 Y N N 1.8 (2.1) 0.1 Y N N 2.5 0.01 Y N N 2.1 1008 1 Y N N 1.3 (2.5) 0.1 Y N N 1.5 0.01 Y N N 1.6 1009 1 Y N N 0.6 (1.8) 0.1 Y N Y 2.5 0.01 Y N N 1.9 1010 1 Y N Y 5.0 (2.5) 0.1 Y N Y 4.6 0.01 Y N N 3.0 (a) (b) (c) (d) 1011 1 Y Y Y 48.7 (2.5) 0.1 Y Y Y > 125 0.01 Y Y Y > 125 1012 1 Y N Y 17.1 (2.5) 0.1 N N N 2.2 0.01 N Y N 2.2 1013 1 Y N N 1.2 (1.8) 0.1 Y N Y 3.1 0.01 Y N Y 12.6 1014 1 Y N N 1.8 (2.5) 0.1 Y N N 1.6 0.01 Y N N 2.3 1015 1 Y N Y 3.1 (2.1) 0.1 Y Y Y 2.9 0.01 Y Y N 2.3 1016 1 Y N N 2.3 (1.9) 0.1 Y N N 2.0 0.01 Y N N 2.0 1017 1 Y N N 1.8 (1.8) 0.1 Y Y Y 2.5 0.01 Y N N 1.8 1018 1 Y N Y 4.2 (1.9) 0.1 Y N Y 24.5 0.01 Y N Y 5.0 1019 1 Y N N 0.1 Y N N 3.0 (2.9) 0.01 Y N Y 3.2 (2.0) 1020 1 Y N N 0.1 Y N N 0.01 Y N N 2.2 (2.0) 1021 1 Y Y Y 247.9 (4.5) 0.1 Y Y Y 44.5 (2.8) 0.01 Y Y Y 2.3 (1.8) 1022 1 Y N N 0.1 Y N Y 3.6 (2.7) 0.01 Y N N 2.2 (2.0) (a) (b) (c) (d) 1023 1 Y N N 0.1 Y N N 3.1 (2.7) 0.01 Y N N 1024 1 Y N Y 7.6 (4.5) 0.1 Y Y Y 5.4 (2.8) 0.01 Y N N 1025 1 Y N N 0.1 Y N N 0.01 Y N N 2.1 (2.0) 1026 1 Y N Y 40.5 (4.5) 0.1 Y Y Y 72.4 (2.8) 0.01 Y N N 2.1 (2.0) 1027 1 Y N N 0.1 Y N N 3.2 (2.9) 0.01 Y N N 2.1 (2.0) 1028 1 Y N Y 20.0 (4.5) 0.1 Y Y Y 4.2 (2.9) 0.01 Y N N 1029 1 Y Y Y 1242.4(4.5) 0.1 Y Y Y 315.0 (2.8) 0.01 Y Y Y 6.0 (1.8) 1030 1 Y N Y 50.0 (4.5) 0.1 Y Y Y 12.5 (2.8) 0.01 Y N N 1031 1 Y N N 0.1 Y N N 3.3 (2.9) 0.01 Y N N 2.1 (2.0) 1032 1 Y N N 0.1 Y N N 3.4 (2.9) 0.01 Y N N 1033 1 Y Y Y 173.9 (4.5) 0.1 Y Y Y 67.7 (2.8) 0.01 Y Y Y 4.1 (1.8) 1034 1 Y N N 0.1 Y Y Y 41.2 (2.9) 0.01 Y N Y 3.6 (1.9) (a) (b) (c) (d) 1035 1 Y N N 0.1 Y N N 0.01 Y N N 2.1 (2.0) 1036 1 Y N N 0.1 Y N Y 7.6 (2.9) 0.01 Y N Y 2.6 (2.0) 1037 1 Y N N 0.1 Y Y Y 503.3 (2.9) 0.01 Y Y Y 35.5 (1.9) 1038 1 Y Y Y 903.8 (4.5) 0.1 Y Y Y 2118.5(2.9) 0.01 Y Y Y 442.2 (1.8) 1039 1 Y N N 0.1 Y N N 3.4 (2.9) 0.01 Y N N 1040 1 Y N Y 4.7 (4.5) 0.1 Y N Y 3.9 (2.9) 0.01 Y N N 1041 1 Y Y Y 2606.2(4.5) 0.1 Y Y Y 360.2 (2.8) 0.01 Y Y Y 6.3 (1.9) 1042 1 Y N N 5.2 (4.5) 0.1 Y N N 3.6 (2.9) 0.01 Y N N 2.3 (2.0) 1043 1 Y N N 0.1 Y N N 3.4 (2.9) 0.01 Y N N 1044 1 Y N Y 147.1 (4.5) 0.1 Y Y Y 623.1 (2.7) 0.01 Y Y Y 38.5 (1.9) 1045 1 Y N Y 68.5 (4.5) 0.1 Y Y Y 18.1 (2.8) 0.01 Y N N 2.2 (2.0) 1046 1 Y N N 0.1 Y N N 0.01 Y N N (a) (b) (c) (d) 1047 1 Y N N 0.1 Y N N 0.01 Y N N 1048 1 Y N Y 100.0 (4.5) 0.1 Y Y Y 139.0 (2.7) 0.01 Y Y Y 3.1 (1.8) 1049 1 Y N N 0.1 Y N N 3.2 (2.9) 0.01 Y N N 1050 1 Y N N 0.1 Y N N 3.3 (2.9) 0.01 Y N N 1051 1 Y N N 0.1 Y N N 0.01 Y N N EXAMPLE 4 Effect of different peroxidase enzvmes on the PBBA enhancement of a chemiluminescent reaction Stock solutions (lmg/ml in O.lmol/l Tris buffer, pH 8.6) of horseradish peroxidase Type VII, Type VIII and Arthromvces ramosus peroxidase (Sigma) were prepared.The luminol-hydrogen peroxide reagent was prepared as described previously. Luminolhydrogen peroxide reagent (100y 1:10 dilution), either 401 of PBBA (O.Olmg/ml in O.lmol/l Tris buffer, pH 8.6) or as a control, 401 of Tris buffer (O.lmol/l, pH 8.6), and 101 of HRP Type VII (1:50,000 dilution, 2ng) were added to a cuvette. The reagents were mixed and the light emission was recorded after 5 minutes using a Berthold Biolumat LB9500C.

