Assessment of Pharmacokinetic, Pharmacodynamic Profile, and Tolerance of Gadopiclenol, A New High Relaxivity GBCA, in Healthy Subjects and Patients With Brain Lesions (Phase I/IIa Study):

Taylor dispersion analysis for measurement of diffusivity and size of gadolinium-based contrast agents

Gadolinium-based contrast agents (GBCA) are complexes of a Gadolinium metal center and a linear or macrocyclic polyamino-carboxylic acid chelating agent. These agents are employed to enhance the visibility of deep abnormalities through MRI techniques. Knowing the precise dimensions of various GBCA is key parameter for understanding their in-vivo and pharmaco-kinetic behaviors, their diffusivity, as well as their relaxivity. However, conventional size characterization techniques fall short when dealing with these tiny molecules (≤1 nm). In this work, we propose to determine the size and diffusivity of gadolinium-based contrast agents using Taylor dispersion analysis (TDA). TDA provided a reliable measurement of the hydrodynamic diameter and the diffusion coefficient. The obtained results were compared to DOSY NMR (Diffusion-ordered Nuclear Magnetic Resonance Spectroscopy) and DFT (Density Functional Theory).

Chiral Pyclen-Based Heptadentate Chelates as Highly Stable MRI Contrast Agents

In recent years, pyclen-based complexes have attracted a great deal of interest as magnetic resonance imaging (MRI) contrast agents (CAs) and luminescent materials, as well as radiopharmaceuticals. Remarkably, gadopiclenol, a Gd(III) bishydrated complex featuring a pyclen-based heptadentate ligand, received approval as a novel contrast agent for clinical MRI application in 2022. To maximize stability and efficiency, two novel chiral pyclen-based chelators and their complexes were developed in this study. Gd-X-PCTA-2 showed significant enhancements in both thermodynamic and kinetic stabilities compared to those of the achiral parent derivative Gd-PCTA. 1H NMRD profiles reveal that both chiral gadolinium complexes (Gd-X-PCTA-1 and Gd-X-PCTA-2) have a higher relaxivity than Gd-PCTA, while variable-temperature 17O NMR studies show that the two inner-sphere water molecules have distinct residence times τMa and τMb. Furthermore, in vivo imaging demonstrates that Gd-X-PCTA-2 enhances the signal in the heart and kidneys of the mice, and the chiral Gd complexes exhibit the ability to distinguish between tumors and normal tissues in a 4T1 mouse model more efficiently than that of the clinical agent gadobutrol. Biodistribution studies show that Gd-PCTA and Gd-X-PCTA-2 are primarily cleared by a renal pathway, with 24 h residues of Gd-X-PCTA-2 in the liver and kidney being lower than those of Gd-PCTA.

Evolving Characteristics of Gadolinium-Based Contrast Agents for MR Imaging: A Systematic Review of the Importance of Relaxivity

Gadolinium-based contrast agents (GBCAs) are widely and routinely used to enhance the diagnostic performance of magnetic resonance imaging and magnetic resonance angiography examinations. T1 relaxivity (r1) is the measure of their ability to increase signal intensity in tissues and blood on T1-weighted images at a given dose. Pharmaceutical companies have invested in the design and development of GBCAs with higher and higher T1 relaxivity values, and "high relaxivity" is a claim frequently used to promote GBCAs, with no clear definition of what "high relaxivity" means, or general concurrence about its clinical benefit. To understand whether higher relaxivity values translate into a material clinical benefit, well-designed, and properly powered clinical studies are necessary, while mere in vitro measurements may be misleading. This systematic review of relevant peer-reviewed literature provides high-quality clinical evidence showing that a difference in relaxivity of at least 40% between two GBCAs results in superior diagnostic efficacy for the higher-relaxivity agent when this is used at the same equimolar gadolinium dose as the lower-relaxivity agent, or similar imaging performance when used at a lower dose. Either outcome clearly implies a relevant clinical benefit. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 3.

Waiting times between examinations with intravascularly administered contrast media: a review of contrast media pharmacokinetics and updated ESUR Contrast Media Safety Committee guidelines

The pharmacokinetics of contrast media (CM) will determine how long safe waiting intervals between successive CT or MRI examinations should be. The Contrast Media Safety Committee has reviewed the data on pharmacokinetics of contrast media to suggest safe waiting intervals between successive contrast-enhanced imaging studies in relation to the renal function of the patient. CLINICAL RELEVANCE STATEMENT: Consider a waiting time between elective contrast-enhanced CT and (coronary) angiography with successive iodine-based contrast media administrations in patients with normal renal function (eGFR > 60 mL/min/1.73 m2) of optimally 12 h (near complete clearance of the previously administered iodine-based contrast media) and minimally 4 h (if clinical indication requires rapid follow-up). KEY POINTS: • Pharmacokinetics of contrast media will guide safe waiting times between successive administrations. • Safe waiting times increase with increasing renal insufficiency. • Iodine-based contrast media influence MRI signal intensities and gadolinium-based contrast agents influence CT attenuation.

Safety, Tolerability, and Pharmacokinetics of a Novel Macrocyclic Gadolinium-Based Contrast Agent, HNP-2006, in Healthy Subjects

OBJECTIVES

Gadolinium-based contrast agents (GBCAs) are indispensable in contrast-enhanced magnetic resonance imaging. A higher risk of gadolinium deposition in linear GBCAs required the introduction of macrocyclic GBCAs with a stable molecular structure. We conducted the first-in-human study to evaluate the safety, tolerability, and pharmacokinetics (PKs) of HNP-2006, a novel macrocyclic GBCA, in healthy male subjects.

MATERIALS AND METHODS

A randomized, placebo-controlled, double-blind, single-ascending dose study was conducted. Subjects received either a single intravenous bolus injection of HNP-2006 or its matching placebo with a treatment-to-placebo ratio of 6:2 at the dose level of 0.02, 0.05, 0.1, 0.2, and 0.3 mmol/kg. Safety was assessed through routine clinical assessments. Blood sampling and urine collection were performed up to 72 hours postdose for PK assessments. Noncompartmental methods were used to calculate PK parameters, and a population PK model was constructed.

RESULTS

Overall, 40 subjects completed the study. Fourteen subjects reported 22 treatment-emergent adverse events (TEAEs). The severity of all TEAEs was mild, and the HNP-2006 dose was associated with the incidence of TEAEs. The most common TEAEs included nausea and dizziness, which occurred within an hour of administration. HNP-2006 was rapidly eliminated by urinary excretion with a half-life of 1.8-2.0 hours and showed a dose-proportional PK. A 2-compartment model had the best fit with the population PK analysis.

CONCLUSIONS

A single intravenous dose of HNP-2006 was well-tolerated and safe up to 0.30 mmol/kg. HNP-2006 was rapidly excreted in urine and exhibited dose-independent PK profiles.

Pharmacokinetics and Tolerability of the Cancer-Targeting MRI Contrast Agent MT218 in Healthy Males

OBJECTIVE

The aim of this study was to evaluate the pharmacokinetics and safety profile of MT218, a peptide-targeted gadolinium-based contrast agent, in healthy males.

