Exposure-Response Analyses for Belzutifan to Inform Dosing Considerations and Labeling.

Belzutifan (Welireg, Merck & Co., Inc., Rahway, NJ, USA) is an oral, potent hypoxia-inducible factor-2α inhibitor, recently approved in the United States for the treatment of von Hippel-Lindau (VHL) disease-associated renal cell carcinoma (RCC) and other VHL disease-associated neoplasms. Safety and efficacy were investigated in two clinical studies: a Phase 1 dose escalation/expansion study in solid tumors and RCC and a Phase 2 study in VHL-RCC. A population pharmacokinetic model was used to estimate belzutifan exposures to facilitate exposure-response (E-R) analyses for efficacy and safety endpoints. Relationships between exposure and efficacy (overall response rate, disease control rate, progression-free survival, best overall tumor size response, and other endpoints), safety outcomes (Grade ≥3 anemia, Grade ≥3 hypoxia, and time to first dose reduction/dose interruption), and pharmacodynamic biomarkers (erythropoietin [EPO] and hemoglobin [Hgb]) were evaluated using various regression techniques and time-to-event analyses. Efficacy E-R was generally flat with non-significant positive trends with exposure. The safety E-R analyses demonstrated a lack of relationship for Grade ≥3 hypoxia and a positive relationship for Grade ≥3 anemia, with incidences also significantly dependent on baseline Hgb. Exposure-dependent reductions in EPO and Hgb were observed. Based on the cumulative benefit-risk assessment in VHL disease-associated neoplasms using E-R, no a priori dose adjustment is recommended for any subpopulation. These analyses supported the benefit-risk profile of belzutifan 120 mg once daily dosing in patients with VHL-RCC for labeling and the overall development program.

Population pharmacokinetic analyses for belzutifan to inform dosing considerations and labeling.

Belzutifan (Welireg, Merck & Co., Inc., Rahway, NJ, USA) is an oral, potent inhibitor of hypoxia-inducible factor 2α, approved for the treatment of certain patients with von Hippel-Lindau (VHL) disease-associated renal cell carcinoma (RCC), central nervous system hemangioblastomas, and pancreatic neuroendocrine tumors. It is primarily metabolized by the polymorphic uridine 5'-diphospho-glucuronosyltransferase (UGT) 2B17 and cytochrome (CYP) 2C19. A population pharmacokinetic (PK) model was built, using NONMEM version 7.3, based on demographics/PK data from three clinical pharmacology (food effect, formulation bridging, and genotype/race effect) and two clinical studies (phase I dose escalation/expansion in patients with RCC and other solid tumors; phase II in patients with VHL). Median (range) age for the combined studies was 55 years (19-84) and body weight was 73.6 kg (42.1-165.8). Belzutifan plasma PK was well-characterized by a linear two-compartment model with first-order absorption and elimination. For patients with VHL, the predicted geometric mean (% coefficient of variation) apparent clearance was 7.3 L/h (51%), apparent total volume of distribution was 130 L (35%), and half-life was 12.39 h (42%). There were no clinically relevant differences in belzutifan PK based on the individual covariates of age, sex, ethnicity, race, body weight, mild/moderate renal impairment, or mild hepatic impairment. In this model, dual UGT2B17 and CYP2C19 poor metabolizers (PMs) were estimated to have a 3.2-fold higher area under the plasma concentration-time curve compared to UGT2B17 extensive metabolizer and CYP2C19 non-PM patients. This population PK analysis enabled an integrated assessment of PK characteristics with covariate effects in the overall population and subpopulations for belzutifan labeling.

Effect of Moxifloxacin plus Pretomanid against Mycobacterium tuberculosis in Log Phase, Acid Phase, and Nonreplicating-Persister Phase in an In Vitro Assay.

