Improving In Vitro-In Vivo Extrapolation of Clearance Using Rat Liver Microsomes for Highly Plasma Protein-Bound Molecules

It is common practice in drug discovery and development to predict in vivo hepatic clearance from in vitro incubations with liver microsomes or hepatocytes using the well-stirred model (WSM). When applying the WSM to a set of approximately 3000 Novartis research compounds, 73% of neutral and basic compounds (extended clearance classification system [ECCS] class 2) were well-predicted within 3-fold. In contrast, only 44% (ECCS class 1A) or 34% (ECCS class 1B) of acids were predicted within 3-fold. To explore the hypothesis whether the higher degree of plasma protein binding for acids contributes to the in vitro-in vivo correlation (IVIVC) disconnect, 68 proprietary compounds were incubated with rat liver microsomes in the presence and absence of 5% plasma. A minor impact of plasma on clearance IVIVC was found for moderately bound compounds (fraction unbound in plasma [fup] ≥1%). However, addition of plasma significantly improved the IVIVC for highly bound compounds (fup <1%) as indicated by an increase of the average fold error from 0.10 to 0.36. Correlating fup with the scaled unbound intrinsic clearance ratio in the presence or absence of plasma allowed the establishment of an empirical, nonlinear correction equation that depends on fup Taken together, estimation of the metabolic clearance of highly bound compounds was enhanced by the addition of plasma to microsomal incubations. For standard incubations in buffer only, application of an empirical correction provided improved clearance predictions. SIGNIFICANCE STATEMENT: Application of the well-stirred liver model for clearance in vitro-in vivo extrapolation (IVIVE) in rat generally underpredicts the clearance of acids and the strong protein binding of acids is suspected to be one responsible factor. Unbound intrinsic in vitro clearance (CLint,u) determinations using rat liver microsomes supplemented with 5% plasma resulted in an improved IVIVE. An empirical equation was derived that can be applied to correct CLint,u-values in dependance of fraction unbound in plasma (fup) and measured CLint in buffer.

LTA4H inhibitor LYS006: Clinical PK/PD and safety in a randomized phase I clinical trial

LYS006 is a novel, highly potent and selective, new-generation leukotriene A4 hydrolase (LTA4H) inhibitor in clinical development for the treatment of neutrophil-driven inflammatory diseases. We describe the complex pharmacokinetic to pharmacodynamic (PD) relationship in blood, plasma, and skin of LYS006-treated nonclinical species and healthy human participants. In a randomized first in human study, participants were exposed to single ascending doses up to 100 mg and multiple ascending doses up to 80 mg b.i.d.. LYS006 showed rapid absorption, overall dose proportional plasma exposure and nonlinear blood to plasma distribution caused by saturable target binding. The compound efficiently inhibited LTB4 production in human blood and skin blister cells, leading to greater than 90% predose target inhibition from day 1 after treatment initiation at doses of 20 mg b.i.d. and above. Slow re-distribution from target expressing cells resulted in a long terminal half-life and a long-lasting PD effect in ex vivo stimulated blood and skin cells despite low plasma exposures. LYS006 was well-tolerated and demonstrated a favorable safety profile up to highest doses tested, without any dose-limiting toxicity. This supported further clinical development in phase II studies in predominantly neutrophil-driven inflammatory conditions, such as hidradenitis suppurativa, inflammatory acne, and ulcerative colitis.

The application of organ-on-chip models for the prediction of human pharmacokinetic profiles during drug development

Organ-on-chip (OoC) technology has led to in vitro models with many new possibilities compared to conventional in vitro and in vivo models. In this review, the potential of OoC models to improve the prediction of human oral bioavailability and intrinsic clearance is discussed, with a focus on the functionality of the models and the application in current drug development practice. Multi-OoC models demonstrating the application for pharmacokinetic (PK) studies are summarized and existing challenges are identified. Physiological parameters for a minimal viable platform of a multi-OoC model to study PK are provided, together with PK specific read-outs and recommendations for relevant reference compounds to validate the model. Finally, the translation to in vivo PK profiles is discussed, which will be required to routinely apply OoC models during drug development.

Absorption, distribution, metabolism, and excretion of [14C]iptacopan in healthy male volunteers and in in vivo and in vitro studies