MATERIALS AND METHODS

This was a double-blind, randomized, placebo-controlled, single-ascending-dose study including 30 healthy male subjects. In each dose group (0.01, 0.02, 0.04, and 0.08 mmol/kg), 4 subjects received MT218 and 2 subjects received placebo (saline) in bolus injections. The highest dose group (0.08 mmol/kg) was assessed in 2 cohorts, 1 fasted and 1 nonfasted. Clinical laboratory tests, vital signs, and electrocardiograms were investigated. Gadolinium concentrations were measured in plasma samples collected before administration and over a 24-hour period postinjection, and in urine specimens collected until 22 days. A noncompartmental model was used for pharmacokinetic analysis. A clinical and biological safety follow-up was carried out for up to 6 months.

RESULTS

No clinically significant modifications in biochemistry, hematology, urinalysis, electrocardiogram parameters, or vital signs were reported at any time point for any treatment group. No serious adverse events were observed in any dose group. Transient dizziness, hyperhidrosis, and injection site coldness were the main adverse events reported in both the MT218 and placebo groups. The mean total apparent clearance decreased slightly with increasing dose, and the median plasma t 1/2 ranged from 1.7 hours in the 0.01 mmol/kg group to 2.7 hours in the 0.08 mmol/kg nonfasted group. MT218 was rapidly excreted via renal filtration with 42.9% to 52.8% of the injected dose measured in urine within the first hour after administration, and 92.5% to 117.3% in urine within 24 hours. No Gd was detected by inductively coupled plasma mass spectrometry in urine after 21 days.

CONCLUSION

Single intravenous administration of MT218 was safely tolerated in the healthy males. Its pharmacokinetic parameters and safety profile are well aligned with those of other gadolinium-based contrast agents.

A Comprehensive Overview of the Efficacy and Safety of Gadopiclenol: A New Contrast Agent for MRI of the CNS and Body

ABSTRACT

This review describes the pharmacokinetics, efficacy, and safety of gadopiclenol, a new macrocyclic gadolinium-based contrast agent (GBCA) recently approved by the Food and Drug Administration at the dose of 0.05 mmol/kg. Gadopiclenol is a high relaxivity contrast agent that shares similar pharmacokinetic characteristics with other macrocyclic GBCAs, including a predominant renal excretion. In pediatric patients aged 2-17 years, the pharmacokinetic parameters (assessed through a population pharmacokinetics model) were comparable to those observed in adults, indicating no need for age-based dose adjustment. For contrast-enhanced magnetic resonance imaging (MRI) of the central nervous system (CNS) and body indications, gadopiclenol at 0.05 mmol/kg was shown to be noninferior to gadobutrol at 0.1 mmol/kg in terms of 3 lesion visualization parameters (ie, lesion border delineation, internal morphology, and contrast enhancement). Moreover, for contrast-enhanced MRI of the CNS, compared with gadobenate dimeglumine at 0.1 mmol/kg, gadopiclenol exhibited superior contrast-to-noise ratio at 0.1 mmol/kg and comparable contrast-to-noise ratio at 0.05 mmol/kg. A pooled safety analysis of 1047 participants showed a favorable safety profile for gadopiclenol. Comparative studies showed that the incidence and nature of adverse drug reactions with gadopiclenol were comparable to those observed with other GBCAs. Importantly, no significant safety concerns were identified in pediatric and elderly patients, as well as in patients with renal impairment. Overall, these findings support the clinical utility and safety of gadopiclenol for MRI in adult and pediatric patients aged 2 years and older in CNS and body indications.

Pharmacokinetics, Safety, and Tolerability of the Novel Tetrameric, High-Relaxivity, Macrocyclic Gadolinium-Based Contrast Agent Gadoquatrane in Healthy Adults

OBJECTIVES

Gadolinium (Gd)-based contrast agents are well established in clinical routine and have been proven safe and effective. However, there is a need for "next-generation" Gd-based contrast agents that would allow lowering the Gd dose used for routine contrast-enhanced magnetic resonance imaging procedures. The objective of this first-in-human study was to investigate the pharmacokinetic profile, safety, and tolerability of gadoquatrane, a novel high-relaxivity Gd-based contrast agent.

MATERIALS AND METHODS

This study was conducted in 2018/2019 as a prospective, randomized, single-blind, single-dose, placebo-controlled, escalating-dose study. Healthy volunteers were randomly assigned (6:2) to intravenous administration of gadoquatrane (0.025 to 0.2 mmol Gd/kg body weight) or placebo. Study procedures included collection of blood samples and excreta for pharmacokinetic analyses and safety assessments.

RESULTS

Forty-nine healthy study participants (mean age ± SD, 35 ± 6.3 years; 24 female) were evaluated. The effective half-life of gadoquatrane in plasma was short and similar in all dose groups (1.4-1.7 hours). Plasma concentrations around the lower quantitation limit (0.0318 μmol Gd/L) were reached 15-72 hours after administration. The volume of distribution at steady state was ~0.2 L/kg in all dose groups. The clearance (total and renal) was ~0.1 L/h per kilogram in all groups. Across dose groups, the exposure of gadoquatrane increased dose-proportionally. Metabolite profiling revealed no hint of degradation in vivo or release of free Gd. Seven of 36 participants (19.4%) receiving gadoquatrane and 4 of 13 participants (30.8%) receiving placebo experienced mild or moderate treatment-emergent adverse events. No serious adverse events occurred. The analysis of the Gd concentration-QTc interval relationship indicated no risk of QT/QTc prolongation (>10 milliseconds) with gadoquatrane at clinical dose levels.

CONCLUSIONS

Gadoquatrane with its high-relaxivity, pharmacokinetic similarity to established Gd-based contrast agents and high tolerability is a promising "next-generation" contrast agent for magnetic resonance imaging.

Preclinical Safety Assessment of Gadopiclenol: A High-Relaxivity Macrocyclic Gadolinium-Based MRI Contrast Agent

OBJECTIVE

Gadopiclenol is a new high-relaxivity macrocyclic gadolinium-based contrast agent for magnetic resonance imaging of the central nervous system and other body regions. The product has been approved by US Food and Drug Administration and is currently being evaluated by European Medicines Agency. For risk assessment of the single diagnostic use in humans, the safety profile of gadopiclenol was evaluated with a series of preclinical studies.

MATERIALS AND METHODS

With exception of dose-ranging studies, all safety pharmacology and toxicology studies were performed in compliance with Good Laboratory Practice principles. Safety pharmacology studies were conducted to assess potential effects on cardiovascular (in vitro and in dogs), respiratory (in rats and guinea pigs), neurological (in rats), and renal endpoints (in rats). Toxicology studies were also performed to investigate acute toxicity (in rats and mice), extended single-dose (in rats and dogs) and repeated-dose toxicity (in rats and dogs), reproductive (in rats), developmental (in rats and rabbits) and juvenile toxicity (in rats), as well as genotoxicity (in vitro and in rats), local tolerance (in rabbits), potential immediate hypersensitivity (in guinea pigs), and potential tissue retention of gadolinium (in rats).

