Emerging Engineered Magnetic Nanoparticulate Probes for Molecular MRI of Atherosclerosis

How Far Have We Come?

Rupinder K Kanwar; Rajneesh Chaudhary; Takuya Tsuzuki; Jagat R Kanwar

Nanomedicine. 2012;7(6):899-916.

Nanoparticulate Probes for Molecular MRI of CAMs, Apoptosis, Angiogenesis & Thrombosis

In order to meet one of the major challenges (i.e., to develop a noninvasive method to detect 'vulnerable' high-risk atherosclerotic plaques prior to thrombosis or plaque rupture/erosion), cardiovascular imaging has evolved impressively in recent years. Nonionizing, high-resolution MRI is presently considered as one of the most promising noninvasive modalities for imaging vessel wall anatomy and atherosclerotic plaque composition (the discrimination of lipid core, fibrosis, intraplaque hemorrhage deposits and calcification). Conventional MRI has an inherent low sensitivity issue with regards to the application of this technique for target-specific imaging of the atherosclerotic plaque. Although the lesion/plaque progression-related biomarkers such as CAMs, macrophages and their scavenger receptors, MMPs, ECM proteins, αvβ₃ integrin, oxLDL and fibrin are upregulated in the diseased tissue; they are often present at relatively low levels (10⁻⁹–10⁻¹³ M/g tissue).^[68,69] Molecular MRI thus relies on the development of new-generation contrast agents. It has recently been shown to play an important role in investigating molecular and cellular targets associated with atherosclerotic plaque development. We have recently reviewed various magnetic contrast nanoplatforms such as superparamagnetic iron oxide nanoparticles (SPION), liposomes, micelles and nanoemulsions that have been prepared by conjugating different targeting ligands, such as monoclonal antibodies, antibody fragments, peptidomimetics, small peptides and recombinant proteins, to nanoparticles.^[10] Both T₁ contrast agents containing either paramagnetic gadolinium (Gd³⁺) ion complexes or SPION-based T₂ contrast agents have been validated with success, at the preclinical and clinical levels, for molecular MRI of atherosclerosis. Since our earlier article was focused on macrophage targeting, here we highlight the emerging MRI probes targeting other clinically promising molecular and cellular players/processes, involved in early atherosclerotic lesion formation to plaque rupture and erosion.

CAMs

CAMs are key players in the recruitment of leukocytes during the immunoinflammatory pathogenesis of atherosclerosis. Therefore, CAMs have been considered as one of the interesting targets for the development of nanoparticulate-based probes for molecular MRI. Due to its strict temporal and spatial expression/regulation, VCAM-1 has received the most attention as an ideal target for imaging and therapy of atherosclerosis. Different VCAM-1 targeting cross-linked iron oxide (CLIO)-based nanoparticulate magnetic resonance (MR) contrast agents have been engineered in the recent past. By employing a phage display approach, Kelly et al. identified a peptide sequence containing a VHSPNKK motif that mediates cell internalization via VCAM-1 in murine endothelium under physiological conditions.^[70] The peptide sequence showed very high affinity to VCAM-1-expressing ECs, low affinity to macrophages and inhibited leukocyte–endothelial interactions, in vitro. Using the peptide sequence, a novel VCAM-1-targeting magnetofluorescent imaging agent (VNP) with CLIO for optical and MR (dual) imaging was synthesized. In vivo, VNP successfully identified VCAM-1-expressing ECs in a murine TNF-α-induced inflammatory model and colocalized with VCAM-1-expressing cells in atherosclerotic lesions of cholesterol-fed apoE^–/– mice. The same team later developed another novel, second-generation VCAM-1-targeted agent with enhanced affinity and sufficient sensitivity.^[71] By employing a linear peptide affinity ligand VHPKQHR, homologous to VLA-4 (a known ligand for VCAM-1), they developed a multivalent agent (VINP-28), detectable by MRI and optical imaging. VINP-28 showed a 20-times higher affinity than the earlier agent VNP, and allowed noninvasive imaging of VCAM-1-expressing ECs and macrophages in atherosclerosis. Atheromata of atorvastatin-treated apoE^–/–mice showed reduced VINP-28 deposition and VCAM-1 expression.

