Role of biotin-binding affinity in streptavidin-based pretargeted radioimmunotherapy of lymphoma

One pretargeting approach to cancer radioimmunotherapy utilizes an antibody-streptavidin conjugate that is first localized to the tumor. A "clearing agent" is then administered to remove the excess bioconjugate from blood, followed by injection of the radiolabeled biotin therapeutic. In this study, the role of streptavidin-biotin affinity in this pretargeting system was investigated for the first time in vivo, with a reduced affinity, site-directed streptavidin mutant and with radiolabeled bis-biotin reagents. The S45A streptavidin mutant (SA-S45A), which displays a faster off-rate for biotin, was utilized with a bivalent biotin carrier that retains high avidity for the streptavidin mutant. Mice were fed either a normal or biotin-deficient diet, yielding serum endogenous biotin concentrations of 31 nM and 5 nM, respectively. Lymphoma-bearing nude mice pretargeted with 1F5 Antibody-SA-Wild Type (WT) bioconjugates produced (125)I-bis-biotin tumor concentrations of 2.2%ID/g and 7.0%ID/g in mice fed normal diets vs biotin-deficient diets. (125)I-bis-biotin tumor concentrations of mice pretargeted with 1F5-SA-S45A were 12%ID/g and 10%ID/g for mice fed normal and biotin-deficient diets, respectively. However, poor clearance of the 1F5-SA-S45A with the biotinylated clearing agent led to high normal organ concentrations of (125)I-bis-biotin. A galactosylated human serum albumin (HSA) modified with bis-biotin was then tested, and normal organ (125)I-bis-biotin concentrations were significantly reduced. Tumor-to-organ ratios achieved for 1F5-SA-S45A with the HSA-bis-biotin clearing agent in mice with high serum biotin were similar to those achieved with 1F5-SA-WT in mice with low serum biotin. These results demonstrate that exchange of bound endogenous biotin with lower affinity streptavidin mutants is possible, and that corresponding use of bis-biotin carriers can nearly eliminate the differences in therapeutic radioactivity at the tumor site in animals on normal vs biotin-deficient diets. The results also interestingly demonstrate, however, that improved clearance agents capable of removing the lower affinity streptavidin-antibody conjugate are needed to achieve comparable specificity in tumor to blood or normal organ ratios.     

Metabolism and pharmacokinetics of progesterone in the cynomolgus monkey (Macaca fascicularis)

[4-14C]Progesterone was administered to two cycling female monkeys during the luteal phase of the cycle, and blood and urine were sampled over a 24 h period. Progesterone had a volume of distribution of 1.75 +/- 0.3 L/kg, and a plasma elimination clearance of 0.06 +/- 0.03 L/kg/min. In comparison to the human, plasma progesterone binding was greater and progesterone clearance was slower in the cynomolgus monkey. The major unconjugated metabolite in plasma was 20 alpha-hydroxy-4-pregnen-3-one. In urine 6.2% of 14C-steroids were unconjugated, 2.3% of which were [14C]progesterone. Thin-layer chromatography (TLC) of conjugated metabolites in urine revealed that 24% had the mobility of sulfates, 19% that of glucuronides, and 52% were more polar. After hydrolysis of conjugates, a major fraction chromatographed with pregnanediol. However, despite evidence for the presence of a 20 alpha-hydroxyl group, none of the pregnanediol isomers could be identified among these 14C-steroids. Nevertheless, over 80% of urinary metabolites had sufficient analogy to pregnanediol to bind to an antiserum specific for ring D and the C-17 side-chain of pregnanediol.     

A capillary gas chromatography-selected ion monitoring mass spectrometry method for the analysis of atractylenolide I in rat plasma and tissues, and application in a pharmacokinetic study

The aim of this paper is to investigate the characteristics of atractylenolide I (AO-I) in the body by a GC-MS method. All bio-samples were cleared up with a liquid-liquid extraction procedure. The calibration curves were linear within a range of 5-1000 ng/mL for plasma samples, 0.06-16.00 microg/g for cerebellum samples, and 0.03-8.00 microg/g for other tissue samples. The limit of quantification (LOQ) for AO-I was 1.0 ng/mL or 1.0 ng/g (S/N>micro=10) in the bio-samples. In the applications, the main pharmacokinetic parameters were firstly obtained as follows: Tmax=0.37+/-0.19 h, Cmax=0.26+/-0.05 microg/mL, AUC=1.95+/-0.30 microgh/mL and ka=10.08+/-5.60 h(-1). The tissue distribution of AO-I in rats after the oral administration of 50.0mg/kg was from 0.225 to 0.031microg/g with a decreasing tendency in different tissues like liver>kidney>spleen>cerebellum>heart>cerebrum>lung. The protein binding in rat plasma, human plasma and bovine serum albumin was 80.8+/-3.9, 90.6+/-3.1 and 60.9+/-5.1%, respectively.     