RESULTS

Safety pharmacology studies conducted at high intravenous (IV) doses showed a satisfactory tolerance of gadopiclenol in the main body systems. After either single or repeated IV dosing (14 and 28 days) in rats and dogs, gadopiclenol was well tolerated even at high doses. The no-observed-adverse-effect level values (ie, the highest experimental dose without adverse effects) representing between 8 times in rats and 44 times in dogs (based on the exposure), the exposure achieved in humans at the intended diagnostic dose, provide a high safety margin. No or only minor and reversible effects on body weight, food consumption, clinical signs, clinical pathology parameters, or histology were observed at the highest doses. The main histological finding consists in renal tubular vacuolations (exacerbated after repeated exposure), which supports a well-known finding for this class of compounds that has no physiological consequence on kidney function. Reproductive toxicity studies showed no evidence of effects on reproductive performance, fertility, perinatal and postnatal development in rats, or reproductive development in rats or rabbits. The safety profile of gadopiclenol in juvenile rats was satisfactory like in adults. Gadopiclenol was not genotoxic in vitro in the Ames test, a mouse lymphoma assay, and a rat in vivo micronucleus test. There were no signs of local intolerance at the injection site after IV and intra-arterial administration in rabbits. However, because of minor signs of intolerance after perivenous administration, misadministration must be avoided. Gadopiclenol exhibited no signs of potential to induce immediate hypersensitivity in guinea pigs.

CONCLUSIONS

High safety margins were observed between the single diagnostic dose of 0.05 mmol/kg in humans and the doses showing effects in animal studies. Gadopiclenol is, therefore, well tolerated in various species (mice, rats, dogs, rabbits, and guinea pigs). All observed preclinical data support the clinical approval.

Detection of Brain Metastases by Contrast-Enhanced MRI: Comparison of Gadopiclenol and Gadobenate in a Mouse Model

OBJECTIVES

The aim of this study was to evaluate the capacity of gadopiclenol, a high-relaxivity gadolinium-based contrast agent to detect brain metastases in mice as a function of dose (0.08 mmol/kg or 0.1 mmol/kg) compared with gadobenate at 0.1 mmol/kg.

MATERIALS AND METHODS

Brain metastases were induced by ultrasound-guided intracardiac implantation of 1.10 5 MDA-MB-231Br cells in the left ventricle of 18 anesthetized Balb/c Nude nu/nu female mice. At day 28 ± 3 after cell injection, each mouse received 2 crossover intravenous injections at 24-hour intervals, randomly selected from 2 doses of gadopiclenol (0.08 mmol/kg or 0.1 mmol/kg) and gadobenate (0.1 mmol/kg) with n = 6 mice/group (3 groups). Brain magnetic resonance imaging sessions were performed at 4 weeks on a 2.35 T magnet with a 3-dimensional T1-weighted high-resolution gradient echo sequence, before and after each injection. Images were blindly and randomly analyzed to detect enhancing lesions. Contrast-to-noise ratio between the metastases and the surrounding healthy parenchyma was calculated, based on region-of-interest signal measurements. In 2 animals per group, an early time point was added to the protocol (day 22 ± 3) to evaluate the sensitivity of detection as a function of time. After the last imaging session, the presence and location of whole-brain metastases were confirmed by histology in 4 mice.

RESULTS

After gadopiclenol, approximately twice as many metastases were detected compared with gadobenate, regardless of the dose. Contrast-to-noise ratios of the detected metastases were 2.3 and 3.3 times higher with gadopiclenol at 0.08 mmol/kg and 0.1 mmol/kg, respectively, compared with gadobenate at 0.1 mmol/kg ( P < 0.0001). Gadopiclenol at the dose of 0.1 mmol/kg resulted in a 1.4-fold higher contrast compared with gadopiclenol at 0.08 mmol/kg ( P < 0.02). In a subset of mice that were imaged 1 week earlier, 2 metastases were detected with gadopiclenol and not with gadobenate.

CONCLUSIONS

The high-relaxivity macrocyclic gadolinium-based contrast agent gadopiclenol allowed higher diagnostic performance for detecting brain enhancing metastases in terms of contrast-to-noise ratio and number of detected metastases compared with gadobenate, at both equal (0.1 mmol/kg) dose and 20% lower Gd dose (0.08 mmol/kg). Tumor detection was higher after gadopiclenol at the dose of 0.1 mmol/kg compared with 0.08 mmol/kg.

MRI Gadolinium-Based Contrast Media: Meeting Radiological, Clinical, and Environmental Needs

Gadolinium-based contrast agents (GBCAs) are routinely used in magnetic resonance imaging (MRI). They are essential for choosing the most appropriate medical or surgical strategy for patients with serious pathologies, particularly in oncologic, inflammatory, and cardiovascular diseases. However, GBCAs have been associated with an increased risk of nephrogenic systemic fibrosis in patients with renal failure, as well as the possibility of deposition in the brain, bones, and other organs, even in patients with normal renal function. Research is underway to reduce the quantity of gadolinium injected, without compromising image quality and diagnosis. The next generation of GBCAs will enable a reduction in the gadolinium dose administered. Gadopiclenol is the first of this new generation of GBCAs, with high relaxivity, thus having the potential to reduce the gadolinium dose while maintaining good in vivo stability due to its macrocyclic structure. High-stability and high-relaxivity GBCAs will be one of the solutions for reducing the dose of gadolinium to be administered in clinical practice, while the development of new technologies, including optimization of MRI acquisitions, new contrast mechanisms, and artificial intelligence may help reduce the need for GBCAs. Future solutions may involve a combination of next-generation GBCAs and image-processing techniques to optimize diagnosis and treatment planning while minimizing exposure to gadolinium. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 3.

Effect of hydration equilibria on the relaxometric properties of Gd(III) complexes: new insights into old systems

We present a detailed relaxometric and computational investigation of three Gd(III) complexes that exist in solution as an equilibrium of two species with a different number of coordinated water molecules: [Gd(H2O)q]3+ (q = 8, 9), [Gd(EDTA)(H2O)q]- and [Gd(CDTA)(H2O)q]- (q = 2, 3). 1H nuclear magnetic relaxation dispersion (NMRD) data were recorded from aqueous solutions of these complexes using a wide Larmor frequency range (0.01-500 MHz). These data were complemented with 17O transverse relaxation rates and chemical shifts recorded at different temperatures. The simultaneous fit of the NMRD and 17O NMR data was guided by computational studies performed at the DFT and CASSCF/NEVPT2 levels, which provided information on Gd⋯H distances, 17O hyperfine coupling constants and the zero-field splitting (ZFS) energy, which affects electronic relaxation. The hydration equilibrium did not have a very important effect in the fits of the experimental data for [Gd(H2O)q]3+ and [Gd(CDTA)(H2O)q]-, as the hydration equilibrium is largely shifted to the species with the lowest hydration number (q = 8 and 2, respectively). The quality of the analysis improves however considerably for [Gd(EDTA)(H2O)q]- upon considering the effect of the hydration equilibrium. As a result, this study provides for the first time an analysis of the relaxation properties of this important model system, as well as accurate parameters for [Gd(H2O)q]3+ and [Gd(CDTA)(H2O)q]-.

