Simultaneous Assessment of Transporter-Mediated Drug-Drug Interactions Using a Probe Drug Cocktail in Cynomolgus Monkey.

We aim to establish an in vivo preclinical model to enable simultaneous assessment of inhibition potential of an investigational drug on clinically relevant drug transporters, organic anion-transporting polypeptide (OATP)1B, breast cancer resistance protein (BCRP), P-glycoprotein (P-gp), and organic anion transporter (OAT)3. Pharmacokinetics of substrate cocktail consisting of pitavastatin (OATP1B substrate), rosuvastatin (OATP1B/BCRP/OAT3), sulfasalazine (BCRP), and talinolol (P-gp) were obtained in cynomolgus monkey-alone or in combination with transporter inhibitors. Single-dose rifampicin (30 mg/kg) significantly (P < 0.01) increased the plasma exposure of all four drugs, with a marked effect on pitavastatin and rosuvastatin [area under the plasma concentration-time curve (AUC) ratio ∼21-39]. Elacridar, BCRP/P-gp inhibitor, increased the AUC of sulfasalazine, talinolol, as well as rosuvastatin and pitavastatin. An OAT1/3 inhibitor (probenecid) significantly (P < 0.05) impacted the renal clearance of rosuvastatin (∼8-fold). In vitro, rifampicin (10 µM) inhibited uptake of pitavastatin, rosuvastatin, and sulfasalazine by monkey and human primary hepatocytes. Transport studies using membrane vesicles suggested that all probe substrates, except talinolol, are transported by cynoBCRP, whereas talinolol is a cynoP-gp substrate. Elacridar and rifampicin inhibited both cynoBCRP and cynoP-gp in vitro, indicating potential for in vivo intestinal efflux inhibition. In conclusion, a probe substrate cocktail was validated to simultaneously evaluate perpetrator impact on multiple clinically relevant transporters using the cynomolgus monkey. The results support the use of the cynomolgus monkey as a model that could enable drug-drug interaction risk assessment, before advancing a new molecular entity into clinical development, as well as providing mechanistic insights on transporter-mediated interactions.

Predicting Human Clearance of Organic Anion Transporting Polypeptide Substrates Using Cynomolgus Monkey: In Vitro-In Vivo Scaling of Hepatic Uptake Clearance.

This work explores the utility of the cynomolgus monkey as a preclinical model to predict hepatic uptake clearance mediated by organic anion transporting polypeptide (OATP) transporters. Nine OATP substrates (rosuvastatin, pravastatin, repaglinide, fexofenadine, cerivastatin, telmisartan, pitavastatin, bosentan, and valsartan) were investigated in plated cynomolgus monkey and human hepatocytes. Total uptake clearance and passive diffusion were measured in vitro from initial rates in the absence and presence of the OATP inhibitor rifamycin SV , respectively. Total uptake clearance values in plated hepatocytes ranged over three orders of magnitude in both species, with a similar rank order and good agreement in the relative contribution of active transport to total uptake between cynomolgus monkey and human. In vivo hepatic clearance for these nine drugs was determined in cynomolgus monkey after intravenous dosing. Hepatic clearances showed a range similar to human parameters and good predictions from respective hepatocyte parameters (with 2.7- and 3.8-fold bias on average, respectively). The use of cross-species empirical scaling factors (determined from cynomolgus monkey data either as the data set average or individual drug values) improved prediction (less bias, better concordance) of human hepatic clearance from human hepatocyte data alone. In vitro intracellular binding in hepatocytes also correlated well between species. It is concluded that the minimal species differences observed for the current data set between cynomolgus monkey and human hepatocyte uptake, both in vitro and in vivo, support future use of this preclinical model to delineate drug hepatic uptake and enable prediction of human in vivo intrinsic hepatic clearance.

In Vitro-In Vivo Extrapolation of OATP1B-Mediated Drug-Drug Interactions in Cynomolgus Monkey.

