A translational model-based approach to inform the choice of the dose in phase 1 oncology trials: the case study of erdafitinib.

PURPOSE: Erdafitinib (JNJ-42756493, BALVERSA) is a tyrosine kinase inhibitor indicated for the treatment of advanced urothelial carcinoma. In this work, a translational model-based approach to inform the choice of the doses in phase 1 trials is illustrated. METHODS: A pharmacokinetic (PK) model was developed to describe the time course of erdafitinib plasma concentrations in mice and rats. Data from multiple xenograft studies in mice and rats were analyzed using the Simeoni tumor growth inhibition (TGI) model. The model parameters were used to derive a range of erdafitinib exposures that might inform the choice of the doses in oncology phase 1 trials. Conversion of exposures to doses was based on preliminary PK assessments from the first-in human (FIH) study. RESULTS: A one-compartment PK disposition model, with linear absorption and dose-dependent clearance, adequately described the PK data in both mice and rats via an allometric scaling approach. The TGI model was able to describe tumor growth dynamics, providing quantitative measurements of erdafitinib antitumor potency in mice and rats. Based on these estimates, ranges of efficacious unbound concentration were identified for erdafitinib in mice (0.642-5.364 µg/L) and rats (0.782-2.565 µg/L). Based on the FIH data, it was possible to transpose exposures into doses and doses of above 4 mg/day provided erdafitinib exposures associated with significant TGI in animals. The findings were in agreement with the results of the FIH trial, in which the first hints of clinical activities were observed at 6 mg. CONCLUSION: The successful modeling exercise of erdafitinib preclinical data showed how translational PK-PD modeling might be a tool to help to inform the choice of the doses in FIH studies.

Joint modeling of efficacy, dropout, and tolerability in flexible-dose trials: a case study in depression.

Many difficulties may arise during the modeling of the time course of Hamilton Rating Scale for Depression (HAM D)scores in clinical trials for the evaluation of antidepressant drugs: (i) flexible designs, used to increase the chance of selecting more efficacious doses, (ii) dropout events, and (iii) adverse effects related to the experimental compound.It is crucial to take into account all these factors when designing an appropriate model of the HAM D time course and to obtain a realistic description of the dropout process. In this work, we propose an integrated approach to the modeling of a double-blind, flexible-dose, placebo-controlled, phase II depression trial that comprises response,tolerability, and dropout. We investigate three different dropout mechanisms in terms of informativeness. Goodness of fit is quantitatively assessed with respect to response (HAM D score) and dropout data. We show that dropout is a complex phenomenon that may be influenced by HAM D evolution, dose changes, and occurrence of drug-related adverse effects.

Testing additivity of anticancer agents in pre-clinical studies: a PK/PD modelling approach.

In clinical oncology, combination regimens may result in a synergistic, additive or antagonistic interaction (i.e. the effect of the combination is greater, similar or smaller than the sum of the effects of the individual compounds). For this reason, during the drug development process, in vivo pre-clinical studies are performed to assess the interaction of anticancer agents given in combination. Starting from a widely used single compound PK/PD model, a new additivity model able to predict the tumour growth inhibition in xenografted mice after the administration of compounds in combination was developed, under the assumption of a pharmacodynamic null interaction. By comparing the predicted curves with actual tumour weight data, possible departures from additivity can be immediately ascertained by visual inspection; a statistical procedure based on a chi(2) test has also been developed for this aim. The advantages of the proposed approach in comparison to other modelling methodologies are discussed and its application to four combination studies is presented.

Pharmacokinetics and tolerability of exemestane in combination with raloxifene in postmenopausal women with a history of breast cancer.