Iptacopan (LNP023) is an oral, small-molecule, first-in-class, highly potent proximal complement inhibitor that specifically binds factor B and inhibits the alternative complement pathway. Iptacopan is currently in development as a targeted treatment for PNH and multiple other complement-mediated diseases. In this study, the absorption, distribution, metabolism, and excretion (ADME) of iptacopan was characterized in six healthy volunteers after a single 100 mg oral dose of [¹⁴C]iptacopan. This was supplemented with an in vivo rat ADME study and metabolite exposure comparisons between human, rat and dog, in addition to in vitro assays, to better understand the clearance pathways and enzymes involved in the metabolism of iptacopan. The fraction of [¹⁴C]iptacopan absorbed was estimated to be about 71%, with a time to maximum concentration (T_max) of 1.5 h and elimination half-life from plasma of 12.3 h. Following a single dose of [¹⁴C]iptacopan, 71.5% of the radioactivity was recovered in feces and 24.8% in urine. [¹⁴C]iptacopan was primarily eliminated by hepatic metabolism. The main biotransformation pathways were oxidative metabolism via CYP2C8, with M2 being the major oxidative metabolite, and acyl glucuronidation via UGT1A1. The two acyl glucuronide metabolites in human plasma, M8 and M9, each accounted for {less than or equal to}10% of the total circulating drug-related material; systemic exposure was also observed in toxicology studies in rat and dog, suggesting a low risk associated with these metabolites. Binding of iptacopan to its target, factor B, in the bloodstream led to a concentration-dependent blood:plasma distribution and plasma protein binding of [¹⁴C]iptacopan. Significance Statement We characterized the pharmacokinetics, excretion, metabolism and elimination of [¹⁴C]iptacopan (an oral, selective small-molecule inhibitor of factor B) - in healthy human subjects. [¹⁴C]iptacopan was primarily eliminated by metabolism. The primary biotransformation pathways were oxidative metabolism via CYP2C8 and acyl glucuronidation via UGT1A1. Direct secretion of iptacopan into urine and potentially bile represented additional elimination mechanisms. Binding of iptacopan to its target, factor B, in the bloodstream led to a concentration-dependent blood:plasma distribution and plasma protein binding of [¹⁴C]iptacopan.

Simplifying the Extended Clearance Concept Classification System (EC3S) to Guide Clearance Prediction in Drug Discovery

PURPOSE

The Extended Clearance Concept Classification System was established as a development-stage tool to provide a framework for identifying fundamental mechanism(s) governing drug disposition in humans. In the present study, the applicability of the EC3S in drug discovery has been investigated. In its current format, the EC3S relies on low-throughput hepatocyte uptake data, which are not frequently generated in a discovery setting.

METHODS

A relationship between hepatocyte uptake clearance and MDCK permeability was first established along with intrinsic clearance from human liver microsomes. The performance of this approach was examined by categorizing 64 drugs into EC3S classes and comparing the predicted major elimination pathway(s) to that observed in humans. As an extension of the work, the ability of the simplified EC3S to predict human systemic clearance based on intrinsic clearance generated using in-vitro metabolic systems was evaluated.

RESULTS

The assessment enabled the use of MDCK permeability and unscaled unbound intrinsic clearance to generate cut-off criteria to categorize compounds into four EC3S classes: Class 12ab, 2cd, 34ab, and 34cd, with major elimination mechanism(s) assigned to each class. The predictivity analysis suggested that systemic clearance could generally be predicted within threefold for EC3S class 12ab and 34ab compounds. For classes 2cd and 34cd, systemic clearance was poorly predicted using in-vitro systems explored in this study.

CONCLUSION

Collectively, our simplified classification approach is expected to facilitate the identification of mechanism(s) involved in drug elimination, faster resolution of in-vitro to in-vivo disconnects, and better design of mechanistic pharmacokinetic studies in drug discovery.

Novel insights into bile acid detoxification via CYP, UGT and SULT enzymes

Bile acid (BA) homeostasis is a complex and precisely regulated process to prevent impaired BA flow and the development of cholestasis. Several reactions, namely hydroxylation, glucuronidation and sulfation are involved in BA detoxification. In the present study, we employed a comprehensive approach to identify the key enzymes involved in BA metabolism using human recombinant enzymes, human liver microsomes (HLM) and human liver cytosol (HLC). We showed that CYP3A4 was a crucial step for the metabolism of several BAs and their taurine and glycine conjugated forms and quantitatively described their metabolites. Glucuronidation and sulfation were also identified as important drivers of the BA detoxification process in humans. Moreover, lithocholic acid (LCA), the most hydrophobic BA with the highest toxicity potential, was a substrate for all investigated processes, demonstrating the importance of hepatic metabolism for its clearance. Collectively, this study identified CYP3A4, UGT1A3, UGT2B7 and SULT2A1 as the major contributing (metabolic) processes in the BA detoxification network. Inhibition of these enzymes by drug candidates is therefore considered as a critical mechanism in the manifestation of drug-induced cholestasis in humans and should be addressed during the pre-clinical development.

Validation of personal protective equipment ensembles, incorporating powered air-purifying respirators protected from contamination, for the care of patients with high-consequence infectious diseases

BACKGROUND

The UK High-Consequence Infectious Diseases (HCID) Network of high-level isolation units provides care for patients with contact- or airborne-transmissible highly infectious and highly dangerous diseases. In most HCID units, the healthcare workers (HCWs) wear personal protective equipment (PPE) ensembles incorporating a powered air-purifying respirator (PAPR) for head and respiratory protection. Some PAPRs have components worn outside/over other PPE, necessitating decontamination of re-usable elements. Two alternative PAPRs, with all re-usable elements worn under PPE, were trialled in this study.

AIM

To undertake scenario-based testing of PAPRs and PPE to determine usability, comfort and ability to remove contaminated PPE without personal cross-contamination.

METHODS

Trained healthcare volunteers (N=20) wearing PAPR/PPE ensembles were sprayed with ultraviolet fluorescent markers. They undertook exercises to mimic patient care, and subsequently, after doffing the contaminated PPE following an established protocol, any personal cross-contamination was visualized under ultraviolet light. Participants also completed a questionnaire to gauge how comfortable they found the PPE.

