Multidentate 2-pyridyl-phosphine ligands - towards ligand tuning and chirality.

In the current work a range of multidentate pyridyl-phosphine ligands are synthesised with tuneable electronic and steric character, through the incorporation of a variety of alcohols into (amino)pyridyl-phosphine frameworks. The stoichiometric reactions of compounds of the type (R2N)xP(2-py)3-x (2-py = 2-pyridyl) with alkyl as well as aryl alcohols result in the formation of (alkoxy)pyridyl-phosphines (RO)xP(2-py)3-x (R = Me, 2-Bu, Ph). This synthetic procedure also allows the introduction of enantiomerically pure alcohols, like (R)-(-)-2-BuOH and (S)-(+)-2-BuOH, and as such provides a very convenient two-step route to chiral multidentate pyridyl-phosphine ligand sets. Using the bis-amino-phosphine (Et2N)2P(2-py), the stepwise introduction of alcohols enables the synthesis of racemic alkoxy-amino-phosphines (R2N)(RO)P(2-py), as well as alkoxy-phosphines (RO)2P(2-py) and therefore offers easy access to a library of different pyridyl-phosphine ligands. Coordination studies of the (amino)pyridyl-phosphines and (alkoxy)pyridyl-phosphines with copper(i) reveal that ligands with two N donor atoms form dimeric arrangements, while (PhO)2P(2-py), in-corporating only one N donor atom, shows completely different coordination behaviour.

Developmental effects of visual environment on species-assortative mating preferences in Lake Victoria cichlid fish.

Local adaptation can be a potent force in speciation, with environmental heterogeneity leading to niche specialization and population divergence. However, local adaption often requires nonrandom mating to generate reproductive isolation. Population divergence in sensory properties can be particularly consequential in speciation, affecting both ecological adaptation and sexual communication. Pundamilia pundamila and Pundamilia nyererei are two closely related African cichlid species that differ in male coloration, blue vs. red. They co-occur at rocky islands in southern Lake Victoria, but inhabit different depth ranges with different light environments. The species differ in colour vision properties, and females exert species-specific preferences for blue vs. red males. Here, we investigated the mechanistic link between colour vision and preference, which could provide a rapid route to reproductive isolation. We tested the behavioural components of this link by experimentally manipulating colour perception - we raised both species and their hybrids under light conditions mimicking shallow and deep habitats - and tested female preference for blue and red males under both conditions. We found that rearing light significantly affected female preference: shallow-reared females responded more strongly to P. pundamilia males and deep-reared females favoured P. nyererei males - implying that visual development causally affects mate choice. These results are consistent with sensory drive predictions, suggesting that the visual environment is key to behavioural isolation of these species. However, the observed plasticity could also make the species barrier vulnerable to environmental change: species-assortative preferences were weaker in females that were reared in the other species' light condition.

The first observation of the [Cp3Mn]- anion; structures of hexagonal [(eta 2-Cp)3MnK.1.5thf] and ion-separated [(eta 2-Cp)3Mn]2[Mg(thf)6].2thf.

Hexagonal [(eta 2-Cp)3MnK.1.5thf] 1 and ion-separated [(eta 2-Cp)3Mn]2[Mg(thf)6].2thf 2 are obtained from reactions of CpK and Cp2Mg, respectively, with manganocene, Cp2Mn; they are the first complexes to be structurally characterised containing the [Cp3Mn]- anion.

Sample pooling to expedite bioanalysis and pharmacokinetic research.