PURPOSE: Raloxifene is a second-generation selective estrogen receptor modulator that reduces the incidence of breast cancer in postmenopausal women. Exemestane, a steroidal aromatase inhibitor, decreases contralateral new breast cancers in postmenopausal women when taken in the adjuvant setting. Preclinical evidence suggests a rationale for coadministration of these agents to achieve complete estrogen blockade. EXPERIMENTAL DESIGN: We tested the safety and tolerability of combination exemestane and raloxifene in 11 postmenopausal women with a history of hormone receptor-negative breast cancer. Patients were randomized to either raloxifene (60 mg PO daily) or exemestane (25 mg PO daily) for 2 weeks. Patients then initiated combination therapy at the same dose levels for a minimum of 1 year. Pharmacokinetic and pharmacodynamic data for plasma estrogens, raloxifene, exemestane, and their metabolites were collected at the end of single-agent therapy and during combination therapy. RESULTS: Plasma concentration-time profiles for each drug were unchanged with monotherapy versus combination therapy. Raloxifene did not affect plasma estrogen levels. Plasma estrogen concentrations were suppressed below the lower limit of detection by exemestane as monotherapy and when administered in combination with raloxifene. The most common adverse events of any grade included arthralgias, hot flashes, vaginal dryness and myalgias. CONCLUSIONS: In this small study, coadministration of raloxifene and exemestane did not affect the pharmacokinetics or pharmacodynamics of either agent to a significant degree in postmenopausal women. The combination of estrogen receptor blockade and suppression of estrogen synthesis is well tolerated and warrants further investigation.

Predicting the active doses in humans from animal studies: a novel approach in oncology.

The success rate of clinical drug development is significantly lower in oncology than in other therapeutic areas. Predicting the activity of new compounds in humans from preclinical data could substantially reduce the number of failures. A novel approach for predicting the expected active doses in humans from the first animal studies is presented here. The method relies upon a PK/PD model of tumour growth inhibition in xenografts, which provides parameters describing the potency of the tested compounds. Anticancer drugs, currently used in the clinic, were evaluated in xenograft models and their potency parameters were estimated. A good correlation was obtained between these parameters and the exposures sustained at the therapeutically relevant dosing regimens. Based on the corresponding regression equation and the potency parameters estimated in the first preclinical studies, the therapeutically active concentrations of new compounds can be estimated. An early knowledge of level of exposure or doses to be reached in humans will improve the risk evaluation and decision making processes in anticancer drug development.

Computational approaches for predicting CYP-related metabolism properties in the screening of new drugs.

The site of biotransformation, the extent and rate of metabolism and the number of active metabolic pathways are among the most important characteristics of the pharmacokinetics of a drug. The catalytic activity of drug metabolizing enzymes is likely the most influential determinant of the pharmacokinetic variability. Metabolic stability is the prerequisite for sustaining the therapeutically relevant concentrations. Metabolic inhibition and induction can give rise to clinically important drug-drug interactions. A variety of computational approaches are currently available for predicting different cytochrome P450 (CYP)-related metabolism endpoints. The present review will describe these approaches and their impact on drug development process. Indications on the available software for the implementation will also be given.

A mathematical model to study the effects of drugs administration on tumor growth dynamics.

A mathematical model for describing the cancer growth dynamics in response to anticancer agents administration in xenograft models is discussed. The model consists of a system of ordinary differential equations involving five parameters (three for describing the untreated growth and two for describing the drug action). Tumor growth in untreated animals is modelled by an exponential growth followed by a linear growth. In treated animals, tumor growth rate is decreased by an additional factor proportional to both drug concentration and proliferating cells. The mathematical analysis conducted in this paper highlights several interesting properties of this tumor growth model. It suggests also effective strategies to design in vivo experiments in animals with potential saving of time and resources. For example, the drug concentration threshold for the tumor eradication, the delay between drug administration and tumor regression, and a time index that measures the efficacy of a treatment are derived and discussed. The model has already been employed in several drug discovery projects. Its application on a data set coming from one of these projects is discussed in this paper.

Nonparametric AUC estimation in population studies with incomplete sampling: a Bayesian approach.