FINDINGS AND CONCLUSIONS

The ensembles were tested under extreme 'worst case scenario' conditions, augmented by physical and manual dexterity tests. Participating volunteers considered the exercise to be beneficial in terms of training and PPE evaluation. Data obtained, including feedback from questionnaires and doffing buddy observations, supported evidence-based decisions on the PAPR/PPE ensemble to be adopted by the HCID Network. One cross-contamination event was recorded in the ensemble chosen; this could be attributed to doffing error, and could therefore be eliminated with further practice.

Time Matters - In vitro Cellular Disposition Kinetics Help Rationalizing Cellular Potency Disconnects

Loss in potency is commonly observed in early drug discovery when moving from biochemical to more complex cellular systems. Among other factors, low permeability is often considered to cause such potency disconnects.We developed a novel cellular disposition assay in MDCK cells to determine passive uptake clearance (PS_inf), cell-to-medium ratios at steady-state (Kp) and the time to reach 90% steady-state (TTSS₉₀) from a single experiment in a high-throughput format.The assay was validated using 40 marketed drugs, showing a wide distribution of PS_inf and K_p values. The parameters generally correlated with transcellular permeability and lipophilicity, while PS_inf data revealed better resolution in the high and low permeability ranges compared to traditional permeability data. A linear relationship between the K_p/PS_inf ratio and TTSS₉₀ was mathematically derived and experimentally validated, demonstrating the dependency of TTSS₉₀ on the rate and extent of cellular accumulation.Cellular disposition parameters could explain potency (IC₅₀) disconnects noted for seven Bruton's tyrosine kinase degrader compounds in a cellular potency assay. In contrast to transcellular permeability, PS_inf data enabled identification of the compounds with IC₅₀ disconnects based on their time to reach equilibrium. Overall, the novel assay offers the possibility to address potency disconnects in early drug discovery.

Universal use of surgical masks is tolerated and prevents respiratory viral infection in stem cell transplant recipients

Prevention of respiratory viral infection in stem cell transplant patients is important due to its high risk of adverse outcome. This single-centre, mixed methods study, conducted before the severe acute respiratory syndrome coronavirus-2 pandemic, explored the barriers and facilitators to a policy of universal mask use by visitors and healthcare workers, and examined the impact of the first year of introduction of the policy on respiratory viral infection rates compared with preceding years, adjusted for overall incidence. Education around universal mask use was highlighted as being particularly important in policy implementation. A significant decrease in respiratory viral infection was observed following introduction.

Novel Bruton's Tyrosine Kinase inhibitor remibrutinib: Drug-drug interaction potential as a victim of CYP3A4 inhibitors based on clinical data and PBPK modeling

Remibrutinib, a novel oral Bruton’s Tyrosine Kinase inhibitor (BTKi) is highly selective for BTK, potentially mitigating the side effects of other BTKis. Enzyme phenotyping identified CYP3A4 to be the predominant elimination pathway of remibrutinib. The impact of concomitant treatment with CYP3A4 inhibitors, grapefruit juice and ritonavir (RTV), was investigated in this study in combination with an intravenous microtracer approach. Pharmacokinetic (PK) parameters, including the fraction absorbed, the fractions escaping intestinal and hepatic first‐pass metabolism, the absolute bioavailability, systemic clearance, volume of distribution at steady‐state, and the fraction metabolized via CYP3A4 were evaluated. Oral remibrutinib exposure increased in the presence of RTV 4.27‐fold, suggesting that remibrutinib is not a sensitive CYP3A4 substrate. The rich PK dataset supported the building of a robust physiologically‐based pharmacokinetic (PBPK) model, which well‐described the therapeutic dose range of 25–100 mg. Simulations of untested scenarios revealed an absence of drug‐drug interaction (DDI) risk between remibrutinib and the weak CYP3A4 inhibitor fluvoxamine (area under the concentration‐time curve ratio [AUCR] <1.25), and a moderate effect with the CYP3A4 inhibitor erythromycin (AUCR: 2.71). Predictions with the moderate and strong CYP3A4 inducers efavirenz and rifampicin, suggested a distinct remibrutinib exposure decrease of 64% and 89%. Oral bioavailability of remibrutinib was 34%. The inclusion of an intravenous microtracer allowed the determination of all relevant remibrutinib PK parameters, which facilitated construction of the PBPK model. This will provide guidance on the selection or restriction of comedications and prediction of DDI risks.

Clinical Investigation of Metabolic and Renal Clearance Pathways Contributing to the Elimination of Fevipiprant Using Probenecid as Perpetrator

