Development of a radioimmunoassay for the anthrapyrazole chemotherapy agent CI-937 and the pharmacokinetics of CI-937 in rats.

The anthracyclines daunorubicin and doxorubicin are cancer chemotherapy agents that complex DNA and are widely utilized clinically. Cumulative cardiotoxicity, however, limits their prolonged use. The novel anthrapyrazole agent, CI-937, which has shown exceptional in vivo anticancer activity and reduced cardiotoxicity in preclinical models has been developed at the Parke-Davis Pharmaceutical Research Division, Warner-Lambert Co. Due to an inability to extract CI-937 reproducibly from biological fluids, high-performance liquid chromatography is not a feasible analytical method. We developed a radioimmunoassay by conjugating CI-937 to porcine thyroglobulin to elicit rabbit antibody which was used with a radioiodinated derivative. The assay was validated for rat plasma using 50 microliters of sample with a resulting limit of quantitation of 100 pg/ml. By dilution of samples the assay can quantitate CI-937 levels up to 16 micrograms/ml. The antiserum is very specific as evidenced by cross-reactivities of less than 0.4% for structural analogues and less than 0.004% for any of the commonly used cancer chemotherapy agents. Analysis of plasma samples from rats treated with a single 5 mg/kg i.v. dose indicated that CI-937 is rapidly cleared from plasma and is extensively bound to tissues.

Development and characterization of a monoclonal antibody which distinguishes the beta-subunit of human chorionic gonadotropin (beta hCG) in the presence of the hCG.

A monoclonal antibody specific for the beta-subunit of human chorionic gonadotropin (beta hCG) has been developed which has a cross reactivity of 0.23% with intact hCT. There was no cross reactivity with other glycoprotein pituitary hormones in the range in which they might be expected to be present in serum. The beta-subunits of hFSH, hTSH and hLH did not inhibit binding of [125I]iodo-beta hCG to the antibody at up to 250 ng/tube. The dissociation constant (Kd) with [125I]iodo-beta hCG was 3.3 x 10(-10), and the reaction had reached equilibrium within 1 h.

A chemical approach to solving bridging phenomena in steroid radioimmunoassays.

Steroid radioimmunoassays (RIA) employ antibodies raised against a carrier protein-steroid conjugate. Individual antibodies may recognize the steroid, the protein or the chemical bridge used to join them together. Use of the same bridge in the tracer results in higher affinity binding of the tracer than the native ligand which in turn results in a loss of sensitivity and precision. We have greatly reduced bridge-binding in a RIA for androstenedione. Conjugates and radioiodinated labels were prepared with either an ester or either chemical bridge. By using an antibody and the corresponding label with the heterologous bridge very sensitive assays were obtained.

A specific radioimmunoassay for androstenedione with reduced bridge-binding.

Antibody used in a steroid radioimmunoassay raised against a steroid hapten-carrier protein conjugate may recognize both the hapten and the chemical bridge to the protein. Use of the same bridge in the radio-isotopic label may lead to higher affinity binding to the label than to the native steroid. Inhibition curves under these conditions are shallow and generally not acceptable for radioimmunoassay procedures. We have developed a radioimmunoassay for androstenedione that employs different bridges at the 11 beta position of the steroid for the protein conjugate and label. The resulting assay has greatly reduced bridge-binding, has an acceptable slope for the standard curve and is very specific as evidenced by low crossreactivies to other steroids.

Perturbation of epidermal growth factor clearance after radioiodination and its implications.