In another interesting study, a model of adoptive human EC (HUVEC) transfer (by implanting in matrigel to athymic nude mice) was used to test the E-selectin-specific MRI agent, consisting of CLIO nanoparticles conjugated to antihuman endothelial selectin, E-selectin antibody (CLIO-F[ab']₂).^[72] High-resolution MR images were obtained before and after the administration of CLIO-F(ab')₂, which showed specific hypointensity only if treated with proinflammatory cytokine IL-1β. A three-times larger CLIO-induced MR signal decrease on T₂* images was measured in HUVEC implants in response to IL-1β treatment. The study observations further revealed that HUVEC-containing neovessels were perfused and that IL-1β inducible E-selectin expression in these vessels was detectable with noninvasive imaging by using targeted nanoparticles.

P-selectin (CD62P) is overexpressed on pathologically activated endothelium surfaces and activated platelets during atherosclerosis initiation, progression, rupture and thrombosis.^[73] More recently, polyethylene glycol and dextran-coated iron oxide nanoparticles, named versatile ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, coupled to an antihuman P-selectin antibody (VH10), were developed and validated preclinically in apoE^–/– mouse as a bimodal magnetofluorescent agent, for MRI and optical imaging of inducible P-selectin expression in human activated platelets involved in early stages of atherosclerosis.^[74] Iron oxide nanoparticles typically in the size range of a few micrometers, known as microparticles of iron oxide (MPIOs), have also been developed and tested as contrast agents for molecular MRI. MPIOs deliver a high payload of iron resulting in stronger MR contrast and represent a novel tool for molecular MRI.^[75] A novel dual CAM targeting strategy has been employed for targeted imaging of VCAM-1 and P-selectin in apoE^–/– mice aorta using MPIOs (4.5 µm) conjugated with monoclonal antibodies against VCAM-1 (VCAM-MPIO) and/or P-selectin (P-selectin-MPIO).^[76] The study showed that dual-ligand MPIOs can be used for functional MRI of these CAMs in mouse atherosclerosis. The strategy employed in this study exploited the opportunity of endovascular accessibility with the use of MPIOs (of similar size to circulating red blood cells) that could convey a substantial contrast payload larger than the one carried by USPIO. As reviewed recently,^[77] iron oxide nanoparticle-based contrast agents while effective for most applications, are not suitable for application in molecular endothelial imaging, due to their small size, where the delivery of sufficient contrast volume is challenging on the 'planar' target that is on the surface of the blood vessel wall. The dual ligand-targeted MPIO approach, targeting VCAM-1 and P-selectin, appears promising for in vivo molecular MRI of CAMs (expressed in vascular inflammation, as well as on activated platelet thrombosis), in atherosclerosis as well as in a diverse range of vascular disease models, such as acute vascular inflammation, thrombosis, ischemia–reperfusion injury and ischemic stroke. To overcome the issue of nonbiodegradable MPIOs, recently biodegradable multimeric (mMPIOs) have been developed for targeting VCAM-1.^[75] These novel mMPIOs are degraded by macrophages in culture. Biodistribution studies following intravenous injection show a faster clearance rate from the body in comparison with equivalently sized monomeric MPIOs. VCAM-mMPIOs specifically bind to IL-1 activated endovascular endothelium in vivo in a brain inflammation murine model. The findings suggest that these mMPIOs may constitute a promising nanoplatform for molecular MRI and should be tested in atherosclerotic models. A slow-clearance blood-pool paramagnetic agent (CMD-A2-Gd-DOTA [1,4,7,10-tetraazacyclododecane-N,N',N',N'tetraacetic acid]:P717) chemically modified to create a functionalized product (F-P717; hydrodynamic radius 5.7 nm) was synthesized as a new macromolecular imaging agent for noninvasive in vivo molecular MRI and evaluated in an apoE^–/– mouse model.^[78] In this study, a biomimetic approach was employed by grafting key chemical groups involved in the interaction between P-selectin and its endogenous ligand (PSGL-1) onto a paramagnetic macromolecular gadolinium agent (carboxymethyl-dextran DOTA-Gd) for dual fluorescence and MRI detection. F-P717 significantly enhanced the MRI signal in the abdominal aortic wall of apoE^–/– mice, with a greater than 50% signal-to-noise ratio increase between 10 and 30 min, but not in control mice. The MRI data were correlated to histopathology and immunofluorescence in mouse aortic tissue and colocalized F-P717 with the inflammatory area revealed by P-selectin labeling.

