Vito Lorusso

Gadolinium chelates with weak binding to serum proteins. A new class of high-efficiency, general purpose contrast agents for magnetic resonance imaging.

RATIONALE AND OBJECTIVES The authors assess the effect of weak protein binding on the efficacy of gadolinium chelates as contrast agents for magnetic resonance imaging (MRI). METHODS Chelates with no (gadopentetate dimeglumine), weak (gadobenate dimeglumine), and strong (B-21326/7) protein binding were compared by in vitro MRI at 2T (spin echo [SE]: repetition time [TR]/echo time [TE] 350/8 mseconds) on solutions in 0.5 mM bovine serum albumin and in rat whole blood, and by in vivo MRI at 2T on rat models of brain tumors (SE TR/TE 350/10 mseconds) and of focal blood-brain barrier disruption (SE TR/TE 400/15 mseconds) after injection of MPP+. Relaxation rate enhancement in the blood of normal rabbits was measured in vivo after administration of contrast agents using IR-Snapshot FLASH. RESULTS Signal intensity enhancement measured in vitro for whole rat blood 0.1 mM in gadobenate was 142% relative to the same concentration of gadopentetate. Peak signal intensity enhancement in brain tumors was 87% +/- 8% and 64% +/- 5% after 0.1 mmol/kg intravenous administration of gadobenate and gadopentetate, respectively; in MPP+ lesions, the peak signal intensity enhancement was 22% +/- 9%, 32% +/- 7%, and 64% +/- 14% after 0.2 mmol/kg intravenous of gadopentetate, gadobenate, and B-21326/7, respectively. In rabbits, the relaxation enhancement of blood 5 minutes after B-21326/7 and gadobenate administration was 323% and 182%, respectively, relative to the same dose (0.1 mmol/kg intravenous) of gadopentetate. CONCLUSIONS Weak protein binding can substantially increase the efficacy of gadolinium chelates as general purpose contrast agents for MRI.

Dose-Related Effects of Repeated ETC-216 (Recombinant Apolipoprotein A-IMilano/1-Palmitoyl-2-Oleoyl Phosphatidylcholine Complexes) Administrations on Rabbit Lipid-Rich Soft Plaques. In Vivo Assessment by Intravascular Ultrasound and Magnetic Resonance Imaging

OBJECTIVES This study sought to evaluate in vivo the minimal dose of apolipoprotein (apo) A-I(Milano) phospholipid complex (recombinant apoA-I(Milano) and 1-palmitoyl-2-oleoyl phosphatidylcholine complexes [ETC-216]) able to induce atherosclerosis regression in a rabbit model of lipid-rich plaques. BACKGROUND A single high dose of recombinant apoA-I(Milano) has promoted atherosclerosis regression in animal models. More recently, regression of atherosclerosis was achieved in coronary patients by repeated infusions of ETC-216. METHODS Thirty-six rabbits underwent perivascular injury at both carotid arteries, followed by a 1.5% cholesterol diet. After 90 days, rabbits were randomly divided into 6 groups and treated 5 times with vehicle or ETC-216 at 5, 10, 20, 40, or 150 mg/kg dose every 4 days. Carotid plaque changes were evaluated in vivo by intravascular ultrasound (IVUS) and magnetic resonance imaging (MRI), performed before and at the end of treatments. Magnetic resonance imaging scans were also recorded after administration of the second dose for rabbits infused with vehicle 40 or 150 mg/kg. RESULTS Atheroma volume in vehicle-treated rabbits increased dramatically between the first and the second IVUS analyses (+26.53%), whereas in ETC-216-treated animals, a reduced progression at the lower doses and a significant regression at the higher doses, up to -6.83%, was detected. Results obtained by MRI analysis correlated significantly with those at IVUS (r = 0.706; p < 0.0001). The MRI evaluations after the second infusion established that a significant regression was achieved with only 2 administrations of the highest dose. CONCLUSIONS These results confirm the efficacy of ETC-216 for atherosclerosis treatment and provide guidance for dose selection and frequency to obtain a significant reduction of plaque volume.

Mixed micelles containing lipophilic gadolinium complexes as MRA contrast agents.

Mixed micelles for MRA are multicomponent systems containing a phospholipid, a biocompatible non-ionic surfactant (e.g. Synporonic(k) F-108) and a lipophilic gadolinium complex. A variety of lipophilic gadolinium complexes were designed taking into account features such as: (i) nature of ligand (cyclic versus acyclic); (ii) lipophilic moiety; (iii) global charge of the complex; and (iv) nature of bond connecting the complex to the lipophilic moiety. All the lipophilic gadolinium complexes after formulation as mixed micelles show high relaxivities in water and in blood (rat). Mixed micelles containing gadolinium complexes bearing only one aliphatic chain cannot be used as MRA contrast agents because they have a high haemolytic effect. Furthermore, in rats they are quickly eliminated from the blood stream. These drawbacks are completely circumvented using gadolinium complexes bearing two aliphatic chains. Mixed micelles containing such complexes show high relaxivities. no haemolytic effect and long blood permanence. This makes them promising candidates as MRA contrast agents. However, elimination, which occurs exclusively through the liver, is not complete, even after 7 days. Complexes containing labile (e.g. ester) bonds between the lipophilic moieties and the chelate subunit are eliminated through both the liver and the kidneys. However, elimination is stiil not complete after 7 days.

