Metabolism and disposition of the anticancer quinolone derivative vosaroxin, a novel inhibitor of topoisomerase II.

Background Vosaroxin is a first-in-class anticancer quinolone derivative that is being investigated for patients with relapsed or refractory acute myeloid leukemia (AML). The primary objective of this study was to quantitatively determine the pharmacokinetics of vosaroxin and its metabolites in patients with advanced solid tumors. Methods This mass balance study investigated the pharmacokinetics (distribution, metabolism, and excretion) of vosaroxin in cancer patients after a single dose of 60 mg/m2 14C-vosaroxin, administered as short intravenous injection. Blood, urine and feces were collected over 168 h after injection or until recovered radioactivity over 24 h was less than 1% of the administered dose (whichever was earlier). Total radioactivity (TRA), vosaroxin and metabolites were studied in all matrices. Results Unchanged vosaroxin was the major species identified in plasma, urine, and feces. N-desmethylvosaroxin was the only circulating metabolite detected in plasma, accounting for <3% of the administered dose. However, in plasma, the combined vosaroxin + N-desmethylvosaroxin AUC0-∞ was 21% lower than the TRA AUC0-∞ , suggesting the possible formation of protein bound metabolites after 48 h when the concentration-time profiles diverged. The mean recovery of TRA in excreta was 81.3% of the total administered dose; 53.1% was excreted through feces and 28.2% through urine. Conclusions Unchanged vosaroxin was the major compound found in the excreta, although 10 minor metabolites were detected. The biotransformation reactions were demethylation, hydrogenation, decarboxylation and phase II conjugation including glucuronidation.

Using disease progression models as a tool to detect drug effect.

Generally, information required for approval of new drugs is dichotomous in that the drug is either efficacious and safe or not. Consequently, the purpose of most confirmatory clinical trials is to test the null hypothesis. The primary reasons for designing hypothesis testing trials are to provide the information required for approval using analyses techniques that are relatively straightforward and free of apparent assumptions. However, the information required for approval is very different from that used by prescribers for decision making. In the clinic, decisions must be made about dose adjustment for individual patients in the presence of additional therapies and co-morbidities. Choice of drug and dosing regimen is therefore a classical risk to benefit decision that is often poorly informed from the results of confirmatory trials. Therefore, providing answers to the more difficult question of how to use the drug in a clinical setting is essential.

Model Evaluation of Continuous Data Pharmacometric Models: Metrics and Graphics.

This article represents the first in a series of tutorials on model evaluation in nonlinear mixed effect models (NLMEMs), from the International Society of Pharmacometrics (ISoP) Model Evaluation Group. Numerous tools are available for evaluation of NLMEM, with a particular emphasis on visual assessment. This first basic tutorial focuses on presenting graphical evaluation tools of NLMEM for continuous data. It illustrates graphs for correct or misspecified models, discusses their pros and cons, and recalls the definition of metrics used.

Why therapeutic drug monitoring is needed for monoclonal antibodies and how do we implement this?

Monoclonal antibodies (mAbs) have improved clinical outcomes for many therapeutic indications. However, extensive between-subject variability (BSV) contributes to therapeutic failures through suboptimal exposure. Therapeutic drug monitoring (TDM) is routinely implemented for inflammatory diseases; improving outcomes and reducing treatment costs. BSV can be more extensive with anticancer mAbs. Clearance BSV is associated with patient factors and disease burden, suggesting that TDM could benefit anticancer mAbs, as was seen with inflammatory disease, however, there are many hurdles.

Clinical Decision Support Tools: The Evolution of a Revolution.

Dashboard systems for clinical decision support integrate data from multiple sources. These systems, the newest in a long line of dose calculators and other decision support tools, utilize Bayesian approaches to fully individualize dosing using information gathered through therapeutic drug monitoring. In the treatment of inflammatory bowel disease patients with infliximab, dashboards may reduce therapeutic failures and treatment costs. The history and future development of modern Bayesian dashboard systems is described.

