Increased Vesicular Monoamine Transporter 2 (VMAT2) and Dopamine Transporter (DAT) Expression in Adolescent Brain Development: A Longitudinal Micro-PET/CT Study in Rodent

Preclinical evaluation and pilot clinical study of [68Ga]Ga-NOTA-H006 for non-invasive PET imaging of 5T4 oncofetal antigen

PURPOSE

Trophoblast glycoprotein, the so-called 5T4, is an oncofetal antigen expressed in many different cancers. However, no 5T4-specific radioligand is employed in the clinic for non-invasive diagnosis. Thus, the aim of the current study was to develop a PET radiotracer for imaging 5T4 expression in preclinical and clinical stages.

METHODS

A VHH library was constructed by camel immunization. The specificity of the VHHs toward 5T4 antigen was screened through phage display biopanning and periplasmic extract enzyme-linked immunosorbent assay. 1,4,7-Triazacyclononane-1,4,7-triacetate acid (NOTA) derivative was conjugated to the selected VHH. After radiolabeling, microPET/CT and ex vivo biodistribution were conducted using BxPC-3 and MDA-MB-468 tumor-bearing mice. Cold VHH was co-injected with the tracer to challenge its binding in vivo. For the pilot clinical study, PET/CT images were acquired at 1 h after injection of tracer in patients with pathologically confirmed primary and metastatic tumors.

RESULTS

A library with a capacity of 1.2 × 1012 colony-forming units was constructed after successful camel immunization. Nb1-40 with a median effect concentration of 0.43 nM was selected. After humanization, the resulting H006 maintained a high affinity towards 5T4. [68Ga]Ga-NOTA-H006 with the molar activities of 6.48-54.2 GBq/µmol was prepared with high radiochemical purity (> 98%). Using [68Ga]Ga-NOTA-H006, microPET/CT revealed a clear visualization of 5T4 expression in BxPC-3 tumor-bearing mice. Ex vivo biodistribution showed that the highest tumor-to-blood ratio (∼ 3-fold) and tumor-to-muscle ratio (∼ 5-fold) were achieved at 60 min post-injection. Co-injection of the cold H006 at a dose of 1.5 mg/kg significantly reduced the tumor uptake (p < 0.0001). In the pilot clinical study, [68Ga]Ga-NOTA-H006 demonstrated its capacity to map 5T4-positive lesions in humans and yielded a mean effective dose of 3.4 × 10- 2 mSv/MBq.

CONCLUSIONS

[68Ga]Ga-NOTA-H006, which can visualize 5T4 expression in vivo, has been successfully developed. This opens up opportunities for non-invasively studying 5T4 expression through nuclear medicine. Further clinical investigations are warranted to explore its clinical value in disease progression and companion diagnosis.

Radiosynthesis and preclinical evaluations of [18F]AlF-RESCA-5F7 as a novel molecular probe for HER2 tumor imaging

HER2 overexpression is associated with various tumor types and prompted the development of targeted therapies. Previously, iso-[211At]SGMAB-5F7 was developed as a HER2-targeted alpha therapy agent, demonstrating promising therapeutic efficacy in the preclinical stage. Aiming for an 18F-labeled tracer for companion diagnostics in clinical translation, we employed the Al18F-RESCA strategy in our current work and investigated whether [18F]AlF-RESCA-5F7 could visualize HER2 expression in vivo. [18F]AlF-RESCA-5F7 was attained with high radiochemical purity (> 99%) and molar activity in the range of 16.5 ± 8.8 GBq/μmol (n = 8). Compared to previously reported radiotracers that contained 5F7 as the HER2-targeting carrier and fluorine-18 as the positron-emitting isotope, the radiosynthesis was simplified to one single step within 30 min. The dissociation constant of [18F]AlF-RESCA-5F7 was determined as 3.3 nM via saturation binding assay using SKOV3 ovarian carcinoma cells. Tumor uptake of the novel tracer in Balb/c nude mice bearing SKOV3 xenografts was 4.69 ± 1.51, 3.34 ± 0.82 and 3.77 ± 0.99 %ID/g at 1, 2, and 4 h post-injection. Even though high retention of radioactivity was seen in the kidneys, micro-PET/CT imaging of [18F]AlF-RESCA-5F7 delineated the tumor up to 4 h post-injection with minimal activity in the gallbladder, intestines, and bone. This study suggests that [18F]AlF-RESCA-5F7 is a promising HER2 PET radiotracer with an eased radiolabeling method. Whether [18F]AlF-RESCA-5F7 could work as a companion diagnostic agent to assist in patient stratification and treatment monitoring of iso-[211At]SGMAB-5F7 warrants further investigation.