The estimation of the AUC in a population without frequent and/or fixed individual samplings is of interest because the number of plasma samples can often be limited due to technical, ethical and cost reasons. Non-linear mixed effect models can provide both population and individual estimates of AUC based on sparse sampling protocols; however, appropriate structural models for the description of the pharmacokinetics are required. Nonparametric solutions have also been proposed to estimate the population AUC and the associated error when particular sampling protocols are adopted. However, they do not estimate the individual AUCs and lack flexibility. Also a semiparametric method has been proposed for addressing the problem of sparse sampling in reasonably well designed studies. In this work, we propose and evaluate a nonparametric Bayesian scheme for AUC estimation in population studies with arbitrary sampling protocols. In the stochastic model representing the whole population, the individual plasma concentration curves and the "mean" population curve are described by random walk processes, allowing the application of the method to the reconstruction of any kind of "regular" curves. Population and individual AUC estimation are performed by numerically computing the posterior expectation through a Markov chain Monte Carlo algorithm.

PNU-145156E, a novel angiogenesis inhibitor, in patients with solid tumors: a phase I and pharmacokinetic study.

Our aim was to establish, in patients with solid tumors, the dose-limiting toxicity, maximum tolerated dose (MTD), and pharmacology of PNU-145156E, a new sulfonated distamycin A derivative that blocked circulating angiogenesis-promoting growth factors in animal studies and exhibited an antitumor effect in murine solid tumors. In a Phase I study, PNU-145156E was administered i.v. every 6 weeks. Included were patients with solid tumors; an Eastern Cooperative Oncology Group performance score

Pharmacokinetics of reboxetine in elderly patients with depressive disorders.

OBJECTIVES: To examine the pharmacokinetic characteristics of the selective norepinephrine reuptake inhibitor, reboxetine, in elderly patients with depression. PATIENTS: Twelve female inpatients (mean age 80 +/- 4 years) with major depressive or dysthymic disorder were enrolled in a 4-week uncontrolled study of oral reboxetine 2-8 mg/day. METHODS: After a one-week washout period, patients were randomized into two groups (groups A and B, n = 6/group). Reboxetine was given twice daily, starting with 2 mg/day during week 1 and increasing by 2 mg/day each week to 8 mg/day in week 4. Pharmacokinetic evaluations were carried out at two dosage levels in each group: at the end of weeks 1 and 3 in group A (2 and 6 mg/day), and at the end of weeks 2 and 4 in group B (4 and 8 mg/day). Blood and urine samples were taken for determination of reboxetine pharmacokinetics. RESULTS: Reboxetine displayed linear pharmacokinetics, with dose-proportional changes, in elderly depressed patients. Mean total urinary recovery ranged from 4.06 to 6.17%. The mean area under the plasma concentration-time curve (AUCtau) and the maximum plasma drug concentration (Cmax) showed considerable variation between patients; at a dosage of 4 mg/day, AUCtau was 1,466-6,866 ngxh/ml and Cmax ranged from 169 to 663 ng/ml. CONCLUSIONS: The pharmacokinetics of reboxetine are linear across the dosage range of 2-8 mg/day in elderly depressed patients, although Cmax and AUCtau values are higher (and more variable) than in young adults. These results support the use of a lower starting dose (4 mg/day) of reboxetine in the elderly.

Pharmacokinetics of single-dose reboxetine in volunteers with renal insufficiency.

Reboxetine is a new selective norepinephrine reuptake inhibitor (selective NRI) for the short- and long-term treatment of depression that is effective and well tolerated at a dose of 8 to 10 mg/day. This study assessed the pharmacokinetics of reboxetine in volunteers with renal impairment. A single 4 mg dose of reboxetine was administered to a total of 18 volunteers with mild (n = 6), moderate (n = 6), or severe (n = 6) renal impairment (creatinine clearance: 56-64, 26-51, and 9-19 ml/min, respectively), and reboxetine concentrations were measured in plasma by HPLC. Mean AUC infinity increased by 43% (mild vs. severe; p < 0.01) as renal function declined, while renal clearance and total urinary excretion of unchanged reboxetine decreased by 67% and 62%, respectively (mild vs. severe; p < 0.01 for both parameters). tmax and t1/2 were not significantly different between groups. In comparison with historical data from young healthy volunteers, AUC infinity and t1/2 are at least doubled in volunteers with renal impairment, while CLr is halved. This pharmacokinetic study has shown that increasing renal dysfunction leads to increasing systemic exposure to reboxetine, particularly in severe renal insufficiency, although reboxetine was well tolerated by all volunteers. Thus, a reduction of the starting dose of reboxetine to 2 mg twice daily would be prudent in patients with renal dysfunction.