Determination of acteoside in Cistanche deserticola and Boschniakia rossica and its pharmacokinetics in freely-moving rats using LC-MS/MS

A sensitive LC-MS/MS method with a simple solid-phase extraction for the determination of acteoside in rat plasma and tissue homogenates was established for the investigation of bioavailability and brain distribution in freely-moving rats. Acteoside in Cistanche deserticola and Boschniakia rossica was also determined. Acteoside and internal standard were separated on a RP-select B column (125mmx4.6mm i.d., particle size 5microm). The mobile phase consisted of 35% methanol and 65% acetic acid-water (1:100, v/v) at a flow-rate of 1mL/min. Acteoside and the internal standard were monitored using the multiple-reaction monitoring (MRM) mode at m/z transitions of 623-->161 and 609-->301, respectively. The acteoside content was 38.4+/-2.4mg/kg (n=3) for B. rossica, which is obviously lower than 21134.2+/-805.5mg/kg (n=3) of C. deserticola. The protein binding in rat plasma was 75.5+/-1.8%. The brain distribution result indicated that acteoside was evenly distributed in brain tissues (brain stem, cerebellum, the rest of the brain, cortex, hippocampus and striatum) which was about 0.45-0.68% of that in plasma (4.5+/-0.5microg/mL) after 15min of acteoside administration (10mg/kg, i.v.). After acteoside was given (3mg/kg, i.v.; 100mg/kg, p.o.), the oral bioavailability (AUC(p.o.)/dose(p.o.))/(AUC(i.v.)/dose(i.v.)) was only 0.12%.     

Comparative plasma pharmacokinetics of meloxicam in sheep and goats following intravenous administration

Meloxicam, a novel cyclooxygenase-2 selective nonsteroidal anti-inflammatory drug (NSAID), has been used extensively in humans and recently in some domestic animal species. Although it is an attractive NSAID for use in small ruminants, meloxicam pharmacokinetics have not been investigated in sheep and goats and this information is essential for rational therapeutic use of the drug in these species. In this investigation, comparative pharmacokinetic properties of meloxicam were studied in sheep and goats after a single intravenous dose of 0.5 mg kg(-1) body mass. Blood samples were collected via jugular venepuncture into heparinised tubes at predetermined times after drug administration. Plasma concentrations of meloxicam were determined by reversed-phase high performance liquid chromatography. The plasma concentrations of meloxicam were detectable in sheep and goats up to 72 and 48 h, respectively. The plasma concentration versus time data of meloxicam in both sheep and goats were adequately described by a two-compartment open model. The values obtained for sheep and goats for distribution half-life, volume of distribution at steady state and volume of the central compartment were almost similar in sheep and goats. The elimination half-life (t(1/2beta)), area under the plasma concentration-time curve (AUC), mean residence time (MRT) and total systemic clearance (Cl(B)) in sheep were significantly different from those of goats. The mean+/-S.E. values of t(1/2beta), MRT, AUC and Cl(B) in sheep were 10.85+/-1.21 h, 15.13+/-1.67 h, 31.88+/-2.97 microg h mL(-1) and 0.016+/-0.002 L h(-1) kg(-1), respectively whereas the respective values in goats were 6.73+/-0.58 h, 9.37+/-0.83 h, 19.23+/-2.23 microg h mL(-1) and 0.03+/-0.01 L h(-1) kg(-1). The results indicate that elimination kinetics of meloxicam differ significantly between sheep and goats and the elimination of the drug tends to be faster in goats compared to sheep.     