In the progression from drug discovery to development, not only pharmacokinetic (PK) characterization needed for lead compound selection often becomes a rate-limiting step, but also high volume of routine sample analysis ensued from numerous required biodisposition studies for the lead compounds and their back-ups often place a burdensome hurdle to the throughput of IND and NDA development phases. Higher throughput of PK screening via cocktail dosing has been reported to accelerate PK screening in the discovery phase. However, concerns on drug-drug interactions and other limitations associated with the cocktail M-in-One dosing (multiple compounds per dose per animal) has prompted the present investigation of sample pooling alongside One-in-One dosing strategy (one compound per dose per animal) as an alternative to the cocktail dosing approach. Using traditional HPLC for bioanalysis as an example, the present study illustrate the concept and usefulness of sample pooling that could facilitate the throughput of PK screening and characterization in both discovery and development phases. Six proprietary dopamine D4 receptor antagonist preleads representing three different chemical classes, used as model compounds (C1-C6), were administered orally to rats. One rat received one compound and three rats were used for each compound. Six unknown plasma samples from six different rats at each time point were pooled. The pooled plasma samples were extracted by a one-step liquid-liquid extraction and concentrations of the six preleads were quantitated simultaneously. By sample pooling, a substantial amount of PK information was obtained at the same time for the six preleads, which requires much less workload than when bioanalysis is dealt with one compound at a time. For the first time in one aspect of innovative bioanalysis, the present investigation has demonstrated that sample pooling following One-in-One dosing can be utilized to enhance the throughput rate in PK screening in discovery phase. The sample pooling approach is likely to be useful in enhancing the throughput of PK characterization in development phase. With the advent of LC-MS and its becoming user-friendly, where separation of drug compounds is no longer an issue, the uniqueness of sample pooling may also pose a new way of thinking in regard to the old ways of handling bioanalysis for traditional PK research.

Second generation "peptoid" CCK-B receptor antagonists: identification and development of N-(adamantyloxycarbonyl)-alpha-methyl-(R)-tryptophan derivative (CI-1015) with an improved pharmacokinetic profile.

We have previously described the design and development of CI-988, a peptoid analogue of CCK-4 with excellent binding affinity and selectivity for the CCK-B receptor. Due to its anxiolytic profile in animal models of anxiety, this compound was developed as a clinical candidate. However, during its development, it was determined that CI-988 had low bioavailability in both rodent and nonrodent species. In the clinic, it was further established that CI-988 had poor bioavailability. Thus, there was a need to identify an analogue with an improved pharmacokinetic (PK) profile. The poor bioavailability was attributed to poor absorption and efficient hepatic extraction. We envisaged that reducing the molecular weight of the parent compound (5, MW = 614) would lead to better absorption. Thus, we synthesized a series of analogues in which the key alpha-methyltryptophan and adamantyloxycarbonyl moieties, required for receptor binding, were kept intact and the C-terminus was extensively modified. This SAR study led to the identification of tricyclo[3.3.1.1(3,7)]dec-2-yl [1S-[1 alpha(S*)2 beta]-[2-[(2-hydroxycyclohexyl)amino]-1-(1H-indol-3- ylmethyl)-1-methyl-2-oxoethyl]carbamate (CI-1015, 31) with binding affinities of 3.0 and 2900 nM for the CCK-B and CCK-A receptors, respectively. The compound showed CCK-B antagonist profile in the rat ventromedial hypothalamus assay with a Ke of 34 nM. It also showed an anxiolytic like profile orally in a standard anxiety paradigm (X-maze) with a minimum effective dose (MED) of 0.1 microgram/kg. Although the compound is less water soluble than CI-988, oral bioavailability in rat was improved nearly 10 times relative to CI-988 when dosed in HP beta CD. The blood-brain permeability of CI-1015 (31) was also enhanced relative to CI-988 (5). On the basis of the overall improved pharmacokinetic profile as well as enhanced brain penetration, CI-1015 (31) was chosen as a development candidate.

Cloning of a Lysobacter enzymogenes gene that encodes an arginyl endopeptidase (endoproteinase Arg-C).

Screening an expression library of Lysobacter enzymogenes DNA allowed us to clone a gene encoding a serine protease that cleaves synthetic substrates C-terminal to Arg and, to a lesser extent, Lys residues. The gene product, which shares sequence homology with the lysyl endopeptidases from L. enzymogenes and Achromobacter lyticus, consists of a signal sequence (24 residues), pro-region ( approximately 195 residues), and catalytic domain ( approximately 244 residues). Downstream of this gene is an open reading frame that lacks a promoter and appears to encode an inactive type I subtilase.

Determination of two CI-1007 sulfate metabolites in monkey plasma and urine.