Combination therapy is a successful approach to treat tuberculosis in patients with susceptible strains of Mycobacterium tuberculosis However, the emergence of resistant strains requires identification of new, effective therapies. Pretomanid (PA824) and moxifloxacin (MXF) are promising options currently under evaluation in clinical trials for the treatment of susceptible and resistant mycobacteria. We applied our recently described screening strategy to characterize the interaction between PA824 and MXF toward the killing of M. tuberculosis in logarithmic growth phase (log phase), acid phase, and nonreplicating-persister (NRP) phase. Respective in vitro data generated for the H37Rv and 18b strains were evaluated in a microdilution plate system containing both drugs in combination. The Universal Response Surface Approach model from Greco et al. (W. R. Greco, G. Bravo, and J. C. Parsons, Pharmacol Rev 47:331-385, 1995) was used to characterize the nature of the interaction between both drugs; synergistic or additive combinations would prompt additional evaluation in the hollow-fiber infection model (HFIM) and in animal studies. The interaction between MXF and PA824 was additive against M. tuberculosis organisms in acid phase (interaction parameter [α] = 5.56e-8 [95% confidence interval {CI} = -0.278 to 0.278] and α = 0.408 [95% CI = 0.105 to 0.711], respectively), NRP phase (α = 0.625 [95% CI = -0.556 to 1.81] and α = 2.92 [95% CI = 0.215 to 5.63], respectively), and log phase (α = 1.57e-6 [95% CI = -0.930 to 0.930] and α = 1.83e-6 [95% CI = -0.929 and 0.929], respectively), prompting further testing of this promising combination for the treatment of tuberculosis in the HFIM and in animal studies.

Population pharmacokinetic modeling to establish the role of P-glycoprotein on ciprofloxacin distribution to lung and prostate following intravenous and intratracheal administration to Wistar rats.

Ciprofloxacin (CIP) is indicated for clinical treatment of urinary and respiratory tract infections. Poor infection site penetration and consequent insufficient exposure to the antimicrobial agent may be the reason for some therapeutic failures. Ciprofloxacin is reported as a substrate for efflux transporters, such as P-glycoprotein, which could be related to the presence of sub-therapeutic drug concentration at the infection site. In the present work we evaluated CIP pharmacokinetics (PK) in plasma and lung and prostate tissues of Wistar rats after intravenous (i.v.) and intratracheal (i.t.) dosing (7 mg/Kg) in the presence and absence of P-gp inhibitor tariquidar (TAR, 15 mg/Kg). Microdialysis was applied to determine free tissue concentration-time profiles and the obtained data were analyzed by non-compartmental and population PK (popPK) analysis. A sequential strategy was used to develop the popPK model: characterization of CIP PK in tissues (Tissue model) was performed subsequently to CIP PK modeling in plasma (Plasma model). Two and three compartmental models were used to simultaneously characterize plasma concentrations after i.t. and i.v. dosing; the distribution model was developed by separating the central compartment into venous and arterial compartment and by adding lung and prostate; TAR was identified as a significant covariate for clearance and volume of distribution of central compartment as well as for inter-compartmental clearance. Our results indicate an impact of P-gp on plasma PK, likely by acting on renal active secretion of CIP. Regarding CIP exposure in lung and prostate tissues, our results suggest a complex interplay between drug transporters; P-gp inhibition by TAR was likely counterbalanced by the activity of other efflux/influx transporters, which could not be fully characterized by our model.

Effect of Linezolid plus Bedaquiline against Mycobacterium tuberculosis in Log Phase, Acid Phase, and Nonreplicating-Persister Phase in an In Vitro Assay.

Tuberculosis is the ninth-leading cause of death worldwide. Treatment success is approximately 80% for susceptible strains and decreases to 30% for extensively resistant strains. Shortening the therapy duration for Mycobacterium tuberculosis is a major goal, which can be attained with the use of combination therapy. However, the identification of the most promising combination is a challenge given the quantity of older and newer agents available. Our objective was to identify promising 2-drug combinations using an in vitro strategy to ultimately be tested in an in vitro hollow fiber infection model (HFIM) and in animal models. We studied the effect of the combination of linezolid (LZD) and bedaquiline (BDQ) on M. tuberculosis strain H37Rv in log- and acid-phase growth and M. tuberculosis strain 18b in log- and nonreplicating-persister-phase growth in a plate system containing a 9-by-8 matrix of concentrations of both drugs alone and in combinations. A characterization of the interaction as antagonistic, additive, or synergistic was performed using the Greco universal response surface approach (URSA) model. Our results indicate that the interaction between LZD and BDQ is additive for bacterial killing in both strains for both of the metabolic states tested. This prescreen strategy was suitable to identify LZD and BDQ as a promising combination to be further tested in the HFIM. The presence of nonoverlapping mechanisms of drug action suggests each drug in the combination will likely be effective in suppressing the emergence of resistance by M. tuberculosis to the companion drug, which holds promise in improving treatment outcomes for tuberculosis.