Streptavidin in antibody pretargeting. 4. Site-directed mutation provides evidence that both arginine and lysine residues are involved in kidney localization

The in vivo application of the protein streptavidin is limited by its propensity to localize to kidney, particularly when it is used as a carrier of radionuclides in Targeted Radionuclide Therapy. Our previous studies demonstrated that modification of recombinant "core" streptavidin (rSAv) by reaction of lysine residues with succinic anhydride and arginine residues with 1,2-cyclohexanedione dramatically decreases the kidney concentrations over that obtained with wild-type rSAv. In this investigation, we explored the role of lysine and arginine residues in kidney localization further by evaluating site-directed mutants of rSAv. In the five mutants studied, the four lysine residues found in each subunit of rSAv were replaced (independently) with an alanine (K80A, K121A, K132A, K134A), and a specific arginine was replaced with a histidine (R59H). The rSAv mutants were prepared from a "core" rSAv construct produced by expression in E. coli that had 124 amino acids (residues 13-136). Another rSAv construct that had 127 amino acids (residues 13-139), used in most of our previous studies, was also included for comparison. As an additional comparison, succinylated rSAv was prepared and evaluated. The rSAv proteins were radioiodinated and injected into athymic mice that were on a biotin-free diet for 5-7 days prior, and biodistribution data were obtained (for most proteins) at 1, 4, 24, and 48 h postinjection. The data obtained show large differences in kidney localizations of the wild-type rSAv and some rSAv mutants. The largest difference in the kidney concentration was noted for the rSAv-K134A mutant (1.90 +/- 0.22%ID/g; 24 h pi) as compared to the wild-type rSAv (31.83 +/-5.26%ID/g) at the same time point. The concentration of rSAv-K134A mutant in kidney was slightly lower than that obtained with succinylated rSAv. At the 24 h time point, the kidney concentrations of the rSAv-R59H mutant (8.95 +/- 2.94%ID/g) and the rSAv-K121A mutant (11.86 +/- 1.61%ID/g) were lower than wild-type rSAv, but the rSAv mutants rSAv-K80A (27.95 +/- 1.82%ID/g) and rSAv-K132A (32.50 +/- 10.09%ID/g) were essentially the same. The data suggests that specific lysine and arginine residues are involved in kidney localization. Possible mechanisms for the observed kidney localization are discussed.     

Size determination of cyanobacterial and higher plant photosystem II by gel permeation chromatography, light scattering, and ultracentrifugation

The oxygen-evolving photosystem II core complexes (PSIIcc) from the thermophilic cyanobacterium Thermosynechococcus elongatus (PSIIccTe) and the higher plant Spinacia oleracea (PSIIccSo) have been isolated from the thylakoid membrane by solubilization with n-dodecyl-beta-d-maltoside, purified and characterized by gel permeation chromatography (GPC), dynamic light scattering (DLS), and analytical ultracentrifugation (AUC). DLS suggests that PSIIcc from both organisms exists as a monomer in dilute solution and aggregates with increasing protein concentration. In contrast to DLS, GPC and AUC showed that PSIIcc of both organisms occur as monomers and dimers, and it became clear from our studies that calibration of GPC columns with soluble proteins leads to wrong estimates of the molecular masses of membrane proteins. At a PSIIcc protein concentration of 0.2 mg/mL, molar masses, M, of 756 +/- 18 kDa and 710 +/- 15 kDa for dimeric PSIIccTe and PSIIccSo, respectively, were determined by analytical ultracentrifugation. At very low protein concentrations, at or below 0.05 mg/mL, the dimeric form of PSIIccTe partially dissociates (20-30%) to form monomers. On the basis of these studies 3-dimensional crystals of PSIIccTe were obtained that contain dimers in the asymmetric unit [Zouni, A. et al. (2001) Nature 409, 739-743]. Using synchrotron radiation the crystals diffract to a resolution of 3.8 A, which has been improved recently to 3.2 A [Biesiadka, J., et al. (2004) Phys. Chem. Chem. Phys. 6, 4733-4736].     

Evaluation of SQ 28,603, an inhibitor of neutral endopeptidase, in conscious monkeys.