The clearance of human epidermal growth factor (hEGF1-53) has been thought to be mediated mainly by a high-capacity receptor system, yet relatively low in vivo clearance rates (<10 mL/min/kg) and long terminal elimination half-lives (>120 min) have been observed in rats receiving the peptide that was iodinated by the oxidative chloramine-T (CT) method. We investigated if a mild, less oxidative iodination by the lactoperoxidase (Enzymobeads, EB) method, which is known to yield an iodinated peptide with receptor-binding equivalence, could produce a labeled peptide that behaves pharmacokinetically similar to the native material. For comparison, a parallel study was also conducted with EB-125I-hEGF1-48, which in its native form has a much reduced receptor binding activity due to the loss of the C-terminal pentapeptide. Plasma radioactivity concentrations were determined by trichloroacetic acid (TCA) precipitation and immunoprecipitation. Rats cleared unlabeled hEGF1-53 and hEGF1-48 markedly faster (CL(tot) > 120 mL/min/kg) than their radiolabeled counterparts. Approximately 96% of the hEGF1-53 dose was cleared during the initial phase (0-4 min), as opposed to only 5-14% for the iodinated peptide. Similar change was also observed for EB-125I-hEGF1-48 and CT-125I-hEGF1-53. The pharmacokinetic behavior of EB-125I-hEGF1-53 was, in fact, comparable to that of CT-125I-hEGF1-53. These observations indicate that receptor-binding equivalence does not have direct relationship with in vivo EGF clearance. Both iodination methods (oxidative CT and less oxidative EB) might have perturbed one or more steps in the cascade of ligand-receptor internalization and intracellular procession, which in turn modified the disposition of the peptides. In addition, the two independent precipitation techniques for the same peptide generated different kinetic outcomes. The overall experimental results suggest that it is unacceptable to use an iodinated form to characterize the disposition of peptides/proteins like EGF with a specific receptor system mediating its clearance.

Considerations in the development of a sensitive HPLC assay for human epidermal growth factors in human plasma.

A sensitive assay was developed for human epidermal growth factors (hEGF) 1-48 (dosed), hEGF 1-53 (endogenous), without interference from potential metabolites hEGFs 1-47 or 1-46. Spiked human plasma samples were injected directly, utilizing on-line immunoaffinity HPLC (anti-hEGF) clean-up. No change in capacity was noted after 81 cycles. After release from the immunoaffinity column, the fragments were further resolved by strong cation-exchange (SCX) via a column switching valve. Method development also required interfacing immunoaffinity, ion-exchange, and detection components. Immunoassays on collected fractions yielded a detection limit of 1 microgram ml-1, although a detection limit of 75 pg ml-1 appears feasible.

Validation of immunoassays for bioanalysis: a pharmaceutical industry perspective.

Immunoassays are bioanalytical methods in which quantitation of the analyte depends on the reaction of an antigen (analyte) and an antibody. Although applicable to the analysis of both low molecular weight xenobiotic and macromolecular drugs, these procedures currently find most consistent application in the pharmaceutical industry to the quantitation of protein molecules. Immunoassays are also frequently applied in such important areas as the quantitation of biomarker molecules which indicate disease progression or regression, and antibodies elicited in response to treatment with macromolecular therapeutic drug candidates. Currently available guidance documents dealing with the validation of bioanalytical methods address immunoassays in only a limited way. This review highlights some of the differences between immunoassays and chromatographic assays, and presents some recommendations for specific aspects of immunoassay validation. Immunoassay calibration curves are inherently nonlinear, and require nonlinear curve fitting algorithms for best description of experimental data. Demonstration of specificity of the immunoassay for the analyte of interest is critical because most immunoassays are not preceded by extraction of the analyte from the matrix of interest. Since the core of the assay is an antigen-antibody reaction, immunoassays may be less precise than chromatographic assays; thus, criteria for accuracy (mean bias) and precision, both in pre-study validation experiments and in the analysis of in-study quality control samples, should be more lenient than for chromatographic assays. Application of the SFSTP (Societe Francaise Sciences et Techniques Pharmaceutiques) confidence interval approach for evaluating the total error (including both accuracy and precision) of results from validation samples is recommended in considering the acceptance/rejection of an immunoassay procedure resulting from validation experiments. These recommendations for immunoassay validation are presented in the hope that their consideration may result in the production of consistently higher quality data from the application of these methods.

Immunochemical evidence for a role of cytochrome P-450 in liver microsomal ethanol oxidation.