Update on Gadolinium Based Contrast Agent Safety, From the AJR Special Series on Contrast Media

Since its introduction 35 years ago, gadolinium-enhanced MRI has fundamentally changed medical practice. While extraordinarily safe, gadolinium-based contrast agents (GBCAs) may have side effects. Four distinct safety considerations include: acute allergic-like reactions, nephrogenic systemic fibrosis (NSF), gadolinium deposition, and symptoms associated with gadolinium exposure. Acute reactions after GBCA administration are uncommon-far less than with iodinated contrast agents-and, while rare, serious reactions can occur. NSF is a rare, but serious, scleroderma-like condition occurring in patients with kidney failure after exposure to American College of Radiology (ACR) Group 1 GBCAs. Group 2 and 3 GBCAs are considered lower risk, and, through their use, NSF has largely been eliminated. Unrelated to NSF, retention of trace amounts of gadolinium in the brain and other organs has been recognized for over a decade. Deposition occurs with all agents, although linear agents appear to deposit more than macrocyclic agents. Importantly, to date, no data demonstrate any adverse biologic or clinical effects from gadolinium deposition, even with normal kidney function. This article summarizes the latest safety evidence of commercially available GBCAs with a focus on new agents, discusses updates to the ACR NSF GBCA safety classification, and describes approaches for strengthening the evidence needed for regulatory decisions.

A year in pharmacology: new drugs approved by the US Food and Drug Administration in 2022

While new drug approvals by the U.S. Food and Drug Administration (FDA) had remained stable or even increased in the first 2 years of the COVID-19 pandemic, the 37 newly approved drugs in 2022 are considerably less than the 53 and 50 new drugs approved in 2020 and 2021, respectively, and less than the rolling 10-year average of 43. As in previous years of this annual review, we assign these new drugs to one of three levels of innovation: first drug against a condition ("first-in-indication"), first drug using a novel molecular mechanism ("first-in-class"), and "next-in-class," i.e., a drug using an already exploited molecular mechanism. We identify two "first-in-indication" (ganaxolon and teplizumab), 20 (54%) "first-in-class," and 17 (46%) "next-in-class" drugs. By treatment area, rare diseases and cancer drugs were once again the most prevalent (partly overlapping) therapeutic areas. Other continuing trends were the use of accelerated regulatory approval pathways and the reliance on biopharmaceuticals (biologics).

Review of the Efficacy and Safety of Gadopiclenol: A Newly Emerging Gadolinium-Based Contrast Agent

Gadolinium-based contrast agents (GBCAs) are one of the most commonly used agents in magnetic resonance imaging. Gadopiclenol is a new GBCA aimed at providing improved diagnostic efficacy with a favorable safety profile. The proposed advantages are due to its specific pharmacological properties, one of which is high relaxivity values. The aim of this review is to assess the efficacy, diagnostic accuracy, and safety of gadopiclenol in comparison to other currently used gadolinium-based contrast agents. PubMed and other database systems were used to identify relevant studies. The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines were followed, resulting in 10 articles that were included in the review. The outcomes were reviewed according to several factors regarding efficacy and accuracy in terms of qualitative and quantitative descriptors relative to properties of enhancement provided by the contrast agent. In terms of safety profile, a number of outcomes were assessed such as the occurrence of serious adverse effects, severe kidney injury, and organ-based contrast retention. Gadopiclenol was found to provide outcomes comparable to other commonly used GBCAs at lower doses with further favorable results at higher doses while maintaining an acceptable safety profile. However, it was found to have high rates of retention within the liver and can cause nonsignificant QT prolongation in healthy individuals, which arguably creates the need for further research regarding more long-term implications of these possible adverse effects.

Design of Bifunctional Pyclen-Based Lanthanide Luminescent Bioprobes for Targeted Two-Photon Imaging

In the past, Lanthanide Luminescent Bioprobes (LLBs) based on pyclen-bearing π-extended picolinate antennas were synthesized and demonstrated well-adapted optical properties for biphotonic microscopy. The objective of this work is to develop a strategy to design bifunctional analogues of the previously studied LLBs presenting an additional reactive chemical group to allow their coupling to biological vectors to reach deep in vivo targeted two-photon bioimaging. Herein, we elaborated a synthetic scheme allowing the introduction of a primary amine on the para position of the macrocyclic pyridine unit. The photophysical and bioimaging studies demonstrate that the introduction of the reactive function does not alter the luminescent properties of the LLBs paving the way for further applications.

Efficacy and Safety of Half-Dose Gadopiclenol versus Full-Dose Gadobutrol for Contrast-enhanced Body MRI

Background Gadopiclenol is a macrocyclic gadolinium-based contrast agent (GBCA) with higher relaxivity compared with standard GBCAs, potentially allowing gadolinium dose reduction without decreasing efficacy. Purpose To investigate whether gadopiclenol at 0.05 mmol/kg is noninferior to gadobutrol at 0.1 mmol/kg for lesion visualization in body MRI. Materials and Methods A randomized, double-blind, crossover, phase 3 study was conducted between August 2019 and December 2020 at 33 centers in 11 countries. Adults with at least one suspected focal lesion in one of three different body regions (head and neck; breast, thorax, abdomen, or pelvis; or musculoskeletal system) underwent two contrast-enhanced MRI examinations, randomized to start with either gadopiclenol or gadobutrol. MRI examinations were read by three blinded expert readers for each respective body region. Readers rated border delineation, internal morphologic characteristics, and visual contrast enhancement. Three additional blinded readers assessed reader preference. For safety analysis, adverse events were recorded. The differences between gadopiclenol- and gadobutrol-enhanced MRI in terms of lesion visualization were analyzed with a generalized linear mixed model using a two-sided paired t test. Results Among 273 participants (mean age, 57 years ± 13 [SD]; 162 women) who underwent both gadopiclenol- and gadobutrol-enhanced MRI and had at least one correlating lesion, 260 participants without major protocol deviations were analyzed for noninferiority. Gadopiclenol was noninferior to gadobutrol for all qualitative visualization parameters and for all readers (lower limit 95% CI of the difference of at least -0.10, which was above the noninferiority margin [-0.35]; P < .001). For most participants (75%-83% [206-228 of 276]), readers reported no preference between gadopiclenol- and gadobutrol-enhanced images. Adverse events did not differ in frequency, intensity, type, or association with GBCA injection (12 of 288 participants receiving gadopiclenol and 16 of 290 receiving gadobutrol). Conclusion Gadopiclenol at 0.05 mmol/kg was comparable with gadobutrol at 0.1 mmol/kg for lesion evaluation at contrast-enhanced body MRI and had a similar safety profile. Clinical trial registration no. NCT03986138 Published under a CC BY 4.0 license. Supplemental material is available for this article. See also the editorial by Bashir and Thomas in this issue.