The potent neutral endopeptidase inhibitor SQ 28,603 (N-(2-(mercaptomethyl)-1-oxo-3-phenylpropyl)-beta-alanine) significantly increased excretion of sodium from 4.9 +/- 2.3 to 14.3 +/- 2.1 muequiv./min and cyclic 3',5'-guanosine monophosphate from 118 +/- 13 to 179 +/- 18 pmol/min after intravenous administration of 300 mumol/kg (approximately 80 mg/kg) in conscious female cynomolgus monkeys. SQ 28,603 did not change blood pressure or plasma atrial natriuretic peptide concentrations in the normal monkeys. In contrast, 1-h infusions of 3, 10, or 30 pmol.kg-1.min-1 of human atrial natriuretic peptide lowered blood pressure by -3 +/- 4, -9 +/- 4, and -27 +/- 3 mmHg (1 mmHg = 133.322 Pa), increased cyclic guanosine monophosphate excretion from 78 +/- 11 to 90 +/- 6, 216 +/- 33, and 531 +/- 41 pmol/min, and raised plasma atrial natriuretic peptide from 7.2 +/- 0.7 to 21 +/- 4, 62 +/- 12, and 192 +/- 35 fmol/mL without affecting sodium excretion. In monkeys receiving 10 pmol.kg-1.min-1 of atrial natriuretic peptide, 300 mumol/kg of SQ 28,603 reduced mean arterial pressure by -13 +/- 5 mmHg and increased sodium excretion from 6.6 +/- 3.2 to 31.3 +/- 6.0 muequiv./min, cyclic guanosine monophosphate excretion from 342 +/- 68 to 1144 +/- 418 pmol/min, and plasma atrial natriuretic peptide from 124 +/- 8 to 262 +/- 52 fmol/mL. In conclusion, SQ 28,603 stimulated renal excretory function in conscious monkeys, presumably by preventing the degradation of atrial natriuretic peptide by neutral endopeptidase.     

Inhibition of platelet-activating factor induced renal hemodynamic and tubular dysfunctions with L-655,240, a new thromboxane-prostaglandin endoperoxide antagonist

The continuous infusion or bolus injection of the platelet-activating factor (PAF) is associated with profound hypotension, marked reductions of renal plasma flow, glomerular filtration, and urinary sodium excretion. All these effects are inhibited by blocking PAF receptors. To examine further the potential mediators of PAF on renal function, we utilized L-655,240 (6 mg/kg, intravenously), a thromboxane-prostaglandin endoperoxide antagonist, to study the systemic and renal response to PAF (0.8 micrograms/kg, intravenously) in the anesthetized dog, using clearance methodology. PAF decreased blood pressure from 115 +/- 7 to 54 +/- 4 mmHg (1 mmHg = 133.3 Pa), renal plasma flow from 105 +/- 6 to 74 +/- 56 mL/min, and glomerular filtration from 43 +/- 3 to 32 +/- 1 mL/min. PAF also reduced urine volume from 1.1 +/- 0.2 to 0.4 +/- 0.1 mL/min, and urinary sodium from 158 +/- 7 to 86 +/- 7 mu equiv./min. L-655,240 alone had no significant effect on blood pressure, renal plasma flow, and filtration rate, at any dose. However, the 6-mg/kg dose resulted in a slight elevation of diuresis, from 1.1 +/- 0.2 to 1.9 +/- 0.1 mL/min, and urinary sodium, from 134 +/- 13 to 212 +/- 19 mu equiv./min. All doses of L-655,240 blocked the effect of PAF on blood pressure. However, the two lower doses of this antagonist (1 and 3 mg/kg) failed to prevent the PAF-induced fall of renal plasma flow and filtration rate, and attenuated the effect on urinary sodium in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Specificity and mechanism of influence of amino acid residues on hepatic clearance of oligopeptides

We have investigated the influence of amino acid residues on hepatic clearance of oligopeptides by determining the rate of disappearance (nmol.(min.g liver)-1) of selective oligopeptides from the medium during isolated rat liver perfusion. (a) N terminus: the rate of disappearance of Ala-Leu was greater (p less than 0.01) than those of Gly-Leu, Phe-Leu, and Arg-Leu (208 +/- 13, 135 +/- 13, 116 +/- 12, and 127 +/- 12, respectively). (b) C terminus: the rate of disappearance of Leu-Ala (244 +/- 18) was significantly greater (p less than 0.01) than that of Leu-Gly (145 +/- 16). (c) Number of residues: with each increase in the number of alanine residues (2-4) there was a significant increase in the rate of peptide disappearance, and conversely, with each increase in the number of glycine residues (2-6) there was a significant decrease in the rate of peptide disappearance. Further studies showed no peptide transport by isolated liver plasma membrane vesicles and no significant correlation between the rates of peptide disappearance and hydrolase activities of the perfusion medium but highly significant correlation with hydrolase activity of plasma membrane. We conclude that certain amino acid residues, such as alanine, enhance hepatic clearance of oligopeptides by increasing their affinity as substrates for plasma membrane peptide hydrolases.     

