Facial recognition of heroin vaccine opiates: type 1 cross-reactivities of antibodies induced by hydrolytically stable haptenic surrogates of heroin, 6-acetylmorphine, and morphine

Novel synthetic compounds similar to heroin and its major active metabolites, 6-acetylmorphine and morphine, were examined as potential surrogate haptens for the ability to interface with the immune system for a heroin vaccine. Recent studies have suggested that heroin-like haptens must degrade hydrolytically to induce independent immune responses both to heroin and to the metabolites, resulting in antisera containing mixtures of antibodies (type 2 cross-reactivity). To test this concept, two unique hydrolytically stable haptens were created based on presumed structural facial similarities to heroin or to its active metabolites. After conjugation of a heroin-like hapten (DiAmHap) to tetanus toxoid and mixing with liposomes containing monophosphoryl lipid A, high titers of antibodies after two injections in mice had complementary binding sites that exhibited strong type 1 ("true") specific cross-reactivity with heroin and with both of its physiologically active metabolites. Mice immunized with each surrogate hapten exhibited reduced antinociceptive effects caused by injection of heroin. This approach obviates the need to create hydrolytically unstable synthetic heroin-like compounds to induce independent immune responses to heroin and its active metabolites for vaccine development. Facial recognition of hydrolytically stable surrogate haptens by antibodies together with type 1 cross-reactivities with heroin and its metabolites can help to guide synthetic chemical strategies for efficient development of a heroin vaccine.

Endogenous morphine-6-glucuronide (M6G) is present in the plasma of patients: validation of a specific anti-M6G antibody for clinical and basic research

Endogenous morphine and its derivatives (morphine-6-glucuronide [M6G]; morphine-3-glucuronide [M3G]) are formed by mammalian cells from dopamine. Changes in the concentrations of endogenous morphine have been demonstrated in several pathologies (sepsis, Parkinson's disease, etc.), and they might be relevant as pathological markers. While endogenous morphine levels are detectable using enzyme-linked immunosorbant assay (ELISA), mass spectrometry (MS) analysis was, so far, the only approach to detect and quantify M6G. This study describes the preparation of a specific anti-M6G rabbit polyclonal antibody and its validation. The specificity of this antibody was assessed against 30 morphine-related compounds. Then, a M6G-specific ELISA-assay was tested to quantify M6G in the plasma of healthy donors, morphine-treated, and critically ill patients. The antibody raised against M6G displays a strong affinity for M6G, codeine-6-glucuronide, and morphine-3-6-glucuronide, whereas only weak cross-reactivities were observed for the other compounds. Both M6G-ELISA and LC-MS/MS approaches revealed the absence of M6G in the plasma of healthy donors (controls, n = 8). In all positive donors treated with morphine-patch (n = 5), M6G was detected using both M6G-ELISA and LC-MS/MS analysis. Finally, in a study on critically ill patients with circulating endogenous morphine (n = 26), LC-MS/MS analysis revealed that 73% of the positive-patients (19 of 26), corresponding to high M6G-levels in M6G-ELISA, contained M6G. In conclusion, we show that endogenous M6G can be found at higher levels than morphine in the blood of morphine-naive patients. With respect to the interest of measuring endogenous M6G in pathologies, we provide evidences that our ELISA procedure represents a powerful tool as it can easily and specifically detect endogenous M6G levels.

Optimizing recombinant antibody function in SPR immunosensing. The influence of antibody structural format and chip surface chemistry on assay sensitivity

BACKGROUND

Recombinant antibody fragments are valuable tools for SPR-based detection of small molecules such as illicit drugs. However, the multiple structural formats of recombinant antibody fragments are largely uncharacterised with respect to their respective performance in SPR sensing. We have expressed a model anti-M3G antibody in both scFv and chimeric Fab formats to examine its sensitivity and binding profiles in a microplate immunoassay format and Biacore. We have further examined the influence of scFv multimerisation, Fab constant region stability and SPR chip surface coating chemistry, on anti-hapten SPR assay development.

