Liver Transporter Assessment via DCE-MRI

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Liver Transporter Assessment via DCE-MRI in Preclinical and Clinical Settings (Conference Abstract)

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Liver Transporter Assessment via DCE-MRI

Liver Transporter Assessment via DCE-MRI in Preclinical and Clinical Settings - PRO 03-02

by Eve S. Shalom on behalf of the TRISTAN Consortium


EMIM 2024

Abstract

Improvement in the non-invasive assessment of hepatocellular function is needed for risk assessment of Drug-Drug Interactions (DDIs) and detection of Drug Induced Liver Injury (DILI) [1]. Many DDIs arise due to perpetrator drugs causing inhibition or induction of hepatic uptake or excretion of victim drugs, which can impact on their efficacy and toxicity. DILI can be caused by inhibited biliary excretion of a victim drug due to harmful accumulation within hepatocytes.

Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) with Gadoxetate offers a potential avenue to probe risk assessment for DDIs and DILI [2], as Gadoxetate is a substrate for several hepatic transporters. TRISTAN Work Package 2 (WP2) focuses on the development of a standardised Gadoxetate DCE-MRI “biomarker” [3] including multi-centre phantom and animal studies to determine translatability of findings to humans.

Recent preclinical work from TRISTAN WP2 has focused on the assessment of sensitivity and reproducibility in identification of hepatocellular uptake and biliary excretion rates across multiple sites and field strengths, to deduce key points of variability. Rat subjects were assessed for the proposed biomarkers with and without six known liver inhibitors with the resulting values assessed. Issues in reproducibility were reported with significant differences between substudies for hepatocellular uptake and biliary excretion rates. However, hepatocellular uptake and biliary excretion rates were found to be above such detection limits for potent liver inhibitor drugs.

Within clinical settings, a study with healthy volunteers has been carried out by TRISTAN WP2 to assess sensitivity of the methodology with the effect of Rifampicin, a known liver inhibitor [4], on the derived hepatocellular biomarker values. The volunteers had DCE-MRI scans consisting of two investigations: (1) a baseline visit and (2) a follow up visit with Rifampicin administered prior scanning. The method reported a measurable and statistically significant reduction of both hepatocellular uptake and biliary excretion rates when Rifampicin was administered.

Both the preclinical and clinical work carried out in WP2 aim to contribute to evidence showing the potential benefit of biomarkers for hepatocyte uptake and biliary efflux for the risk assessment of DILI and DDI in both preclinical and clinical settings. This talk will cover details of these investigations which were undertaken as part of TRISTAN WP2 activities.

Liver Transporter Assessment via DCE-MRI
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Imaging of Harm

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Imaging of harm: why we need translational imaging biomarkers in drug safety safety assessment (Conference Abstract)

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Imaging of Harm

Imaging of harm: why we need translational imaging biomarkers in drug safety safety assessment - PRO 03-01

by John W. Waterton on behalf of the TRISTAN Consortium


EMIM 2024

Abstract

Imaging metrics ("biomarkers"[1]) have a prominent role in predicting and detecting treatment benefit, for example as pharmacodynamic biomarkers or as companion diagnostics. However, all treatments involve risk of harm as well as possible benefit, so imaging biomarkers of harm or risk of harm (so-called "safety" biomarkers) are of equal or greater value than imaging biomarkers of treatment efficacy.
Imaging biomarkers of safety can be used in several ways. In toxicology studies in animals they can identify toxicity, determine therapeutic margin, or evaluate reversibility. In human trials, they can be used to halt dose escalation before overt toxicity, to characterise rare adverse events, or to evaluate reversibility. More generally, imaging biomarkers of safety can be used to monitor patients at risk of harm, so that treatment can be adjusted, or to deny particular treatments to patient at risk of harm from that treatment.
The development, validation and deployment of such biomarkers poses unique challenges. While efficacy biomarkers can easily be investigated in patients who elect to receive beneficial therapies, it is often ethically difficult or impossible to deliberately expose human subjects to harmful therapies. Moreover, to prepare for the case of rare and sporadic adverse events, the biomarker needs to be reproducibly available in any hospital in the world where the biomarker might be needed.
Imaging biomarkers of safety are particularly prominent in oncology, in Alzheimer's research, in neurology and rheumatology[2]. This work[3] aims to discover and develop imaging safety biomarkers addressing: harmful changes in liver transporter fluxes, maldistribution (with potentially harmful consequences) of biologic therapies, and drug-induced interstitial lung disease.

