Pharmacokinetics of the Antimalarial Drug, AQ-13, in Rats and Cynomolgus Macaques

The purpose of this study was to evaluate the bioavailability and pharmacokinetics of a new antimalarial drug, AQ-13, a structural analog of chloroquine (CQ) that is active against CQ-resistant Plasmodium species, in rats and cynomolgus macaques. Sprague-Dawley rats ( n = 4 /sex) were administered a single dose of AQ-13 intravenously (i.v.) (10 mg/kg) or orally (20 or 102 mg/kg). Blood and plasma samples were collected at several timepoints. AQ-13 achieved Cmax after oral administration at approximately 3 to 4 h and could be detected in blood for 2 to 5 days after oral administration. The ratio of area under the curve (AUC) values at the high and low dose for AQ-13 deviated from an expected ratio of 5.0, indicating nonlinear kinetics. A metabolite peak was noted in the chromatograms that was identified as monodesethyl AQ-13. Oral bioavailability of AQ-13 was good, approximately 70%. The pharmacokinetics of AQ-13 was also determined in cynomolgus macaques after single (i.v., 10 mg/kg; oral, 20 or 100 mg/kg) and multiple doses (oral loading dose of 50, 100, or 200 mg/kg on first day followed by oral maintenance dose of 25, 50, or 100 mg/kg, respectively, for 6 days). The AUC and Cmax values following single oral dose administration were not dose proportional; the Cmax value for AQ-13 was 15-fold higher following an oral dose of 100 mg/kg compared to 20 mg/kg. MonodesethylAQ-13 was a significant metabolite formed by cynomolgus macaques and the corresponding Cmax values for this metabolite increased only 3.8-fold over the dose range, suggesting that the formation of monodesethyl AQ-13 is saturable in this species. The bioavailability of AQ-13 in cynomolgus macaques following oral administration was 23.8% for the 20-mg/kg group and 47.6% for the 100-mg/kg group. Following repeat dose administration, high concentrations of monodesethyl AQ-13 were observed in the blood by day 4, exceeding the AQ-13 blood concentrations through day 22. Saturation of metabolic pathways and reduced metabolite elimination after higher doses are suggested to play a key role in AQ-13 pharmacokinetics in macaques. In summary, the pharmacokinetic profile and metabolism ofAQ-13 are very similar to that reported in the literature for chloroquine, suggesting that this new agent is a promising candidate for further development for the treatment of chloroquine-resistant malaria.

Pharmacokinetics in animals and humans of a first-in-class peptide deformylase inhibitor

BB-83698, a potent and selective inhibitor of peptide deformylase, was the first compound of this novel antibacterial class to progress to clinical trials. Single- and/or multiple-dose studies with doses ranging from 10 to 50 mg of BB-83698/kg of body weight were done with mice, rats, and dogs. Intravenous pharmacokinetics were characterized by low to moderate clearances and moderate volumes of distribution for all species. In dogs, but not in rodents, central nervous system (CNS) effects were dose limiting for intravenously administered BB-83698 and were suspected to be related to a high maximum concentration of the agent in plasma (Cmax) rather than to total systemic exposure. Controlled infusion studies with dogs demonstrated that CNS effects could be avoided without compromising systemic exposure by reducing the Cmax. A randomized, double-blind, placebo-controlled, five-way-crossover, single-dose-escalation, phase I study to explore the safety, tolerability, and pharmacokinetics of intravenous BB-83698 at doses ranging from 10 to 475 mg was performed with healthy male volunteers. Systemic exposures were generally in linear relationships with administered doses in animals and humans. Pharmacokinetics were consistent, predictable, and exhibited good allometric scaling among all species (r2 >0.98). Moreover, BB-83698 dosing in humans proceeded to a predicted efficacious exposure (the area under the concentration-time curve/MIC ratio, up to 184) without any clinically significant adverse effects.

Oral anti-pneumococcal activity and pharmacokinetic profiling of a novel peptide deformylase inhibitor

OBJECTIVE

BB-81384, a novel peptide deformylase (PDF) inhibitor, was characterized in terms of enzyme inhibition profile, antibacterial activity, rodent pharmacokinetics and oral efficacy in murine infection models.

METHODS

MICs were determined by standard NCCLS broth microdilution. Selectivity of metalloenzyme inhibition was determined with a limited panel of enzymes via standard biochemical assays. Profiling of the pharmacokinetics and select tissue disposition in mice was determined and compared with that of the macrolide, azithromycin. In vivo murine efficacy studies using Streptococcus pneumoniae were conducted using a peritonitis model, as well as lung and thigh burden models of infection.