Apoptosis

Apoptosis of intraplaque cells and ECs is linked to plaque destabilization, vulnerability, de-endothelization and erosion. Since annexin V has a high binding affinity for phosphotidylserine residues translocated to the outer leaflet of the plasma membrane in apoptotic cells, a nanoplatform was developed using annexin V^– to potentially deliver superparamagnetic contrast agents for MRI to sites containing apoptotic cells, such as high-grade atherosclerotic lesions.^[79] Biochemically derivatized (annexin V) SPIONs were tested in two rabbit models of human atherosclerosis and myocardial infarction, namely Watanabe heritable hyperlipidemic rabbit and Watanabe heritable hyperlipidemic myocardial infarction, respectively. The latter rabbit model has plaque morphology that resembles the human vulnerable plaques and myocardial infarctions. Postinjection vascular targeting by annexin V-SPIONs was atheroma-specific and signal hypointensity was seen in atheromatous lesions, but not in the healthy arteries in a rabbit. Another study demonstrates the feasibility of obtaining high-resolution MR images of cardiomyocyte apoptosis in vivo with the novel CLIO nanoparticles (annexin-CLIO-Cy5.5; a bimodal [magnetic and near-infrared fluorescence] nanoparticle).^[80] This nanoparticulate agent validated in a left anterior descending coronary artery ligation model may have utility in apoptosis detection in atherosclerotic plaques.

Plaque Angiogenesis

During angiogenesis, targeting the specific proteins expressed excessively in angiogenic blood vessels is the key point in developing anti-angiogenic therapeutics and theranostics. Although angiogenesis research and diagnostics were originally the domain of cancer nanomedicine,^[81] recently the potential of angiogenesis targeting in atherosclerosis instability and inflammation has emerged. The presence of the neovessels has been associated with plaque inflammation and instability. Plaque neovessels can be targeted by using αvβ₃ integrin biomarkers as the activated ECs express these surface integrins that are not expressed by resting ECs of blood vessels in nondiseased tissues. Two strategies have been employed to image plaque angiogenesis: one approach relies on targeting αvβ₃ integrin biomarkers; the second is to directly measure the effect of increased blood in the adventitia due to angiogenesis by applying a dynamic contrast-enhanced MRI method.^[82] Winter et al. prepared paramagnetic Gd-diethylenetriaminepentacetate-bis-oleate-containing nanoemulsions of perfluorocarbon, functionalized to detect plaque angiogenesis by coupling with a Arg-Gly-Asp mimetic.^[83] These paramagnetic nanoparticles noninvasively targeted the αvβ₃ integrin expression in the aortic wall of hyperlipidemic rabbits during early atherosclerosis. Specific detection of the neovasculature within 2 h postinjection was performed by routine MRI at a clinically relevant field strength (1.5 T). The same team later showed that a single application of αvβ₃ integrin-targeted paramagnetic nanoemulsion for site-specific delivery of fumagillin (an endothelium-selective anti-angiogenic compound) is enough to inhibit angiogenesis in a rabbit model.^[84] In their next follow-up study, it was demonstrated that these nanoparticles decreased aortic angiogenesis for 3 weeks after treatment and their anti-angiogenic effect was acute, but this effect was prolonged when given in combination with oral atorvastatin.^[85] These findings indicate that this theranostic nanomedicine-based approach could translate into a clinically relevant strategy to evaluate prolonged anti-angiogenic treatment and atherosclerotic plaque stability.

Thrombosis (Platelet Activation/Aggregation & Fibrin Targeting)

Thrombi can be found at the later stages of atherosclerosis, and plaque rupture or erosion is regarded as the precipitating event for thrombus formation. Platelets not only play a role in the development of atherosclerosis, but are the key to thrombus formation. Thrombi also contain highly abundant fibrin protein. Therefore, noninvasive imaging of activated platelets and fibrin is of great clinical interest. Von Zur Muhlen et al. evaluated the ability of a MRI contrast agent consisting of MPIOs (1-µm size) and a single-chain antibody that selectively binds to ligand-induced binding sites (LIBS) on the activated platelet glycoprotein IIb/IIIa (also known as integrin αIIbβ₃).^[86] The study was carried out in vivo using a mouse model of ferric chloride-induced carotid artery thrombosis. With LIBS-MPIO, activated platelets can be detected by in vivo MRI with excellent contrast properties and the agent also allowed monitoring of thrombolytic (urokinase) therapy. Furthermore, through ex vivo MRI and histological observations of the surface of symptomatic human carotid plaques, LIBS-MPIOs binding was confirmed to areas of platelet adhesion/aggregation but not for control MPIOs. In their later study, the same group tested the capability of a LIBS-MPIO contrast agent to target activated platelets deposited on injured vessel walls in a mouse model of endothelial injury.^[87] The agent being able to convey a substantial contrast payload conferred functional specificity to image-activated platelets adhering to the vessel wall.

