The effect of liver dysfunction on the pharmacokinetic disposition of belinostat and its five metabolites in patients with advanced cancers.

Belinostat was approved in 2014 for the treatment of relapsed or refractory peripheral T-cell lymphoma, however, there was insufficient data to recommend a dose in patients with moderate to severe hepatic impairment. The purpose of this analysis was to characterize the pharmacokinetic disposition of belinostat and its five metabolites in patients with advanced cancers and varying degrees of liver dysfunction. A population pharmacokinetic model was therefore developed to describe the parent-metabolite system. The final model was then implemented to assess the effect of liver impairment on each metabolic pathway of belinostat. It was determined that significant pharmacokinetic differences could only be demonstrated in patients with severe hepatic impairment. The final model estimated a 35%-47% reduction in metabolic clearance attributed to UGT1A1/2B7 glucuronidation, CYP2A6/3A4/2C9 metabolism, and ß-oxidation. These hepatic impairment effects reduced between-subject variability by only 5%-8% for their respective parameter, with a large amount of remaining unexplained variability. With further validation, this model can be leveraged to assess the need for dose adjustments in this patient population.

Evaluating the indotecan-neutropenia relationship in patients with solid tumors by population pharmacokinetic modeling and sigmoidal Emax regressions.

PURPOSE: This study aimed at characterizing indotecan population pharmacokinetics and explore the indotecan-neutropenia relationship in patients with solid tumors. METHODS: Population pharmacokinetics were assessed using nonlinear mixed-effects modeling of concentration data from two first-in-human phase 1 trials evaluating different dosing schedules of indotecan. Covariates were assessed in a stepwise manner. Final model qualification included bootstrap simulation, visual and quantitative predictive checks, and goodness-of-fit. A sigmoidal Emax model was developed to describe the relationship between average concentration and maximum percent neutrophil reduction. Simulations at fixed doses were conducted to determine the mean predicted decrease in neutrophil count for each schedule. RESULTS: 518 concentrations from 41 patients supported a three-compartment pharmacokinetic model. Body weight and body surface area accounted for inter-individual variability of central/peripheral distribution volume and intercompartmental clearance, respectively. Estimated typical population values were CL 2.75 L/h, Q3 46.0 L/h, and V3 37.9 L. The estimated value of Q2 for a typical patient (BSA = 1.96 m2) was 17.3 L/h, while V1 and V2 for a typical patient (WT = 80 kg) was 33.9 L and 132 L. The final sigmoidal Emax model estimated that half-maximal ANC reduction occurs at an average concentration of 1416 µg/L and 1041 µg/L for the daily and weekly regimens, respectively. Simulations of the weekly regimen demonstrated lower percent reduction in ANC compared to the daily regimen at equivalent cumulative fixed doses. CONCLUSION: The final PK model adequately describes indotecan population pharmacokinetics. Fixed dosing may be justified based on covariate analysis and the weekly dosing regimen may have a reduced neutropenic effect.

Characterization of drug-drug interactions on the pharmacokinetic disposition of busulfan in paediatric patients during haematopoietic stem cell transplantation conditioning.

AIM: The study objective was to develop a population pharmacokinetic model for busulfan to comprehensively examine drug-drug interactions in paediatric patients undergoing haematopoietic stem cell transplantation. Currently, there is limited evidence to substantiate potential drug-drug interactions with busulfan. METHODS: This retrospective study population was comprised of 250 patients receiving, on average, 0.8 mg/kg intravenous busulfan as pretreatment. All model analyses were conducted using nonlinear mixed effects modelling in Pumas v2.0. The metabolic pathways of primary interest were glutathione conjugation and cytochrome P450 (CYP) activity. Concomitant medications were categorized as CYP inhibitors, inducers or glutathione S-transferase depleters, and included in the model as conditional covariates. A bootstrap simulation and visual predictive check were conducted to qualify the final model. RESULTS: The final 1-compartment model incorporates covariates of weight and age in relation to their effects on both total body clearance and volume of distribution. The estimated typical values of clearance and volume were 1.138 L/h (CI: 1.095-1.179 L/h) and 3.527 L (CI: 3.418-3.621 L), respectively. No significant changes in clearance were observed when medications that alter proposed hepatic and metabolic pathways of busulfan were coadministered. CONCLUSION: To the best of our knowledge, this is the largest single centre study of busulfan in children and the first to quantify the maturation effect of both clearance and volume. This study could not demonstrate a difference in busulfan clearance when comparing patients who received medications that alter the glutathione S-transferase, CYP3A4 or CYP2C9 pathway to those who did not.

Inhibiting p21-Activated Kinase Induces Cell Death in Vestibular Schwannoma and Meningioma via Mitotic Catastrophe.

HYPOTHESIS: p21-activated kinase (PAK) regulates signaling pathways that promote cell survival and proliferation; therefore, pharmacological inhibition of PAK will induce cell death in vestibular schwannomas (VS) and meningiomas. BACKGROUND: All VS and many meningiomas result from loss of the neurofibromatosis type 2 (NF2) gene product merlin, with ensuing PAK hyperactivation and increased cell proliferation/survival. METHODS: The novel small molecule PAK inhibitors PI-8 and PI-15-tested in schwannoma and meningioma cells-perturb molecular signaling and induce cell death. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, flow cytometry, and terminal deoxynucleotidyl transferase dUTP nick end labeling assay analyzed PAK inhibitors' effect on cell viability, cell cycle, and cell death, respectively. Western blots evaluated activation and expression of cell proliferation, apoptotic, and mitotic catastrophe markers. Light microscopy evaluated cell morphology, and immunocytochemistry analyzed cellular localization of phospho-Merlin and autophagy-related protein. RESULTS: Treatment with PI-8 and PI-15 decreased cell viability at 0.65 to 3.7 µM 50% inhibitory concentration (IC50) in schwannoma and meningioma cells. Terminal deoxynucleotidyl transferase dUTP nick end labeling and immunocytochemistry studies show that PI-8 and PI-15 induce mitotic catastrophe but not apoptosis in HEI193 cells while in BenMen1 cells, PI-8 induces autophagy and mitotic catastrophe. PI-15 induces apoptosis in BenMen1 cells. PAK inhibitor treated cells show phospho-Merlin localized to over-duplicated centrosomes of dividing cells, multiple enlarged nuclei, and misaligned/missegregated chromosomes-markers for mitotic catastrophe. Increased autophagy-related protein levels in the nucleus confirmed this cell death type. PI-8 and PI-15 inhibits PAK in both cell lines. However, only PI-15 inhibits v-akt murine thymoma viral oncogene homolog in BenMen1 cells. CONCLUSION: PAK inhibitors induce cell death in schwannoma and meningioma cells, at least in part, by mitotic catastrophe.