Developing Exposure/Response Models for Anticancer Drug Treatment: Special Considerations.

Anticancer agents often have a narrow therapeutic index (TI), requiring precise dosing to ensure sufficient exposure for clinical activity while minimizing toxicity. These agents frequently have complex pharmacology, and combination therapy may cause schedule-specific effects and interactions. We review anticancer drug development, showing how integration of modeling and simulation throughout development can inform anticancer dose selection, potentially improving the late-phase success rate. This article has a companion article in Clinical Pharmacology & Therapeutics with practical examples.

Optimizing oncology therapeutics through quantitative translational and clinical pharmacology: challenges and opportunities.

Despite advances in biomedical research that have deepened our understanding of cancer hallmarks, resulting in the discovery and development of targeted therapies, the success rates of oncology drug development remain low. Opportunities remain for objective dose selection informed by exposure-response understanding to optimize the benefit-risk balance of novel therapies for cancer patients. This review article discusses the principles and applications of modeling and simulation approaches across the lifecycle of development of oncology therapeutics. Illustrative examples are used to convey the value gained from integration of quantitative clinical pharmacology strategies from the preclinical-translational phase through confirmatory clinical evaluation of efficacy and safety.

Use of an indirect pharmacodynamic stimulation model of MX protein induction to compare in vivo activity of interferon alfa-2a and a polyethylene glycol-modified derivative in healthy subjects.

Interferon alfa-2a was chemically modified by the covalent attachment of a polyethylene glycol (PEG) moiety to enhance its circulating half-life and to reduce its immunogenicity. A comparative evaluation of the pharmacokinetics of the PEG-modified interferon alfa-2a showed a greater than twofold increase in the circulating half-life as a result of this chemical modification. An indirect physiologic response model was developed to characterize the time course of the MX protein response after subcutaneous administration of single ascending doses of either interferon alfa-2a or PEG-interferon alfa-2a in healthy volunteers. Analysis of the pharmacokinetic-pharmacodynamic relationship suggested that the PEG-modified interferon alfa-2a could not be administered less than twice weekly and therefore offered little therapeutic advantage over its unmodified counterpart, which is administered three times weekly. These results were consistent with findings in phase II trials. This study substantiates the usefulness of pharmacodynamic modeling as a tool for the development of dose recommendations and for the early selection of drug candidates in the drug development process.

A population pharmacokinetic-pharmacodynamic and logistic regression analysis of lotrafiban in patients.

OBJECTIVE: Our objective was to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of lotrafiban, an oral glycoprotein IIb/IIIa inhibitor, in patients with a recent myocardial infarction, unstable angina, transient ischemic attack, or stroke. METHODS: A 12-week, double-blind, multi-center, placebo-controlled, parallel-group, phase II study of lotrafiban (the Anti-platelet Useful Dose Study) was conducted in patients. Lotrafiban or placebo was administered as a twice daily oral dose at four dose levels (5-100 mg) for 12 weeks with daily doses of aspirin (300-325 mg). The pharmacokinetics of lotrafiban were characterized with the use of a population approach and were described by a two-compartment model with first order absorption and first order elimination. The pharmacodynamic data, ex vivo platelet aggregation, were described with the use of a direct effect inhibitory sigmoidal model with a baseline. The relationship between the severity of bleeding episodes and predicted steady-state lotrafiban exposure was characterized by logistic regression. RESULTS: Pharmacokinetic analysis showed that increasing age and decreasing creatinine clearance resulted in increased exposure to lotrafiban. The concentration-effect relationship was steep, with near complete inhibition of platelet aggregation at lotrafiban concentrations in excess of 20 ng/mL. Logistic regression showed that at exposures that exceeded approximately 835 ng. h/mL, the severity of adverse bleeding events increased considerably; this suggested that dosing recommendations should be generated to minimize the likelihood of patients having an area under the plasma concentration-time curve from 0 to 24 hours in excess of this value. CONCLUSIONS: Patients whose age exceeded 65 years or whose creatinine clearance was less than 60 mL/min should be given a lower dose of lotrafiban than younger patients with good renal function.