Fibrin is a highly expressed and clinically relevant target of atherosclerosis. Fibrin deposition is not only one of the earliest signs of plaque rupture or erosion, it also accounts for (along with intraplaque hemorrhage) a considerable part of the core of growing lesions.^[88] Fibrin is one of the key elements in thrombus formation following plaque rupture. Flacke and coworkers tested a fibrin-specific paramagnetic MR contrast agent that could allow clinically enhanced, sensitive detection and quantification of occult microthrombi within the intimal surface of atherosclerotic vessels in symptomatic patients and provide direct evidence to support acute therapeutic intervention.^[89] The contrast agent was formulated using liquid perfluorocarbons as the core. A lipid-encapsulated liquid perfluorocarbon nanoemulsion conjugated to antifibrin F(ab)' fragments on the outer lipid membrane surface was synthesized with high avidity and a prolonged systemic half-life. It could carry high Gd-diethylenetriaminepentaacetate payloads for high detection sensitivity. The study demonstrated the enhanced sensitive detection of clots both in vitro and in vivo. Human fibrin clots targeted in vitro with paramagnetic nanoparticles presented a highly detectable, homogeneous T₁-weighted contrast enhancement that improved with increasing gadolinium levels (0, 2.5 and 20 mol% Gd) and 1.5 T. Higher-resolution scans and scanning electron microscopy revealed that the nanoparticles were present as a thin layer over the clot surface. The nanoparticulate paramagnetic contrast agent described above was shown previously to detect human fibrin clots in vitro with sizes from 0.5 to 7.0 mm with high-resolution MRI at 4.7 T.^[90]In vivo contrast enhancement under open-circulation conditions was assessed in dogs. The results of the study suggest that molecular imaging with fibrin-targeted paramagnetic nanoparticles can provide sensitive detection and localization of fibrin. In the light of recent safety concerns in some patients with renal disease or following liver transplant, leading to US FDA restrictions over the use of gadolinium-based contrast agents, Lanza's team has recently extended their fibrin targeting work to use manganese-based MR as T₁ imaging probes.^[91] They are the first to report synthesis and MR characterization of fibrin-specific 'soft' type manganese oxide nanocolloids and manganese oleate nanocolloids incorporating divalent manganese.^[91] These nanocolliods were constrained to the vasculature by size (>120 nm) to avoid extravasation into nontarget, nonclearance tissues within the arterial wall or beyond. They also synthesized manganese(III)-labeled nanobialys (porphyrin encapsulated in an inverted micelle) as a potential theranostic agent.^[92] All these nanoparticulate agents were targeted to fibrin via a fibrin-specific monoclonal antibody using classic biotin–avidin interactions. In both studies, utility of these contrast agents in MR-targeted imaging was supported by their high particulate r1 relaxivities (at 1.5 and 3.0 T) and the strong MR contrast enhancement of T₁-weighted MR images, when targeted to in vitro clots. The efficacies of these contrast agents in vivo have yet to be investigated.