Hepatic organic anion-transporting polypeptides (OATP) 1B1 and 1B3 are clinically relevant transporters associated with significant drug-drug interactions (DDIs) and safety concerns. Given that OATP1Bs in cynomolgus monkey share >90% degree of gene and amino acid sequence homology with human orthologs, we evaluated the in vitro-in vivo translation of OATP1B-mediated DDI risk using this preclinical model. In vitro studies using plated cynomolgus monkey hepatocytes showed active uptake Km values of 2.0 and 3.9 µM for OATP1B probe substrates, pitavastatin and rosuvastatin, respectively. Rifampicin inhibited pitavastatin and rosuvastatin active uptake in monkey hepatocytes with IC50 values of 3.0 and 0.54 µM, respectively, following preincubation with the inhibitor. Intravenous pharmacokinetics of 2H4-pitavastatin and 2H6-rosuvastatin (0.2 mg/kg) and the oral pharmacokinetics of cold probes (2 mg/kg) were studied in cynomolgus monkeys (n = 4) without or with coadministration of single oral ascending doses of rifampicin (1, 3, 10, and 30 mg/kg). A rifampicin dose-dependent reduction in i.v. clearance of statins was observed. Additionally, oral pitavastatin and rosuvastatin plasma exposure increased up to 19- and 15-fold at the highest dose of rifampicin, respectively. Use of in vitro IC50 obtained following 1 hour preincubation with rifampicin (0.54 µM) predicted correctly the change in mean i.v. clearance and oral exposure of statins as a function of mean unbound maximum plasma concentration of rifampicin. This study demonstrates quantitative translation of in vitro OATP1B IC50 to predict DDIs using cynomolgus monkey as a preclinical model and provides further confidence in application of in vitro hepatocyte data for the prediction of clinical OATP1B-mediated DDIs.

IMI - Oral biopharmaceutics tools project - Evaluation of bottom-up PBPK prediction success part 3: Identifying gaps in system parameters by analysing In Silico performance across different compound classes.

Three Physiologically Based Pharmacokinetic software packages (GI-Sim, Simcyp® Simulator, and GastroPlus™) were evaluated as part of the Innovative Medicine Initiative Oral Biopharmaceutics Tools project (OrBiTo) during a blinded "bottom-up" anticipation of human pharmacokinetics. After data analysis of the predicted vs. measured pharmacokinetics parameters, it was found that oral bioavailability (Foral) was underpredicted for compounds with low permeability, suggesting improper estimates of intestinal surface area, colonic absorption and/or lack of intestinal transporter information. Foral was also underpredicted for acidic compounds, suggesting overestimation of impact of ionisation on permeation, lack of information on intestinal transporters, or underestimation of solubilisation of weak acids due to less than optimal intestinal model pH settings or underestimation of bile micelle contribution. Foral was overpredicted for weak bases, suggesting inadequate models for precipitation or lack of in vitro precipitation information to build informed models. Relative bioavailability was underpredicted for both high logP compounds as well as poorly water-soluble compounds, suggesting inadequate models for solubility/dissolution, underperforming bile enhancement models and/or lack of biorelevant solubility measurements. These results indicate areas for improvement in model software, modelling approaches, and generation of applicable input data. However, caution is required when interpreting the impact of drug-specific properties in this exercise, as the availability of input parameters was heterogeneous and highly variable, and the modellers generally used the data "as is" in this blinded bottom-up prediction approach.

IMI - Oral biopharmaceutics tools project - Evaluation of bottom-up PBPK prediction success part 2: An introduction to the simulation exercise and overview of results.

Orally administered drugs are subject to a number of barriers impacting bioavailability (Foral), causing challenges during drug and formulation development. Physiologically-based pharmacokinetic (PBPK) modelling can help during drug and formulation development by providing quantitative predictions through a systems approach. The performance of three available PBPK software packages (GI-Sim, Simcyp®, and GastroPlus™) were evaluated by comparing simulated and observed pharmacokinetic (PK) parameters. Since the availability of input parameters was heterogeneous and highly variable, caution is required when interpreting the results of this exercise. Additionally, this prospective simulation exercise may not be representative of prospective modelling in industry, as API information was limited to sparse details. 43 active pharmaceutical ingredients (APIs) from the OrBiTo database were selected for the exercise. Over 4000 simulation output files were generated, representing over 2550 study arm-institution-software combinations and approximately 600 human clinical study arms simulated with overlap. 84% of the simulated study arms represented administration of immediate release formulations, 11% prolonged or delayed release, and 5% intravenous (i.v.). Higher percentages of i.v. predicted area under the curve (AUC) were within two-fold of observed (52.9%) compared to per oral (p.o.) (37.2%), however, Foral and relative AUC (Frel) between p.o. formulations and solutions were generally well predicted (64.7% and 75.0%). Predictive performance declined progressing from i.v. to solution and immediate release tablet, indicating the compounding error with each layer of complexity. Overall performance was comparable to previous large-scale evaluations. A general overprediction of AUC was observed with average fold error (AFE) of 1.56 over all simulations. AFE ranged from 0.0361 to 64.0 across the 43 APIs, with 25 showing overpredictions. Discrepancies between software packages were observed for a few APIs, the largest being 606, 171, and 81.7-fold differences in AFE between SimCYP and GI-Sim, however average performance was relatively consistent across the three software platforms.