Comparison of organ uptake and disappearance half-time of human epidermal growth factor and insulin

Epidermal growth factor (EGF), which was originally identified in salivary glands and saliva, has been also found in the kidney and urine, suggesting that the kidney may be an alternate source of this peptide. Liver was considered as the major site of the degradation of EGF but the involvement of other organs has been little studied. Therefore, we carried out comparative studies on the organ uptake and the disappearance half-time of EGF and insulin (having similar molecular size) in the same model of anesthetized dog with arterial (from aorta) and venous (from mesenteric, portal, hepatic, renal, femoral and jugular veins) blood sampling from various organs. Basal plasma level of EGF (1.32 +/- 0.33 pmol/l) and insulin (62.1 +/- 13.8 pmol/l) in the aorta was not significantly different from that recorded at various sampling sites. During i.v. infusion of EGF at 41.6 and 166.6 pmol/kg/h, the respective arterial EGF concentrations averaged 103 +/- 21 and 240 +/- 49 pmol/kg/h and the percent reduction in plasma EGF after passage through the head, leg, intestines and liver was about 30-50% and that after passage through the kidney was about 95%. During insulin (6.9 pmol/kg/h) infusion, the arterial hormone level averaged 227 +/- 21 pmol/l and this level was significantly reduced (by 23-42%) after passage through the head, leg, intestine, liver and kidney but no significant difference was found between various venous sampling sites. EGF and insulin appearing in the urine during EGF or insulin infusion accounted for about 40 and 7% of the difference between the entering and leaving renal masses of the peptide. Mean disappearance half time on stopping of EGF and insulin infusion was, respectively, 2.32 +/- 0.58 and 6.88 +/- 1.25 min. We conclude that unlike insulin, which is removed to similar extent by various organs including the kidney and the liver, EGF is taken up mainly by kidney and EGF present in urine originates mainly from renal clearance of peptide.     

Alveolar and lung liquid clearance in anesthetized rabbits

Alveolar and lung liquid clearance were studied over 8 h in intact anesthetized ventilated rabbits by instillation of either isosmolar Ringer lactate (2 ml/kg) or autologous plasma (2 or 3 ml/kg) into one lower lobe. The half time for lung liquid clearance of the isosmolar Ringer lactate was 3.3 h and that for plasma clearance was 6 h. In the plasma experiments, the alveolar protein concentration after 1 h was 5.2 +/- 0.8 g/dl, which was significantly greater than the initial instilled protein concentration of 4.3 +/- 0.7 g/dl (P less than 0.05). Thus alveolar protein concentration increased by 21 +/- 12% over 1 h, which matched clearance from the entire lung of 19 +/- 11% of the instilled volume. Overall the rate of alveolar and lung liquid clearance in rabbits was significantly faster than in prior studies in dogs and sheep. The fast alveolar liquid clearance rate in rabbits was not due to higher endogenous catecholamine release, because intravenous and alveolar (5 x 10(-5) M) propranolol did not slow the clearance. Also, beta-adrenergic therapy with alveolar terbutaline (10(-5) or 10(-4) M) did not increase the alveolar or lung liquid clearance rates. Phloridzin (10(-3) M) did not slow alveolar liquid clearance. However, amiloride (10(-4) M) inhibited 75% of the basal alveolar liquid clearance in rabbits, thus providing evidence that alveolar liquid clearance in rabbits depends primarily on sodium-dependent transport. This rabbit study provides further evidence for important species differences in the basal rates of alveolar liquid and solute clearance as well as the response to beta-adrenergic agonists and ion transport inhibitors.     