Efficacy and Safety of Gadopiclenol for Contrast-Enhanced MRI of the Central Nervous System: The PICTURE Randomized Clinical Trial

OBJECTIVES

Developing new high relaxivity gadolinium-based contrast agents (GBCAs) for magnetic resonance imaging (MRI) allowing dose reduction while maintaining similar diagnostic efficacy is needed, especially in the context of gadolinium retention in tissues. This study aimed to demonstrate that contrast-enhanced MRI of the central nervous system (CNS) with gadopiclenol at 0.05 mmol/kg is not inferior to gadobutrol at 0.1 mmol/kg, and superior to unenhanced MRI.

MATERIALS AND METHODS

PICTURE is an international, randomized, double-blinded, controlled, cross-over, phase III study, conducted between June 2019 and September 2020. Adult patients with CNS lesions were randomized to undergo 2 MRIs (interval, 2-14 days) with gadopiclenol (0.05 mmol/kg) then gadobutrol (0.1 mmol/kg) or vice versa. The primary criterion was lesion visualization based on 3 parameters (border delineation, internal morphology, and contrast enhancement), assessed by 3 off-site blinded readers. Key secondary outcomes included lesion-to-background ratio, enhancement percentage, contrast-to-noise ratio, overall diagnostic preference, and adverse events.

RESULTS

Of the 256 randomized patients, 250 received at least 1 GBCA administration (mean [SD] age, 57.2 [13.8] years; 53.6% women). The statistical noninferiority of gadopiclenol (0.05 mmol/kg) to gadobutrol (0.1 mmol/kg) was achieved for all parameters and all readers (n = 236, lower limit 95% confidence interval of the difference ≥-0.06, above the noninferiority margin [-0.35], P < 0.0001), as well as its statistical superiority over unenhanced images (n = 239, lower limit 95% confidence interval of the difference ≥1.29, P < 0.0001).Enhancement percentage and lesion-to-background ratio were higher with gadopiclenol for all readers ( P < 0.0001), and contrast-to-noise ratio was higher for 2 readers ( P = 0.02 and P < 0.0001). Three blinded readers preferred images with gadopiclenol for 44.8%, 54.4%, and 57.3% of evaluations, reported no preference for 40.7%, 21.6%, and 23.2%, and preferred images with gadobutrol for 14.5%, 24.1%, and 19.5% ( P < 0.001).Adverse events reported after MRI were similar for gadopiclenol (14.6% of patients) and gadobutrol (17.6%). Adverse events considered related to gadopiclenol (4.9%) and gadobutrol (6.9%) were mainly injection site reactions, and none was serious.

CONCLUSIONS

Gadopiclenol at 0.05 mmol/kg is not inferior to gadobutrol at 0.1 mmol/kg for MRI of the CNS, confirming that gadopiclenol can be used at half the gadolinium dose used for other GBCAs to achieve similar clinical efficacy.

Detection and Diagnosis of Cardiac Amyloidosis in Egypt

Cardiac amyloidosis is a life-threatening disease that occurs when amyloid proteins, most commonly immunoglobulin light chain or transthyretin, mutate or become unstable, misfold, deposit as amyloid fibrils, and accumulate in the myocardium. Early diagnosis of cardiac amyloidosis is hindered by insufficient awareness, specifically regarding clinical red flags and diagnostic pathways. Cardiac amyloidosis diagnosis comprises two important phases, clinical suspicion (phase one) followed by definitive diagnosis (phase two). Each phase is associated with specific clinical techniques. For example, clinical features, electrocardiography, echocardiography, and cardiac magnetic resonance imaging serve to raise suspicion of cardiac amyloidosis and facilitate early diagnosis, whereas laboratory tests (i.e., blood or urine electrophoresis with immunofixation), biopsy, scintigraphy-based nuclear imaging, and genetic testing provide a definitive diagnosis of cardiac amyloidosis. In Egypt, both the lack of cardiac amyloidosis awareness amongst healthcare providers and the unavailability of clinical expertise for the use of diagnostic techniques must be overcome to improve the prognosis of cardiac amyloidosis in the region. Previously published diagnostic algorithms for cardiac amyloidosis have amalgamated techniques that can raise clinical suspicions of cardiac amyloidosis with those that definitively diagnose cardiac amyloidosis. Though such algorithms have been successful in developed countries, diagnostic tools like echocardiography, scintigraphy, and cardiac magnetic resonance imaging are not ubiquitously available across Egyptian facilities. This review presents the current state of knowledge regarding cardiac amyloidosis in Egypt and outlines a new diagnostic algorithm which leverages regional nuclear imaging expertise. Importantly, the proposed diagnostic algorithm guides accurate amyloid-typing to mitigate misdiagnosis and erroneous treatment selection and improve the cardiac amyloidosis diagnostic accuracy in Egypt.

2022 FDA TIDES (Peptides and Oligonucleotides) Harvest

A total of 37 new drug entities were approved in 2022; although that year registered the lowest number of drug approvals since 2016, the TIDES class consolidated its presence with a total of five authorizations (four peptides and one oligonucleotide). Interestingly, 23 out of 37 drugs were first-in-class and thus received fast-track designation by the FDA in categories such as breakthrough therapy, priority review voucher, orphan drug, accelerated approval, and so on. Here, we analyze the TIDES approved in 2022 on the basis of their chemical structure, medical target, mode of action, administration route, and common adverse effects.

Pharmacokinetics, Safety, and Efficacy of Gadopiclenol in Pediatric Patients Aged 2 to 17 Years

OBJECTIVES

The aim of this study was to evaluate the pharmacokinetic (PK) profile, safety, and efficacy of gadopiclenol, a new high-relaxivity gadolinium-based contrast agent, in children aged 2 to 17 years.

MATERIALS AND METHODS

Children scheduled to undergo contrast-enhanced magnetic resonance imaging of the central nervous system (CNS cohort) or other organs (body cohort) were included sequentially into 3 age groups (12-17, 7-11, and 2-6 years). Gadopiclenol was administered at the dose of 0.05 mmol/kg. A sparse sampling approach was applied, with 4 blood samples per child collected up to 8 hours postinjection. Population PK modeling was used for the analysis, including the CNS cohort and adult subjects from a previous study. Adverse events were recorded, and efficacy was assessed for all children.

RESULTS

Eighty children were included, 60 in the CNS cohort and 20 in the body cohort. The 2-compartment model with linear elimination from the central compartment developed in adults was also suitable for children. Pharmacokinetic parameters were very similar between adults and children. Terminal elimination half-life was 1.82 hours for adults and 1.77 to 1.29 hours for age groups 12-17 to 2-6 years. The median clearance ranged from 0.08 L/h/kg in adults and 12-17 years to 0.12 L/h/kg in 2-6 years. The median central and peripheral volumes of distribution were 0.11 to 0.12 L/kg and 0.06 L/kg, respectively, for both adults and children. Simulations of plasma concentrations showed minor differences, and median area under the curve was 590 mg·h/L for adults and 582 to 403 mg·h/L for children. Two patients (2.5%) experienced nonserious adverse events considered related to gadopiclenol: a mild QT interval prolongation and a moderate maculopapular rash. Despite the limited number of patients, this study showed that gadopiclenol improved lesion detection, visualization, and diagnostic confidence.