Species-differences in disposition and reductive metabolism of methoxymorpholinodoxorubicin (PNU 152243), a new potential anticancer agent.

Plasma pharmacokinetics, excretion balance and urinary metabolites of methoxymorpholino doxorubicin (MMDX) were investigated in male and female rats and in female dogs after i.v. administration of the(14)C-labelled drug. The mean total recovery of radioactivity in 96 h (urine plus faeces) was approximately 74 and 60% dose in male and female rats, respectively, while in female dogs approximately 72% dose was recovered in 336 h. Most of the radioactivity was present in faeces, with the urinary elimination accounting for only 3-4% dose in rats and dogs. These data suggest that biliary excretion is an important route of elimination of MMDX and/or its metabolites in both species. No differences were observed in the urinary metabolic profile of male and female rats. Two main peaks were present in radiochromatograms of urine from rats and dogs, i.e. MMDX and its 13-dihydro metabolite (MMDX-ol), accounting for approximately 25 and 20% of total radioactivity in 0-24-h urine in rats and 30 and 36% in dogs. The MMDX-ol/MMDX ratio in dog urine was higher than that observed in rat urine. No aglycones were detected in the urine samples from either species. In the rat, the plasma concentration-time profile suggested that the disposition of MMDX, MMDX-ol and total radioactivity is not sex-dependent. MMDX was the major species present in the systemic circulation; its AUC (0-96 h) accounted for 70% of total plasma radioactivity with the sum of AUC (MMDX) plus AUC (MMDX-ol) accounting for 77% of total radioactivity. In the dog, the sum of AUC (MMDX) plus AUC (MMDX-ol) amounted to 8% of radioactivity AUC(0-t(z) indicating that an important proportion of other(s) unknown metabolite(s) is present in dog plasma. Plasma levels of MMDX-ol in the rat were approximately 10-fold lower than those of the parent compound, whereas they were three times higher than those of MMDX in the dog. These data show that the reduction of the 13-keto group of MMDX is species-dependent, and occurs preferentially in the dog compared to the rat.

Effect of rifabutin on ethambutol pharmacokinetics in healthy volunteers.

The effect of repeated administration of rifabutin on the pharmacokinetics and metabolism of ethambutol was evaluated in ten healthy volunteers. The subjects received a single oral administration of 1200 mg ethambutol on days 1 and 10 and a single daily oral dose of 300 mg rifabutin from days 3 to 9. No statistically significant difference was found in plasma pharmacokinetics (C(max), t(max), AUC, half-life and MRT) and in the renal clearance, whereas a significant decrease in the amount of unchanged ethambutol excreted in urine was observed. The decrease observed in ethambutol urinary excretion may be accounted for by taking into consideration the variability of the urinary excretion of ethambutol reported in the literature. However, a slight, likely not clinically relevant, induction or activation of kidney alcohol and/or aldehyde dehydrogenase isoenzymes by rifabutin cannot be ruled out at present. Evidence exists in the present study for autoinduction of rifabutin metabolism; this is shown by the lower plasma concentrations obtained 24 h after the seventh dose as compared to the theoretical concentrations.

Hemodynamic effects of reboxetine in healthy male volunteers.