Fevipiprant, an oral, nonsteroidal, highly selective, reversible, and competitive prostaglandin D₂ receptor 2 antagonist, is eliminated by glucuronidation and by direct renal excretion predominantly via organic anion transporter (OAT) 3. This study aimed to assess the effect of simultaneous UDP-glucuronosyltransferase (UGT) and OAT3 inhibition by probenecid on the pharmacokinetics of fevipiprant and its acyl glucuronide (AG) metabolite to support the dosing recommendation of fevipiprant in the presence of drugs inhibiting these pathways; however, phase III clinical trial results did not support its submission. This was a single-center, open-label, single-sequence, two-period crossover study in healthy subjects. Liquid chromatography with tandem mass spectrometry was used to measure concentrations of fevipiprant and its AG metabolite in plasma and urine. In the presence of probenecid, the mean maximum concentrations of fevipiprant increased approximately 1.7-fold, and the area under the concentration-time curve in plasma increased approximately 2.5-fold, whereas the mean apparent volume of distribution and the AG metabolite:fevipiprant ratio decreased. The apparent systemic clearance decreased by approximately 60% and the renal clearance decreased by approximately 88% in the presence of probenecid. Using these data and those from previous studies, the relative contribution of OAT and UGT inhibition to the overall effect of probenecid was estimated. Furthermore, a general disposition scheme for fevipiprant was developed, showing how a perpetrator drug such as probenecid, which interferes with two key elimination pathways of fevipiprant, causes only a moderate increase in exposure and allows estimation of the drug-drug inhibition when only one of the two pathways is inhibited. SIGNIFICANCE STATEMENT: In this drug-drug interaction (DDI) study, probenecid was used as a tool to inhibit both glucuronidation and active renal secretion of fevipiprant. The combination of plasma and urine pharmacokinetic data from this study with available data allowed the development of a quantitative scheme to describe the fate of fevipiprant in the body, illustrating why the DDI effect on fevipiprant is weak-to-moderate even if a perpetrator drug inhibits several elimination pathways.

Predicting Oral Absorption for Compounds Outside the Rule of Five Property Space

The estimation of the extent of absorption of drug candidates intended for oral drug delivery is an important selection criteria in drug discovery. The use of cell-based transwell assays examining flux across cell-monolayers (e.g., Caco-2 or MDCK cells) usually provide satisfactory predictions of the extent of absorption in vivo. These predictions often fall short of expection for molecules outside the traditional low molecular weight property space. In this manuscript the transwell permeability assay was modified to circumvent potential issues that can be encountered when evaluating the aforementioned drug molecules. Particularly, the addition of albumin in the acceptor compartment to reduce potential binding to cells and the acceptor compartment, improved the predictive power of the assay. Cellular binding and lysosomal trapping effects are significantly reduced for larger molecules, particularly lipophilic bases under these more physiological conditions, resulting in higher recovery values and a better prediction power. The data indicate that lysosomal trapping does not impact the rate of absorption of lipophilic bases in general but is rather an exception. Finally, compounds believed to permeate by passive mechanisms were used in a calibration curve for the effective prediction of the fraction absorbed of molecules of interest in current medicinal chemistry efforts.

Fevipiprant has a low risk of influencing co-medication pharmacokinetics: Impact on simvastatin and rosuvastatin in different SLCO1B1 genotypes

Fevipiprant, a prostaglandin D₂ receptor 2 antagonist, is in clinical development as a treatment for asthma. The goal of this study was to assess the potential of fevipiprant to cause drug-drug interactions (DDI) as a perpetrator, that is, by altering the pharmacokinetics (PK) of co-medications. In vitro drug interaction studies of clinically relevant drug metabolizing enzymes and transporters were conducted for fevipiprant and its acyl glucuronide (AG) metabolite. Comparison of K_i values with unbound systemic or portal vein steady-state plasma exposure of fevipiprant and its AG metabolite revealed the potential for inhibition of organic anion transporting polypeptide 1B1 (OATP1B1) transporters (R-value of 5.99), while other targets including cytochrome P450 enzymes were not, or only marginally, inhibited. Consequently, an open-label, two-part, two-period, single-sequence clinical study assessed the effect of fevipiprant 450 mg QD on the pharmacokinetics of simvastatin 20 mg and rosuvastatin 20 mg, two statins with different dependency in OATP1B1-mediated hepatic uptake, in healthy adult volunteers. The study also assessed the pharmacogenetics of the SLCO1B1 gene, which encodes OATP1B1. Clinically, fevipiprant 450 mg QD showed a low potential for interaction and increased the peak concentrations of simvastatin acid and rosuvastatin by 2.23- and 1.87-fold, respectively, with little or no impact on total exposure. Genotype analysis confirmed that SLCO1B1 genotype influences statin pharmacokinetics to a similar extent either with or without fevipiprant co-administration. In summary, fevipiprant at 450 mg QD has only minor liabilities as a perpetrator for DDI.

Examining P-gp efflux kinetics guided by the BDDCS - Rational selection of in vitro assay designs and mathematical models

The generation of reliable kinetic parameters to describe P-glycoprotein (P-gp) activity is essential for predicting the impact of efflux transport on gastrointestinal drug absorption. The compound-specific selection of in vitro assay designs and ensuing data analysis methods is explored in this manuscript. We measured transcellular permeability and cellular uptake of five P-gp substrates in Caco-2 and LLC-PK1 MDR1 cells. Kinetic parameters of P-gp-mediated efflux transport (K_m, V_max) were derived from conventional and mechanistic compartmental models. The estimated apparent K_m values based on medium concentrations in the conventional permeability model indicated significant differences between the cell lines. The respective intrinsic K_m values based on unbound intracellular concentrations in the mechanistic compartmental models were significantly lower and comparable between cell lines and assay formats. Non-specific binding or lysosomal trapping were shown to cause discrepancies in the kinetic parameters obtained from different assay formats. A guidance for the selection of in vitro assays and kinetic assessment methods is proposed in line with the Biopharmaceutics Drug Disposition Classification System (BDDCS). The recommendations are expected to aid the acquisition of robust and reproducible kinetic parameters of P-gp-mediated efflux transport.

