Gezim Lahu

Modeling of tumor growth and anticancer effects of combination therapy

Combination therapies are widely used in the treatment of patients with cancer. Selecting synergistic combination strategies is a great challenge during early drug development. Here, we present a pharmacokinetic/pharmacodynamic (PK/PD) model with a smooth nonlinear growth function to characterize and quantify anticancer effect of combination therapies using time-dependent data. To describe the pharmacological effect of combination therapy, an interaction term was introduced into a semi-mechanistic anticancer PK/PD model. This approach enables testing of a pharmacological hypothesis with respect to an anticipated pharmacological synergy of drug combinations, such as an assumed pharmacological synergy of complementary inhibition of a particular signaling pathway. The model was applied to three real data sets derived from preclinical screening experiments using xenograft mice. The suggested model fitted well the observed data from mono- to combination-therapy and allowed physiologically meaningful interpretation of the experiments. The tested drug combinations were assessed for their ability to act as synergistic modulators of tumor growth inhibition by the interaction parameter ψ. The presented approach has practical implications because it can be applied to standard xenograft experiments and may assist in the selection of both optimal drug combinations and administration schedules. The unique feature of the presented approach is the ability to characterize the nature of combined drug interaction as well as to quantify the intensity of such interactions by assessing the time course of combined drug effect.

Repeatability of and Relationship between Potential COPD Biomarkers in Bronchoalveolar Lavage, Bronchial Biopsies, Serum, and Induced Sputum

Chronic Obstructive Pulmonary Disease (COPD) is a chronic inflammatory disease, primarily affecting the airways. Stable biomarkers characterizing the inflammatory phenotype of the disease, relevant for disease activity and suited to predict disease progression are needed to monitor the efficacy and safety of drug interventions. We therefore analyzed a large panel of markers in bronchoalveolar lavage, bronchial biopsies, serum and induced sputum of 23 healthy smokers and 24 smoking COPD patients (GOLD II) matched for age and gender. Sample collection was performed twice within a period of 6 weeks. Assays for over 100 different markers were validated for the respective matrices prior to analysis. In our study, we found 51 markers with a sufficient repeatability (intraclass correlation coefficient >0.6), most of these in serum. Differences between groups were observed for markers from all compartments, which extends (von-Willebrand-factor) and confirms (e.g. C-reactive-protein, interleukin-6) previous findings. No correlations between lung and serum markers were observed, including A1AT. Airway inflammation defined by sputum neutrophils showed only a moderate repeatability. This could be improved, when a combination of neutrophils and four sputum fluid phase markers was used to define the inflammatory phenotype.In summary, our study provides comprehensive information on the repeatability and interrelationship of pulmonary and systemic COPD-related markers. These results are relevant for ongoing large clinical trials and future COPD research. While serum markers can discriminate between smokers with and without COPD, they do not seem to sufficiently reflect the disease-associated inflammatory processes within the airways.

Effects of rifampicin on the pharmacokinetics of roflumilast and roflumilast N-oxide in healthy subjects.

AIMS To evaluate the effect of co-administration of rifampicin, an inducer of cytochrome P450 (CYP)3A4, on the pharmacokinetics of roflumilast and roflumilast N-oxide. Roflumilast is an oral, once-daily phosphodiesterase 4 (PDE4) inhibitor, being developed for the treatment of chronic obstructive pulmonary disease. Roflumilast is metabolized by CYP3A4 and CYP1A2, with further involvement of CYP2C19 and extrahepatic CYP1A1. In vivo, roflumilast N-oxide contributes >90% to the total PDE4 inhibitory activity. METHODS Sixteen healthy male subjects were enrolled in an open-label, three-period, fixed-sequence study. They received a single oral dose of roflumilast 500 microg on days 1 and 12 and repeated oral doses of rifampicin 600 mg once daily on days 5-15. Plasma concentrations of roflumilast and roflumilast N-oxide were measured for up to 96 h. Test/Reference ratios and 90% confidence intervals (CIs) of geometric means for AUC and C(max) of roflumilast and roflumilast N-oxide and for oral apparent clearance (CL/F) of roflumilast were estimated. RESULTS During the steady-state of rifampicin, the AUC(0-infinity) of roflumilast decreased by 80% (point estimate 0.21; 90% CI 0.16, 0.27); C(max) by 68% (0.32; CI 0.26, 0.39); for roflumilast N-oxide, the AUC(0-infinity) decreased by 56% (0.44; CI 0.36, 0.55); C(max) increased by 30% (1.30; 1.15, 1.48); total PDE4 inhibitory activity decreased by 58% (0.42; 0.38, 0.48). CONCLUSIONS Co-administration of rifampicin and roflumilast led to a reduction in total PDE4 inhibitory activity of roflumilast by about 58%. The use of potent cytochrome P450 inducers may reduce the therapeutic effect of roflumilast.