Population Pharmacokinetic Modeling to Describe the Total Plasma and Free Brain Levels of Fluconazole in Healthy and Cryptococcus neoformans Infected Rats: How Does the Infection Impact the Drug's Levels on Biophase?

PURPOSE: The present work aimed to evaluate the influence of experimental meningitis caused by C. neoformans on total plasma and free brain concentrations of fluconazole (FLC) in Wistar rats. METHOD: The infection was induced by the administration of 100 µL of inoculum (1.105 CFU) through the tail vein. Free drug in the brain was assessed by microdialisys (µD). Blood and µD samples were collected at pre-determined time points up to 12 h after intravenous administration of FLC (20 mg/kg) to healthy and infected rats. The concentration-time profiles were analyzed by non-compartmental and population pharmacokinetics approaches. RESULTS: A two-compartmental popPK model was able to simultaneously describe plasma and free drug concentrations in the brain for both groups investigated. Analysis of plasma and µD samples showed a better FLC distribution on the brain of infected than healthy animals (1.04 ± 0.31 vs 0.69 ± 0.14, respectively). The probability of target attainment was calculated by Monte Carlo simulations based on the developed popPK model for 125 mg/kg dose for rats and 400-2000 mg for humans. CONCLUSIONS: FLC showed a limited use in monotherapy to the treatment of criptoccocosis in rats and humans to value of MIC >8 µg/mL.

Beyond the "Lock and Key" Paradigm: Targeting Lipid Rafts to Induce the Selective Apoptosis of Cancer Cells.

For more than 40 years, the fluid mosaic model of cellular membranes has supported our vision of an inert lipid bilayer containing membrane protein receptors that are randomly hit by extracellular molecules to trigger intracellular signaling events. However, the notion that compartmentalized cholesterol- and sphingomyelin-rich membrane microdomains (known as lipid rafts) spatially arrange receptors and effectors to promote kinetically favorable interactions necessary for the signal transduction sounds much more realistic. Despite their assumed importance for the dynamics of ligand-receptor interactions, lipid rafts and biomembranes as a whole remain less explored than the other classes of biomolecules because of the higher variability and complexity of their membrane phases, which rarely provide the detailed atomic-level structural data in X-ray crystallography assays necessary for molecular modeling studies. The fact that some alkylphospholipids (e.g. edelfosine: 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine) selectively induce the apoptotic death of cancer cells by recruiting Fas death receptors and the downstream signaling molecules into clusters of lipid rafts suggests these potential drug targets deserve a more in-depth investigation. Herein, we review the structure of lipid rafts, their role in apoptotic signaling pathways and their potential role as drug targets for the treatment of cancer.

Development of an Enantioselective and Biomarker-Informed Translational Population Pharmacokinetic/Pharmacodynamic Model for Etodolac.

Cyclooxygenase-2 (COX-2) isoform has a critical role in the development of pain. Inhibition of COX-2 in vitro serves as a biomarker for nonsteroidal anti-inflammatory drugs (NSAIDs). The NSAID concentrations yielding 80% COX-2 inhibition (IC80) correlate with therapeutic doses to achieve analgesia across multiple COX-2 inhibitors. However, there are no time-course models relating COX-2 inhibition with decreased pain. This study aimed to characterize the relationship between NSAID concentrations, in vitro COX-2 inhibition, and acute pain decrease in humans over time by a translational approach using clinical pharmacokinetic and literature reported in vitro and clinical pharmacodynamic data. In a two-way cross-over study, eight healthy volunteers received 300 and 400 mg racemic etodolac, a preferential COX-2 inhibitor. R- and S-etodolac were determined by LC-MS/MS and simultaneously modeled. Literature in vitro IC50 data for COX-2 inhibition by S-etodolac were used to fit adjusted pain score profiles from dental patients receiving etodolac. External model qualification was performed using published ibuprofen data. Etodolac absorption was highly variable due to gastric transit kinetics and low aqueous solubility. The disposition parameters differed substantially between enantiomers with a total clearance of 2.21 L/h for R-etodolac and 26.8 L/h for S-etodolac. Volume of distribution at steady-state was 14.6 L for R-etodolac and 45.8 L for S-etodolac. Inhibition of COX-2 by 78.1% caused a half-maximal pain decrease. The time-course of pain decrease following ibuprofen was successfully predicted via the developed translational model. This proposed enantioselective pharmacodynamic-informed approach presents the first quantitative time-course model for COX-2 induced pain inhibition in patients.