Antibodies to cytochrome P-450 isozyme 3a, the ethanol-inducible isozyme in rabbit liver, were used to determine the role of this enzyme in the microsomal oxidation of alcohols and the p-hydroxylation of aniline. P-450 isozymes, 2, 3b, 3c, 4, and 6 did not crossreact with anti-3a IgG as judged by Ouchterlony double diffusion, and radioimmunoassays indicated a crossreactivity of less than 1%. Greater than 90% of the activity of purified form 3a toward aniline, ethanol, n-butanol, and n-pentanol was inhibited by the antibody in the reconstituted system. The catalytic activity of liver microsomes from control or ethanol-treated rabbits was unaffected by the addition of either desferrioxamine (up to 1.0 mM) or EDTA (0.1 mM), suggesting that reactions involving the production of hydroxyl radicals from H2O2 and any contaminating iron in the system did not make a significant contribution to the microsomal activity. The addition of anti-3a IgG to hepatic microsomes from ethanol-treated rabbits inhibited the metabolism of ethanol, n-butanol, n-pentanol, and aniline by about 75, 70, 80, and 60%, respectively, while the inhibition of the activity of microsomes from control animals was only about one-half as great. The rate of microsomal H2O2 formation was inhibited to a lesser extent than the formation of acetaldehyde, thus suggesting that the antibody was acting to prevent the direct oxidation of ethanol by form 3a. Under conditions where purified NADPH-cytochrome P-450 reductase-catalyzed substrate oxidations was minimal, the P-450 isozymes other than 3a had low but significant activity toward the four substrates examined. The residual activity at maximal concentrations of the antibody most likely represents the sum of the activities of P-450 isozymes other than 3a present in the microsomal preparations. The results thus indicate that the enhanced monooxygenase activity of liver microsomes from ethanol-treated animals represents catalysis by P-450 isozyme 3a.

Elucidation of peptide metabolism by on-line immunoaffinity liquid chromatography mass spectrometry.

An immunoaffinity chromatography extraction capillary liquid chromatography separation has been coupled to electrospray ionization mass spectrometry for on-line characterization of drug metabolites of a therapeutic peptide in plasma. It is demonstrated that the selectivity, sensitivity and molecular weight data provided by immunoaffinity chromatography coupled to liquid chromatography/mass spectrometry provides a means of rapidly achieving qualitative determinations of small amounts of material in complicated biological matrices such as plasma. The ability to detect the peptide in rat plasma at a level of 10 ng/mL is demonstrated using this method. In addition, experiments to study the epitope of the peptide by enzymatic digestion and mass spectrometry are also discussed. The method is proposed as an alternative approach to studying the metabolism of therapeutic peptides.

On-probe immunoaffinity extraction by matrix-assisted laser desorption/ionization mass spectrometry.

A simple and effective method has been proposed in this work for combination of immunoaffinity extraction with MALDI MS. In this method, an antibody is attached to the surface of a MALDI probe tip via a thin nitrocellulose film. This allows the corresponding antigen to be selectively captured and concentrated on the probe tip from complex plasma solution for MALDI MS analysis. The whole procedure can be completed within 1 h. This combination offers several excellent performance features in the analysis of SNX-111, a therapeutic peptide. It combines the high specificity of affinity chromatography with the high sensitivity of mass spectrometry in a rapid analysis. Direct mass detection provides unambiguous determination by the observation of signals at characteristic m/z values. This method has been used successfully to determine the therapeutic peptide at relevant doses.

Immunochemical evidence for induction of the alcohol-oxidizing cytochrome P-450 of rabbit liver microsomes by diverse agents: ethanol, imidazole, trichloroethylene, acetone, pyrazole, and isoniazid.

