Promising New 18F-Labeled Tracers for PET Myocardial Perfusion Imaging

Construction and Preliminary Evaluation of Two 18F-Labeled Radiopharmaceuticals for Myocardial Perfusion Imaging

AIMS

PET myocardial perfusion imaging (MPI) is the gold standard for the noninvasive diagnosis of ischemic myocardial. Construction of 18F-labeled PET MPI probe showed benefits to reduce the imaging cost, and enhance the image quality and patient-friendliness.

METHODS

Two 18F-labeled MPI probes (18F-BoMPI) were developed. Detailed in vitro/vivo evaluation including photophysical properties, in vitro stability, myocardial cell uptake kinetics and mechanisms, cytotoxicity and IC50, biodistribution and plasma clearance curve were investigated. Resting and stressing myocardial perfusion PET imaging were performed in healthy and myocardial ischemic mice.

RESULTS

18F-BoMPI could be quickly labeled and easily postprocessed, and demonstrated excellent in vitro stability. Cell assays indicated that 18F-BoMPI exhibited mitochondria-targeting but potential-independent myocardial uptake. In vivo evaluation revealed the effective myocardial uptake and rapid background clearance. PET MPI confirmed effective probe accumulation in the healthy heart, but rapidly clearance in the background, making heart clearly delineated in the images. Ischemic myocardial could be clearly distinguished as the region of radioactivity sparsity in PET MPI.

CONCLUSION

The 18F-labeled probes showed great potentials to reduce the practicability threshold of PET MPI.

Phase I, first-in-human study of XTR004, a novel 18F-labeled tracer for myocardial perfusion PET: Biodistribution, radiation dosimetry, pharmacokinetics, and safety after a single injection at rest

OBJECTIVES

This study assessed the imaging characteristics, pharmacokinetics and safety of XTR004, a novel 18F-labeled Positron Emission Tomography (PET) myocardial perfusion imaging tracer, after a single injection at rest in humans.

METHODS

Eleven healthy subjects (eight men and three women) received intravenous XTR004 (239-290 megabecquerel [MBq]). Safety profiles were monitored on the dosing day and three follow-up visits. Multiple whole-body PET scans were conducted over 4.7 h to evaluate biodistribution and radiation dosimetry. Blood and urine samples collected for 7.25 h were metabolically corrected to characterize pharmacokinetics.

RESULTS

In the first 0-12 min PET images of ten subjects, liver (26.81 ± 4.01), kidney (11.43 ± 2.49), lung (6.75 ± 1.76), myocardium (4.72 ± 0.67) and spleen (3.1 ± 0.84) exhibited the highest percentage of the injected dose (%ID). Myocardial uptake of XTR004 in the myocardium initially reached 4.72 %ID and 7.06 g/mL, and negligibly changed within an hour (Δ: 7.20%, 5.95%). The metabolically corrected plasma peaked at 2.5 min (0.0013896 %ID/g) and halved at 45.2 min. Whole-body effective dose was 0.0165 millisievert (mSv)/MBq. Cumulative urine excretion was 8.18%. Treatment-related adverse events occurred in seven out of eleven subjects (63.6%), but no severe adverse event was reported.

CONCLUSIONS

XTR004 demonstrated a favorable safety profile, rapid, high, and stable myocardial uptake and excellent potential for PET myocardial perfusion imaging (MPI). Further exploration of XTR004 PET MPI for detecting myocardial ischemia is warranted.

PET-Based Imaging of Ischemic Heart Disease

PET-based cardiac nuclear imaging plays a large role in the management of ischemic heart disease. Compared with conventional single-photon emission CT myocardial perfusion imaging, PET provides superior accuracy in diagnosis of coronary artery disease and, with the incorporation of myocardial blood flow and coronary flow reserve, adds value in assessing prognosis for established coronary and microvascular disease. This review describes these and other uses of PET in ischemic heart disease, including assessing myocardial viability in ischemic cardiomyopathy. Developments in novel PET flow tracers and molecular imaging tools to assess atherosclerotic plaque vulnerability, vascular calcification, and vascular remodeling also are described.

Precision Medicine and PET/Computed Tomography in Cardiovascular Disorders

PET/computed tomography (CT) can evaluate the metabolic and anatomic involvement of a variety of inflammatory, infectious, and malignant cardiovascular disorders. PET/CT is useful in evaluating coronary vasculature, hibernating myocardium, cardiac sarcoidosis, cardiac amyloidosis, cerebrovascular disease, acute aortic syndromes, cardiac and vascular neoplasms, cardiac and vascular infections, and vasculitis. Novel targeted radiopharmaceutical agents and novel use of established techniques show promise in diagnosing and monitoring cardiovascular diseases.