Two HPLC assays were developed and validated for simultaneous quantitation of two sulfate metabolites, PD 163637 (VI) and PD 163639 (VIII), of an investigational antipsychotic drug CI-1007 (I) in monkey plasma and urine. VI and VIII were identified as major metabolites in monkey plasma, and both were excreted in urine. Monkey plasma samples were directly injected after deproteinization, and urine samples were analyzed after a clean-up procedure using methyl-tert.-butyl ether. Liquid chromatographic separation was achieved on a Zorbax RX C8 analytical column using gradient elution. Column effluent was monitored using fluorescence detection with excitation and emission wavelengths of 254 and 330 nm, respectively. Minimum quantitation limit was 50 ng/ml in plasma and 100 ng/ml in urine. Linearity was demonstrated up to 3000 ng/ml in plasma and urine. Recoveries of the analytes from plasma and urine were greater than 85%. The assay has been applied to the determination of VI and VIII in plasma and urine samples from monkeys receiving oral administration of I.

Pharmacokinetics and pharmacodynamics of an investigational antipsychotic agent, CI-1007, in rats and monkeys.

PURPOSE: To study the pharmacokinetics (PK) and pharmacodynamics (PD) of an investigational antipsychotic agent, CI-1007, in rats and monkeys. METHODS: CI-1007 and a pharmacologically active metabolite, PD 147693 (M1), were evaluated in animal antipsychotic tests (inhibition of dopamine neuron firing and spontaneous locomotor activity in rats, and inhibition of continuous avoidance in monkeys). Plasma concentrations of CI-1007 and M1 were determined using validated HPLC assays. Log-linear and link models were used for PK/PD analysis. RESULTS: CI-1007 and M1 have shown similar effects on dopamine neuron firing (2.5 mg/kg i.p.), and produced dose-related effects on spontaneous locomotor activity in rats (0.3-30 mg/kg p.o.) and on continuous avoidance in monkeys (0.6-1.2 mg/kg p.o.). After pharmacologically active CI-1007 doses, mean plasma CI-1007 Cmax increased from 19 to 200 ng/ml in Sprague-Dawley rats at doses of 3-30 mg/ kg, and from 8.1 to 34 ng/ml in squirrel monkeys at doses of 0.6-1.2 mg/kg, but corresponding plasma M1 Cmax values were near or below the limit of quantitation (5 ng/ml). CI-1007 EC50 was 31.1 ng/ml in rats, calculated from a long-linear regression. In monkeys, CI-1007 ECe50, gamma, and Keo at 0.6 and 1.2 mg/kg were 4.8 and 4.5 ng/ml, 1.9 and 2.0, and 0.47 and 0.48 hr-1, respectively, calculated by the link model. CONCLUSIONS: CI-1007 has shown dose-related pharmacokinetics and pharmacodynamics in rats and monkeys. Although M1 produces antipsychotic-like effects similar to CI-1007, the contribution of M1 to the activity of the parent drug may not be significant in rats and monkeys as based on plasma levels. CI-1007 plasma concentration correlates log-linearly with inhibition effect from the rat locomotor study. The counter-clockwise hysteresis relationship of CI-1007 plasma concentration and inhibition effect from the monkey avoidance test was described by a link model, and the resulting Ce (concentration in effect compartment) versus effect profile exhibits a sigmoidal curve.

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.

The tachykinin NK1 receptor antagonist PD 154075 blocks cisplatin-induced delayed emesis in the ferret.

The activity of a selective tachykinin NK1 receptor antagonist, PD 154075 ([(2-benzofuran)-CH2OCO]-(R)-alpha-MeTrp-(S)-NHCH(CH3) Ph), was examined in radioligand binding studies, in a [Sar9,Met(O2)11]substance P-induced foot-tapping model in the gerbil, and in cisplatin-induced acute and delayed emesis in the ferret. In radioligand binding studies, PD 154075 showed nanomolar affinity for the human, guinea-pig, gerbil, dog and ferret NK1 receptors with an approximate 300 times lower affinity for the rodent NK1 receptor. Using NK2,NK3 receptors and a range of other receptor ligands, PD 154075 was shown to exhibit a high degree of selectivity and specificity for the human type NK1 receptor. Following subcutaneous administration PD 154075 dose dependently (1-100 mg/kg) antagonised the centrally mediated [Sar9,Met(O2)11] substance P-induced foot tapping in the gerbil with a minimum effective dose (MED) of 10 mg/kg. The ability of PD 154075 to readily penetrate into the brain following oral administration was confirmed by its extraction and high performance liquid chromatography assay from the rat brain. PD 154075 was shown to achieve a relatively fast and sustained brain concentration (brain/plasma ratios ranged from 0.27 to 0.41 during the time period of 0.25-12 h). Further pharmacokinetic studies revealed that the absolute oral bioavailability of PD 154075 in the rat was (mean +/- S.D.) 49 +/- 15%. PD 154075 (1-30 mg/kg, i.p.) dose dependently antagonised the acute vomiting and retching in the ferret measured for 4 h following administration of cisplatin (10 mg/kg, i.p.) with a MED of 3 mg/kg. The administration of a lower dose of cisplatin (5 mg/kg, i.p.) in the ferret induces both an acute (day 1) and delayed (days 2 and 3) phase of emesis. The i.p. administration of PD 154075, 10 mg/kg three times a day for 3 days, almost completely blocked both the acute and delayed emetic responses. In the same study, the 5-HT3 receptor antagonist ondansetron (1 mg/kg, i.p., t.i.d.) was also very effective against the acute emetic response observed during the first 4 h following cisplatin, but it was only weakly active against the delayed response. In conclusion, PD 154075 is a selective and specific high affinity NK1 receptor antagonist with good oral bioavailability which is effective against both acute and delayed emesis induced by cisplatin in the ferret.