Imaging of Harm
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Assessing BSEP by 18F-FCA in rats

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Formulation effects of Bile Salt Export Pump inhibitor Bosentan and its in vivo PET Imaging assessment using 18F-3β-Fluoro cholic acid (18F-FCA) in male rats (Conference Abstract)

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Assessing BSEP by 18F-FCA in rats

Formulation effects of Bile Salt Export Pump inhibitor Bosentan and its in vivo PET Imaging assessment using 18F-3β-Fluoro cholic acid (18F-FCA) in male rats

by Bhasker Radaram, Tinamarie Skedzielewski, Stephen Lenhard, Tolulope Aweda, Shih-Hsun Cheng, Glenn Moran, Andrew Gehman, Simon Campbell, Hasan Alsaid on behalf of the TRISTAN Consortium


WMIC 2023

 

Abstract

Introduction: Bile acids are amphiphilic steroid derivatives produced by hepatocytes that play a key role in digestion of lipids and uptake of fat-soluble vitamins. Bile Salt Export Pump (BSEP) is an efflux transporter that plays a critical role in the secretion of bile salts into the bile. In many species such as humans and rodents, cholic acid is the largest key constituent of the bile acid spectrum. Inhibition of BSEP function by drugs such as Bosentan has resulted in the buildup of bile salts in the liver and lead to drug-induced liver injury (DILI). Formulation of drugs in DMSO (Dimethyl Sulfoxide) poses a safety risk in rodents . To better mitigate the formulation challenges for animal safety, herein, we report the formulation effects of Bosentan in PEG400 and assessed by 18F-3β-Fluorocholic acid (18F-3β-FCA) to examine hepatobiliary transport in vivo in the presence and absence of BSEP inhibitor Bosentan.

Methods: All animal procedures complied with the guidelines of the Institutional Animal Care and Use Committee at GSK following the guidance of Animal Use. 18F-3β-FluoroCholic Acid (18F-FCA) was produced as per literature procedure  using an automated ELIXYS Box (Sofie Biosciences, Inc). Wistar (Han) IGS white (albino) outbred male rats (strain 273), 6-11 weeks old with the body weights of 250-410 g were randomized in control (no treatment) and Bosentan treated groups. All animals were fasted for at least 4 hrs before PET imaging to reduce tracer metabolic variability. Rats in the Bosentan treated group (n=4) received 50 mg/Kg Bosentan in PEG400 (iv slow bolus infusion (0.2 mL/min) 1 hr prior to PET imaging. Dynamic PET imaging was acquired using the Mediso LFER150 PET scanner for 1 hr starting with iv injection of 18F-3β-FCA (400 µCi per rat in 200 µL 8% EtOH/PBS). At the end of the PET data acquisition, blood samples were collected for total bile salt analysis. Statistical analysis was performed using two sample t-test with equal variances.

Results: 18F-FCA radiosynthesis was achieved with radiochemical yields (RCY) of 6.64±0.64% (d.c) (n=9) with high radiochemical purity (>99%). Formulation of Bosentan in PEG400 was tolerated in all animals with no sign of pain or distress. However, the Bosentan treated group did not show any inhibition (mean 18F-FCA uptake) compared to the control group (figure 1a) and effluxed to the gallbladder and intestines. The total bile salt analysis  was two folds greater in the Bosentan treated group compared to the control group although this difference was not statistically significant.

Conclusions: In summary, Bosentan in the PEG400 formulation improved the tolerability and animal safety compared to the 100% DMSO formulation. However, it did not show a BSEP inhibition compared to the previously published Bosentan formulation in 100% DMSO.