Comparative evaluation of the algorithms for parametric mapping of the novel myocardial PET imaging agent 18F-FPTP

Objective

(¹⁸F-fluoropentyl)triphenylphosphonium salt (¹⁸F-FPTP) is a new promising myocardial PET imaging tracer. It shows high accumulation in cardiomyocytes and rapid clearance from liver. We performed compartmental analysis of ¹⁸F-FPTP PET images in rat and evaluated two linear analyses: linear least-squares (LLS) and a basis function method (BFM) for generating parametric images. The minimum dynamic scan duration for kinetic analysis was also investigated and computer simulation undertaken.

Methods

¹⁸F-FPTP dynamic PET (18 min) and CT images were acquired from rats with myocardial infarction (MI) (n = 12). Regions of interest (ROIs) were on the left ventricle, normal myocardium, and MI region. Two-compartment (K₁ and k₂; 2C2P) and three-compartment (K₁–k₃; 3C3P) models with irreversible uptake were compared for goodness-of-fit. Partial volume and spillover correction terms (V_a and α = 1 − V_a) were also incorporated. LLS and BFM were applied to ROI- and voxel-based kinetic parameter estimations. Results were compared with the standard ROI-based nonlinear least-squares (NLS) results of the corresponding compartment model. A simulation explored statistical properties of the estimation methods.

Results

The 2C2P model was most suitable for describing ¹⁸F-FPTP kinetics. Average K₁, k₂, and V_a values were, respectively, 6.8 (ml/min/g), 1.1 (min⁻¹), and 0.44 in normal myocardium and 1.4 (ml/min/g), 1.1 (min⁻¹), and 0.32, in MI tissue. Ten minutes of data was sufficient for the estimation. LLS and BFM estimations correlated well with NLS values for the ROI level (K₁: y = 1.06x + 0.13, r² = 0.96 and y = 1.13x + 0.08, r² = 0.97) and voxel level (K₁: y = 1.22x − 0.30, r² = 0.90 and y = 1.26x + 0.00, r² = 0.92). Regional distribution of kinetic parametric images (αK₁, K₁, k₂, V_a) was physiologically relevant. LLS and BFM showed more robust characteristics than NLS in the simulation.

Conclusions

Fast kinetics and highly specific uptake of ¹⁸F-FPTP by myocardium enabled quantitative analysis with the 2C2P model using only the initial 10 min of data. LLS and BFM were feasible for estimating voxel-wise parameters. These two methods will be useful for quantitative evaluation of ¹⁸F-FPTP distribution in myocardium and in further studies with different conditions, disease models, and species.

Electronic supplementary material

The online version of this article (doi:10.1007/s12149-017-1171-6) contains supplementary material, which is available to authorized users.

Research Progress on 18F-Labeled Agents for Imaging of Myocardial Perfusion with Positron Emission Tomography

Coronary artery disease (CAD) is the leading cause of death in the world. Myocardial perfusion imaging (MPI) plays a significant role in non-invasive diagnosis and prognosis of CAD. However, neither single-photon emission computed tomography nor positron emission tomography clinical MPI agents can absolutely satisfy the demands of clinical practice. In the past decades, tremendous developments happened in the field of ¹⁸F-labeled MPI tracers. This review summarizes the current state of ¹⁸F-labeled MPI tracers, basic research data of those tracers, and the future direction of MPI tracer research.

Synthesis and Evaluation of [(18) F]-Ammonium BODIPY Dyes as Potential Positron Emission Tomography Agents for Myocardial Perfusion Imaging

Recently, we demonstrated the potential of a [(18) F]-trimethylammonium BODIPY dye for cardiac imaging. This is the first example of the use of the [(18) F]-ammonium BODIPY dye for positron emission tomography (PET) myocardial perfusion imaging (MPI). In this report, we extend our study to other ammonium BODIPY dyes with different nitrogen substituents. These novel ammonium BODIPY dyes were successfully prepared and radiolabeled by the SnCl4 -assisted (18) F-(19) F isotopic exchange method. The microPET results and the biodistribution data reveal that nitrogen substituent changes have a significant effect on the in vivo and pharmacological properties of the tracers. Of the novel [(18) F]-ammonium BODIPY dyes prepared in this work, the [(18) F]-dimethylethylammonium BODIPY is superior in terms of myocardium uptake and PET imaging contrast. These results support our hypothesis that the ammonium BODIPY dyes have a great potential for use as PET/optical dual-modality MPI probes.