Mixed stimuli-responsive magnetic and gold nanoparticle system for rapid purification, enrichment, and detection of biomarkers

A new diagnostic system for the enrichment and detection of protein biomarkers from human plasma is presented. Gold nanoparticles (AuNPs) were surface-modified with a diblock copolymer synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The diblock copolymer contained a thermally responsive poly(N-isopropylacrylamide) (pNIPAAm) block, a cationic amine-containing block, and a semi-telechelic PEG?-biotin end group. When a mixed suspension of 23 nm pNIPAAm-modified AuNPs was heated with pNIPAAm-coated 10 nm iron oxide magnetic nanoparticles (mNPs) in human plasma, the thermally responsive pNIPAAm directed the formation of mixed AuNP/mNP aggregates that could be separated efficiently with a magnet. Model studies showed that this mixed nanoparticle system could efficiently purify and strongly enrich the model biomarker protein streptavidin in spiked human plasma. A 10 ng/mL streptavidin sample was mixed with the biotinylated pNIPAAm-modified AuNPs and magnetically separated in the mixed nanoparticle system with pNIPAAm mNPs. The aggregates were concentrated into a 50-fold smaller fluid volume at room temperature where the gold nanoparticle reagent redissolved with the streptavidin target still bound. The concentrated gold-labeled streptavidin could be subsequently analyzed directly using lateral flow immunochromatography. This rapid capture and enrichment module thus utilizes the mixed stimuli-responsive nanoparticle system to achieve concentration of a gold-labeled biomarker that can be directly analyzed using lateral flow or other rapid diagnostic strategies.     

Increased plasma apoA-IV level is a marker of abnormal postprandial lipemia: a study in normoponderal and obese subjects.

Plasma apolipoprotein A-IV (apoA-IV) levels are found elevated in hypertriglyceridemic patients. However, the relationship between plasma apoA-IV level and postprandial lipemia is not well known and remains to be elucidated. Thus, our objective was to study the relationship between plasma apoA-IV and postprandial TG after an oral fat load test (OFLT). Plasma apoA-IV was measured at fast and during an OFLT in 16 normotriglyceridemic, normoglucose-tolerant android obese subjects (BMI = 34.6 +/- 2.9 kg/m(2)) and 30 normal weight controls (BMI = 22.2 +/- 2.3 kg/m(2)). In spite of not statistically different fasting plasma TG levels in controls and obese patients, the former group showed an altered TG response after OFLT, featuring increased nonchylomicron TG area under the curve (AUC) compared with controls (516 +/- 138 vs. 426 +/- 119 mmol/l x min, P < 0.05). As compared to controls, obese patients showed increased apoA-IV levels both at fast (138.5 +/- 22.4 vs. 124.0 +/- 22.8 mg/l, P < 0.05) and during the OFLT (apoA-IV AUC: 79,833 +/- 14,281 vs. 68,176 +/- 17,463 mg/l x min, P < 0.05). Among the whole population studied, as among the control and obese subgroups, fasting plasma apoA-IV correlated significantly with AUC of plasma TG (r = 0.60, P < 0.001), AUC of chymomicron TG (r = 0.45, P < 0.01), and AUC of nonchylomicron TG (r = 0.62, P < 0.001). In the multivariate analysis, fasting apoA-IV level constituted an independent and highly significant determinant of AUC of plasma TG, AUC of chymomicron TG, AUC of nonchylomicron TG, and incremental AUC of plasma TG. In conclusion, we show a strong link between fasting apoA-IV and postprandial TG metabolism. Plasma fasting apoA-IV is shown to be a good marker of TG response after an OFLT, providing additional information on post-load TG response in conjunction with other known factors such as fasting TGs.     

Pharmacokinetic study of orphenadrine using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS)

We developed and validated a simple, rapid, and accurate HPLC-MS/MS method with simple protein precipitation for the determination of orphenadrine. Injection-to-injection running time was 3 min with a retention time of orphenadrine of 1.1 min. The linear assay range was 1-200 ng/mL (r2 > 0.99). The intra- and inter-assay imprecisions were CV 0.6-4.2% and CV 1.6-6.1%, respectively. The accuracy, extraction recovery, specificity and stability were satisfactory. Using the measured plasma concentrations of orphenadrine in 24 healthy subjects, pharmacokinetic profiles of orphenadrine were evaluated (AUC(0-72,) 1565+/-731 ng h/mL, Cmax 82.8+/-26.2 ng/mL, Tmax 3.0+/-0.9 h, elimination half-life 25.8+/-10.3 h).     