RESULTS

Under optimised competition ELISA conditions, the anti-M3G scFv was found to have an IC(50) value of 30 ng/ml, while the most stable Fab construct exhibited an IC(50) value of 2.4 ng/ml. In SPR competition assay on an M3G-OVA-coated SPR chip surface, the two constructs again differed in sensitivity, with IC(50) values of 117 and 19 ng/ml for the scFv and Fab, respectively (the scFv also exhibiting poor linearity of response). However, when the SPR chip surface was directly coated with M3G, both antibody constructs exhibited good linearity of response, similar high sensitivity IC(50) values (scFv 30 ng/ml, Fab 14 ng/ml) and high reproducibility (50 effective regenerations for M3G-OVA, 200 for M3G direct). During SPR assay development it was noticed that scFv and Fab constructs gave differing off-rate profiles. Subsequent HPLC, ELISA and electrophoretic analyses then confirmed that a portion of the scFv population multimerises. Bivalent scFv was found to profoundly affect the dissociation curve for scFv in stringent SPR kinetic analyses, leading to a 40-fold difference in calculated off-rate values (Fab off rate 4.7 x 10(-3)S(-1), scFv off rate 1.03 x 10(-2)S(-1)).

CONCLUSION

The structural format of recombinant antibody fragments and chip functionalisation methodology can both profoundly affect the function of anti-M3G SPR assay, with direct coating and Fab format proving to be optimal. The confirmation of scFv multimerisation and resulting changes in SPR kinetics profile, in comparison with a Fab, further suggest that caution must be taken in the interpretation of SPR sensorgrams, which are commonly used in the 'affinity ranking' of scFv panels in which the extent of dimerisation in each sample is unknown.

Novel assay format permitting the prolonged use of regeneration-based sensor chip technology

A polyclonal antibody raised against morphine-3-glucuronide (M3G, the main metabolite of heroin and morphine) was used in the development of a novel assay format using a surface plasmon resonance (SPR)-based biosensor. Previously developed assays have generated calibration curves based on differences in the quantity of response units binding to the surface of a chip coated with the analyte. The novel assay described here was based on the development of a standard curve using the slope of a series of consecutive binding interactions. Using this format, regeneration between each assay cycle was no longer required. This increased the useable life span of the chip surface and, as a result, decreased the cost associated with the assay. Thus, at least 15 binding interactions could be carried out before the saturation of antibody on the surface of the chip caused the response to deviate significantly from linearity. After 15 nonregenerated binding interactions, the slope still remained within 1.5% of the slope after a single binding event. Analysis time, and the sample volumes required were also markedly decreased while sensitivity was enhanced. The inhibition assay developed had a detection range of 270 to 17,500 pg ml(-1).

Identification of scFv antibody fragments that specifically recognise the heroin metabolite 6-monoacetylmorphine but not morphine

Use of phage display of recombinant antibodies and large repertoire naïve antibody libraries for identifying antibodies of high specificity has been extensively reported. Nevertheless, there have been few reported antibodies to haptens that have originated from naïve antibody libraries with potential use in diagnostics. We have used chain shuffling of lead single-chain fragment variable (scFv) antibodies, isolated from a naïve antibody library, to screen for antibodies that specifically recognise the major metabolite of heroin, 6-monoacetylmorphine (6MAM). The antibodies were identified by screening high-density colonies of Escherichia coli expressing soluble scFv antibody fragments without prior expression on bacteriophage (phage display). The antibodies recognise 6MAM with affinities of 1-3x10(-7) M with no crossreactivity to morphine. These antibodies can potentially be used for developing a rapid immunoassay in drug-testing programs. To our knowledge, this is the first report of an antibody that distinguishes 6MAM from its de-acetylated form, morphine.

Production of a recombinant anti-morphine-3-glucuronide single-chain variable fragment (scFv) antibody for the development of a "real-time" biosensor-based immunoassay

A recombinant single-chain variable fragment (scFv) antibody to morphine-3-glucuronide (M3G) was produced using genetic material obtained from the spleen cells of mice immunised with a morphine-3-glucuronide-bovine serum albumin (M3G-BSA) conjugate. Immunoglobulin light (V(L)) and heavy (V(H)) chain genes were amplified and cloned into pAK vectors for generation of recombinant antibody fragments in Escherichia coli. A competition ELISA assay was developed in PBS to characterise the ability of the antibody fragments to recognise free drug and the detection limits were found to be as low as 3 ng ml(-1). Surface plasmon resonance-based inhibition immunoassays were developed. The recombinant antibody was pre-incubated with various concentrations of free drug followed by injection over a morphine-3-glucuronide-thyroglobulin (M3G-THY) immobilised surface. The response of antibody binding to the surface of the chip was inversely proportional to the amount of free drug in solution. Regeneration conditions for antibody binding to the surface were optimised resulting in a binding-regeneration capacity of at least 30 cycles. The inhibition assay for M3G was tested with assay ranges between 3 and 195 ng ml(-1) and 3 and 97 ng ml(-1) in PBS and urine, respectively.