 

Assessing BSEP by 18F-FCA in rats
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Qualified imaging biomarkers

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Towards a qualified imaging biomarker of liver transporter function (Conference Presentation)

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Qualified imaging biomarkers

Towards a qualified imaging biomarker of liver transporter function

by John C Waterton on behalf of the TRISTAN Consortium


EMIM 2023

Abstract

Drugs and other xenobiotics are commonly eliminated via the liver. Uptake by the hepatocyte, and subsequent efflux, involves several transporters with different specificities. If a drug's  uptake is perturbed, a drug may be cleared less (or more) rapidly from the blood, leading to harmful overdosing or alternatively lack of efficacy.  Where one drug inhibits or enhances the uptake flux of a second drug, this is called a Drug-Drug Interaction (DDI).  DDIs can complicate the safe prescribing of medicines to patients who require different drugs which are substrates for the same transporter.  If its efflux is inhibited, harmful levels of drug may accumulate in the hepatocyte leading to drug-induced liver injury (DILI).

While hepatocyte uptake and efflux kinetics cannot be unambiguously determined from blood levels, imaging biomarkers from nuclear medicine or MR can provide more specificity (1).  Gadoxetate, a MR contrast agent with regulatory approval in most jurisdictions, has previously proved useful in this context.

Drug developers and regulatory authorities are very unlikely to rely on such imaging biomarkers unless they trust the acquisition, analysis and interpretation.  In particular they must be highly confident that an apparently negative finding ("drug does not perturb liver transporter fluxes") is a true indication of the drug's safety, and not an artefact of quirks in the methodology or irreproducibility between centres.  To address this, FDA established its biomarker qualification program (BQP) to provide confidence in the biomarker data in a specific context of use. Of note, of the 58 biomarkers listed in the qualification programme, a high proportion (31%) are imaging biomarkers and an equally high proportion (31%) are safety biomarkers, suggesting the importance of this route for imaging biomarkers of safety (i.e. lack-of-harm).

 

Qualified imaging biomarkers
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Assess Drug-induced inhibition of liver function

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Measurement of drug-induced inhibition of liver function with dynamic gadoxetate-enhanced MRI: a validation study in healthy volunteers  (Conference Abstract)

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Assess Drug-induced inhibition of liver function

Measurement of drug-induced inhibition of liver function with dynamic gadoxetate-enhanced MRI: a validation study in healthy volunteers 

by Thazin Min, Marta Tibiletti, Paul Hockings, Alexandra Galetin, Ebony Gunwhy, Gerry Kenna, Nicola Melillo, Geoff Parker, Gunnar Schuetz, Daniel Scotcher, John Waterton, Ian Rowe, Steven Sourbron on behalf of the TRISTAN Consortium


ISMRM 2024

 

Abstract

 

Numerous clinically relevant drug-drug interactions (DDIs) arise via inhibition or induction of hepatic uptake or excretion of victim drugs, which may impact on their efficacy and toxicity. DDIs are assessed during drug development by a combination of in-vitro and in-silico methods, but predictions are difficult to verify clinically – especially when DDIs arise via inhibition of the liver’s excretory function. Consequently, clinical trials risk either underestimating DDIs, and so potentially harming study subjects, or overestimating DDI’s and consequently failing to show efficacy.

This reveals a critical need for noninvasive methods which may be used to determine drug exposure within the tissue of interest in vivo. Preclinical studies in rats have shown that drug-induced inhibition of liver uptake and excretion can be measured with dynamic gadoxetate-enhanced MRI [1]. The aim of this study was to verify whether this finding translates to humans, by measuring the change in liver gadoxetate uptake and excretion after administration of rifampicin, a known inhibitor drug.