RESULTS

BB-81384 selectively inhibited PDF with an IC(50) approximately 10 nM and with MICs < 0.5 mg/L against most S. pneumoniae pathogens. Pharmacokinetic analysis revealed good oral bioavailability and moderate clearance and volume of distribution. BB-81384 partitioning to lung tissue was similar in terms of magnitude and kinetics to that of the plasma compartment. Single-administration oral efficacy in a mouse peritonitis model was evident with an ED(50) of 30 mg/kg. BB-81384 reduced the bacterial load by approximately 5 and 3 log units in organ-burden models of lung and thigh infection, respectively.

CONCLUSION

BB-81384, a novel PDF inhibitor with good activity against S. pneumoniae in vitro, was the first compound of this class to be profiled for oral pharmacokinetics and tissue disposition and to demonstrate oral anti-pneumococcal efficacy in mice.

Phase 1 trial of FVIII gene transfer for severe hemophilia A using a retroviral construct administered by peripheral intravenous infusion

In a phase 1 dose escalation study, 13 subjects with hemophilia A received by peripheral intravenous infusion a retroviral vector carrying a B-domain-deleted human factor VIII (hFVIII) gene. Infusions were well tolerated. Tests for replication competent retrovirus have been negative. Polymerase chain reaction (PCR) analyses demonstrate the persistence of vector gene sequences in peripheral blood mononuclear cells in 3 of 3 subjects tested. Factor VIII was measured in serial samples using both a one-stage clotting assay and a chromogenic assay. While no subject had sustained FVIII increases, 9 subjects had FVIII higher than 1% on at least 2 occasions 5 or more days after infusion of exogenous FVIII, with isolated levels that ranged from 2.3% to 19%. Pharmacokinetic parameters of exogenous FVIII infused into subjects 13 weeks after vector infusion showed an increased half-life (T1/2; P <.02) and area under the curve (AUC, P <.04) compared with prestudy values. Bleeding frequency decreased in 5 subjects compared with historical rates. These results demonstrate that this retroviral vector (hFVIII(V)) is safe and, in some subjects, persists more than a year in peripheral blood mononuclear cells, with measurable factor VIII levels and with increased available FVIII activity (increased T1/2 and AUC) after infusion of exogenous FVIII concentrate.

Analysis of 2beta-carbomethoxy-3beta-(4-fluorophenyl)-N-(3-iodo-E-allyl)nortropane in rat plasma. II. Pharmacokinetic profile in male and female Sprague-Dawley rats evaluated by capillary electrophoresis

This paper describes a pharmacokinetic study performed in Sprague-Dawley rats after i.v. administration of a single 6-mg/kg dose of 2beta-carbomethoxy-3beta-(4-fluorophenyl)-N-(3-iodo-E-allyl)nortropane (Altropane). Plasma samples were collected from the retro-orbital sinus at times up to 3 h after drug administration, extracted by solid-phase extraction, and the drug levels determined by capillary electrophoresis (CE). Pharmacokinetic parameters were determined by a standard noncompartmental model using WinNonlin version 1.5. The maximum plasma concentrations, clearances of the drug, and areas under the curve for male and female rats were 5.74 and 7.26 microg/ml, 135.7 and 98.5 ml/kg x min, and 44.23 and 60.92 microg x min/ml, respectively. The drug was cleared very rapidly from the systemic circulation, with a terminal t(1/2) of 7 to 10 min and a mean residence time of about 11 min for both sexes. The volume of distribution was approximately 1 l/kg. No metabolites were detected when the samples were analyzed individually. However, after samples were pooled and concentrated, traces of two unknown peaks that may represent metabolites were detected in concentrates from the last two timepoints. Part I of this work [J. Chromatogr. A, 895 (2000) 87] describes validation of CE methods for the analysis of aqueous and plasma samples of Altropane, including its solid-phase extraction from rat plasma.