CONCLUSIONS

The PK profile of gadopiclenol in children aged 2 to 17 years was similar to that observed in adults. Thus, there is no indication for age-based dose adaptation, and comparable plasma gadopiclenol concentrations are predicted to be achieved with body weight-based dosing in this population. Gadopiclenol at 0.05 mmol/kg seems to have a good safety profile in these patients and could improve lesion detection and visualization, therefore providing better diagnostic confidence.

Long-term Gadolinium Retention in the Healthy Rat Brain: Comparison between Gadopiclenol, Gadobutrol, and Gadodiamide

Background Safety concerns caused by gadolinium retention call for the development of high-relaxivity gadolinium-based contrast agents (GBCAs) allowing minimal dosing. Purpose To investigate brain gadolinium retention in healthy rats after exposure to gadopiclenol (Elucirem, Guerbet; macrocyclic GBCA) compared with gadobutrol (Gadovist or Gadavist, Bayer; macrocyclic GBCA) and gadodiamide (Omniscan, GE Healthcare; linear GBCA) over 1 year. Materials and Methods In this study conducted between May 2018 and April 2020, 9-week-old healthy Sprague Dawley rats received five injections of either gadopiclenol, gadobutrol, or gadodiamide (2.4 mmol of gadolinium per kilogram of body weight for each), or saline (control animals) over a period of 5 weeks. Rats were randomly assigned to different groups (six female and six male rats per group). MRI examinations were performed before euthanasia at 1, 3, 5, or 12 months after the last injection. Brains were sampled to determine the total gadolinium content via inductively coupled plasma mass spectrometry (ICP-MS), to characterize gadolinium species with size exclusion chromatography (SEC)-ICP-MS, and to perform elemental mapping with laser ablation (LA)-ICP-MS. Mann-Whitney tests were performed on pairwise comparisons of the same time points. Results For both macrocyclic agents, no T1 signal hyperintensities were observed in the cerebellum, and approximately 80% of gadolinium washout was found between 1 month (gadobutrol, 0.30 nmol/g; gadopiclenol, 0.37 nmol/g) and 12 months (gadobutrol, 0.062 nmol/g; gadopiclenol, 0.078 nmol/g). After 12 months, only low-molecular-weight gadolinium species were detected in the soluble fraction. Gadodiamide led to significantly higher gadolinium concentrations after 1 month in the cerebellum (gadodiamide, 2.65 nmol/g; P < .001 vs both macrocyclics) combined with only 15% washout after 12 months (gadodiamide, 2.25 nmol/g) and with gadolinium detected bound to macromolecules. Elemental bioimaging enabled visualization of gadolinium deposition patterns colocalized with iron. Conclusion Gadopiclenol and gadobutrol demonstrated similar in vivo distribution and washout of gadolinium in the healthy rat brain, markedly differing from gadodiamide up to 12 months after the last injection. © RSNA, 2022 Online supplemental material is available for this article.

Small Brain Lesion Enhancement and Gadolinium Deposition in the Rat Brain: Comparison Between Gadopiclenol and Gadobenate Dimeglumine

OBJECTIVES

The aim of the set of studies was to compare gadopiclenol, a new high relaxivity gadolinium (Gd)-based contrast agent (GBCA) to gadobenate dimeglumine in terms of small brain lesion enhancement and Gd retention, including T1 enhancement in the cerebellum.

MATERIALS AND METHODS

In a first study, T1 enhancement at 0.1 mmol/kg body weight (bw) of gadopiclenol or gadobenate dimeglumine was evaluated in a small brain lesions rat model at 2.35 T. The 2 GBCAs were injected in an alternated and cross-over manner separated by an interval of 4.4 ± 1.0 hours (minimum, 3.5 hours; maximum, 6.1 hours; n = 6). In a second study, the passage of the GBCAs into cerebrospinal fluid (CSF) was evaluated by measuring the fourth ventricle T1 enhancement in healthy rats at 4.7 T over 23 minutes after a single intravenous (IV) injection of 1.2 mmol/kg bw of gadopiclenol or gadobenate dimeglumine (n = 6/group). In a third study, Gd retention at 1 month was evaluated in healthy rats who had received 20 IV injections of 1 of the 2 GBCAs (0.6 mmol/kg bw) or a similar volume of saline (n = 10/group) over 5 weeks. T1 enhancement of the deep cerebellar nuclei (DCN) was assessed by T1-weighted magnetic resonance imaging at 2.35 T, performed before the injection and thereafter once a week up to 1 month after the last injection. Elemental Gd levels in central nervous system structures, in muscle and in plasma were determined by inductively coupled plasma mass spectrometry (ICP-MS) 1 month after the last injection.

RESULTS

The first study in a small brain lesion rat model showed a ≈2-fold higher number of enhanced voxels in lesions with gadopiclenol compared with gadobenate dimeglumine. T1 enhancement of the fourth ventricle was observed in the first minutes after a single IV injection of gadopiclenol or gadobenate dimeglumine (study 2), resulting, in the case of gadopiclenol, in transient enhancement during the injection period of the repeated administrations study (study 3). In terms of Gd retention, T1 enhancement of the DCN was noted in the gadobenate dimeglumine group during the month after the injection period. No such enhancement of the DCN was observed in the gadopiclenol group. Gadolinium concentrations 1 month after the injection period in the gadopiclenol group were slightly increased in plasma and lower by a factor of 2 to 3 in the CNS structures and muscles, compared with gadobenate dimeglumine.

CONCLUSIONS

In the small brain lesion rat model, gadopiclenol provides significantly higher enhancement of brain lesions compared with gadobentate dimeglumine at the same dose. After repeated IV injections, as expected for a macrocyclic GBCA, Gd retention is minimalized in the case of gadopiclenol compared with gadobenate dimeglumine, resulting in no T1 hypersignal in the DCN.

How the Chemical Properties of GBCAs Influence Their Safety Profiles In Vivo

The extracellular class of gadolinium-based contrast agents (GBCAs) is an essential tool for clinical diagnosis and disease management. In order to better understand the issues associated with GBCA administration and gadolinium retention and deposition in the human brain, the chemical properties of GBCAs such as relative thermodynamic and kinetic stabilities and their likelihood of forming gadolinium deposits in vivo will be reviewed. The chemical form of gadolinium causing the hyperintensity is an open question. On the basis of estimates of total gadolinium concentration present, it is highly unlikely that the intact chelate is causing the T1 hyperintensities observed in the human brain. Although it is possible that there is a water-soluble form of gadolinium that has high relaxitvity present, our experience indicates that the insoluble gadolinium-based agents/salts could have high relaxivities on the surface of the solid due to higher water access. This review assesses the safety of GBCAs from a chemical point of view based on their thermodynamic and kinetic properties, discusses how these properties influence in vivo behavior, and highlights some clinical implications regarding the development of future imaging agents.

Safety and Gadolinium Distribution of the New High-Relaxivity Gadolinium Chelate Gadopiclenol in a Rat Model of Severe Renal Failure

OBJECTIVE

The aim of this study was to investigate the toxicological profile of gadopiclenol, a new high-relaxivity macrocyclic gadolinium-based contrast agent (GBCA), in renally impaired rats, in comparison with 2 other macrocyclic GBCAs, gadoterate meglumine and gadobutrol, and 1 linear and nonionic GBCA, gadodiamide.