Analytical considerations for trace determinations of drugs in breast milk.

Recent scientific and regulatory interest in lacteal excretion of drugs has prompted this review of bioanalytical sample preparation techniques for milk. The composition and properties of milk are reviewed, with emphasis on how the sample preparation is affected. The most important principals of mammary gland pharmacology, including protein binding, ion trapping and liquid solubility, are described. Because adequate milk volume is difficult to obtain from some smaller rodent species, special arrangements for sample collection, control preparation and assay standardization often need to be made. Several commonly-used sample preparation approaches for drugs in milk, including direct injection, dialysis and ultrafiltration, protein precipitation, liquid-liquid extraction, solid-phase extraction and immunoaffinity extraction. Have been reported with varying degrees of success. The advantages and disadvantages of each of these approaches is discussed.

Development of HPLC plasma assays for CAM 4515 and CAM 4750, two new nonpeptide tachykinin antagonists, and application to bioavailability studies.

CAM 4515 and CAM 4750 are new nonpeptide tachykinin NK1 receptor antagonists with different lipophilicities. Two separate, simple, and sensitive HPLC methods for the quantitation of these two compounds in plasma and the evaluation of their oral bioavailability in rats were developed and validated. Extraction of CAM 4515 from plasma involved protein precipitation with acetonitrile, while that for CAM 4750 involved a one-step liquid-liquid extraction with methylene chloride. The analytes in extracts were chromatographed on a C18 column using two different separation buffers, 47% 0.02 M sodium citrate (pH 3.5)-53% acetonitrile for CAM 4515 and 59% 0.02 M potassium phosphate dibasic (pH 7.0)-41% acetonitrile for CAM 4750, and both compounds were detected by fluorescence (excitation 278 nm; emission 342 nm). Stability profiles of both drugs at -20 degrees C or room temperature in plasma and in reconstituted buffers were good. The limit of quantitation for both drugs was 5 ng ml-1 with good linearity from 5 to 1000 ng ml-1 using 100-200 microliters of plasma. Excellent precision (relative standard deviation < 8.3%) and accuracy (relative error +/- 9.2%) were observed for both CAM 4515 and CAM 4750. Oral bioavailability studies were conducted for each compound in rats receiving a p.o. dose of 20 mg kg-1 and an i.v. dose of 5 mg kg-1. The absolute oral bioavailability of CAM 4750 (80%) was estimated to be 40-fold greater than that of CAM 4515 (2%). The experimental results suggest that incorporation of a pyridine group into the structural backbone may greatly improve bioavailability.

Development and validation of two solid-phase enzyme immunoassays (ELISA) for quantitation of human epidermal growth factors (hEGFs).