The above experiment was repeated and the HRP Type VII was replaced by HRP Type VIII (2ng) or Arthromvces ramosus peroxide (20pg).

The measured light output and signal:background ratios are shown in Table 5. PBBA did not increase the level of light output with any of the peroxidases tested, but the signal to background ratio was improved in all cases due to the background reduction caused by PBBA.

TABLE 5 Signal Signal: Signal Signal: Reagent Background Reagent Background with no PBBA PBBA Blank 27,820 58,759 HRP Type VII 49,703 1.8 77,694 1.3 HRP Type VIII 156,204 5.6 280,472 4.8 Arthromvces rasmosus 58,208 2.1 84,071 1.4 EXAMPLE 5 Assav of peroxidase-antibodv conjuaate utilizing PBBA Anti-mouse IgG (whole molecule) peroxidase conjugate (Sigma Chemical Co.) was diluted (1:5000) in 0.1 mol/l Tris buffer (pH 8.6). The luminol-hydrogen peroxide was prepared as described previously.The following reagents were added to a cuvette: 100111 of luminol-hydrogen peroxide (1:10 dilution), either 401 of PBBA (0.01 mg/ml in 0.1 mol/l Tris buffer) or as a control, 40p1 of Tris buffer (0.1 mol/l, pH 8.6), and different amounts of anti-mouse IgG (5111, 10111, 20p1, 30p1, 40111). The reagents were mixed and the light emission was measured using a Berthold Biolumat LB9500C.