Bilayer composition, temperature, speciation effects and the role of bilayer chain ordering on partitioning of dexamethasone and its 21-phosphate.

PURPOSE: Models to predict membrane-water partition coefficients (Kp) as a function of drug structure, membrane composition, and solution properties would be useful. This study explores the partitioning of dexamethasone (Dex) and its ionizable 21-phosphate (Dex-P) in liposomes varying in acyl chain length, physical state, and pH. METHODS: DMPC:mPEG DMPE, DPPC:mPEG DPPE, and DSPC:mPEG DSPE (95:5 mol%) liposomes were prepared by thin film hydration. Kp values for Dex and Dex-P were determined from pH 1.5-8 by equilibrium dialysis and equilibrium solubility (Dex). RESULTS: Dex Kp values at 25°C were 705 ± 24, 106 ± 11, and 58 ± 9 in DMPC, DPPC, and DSPC, increasing to 478 ± 20 in DPPC liposomes at 45°C. Both neutral and anionic species contributed to the Kp of Dex-P versus solution pH (1.5-8). A linear correlation was found between the natural logarithm of Kp and the inverse of bilayer free surface area (1/afree) where afree is a parameter reflecting chain ordering that depends on bilayer composition and temperature. CONCLUSIONS: Models of the pH dependence of partitioning of ionizable compounds must include contributions of both neutral and ionized species. Bilayer free surface area may be an important variable to predict Kp of drug molecules versus lipid composition and temperature.

Determination of drug release kinetics from nanoparticles: overcoming pitfalls of the dynamic dialysis method.

Dynamic dialysis is one of the most common methods for the determination of release kinetics from nanoparticle drug delivery systems. Drug appearance in the "sink" receiver compartment is a consequence of release from the nanoparticles into the dialysis chamber followed by diffusion across the dialysis membrane. This dual barrier nature inherent in the method complicates data interpretation and may lead to incorrect conclusions regarding nanoparticle release half-lives. Although the need to consider the barrier properties of the dialysis membrane has long been recognized, there is insufficient quantitative appreciation for the role of the driving force for drug transport across that membrane. Reversible nanocarrier binding of the released drug reduces the driving force for drug transport across the dialysis membrane leading to a slower overall apparent release rate. This may lead to the conclusion that a given nanoparticle system will provide a sustained release in vivo when it will not. This study demonstrates these phenomena using model lipophilic drug-loaded liposomes varying in lipid composition to provide variations in bilayer permeability and membrane binding affinities. Model simulations of liposomal transport as measured by dynamic dialysis were conducted to illustrate the interplay between the liposome concentration, membrane/water partition coefficient, and the apparent release rate. Reliable determination of intrinsic liposomal bilayer permeability coefficients for lipophilic drugs by dynamic dialysis requires validation of drug release kinetics at varying nanoparticle concentration and the determination of membrane binding coefficients along with appropriate mechanism-based mathematical modeling to ensure the reliability and proper interpretation of the data.

Enhanced active liposomal loading of a poorly soluble ionizable drug using supersaturated drug solutions.

Nanoparticulate drug carriers such as liposomal drug delivery systems are of considerable interest in cancer therapy because of their ability to passively accumulate in solid tumors. For liposomes to have practical utility for antitumor therapy in patients, however, optimization of drug loading, retention, and release kinetics are necessary. Active loading is the preferred method for optimizing loading of ionizable drugs in liposomes as measured by drug-to-lipid ratios, but the extremely low aqueous solubilities of many anticancer drug candidates may limit the external driving force, thus slowing liposomal uptake during active loading. This report demonstrates the advantages of maintaining drug supersaturation during active loading. A novel method was developed for creating and maintaining supersaturation of a poorly soluble camptothecin analogue, AR-67 (7-t-butyldimethylsilyl-10-hydroxycamptothecin), using a low concentration of a cyclodextrin (sulfobutylether-ß-cyclodextrin) to inhibit crystallization over a 48 h period. Active loading into liposomes containing high concentrations of entrapped sodium or calcium acetate was monitored using drug solutions at varying degrees of supersaturation. Liposomal uptake rates increased linearly with the degree of supersaturation of drug in the external loading solution. A mathematical model was developed to predict the rate and extent of drug loading versus time, taking into account the chemical equilibria inside and outside of the vesicles and the transport kinetics of various permeable species across the lipid bilayer and the dialysis membrane. Intraliposomal sink conditions were maintained by the high internal pH caused by the efflux of acetic acid and exchange with AR-67, which undergoes lactone ring-opening, ionization, and membrane binding in the interior of the vesicles. The highest drug to lipid ratio achieved was 0.17 from a supersaturated solution at a total drug concentration of 0.6 mg/ml. The rate and extent of loading was similar when a different intraliposomal metal cation (sodium) was used instead of calcium. The proposed method may have general application in overcoming the formulation challenges associated with the liposomal delivery of poorly soluble, ionizable anticancer agents.