Application of the CEDIA 6-MAM assay to routine drugs-of-abuse screening

A total of 1010 urine specimens obtained from General Practitioners, drug dependency units, and hospitals throughout the West Midlands were screened using the Microgenics CEDIA 6-monoacetylmorphine (6-MAM) assay as a means of establishing its effectiveness as a screening technique to monitor heroin abuse. A total of 282 specimens screened positive for 6-MAM using the CEDIA 6-MAM assay. However, the presence of 6-MAM could not be confirmed by gas chromatography-mass spectrometry in 21 (7%) of the CEDIA-positive specimens. Morphine was identified in all of these specimens at free concentrations ranging between 410 microg/L to 2010 microg/L. The data presented from this preliminary investigation suggests that either there are substances present within the urine specimens, as yet undetermined, which are interfering with the assay or that there may be a greater degree of cross reactivity to other opiates than previously published. 6-MAM assays may be potentially useful rapid screening techniques for high-throughput drugs-of-abuse screening laboratories performing employment and pre-employment screening. However, all positive results will still need to be confirmed by a more sensitive and specific technique.

Laboratory analysis of remotely collected oral fluid specimens for opiates by immunoassay

The performance characteristics of a method for detecting opiates (morphine, codeine, heroin, and 6-acetylmorphine [6-AM]) in oral fluid specimens were examined and compared with methods for urine specimens. The oral fluid was easily obtained using a simple device that collects between 1 and 1.5 mL of fluid for laboratory analysis. Simultaneously collected specimens from 60 known opiate abusers from a drug-treatment center were first tested using an immunoassay cutoff of 10 ng/mL in oral fluids and 2,000 ng/mL in urine. Using a second aliquot, opiate confirmation in urine was performed by gas chromatography-mass spectrometry (GC-MS) and in oral fluids by GC-MS-MS. The combined immunoassay and GC-MS-MS procedures were completed with less than 250 pL of oral fluid. Opiates identified in oral fluid specimens from heroin users included morphine, codeine, heroin, and 6-AM. The immunoassay was tested for precision, stability, and the effects of potential cross-reactants. The results yielded 93.6% agreement between oral fluid and urine, suggesting that oral fluid may be a reliable matrix for opiate detection.

Assessment of an automated immunoassay based on kinetic interaction of microparticles in solution for determination of opiates and cocaine metabolite in urine

A recently introduced automated immunoassay which is based on kinetic interaction of microparticles in solution (Roche ONLINE), was evaluated for the detection of cocaine metabolite benzoylecgonine (BE) and opiates in human urine. Cross-reactivity for the opiates morphine (100%), codeine (88%), 6-monoacetylmorphine (88%), and morphine 3-glucuronide (72%) was assessed. Analytical recovery evaluated on blank urines spiked with 0, 250, 300, 350, and 500 micrograms/L of morphine and BE (n = 10), varied from 85.2 to 100.2% for opiates and from 81.4 to 93.1% for the cocaine metabolite. The within-day precision ranged from 1.4 to 4.7% for morphine and from 4.2 to 4.8% for BE. The repeatability of the standards over 1 month was 1.0-3.3% for opiates and 1.7-5.1% for BE, and thus allowing measurements to continue over 30 days without re-calibration. This method compared favourably with the SYVA EMIT d.a.u system and gas chromatography/mass spectroscopy (GC/MS) methods.