BACKGROUND: Reboxetine [(R,S)-2[(R,S)-alpha-(2-ethoxyphenoxy)benzyl]morpholine methanesulfonate] is a racemic compound that consists of equal proportions of R,R- and S,S-enantiomers. This study investigated the hemodynamic effects of reboxetine and the R,R-enantiomer compared with placebo in volunteers. The pharmacokinetics of reboxetine and its enantiomers were also investigated in the study. METHODS: Nine healthy, male volunteers received single doses of 4 mg reboxetine, 2 mg R,R-enantiomer, and placebo at weekly intervals. Reboxetine and the R,R-enantiomer were well tolerated in all volunteers. RESULTS: The heart rates of patients in the supine and standing positions were increased after reboxetine administration compared with the R,R-enantiomer (P < .05, except supine heart rate at 6 hours) and placebo (P < .05). Supine systolic and diastolic blood pressure was also increased by 3 +/- 4 and 1 +/- 4 mm Hg, respectively, after reboxetine compared with R,R-enantiomer (-2 +/- 4 and -4 +/- 3 mm Hg) and placebo (-4 +/- 4 and -4 +/- 4 mm Hg) administration. The systolic and diastolic blood pressure measurements for subjects while standing did not differ significantly among treatments. There was no significant difference between the maximum plasma concentration, mean time to maximum plasma concentration, plasma half-life, or area under the plasma concentration-time curve (AUC) of the R,R-enantiomer after reboxetine or R,R-enantiomer administration. The ratio of the mean AUC values for the R,R- and S,S-enantiomers was 2.1. CONCLUSION: These findings suggest that the S,S-enantiomer is responsible for the hemodynamic effects of reboxetine in humans. Increases in supine blood pressure after reboxetine administration may be interpreted as regression to the mean value and not caused by any treatment effect.

Dose proportionality of reboxetine enantiomers in healthy male volunteers.

Reboxetine is a racemic mixture of FCE 22071 and FCE 21684 enantiomers. The pharmacokinetics of the enantiomers of reboxetine were observed to be linear in male healthy subjects (n = 6) after the administration of 1.5, 3, 4.5 mg dose of reboxetine as solutions. Kinetic analysis was based on chiral HPLC assay of the enantiomers in plasma collected up to 72 h after each administration. C(max) and AUC were more than double for FCE 22071 (C(max): 38.3+/-13.5, 76. 6+/-26.3, 99.8+/-24.1 ng/mL and AUC(infinity): 605.8+/-233.2, 1288. 3+/-796.4, 1780.7+/-669.3 ng. h/mL for 1.5, 3, 4.5 mg, respectively) than for FCE 21684 (C(max): 15.2+/-5.3, 34.6+/-14.0, 43.1+/-12.3 ng/mL and AUC(infinity): 247.0+/-103.9, 529.1+/-278.4, 773.0+/-355.3 ng. h/mL), whatever the administered dose. The half-lives of the enantiomers were similar (FCE 22071: 13.1, 11.0, 12.6 h and FCE 21684: 12.8, 11.2, 12.2 h after 1.5, 3, 4.5 mg, respectively) and not substantially affected by the dose level.

Absolute bioavailability of reboxetine enantiomers and effect of gender on pharmacokinetics.

The absolute bioavailability of reboxetine enantiomers was assessed in six male and six female volunteers. In a two-way crossover study, subjects received 1.0 mg reboxetine orally and 0.3 mg reboxetine as an intravenous bolus. The R,R(-) and S,S(+) enantiomers in serial plasma and urine samples were determined by a validated LC-MS-MS method. There were no significant differences between treatments for clearance or dose-corrected AUC(0-infinity) values. The absolute bioavailability was 0.919 and 1.02 for R,R(-) reboxetine and S,S(+) reboxetine, respectively. A secondary objective of the study was to assess gender effects on pharmacokinetics of the enantiomers. Significant differences in volume of distribution between genders were observed, but differences in weight-corrected volumes were not significant. Weight-corrected systemic clearance and oral clearance tended to be lower in males, but this difference reached statistical significance only for weight-corrected oral clearance of R,R(-) reboxetine. C(max) after oral administration was 40 and 48% higher in women than men for R,R(-) reboxetine and S,S(+) reboxetine, respectively. These results indicate that reboxetine enantiomers are well absorbed after oral administration and that little first-pass metabolism occurs. There are no clinically significant effects of gender on the pharmacokinetics of reboxetine enantiomers.

A phase I and pharmacokinetic study of tallimustine [PNU 152241 (FCE 24517)] in patients with advanced cancer.