Isozyme 3a of rabbit liver microsomal cytochrome P-450, also termed P-450ALC, was previously isolated in this laboratory from animals administered ethanol or imidazole, and the purified cytochrome was shown to function in the reconstituted system as an oxygenase in catalyzing the oxidation of ethanol and other alcohols. Although liver microsomes from animals treated in various ways exhibit increased alcohol-oxidizing activity, evidence was not available as to whether this was due to enzyme induction or to other factors influencing the activity. Immunochemical quantitation of P-450 isozyme 3a has now been achieved by use of purified antibody to this cytochrome in NaDodSO4/PAGE/blotting and dot-blotting techniques. The specific content of isozyme 3a in liver microsomes was found to be increased from 2- to greater than 4-fold by administration of the following agents, in increasing order of effectiveness as inducers: isoniazid, trichloroethylene, pyrazole, ethanol, imidazole, and acetone. Isozyme 3a represents about 5% of the total P-450 in control animals and is increased to as high as 27% by acetone treatment. Isozyme 3a-dependent butanol-oxidation activity, determined by the inhibitory effect of antibody on the various microsomal preparations, was found to increase proportionally with increased content of this cytochrome.

Lectin binding studies on murine peritoneal cells: physicochemical characterization of the binding of lectins from Datura stramonium, Evonymus europaea, and Griffonia simplicifolia to murine peritoneal cells.

Purified 125I-labeled lectins from Datura stramonium, Evonymus europaea, and Griffonia simplicifolia (I-B4 isolectin) were used to analyze changes in the expression of carbohydrates on the surface of resident (PC) and thioglycollate-stimulated murine (C57B/6J) peritoneal exudate cells (PEC). The lectins from D. stramonium, E. europaea, and G. simplicifolia I-B4 bind specifically to PEC with relatively high affinity (Kd = 5.65 +/- 1.08 X 10(-7) M, 1.08 +/- 0.12 X 10(-8) M, and 1.33 +/- 0.15 X 10(-7) M, respectively). Assuming a single lectin molecule binds to each cell surface saccharide, the number of receptor sites per cell ranged for different cell samples from 22.3 to 50.0 X 10(6), from 3.8 to 4.8 X 10(6), and from 2.0 to 16.8 X 10(6) for D. stramonium, E. europaea, and G. simplicifolia I-B4 lectins, respectively. There were approximately 3- to 7-fold, 16- to 20-fold, and 2- to 20-fold increases in binding capacity for D. stramonium, E. europaea and G. simplicifolia I-B4, respectively, compared to the binding to resident, peritoneal cells. Scatchard plots of the binding of all three lectins to PEC were linear, suggesting that the receptor sites for these lectins are homogeneous and noninteracting. The binding capacity of these lectins to PEC was unchanged after trypsin digestion of cells. The expression of carbohydrates on the surface of PEC was also monitored by an agglutination assay. PEC were agglutinated by all three lectins whereas PC either were not agglutinated or were agglutinated only at high lectin concentrations. On the basis of our knowledge of the carbohydrate binding specificity of the D. stramonium and G. simplicifolia I-B4 lectins, we postulate that, parallel with thioglycolate stimulation, there is an increase in the number of N-acetyllactosamine residues and terminal alpha-D-galactosyl end groups. The blood group B, and H type 1 determinants--DGa1 alpha 1,3[LFuc alpha 1,2]DGa1 beta 1,3(or 4)DGlcNAc and LFuc alpha 1,2DGa1 beta 1,3DG1cNAc, respectively, as well as DGa1 alpha 1,3DGa1 beta 1,3(or 4)DGlcNAc--may be considered to be possible receptors for the E. europaea lectin. These glycoconjugates, present on the surface of peritoneal exudate cells, provide new chemical markers for studying the differentiation of resident peritoneal cells.

The measurement of testosterone and oestradiol-17 beta using iodinated tracers and incorporating an affinity chromatography extraction procedure.