METHODS

Renal failure was induced by adding 0.75% wt/wt adenine to the diet for 3 weeks. During the second week of adenine-enriched diet, the animals (n = 8/group × 5 groups) received 5 consecutive intravenous injections of GBCA at 2.5 mmol/kg per injection, resulting in a cumulative dose of 12.5 mmol/kg or saline followed by a 3-week treatment-free period after the last injection. The total (elemental) gadolinium (Gd) concentration in different tissues (brain, cerebellum, femoral epiphysis, liver, skin, heart, kidney, spleen, plasma, urine, and feces) was measured by inductively coupled plasma mass spectrometry. Transmission electron microscopy (and electron energy loss spectroscopy analysis of metallic deposits) was used to investigate the presence and localization of Gd deposits in the skin. Relaxometry was used to evaluate the presence of dissociated Gd in the skin, liver, and bone. Skin histopathology was performed to investigate the presence of nephrogenic systemic fibrosis-like lesions.

RESULTS

Gadodiamide administrations were associated with high morbidity-mortality but also with macroscopic and microscopic skin lesions in renally impaired rats. No such effects were observed with gadopiclenol, gadoterate, or gadobutrol. Overall, elemental Gd concentrations were significantly higher in gadodiamide-treated rats than in rats treated with the other GBCAs for all tissues except the liver (where no significant difference was found with gadopiclenol) and the kidney and the heart (where statistically similar Gd concentrations were observed for all GBCAs). No plasma biochemical abnormalities were observed with gadopiclenol or the control GBCAs. Histopathology revealed a normal skin structure in the rats treated with gadopiclenol, gadoterate, and gadobutrol, contrary to those treated with gadodiamide. No evidence of Gd deposits on collagen fibers and inclusions in fibroblasts was found with gadopiclenol and its macrocyclic controls, unlike with gadodiamide. Animals of all test groups had Gd-positive lysosomal inclusions in the dermal macrophages. However, the textures differed for the different products (speckled texture for gadodiamide and rough-textured appearance for the 2 tested macrocyclic GBCAs).

CONCLUSIONS

No evidence of biochemical toxicity or pathological abnormalities of the skin was observed, and similar to other macrocyclic GBCAs, gadoterate and gadobutrol, tissue retention of Gd was found to be low (except in the liver) in renally impaired rats treated with the new high-relaxivity GBCA gadopiclenol.

Pharmacokinetics, Dialysability, and Safety of Gadopiclenol, a New Gadolinium-Based Contrast Agent, in Patients With Impaired Renal Function

OBJECTIVES

The aims of this study were to evaluate the pharmacokinetics (PK) of gadopiclenol, a new macrocyclic gadolinium based-contrast agent, in subjects with impaired renal function, and to assess its dialysability in subjects with end-stage renal disease (ESRD).

METHODS AND MATERIALS

This 2-center, open-label, phase 1 study included 5 successive cohorts of 8 adult subjects: healthy subjects (cohort 1), subjects with mild (cohort 2), moderate (cohort 3), severe (cohort 4) renal impairment, or ESRD (cohort 5), who received a single intravenous injection of gadopiclenol (0.1 mmol/kg). Blood and urine samples were collected at different time points in cohorts 1 to 4, and blood and dialysate samples were collected at each hemodialysis session (4-hour session on day 1, day 3, and day 5) in cohort 5. Gadopiclenol elimination and safety were assessed for up to 6 months. Pharmacokinetics parameters were calculated using noncompartmental analysis.

RESULTS

A total of 40 subjects were included, with a mean age of 51.5 years (range, 18-71 years). No significant difference in the mean maximum concentration values and the distribution volume was observed among cohorts 1 to 4. Urinary excretion of unchanged gadopiclenol was delayed with the degree of renal impairment and ranged between 96% and 84% in subjects with mild to severe renal impairment. Compared with that of healthy subjects, the mean area under the plasma concentration curve was 54%, 148%, and 769% higher in subjects with mild, moderate, or severe renal impairment, respectively. The mean terminal half-life was prolonged with the degree of renal impairment (1.9, 3.3, 3.8, and 11.7 hours for cohorts 1-4). In ESRD subjects, gadopiclenol was effectively removed from the plasma (95% to 98%) after the first hemodialysis session. Gadopiclenol concentration in plasma was below the limit of quantification for all subjects after the second hemodialysis session. Gadopiclenol concentration was below limit of quantification in all plasma and urine samples collected at 1, 3, and 6 months. Five subjects (12.5%) experienced adverse events related to gadopiclenol, none serious and all resolved. Laboratory measurements, vital signs, and electrocardiography did not raise any safety concern.

CONCLUSIONS

Gadopiclenol elimination half-life was prolonged in subjects with mild to severe renal impairment, yet its renal clearance remains complete or nearly complete. In ESRD subjects, gadopiclenol was effectively removed from the plasma after 1 hemodialysis session, and up to 3 hemodialysis sessions were sufficient to completely clear it. No safety concern was raised. Therefore, no dose adjustment seems necessary in this patient population.

Macrocyclic Pyclen-Based Gd3+ Complex with High Relaxivity and pH Response

We report the synthesis and characterization of the macrocyclic ligand 2,2'-((2-(3,9-bis(carboxymethyl)-3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-6-yl)ethyl)azanediyl)diacetic acid (H₄L) and several of its complexes with lanthanide ions. The structure of the free ligand was determined using X-ray diffraction measurements. Two N atoms of the pyclen moiety in the trans position are protonated in the solid state, together with the exocyclic N atom and one of the carboxylate groups of the ligand. The relaxivity of the Gd³⁺ complex was found to increase from 6.7 mM^-1 s^-1 at pH 8.6 to 8.5 mM^-1 s^-1 below pH ≈ 6.0. Luminescence lifetime measurements recorded from H₂O and D₂O solutions of the Eu³⁺ complex evidence the presence of a single complex species in solution at low pH (∼5.0) that contains two inner-sphere water molecules. DFT calculations suggest that the coordination environment of the Ln³⁺ ion is fulfilled by the four N atoms of the pyclen unit, two oxygen atoms of the macrocyclic acetate groups, and an oxygen atom of an exocyclic carboxylate group. The two inner-sphere water molecules complete coordination number nine around the metal ion. At high pH (∼9.3), the lifetime of the excited ⁵D₀ level of Eu³⁺ displays a biexponential behavior that can be attributed to the presence of two species in solution with hydration numbers of q = 0 and q = 1. The ¹H NMR and DOSY spectra recorded from solutions of the Eu³⁺ and Y³⁺ complexes reveal a structural change triggered by pH and the formation of small aggregates at high pH values.

Randomized study of the effect of gadopiclenol, a new gadolinium-based contrast agent, on the QTc interval in healthy subjects

AIMS

We investigated the effect of gadopiclenol, a new gadolinium-based contrast agent, on the QTc interval at clinical and supraclinical dose, considering the relative hyperosmolarity of this product.