Pharmacology, Clinical Efficacy, and Tolerability of Phosphodiesterase-4 Inhibitors: Impact of Human Pharmacokinetics

Since more than two decades anti-inflammatory effects of inhibitors of phosphodiesterase-4 have been described in numerous cellular and animal studies and were finally confirmed in clinical trials. The path from an early, pioneering study with Ro20-1724 showing reduction of psoriatric plaque size in 1979 to modern PDE4 inhibitors such as oral apremilast in development for psoriasis, the inhaled PDE4 inhibitor GSK256066 in development for asthma and COPD and finally roflumilast, the first PDE4 inhibitor approved and currently marketed as an oral, once-daily remedy for severe COPD was marked by large progress in chemical optimization based on improved understanding of PDE4 biology and drug-like properties determining the appropriate pharmacokinetic profile. In this chapter aspects of the pharmacology and clinical efficacy of PDE4 inhibitors, which have been in clinical development over the years are summarized with specific emphasis on their clinical pharmacokinetic properties.

Effect of single and repeated doses of ketoconazole on the pharmacokinetics of roflumilast and roflumilast N-oxide.

Effects of single and multiple doses of oral ketoconazole on roflumilast and its active metabolite, roflumilast N‐oxide, were investigated in healthy subjects. In study 1, subjects (n = 26) received oral roflumilast 500 μg once daily for 11 days and a concomitant 200‐mg single dose of ketoconazole on day 11. In study 2, subjects (n = 16) received oral roflumilast 500 μg on days 1 and 11 and a repeated dose of ketoconazole 200 mg twice daily from days 8 to 20. Coadministration of single‐dose ketoconazole with steady‐state roflumilast increased the AUC of roflumilast by 34%; Cmax was unchanged. For roflumilast N‐oxide, AUC and Cmax decreased by 12% and 20%, respectively. Repeated doses of ketoconazole increased the AUC and Cmax of roflumilast by 99% and 23%, respectively; for roflumilast N‐oxide, AUC was unchanged, and Cmax decreased by 38%. No clinically relevant adverse events were observed. Coadministration of ketoconazole and roflumilast does not require dose adjustment of roflumilast.

Population Pharmacokinetic Modelling of Roflumilast and Roflumilast N-Oxide by Total Phosphodiesterase-4 Inhibitory Activity and Development of a Population Pharmacodynamic-Adverse Event Model