 

Assess Drug-induced inhibition of liver function
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AIF for tracer kinetic modelling

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Arterial input function selection for tracer kinetic modelling in rat liver: individual-, population-, or model-derived? (Conference Abstract)

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AIF for tracer kinetic modelling

Arterial input function selection for tracer kinetic modelling in rat liver: individual-, population-, or model-derived?

by Ebony R. Gunwhy, Steven Sourbron, Sirisha Tadimalla, Catherine D. G. Hines, Claudia Green, Iina Laitinen, Paul D. Hockings, Gunnar Schütz, John C. Waterton, Gerry Kenna on behalf of the TRISTAN Consortium


ISMRM 2023

 

Abstract

In normal hepatic function, toxins are absorbed and consequently excreted by the liver. As a liver-specific contrast agent which is actively taken up by the hepatocytes of the liver, gadoxetate dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) combined with tracer-kinetic (TK) modelling has the potential to be a useful tool for assessing hepatic transporter-mediated drug injury in animals and humans in vivo. However, in small animal studies, the ratio of main vessel diameter to scanning resolution is small, making it difficult to reliably measure the plasma arterial input function (AIF), cp(t). Signal data acquired from spleen ROIs are therefore typically used as a substitute, though these can also be unreliable. The aim of this study was to investigate the accuracy of modelling gadoxetate signals in rat liver when using signal data acquired from individual spleen ROIs as AIF and compare this with two alternatives, i.e., using 1) pooled spleen data as AIF, and 2) a standardised AIF derived from a simplified, two-compartment model of the rat circulation (hereafter referred to as the fixed model AIF).

 

AIF for tracer kinetic modelling
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Comparison of Gadoxetate DCE-MRI models

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Repeatability of hepatocellular uptake and efflux in the rat liver: A comparison of Gadoxetate DCE-MRI models (Conference Abstract)

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Comparison of Gadoxetate DCE-MRI models

Repeatability of hepatocellular uptake and efflux in the rat liver: A comparison of Gadoxetate DCE-MRI models 

by Sirisha Tadimalla, Claudia Green, Denise Steinmann, Sascha Koehler, Hans-Paul Juretschke, Iina Laitinen, John C. Watertone, Paul D. Hockingsg, Catherine D. Hines, Gunnar Schütz, Steven Sourbron on behalf of the TRISTAN Consortium


ISMRM 2019

Conference Abstract

 

Comparison of Gadoxetate DCE-MRI models
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Gadoxetate DCE-MRI liver models

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A classification of Gadoxetate DCE-MRI liver models (Conference Abstract)

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Gadoxetate DCE-MRI liver models

A classification of Gadoxetate DCE-MRI liver models

by Sirisha Tadimalla and Steven Sourbron 


ISMRM 2019

Conference Abstract

 

Gadoxetate DCE-MRI liver models
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PBPK Modelling to Predict Hepatic Transporter Mediated DDI

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Use of In Vivo Imaging and Physiologically-Based Kinetic Modelling to Predict Hepatic Transporter Mediated Drug–Drug Interactions in Rats

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PBPK Modelling to Predict Hepatic Transporter Mediated DDI

Use of In Vivo Imaging and Physiologically-Based Kinetic Modelling to Predict Hepatic Transporter Mediated Drug–Drug Interactions in Rats

by Nicola Melillo, Daniel Scotcher, J. Gerry Kenna, Claudia Green, Catherine D. G. Hines, Iina Laitinen, Paul D. Hockings, Kayode Ogungbenro, Ebony R. Gunwhy, Steven Sourbron, John C. Waterton, Gunnar Schuetz and Aleksandra Galetin on behalf of the TRISTAN Consortium