Hydroxy fatty acid based polyanhydride as drug delivery system: synthesis, characterization, in vitro degradation, drug release, and biocompatibility.

Low molecular weight hydroxy fatty acid based polyanhydrides were synthesized by one pot method, a variable of typical melt-condensation and characterized by FTIR, NMR, DSC, and GPC. Polymer degrades by both surface and bulk erosion as trailed by weight loss, anhydride loss and surface morphology. Control over drug release was accessed with drugs featuring different aqueous solubility, that is, methotrexate (hydrophobic) and 5-fluorouracil (hydrophilic). Effect of loading, at 5, 10, and 20% w/w of methotrexate on release profiles was also studied and negligible effect was discovered. Biocompatibility of polymers was evaluated in SD rats after SC injection of the polymer. Histopathology revealed initial inflammation of the tissues near the injection site however healed with time. Overall, these polymers were found good to control the release of the entrapped drug and were found biocompatible in preliminary in vivo study. Due to their low melting temperatures they can be injected locally (SC or intratumorally) to from regional in situ depot and have a great potential as a drug carrier for localized delivery of anticancer drugs.

Exploiting EPR in polymer drug conjugate delivery for tumor targeting.

Treatment of tumor tissue without affecting normal cells has always been formidable task for drug delivery scientists and this task is effectively executed by polymer drug conjugate (PDC) delivery. The novelty of this concept lies in the utilization of a physical mechanism called enhanced permeability and retention (EPR) for targeting tumors. EPR is a physiological phenomenon that is customary for fast growing tumor and solves the problem of targeting the miscreant tissue. PDCs offer added advantages of reduced deleterious effects of anticancer drugs and augmentation of its formulation capability (e.g. Solubility). There are now at least eleven PDCs that have entered phase I/II/III clinical trial as anticancer drugs. PDCs once entered into the tumor tissue, taking advantage of EPR, are endocytosed into the cell either by simple or receptor mediated endocytosis. Various polymeric carriers have been used with hydrolyzable linker arm for conjugation with bioactive moiety. The hydrolyzable linkages of PDC are broken down by acid hydrolyses of lysosomes and releases the drug. High concentrations of the chemotherapeutic agent are maintained near the nucleus, the target site. Passive targeting by PDCs is due to the physiological event of EPR, which is becoming one of the major thrust areas for targeting solid tumors.

Copolymers of pharmaceutical grade lactic acid and sebacic acid: drug release behavior and biocompatibility.

Pharmaceutical grade D,L-lactic acid, which is rather an economic source in comparison to lactide monomer, was utilized for synthesis of a series of copolymers with sebacic acid. Polymers were characterized by GPC, FTIR, NMR and DSC techniques, and formulated into blank and methotrexate (MTX) loaded microspheres by emulsion-solvent evaporation method. In vitro degradation of blank microspheres was studied by FTIR, GPC and SEM analysis. MTX loaded microspheres showed the encapsulation efficiency of 44-64% and were in the size range of 40-60 microm. These were used to study the release profile of the encapsulated drug. The release was found to be affected by the pH and buffer concentration of the release medium which was in turn revealed by solubility studies of MTX. The overall study demonstrates significance of drug as well as polymer properties on release. Biocompatibility of polymer was evaluated by injecting microspheres subcutaneously into Sprague-Dawley (SD) rat and no local histopathological abnormalities were found.

Role of polyanhydrides as localized drug carriers.

Many drugs that are administered in an unmodified form by conventional systemic routes fail to reach target organs in an effective concentration, or are not effective over a length of time due to a facile metabolism. Various types of targeting delivery systems and devices have been tried over a long period of time to overcome these problems. Targeted delivery or localized drug delivery offers an advantage of reduced body burden and systemic toxicity of the drugs, especially useful for highly toxic drugs like anticancer agents. Local drug delivery via polymer is a simple approach and hypothesized to avoid the above stated problems. Polyanhydrides are a unique class of polymer for drug delivery because some of them demonstrate a near zero order drug release and relatively rapid biodegradation in vivo. Further, the release rate of polyanhydride fabricated device can be altered over a thousand fold by simple changes in the polymer backbone. Hence, these are one of the best-suited polymers for drug delivery, with biodegradability and biocompatibility. The review focuses on the advantages of polyanhydride carriers in localized drug delivery along with their degradability behavior, toxicological profile and role in various disease conditions.