'VIOLET': a fluorescence-based simulation exercise for training healthcare workers in the use of personal protective equipment

Background

Healthcare workers caring for patients with high-consequence infectious diseases (HCIDs) require protection from pathogen exposure, for example by wearing personal protective equipment (PPE). Protection is acquired through the inherent safety of the PPE components, but also their safe and correct use, supported by adequate training and user familiarity. However, the evidence base for HCID PPE ensembles and any associated training is lacking, with subsequent variation between healthcare providers.

Aim

To develop an evidence-based assessment and training tool for evaluating PPE ensembles and doffing protocols, in the assessment of patients with suspected HCIDs.

Methods

VIOLET (Visualising Infection with Optimised Light for Education and Training) comprises a healthcare mannequin adapted to deliver simulated bodily fluids containing UV-fluorescent tracers. On demand and remotely operated, the mannequin projectile vomits (blue), coughs (red), has diarrhoea (yellow) and is covered in sweat (orange). Wearing PPE, healthcare staff participate in an HCID risk assessment and examination of the ‘patient’, thereby becoming exposed to these bodily fluids. Contamination of PPE is visualized and body-mapped under UV light before and after removal. Observational findings and participant feedback, around its use as a training exercise, is also recorded.

Findings

Significant contamination from different exposure events was seen, enabling evaluation of PPE and doffing procedures used. Observational data and participant feedback demonstrated its strengths and success as a training technique.

Conclusion

Simulation exercises using VIOLET provide evidence-based assessment of PPE ensembles, and are a valuable resource for training of healthcare staff in wearing and safe doffing of PPE.

Use of ultraviolet-fluorescence-based simulation in evaluation of personal protective equipment worn for first assessment and care of a patient with suspected high-consequence infectious disease

BACKGROUND

Variations currently exist across the UK in the choice of personal protective equipment (PPE) used by healthcare workers when caring for patients with suspected high-consequence infectious diseases (HCIDs).

AIM

To test the protection afforded to healthcare workers by current PPE ensembles during assessment of a suspected HCID case, and to provide an evidence base to justify proposal of a unified PPE ensemble for healthcare workers across the UK.

METHODS

One 'basic level' (enhanced precautions) PPE ensemble and five 'suspected case' PPE ensembles were evaluated in volunteer trials using 'Violet'; an ultraviolet-fluorescence-based simulation exercise to visualize exposure/contamination events. Contamination was photographed and mapped.

FINDINGS

There were 147 post-simulation and 31 post-doffing contamination events, from a maximum of 980, when evaluating the basic level of PPE. Therefore, this PPE ensemble did not afford adequate protection, primarily due to direct contamination of exposed areas of the skin. For the five suspected case ensembles, 1584 post-simulation contamination events were recorded, from a maximum of 5110. Twelve post-doffing contamination events were also observed (face, two events; neck, one event; forearm, one event; lower legs, eight events).

CONCLUSION

All suspected case PPE ensembles either had post-doffing contamination events or other significant disadvantages to their use. This identified the need to design a unified PPE ensemble and doffing procedure, incorporating the most protective PPE considered for each body area. This work has been presented to, and reviewed by, key stakeholders to decide on a proposed unified ensemble, subject to further evaluation.

Application of the extended clearance concept classification system (ECCCS) to predict the victim drug-drug interaction potential of statins

BACKGROUND

During drug development, it is an important safety factor to identify the potential of new molecular entities to become a victim of drug-drug interactions (DDIs). In preclinical development, however, anticipation of clinical DDIs remains challenging due to the lack of in vivo human pharmacokinetic data.

METHODS

We applied a recently developed in vitro-in vivo extrapolation method, including hepatic metabolism and transport processes, herein referred to as the Extended Clearance Concept Classification System (ECCCS). The human hepatic clearances and the victim DDI potentials were predicted for atorvastatin, cerivastatin, fluvastatin, lovastatin acid, pitavastatin, pravastatin, rosuvastatin, and simvastatin acid.

RESULTS

Hepatic statin clearances were well-predicted by the ECCCS with six out of eight clearances projected within a two-fold deviation to reported values. In addition, worst-case DDI predictions were projected for each statin. Based on the ECCCS class assignment (4 classes), the mechanistic interplay of metabolic and transport processes, resulting in different DDI risks, was well-reflected by our model. Furthermore, predictions of clinically observed statins DDIs in combination with relevant perpetrator drugs showed good quantitative correlations with clinical observations.

CONCLUSIONS

The ECCCS represents a powerful tool to anticipate the DDI potential of victim drugs based on in vitro drug metabolism and transport data.