Pharmaceutics 15, Nr. 3 (10. März 2023): 896. doi: 10.3390/pharmaceutics15030896

Abstract

Gadoxetate, a magnetic resonance imaging (MRI) contrast agent, is a substrate of organic-anion-transporting polypeptide 1B1 and multidrug resistance-associated protein 2. Six drugs, with varying degrees of transporter inhibition, were used to assess gadoxetate dynamic contrast enhanced MRI biomarkers for transporter inhibition in rats. Prospective prediction of changes in gadoxetate systemic and liver AUC (AUCR), resulting from transporter modulation, were performed by physiologically-based pharmacokinetic (PBPK) modelling. A tracer-kinetic model was used to estimate rate constants for hepatic uptake (khe), and biliary excretion (kbh). The observed median fold-decreases in gadoxetate liver AUC were 3.8- and 1.5-fold for ciclosporin and rifampicin, respectively. Ketoconazole unexpectedly decreased systemic and liver gadoxetate AUCs; the remaining drugs investigated (asunaprevir, bosentan, and pioglitazone) caused marginal changes. Ciclosporin decreased gadoxetate khe and kbh by 3.78 and 0.09 mL/min/mL, while decreases for rifampicin were 7.20 and 0.07 mL/min/mL, respectively. The relative decrease in khe (e.g., 96% for ciclosporin) was similar to PBPK-predicted inhibition of uptake (97–98%). PBPK modelling correctly predicted changes in gadoxetate systemic AUCR, whereas underprediction of decreases in liver AUCs was evident. The current study illustrates the modelling framework and integration of liver imaging data, PBPK, and tracer-kinetic models for prospective quantification of hepatic transporter-mediated DDI in humans.

PBPK Modelling to Predict Hepatic Transporter Mediated DDI
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Assessing Hepatic Transporter Function in Rats

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Assessment of Hepatic Transporter Function in Rats Using Dynamic Gadoxetate-Enhanced MRI: A Reproducibility Study

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Assessing of Hepatic Transporter Function in Rats

Assessment of Hepatic Transporter Function in Rats Using Dynamic Gadoxetate-Enhanced MRI: A Reproducibility Study

by Gunwhy, Ebony R., Catherine D. G. Hines, Claudia Green, Iina Laitinen, Sirisha Tadimalla, Paul D. Hockings, Gunnar Schütz, J. Gerry Kenna, Steven Sourbron, und John C. Waterton on behalf of the TRISTAN Consortium


Magnetic Resonance Materials in Physics, Biology and Medicine 37, Nr. 4 (6. August 2024): 697–708. doi: 10.1007/s10334-024-01192-5

Abstract

Objective
Previous studies have revealed a substantial between-centre variability in DCE-MRI biomarkers of hepatocellular function in rats. This study aims to identify the main sources of variability by comparing data measured at different centres and field strengths, at different days in the same subjects, and over the course of several months in the same centre.

Materials and methods
13 substudies were conducted across three facilities on two 4.7 T and two 7 T scanners using a 3D spoiled gradient echo acquisition. All substudies included 3–6 male Wistar-Han rats each, either scanned once with vehicle (n = 76) or twice with either vehicle (n = 19) or 10 mg/kg of rifampicin (n = 13) at follow-up. Absolute values, between-centre reproducibility, within-subject repeatability, detection limits, and effect sizes were derived for hepatocellular uptake rate (Ktrans) and biliary excretion rate (kbh). Sources of variability were identified using analysis of variance and stratification by centre, field strength, and time period.

Results
Data showed significant differences between substudies of 31% for Ktrans (p = 0.013) and 43% for kbh (p < 0.001). Within-subject differences were substantially smaller for kbh (8%) but less so for Ktrans (25%). Rifampicin-induced inhibition was safely above the detection limits, with an effect size of 75 ± 3% in Ktrans and 67 ± 8% in kbh. Most of the variability in individual data was accounted for by between-subject (Ktrans = 23.5%; kbh = 42.5%) and between-centre (Ktrans = 44.9%; kbh = 50.9%) variability, substantially more than the between-day variation (Ktrans = 0.1%; kbh = 5.6%). Significant differences in kbh were found between field strengths at the same centre, between centres at the same field strength, and between repeat experiments over 2 months apart in the same centre.

Discussion
Between-centre bias caused by factors such as hardware differences, subject preparations, and operator dependence is the main source of variability in DCE-MRI of liver function in rats, closely followed by biological between-subject differences. Future method development should focus on reducing these sources of error to minimise the sample sizes needed to detect more subtle levels of inhibition.

 

Assessing Hepatic Transporter Function in Rats
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