The results are shown in Table 6. In the presence of PBBA the light emission was increased and the signal to background ratio for the assay of the HRP conjugate was significantly improved.

TABLE 6 Anti-mouse Signal Signal: Signal Signal: IgG-HRP with Background no PBBA Background (ml) PBBA 0 18,832 23,112 5 27,665 1.5 17,858 0.8 10 32,849 1.7 27,458 1.2 20 68,994 3.7 29,850 1.3 30 407,087 21.6 32,417 1.4 EXAMPLE 6 Enhanced chemiluminescent anti-oxidant assav using PBBA The luminol-peroxide reagent (100p1), PBBA (40U1, 1:100 dilution of 1 mg/ml) and HRP (10111, 1:50,000 dilution of lmg/ml stock) were mixed together and the light emission measured for 25 minutes. A sample of human serum (2p1, 1:10 dilution in 0.1 mol/l Tris buffer, pH 8.6) was added and the light emission measured for a further 75 minutes.

Table 7 shows that addition of serum quenched the light emission and that after a 34 minute lag the light emission returns to its original level.

TABLE 7 Time (minutes) Light units Time (minutes) Light units 0 5 50 5 10 16 60 15 20 68 70 49 (serum added) + 25 88 80 60 26 3 90 81 30 3 100 90 EXAMPLE 7 Effect of para-iodophenvlboronic acid (PIBA) (5006) as an enhancer of a chemiluminescent reaction The experiment of Example 1 was repeated using PIBA in place of PBBA. Various dilutions of PIBA (Cookson Chemicals Ltd., Southampton, UK, lmg/ml stock in DMSO) in Tris buffer were used. Table 8 shows the effect PIBA has on the signal:background ratio of a chemiluminescent reaction measured after 1 minute.

TABLE 8 4-Iodophenylboronic acid (PIBA) enhancement of the HRP-luminol-peroxide reaction PIBA Light emission at 1 minute Signal:Background 11g Background Signal Ratio 0 15,016 91,665 6.1 0.01 12,862 78,419 6.1 0.1 13,221 74,487 7.1 1 10,282 324,312 31.5 10 5,517 540,760 98 20 3,837 135,065 35.2 EXAMPLE 8 Use of an oraanoboron enhancer in a chemiluminescent assav for a) peroxide and b) luminol a) Effect of 4-biphenYlboronic acid on a chemiluminescent assav for peroxide The assay reagent consisted of the following reagents: 101 4-biphenylboronic acid (1:20 dilution of a lmg/ml stock in DMSO), 101 horseradish peroxidase (1::500,000 dilution of a lmg/ml stock Type VIA in 0.1 mol/l Tris buffer pH 8.6) and 100111 luminol (0.025 g/l in 0.1 mol/l Tris buffer pH 8.6). These were mixed together and the light emission measured. A 10p1 sample of a hydrogen peroxide solution (dilutions of a stock, 31111 30% w/v hydrogen peroxide/ml in Tris buffer) was added, the contents of the assay tube mixed and the light emission recorded. The results are summarised in Table 9.

From Table 9 it can be seen that there was a dose-dependent increase in light output up to 2.4moles of peroxide.

TABLE 9 Enhanced chemiluminescent assav for peroxide Hydrogen peroxide Light emission pmoles at 5 minutes 0 525 0.00024 659 0.0024 1,500 0.024 40,682 0.24 584,638 2.4 620,551 24 339,291 b) Effect of 4-biphenviboronic acid on a chemiluminescent assav for luminol The assay reagent consisted of the following reagents: 10p1 4-biphenylboronic acid (1:20 dilution of a lmg/ml stock in DMSO), 101 horseradish peroxidase (1:500,000 dilution of a lmg/ml stock Type VIA in 0.1 mol/l Tris buffer pH 8.6) and 100111 hydrogen peroxide solution (31111 30 /0 w/v hydrogen peroxide diluted in l00ml Tris buffer). These were mixed together and the light emission measured. A 101.11 sample of a luminol solution (dilutions of a 0.25g/l in 0.1 mol/l Tris buffer pH 8.6 stock) was added, the contents of the assay tube mixed and the light emission recorded. The results are summarised in Table 10.

