Investigation of a Potential Scintigraphic Tracer for Imaging Apoptosis: Radioiodinated Annexin V-Kunitz Protease Inhibitor Fusion Protein

Radiolabeled annexin V (ANV) has been widely used for imaging cell apoptosis. Recently, a novel ANV-Kunitz-type protease inhibitor fusion protein, ANV-6L15, was found to be a promising probe for improved apoptosis detection based on its higher affinity to phosphatidylserine (PS) compared to native ANV. The present paper investigates the feasibility of apoptosis detection using radioiodinated ANV-6L15. Native ANV and ANV-6L15 were labeled with iodine-123 and iodine-125 using Iodogen method. The binding between the radioiodinated proteins and erythrocyte ghosts or chemical-induced apoptotic cells was examined. ANV-6L15 can be radioiodinated with high yield (40%−60%) and excellent radiochemical purity (>95%). 123I-ANV-6L15 exhibited a higher binding ratio to erythrocyte ghosts and apoptotic cells compared to 123I-ANV. The biodistribution of 123I-ANV-6L15 in mice was also characterized. 123I-ANV-6L15 was rapidly cleared from the blood. High uptake in the liver and the kidneys may limit the evaluation of apoptosis in abdominal regions. Our data suggest that radiolabled ANV-6L15 may be a better scintigraphic tracer than native ANV for apoptosis detection

Synthesis, characterization and structure-activity relationships of gallium, indium, and copper-labeled radio-pharmaceuticals for myocardial imaging with PET

The development of radiopharmaceuticals labeled with positron-emitting \sp{68}Ga, obtained from a long-lived \sp{68}Ge/\sp{68}Ga generator system, could facilitate more widespread use of positron emission tomography (PET) in diagnostic imaging. Monocationic gallium complexes with hexadentate bis(salicylaldimine) ligands derived from N,N\sp\prime-bis(3-aminopropyl)ethylenediamine (BAPEN) have been found to provide the desired myocardial uptake and retention of radiotracers in animal models. Attempts to improve the myocardial uptake and heart-to-background ratios have been undertaken with studies on 22 gallium complexes structurally related to the reported lead compound, Ga(III) (bis(4,6-MeO\sb2sal)BAPEN) \sp+. By screening in the rat model, the results indicate: (1) ligand modification by introducing methyl groups into the propylene fragment of the BAPEN backbone significantly improves the biological properties of radiotracers; (2) the lipophilicity increases produced by introducing long-chain substituents onto the aromatic rings fail to improve the biological behavior of these tracers; and (3) 3-MeO-substitution of the aromatic rings consistently results in tracers that exhibit superior heart-to-background ratios relative to other aromatic ring modifications. These results led to intensive studies of new hexadentate Schiff-base ligands derived from alkyl-derivatized linear tetraamines. By converting the central secondary amines to N-methyl-substituted tertiary amines and combining the 3-MeO aromatic ring substitution, the resulting \sp{67}Ga (bis(3-MeOsal)-N,N\sp\prime-DMBAPEN) \sp+ complex was found to afford the best myocardial uptake seen with this class of compounds along with superb heart-to-liver ratios in the rat model. A series of seven cationic \sp{111}In complexes with hexadentate bis(salicylaldimine) ligands were also prepared and screened in the rat model. Like their \sp{67}Ga analogs, these \sp{111}In complexes were found to consistently afford significant myocardial uptake and retention of tracer following intravenous injection. A novel dithiadioxime complex of copper(II), chloro (3,3\sp\prime -(1,3-propanedithia)bis(3-methyl-2-butanone oximato)(1-)- (S,S\sp\prime,N,N\sp\prime) copper(II) monohydrate, was also prepared, characterized by X-ray crystallography, and radiolabeled with \sp{67}Cu. The \sp{67}Cu-dithiadioxime complex is stable in ethanol solution but appears to decompose upon dilution with normal saline

Pharmacodynamic Analysis of Magnetic Resonance Imaging-Monitored Focused Ultrasound-Induced Blood-Brain Barrier Opening for Drug Delivery to Brain Tumors

Microbubble-enhanced focused ultrasound (FUS) can enhance the delivery of therapeutic agents into the brain for brain tumor treatment. The purpose of this study was to investigate the influence of brain tumor conditions on the distribution and dynamics of small molecule leakage into targeted regions of the brain after FUS-BBB opening. A total of 34 animals were used, and the process was monitored by 7T-MRI. Evans blue (EB) dye as well as Gd-DTPA served as small molecule substitutes for evaluation of drug behavior. EB was quantified spectrophotometrically. Spin-spin (R1) relaxometry and area under curve (AUC) were measured by MRI to quantify Gd-DTPA. We found that FUS-BBB opening provided a more significant increase in permeability with small tumors. In contrast, accumulation was much higher in large tumors, independent of FUS. The AUC values of Gd-DTPA were well correlated with EB delivery, suggesting that Gd-DTPA was a good indicator of total small-molecule accumulation in the target region. The peripheral regions of large tumors exhibited similar dynamics of small-molecule leakage after FUS-BBB opening as small tumors, suggesting that FUS-BBB opening may have the most significant permeability-enhancing effect on tumor peripheral. This study provides useful information toward designing an optimized FUS-BBB opening strategy to deliver small-molecule therapeutic agents into brain tumors

Brain Imaging of Vesicular Monoamine Transporter Type 2 in Healthy Aging Subjects by ¹⁸F-FP-(+)-DTBZ PET

<div><p></p><p>¹⁸F-FP-(+)-DTBZ is a novel PET radiotracer targeting vesicular monoamine transporter type 2 (VMAT2). The goal was to explore the image features in normal human brains with ¹⁸F-FP-(+)-DTBZ as a reference of molecular landmark for clinical diagnosis in Parkinson's disease (PD) and related disorders.</p><p>Materials and Methods</p><p>A total of 22 healthy subjects (59.3±6.0 years old) including 7 men and 15 women were recruited for MRI and ¹⁸F-FP-(+)-DTBZ PET scans. A total number of 55 brain VOIs were selected for quantitation analysis. The regional specific uptake ratio (SUR) was calculated with occipital as reference from MRI-based spatially normalized ¹⁸F-FP-(+)-DTBZ images. Regional percentage SUR to that of anterior putamen was calculated. Average SUR images were displayed in 2D and 3D space to illustrate the image patterns. The correlation between age and regional VMAT2 uptake was also examined.</p><p>Results</p><p>Visual assessment showed symmetric uptake of ¹⁸F-FP-(+)-DTBZ and obviously highest in striatum, followed by nucleus accumbens, hypothalamus, substantia nigra, and raphe nuclei. Quantification analysis revealed striatal VMAT2 density of anterior putamen>posterior putamen>caudate nucleus. Other subcortical regions were with moderate VMAT2 distribution (6∼51% SUR of anterior putamen), while slightly lower VMAT2 was observed in cerebellum (10.60% SUR) and much lower in neocortex (<5% SUR). No significant correlation of SUR to age was found in subcortical regions.</p><p>Conclusion</p><p>Using ¹⁸F-FP-(+)-DTBZ PET, we showed the 2D and 3D imaging features of the VMAT2 distribution <i>in vivo</i> in healthy aging brains. The <i>in vivo</i> imaging characteristics of VMAT2 is consistent with the expression of VMAT2 in a recent autopsy study. Therefore, 3D visualization and higher image quality of ¹⁸F-FP-(+)-DTBZ PET imaging might potentially be a powerful biomarker in detecting VMAT2 distribution of subcortical regions, and for Parkinson's disease and related neuropsychiatric disorders involving related monoaminergic systems.</p></div