A population pharmacokinetic-pharmacodynamic analysis of single doses of clenoliximab in patients with rheumatoid arthritis.

Clenoliximab (IDEC-151) is a macaque-human chimeric monoclonal antibody (immunoglobulin G4) specific for the CD4 molecule on the surface of T lymphocytes. It is being studied in patients with rheumatoid arthritis in which T cell activation orchestrates inflammation and tissue damage. In this initial study in humans, the pharmacokinetics and pharmacodynamics of clenoliximab were investigated after single intravenous infusion. Blood was collected up to 12 weeks after dose administration to measure clenoliximab concentration, CD4+ T-cell count, CD4 antigen coating, and CD4 cell surface density. Clenoliximab displayed nonlinear pharmacokinetic behavior and caused an 80% reduction in CD4 density for up to 3 weeks, without depleting T cells. A pharmacokinetic-pharmacodynamic model was developed that described the relationship between antibody concentration, antigen coating, and the observed decreases in CD4 cell surface density. This was used to anticipate the effects of clenoliximab in untested regimens and optimize the design of future clinical trials.

Simultaneous modeling of the pharmacokinetics and pharmacodynamics of midazolam and diazepam.

The pharmacokinetics and pharmacodynamics of midazolam and diazepam were compared after intravenous infusions of 0.03 and 0.07 mg/kg midazolam and 0.1 and 0.2 mg/kg diazepam on four separate occasions in 12 healthy male subjects in a randomized four-way crossover design. The Digit Symbol Substitution Test (DSST) was used as a measure of drug effect. Subjects performed three practice tests before dosing to account for any effects caused by familiarization ("learning curve") with the testing procedure. Pharmacokinetic and pharmacodynamic data were simultaneously fitted to a semiparametric model. In this model, a pharmacokinetic model related dose to plasma concentrations, a link model related plasma concentrations to the concentration at the effect site, and a pharmacodynamic model related the effect site concentration to the observed effect. The plasma-effect site equilibrium half-life was approximately 2 1/2 times longer for midazolam than for diazepam, which is in good agreement with previously published data. Based on the estimated effect site concentration at which half of the maximal effect was reached, midazolam had approximately a sixfold greater intrinsic potency than diazepam. This difference in potency was also observed in a previous study that used transformed electroencephalographic (EEG) data to assess pharmacodynamic activity. The findings reported here with a clinically relevant pharmacodynamic marker (DSST) confirm the utility of surrogate drug effect measures such as EEG. This work also shows the feasibility of conducting pharmacokinetic pharmacodynamic analysis during the drug development process.

Determination of humanized anti-Tac in human serum by a sandwich enzyme linked immunosorbent assay.

A 'sandwich' enzyme-linked immunosorbent assay has been developed for measuring humanized anti-Tac (HAT), a humanized antibody to the IL-2 receptor on activated T cells (Tac), in human serum. The working range of this assay is 25-400 ng/ml with an overall precision of 5%. In this assay, the analyte, HAT, is sandwiched between Tac which is bound to a microtiter plate and biotinylated Tac that is conjugated to peroxidase labelled streptavidin. This assay was utilized to determine the pharmacokinetic parameters of HAT in patients with graft-versus-host disease.

A phase I trial of humanized anti-interleukin 2 receptor antibody in renal transplantation.