Background:Roflumilast is an oral, selective phosphodiesterase (PDE)-4 inhibitor in development for the treatment of chronic obstructive pulmonary disease (COPD). Both roflumilast and its metabolite roflumilast N-oxide have anti-inflammatory properties that contribute to overall pharmacological activity.Objectives:To model the pharmacokinetics of roflumilast and roflumilast N-oxide, evaluate the influence of potential covariates, use the total PDE4 inhibitory activity (tPDE4i) concept to estimate the combined inhibition of PDE4 by roflumilast and roflumilast N-oxide, and use individual estimates of tPDE4i to predict the occurrence of adverse events (AEs) in patients with moderate-to-severe COPD.Methods:We modelled exposure to roflumilast and roflumilast N-oxide (21 studies provided the index dataset and five separate studies provided the validation dataset), extended the models to COPD (using data from two studies) and assessed the robustness of the parameter estimates. A parametric bootstrap estimation was used to quantify tPDE4i in subpopulations. We established logistic regression models for each AE occurring in >2% of patients in a placebo-controlled trial that achieved a p-value of <0.2 in a permutation test. The exposure variables were the area under the plasma concentration-time curve (AUC) of roflumilast, the AUC of roflumilast N-oxide and tPDE4i. Individual AUC values were estimated from population models.Results:Roflumilast pharmacokinetics were modelled with a two-compartment model with first-order absorption including a lag time. A one-compartment model with zero-order absorption was used for roflumilast N-oxide. The final models displayed good descriptive and predictive performance with no appreciable systematic trends versus time, dose or study. Posterior predictive checks and robustness analysis showed that the models adequately described the pharmacokinetic parameters and the covariate effects on disposition. For roflumilast, the covariates of sex, smoking and race influenced clearance; and food influenced the absorption rate constant and lag time. For roflumilast N-oxide, age, sex and smoking influenced clearance; age, sex and race influenced the fraction metabolized; bodyweight influenced the apparent volume of distribution; and food influenced the apparent duration of formation. The COPD covariate increased the central volume of distribution of roflumilast by 184% and reduced its clearance by 39%; it also reduced the estimated volume of distribution of roflumilast N-oxide by 21% and reduced its clearance by 7.9%. Compared with the reference population (male, non-smoking, White, healthy, 40-year-old subjects), the relative geometric mean [95%CI] tPDE4i was higher in patients withCOPD(12.6%[−6.6, 35.6]), women (19.3%[8.2, 31.6]), Black subjects (42.1% [16.4, 73.4]), Hispanic subjects (28.2% [4.1, 57.9]) and older subjects (e.g. 8.3% [−11.2, 32.2] in 60-year-olds), and was lower in smokers (−19.1% [−34.0, −0.7]). Among all possible subgroups in this analysis, the subgroup with maximal tPDE4i comprised elderly, Black, female, non-smoking, COPD patients (tPDE4i 217% [95% CI 107, 437] compared with the value in the reference population). The probability of a patient with tPDE4i at the population geometric mean [95% CI] was 13.0% [7.5, 18.5] for developing diarrhoea, 6.0% [2.6, 9.4] for nausea and 5.1% [1.9, 8.6] for headache.Conclusions:Covariate effects have a limited impact on tPDE4i. There was a general association between tPDE4i and the occurrence of common AEs in patients with COPD.

Effect of repeated dose of erythromycin on the pharmacokinetics of roflumilast and roflumilast N-oxide.

OBJECTIVE To investigate the effects of steady state erythromycin on the pharmacokinetics of roflumilast and its pharmacodynamically active metabolite roflumilast N-oxide in healthy subjects. Both roflumilast and roflumilast N-oxide have similar intrinsic PDE4 inhibitory activity; the total PDE4 inhibition (tPDE4i) in humans is likely due to the combined effect of roflumilast and roflumilast N-oxide. METHODS Subjects (n = 16) received single oral roflumilast 500 microg once daily (Days 1 and 15), and repeated oral erythromycin 500 mg three times daily (Days 9 - 21). Percent ratios of Test/Reference (Reference: roflumilast alone; Test: roflumilast and steady-state erythromycin) were calculated for the geometric means and their 90% confidence intervals for systemic exposure (AUC), maximum concentration (Cmax) (roflumilast and roflumilast N-oxide), and apparent clearance of roflumilast. RESULTS After co-administration of erythromycin and roflumilast, the mean AUC and Cmax of roflumilast increased by 70% and 40%, respectively. The mean apparent clearance of roflumilast decreased from 8.2 l/h (Reference) to 4.8 l/h (Test). Steady-state erythromycin did not alter the mean AUC of roflumilast N-oxide, however, the mean Cmax decreased by 34%. The AUCroflumilast N-oxide/AUCroflumilast ratio decreased from 10.6 (Reference) to 6.4 (Test). Co-administration of erythromycin and roflumilast did not influence the integrated total exposure to roflumilast and roflumilast N-oxide, i.e. mean tPDE4i. No clinically relevant adverse events were observed during the study. CONCLUSIONS Co-administration of erythromycin (a moderate CYP3A4 inhibitor) and roflumilast does not require dose adjustment of roflumilast.