Tallimustine [PNU 152241 (FCE 24517)] is a synthetic derivative of the DNA minor groove binder distamycin A, in which the NH2-terminal formyl group is substituted by benzoyl mustard. In this Phase I clinical trial, patients with advanced solid tumors received i.v. bolus injections of tallimustine daily for 3 consecutive days. Patients were treated at six dosage levels of 33.3 micrograms/m2/day to 250 micrograms/m2/day for 3 consecutive days, with courses of therapy repeated every 28 days. Detailed pharmacokinetic blood sampling was performed during the first 3 days of the first course of tallimustine. The plasma samples were analyzed by high-performance liquid chromatography with UV detection. Forty-eight eligible patients were treated at all six dosage levels. The dominant dose-related toxicity of tallimustine was neutropenia, becoming dose limiting at 250 micrograms/m2/day. At this dosage level, one patient experienced febrile neutropenia, and a second patient died on study of indeterminate cause. Thrombocytopenia was not observed, and only 10 patients developed anemia < 8.0 gm/dl. Sporadic elevation of liver enzymes or bilirubin was observed but was not dose related. Pharmacokinetic analysis gave reliable results for 33 patients. For most patients, analysis of the data best fit a three-exponential model. Dose-related increases in areas under the concentration-time curve and end-of-infusion concentrations were observed. There was no significant plasma accumulation of tallimustine over the 3 days of administration. The terminal half-life of tallimustine in individual patients ranged from 6.83 to 39.02 h following the last dose. In summary, the recommended Phase II dosage for tallimustine is 200 micrograms/m2/day for 3 consecutive days every 28 days. Neutropenia is the principal toxicity of this agent at this dosage and schedule.

Computer-assisted analysis of methylation status of individual interphase nuclei in human cultured cells.

This paper demonstrates that (a) differences in the methylation levels of interphase nuclei can be measured on a cell-by-cell basis, (b) the binding sites of beta-satellite DNA and 5-methylcytosine (5MeC)-rich regions can be localised in interphase nuclei and metaphase chromosomes by sequential in situ hybridization and indirect immunolabelling, and (c) quantitative differences in the relative extensions of beta-satellite DNA and anti-5MeC antibody binding areas can also be measured. This goal was achieved by indirect immunolabelling by anti-5MeC antibodies (Reynaud et al.: Cancer Lett. 61:255-262, 1991) of control and 5-azacytidine-treated human cell cultures. A quantitative analysis of the number, total, and mean areas of labelled heterochromatic regions and the optical densities of euchromatin and heterochromatin was performed for the cells on microscope slides. Dedicated software was used to select and measure the areas of cytological interest. In additional experiments, DAPI-stained slides from control cultures were sequentially treated by in situ hybridization with beta-satellite DNA probe and indirect immunofluorescent labelling with anti-5MeC antibodies. Fluorescent signals of probe and antibodies were pseudocoloured and merged on digital images. The relative locations of probe- and antibody-positive areas were analysed on metaphases and nuclei, and their extensions were quantified in interphase nuclei. Our results show that (a) our analysis can successfully detect different levels of DNA methylation within individual nuclei, (b) in metaphase chromosomes the antibody binding sites are mostly coincident with the hybridisation sites, and (c) in interphase nuclei a quite different picture is consistently observed.

A study of the pharmacokinetics and tolerability of ritipenem acoxil in healthy volunteers following multiple oral dosing.

The pharmacokinetics of ritipenem acoxil, the oral prodrug of the antibiotic ritipenem, were studied in volunteers after single and repeated dosing (500 mg, three times daily for 10 days). Concentrations of ritipenem and open beta-lactam ring metabolites were measured using HPLC/UV. Ritipenem did not accumulate significantly in plasma, owing to its half-life of about 0.7 h; the area under the curve for 0-8 h was on average about 10 mg x h/L. Plasma pharmacokinetics of ritipenem and metabolites were time-independent. A decrease of ritipenem renal clearance (87 versus 132 mL/min) and a slight increase in the amount of metabolites excreted in urine were observed following repeated dosing.