Contradistinction between doxorubicin and epirubicin: in-vivo metabolism, pharmacokinetics and toxicodynamics after single- and multiple-dosing in rats

There is compelling in-vitro evidence that the evaluation of doxorubicin or epirubicin pharmacokinetics based solely on plasma concentration may not fully elucidate the differences between the two drugs. Both compounds bind to erythrocytes and their different binding to haemoglobin may influence their disposition in the body. The purpose of the present study was to compare the pharmacokinetics and metabolism of doxorubicin and epirubicin based on the plasma concentration, amount associated with blood cells and simultaneous monitoring of biliary and urinary elimination of unchanged drug and metabolites after single- and multiple-dose injections. The level of sarcoplasmic reticulum Ca2+ATPase in the heart was also measured as a biomarker of cardiotoxicity. Male Sprague-Dawley rats were treated in a parallel design with doxorubicin or epirubicin on a multiple-dosing basis (4 mg kg(-1) per week) or as a single dose injection (20 mg kg(-1)). Blood, urine and bile samples were collected periodically after each dose in the multiple-dosing regimen and the single dose injection, and at the end of each experiment the hearts were removed. The concentrations of each drug in plasma, blood cells, bile and urine samples were determined, and by simultaneous curve-fitting of plasma and bile data according to compartmental analysis, the pharmacokinetic parameters and constants were estimated. The concentration of drug associated with blood cells was analysed according to non-compartmental analysis. The bile and urine samples provided the in-vivo metabolic data. The level of Ca2+ATPase in the heart, determined by Western blotting, was used as the toxicodynamic parameterto correlate with the kinetic data. Multiple-dosing regimens reduced the total plasma clearance and increased the area under the plasma concentration-time curve of both drugs. Also, the area under the curve of doxorubicin associated with blood cells increased with the weekly doses, and the related mean residence time (MRT) and apparent volume of distribution (Vdss) were steadily reduced. In contrast to doxorubicin, the MRT and Vdss of epirubicin increased significantly. Metabolic data indicated significant differences in the level of alcohol and aglycones metabolites. Doxorubicinol and doxorubicin aglycones were significantly greater than epirubicinol and epirubicin aglycone, whereas epirubicinol aglycone was greater than doxorubicinol aglycone. The area under the blood cells concentration-time curve correlated linearly with the changes in Ca2+ATPase net intensity. The results of this study demonstrate the importance of the kinetics of epirubicin and doxorubicin associated with blood cells. Linear correlation between the reduction of net intensity of the biomarker with the area under the curve of doxorubicin associated with blood cells confirms that the differences between the two compounds are related to their interaction with blood cells. This observation together with the observed differences in metabolism may underline a significant role for blood cells in distribution and metabolism of doxorubicin and epirubicin.

Contradistinction between doxorubicin and epirubicin: in-vitro interaction with blood components

The molecular structure and anti-tumour activity of doxorubicin and epirubicin are similar. However, the incidence of their cardiotoxicity occurs at different cumulative dose concentrations. The purpose of this study was to investigate the in-vitro interaction of these two drugs with different blood components, namely intact erythrocytes, haemoglobin and erythrocyte ghosts. Plasma protein binding was also evaluated. The intended goal was to identify the most relevant samples among total blood, plasma or blood cells for pharmacokinetic analysis. The methodology involved the incubation of each of the blood components (the intact erythrocytes, erythrocyte ghosts, haemoglobin and plasma proteins) at physiological pH and temperature with different concentrations of each drug, followed by measurement by HPLC and fluorometry at excitation and emission wavelengths of 480 and 580 nm, respectively. The results indicated that the binding of doxorubicin and epirubicin to plasma proteins, erythrocyte ghosts and intact erythrocytes was essentially the same. However, the binding of both compounds to intact erythrocytes was significantly different from erythrocyte ghosts, which indicates that haemoglobin plays an important role in the binding to and uptake by erythrocytes. The isotherms of binding to haemoglobin revealed that the maximum binding of doxorubicin was approximately 0.42 microg mg(-1) haemoglobin; for epirubicin this value was ten times greater than for doxorubicin. The Scatchard plot of binding of both drugs to haemoglobin exhibited two distinct binding sites for each drug. The constant of association of high affinity and low capacity binding sites was significantly greater for epirubicin, whereas the constant of association of low affinity and high capacity binding sites was significantly higher for doxorubicin. The number of high affinity binding sites per mg of haemoglobin was estimated to be 0.072 for doxorubcin and 0.030 for epirubicin. The number of low affinity binding sites was significantly greater for epirubicin (1.963) than for doxorubicin (0.305). Since the combined number of binding sites for epirubicin was more than doxorubicin, and the total uptake by erythrocytes remained the same for both drugs, it was concluded that epirubicin, being a more lipophilic compound, may diffuse more freely into the cells. Therefore, it binds more to haemoglobin, whereas doxorubicin remains more adsorbed on the surface of the cells due to its self-association property. It was concluded that the interaction of both drugs with erythrocytes, although it appears to be similar, is significantly different due to the interaction with haemoglobin. The difference in this interaction is expected to influence the disposition of both drugs in-vivo.