The efficacy of murine monoclonal anti-interleukin 2 alpha chain receptor (Tac) antibodies is limited by a short half-life and the development of antibodies to the heterologous protein. The safety, pharmacokinetics-dynamics, and immunosuppressive effect of a humanized anti-Tac antibody (HAT) was evaluated in 12 renal transplant recipients. Ten patients received living related transplants (three HLA-identical matches and seven one-haplotype or zero-haplotype matches) and two patients received cadaver organs. The patients were divided into four HAT treatment arms: 0.5 mg/kg/week (n=4), 1 mg/kg/week (n=2), 0.5 mg/kg every other week (n=3), and 1 mg/kg every other week (n=3). The first dose of HAT was given within 12 hr before transplantation, and four additional doses were given after transplantation. Patients were also placed on cyclosporine, steroids, and azathioprine. Only one patient, a recipient of a cadaver kidney in the lowest HAT treatment arm, had a reversible rejection episode. The 10 recipients of living related transplants were compared with 17 historical controls treated with an identical immunosuppressive regimen except for HAT. Whereas none of the HAT-treated living related donor recipients had a rejection episode, 6 of 17 (41%) of the historical controls had a rejection episode in the first year after transplantation. There were no first-dose reactions after HAT therapy or other subsequent side effects. None of the patients experienced opportunistic infections or malignancies. One patient developed low-titer anti-HAT antibodies, although the patient maintained high serum HAT concentrations throughout the study. Immune monitoring showed that there were no changes in the percentage or absolute counts of CD3 cells or T-cell subsets after HAT therapy. However, there was a significant decrease in the number of circulating lymphocytes that expressed free Tac. The overall harmonic mean half-life of HAT was 273 hr. The results of this study indicate that HAT given at 1 mg/kg every other week for a total of five doses may provide therapeutic HAT concentration levels and result in good saturation of Tac receptors for at least 12 weeks after transplantation. In summary, HAT is safe and is well tolerated by patients. Its long half-life and lack of immunization could make it a very useful immunosuppressive drug.

The comparison and characterisation of glycolytic mycoplasmas isolated from the respiratory tract of sheep.

Nine strains of glycolytic mycoplasmas isolated from the respiratory tract of apparently healthy sheep, pneumonic sheep and sheep with pulmonary adenomatosis (SPA) were compared with a Queensland strain (Y98) of Mycoplasma ovipneumoniae. All strains were very similar in their reactions in 14 biochemical tests and in their sensitivities to optochin, digitonin, sodium polyanethol sulphonate, and 11 antibiotics. Polyacrylamide-gel electrophoresis and serological cross-reactions by the agar-gel double diffusion, metabolic inhibition (MI) and growht-inhibition (GI) tests also showed that all strains could be classified as M. ovipneumoniae. The MI and GI tests, however, showed considerable intraspecific differences among strains, with apparent polarisation of SPA strains and non-SPA strains at opposite ends of the antigenic spectrum. Two representative strains were tested by the MI test against antisera to 39 mycoplasma species or serogroups, with negative results.

Pretreatment with ranitidine does not reduce the bioavailability of orally administered topotecan.

PURPOSE: The purpose of this randomized, two-period crossover study was to determine the pharmacokinetics of orally administered topotecan in the presence and absence of oral ranitidine. METHODS: Patients with solid malignant tumors refractory to standard treatment were given topotecan orally on a daily times five schedule repeated every 21 days. Topotecan was given initially at 2.3 mg/m2 per day; dose adjustments were permitted after the first dose of course 2 if necessary. Blood samples for pharmacokinetic assessments were drawn at protocol-specified times for up to 10 h following oral administration of topotecan on day 1 of courses 1 and 2. Patients were randomly assigned to receive a total of nine doses of ranitidine: 150 mg twice daily for 4 days before day 1 of one of the first two courses and 150 mg given 2 h before the first topotecan dose. Plasma samples were assayed for concentrations of active topotecan lactone (TPT-L) and total topotecan (TPT-T, lactone plus open-ring carboxylate form) using high-performance liquid chromatography with fluorescence detection. After completion of courses 1 and 2, patients could continue on therapy for days 1-5 of every 21 days if not withdrawn due to unacceptable toxicity, disease progression, protocol violation, or by request. Patients continued on treatment for a maximum of six courses. RESULTS: No pharmacokinetic parameter for either TPT-L or TPT-T differed significantly during administration of topotecan with ranitidine compared with topotecan alone (n = 13). Geometric mean ratios (95% confidence intervals, CIs) of areas under the curve in the presence and absence of ranitidine were 0.94 (0.80, 1.10) for TPT-L and 0.97 (0.80, 1.16) for TPT-T. Corresponding ratios (CIs) of peak plasma concentrations in the presence and absence of ranitidine were 1.06 (0.78, 1.44) for TPT-L and 1.07 (0.84, 1.38) for TPT-T. The median difference in time to peak plasma concentration was 0.0 h for TPT-L and -0.5 h for TPT-T (i.e. slightly faster in the presence of ranitidine). CONCLUSIONS: Administration of ranitidine prior to oral topotecan resulted in a similar extent of absorption. A slightly faster rate of absorption of topotecan was also observed, which is unlikely to be of clinical significance. Dosage adjustments of orally administered topotecan should not be necessary in patients who are pretreated with ranitidine, an H2 antagonist, or another agent that comparably raises gastric pH.