Pharmacokinetics and safety of iomeprol in healthy volunteers and in patients with renal impairment or end-stage renal disease requiring hemodialysis.

Lorusso V, Taroni P, Alvino S, et al. Pharmacokinetics and safety of iomeprol in healthy volunteers and in patients with renal impairment or end-stage renal disease requiring hemodialysis. Invest Radiol 2001;36:309–316. rationale and objectives. To present the results of two studies conducted to evaluate the pharmacokinetics and safety of iomeprol in healthy volunteers and in patients with various degrees of renal impairment. methods. In these two open-label, single-dose, phase I studies, a 50-mL dose of iomeprol 400 was administered intravenously to a total of 30 subjects of either sex. In study 1, six healthy volunteers with normal renal function, six patients with mild renal failure, six patients with moderate renal failure, and four patients with severe renal failure were enrolled. In study 2, eight patients with end-stage renal disease requiring hemodialysis were enrolled. Safety was determined by predose and postdose (up to 10 days) measurement of vital signs, hematology, blood chemistry, urinalysis, electrocardiogram, physical examinations, and the incidence of adverse events. Pharmacokinetics was determined by measuring iomeprol levels in plasma, urine, feces, and dialysate samples, by using a validated high-performance liquid chromatography assay, up to 7 days after administration. results. The plasma concentration of iomeprol declined biexponentially in both healthy subjects and patients. As expected, mean body and renal clearances decreased progressively with increasing renal impairment, with a significant correlation with the glomerular filtration rate. The elimination half-life increased progressively with increasing renal impairment. The extraction efficiency of dialyser was estimated as approximately 40%, and dialysis clearance of iomeprol was approximately 1.26 mL · min−1 · kg−1 (80.6 mL/min), slightly less than the body clearance previously observed in healthy subjects. It appears that dialysis is almost as efficient as renal function in healthy subjects in the removal of iomeprol. After a single dialysis session, approximately 58% of the dose was recovered in dialysate. Mild to moderate adverse events were reported by 17 of 30 subjects; none was clinically meaningful. One serious adverse event, unrelated to iomeprol, was reported. No clinically meaningful findings were noted for other safety parameters. conclusions. Iomeprol was almost completely eliminated both in patients with renal impairment and in patients receiving dialysis. No dose adjustment appears to be necessary either in patients with renal impairment or with end-stage renal disease requiring hemodialysis. In this risk population, iomeprol 400 was safe and well tolerated.

Magnetic resonance contrast agents : From the bench to the patient

Magnetic Resonance Imaging is gaining a prominent role in the routine clinical investigation. To further improve this technique it is crucial that contrast agents are developed with more optimal organ specificity. This will not only result in a better diagnostic efficiency but also in a reduction of the amount of the agent administered. A combination of techniques has been employed to increase the target selectivity of the contrast agent and thereby the feasibility to visualize different organs. The organ targeting is based on the understanding of the mechanisms involved in the interaction of the agent with plasma proteins (albumin in particular) as well as the different membrane transporters involved in the uptake and in the excretion of the agent from the organ. The physicochemical properties of the contrast agents play a major role in the interaction with these various proteins. In this review we address the relationship between the structure of the contrast agents and their binding to different plasma proteins and membrane transporters in different organs, with special reference to the liver and kidney. The present and potentially future applications of these concepts in the clinical setting are also discussed.

Evaluation of neovessels in atherosclerotic plaques of rabbits using an albumin-binding intravascular contrast agent and MRI

To test whether B‐22956/1, a novel intravascular contrast agent with a high affinity to serum albumin (Bracco Imaging SpA.), allowed quantifying neovessel and macrophage density in atherosclerotic plaques of rabbits using MRI.

Pharmacokinetics and tissue distribution in animals of gadobenate ion, the magnetic resonance imaging contrast enhancing component of gadobenate dimeglumine 0.5 M solution for injection (MultiHance).

OBJECTIVE Evaluation of the pharmacokinetic behavior of gadobenate dimeglumine, a new multipurpose parenteral contrast agent for magnetic resonance imaging. METHODS The pharmacokinetics were evaluated in rats, rabbits, dogs and monkeys after intravenous injections of non-labelled gadobenate dimeglumine and, for biodistribution studies, 153Gd-labelled gadobenate dimeglumine. Assays were performed by high performance liquid chromatography, X-ray fluorescence and gamma spectrometry. The binding of gadobenate ion to animal and human serum albumin was studied by equilibrium dialysis. RESULTS After intravenous injection gadobenate dimeglumine distributes into plasma and extracellular fluid as well as into the intrahepatocytic space. Gadobenate ion is cleared from plasma by renal and biliary excretion. It does not accumulate in specific tissues, except temporarily in tissues related to its elimination. Gadobenate ion is not metabolized. Its binding to plasma proteins is too weak to be detected by equilibrium dialysis. CONCLUSIONS Gadobenate dimeglumine combines the properties of an extracellular-fluid agent with those of a hepatobiliary agent. Its complete elimination and biological stability satisfy the requirements for its safe use in humans.