From Table 10 it can be seen that there was a dose-dependent increase in light output at all concentrations of luminol tested.

TABLE 10 Enhanced chemiluminescent assav for luminol Luminol Light emission pmoles at 10 minutes 0 54 0.00125 145 0.0125 620 0.125 5,161 1.25 55,873 12.5 358,184 125 834,089 EXAMPLE 9 Effect of 4-(2-carboxyethenyl)phenylboronic acid (CPA) (5007) as an enhancer of a chemiluminescent reaction The experiment of Example 1 was repeated using CPA in place of PBBA. Various dilutions of CPA (Cookson Chemicals Ltd., Southampton, UK, 0.01-20 pg in 1 mg/ml Tris buffer, pH 8.6) were used. Table 11 shows the effect CPA had on the light output (signal) and signal to background ratio of a chemiluminescent reaction measured using an Amerlite mi cropl ate reader (Kodak Clinical Diagnostics, Amersham, UK).

TABLE 11 CPA Signal Signal Signal: (lug) (with HRP) (no HRP) Background ratio 0 0.37 0.088 4.2 0.01 0.41 0.094 4.4 0.02 0.46 0.09 5.1 0.05 0.68 0.09 7.6 0.1 1.23 0.09 14.2 0.2 2.37 0.08 28.2 0.5 4.57 0.07 63.4 1.0 5.58 0.06 93.0 10 2.49 0.02 124.9 20 0.88 0.003 43.9

Claims (15)

1. CLAIMS 1. A method of increasing the light output and/or signal: background ratio of light output from a chemiluminescent reaction of a dihydrophthalazinedione (DPD), a peroxidase enzyme catalyst and an oxidant, by carrying out this reaction in the presence of an enhancer, "signal" being in the presence of the peroxidase, "background" in its absence, characterised in that the enhancer includes compounds of formula (I)