The Targeted Oral, Once‐Daily Phosphodiesterase 4 Inhibitor Roflumilast and the Leukotriene Receptor Antagonist Montelukast Do Not Exhibit Significant Pharmacokinetic Interactions

This nonrandomized, fixed‐sequence, 3‐period study investigated potential pharmacokinetic interactions between the leukotriene receptor antagonist montelukast, approved for the treatment of asthma, and roflumilast, an oral, once‐daily phosphodiesterase 4 inhibitor in clinical development for asthma and chronic obstructive pulmonary disease. Pharmacokinetic interactions are of interest because both drugs may be coadministered and share a common metabolic pathway via cytochrome P450 3A. Single‐dose montelukast (10 mg, po) was administered alone in period 1, followed by repeated once‐daily roflumilast alone (500 μg, po) for 12 days (period 2). In period 3, 500 μg qd roflumilast was coadministered with 10 mg qd montelukast for 8 days. Different pharmacokinetic parameters were evaluated for montelukast alone, for steady‐state roflumilast and its pharmacologically active metabolite roflumilast N‐oxide alone, for single‐dose montelukast when coadministered with steady‐state roflumilast, and for steady‐state roflumilast and its N‐oxide metabolite when coadministered with steady‐state montelukast. The AUC and Cmax of montelukast were modestly increased by 9% and 8%, respectively, when single‐dose montelukast was coadministered with steady‐state roflumilast. The pharmacokinetics of roflumilast and roflumilast N‐oxide in steady state remained unchanged when repeat‐dose montelukast was coadministered at steady‐state. Concomitant administration of both drugs was well tolerated. These findings suggest that no dose adjustment is warranted for either drug when roflumilast and montelukast are coadministered.

Effect of Steady‐State Enoxacin on Single‐Dose Pharmacokinetics of Roflumilast and Roflumilast N‐Oxide

Roflumilast is an oral phosphodiesterase 4 (PDE4) inhibitor for the treatment of chronic obstructive pulmonary disease (COPD). It is metabolized by CYP1A2 and CYP3A4 to its primary metabolite, roflumilast N‐oxide, through which >90% total PDE4 inhibitory activity (tPDE4i) is mediated. Fluoroquinolones, of which enoxacin is the most potent CYP1A2 inhibitor, are used to treat COPD exacerbations. This phase I, open, nonrandomized, fixed‐sequence, 2‐period study evaluated the effects of steady‐state enoxacin on the single‐dose pharmacokinetics of roflumilast and roflumilast N‐oxide. Twenty healthy participants received roflumilast, 500 μg once daily, on days 1 and 12, and enoxacin, 400 mg twice daily, on days 7 to 18. Pharmacokinetic profiles were obtained for days 1 to 6 and 12 to 19. The safety and tolerability of all treatments were also assessed. In 19 evaluable participants, coadministration led to 56% higher mean systemic exposure, 20% higher mean peak concentrations, and 36% lower mean apparent oral clearance compared with roflumilast alone. For roflumilast N‐oxide, 23% higher mean systemic exposure and 14% lower mean peak concentrations were seen after coadministration. Roflumilast was well tolerated both alone and in combination with enoxacin. A weak interaction was shown between roflumilast and enoxacin, as mean tPDE4i increased by 25%, but is unlikely to have clinical relevance.

No Dose Adjustment on Coadministration of the PDE4 Inhibitor Roflumilast With a Weak CYP3A, CYP1A2, and CYP2C19 Inhibitor: An Investigation Using Cimetidine

This nonrandomized, fixed‐sequence, 2‐period crossover study investigated potential pharmacokinetic interactions between the phosphodiesterase 4 inhibitor roflumilast, currently in clinical development for the treatment of chronic obstructive pulmonary disease, and the histamine 2 agonist cimetidine. Participants received roflumilast, 500 μg once daily, on days 1 and 13. Cimetidine, 400 mg twice daily, was administered from days 6 to 16. Pharmacokinetic analysis of roflumilast and its active metabolite roflumilast N‐oxide was performed, and the ratio of geometric means for roflumilast alone and concomitantly with steady‐state cimetidine was calculated. The effect of cimetidine on the total PDE4 inhibitory activity (tPDE4i; total exposure to roflumilast and roflumilast N‐oxide) was also calculated. Coadministration of steady‐state cimetidine increased mean tPDE4i of roflumilast and roflumilast N‐oxide by about 47%. The maximum plasma concentration (Cmax) of roflumilast increased by about 46%, with no effect on Cmax of roflumilast N‐oxide. The increase in tPDE4i of roflumilast and roflumilast N‐oxide following coadministration with cimetidine was mainly due to the inhibitory effect of cimetidine on cytochrome P450 (CYP) isoenzymes CYP1A2, CYP3A, and CYP2C19. These moderate changes indicate that dose adjustment of roflumilast is not required when coadministered with a weak inhibitor of CYP1A2, CYP3A, and CYP2C19, such as cimetidine.