Effects of pretreatment with 8018 on the toxicokinetics of soman in rabbits and distribution in mice

The effects of 8018 [3-(2'-phenyl-2'-cyclopentyl-2'-hydroxyl-ethoxy)quinuclidine] on the elimination of soman in rabbits blood and distribution in mice brain and diaphragm were investigated using the chirasil capillary gas chromatographic analysis method. In all experiments, the concentration of P(+)soman was below the detection limit (<0.1 ng x mL(-1)). 8018 (1 mg x kg(-1), im, 10 min pre-treated) could significantly reduce the concentration of P(-)soman in rabbit blood from 53.6 +/- 13.3 to 26.2 +/- 9.70 ng x mL(-1) blood as compared to soman-treated control animal at 15 s following soman injection (43.2 microg x kg(-1), iv). Toxicokinetic parameters showed 8018 could increase clearance (CL((S))) from 20.8 +/- 1.54 to 38.2 +/- 15.3 mLx kg(-1) x s(-1) and reduce AUC of P(-)soman from 2.08 +/- 0.151 to 1.30 +/- 0.564 mg x s x L(-1). 8018 could reduce the concentration P(-)soman in diaphragm from 74.7, 70.5, 88.7 ng x g(-1) to 54.5 45.6, 50.0 ng x g(-1) at the time of 30, 90, 120 s after intoxication of soman subcutaneously vs. soman control respectively, but it had no influence on the concentration of free P(-)soman in brain. Isotope trace experiments showed that it could significantly increase the distribution amount of bound [3H]soman in mice plasma and small intestine during 0-120 min after mice received [3H]soman (0.544 GBq.119 microg x kg(-1), sc) compared to soman control group.     

Effects of atrial natriuretic peptide infusion and its metabolism in patients with chronic renal failure.

Synthetic alpha-human atrial natriuretic peptide (hANP) was infused continuously at a rate of 80 ng/kg/min for 20 min into normal volunteers and patients with chronic renal failure (CRF) receiving hemodialysis. Blood pressure (BP) decreased significantly both in normals and in patients with CRF. The magnitude and the duration of the decrease, however, were greater in patients with CRF. The plasma aldosterone concentration (PAC) decreased significantly in normals and only minimally in patients with CRF. The half time (T1/2) of plasma hANP in patients with CRF (M +/- SE: 4.5 +/- 0.5 min) was longer than that in normals (1.8 +/- 0.2 min). Moreover, the metabolic clearance rate in patients with CRF (64 +/- 7 ml/kg/min) was less than in normals (150 +/- 20 ml/kg/min). Thus, the T1/2 in plasma of hANP in patients with CRF was noticeably longer than in a normal control group. These findings suggest that hANP suppresses PAC regardless of electrocyte imbalances and/or volume change induced by kidney dysfunction and that the kidney may be important in degrading hANP.     

Stereoselective disposition of ibuprofen and flurbiprofen in rats

(R)-2-Arylpropionates are often inverted to the pharmacologically active S-enantiomers in vivo, although there is significant interspecies variability in inversion. In order to provide a basis for determining the biochemical consequences of this unique process using rats as a model, it was important to establish the pharmacokinetic disposition of the enantiomers of ibuprofen, a drug well inverted in man and flurbiprofen, a drug apparently poorly inverted in man. Rats were dosed i.v. with a single dose of (R)- or (S)-ibuprofen (20 mg/kg), (R,S)-ibuprofen (40 mg/kg), (R)- or (S)-flurbiprofen (10 mg/kg), or (R,S)-flurbiprofen (20 mg/kg). Each treatment group consisted of six animals. Serial blood samples were withdrawn over a period of 6 h for ibuprofen and 10 h for flurbiprofen. These drugs were assayed in plasma by a stereospecific HPLC assay. The pharmacokinetics of the ibuprofen and flurbiprofen enantiomers were evaluated using a two-compartment open model with conversion of the R- to S-enantiomers in the central compartment. There was 50 +/- 4% inversion of (R)-ibuprofen, a figure similar to that observed in man and (R)-ibuprofen had a higher clearance (12.6 +/- 1.3 ml/min/kg) than (S)-ibuprofen (7.7 +/- 0.7 ml/min/kg; P less than 0.01). The clearance of (R)-flurbiprofen after racemate (2.3 +/- 0.1 ml/min/kg) was higher than its clearance when administered alone (1.7 +/- 0.2 ml/min/kg; P less than 0.01), indicating a pharmacokinetic interaction between the enantiomers (most probably at plasma protein binding sites). A corresponding difference was not observed for ibuprofen. There was a small amount of inversion of (R)-flurbiprofen as determined by area analysis (4.5 +/- 1.6%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Improvement of pharmacokinetics of radioiodinated Tyr(3)-octreotide by conjugation with carbohydrates