Evaluation of a differential radioimmunoassay technique for the determination of morphine and morphine-6-glucuronide in human plasma

A modified differential radioimmunoassay (RIA) technique for the measurement of morphine and its active metabolite, morphine-6-glucuronide (M6G), in plasma is described. Plasma samples were assayed following appropriate dilution, using a morphine specific antiserum and the results subtracted from those obtained with an antiserum which cross-reacts with both morphine and M6G. The sensitivity of measurement for morphine and M6G was 0.88 and 0.27 nmol l-1, respectively and inter-assay variation ranged from 3.4 to 11.0%. Recovery of morphine and M6G was quantitative over a range of concentrations (1-5000 nmol l-1). The presence of either M6G or morphine-3-glucuronide (M3G) did not affect the recovery of morphine. M6G was quantitatively recovered in the presence of morphine but high concentrations (> 1:20) of M3G caused some overestimation of M6G. Results obtained by differential RIA for both morphine and M6G correlated well with the results of HPLC analysis. The assay has been applied to the measurement of M6G in plasma following its administration to human volunteers.

Antibodies as a means of isolating and characterizing biologically active substances: presence of a non-peptide, morphine-like compound in the central nervous system

Antibodies generated against small molecular weight substances such as drugs are being used to isolate and characterize biologically active agonists. A morphine-like compound can be extracted from brain of various species which has determinant groups that are recognized by specific morphine antibodies. It has a regional distribution which can be quantitated as immuno-equivalents. Immunological, chemical and chromatographic tests show great similatiries of the compound to morphine. This morphine-like compound has biological activity as it inhibits the electrically induced contractions both of the guinea pig ileum and mouse vas deferens but the inhibition is not reversed by naloxone or naltrexone.

The production and characterization of antibodies reactive with meperidine

Meperidinic acid was converted to O-meperidinyl-glycollic acid and covalently attached to bovine serum albumin. Rabbits injected with this conjugate produced antibodies reactive with meperidine which were measured by the ammonium sulfate method. The specificities of these antisera were studied by competitive inhibition of the binding of 100 pmol/ml of 3H-meperidine to antibody by the prior addition of increasing concentrations of various unlabeled compounds. The concentrations in nanomoles per milliliter of various unlabeled opiods required to inhibit 3H-meperidine binding by 50% (I50) were: meperidine, 0.08; O-meperidinyl-glycollic acid, 1.7; methadone, 580; heroin, 1750; codeine, 2600; and morphine, 4200. Several psychopharmacologically active compounds were found to have I50 values comparable to the nonmeperidine opioids: hydroxyzine. HCl, 460; propoxyphene, 4,500; diazepam, 6,500; and cocaine, 10,800. The metabolites of meperidine exhibited the following I50 values: normeperidine, 0.7; meperidinic acid and normeperidinic acid, 210. A radioimmunoassay for meperidine which employs this antiserum was shown to be approximately 100 times more sensitive than the spectrophotometric method of Burns et al. (J. Pharmacol. Exp Ther. 114: 289-293, 1955). In this assay only normeperidine and some of the meperidine congeners might be expected to interfere with the measurement of meperidine. The degree of normeperidine interference was shown to be comparable to that present in the existing assay method.

Iodination of morphine and dihydromorphine, as related to radioimmunoassay

Direct iodination of morphine or dihydromorphine with iodine-125 results in products that bind to antibody raised by immunization of animals with a 3-O-carboxymethylmorphine/bovine serum albumin immunogen. Iodination of morphine or dihydromorphine with iodine-127 under identical conditions failed to yield these immunologically active products, suggesting that the results obtained with iodine-125 are in part due to a radiolytic reaction not observed with the iodine-127.

Delayed clearance of morphine from the circulation of rabbits immunized with morphine-6-hemisuccinate bovine serum albumin

Morphine clearance from the circulation of normal rabbits and rabbits with circulating anti-morphine antibody was studied. Individual animals were injected with 14C trace-labeled morphine in saline (6 mg morphine/kg body weight). The rabbits were bled at various times after morphine injection and the amount of morphine present in the serum at each time interval was determined. Morphine could be detected in the serum of normal animals for 1 week following injection and up to 12 weeks following injection in at least one animal with antibodies to morphine. The rate of morphine clearance in animals immunized to morphine-6-hemisuccinate-bovine serum albumin was not significantly different from normal during the first 4 hr after morphine injection. However, by 24 hr after injection, the rate of morphine clearance in morphine-6-hemisuccinate-bovine serum albumin-immunized animals was significantly slower than in normal animals. The amount of morphine present in the sera of the rabbits 24 hr after injection was related to the antigen-binding capacity and independent of antibody avidity. However, the rate of morphine clearance at times greater than 24 hr after injection was related to the average antibody avidity and not related to the antigen-binding capacity.