PURPOSE: The purpose of the present investigation was to develop and validate two separate enzyme-linked immunosorbent assays (ELISA) for quantitation of exogenous human epidermal growth factor (hEGF1-53) and its truncated fragment (hEGF1-48) in rat plasma. METHODS: The present assay systems were based on the sandwiching of the antigen between a monoclonal mouse anti-hEGF1-53 antibody, pre-coated on a 96-well polystyrene plate, and a polyclonal rabbit anti-hEGF1-48 antibody, which is then detected with a peroxidase-labeled goat anti-rabbit antibody. RESULTS: The calibration curves for hEGF1-48 and hEGF1-53 in plasma were validated over a concentration range of 7.8-250 and 62.5-1000 pg/ml, respectively. Determined from replicate assays of hEGF1-48 quality control samples, the intra-assay precision and accuracy were < or = 8.8% RSD and within +/- 9.8%; and the inter-assay precision and accuracy were < or = 14.8% RSD and within +/- 9.7% RE, respectively. Determined from replicate assays of hEGF1-53 quality control samples, the intra-assay precision and accuracy were < or = 10.0% RSD and within +/- 8.5%; and the inter-assay precision and accuracy were < or = 10.0% RSD and within +/- 5.7% RE, respectively. The limit of quantitation of the hEGF1-48 and hEGF1-53 assay using 200 microliters plasma per well is 7.8 and 62.5 pg/ml, respectively. These two ELISA methods are specific to hEGFs and do not cross-react with mouse EGF or other growth factors (TGF alpha, TGF beta, PDGF, and FGF) or lymphokines (IL1 beta and TNF alpha). These validated methods have been routinely applied to assay of plasma samples from various pharmacokinetic studies in rats receiving intravenous hEGFs. Both assay methods were also adapted to assay endogenous hEGFs in biological fluids of different animal species. CONCLUSIONS: Two sensitive ELISA methods have been validated for quantitation of hEGF1-53 and hEGF1-48 in rat plasma. Their utility has been demonstrated in the application of assaying immunoreactive concentration of exogenous and endogenous epidermal growth factors.

Design and evaluation of an automated solid-phase extraction method development system for use with biological fluids.

An automated solid-phase extraction method development system, utilizing a Zymate XP robot and a custom-designed solid-phase extraction manifold, has been developed and validated. This system spikes blank liquid matrix, such as plasma, with solutions containing drug, internal standard, and up to three metabolites. Samples are then buffered or diluted with an appropriate reagent. After these samples and corresponding blanks have been prepared, solid-phase cartridges containing selected sorbents are automatically conditioned. Samples are robotically vortexed and transferred to the conditioned cartridges, and analytes are extracted. Validation of this robotic system demonstrated acceptable precision and accuracy for three types of liquid transfer, including metering pump ( < 6% RSD and RE for > or = 2.0 mL dispensation), syringe-based laboratory station ( < or = 2.9% RSD and 0.5% RE for volumes between 0.25 and 1.00 mL), and syringe hands ( < 3.5% RSD and RE for volumes between 0.10 and 1.00 mL). For two example compounds, the system provided data which effectively distinguished good solid-phase sorbents from marginal ones through precision, recovery, and chromatographic selectivity. Solid-phase extraction of these compounds from human plasma gave precision (2-10% RSD) and extraction efficiency (96 +/- 6%) comparable to results obtained from manual extractions (92 +/- 11%).

Three complementary liquid chromatographic methods for determination of the peptoid cholecystokinin-B antagonist, CI-988, in rat plasma.

Three different liquid chromatographic methods (two quantitative methods which employ fluorescence detection and one qualitative method which employs selected ion-monitoring detection) were developed and validated to provide complementary specificity for determination of CI-988, a cholecystokinin-B antagonist, in rat plasma. The first quantitative method involves isocratic separation of "non-ionized" CI-988 and internal standard on a C-18 column, whereas the alternative quantitative method involves isocratic separation of the "anionic" analytes. These two quantitative HPLC methods rely on the intrinsic fluorescence of CI-988 and internal standard for detection, and both methods are equally sensitive (linear range of 2.0-1000 ng ml-1), accurate (+/- 15% relative error), and precise (< or = 15% relative standard deviation). Plasma CI-988 concentrations for samples (N = 69) assayed with the "non-ionized" separation are linearly correlated with concentrations for the same samples assayed with the "anionic" separation (y = 1.08 chi - 0.57, R = 0.999). In addition, a third qualitative method, HPLC-thermospray mass spectrometry, was developed to provide complementary evaluation of assay specificity through the use of selected CI-988 fragment ion monitoring. When investigating an anomalous chromatographic result that calls into question the specificity of a method, the availability and use of alternative validated chromatographic separations and orthogonal detection schemes are beneficial.

Absorption of Cam-2445, and NK1 neurokinin receptor antagonist: in vivo, in situ, and in vitro evaluations.

