Effect of renal function on the pharmacokinetics of palifermin.

Palifermin (deltaN23KGF) decreases the incidence, severity, and duration of oral mucositis. The objectives of this open-label study were to evaluate the pharmacokinetics of single-dose palifermin in subjects with varying degrees of renal function. A single 90-mcg/kg intravenous dose of palifermin was administered to 31 subjects with varying levels of renal function (normal to requiring hemodialysis). Pharmacokinetic analyses were conducted using serum palifermin concentrations. There was considerable overlap in mean palifermin serum clearance among the groups, ranging from 318 to 495 mL/h/kg, indicating that the level of renal function did not affect clearance in humans; thus, no dose adjustment of palifermin is indicated for patients with renal dysfunction.

Enhanced covalent binding of tolmetin to proteins in humans after multiple dosing.

The in vivo stability of tolmetin-plasma protein adducts was characterized in six healthy human volunteers after a 400 mg single dose and after a multiple-dose regimen of 400 mg tolmetin every 12 hours for 10 days. Although the mean +/- SD maximum bound concentration was only 2.72 +/- 0.98 ng drug/mg protein after a single dose, it was almost an order of magnitude higher after multiple dosing. The protein adduct exhibited an average half-life of 4.8 +/- 0.9 days in contrast to the much shorter 5-hour half-lives for tolmetin and its glucuronide.

Basic principles of pharmacokinetics.

Pharmacokinetics may be defined as what the body does to a drug. It deals with the absorption, distribution, and elimination of drugs but also has utility in evaluating the time course of environmental (exogenous) toxicologic agents as well as endogenous compounds. An understanding of 4 fundamental pharmacokinetic parameters will give the toxicologic pathologist a strong basis from which to appreciate how pharmacokinetics may be useful. These parameters are clearance, volume of distribution, half-life, and bioavailability.

Synthesis and mass-spectrometric characterization of human serum albumins modified by covalent binding of two non-steroidal anti-inflammatory drugs: tolmetin and zomepirac.

Human serum albumins modified by covalently bound tolmetin or zomepirac were synthesized as models for similar products formed in vivo from acyl glucuronides. Activated esters of both drugs were prepared with 1-ethyl-3-(3-dimethylaminopropyl)-carbodi-imide, and then allowed to react with human serum albumin. Tryptic digests of both protein products were analysed by HPLC to identify peptides containing covalently bound drugs, and binding sites on albumin were identified by high-performance tandem MS. Three binding sites were common to both products, i.e. lysine-195, -199 and -351. Three further modified residues were identified for the tolmetin-albumin product, i.e. aspartic acid 1, and lysine-524 and -536.

Stereoselective binding properties of naproxen glucuronide diastereomers to proteins.

The stability of naproxen glucuronide (NAP-G) diastereomers was investigated in buffer, 0.3% and 3% human serum albumin (HSA) solutions, and human plasma. R-NAP-G was found to be less stable in phosphate buffer than its S-diastereomer, whereas incubation media containing protein in general increased the degradation rate of NAP-G but also caused a change of the stereoselective stability where the R-NAP-G was more stable than S-NAP-G. Reversible binding of NAP-Gs to HSA (0.3%) was investigated and compared with the corresponding properties of naproxen (NAP) enantiomers. NAP-G diastereomers exhibited a considerable and stereoselective affinity to HSA, although less than that observed for the NAP enantiomers. In vitro irreversible binding of NAP-Gs to HSA, human and rat plasma proteins was also investigated. Irreversible binding was higher for R-NAP-G (50 microM) than for S-NAP-G (50 microM) in all incubation media. This stereoselective difference was observed with HSA containing medium as well as in rat and human plasma. Incubation with unconjugated NAP did not lead to irreversible binding. Preincubation of HSA with acetylsalicylic acid (approximately 11 mM) and glucuronic acid (50 mM) decreased the extent of irreversible binding suggesting involvement of lysine residues for covalent binding. Preincubation with S-NAP also decreased the irreversible binding yield.

Stereoselective reversible binding properties of the glucuronide conjugates of fenoprofen enantiomers to human serum albumin.

The stereoselective binding of fenoprofen enantiomers and fenoprofen glucuronide diastereomers to human serum albumin (HSA) was investigated using an ultrafiltration method. Fenoprofen glucuronides exhibit a considerable and stereoselective affinity to HSA, although less than seen for the parent drug. The (R)-glucuronide shows a higher affinity to HSA than the (S)-diastereomer. With the enantiomers, no significant difference could be detected. Diazepam and probenecid reduced the binding of the glucuronides, as well as that of the fenoprofen enantiomers. These results suggest that parent drug and its glucuronide metabolites occupy the same binding region on the albumin molecule. Both fenoprofen enantiomers, as well as racemic fenoprofen, are capable of reducing the extent of reversibly bound fenoprofen glucuronide.