The development of sensitive radioimmunoassays (RIA) for testosterone and oestradiol-17 beta, utilising 125I-radioligands, is described. Use of an homologous bridge at the same site of attachment, for both the radioligand and the steroid-carrier protein conjugate employed in raising antibodies, normally results in a loss of assay sensitivity and precision. This was overcome in the oestradiol assay by utilising an heterologous configuration at the site of attachment (11 alpha vs 11 beta). In contrast, for testosterone, even though an homologous bridge and site of attachment was used for the radioligand and the steroid-carrier protein conjugate, a very sensitive assay with extremely high antibody titres (dilution of 1:2 X 10(6] was achieved. This finding was repeated with a different antiserum suggesting that the "bridge binding" phenomenon may be related to the position of attachment to the steroid molecule. In addition, an antibody-Sepharose 4B affinity chromatography extraction procedure has been developed for both oestradiol and testosterone. This approach allows the measurement of very low concentrations of steroids from large volumes of a variety of biological fluids. As antibody-linked Sepharose 4B uses high concentrations of antibody, steroids of similar structure are extracted from biological fluids. However, the cross-reactivity of these related steroids are very low in the RIA's, ensuring good specificity.

Clinical pharmacokinetics of procaterol: dose proportionality after administration of single oral doses.

Procaterol is a potent, orally active beta 2-agonist bronchodilator useful in the treatment of reversible bronchospastic disease. It is effective when administered as single or multiple (Q8H) 50 and 75 micrograms doses. As part of the clinical development of procaterol, the pharmacokinetics and dose proportionality of single 25, 50, 75, and 100 micrograms doses were investigated in 14 healthy subjects. Serial blood samples were collected for 16 h and urine was quantitatively collected for 48 h following administration of each dose. Procaterol concentrations in plasma and urine were determined using sensitive and specific radioimmunoassay methods. Mean values for tmax, the apparent elimination rate constant, Cl/F, renal clearance, and per cent of dose excreted unchanged in urine were similar for all doses. Dose-normalized AUC, Cmax, and amount excreted unchanged in urine (Ae) were also similar across dosage levels. Thus, the pharmacokinetics of procaterol appear to be proportional to dose over the range of doses studied.

Clinical pharmacokinetics and relative bioavailability of oral procaterol.

The pharmacokinetics and relative oral bioavailability of procaterol, an orally active beta 2-adrenergic agonist bronchodilator were evaluated in healthy volunteers. Procaterol was rapidly absorbed after oral administration. Mean plasma procaterol concentration-time profiles and pharmacokinetic parameters for both formulations were essentially superimposable. Following tablet administration, the mean Cmax was 358 pg/mL and the corresponding mean tmax was 1.6 hr. Mean renal clearance was 163 mL/min and accounted for approximately one-sixth of the mean apparent oral plasma clearance (988 mL/min). The mean apparent elimination half-life of procaterol was 4.2 hr. Hepatic metabolism appears to be the primary mechanism for elimination of procaterol from the body, and first-pass metabolism may limit systemic bioavailability.

Cross-reactivity of fosphenytoin in two human plasma phenytoin immunoassays.

The cross-reactivity of fosphenytoin, a phosphate ester prodrug of phenytoin, was investigated in the Abbott phenytoin TDx/TDxFLx fluorescence polarization immunoassay (TDx) and the Behring Diagnostics phenytoin Emit 2000 enzyme-multiplied immunoassay (Emit). The first part of our study investigating cross-reactivity utilized in vitro correlation of the two immunoassays with a validated and specific phenytoin HPLC method used to assay plasma samples prepared in several phenytoin and fosphenytoin concentration combinations. Fosphenytoin cross-reacted with both immunoassays, but to a greater extent with TDx. In the second part of the study, empirically-derived models that best explained the in vitro data were used to predict "immunoassay-derived" phenytoin concentrations in plasma samples collected from actual patients after intravenous (i.v.) or intramuscular (i.m.) fosphenytoin dosing. The greatest degree of phenytoin concentration overestimation occurred at times when fosphenytoin concentrations were highest: within 1 to 2 h after i.v. infusion or during the first 2 to 4 h after i.m. injection. It is recommended that phenytoin concentrations not be monitored using these or other potentially nonspecific immunoanalytical methods for at least 2 h after i.v. fosphenytoin infusion or 4 h after i.m. fosphenytoin injection.