Pharmacokinetics of hERG Channel Blocking Voacangine in Wistar Rats Applying a Validated LC-ESI-MS/MS Method.

Herbal preparations from Voacanga africana are used in West and Central African folk medicine and are also becoming increasingly popular as a legal high in Europe. Recently, the main alkaloid voacangine was found to be a potent human ether-à-go-go-related gene channel blocker in vitro. Blockage of this channel might imply possible cardiotoxicity. Therefore, the aim of this study was to characterise voacangine in vivo to assess its pharmacokinetics and to estimate if further studies to investigate its cardiotoxic risk are required. Male Wistar rats received different doses of voacangine as a pure compound and as a hydro-ethanolic extract of V. africana root bark with a quantified amount of 9.71 % voacangine. For the obtained data, a simultaneous population pharmacokinetics model was successfully developed, comprising a two-compartment model for i. v. dosing and a one-compartmental model with two first-order absorption rates for oral dosing. The absolute bioavailability of voacangine was determined to be 11-13 %. Model analysis showed significant differences in the first absorption rate constant for voacangine administered as a pure compound and voacangine from the extract of V. africana. Taking into account the obtained low bioavailability of voacangine, its cardiotoxic risk might be neglectable in healthy consumers, but may have a serious impact in light of drug/drug interactions and impaired health conditions.

Enantioselective analysis of etodolac in human plasma by LC-MS/MS: Application to clinical pharmacokinetics.

Etodolac is a non-steroidal anti-inflammatory drug with preferential inhibition of cyclooxigenase-2 and is widely used in the management of pain in patients with inflammatory arthritis. Etodolac is available as a racemic mixture of (-)-(R)-Etodolac and (+)-(S)-Etodolac; cyclooxigenases inhibition is attributed to (+)-(S)-Etodolac. According to our knowledge, this is the first method for determination of etodolac enantiomers in plasma using LC-MS/MS. Plasma extraction were performed with 25µL of plasma and 1mL of n-hexane:ethyl acetate (95:5); racemic ibuprofen was used as internal standard. Resolution of enantiomers were performed in a Chiralcel(®)OD-H column; deprotonated [M-H](-) and their respective ion products were monitored at transitions of 286>242 for etodolac enantiomers and 205>161 for ibuprofen. The quantitation limit was 3.2ng/mL for both enantiomers in plasma. The method was applied to study the pharmacokinetics of etodolac enantiomers after the administration of a 300 and 400mg dose of racemic drug to a healthy volunteer. Analysis of plasma samples showed higher plasma concentration of (-)-(R)-Etodolacfor both doses (300mg dose: AUC(0-∞)49.80 versus 4.55ugh/mL;400mg dose: AUC(0-∞) 63.90 versus 6.00ugh/mL) with an (R)-(+)/(S)-(-) ratio of approximately 11.

Influence of glomerular filtration rate on the pharmacokinetics of cyclophosphamide enantiomers in patients with lupus nephritis.