Reactivity of tolmetin glucuronide with human serum albumin. Identification of binding sites and mechanisms of reaction by tandem mass spectrometry.

The structures of adducts formed from in vitro incubation of a drug (tolmetin) glucuronide (TG) and human serum albumin (HSA), and the preferred binding sites on this protein were determined by mass spectrometry. In addition, the concentration dependence of covalent modification of HSA by TG was studied at three different concentration ratios of TG to HSA. Protein adducts were enzymatically digested and peptide fragments were separated by HPLC. Tolmetin-containing peptides (indicated by absorbance at 313 nm) were analyzed by liquid secondary-ion mass spectrometry, continuous flow-fast atom bombardment mass spectrometry, and collision-induced dissociation using a four-sector tandem mass spectrometer, matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry, and in selected cases by Edman sequencing. The identified peptides contained tolmetin linked covalently via a glucuronic acid to a protein lysine group (lysine 199 and to a lesser extent lysines 195 and 525) or tolmetin directly linked to lysines (lysines 199 and 541), serines (serines 220, 232, and 480), or arginines (arginine 222). In addition, there was indirect evidence for binding of TG to lysine 541, and binding of tolmetin to arginine 521. Our results establish that the binding of these reactive metabolites to nucleophilic sites of proteins occur via two different mechanisms: one involving imine (Schiff base) formation and the other involving nucleophilic displacement of glucuronic acid. Our data suggest, however, that the former, in which the glucuronic acid moiety of the acyl glucuronide is retained within the adducts, is favored at lower (closer to physiological) metabolite concentrations.

Pharmacokinetics of a hematoregulatory peptide (SK&F107647) in healthy male volunteers and in patients with colorectal or pancreatic adenocarcinoma not amenable to standard therapy.

PURPOSE: To describe the pharmacokinetics of SK&F 107647, a synthetic hematoregulatory peptide, in healthy volunteers and in patients with adenocarcinoma. METHODS: SK&F 107647 pharmacokinetics were evaluated in 2 dose-escalation studies. Volunteers received SK&F 107647 as single 15-minute iv infusion doses of 1, 10, 100, 500, and 1,000 microg/kg. Cancer patients received 2-hour iv infusions of 0.001, 0.01, 0.1 and 1 microg/kg once daily for 10 days. Drug concentrations were quantified in plasma and urine of healthy volunteers and on days 1 and 10 in plasma of cancer patients receiving the two top dose levels. RESULTS: In volunteers, mean clearance (CL) ranged from 76.7 to 101 ml/hour/kg; mean volume of distribution at steady-state (Vss) ranged from 175 to 268 ml/kg. Most of the administered dose was renally excreted as intact peptide within 24 hours postinfusion. In patients, mean CL was 57.6 ml/hour/kg, mean Vss ranged from 128 to 150 ml/kg and terminal half-life from 2.1 to 3.4 hours. There was little accumulation of drug. In both studies, linear pharmacokinetics was observed. Clearance approached normal glomerular filtration rate (GFR) in volunteers and correlated with creatinine clearance in cancer patients. CONCLUSIONS: SK&F 107647 exhibits linear pharmacokinetics, a small Vss, and clearance, primarily renal, approaching normal GFR.

Preclinical efficacy and safety of pascolizumab (SB 240683): a humanized anti-interleukin-4 antibody with therapeutic potential in asthma.

The type 2 helper T cell (T(H)2) cytokine interleukin (IL)-4 is thought to play a central role in the early stages of asthma. In an effort to develop an antibody treatment for asthma that neutralizes the effects of IL-4, a murine monoclonal antibody, 3B9, was generated with specificity for human IL-4. In vitro studies demonstrated that 3B9 inhibited IL-4-dependent events including IL-5 synthesis, (T(H)2) cell activation and up-regulation of immunoglobulin E expression. 3B9 was then humanized (pascolizumab, SB 240683) to reduce immunogenicity in humans. SB 240683 demonstrated species specificity for both monkey and human IL-4 with no reactivity to mouse, rat, cow, goat or horse IL-4. Pascolizumab inhibited the response of human and monkey T cells to monkey IL-4 and effectively neutralized IL-4 bioactivity when tested against several IL-4-responsive human cell lines. Affinity studies demonstrated rapid IL-4 binding by pascolizumab with a slow dissociation rate. In vivo pharmacokinetic and chronic safety testing in cynomolgus monkeys demonstrated that pascolizumab was well tolerated, and no adverse clinical responses occurred after up to 9 months of treatment. Three monkeys developed an anti-idiotypic response that resulted in rapid pascolizumab clearance. However, in the chronic dosing study the antibody response was transient and not associated with clinical events. In conclusion, pascolizumab is a humanized anti-IL-4 monoclonal antibody that can inhibit upstream and downstream events associated with asthma, including (T(H)2) cell activation and immunoglobulin E production. Clinical trials are under way to test the clinical efficacy of pascolizumab for asthma.