Prediction of organic anion-transporting polypeptide 1B1- and 1B3-mediated hepatic uptake of statins based on transporter protein expression and activity data

Organic anion-transporting polypeptides (OATP) 1B1 and OATP1B3 are drug transporters mediating the active hepatic uptake of their substrates. Because they exhibit overlapping substrate specificities, the contribution of each isoform to the net hepatic uptake needs to be considered when predicting drug-drug interactions. The relative contribution of OATP1B1- and OATP1B3-mediated uptake of statins into hepatocytes was estimated based on either relative transporter protein expression data or relative activity data. Therefore, kinetics of eight statins and OATP1B1- and OATP1B3-specific reference substrates was determined in OATP1B1- and OATP1B3-expressing human embryonic kidney 293 cells and in human cryopreserved hepatocytes. Absolute OATP1B1 and OATP1B3 protein abundance was determined by liquid chromatography-tandem mass spectrometry in all expression systems. Transporter activity data generated in recombinant cell lines were extrapolated to hepatocyte values using relative transporter expression factors (REF) or relative activity factors (RAF). Our results showed a pronounced OATP1B1 and comparatively low OATP1B3 protein expression in the investigated hepatocyte lot. Based on REF scaling, we demonstrated that the active hepatic uptake clearances of reference substrates, atorvastatin, pravastatin, rosuvastatin, and simvastatin were well predicted within twofold error, demonstrating that OATP1B1 and OATP1B3 were major contributors. For other statins, the net hepatic uptake clearance was underpredicted, suggesting the involvement of other hepatic uptake transporters. Summarized, we showed that REF- and RAF-based predictions were highly similar, indicating a direct transporter expression-activity relationship. Moreover, we demonstrated that the REF-scaling method provided a powerful tool to quantitatively assess the transporter-specific contributions to the net uptake clearance of statins in hepatocytes.

In vitro-in vivo extrapolation method to predict human renal clearance of drugs

Renal clearance is a key determinant of the elimination of drugs. To date, only few in vitro-in vivo extrapolation (IVIVE) approaches have been described to predict the renal organ clearance as the net result of glomerular filtration, tubular secretion, and tubular reabsorption. In this study, we measured in LLC-PK1 cells the transport of 20 compounds that cover all four classes of the Biopharmaceutical Drug Disposition System. These data were incorporated into a novel kidney model to predict all renal clearance processes in human. We showed that filtration and secretion were main contributors to the renal organ clearance for all compounds, whereas reabsorption was predominant for compounds assigned to classes 1 and 2. Our results suggest that anionic drugs were not significantly secreted in LLC-PK1 cells, resulting in under-predicted clearances. When all study compounds were included a high overall correlation between the reported and predicted renal organ clearances was obtained (R² = 0.83). The prediction accuracy in terms of percentage within twofold and threefold error was 70% and 95%, respectively. In conclusion, our novel IVIVE method allowed to predict the human renal organ clearance and the contribution of each underlying process.

Brain accumulation of sunitinib is restricted by P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) and can be enhanced by oral elacridar and sunitinib coadministration

Sunitinib is an orally active, multitargeted tyrosine kinase inhibitor which has been used for the treatment of metastatic renal cell carcinoma and imatinib-resistant gastrointestinal stromal tumors. We aimed to investigate the in vivo roles of the ATP-binding cassette drug efflux transporters ABCB1 and ABCG2 in plasma pharmacokinetics and brain accumulation of oral sunitinib, and the feasibility of improving sunitinib kinetics using oral coadministration of the dual ABCB1/ABCG2 inhibitor elacridar. We used in vitro transport assays and Abcb1a/1b(-/-) , Abcg2(-/-) and Abcb1a/1b/Abcg2(-/-) mice to study the roles of ABCB1 and ABCG2 in sunitinib disposition. In vitro, sunitinib was a good substrate of murine (mu)ABCG2 and a moderate substrate of human (hu)ABCB1 and huABCG2. In vivo, the systemic exposure of sunitinib after oral dosing (10 mg kg(-1) ) was unchanged when muABCB1 and/or muABCG2 were absent. Brain accumulation of sunitinib was markedly (23-fold) increased in Abcb1a/b/Abcg2(-/-) mice, but only slightly (2.3-fold) in Abcb1a/b(-/-) mice, and not in Abcg2(-/-) mice. Importantly, a clinically realistic coadministration of oral elacridar and oral sunitinib to wild-type mice resulted in markedly increased sunitinib brain accumulation, equaling levels in Abcb1a/1b/Abcg2(-/-) mice. This indicates complete inhibition of the blood-brain barrier (BBB) transporters. High-dose intravenous sunitinib could saturate BBB muABCG2, but not muABCB1A, illustrating a dose-dependent relative impact of the BBB transporters. Brain accumulation of sunitinib is effectively restricted by both muABCB1 and muABCG2 activity. Complete inhibition of both transporters, leading to markedly increased brain accumulation of sunitinib, is feasible and safe with a clinically realistic oral elacridar/sunitinib coadministration.