Senpan et al. have prepared a T₁-weighted colloidal iron oxide nanoparticle platform (CION), which was achieved by entrapping oleate-coated magnetite particles within a cross-linked phospholipid nanoemulsion.^[93] The developed CIONs with fibrin-specific functional groups caused signal enhancement in T₁-weighted ex vivo MRI of fibrin in ruptured atherosclerotic plaques from human carotid endarterectomy specimens without blooming artifacts. Fumagillin was also incorporated into these CIONs in an in vitro demonstration of their potential as theranostic agents. It is important to note that use of iron oxide nanoparticles as T₂ imaging contrast agents typically results in negative contrast effects, markedly delayed imaging (they can only be imaged 24 h or more, after systemic administration due to persistent blood pool interference) and is associated with prominent dipole blooming artifacts. This study shows an interesting attempt to tailor the magnetic properties of iron oxide nanoparticles to decrease the r2/r1 ratio, which thereby enables T₁-weighted (positive contrast) MRI. McCarthy and coworkers have synthesized novel efficient multimodal nanoagents targeted to fibrin and activated factor XIII (FXIIIa), the two different constituents of thrombi.^[94] FXIIIa is responsible for the cross-linking of fibrin α- and γ-chains to stabilize thrombi and increase fibrinolytic resistance. As its activity diminishes over time, it is considered a hallmark of biologically acute thrombi. The nanoagents are targeted by conjugating peptide-targeted ligands to the surface of fluorescently labeled CLIO nanoparticles and functionalized with a fibrin-targeting peptide (GPRPPGGSKGC), and α₂-antiplasmin (α₂AP)-based peptide (GNQEQVSPLTLLKC) to target FXIIIa by both MRI and optical imaging modalities. The incorporation of two spectrally distinct fluorescent dyes, namely VT680 and Cy7, enabled simultaneous fluorescence imaging of FXIIIa and fibrin via multichannel fluorescence imaging approaches. Through in vitro near-infrared fluorescence and MRI, nanoagents were shown to bind with high affinities to clots. In vivo studies in a FeCl₃-induced thrombosis mouse model and ex vivo analysis demonstrated further that both nanoagents readily accumulated within vascular thrombi preferentially over analogously synthesized control agents.

1 2 3 4 5

Next Section

Abstract and Introduction
Pathogenesis of Atherosclerosis
Nanoparticulate Probes for Molecular MRI of CAMs, Apoptosis, Angiogenesis & Thrombosis
Conclusion
Future Perspective
References
Sidebar

Table 1. Summary of nanoparticulate contrast agents targeting cell adhesion molecules, apoptosis, plaque angiogenesis and thrombosis (platelet activation/aggregation and fibrin targeting).
Nanoparticle contrast agents	Molecular/cellular targets	Models	Imaging modalities	Ref.
*Cell adhesion molecule targeting*
VNP (CLIO-based nanoparticle contrast agent)	VCAM-1	TNF-α induced CL57BL/6 mice, ApoE^–/– mice	MR and fluorescence imaging	[70]
VINP-28 (CLIO-based nanoparticle contrast agent)	VCAM-1	ApoE^–/– mice; atrovastatin-response monitoring	MR and fluorescence imaging	[71]
CLIO-F(ab')₂ ^†; CLIO-based contrast agent	E-selectin	Athymic nu/nu mice; HUVEC implants	MRI	[72]
USPIO-based contrast agent	P-selectin	ApoE^–/– mice	MR and fluorescence imaging	[74]
Multimeric MPIO-based contrast agent (biodegradable)	VCAM-1	Murine brain inflammation model	MRI	[75]
MPIO-based contrast agent	VCAM-1 and P-selectin (dual ligand)	ApoE^–/– mice	MRI	[76]
Carboxymethyldextran-DOTA-Gd-based contrast agent	P-selectin	ApoE^–/– mice	MR and fluorescence imaging	[78]
*Apoptosis targeting*
Annexin V-SPION	Phosphatidylserine residues (apoptotic cells)	WHHL/WHHLMI rabbit strains	MRI	[79]
Annexin-CLIO-Cy5.5	Phosphatidylserine residues (apoptotic cardiomocytes)	Left anterior descending coronary artery ligation CL57BL/6 mice	MR and NIRF imaging	[80]
*Plaque angiogenesis targeting*
RGD-coupled Gd-DTPA-BOA-based nanoemulsion	αvβ₃-integrin	Hyperlipidemic New Zealand white rabbits	MRI	[83]
RGD-coupled, fumagillin-loaded Gd-DTPA-BOA-based nanothernostic agent	αvβ₃-integrin	Hyperlipidemic New Zealand white rabbits (fumagillin-response monitoring)	MRI	[84]
RGD-coupled, fumigillin-loaded Gd-DTPA-BOA-based nanothernostic agent	αvβ₃-integrin	Hyperlipidemic New Zealand white rabbits (combined therapeutic response monitoring atrovastatin and fumagillin)	MRI	[85]
*Thrombosis targeting (platelet activation/aggregation & fibrin targeting)*
MPIO-based contrast agent	Activated platelet GPIIb/IIIa (αIIbβ₃-integrin)	Ferric chloride-induced carotid artery mouse model	MRI	[87]
Gd-DTPA-loaded perfluorocarbon nanoemulsion	Fibrin	Dog (open circulation)	MRI	[89]
Collidal iron oxide nanoparticle	Fibrin	Human carotid endarterectomy specimens (ex vivo)	MRI	[93]
Manganese nanocolloids	Fibrin	In vitro clot binding	MRI	[91]
Manganese nanobialys	Fibrin	In vitro clot binding	MRI	[92]
Fluorescent CLIO-based nanoagents	Fibrin and FXIIIa	In vitro and in vivo (FeCl₃-induced thrombosis; mouse model)	MR and NIRF imaging	[94]