Cam-2445 is a selective, high-affinity NK1 receptor antagonist that is a potentially useful treatment for arthritis, asthma, migraine, anxiety, psychosis, and emesis. Cam-2445 exhibits low aqueous solubility and high lipophilicity and has a molecular weight of 470. Cam-2445 has poor oral bioavailability and the purpose of this research was to examine the potential barriers to the oral bioavailability of Cam-2445. Cam-2445 was relatively stable at 37 degrees C in 0.1 N HCl, 5 microM alpha-chymotrypsin, rat intestinal perfusate, and in rat jejunal brush border membrane suspension. High permeability was observed from CACO-2 cells and from rat single-pass intestinal perfusions. Cam-2445 was administered as a solution to rats by intravenous (i.v.), oral (p.o.), intraduodenal (i.d.), and intraportal (i.p.v.) routes. The total oral bioavailability was poor at 1.4%. Absorption appeared to be rapid after i.d. dosing; bioavailability was 26%, and 54% of the dose was absorbed intact into the portal system. After i.p.v. dosing, 48% of the dose was available to the systemic circulation. The elimination t1/2 after i.d. dosing (2.91 h) was comparable to that i.v. dosing (2.93 h), whereas it was significantly longer after p.o. dosing (12.4 h). The p.o. dose apparently precipitated in the gastrointestinal (GI) tract, resulting in low oral bioavailability. These results indicated that neither stability in the GI tract nor membrane transport were major obstacles to the absorption of Cam-2445. While hepatic extraction of 52% was significant, the low aqueous solubility of Cam-2445, as well as the differences noted between p.o. and i.d. studies, strongly support GI dissolution and/or precipitation as the limiting factor for the oral bioavailability of the compound.

Disposition kinetics of human epidermal growth factor (hEGF1-53) and its truncated fragment (hEGF1-48) in rats.

Clearance of human epidermal growth factor (hEGF1-53) has been proposed to be mediated by a receptor pathway involving a typical cascade of ligand-receptor endocytosis and lysosomal degradation. Deletion of the C-terminal pentapeptide from hEGF1-53, which yields hEGF1-48, is known to be associated with a marked reduction in receptor binding. We defined the intravenous (iv)-bolus (acute exposure) and the iv-infusion (prolonged exposure) pharmacokinetics of hEGF1-53 and hEGF1-48 in rats to investigate the impact of the deletion of C-terminal pentapeptide on the EGF clearance using a validated, sensitive ELISA method for quantitation of the peptides in plasma. Both peptides at the low iv bolus dose of 10 micrograms/kg were cleared from plasma with unusually high clearances (CLtot: 128 +/- 31 ml/min/kg for hEGF1-53 and 168 +/- 47 ml/min/kg for hEGF1-48), which are virtually complete within 4-min postdose, and the difference in the overall pharmacokinetics is of minor significance. A 10-fold increase in bolus dose to 100 micrograms/kg decreased clearances 3- to 6-fold, indicating a nonlinear kinetics for both peptides; however, hEGF1-48 was cleared (52 +/- 11 ml/min/kg) 2.5-fold faster than hEGF1-53. A similar nonlinear kinetics was also noticed for both peptides when they were administered by a 2-hr iv infusion at 30 and 300 micrograms/kg doses. hEGF1-48 at the low and high infusion doses was cleared at 126 +/- 16 and 33.7 +/- 14.5 ml/min/kg, respectively, which are 4-fold greater than the corresponding clearance rates of hEGF1-53. These observations suggest that a) deletion of C-terminal pentapeptide is associated with a faster clearance of the growth factor and b) the receptor clearance pathway may be more sensitive to saturation with hEGF1-53 than with hEGF1-48 at low microgram dose levels. hEGF1-53 at the low infusion dose of 30 micrograms/kg was cleared (32.1 +/- 6.2 ml/min/kg) 4-fold slower in comparison with the low bolus dose of 10 micrograms/kg, indicating a remarkable injection mode-dependent disposition kinetics for hEGF1-53, which does not exist for hEGF1-48. The overall results suggest that deletion of C-terminal pentapeptide leads to faster clearance of the growth factor, and the degree of the impact of deletion of C-terminal pentapeptide on the global pharmacokinetics is also dependent on the length of exposure of the receptor to the ligand. The negative relationship between receptor binding and plasma clearance for the two peptides remains to be elucidated at the molecular and receptor levels.