Among a variety of other factors, the clearance kinetics and routes of excretion of radiopharmaceuticals are of crucial importance for early and high tumor/background ratios and thus signal intensity in diagnostic imaging by single photon emission tomography (SPECT) or positron emission tomography (PET). To overcome the unfavorable pharmacokinetics of radiohalogenated octreotide analogues, we evaluated three carbohydrated conjugates of Tyr(3)-octreotide (TOC). Glucose ([(125)I]Gluc-TOC), maltose ([(125)I]Malt-TOC), and maltotriose ([(125)I]Mtr-TOC) derivatives of [(125)I]TOC were synthesized via Maillard reaction and subsequent radioiodination. In cells transfected with sst1-sst5, I-Malt-TOC, and I-Mtr-TOC show sst-subtype binding profiles similar to I-TOC with high affinity for sst2. Comparative biodistribution studies 10, 30, and 60 min pi in nude mice bearing rat pancreatic tumor xenografts showed fast blood clearance for all glycosylated derivatives. Due to their markedly increased hydrophilicity, [(125)I]Gluc-TOC and [(125)I]Malt-TOC were mainly cleared via the kidneys, which led to a significant decrease in activity accumulation in liver and intestine (5.3 and 1.4 versus 10.6%ID/g for [(125)I]TOC in the liver, 1.7 and 1.0 versus 3.8%ID/g for [(125)I]TOC in the intestine 60 min pi). For all compounds, hydrophilicity and uptake in liver and intestines correlate. Uptake of the carbohydrate conjugates in the kidney was comparable. Compared to the parent compound, the accumulation of the carbohydrated compounds in sst-rich tissues (pancreas, adrenals) was increased by a factor of 1.5-3.5. While tumor uptake of [(125)I]TOC (6.7 +/- 2.6%ID/g), [(125)I]Malt-TOC (5.3 +/- 1.9%ID/g), and [(125)I]Mtr-TOC (4.9 +/- 2.2%ID/g) at 30 min postinjection was comparable, accumulation of [(125)I]Gluc-TOC was significantly increased (10.1 +/- 2.8%ID/g at 30 min pi). Somatostatin receptor specificity of tumor uptake was confirmed by pretreatment, competition, and displacement experiments in vivo using 0.8 mg TOC/kg and gamma-camera imaging. Glycosylation proved to be a powerful tool for the development of high affinity sst ligands with excellent excretion profiles and improved tumor accumulation.     

Effect of the ET(B) receptor agonist, IRL-1620, on paclitaxel plasma pharmacokinetics of breast tumor rats

Endothelin (ET)-B receptors are expressed in human breast carcinoma. We previously demonstrated that intravenous administration of the ET(B) receptor agonist, IRL-1620, to tumor-bearing rats, increased blood perfusion and enhanced delivery of paclitaxel to breast tumor tissue. The present study was conducted to determine whether IRL-1620 alters the pharmacokinetics of paclitaxel. Breast tumor-bearing rats were given 0.3 ml/kg saline or 3 nmol/kg IRL-1620 by intravenous (iv) administration. Fifteen minutes after saline or IRL-1620, 40 microCi/rat 3H-Paclitaxel was administered iv and serial plasma samples were collected until 24 hrs. 3H-Paclitaxel radioactivity in the plasma samples was measured by liquid scintillation counting. Data were fit to a three-compartment model and pharmacokinetic parameters were generated using WinNonlin software. IRL-1620 did not produce any change in the plasma paclitaxel pharmacokinetics of tumor-bearing rats. The AUC(0-infinity) (9.43 +/- 3.18 microg-hr/ml), clearance (0.69 +/- 0.17 l/hr/kg), volume of distribution (10.31 +/- 4.54 l/kg), and half-life (1.0 +/- 0.32 hrs) of paclitaxel were similar between rats treated with saline or IRL-1620. In conclusion, the ET(B) receptor agonist, IRL-1620, does not alter paclitaxel plasma pharmacokinetics and, therefore, could be used to augment the delivery of paclitaxel to the tumor tissue.