†CLIO conjugated to antihuman E-selectin antibody fragment.
BOA: Bis-oleate; CLIO: Cross-linked iron oxide; DOTA: 1,4,7,10-tetraazacyclododecane-N,N',N',N'tetraacetic acid; DTPA: Diethylenetriaminepentacetate; FXIIIa: Activated factor XIII; Gd: Gadolinium; GP: Glycoprotein; HUVEC: Human umbilical vein endothelial cell; MPIO: Microparticles of iron oxide; MR: Magnetic resonance; NIRF: Near-infrared fluorescence; RGD: Arg-Gly-Asp; SPION: Superparamagnetic iron oxide nanoparticle; USPIO: Ultrasmall superparamagnetic iron oxide; VNP: VCAM-1-targeting magnetofluorescent imaging agent; WHHL: Watanabe heritable hyperlipidemic rabbit; WHHLMI: Watanabe heritable hyperlipidemic myocardial infarction.
Adapted from [10].

Sidebar

Executive Summary

Atherosclerosis, as a result of plaque rupture, threatens to become a leading cause of death worldwide by 2020 through its acute clinical manifestations, such as myocardial infarction and stroke.
In the multifactorial and complex pathogenesis of atherosclerosis, lesion formation begins when arterial endothelium becomes dysfunctional, stressed and activated by range of risk factors.
Recruitment of monocytes and, to a lesser extent, T lymphocytes, is one of the earliest cellular responses in atherosclerotic lesion formation. Expression of cell adhesion molecules along with chemokines and proinflammatory cytokines by an activated endothelium plays a key role in this process.
Lesions progress from early fatty streaks to advanced complex plaques. Endothelial cells, monocyte-derived macrophages, T lymphocytes and smooth muscle cells are the major players in the pathogenesis of atherosclerosis.
Heightened inflammation, angiogenesis and apoptosis contribute to plaque destabilization and enhanced plaque vulnerability/rupture.
In the recent past, in order to identify high-risk vulnerable plaques prior to thrombosis or rupture and erosion, cardiovascular imaging has evolved impressively.
In particular, high-resolution, nonionizing MRI has emerged as one of the most promising noninvasive safe modalities for imaging vessel wall anatomy and atherosclerotic plaque composition.
With the development of new generation-targeted nanoparticulate magnetic resonance contrast agents, molecular MRI has widened the scope of conventional MRI for functional characterization of the atherosclerosis process at the cellular and molecular levels, with remarkable clinical interest.
Superparamagnetic and paramagnetic nanoparticulate probes with T 1 and T 2 contrast mechanisms, respectively, have been synthesized to target the clinically promising molecular and cellular players of atherosclerotic plaque.
Preclinical and clinical data indicate that molecular MRI of atherosclerosis with emerging nanoparticulate-based probes is already playing an important role in basic science investigations and in drug development for targeting atherosclerosis.
The probes targeting cell adhesion molecules (VCAM-1, P- and E-selectins), plaque angiogenesis, thrombi and apoptosis are still at the stage of preclinical testing and under development. A number of steps and issues involved in clinical product development need to be resolved of before their clinical benefits can be obtained.
As the pathogenesis of atherosclerosis is better understood, nanoparticulate probes with improved targeting and drug delivery potential can be developed.
In future, through multidisciplinary collaborations, the wide spread use of molecular MRI for clinical benefits holds much promise in diagnosis, to risk stratify patients and to allow long-term and serial monitoring of drug response.

Comments

Commenting is limited to medical professionals. To comment please Log-in.

Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.