Double-transduced MDCKII cells to study human P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) interplay in drug transport across the blood-brain barrier

P-glycoprotein (P-gp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) combination knockout mice display disproportionately increased brain penetration of shared substrates, including topotecan and several tyrosine kinase inhibitors, compared to mice deficient for only one transporter. To better study the interplay of both transporters also in vitro, we generated a transduced polarized MDCKII cell line stably coexpressing substantial levels of human ABCB1 and ABCG2 (MDCKII-ABCB1/ABCG2). Next, we measured concentration-dependent transepithelial transport of topotecan, sorafenib and sunitinib. By blocking either one or both of the transporters simultaneously, using specific inhibitors, we aimed to mimic the ABCB1-ABCG2 interplay at the blood-brain barrier in wild-type, single or combination knockout mice. ABCB1 and ABCG2 contributed to similar extents to topotecan transport, which was only partly saturable. For sorafenib transport, ABCG2 was the major determinant at low concentrations. However, saturation of ABCG2-mediated transport occurred at higher sorafenib concentrations, where ABCB1 was still fully active. Furthermore, sunitinib was transported equally by ABCB1 and ABCG2 at low concentrations, but ABCG2-mediated transport became saturated at lower concentrations than ABCB1-mediated transport. The relative impact of these transporters can thus be affected by the applied drug concentrations. A comparison of the in vitro observed (inverse) transport ratios and cellular accumulation of the drugs at low concentrations with in vivo brain penetration data from corresponding Abcb1a/1b⁻/⁻, Abcg2⁻/⁻ and Abcb1a/1b;Abcg2⁻/⁻ mouse strains revealed very similar qualitative patterns for each of the tested drugs. MDCKII-ABCB1/ABCG2 cells thus present a useful in vitro model to study the interplay of ABCB1 and ABCG2.

Differential impact of P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) on axitinib brain accumulation and oral plasma pharmacokinetics

The second-generation tyrosine kinase inhibitor and anticancer drug axitinib is a potent, orally active inhibitor of the vascular endothelial growth factor receptors 1, 2, and 3. Axitinib has clinical activity against solid tumors such as metastatic renal cell carcinoma and advanced pancreatic cancer. We studied axitinib transport using Madin-Darby canine kidney II cells overexpressing human ABCB1 or ABCG2 or murine Abcg2. Axitinib was a good substrate of ABCB1 and Abcg2, whereas transport activity by ABCG2 was moderate. These transporters may therefore contribute to axitinib resistance in tumor cells. Upon oral administration of axitinib, Abcg2(-/-) and Abcb1a/1b;Abcg2(-/-) mice displayed 1.7- and 1.8-fold increased axitinib areas under the plasma concentration-time curve from 0 to 4 compared with those of wild-type mice. Plasma concentrations in Abcb1a/1b(-/-) mice were not significantly increased. In contrast, relative brain accumulation of axitinib in Abcb1a/1b(-/-) and Abcb1a/1b;Abcg2(-/-) mice was, respectively, 6.8- and 13.9-fold higher than that in wild-type mice at 1 h and 4.9- and 20.7-fold at 4 h after axitinib administration. In Abcg2(-/-) mice, we found no significant differences in brain accumulation compared with those in wild-type mice. Thus, Abcb1 strongly restricts axitinib brain accumulation and completely compensates for the loss of Abcg2 at the blood-brain barrier, whereas Abcg2 can only partially take over Abcb1-mediated axitinib efflux. Hence, Abcg2 has a stronger impact on axitinib oral plasma pharmacokinetics, whereas Abcb1 is the more important transporter at the blood-brain barrier. These findings illustrate that in vitro transport data for ABCB1 and ABCG2 cannot always be simply extrapolated to the prediction of the relative impact of these transporters on oral availability versus brain penetration.

Oral administration of glucagon-like peptide 1 or peptide YY 3-36 affects food intake in healthy male subjects

BACKGROUND

Peripheral infusion of glucagon-like peptide 1 (GLP-1) or peptide YY 3-36 (PYY3-36) reduces food intake in healthy, obese, and diabetic subjects. In vivo, both peptides are cosecreted from intestinal L cells; GLP-1 is subject to rapid breakdown by dipeptidyl peptidase IV, and together with PYY3-36 it is likely to be degraded in the liver before entering the systemic circulation. The largest concentrations are observed in the splanchnic blood rather than in the systemic circulation.

OBJECTIVE

In contrast with peripheral infusion, oral delivery of sodium N-[8-(2-hydroxybenzoyl) amino] caprylate (SNAC) mimics endogenous secretion. We aimed to investigate how this affects food intake.

DESIGN

Twelve healthy male subjects were studied in a randomized, double-blind, placebo-controlled, 4-way crossover trial. Each subject received in random order 2.0 mg GLP-1, 1.0 mg PYY3-36, or 2.0 mg GLP-1 plus 1.0 mg PYY3-36; the peptides were mixed with SNAC. The placebo treatment was the delivery agent alone. Food intake during an ad libitum test meal was measured.

RESULTS

Both peptides were rapidly absorbed from the gut, leading to plasma concentrations several times higher than those in response to a normal meal. GLP-1 alone, but not PYY3-36, reduced total energy intake significantly, with marked effects on glucose homeostasis. Coadministration of both peptides reduced total energy intake by 21.5% and fullness at meal onset (P < 0.05) but not total 24-h energy intake.

CONCLUSION

The results show a marked effect of orally administered GLP-1 and PYY3-36 on appetite by showing enhanced fullness at meal onset and reduced energy intake. This trial was registered at clinicaltrials.gov as NCT00822705.