Pharmacokinetics and pharmacodynamics of SB-240563, a humanized monoclonal antibody directed to human interleukin-5, in monkeys.

The pharmacokinetics (PK) of SB-240563 have been investigated after i.v. and s.c. administration to cynomolgus monkeys. Approximately linear PK was observed following i.v. administration over a 6000-fold dose range (0.05-300 mg/kg). After i.v. dosing, SB-240563 concentration declined in a biexponential manner with a mean terminal half-life of 13 +/- 2 days. The plasma clearance and volume of distribution at steady state were approximately 0.2 ml/h/kg and 70 ml/kg, respectively. Following s.c. administration, SB-240563 was completely absorbed into the systemic circulation. Because interleukin-5 is known to stimulate production, activation, and maturation of eosinophils, eosinophil counts were measured to assess pharmacologic activity of SB-240563. The maximal response (81-96% decrease in eosinophil count relative to baseline) following a single s.c. administration occurred at 3 weeks postdosing. Suppression of eosinophil count also was observed following multiple monthly administrations of SB-240563 to monkeys. The pharmacokinetic/pharmacodynamic relationship was generally well described with an indirect pharmacologic response model with an estimated IC(50) value of 1.43 microg/ml. The combination of a low IC(50) value for reduction of circulating eosinophils and a long terminal half-life suggests the possibility of an infrequent dosing regimen for SB-240563 for treatment of diseases associated with increased eosinophil function such as asthma.

Preclinical efficacy and safety of mepolizumab (SB-240563), a humanized monoclonal antibody to IL-5, in cynomolgus monkeys.

BACKGROUND: Allergic respiratory diseases are characterized by large numbers of eosinophils and their reactive products in airways and blood; these are believed to be involved in progressive airway damage and remodeling. IL-5 is the principal cytokine for eosinophil maturation, differentiation, and survival. Mepolizumab (SB-240563), a humanized monoclonal antibody (mAb) specific for human IL-5, is currently in clinical trials for treatment of asthma. OBJECTIVE: The purpose of this study was to characterize the pharmacologic activity and long-term safety profile of an anti--human IL-5 mAb to support clinical trials in asthmatic patients. METHODS: Naive and Ascaris suum -sensitive cynomolgus monkeys received various dose levels of mepolizumab and were monitored for acute and chronic pharmacologic and toxic responses. RESULTS: To support preclinical safety assessment, cynomolgus monkey IL-5 was cloned, expressed, and characterized. Although monkey IL-5 differs from human IL-5 by 2 amino acids (Ala27Gly and Asn40His), mepolizumab has comparable inhibitory activity against both monkey IL-5 and human IL-5. In A suum--sensitive monkeys, single doses of mepolizumab significantly reduced blood eosinophilia, eosinophil migration into lung airways, and levels of RANTES and IL-6 in lungs for 6 weeks. However, mepolizumab did not affect acute bronchoconstrictive responses to inhaled A suum. In an IL-2--induced eosinophilia model (up to 50% blood eosinophilia), 0.5 mg/kg mepolizumab blocked eosinophilia by >80%. Single-dose and chronic (6 monthly doses) intravenous and subcutaneous toxicity studies in naive monkeys found no target organ toxicity or immunotoxicity up to 300 mg/kg. Monkeys did not generate anti-human IgG antibodies. Monthly mepolizumab doses greater than 5 mg/kg caused an 80% to 100% decrease in blood and bronchoalveolar lavage eosinophils lasting 2 months after dosing, and there was no effect on eosinophil precursors in bone marrow after 6 months of treatment. Eosinophil decreases correlated with mepolizumab plasma concentrations (half-life = 13 days). CONCLUSION: These studies demonstrate that chronic antagonism of IL-5 by mepolizumab in monkeys is safe and has the potential, through long-term reductions in circulating and tissue-resident eosinophils, to be beneficial therapy for chronic inflammatory respiratory diseases.