Assessing Changes in Gadoxetate Metabolism by the Liver Using MRI

The identification of drugs at risk of drug-drug interactions (DDI) early in the drug development life cycle is key to avoid late stage drug development failures. A critical gap in current methodologies is for tools that are widely available and safe to use in humans, and specifically can distinguish between perturbation of hepatocellular uptake, excretion or both.

Dynamic gadoxetate enhanced magnetic resonance imaging (DGE-MRI) is a technique that can potentially fill this gap. The MRI contrast agent gadoxetate is used in clinical routine, it is known to be taken up in hepatocytes by transporters OATPB1 and excreted to bile by MRP2 transporters, and the respective uptake and excretion rates can be quantified with DGE-MRI using suitable MRI scans and data modelling.

Studies in animal models using DGE-MRI on 6 different drugs have clearly demonstrated various levels of drug-induced inhibition of gadoxetate uptake and excretion. Recently, a proof-of-concept study in healthy human volunteers using DGE-MRI to characterise a single drug (rifampicin) has shown a systematic 95% reduction in gadoxetate uptake and 40% reduction in excretion.

Aims

Study objectives The purpose of the current study is to expand on these previous results and use DGE-MRI to measure the inhibition of gadoxetate uptake and excretion in volunteers with two other test drugs, metformin and ciclosporin (Neoral). These drugs are selected because they are commonly used in clinical practice, have a good safety profile and are known to inhibit OATP1B1 and MRP2 function. They should therefore also produce a measurable effect on gadoxetate uptake and excretion rates. If we can show that this is indeed measurable, the results will add further evidence that these effects can be detected by DGE-MRI, improve our understanding of relevant effect size and limits of detection, and help us identify thresholds above which reduction in gadoxetate uptake or excretion would be of concern.

Study endpoints

1. The effect of a clinical dose of metformin on hepatocellular gadoxetate uptake and excretion in healthy volunteers.
2. The effect of a clinical dose of ciclosporin (Neoral) on hepatocellular gadoxetate uptake and excretion in healthy volunteers.

Long-term aims On the longer term we expect these data to help build a case that DGE-MRI can be a useful tool to assess transported-mediated DDI risk in early drug development. The study results will be included in an application to FDA's biomarker qualification program as described in a biomarker qualification plan (submitted to FDA) following acceptance by the FDA of a letter of intent outlining the rationale for this biomarker in drug development.

Methods

This is a single centre, prospective observational study including healthy volunteer participants. 6 participants will be recruited to each immediate-release metformin and ciclosporin (Neoral) drug arms (12 total). After screening and consent, each subject will attend two hospital visits no less than 7 days apart. On each visit they will undergo DGE-MRI in the morning, and once again after a 2-hour break to allow for sufficient time to measure biliary gadoxetate clearance. On the second visit one of the two test drugs will be administered before the first scan. Each DGE-MRI scan will be performed using 25% (¼) of a clinical dose of gadoxetate. Immediate-release metformin and ciclosporin (Neoral) will be used at standardised dosages (1000mg and 100mg, respectively). Blood samples will be taken before drug administration and before each scan for comparative assessment with liver function tests (LFT).

The work is outlined below.

1. Visit A, Screening: After eligibility screening, informed consent for participation will be taken. A clinical examination including observations and blood tests for renal and liver function will be taken. If renal function shows eGFR\<30mL/min/1.73m2, liver function parameters exceed laboratory normal values or clinical examination findings are not compatible with the inclusion criteria, the participants will be removed from the study.
2. Visit B, Baseline Scan: Participants will have two DGE-MRI scans with 25% (¼) standard clinical dose of gadoxetate administered at each. Blood samples (\<5mL) will be taken before each scan to assess liver function.
3. Visit C, Treatment Scan: After giving informed consent, participants will receive a single dose of either metformin or ciclosporin (Neoral) followed by an initial DGE-MRI scan at 25% (¼) standard clinical dose of gadoxetate. Metformin (1000mg) or ciclosporin (100mg, Neoral) will be administered 2 and 1 hour before gadoxetate injection, respectively. This is followed by another DGE-MRI at the same dose after a break of 60-120 minutes. LFTs (\<5mL blood) will be taken before metformin/ciclosporin (Neoral) administration, and also before each scan (totalling 3 blood tests).

Analyses

All images will be reviewed by a qualified abdominal radiologist to check for incidental findings.

Gadoxetate uptake and excretion kinetic rate constants will be measured with and without the drug for all participants. The primary outcome measure is the effect size of the drug on uptake and excretion.

The primary analyses will be done at the University of Sheffield.

Safety

The modelling and use of gadoxetate as a research biomarker was established in the proof-of-concept study conducted at the University of Leeds. Gadoxetate will be used at 25% (¼) standard clinical dose for each scan. This dose was established in the precursor study as the requisite dose to enable analyses of gadoxetate kinetics whilst not exposing participants unnecessarily to higher doses of the gadoxetate. At 25% of standard clinical dose, gadoxetate is not licensed for the diagnostic use. The administration of gadoxetate will be authorised by the clinical lead, Dr Benjamin Rea.

Both Metformin and Ciclosporin have an excellent safety profile and record, and therefore the risk posed to a healthy volunteer with no history of polypharmacy or comorbidities from a one off dose, is negligible. Routine clinical exclusions will be applied pertaining to the administration of gadoxetate, metformin and ciclosporin (Neoral) as well as contraindications to MRI imaging.

There will be no monitoring procedures undertaken following completion of this study but the research fellow will remain contactable following completion of the study for further queries.