   in which R, W, X, Y and Z have the following meanings;; R is selected from hydrogen, n-butyl, 0, O-propy lene (a cyclic ether), 4'-chlorophenyl and 3',5'-dichlorophenyl, W is selected from hydrogen, hydroxy, methyl, methoxy and chloro, X is selected from hydrogen, methyl, chloro, amino and nitro, Y is selected from hydrogen, methyl, carboxy, chloro, bromo, iodo, phenyl, phenoxy, 4'-chloroanilino, 4'-boronylphenyl, 4'-bromophenyl, 2'-carboxyethenyl and trimethylsilyl, Z is selected from hydrogen, 5-chloro, 5-bromo, 5-(3'-trifluoromethyl)phenylazo, or 6-chloro, W and X together may represent a fused benzene ring and X and Y together may represent a fused benzene ring substituted by hydroxy in the 6 position of the naphthalene ring numbering, provided that when R is hydrogen, W, X, Y,Z are each separately hydrogen; when R, W, X and Z are each hydrogen Y is selected from iodo, bromo, chloro, trimethylsilyl, phenoxy, phenyl ,- 4'-chloroanilino, methyl, 4'-boronylphenyl, 2'-carboxyethenyl; when Y is hydrogen and the Rs together represent O,O-propylene (a cyclic ether), X is hydrogen; when R,W and Z are each hydrogen, X and Y together represent a fused benzene ring substituted by hydroxy in the 6-position of the naphthalene ring numbering; when W, X and Z are each hydrogen, R is n-butyl and Y is bromo or 4'-bromophenyl; when W, X and Z are each hydrogen, R is 4-chlorophenyl and Y is chloro; when W and Y are each hydrogen, R is 3',5'-dichlorophenyl, Y is chloro and Z is 5-chloro; when W is methoxy, Z is 5-bromo; when W is hydroxy, z is 5-(3'-trifluoromethyl)phenylazo; when W is chloro, X is chloro; when Y is chloro, X is nitro or chloro; when Y is carboxy, X is nitro; when W and Y are each chloro and X is amino, Z is 6-chloro; and the compounds bis(catechol)borate, boroglycine, pentaerythritol borate, 4-(3'-borono-4'-hydroxyphenylazo)benzoic acid, diphenylisobutoxyborane, diphenylboronic anhydride, dimethylphenylboronic acid (substitution pattern not established) and the sodium salt of 3-nitrophenylboronic acid.
2. 2. A method according to Claim 1, characterised in that the enhancer is para-iodophenylboronic acid, para-bromophenylboronic acid, 4-bi-phenylboronic acid, 4-(trimethylsilyl)benzeneboronic acid, 2-hydroxy-5-(3'-(trifluoromethyl)phenylazo)benzeneboronic acid, boroglycine, 4-chloro-3-nitrophenylboronic acid, 4-chlorophenyl-boronic acid, 4-(2'-carboxyethenyl)phenylboronic acid, 4-(4'-bromophenyl )phenyl-di-n-butoxyborane, 4-chlorophenyl-di (4'-chlorophenoxy)borane, 4-4'-bis(phenylboronic acid), diphenylboronic anhydride, 4-chloroanilinophenylboronic acid or 4-bromo-phenyl-di-n-butoxyborane.
3. 3. A method according to any preceding claim wherein the peroxidase enzyme is free or conjugated to a ligand and the presence or amount of the peroxidase is determined from the presence or amount of light output.
4. 4. A method according to any preceding claim wherein the peroxidase is horseradish peroxidase.
5. 5. A method according to any preceding claim wherein the oxidant is hydrogen peroxide.
6. 6. A method according to any preceding claim wherein the DPD is luminol.
7. 7. A method according to any preceding claim wherein the chemiluminescent reaction is carried out at a pH of from 7.5 to 9.
8. 8. A method according to any preceding claim for use in diagnostic assay for peroxidase.
9. 9. A kit for use in diagnostic assay comprising in separate containers a chemiluminescent dihydrophthalazinedione (DPD); a peroxidase enzyme catalyst; and an enhancer which increases the signal:background ratio of light output, "signal" being in the presence of the peroxidase, "background" in its absence, characterised in that the enhancer is any one of the enhancers of Claim 1.
10. 10. A kit according to Claim 9 wherein the enhancer is para iodophenylboronic acid, para-bromophenylboronic acid, 4-biphenylboronic acid, 4-(trimethylsilyl)benzeneboronic acid, 2-hydroxy-5-(3'-(trifluoromethyl)phenylazo)benzeneboronic acid, boroglycine, 4-chloro-3-nitrophenylboronic acid, 4-chlorophenylboronic acid, 4-(2'-carboxyethenyl)phenylboronic acid, 4-(4'bromophenyl)phenyl-di-n-butoxyborane, 4-chlorophenyl-di-(4'chlorophenoxy)borane, 4-4'-bis(phenylboronic acid), diphenyl boronic anhydride, 4-chloroanilinophenylboronic acid id and 4-bromophenyl-di-n-butoxyborane.
11. 11. A kit according to Claim 9 or 10 wherein the peroxidase is conjugated to a ligand.
12. 12. A kit according to Claim 9, 10 or 11 wherein the peroxidase is horseradish peroxidase.
13. 13. A kit according to any one of Claims 9 to 12 which further comprises an oxidant.
14. 14. A kit according to Claim 13 wherein the oxidant is hydrogen peroxide.
15. 15. A kit according to any one of Claims 9 to 14 wherein the DPD is luminol.