The pharmacokinetics of cyclophosphamide (CYC) enantiomers were evaluated in patients with lupus nephritis distributed in 2 groups according to creatinine clearance: group 1 (90.6-144.6 mL/min/1.73 m(2)) and group 2 (42.8-76.4 mL/min/1.73 m(2)). All patients were treated with 0.75 to 1.3 g of racemic CYC as a 2-hour infusion and with 1 mg intravenous midazolam as a drug-metabolizing marker. CYC enantiomers and midazolam concentrations in plasma were measured by liquid chromatography/tandem mass spectrometry (LC/MS/MS). The following differences (Wilcoxon test, P < or = .05) were observed between the (S)-(-) and (R)-(+) enantiomers: AUC(0-infinity) 152.41 vs 129.25 microg.h/mL, CL 3.28 vs 3.89 L/h, Vd 31.38 vs 29.74 L, and t((1/2)) 6.79 vs 5.56 h for group 1 and AUC(0-infinity) 167.20 vs 139.08 microg.h/mL, CL 2.99 vs 3.59 L/h, and t((1/2)) 6.15 vs 4.99 h for group 2. No differences (Mann test, P < or = .05) were observed between groups 1 and 2 in the pharmacokinetic parameters of both enantiomers. No significant relationship was observed between midazolam clearance (2.92-16.40 mL/min.kg) and clearance of each CYC enantiomer. In conclusion, CYC kinetic disposition is enantioselective, resulting in higher exposures of the (S)-(-) enantiomer in lupus nephritis patients, and the pharmacokinetic parameters of both enantiomers are not altered by the worsening of renal condition.

Determination of cyclophosphamide enantiomers in plasma by LC-MS/MS: Application to pharmacokinetics in breast cancer and lupus nephritis patients.

This article describes the enantioselective analysis of cyclophosphamide (CPA) in human plasma using LC-MS/MS. CPA enantiomers were extracted from plasma using a mixture of ethyl acetate and chloroform (75:25, v/v). The enantiomers were separated on a Chiralcel(R) OD-R column, with the mobile phase consisting of a mixture of acetonitrile and water (75:25, v/v) plus 0.2% formic acid. The protonated ions and their respective product ions were monitored using two functions, 261 > 141 for CPA enantiomers and 189 > 104 for the internal standard (antipyrine). Recovery rates were higher than 95% and the quantification limit was 2.5-ng/ml plasma for both enantiomers. The coefficients of variation and the relative errors obtained for the validation of intra- and interassay precision and accuracy were less than 10%. The method was applied for the investigation of the enantioselective pharmacokinetics of CPA in a lupus nephritis patient treated with 1 g CPA infused over 2 h and in a breast cancer patient treated with 0.9 g infused over 1 h. No stereoselectivity in the pharmacokinetic parameters was observed for either patient. Clearance values of 2.63 and 2.93 l/h and of 3.36 and 3.61 l/h for (-)-(S) and (+)-(R)-CPA were obtained for the breast cancer and lupus nephritis patient, respectively.

Stereoselective disposition of fenoprofen in plasma and synovial fluid of patients with rheumatoid arthritis.

The simultaneous disposition of fenoprofen enantiomers in synovial fluid and plasma was studied in 11 patients with arthritis and chronic knee effusions treated with a single oral dose of 600 mg rac-fenoprofen. A plasma sample and a synovial fluid sample were collected simultaneously from each patient up to 16 h after the administration of fenoprofen. A stereospecific assay for fenoprofen using LC-MS-MS was developed and applied successfully to the analysis of the enantiomers in plasma (LOQ = 10 ng of each enantiomer/ml) and synovial fluid (LOQ = 25 ng of each enantiomer/ml). The values of the area under the curve (AUC) for the S-(+)-fenoprofen eutomer were approximately 2.5 times higher in plasma than in synovial fluid (256 vs 104 microg h/ml), while the values for the R-(-)-fenoprofen distomer were about four times higher in plasma than in synovial fluid (42.5 vs 10.5 microg h/ml). These data demonstrate accumulation of the S-(+)-fenoprofen eutomer in plasma and in synovial fluid, with concentrations versus time AUC (+)/(-) ratios of 6.0 in plasma and 9.9 in synovial fluid, suggesting a greater accumulation of the eutomer at the active site represented by synovial fluid than in plasma. This result demonstrates the importance of enantioselective methods and of analysis of synovial fluid rather than plasma in studies of the pharmacokinetics-pharmacodynamics of fenoprofen.