Orally administered glucagon-like peptide-1 affects glucose homeostasis following an oral glucose tolerance test in healthy male subjects

Glucagon-like peptide-1 (GLP-1) exerts several effects on glucose homeostasis and reduces food intake. After its release from intestinal L cells, GLP-1 is subject to (i) rapid breakdown by dipeptidyl peptidase IV and (ii) high liver extraction. The highest concentrations of GLP-1 are found in the splanchnic blood rather than in the systemic circulation. An oral delivery system would mimic endogenous secretion. Here we investigated the pharmacokinetic/pharmacodynamic (PK/PD) effects of a single dose (2 mg) of oral GLP-1 administered prior to an oral glucose tolerance test (OGTT) in 16 healthy males. GLP-1 was rapidly absorbed from the gut, leading to tenfold higher plasma concentrations compared with controls. The PD profile was consistent with reported pharmacology; GLP-1 significantly stimulated basal insulin release (P < 0.027), with marked effects on glucose levels. The postprandial glucose peak was delayed with GLP-1, suggesting an effect on gastric emptying.

Regulation of BCRP (ABCG2) and P-glycoprotein (ABCB1) by cytokines in a model of the human blood-brain barrier

Brain capillary endothelial cells form the blood-brain barrier (BBB), a highly selective permeability membrane between the blood and the brain. Besides tight junctions that prevent small hydrophilic compounds from passive diffusion into the brain tissue, the endothelial cells express different families of drug efflux transport proteins that limit the amount of substances penetrating the brain. Two prominent efflux transporters are the breast cancer resistance protein and P-glycoprotein (P-gp). During inflammatory reactions, which can be associated with an altered BBB, pro-inflammatory cytokines are present in the systemic circulation. We, therefore, investigated the effect of the pro-inflammatory cytokines interleukin-1beta (IL-1beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) on the expression and activity of BCRP and P-gp in the human hCMEC/D3 cell line. BCRP mRNA levels were significantly reduced by IL-1beta, IL-6 and TNF-alpha. The strongest BCRP suppression at the protein level was observed after IL-1beta treatment. IL-1beta, IL-6 and TNF-alpha also significantly reduced the BCRP activity as assessed by mitoxantrone uptake experiments. P-gp mRNA levels were slightly reduced by IL-6, but significantly increased after TNF-alpha treatment. TNF-alpha also increased protein expression of P-gp but the uptake of the P-gp substrate rhodamine 123 was not affected by any of the cytokines. This in vitro study indicates that expression levels and activity of BCRP, and P-gp at the BBB may be altered by acute inflammation, possibly affecting the penetration of their substrates into the brain.

The human brain endothelial cell line hCMEC/D3 as a human blood-brain barrier model for drug transport studies

The human brain endothelial capillary cell line hCMEC/D3 has been developed recently as a model for the human blood-brain barrier. In this study a further characterization of this model was performed with special emphasis on permeability properties and active drug transport. Para- or transcellular permeabilities (P(e)) of inulin (0.74 x 10(-3) cm/min), sucrose (1.60 x 10(-3) cm/min), lucifer yellow (1.33 x 10(-3) cm/min), morphine (5.36 x 10(-3) cm/min), propranolol (4.49 x 10(-3) cm/min) and midazolam (5.13 x 10(-3) cm/min) were measured. By addition of human serum the passive permeability of sucrose could be reduced significantly by up to 39%. Furthermore, the expression of a variety of drug transporters (ABCB1, ABCG2, ABCC1-5) as well as the human transferrin receptor was demonstrated on the mRNA level. ABCB1, ABCG2 and transferrin receptor proteins were detected and functional activity of ABCB1, ABCG2 and the ABCC family was quantified in efflux experiments. Furthermore, ABCB1-mediated bidirectional transport of rhodamine 123 was studied. The transport rate from the apical to the basolateral compartment was significantly lower than that in the inverse direction, indicating directed p-glycoprotein transport. The results of this study demonstrate the usefulness of the hCMEC/D3 cell line as an in vitro model to study drug transport at the level of the human blood-brain barrier.

Hypericum perforatum: which constituents may induce intestinal MDR1 and CYP3A4 mRNA expression?

In vitro and in vivo studies suggest that extracts of St John's wort (Hypericum perforatum, L .; SJWE) interact with various drugs, by enhancing their elimination, due to induction of intestinal and hepatic cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (P-gp), the gene product of multidrug resistance gene 1 (MDR1/ABCB1). The aim of our study was to identify the major constituents responsible for this induction and their relative importance. Therefore, plant extracts were investigated that vary in these constituents with respect to their effect on mRNA expression of MDR1/CYP3A4. First, different pure constituents of Hypericum perforatum L . were investigated. Secondly, diverse SJWE with different concentrations of hyperforin, quercitrin and hypericin were investigated. The concentrations of hyperforin, hypericin, and quercitrin in the plant extracts were determined by HPLC, and an "artificial extract" containing the same mixture of these constituents was investigated. Different plant extracts, pure constituents or "artificial extracts" were applied to the human colon carcinoma-derived cell line (LS180) and the induction of MDR1 and CYP3A4 expression was analyzed by quantitative RT-PCR. MDR1 and CYP3A4 mRNA expression were both induced by single constituents of SJW such as hypericin and hyperforin in a concentration of 10 microM. Additionally, CYP3A4 mRNA expression was induced by quercitrin. SJW extracts containing hyperforin induced significantly MDR1 mRNA expression, whereas no CYP3A4 induction was observed after treatment with any of the investigated SJWE. These effects could be mimicked by "artificial extracts" containing the same compositions of hyperforin, hypericin and quercitrin as the plant extracts.