METHODS

This was a single centre, randomized, double-blind, placebo- and positive-controlled, 4-way crossover study. Forty-eight healthy male and female subjects were included to receive single intravenous (i.v.) administrations of gadopiclenol at the clinical dose of 0.1 mmol kg^-1 , standard for current gadolinium-based contrast agents, the supraclinical dose of 0.3 mmol kg^-1 , placebo and a single oral dose of 400 mg moxifloxacin.

RESULTS

The largest time-matched placebo-corrected, mean change from-baseline in QTcF (ΔΔQTcF) was observed 3 hours after administration of 0.1 mmol kg^-1 gadopiclenol (2.39 ms, 90% confidence interval [CI]: 0.35, 4.43 ms) and 5 minutes after administration of 0.3 mmol kg^-1 (4.81 ms, 90%CI: 2.84, 6.78 ms). The upper limit of the 90% CI was under the threshold of 10 ms, demonstrating no significant effect of gadopiclenol on QTc interval. From 1.5 to 4 hours postdose moxifloxacin, the lower limit of the 90% CI of ΔΔQTcF exceeded 5 ms demonstrating assay sensitivity. Although there was a positive slope, the concentration-response analysis estimated that the values of ΔΔQTcF at the maximal concentration of gadopiclenol at 0.1 and 0.3 mmol kg^-1 were 0.41 and 2.23 ms, respectively, with the upper limit of the 90% CI not exceeding 10 ms. No serious or severe adverse events or treatment discontinuations due to adverse events were reported.

CONCLUSION

This thorough QT/QTc study demonstrated that gadopiclenol did not prolong the QT interval at clinical and supraclinical doses and was well tolerated in healthy volunteers. The positive slope of the QTc prolongation vs concentration relationship suggests that hyperosmolarity could be associated with QTc prolongation. However, the amplitude of this effects is unlikely to be associated with proarrhythmia.

Physicochemical and Pharmacokinetic Profiles of Gadopiclenol: A New Macrocyclic Gadolinium Chelate With High T1 Relaxivity

Objectives

We aimed to evaluate gadopiclenol, a newly developed extracellular nonspecific macrocyclic gadolinium-based contrast agent (GBCA) having high relaxivity properties, which was designed to increase lesion detection and characterization by magnetic resonance imaging.

Methods

We described the molecular structure of gadopiclenol and measured the r₁ and r₂ relaxivity properties at fields of 0.47 and 1.41 T in water and human serum. Nuclear magnetic relaxation dispersion profile measurements were performed from 0.24 mT to 7 T. Protonation and complexation constants were determined using pH-metric measurements, and we investigated the acid-assisted dissociation of gadopiclenol, gadodiamide, gadobutrol, and gadoterate at 37°C and pH 1.2. Applying the relaxometry technique (37°C, 0.47 T), we investigated the risk of dechelation of gadopiclenol, gadoterate, and gadodiamide in the presence of ZnCl₂ (2.5 mM) and a phosphate buffer (335 mM). Pharmacokinetics studies of radiolabeled ¹⁵³Gd-gadopiclenol were performed in Beagle dogs, and protein binding was measured in rats, dogs, and humans plasma and red blood cells.

Results

Gadopiclenol [gadolinium chelate of 2,2′,2″-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-3,6,9-triyl)tris(5-((2,3-dihydroxypropyl)amino)-5-oxopentanoic acid); registry number 933983-75-6] is based on a pyclen macrocyclic structure. Gadopiclenol exhibited a very high relaxivity in water (r₁ = 12.2 mM⁻¹·s⁻¹ at 1.41 T), and the r₁ value in human serum at 37°C did not markedly change with increasing field (r₁ = 12.8 mM⁻¹·s⁻¹ at 1.41 T and 11.6 mM⁻¹·s⁻¹ at 3 T). The relaxivity data in human serum did not indicate protein binding. The nuclear magnetic relaxation dispersion profile of gadopiclenol exhibited a high and stable relaxivity in a strong magnetic field. Gadopiclenol showed high kinetic inertness under acidic conditions, with a dissociation half-life of 20 ± 3 days compared with 4 ± 0.5 days for gadoterate, 18 hours for gadobutrol, and less than 5 seconds for gadodiamide and gadopentetate. The pharmacokinetic profile in dogs was typical of extracellular nonspecific GBCAs, showing distribution in the extracellular compartment and no metabolism. No protein binding was found in rats, dogs, and humans.

Conclusions

Gadopiclenol is a new extracellular and macrocyclic Gd chelate that exhibited high relaxivity, no protein binding, and high kinetic inertness. Its pharmacokinetic profile in dogs was similar to that of other extracellular nonspecific GBCAs.

Contrast-to-Dose Relationship of Gadopiclenol, an MRI Macrocyclic Gadolinium-based Contrast Agent, Compared with Gadoterate, Gadobenate, and Gadobutrol in a Rat Brain Tumor Model

Background Detection of cerebral lesions at MRI may benefit from a chemically stable and more sensitively detected gadolinium-based contrast agent (GBCA). Gadopiclenol, a macrocyclic GBCA with at least twofold higher relaxivity, is currently undergoing clinical trials in humans. Purpose To determine the relationship between MRI contrast enhancement and the injected dose of gadopiclenol in a glioma rat model compared with those of conventional GBCA at label dose. Materials and Methods Between April and July 2012, 32 rats implanted with C6 glioma received two intravenous injections at a 24-hour interval. The injections were randomly selected among five doses of gadopiclenol (0.025, 0.05, 0.075, 0.1, and 0.2 mmol/kg) and three reference GBCAs (gadoterate meglumine, gadobutrol, and gadobenate dimeglumine) at 0.1 mmol/kg. MRI tumor enhancement was assessed on T1-weighted images before and up to 30 minutes after injection. Two blinded radiologists visually and qualitatively scored contrast enhancement, border delineation, and visualization of tumor morphology. Quantitatively, variations in contrast-to-noise ratio (ΔCNR) between tumor and contralateral parenchyma were calculated at each time point and were compared for each treatment at 5 minutes by using a mixed model after normality test. Results A total of 24 rats underwent the complete protocol (n = 5-7 per group). A linear dose-dependent ΔCNR relationship was observed between 0.025 and 0.1 mmol/kg for gadopiclenol (R ² = 0.99). No difference in ΔCNR was observed between the three reference GBCAs (P ≥ .55). Gadopiclenol resulted in twofold higher ΔCNR at 0.1 mmol/kg (P < .001 vs gadobutrol and gadoterate, P = .002 vs gadobenate) and similar ΔCNR at 0.05 mmol/kg (P = .56, P > .99, and P = .44 compared with gadobutrol, gadobenate, and gadoterate, respectively). For both readers, 0.05 mmol/kg of gadopiclenol improved contrast enhancement, border delineation, and visualization of tumor morphology (scores > 3 compared with scores between 2 and 3 for the marketed GBCA). Conclusion Gadopiclenol at 0.05 mmol/kg yielded comparable change in contrast-to-noise ratio and morphologic characterization of brain tumors compared with gadobenate, gadoterate, or gadobutrol at 0.1 mmol/kg. Published under a CC BY 4.0 license. Online supplemental material is available for this article. See also the editorial by Tweedle in this issue.