In vitro and in vivo hepatic transport of the magnetic resonance imaging contrast agent B22956/1: role of MRP proteins

The molecular mechanisms of the hepatic transport of B22956/1, a new gadolinium complex from the class of intravascular contrast agents for MRI, which undergoes extensive biliary elimination, were studied. Biliary and urinary elimination of B22956/1 were measured in normal and in mutant MRP2 lacking rats (TR(-)); cellular trafficking of the compound was assessed in wild and MRP1 or MRP2 transfected MDCKII cells. Eight hours after IV injection of B22956/1, 90+/-8% of the dose was recovered in the bile of normal rats. By contrast, in TR(-) rats, the biliary excretion was significantly lower (14+/-3%) while 55+/-9% of the compound was found in urine. In vitro, the cellular accumulation of B22956/1 was significantly lower in both MRP1 and MRP2 transfected cells as compared to wild type MDCKII cells, and the cellular efflux was prevented by the MRP inhibitor MK571, indicating the involvement of both MRP2 and MRP1 in the transport of B22956/1. Due to the distinct cellular localization of the proteins, MRP2 accounts for the biliary and urinary excretion of the compound, while MRP1 prevents cellular accumulation of the MRI agent. B22956/1 may be useful in clinical conditions where a defective biliary transport is present.

Effect of tamoxifen in an experimental model of breast tumor studied by dynamic contrast-enhanced magnetic resonance imaging and different contrast agents

Objectives:The aim of this study was to compare the efficacy of gadoteridol, B22956/1 (a new protein binding blood pool contrast agent), and (Gd-DTPA)37-albumin in detecting, by dynamic contrast-enhanced magnetic resonance imaging (MRI), the effect in vivo of tamoxifen in an experimental model of breast tumor implanted in rats. Materials and Methods:Tumors were induced by subcutaneous injection of 106 mammary adenocarcinoma cells (13762 MAT B III). Treatment with tamoxifen (or vehicle) started on day 4 after implantation. On day 10 after implantation, animals were observed by MRI using B22956/1 (or gadoteridol) and, 24 hours later, using (Gd-DTPA)37–albumin. Results:Dynamic contrast-enhanced magnetic resonance imaging data showed that tamoxifen treatment decreased vascular permeability to B22956/1, whereas no difference was detectable in permeability to gadoteridol or to (Gd-DTPA)37–albumin. No effect on fractional plasma volume was detected with either of contrast agents. Conclusions:B22956/1 is superior to both small Gd chelates and macromolecular contrast agents in the assessment of the effect of tamoxifen treatment on tumor vasculature.

Pharmacokinetics and safety of gadobenate dimeglumine (multihance) in subjects with impaired liver function.

Davies BE, Kirchin MA, Bensel K, et al. Pharmacokinetics and safety of gadobenate dimeglumine (Multihance) in subjects with impaired liver function. Invest Radiol 2002;37:299–308. rationale and objectives. To characterize the pharmacokinetics of gadolinium and to evaluate the safety of gadobenate dimeglumine (Gd-BOPTA) compared with placebo, in subjects with impaired liver function. methods. Volunteer adult subjects with hepatic impairment (Child-Pugh classification B or C) received, randomly and in double-blind fashion, either 0.1 mmol/kg gadobenate dimeglumine (n = 11) or placebo (n = 5) by intravenous injection. Blood and urine gadolinium concentrations were determined by ICP-AES and data were analyzed by compartmental and noncompartmental modeling. A full safety evaluation was performed. No magnetic resonance imaging was performed. results. A bi-exponential model fit the gadolinium blood concentration-time data for 10 of 11 subjects administered Gd-BOPTA. The mean (CV%) distribution and elimination half-lives for these subjects were 0.18 (71.9) and 2.18 (44.2) hours, respectively. Non-parametric analysis of all 11 subjects revealed a mean (CV%) area under the curve [0-inf] of 138 (41.9) &mgr;g(Gd)·h/mL. Mean (CV%) values for blood clearance, steady-state volume of distribution, and renal clearance were 172 (36.0) mL/minute, 22.9 (16.7) L, and 142 (49.0) mL/minute, respectively. A mean (CV%) of approximately 80% (24.5) of the administered dose was excreted in urine during 60 to 72 hours. No safety concerns were apparent. conclusion. Hepatic impairment did not modify the pharmacokinetics of gadobenate dimeglumine compared with values reported elsewhere for healthy subjects. The contrast agent was well tolerated and safe with an overall incidence of adverse events comparable to that of placebo.