Protein electrophoretic pattern of Pasteurella haemolytica.

Electrophoresis in polyacrylamide gels of the constituent proteins of the 12 serotypes and an untypable strain of Pasteurella haemolytica showed a pattern of bands that divided the group into two. This division conformed to the A and T biotype groupings of Smith (1959) although the serotype A9 showed only minor band difference from the three T serotypes 3, 4 and 10. It was not possible by this method to separate all the type strains from each other by the specific recognition of the patterns of protein mobilities produced.

Adaptation of the guaiacol (peroxidase) test for haptoglobins to a microtitration plate system.

The optimal operational method was determined for performance of an adapted guaiacol test in microtitration ELISA plates for quantitative detection of haptoglobins in sheep serum. The test correlated well with assay on Sephadex G100 but was more sensitive, though with lowered reproducibility, at low levels of haptoglobin. The modified test permits both rapid testing of large numbers of samples and the calculation of results using a simple computer program.

Experimental studies of neurotoxic activity in blood fractions from acute cases of grass sickness.

Plasma, serum and cells were prepared from blood taken from acute cases of grass sickness, and plasma was fractionated by gel filtration and salt precipatation. These preparations were all tested for neurotoxic activity by injection into ponies. Plasma and serum were found to produce the neurohistological changes seen in grass sickness, as was a plasma protein fraction of molecular weight 30,000 or greater. Activity was retained following storage at--75 degrees C for 15 months. Plasma given orally to a pony produced no detectable effect, nor was activity demonstrated following the injection of plasma or the high molecular weight fraction to mice, rats, guinea-pigs or rabbits.

Serum protein changes in grass sickness.

Polyacrylamide gel electrophoresis was used to compare serum taken from ponies before and during clinical illness confirmed as grass sickness. A consistent rise in the level of haptoglobin was seen in serum from animals which had shown symptoms for more than two days. Serum albumin was also shown to have altered mobility at the onset of clinical disease. Estimation of the haemoglobin-binding capacity confirmed the haptoglobin increase. This haptoglobin has been purified and some of its properties determined. In contrast to the situation in acute inflammatory conditions no other acute-phase proteins increased to a significant extent in grass sickness. It is concluded that the neurotoxin known to be present in sera of animals experiencing acute grass sickness cannot itself be detected by polyacrylamide gel electrophoresis but may be bound to serum albumin.

Basic concepts in population modeling, simulation, and model-based drug development: part 3-introduction to pharmacodynamic modeling methods.

Population pharmacodynamic (PD) models describe the time course of drug effects, relating exposure to response, and providing a more robust understanding of drug action than single assessments. PD models can test alternative dose regimens through simulation, allowing for informed assessment of potential dose regimens and study designs. This is the third paper in a three-part series, providing an introduction into methods for developing and evaluating population PD models. Example files are available in the Supplementary Data.