A review of the neurotransmitter system associated with cognitive function of the cerebellum in Parkinson's disease

The dichotomized brain system is a concept that was generalized from the 'dual syndrome hypothesis' to explain the heterogeneity of cognitive impairment, in which anterior and posterior brain systems are independent but partially overlap. The dopaminergic system acts on the anterior brain and is responsible for executive function, working memory, and planning. In contrast, the cholinergic system acts on the posterior brain and is responsible for semantic fluency and visuospatial function. Evidence from dopaminergic/cholinergic imaging or functional neuroimaging has shed significant insight relating to the involvement of the cerebellum in the cognitive process of patients with Parkinson's disease. Previous research has reported evidence that the cerebellum receives both dopaminergic and cholinergic projections. However, whether these two neurotransmitter systems are associated with cognitive function has yet to be fully elucidated. Furthermore, the precise role of the cerebellum in patients with Parkinson's disease and cognitive impairment remains unclear. Therefore, in this review, we summarize the cerebellar dopaminergic and cholinergic projections and their relationships with cognition, as reported by previous studies, and investigated the role of the cerebellum in patients with Parkinson's disease and cognitive impairment, as determined by functional neuroimaging. Our findings will help us to understand the role of the cerebellum in the mechanisms underlying cognitive impairment in Parkinson's disease.

Resting-State Functional MRI and PET Imaging as Noninvasive Tools to Study (Ab)Normal Neurodevelopment in Humans and Rodents

Neurodevelopmental disorders (NDDs) are a group of complex neurologic and psychiatric disorders. Functional and molecular imaging techniques, such as resting-state functional magnetic resonance imaging (rs-fMRI) and positron emission tomography (PET), can be used to measure network activity noninvasively and longitudinally during maturation in both humans and rodent models. Here, we review the current knowledge on rs-fMRI and PET biomarkers in the study of normal and abnormal neurodevelopment, including intellectual disability (ID; with/without epilepsy), autism spectrum disorder (ASD), and attention deficit hyperactivity disorder (ADHD), in humans and rodent models from birth until adulthood, and evaluate the cross-species translational value of the imaging biomarkers. To date, only a few isolated studies have used rs-fMRI or PET to study (abnormal) neurodevelopment in rodents during infancy, the critical period of neurodevelopment. Further work to explore the feasibility of performing functional imaging studies in infant rodent models is essential, as rs-fMRI and PET imaging in transgenic rodent models of NDDs are powerful techniques for studying disease pathogenesis, developing noninvasive preclinical imaging biomarkers of neurodevelopmental dysfunction, and evaluating treatment-response in disease-specific models.

Brain glucose metabolism and dopamine transporter changes in rats with morphine-induced conditioned place preference

Addiction to morphine is a chronic brain disease leading to compulsive abuse. Drug addiction animal models with and without conditioned place preference (CPP) training have been used to investigate cue-elicited drug craving. We used ¹⁸ F-fluorodeoxyglucose (¹⁸ F-FDG) and ¹¹ C-2-β-carbomethoxy-3-β-(4-fluorophenyl)tropane (¹¹ C-CFT) micro-PET/CT scans to examine the regional changes in brain glucose metabolism and dopamine transporter (DAT) availability to study their relationship underlying drug memory in morphine-treated rat models with and without CPP. Standardized uptake value ratio (SUVr) of ¹⁸ F-FDG significantly decreased in the medial prefrontal cortex (mPFC) and cingulate with short-term morphine administration compared with the baseline condition. Voxelwise analysis indicated glucose metabolism alterations in the somatosensory cortex, hippocampus and cingulate in morphine-treated rats and in the striatum, thalamus, medial prefrontal cortex, primary motor cortex and many regions in the cortex in the CPP group compared with the baseline condition. Alterative glucose metabolism was also observed in the striatum, primary somatosensory cortex and some cortical regions in the CPP group compared with morphine alone group. DAT expression alterations were only observed in the long-term morphine compared with the short-term morphine group. This study shows that cerebral glucose metabolism significantly altered during morphine administration and CPP process mainly in the mPFC, striatum and hippocampus, which indicates that the function of these brain regions is involved in cue-induced craving and memory retrieval.

Experimental and Clinical Biomarkers for Progressive Evaluation of Neuropathology and Therapeutic Interventions for Acute and Chronic Neurological Disorders

This article describes commonly used experimental and clinical biomarkers of neuronal injury and neurodegeneration for the evaluation of neuropathology and monitoring of therapeutic interventions. Biomarkers are vital for diagnostics of brain disease and therapeutic monitoring. A biomarker can be objectively measured and evaluated as a proxy indicator for the pathophysiological process or response to therapeutic interventions. There are complex hurdles in understanding the molecular pathophysiology of neurological disorders and the ability to diagnose them at initial stages. Novel biomarkers for neurological diseases may surpass these issues, especially for early identification of disease risk. Validated biomarkers can measure the severity and progression of both acute neuronal injury and chronic neurological diseases such as epilepsy, migraine, Alzheimer's disease, Parkinson's disease, Huntington's disease, traumatic brain injury, amyotrophic lateral sclerosis, multiple sclerosis, and other brain diseases. Biomarkers are deployed to study progression and response to treatment, including noninvasive imaging tools for both acute and chronic brain conditions. Neuronal biomarkers are classified into four core subtypes: blood-based, immunohistochemical-based, neuroimaging-based, and electrophysiological biomarkers. Neuronal conditions have progressive stages, such as acute injury, inflammation, neurodegeneration, and neurogenesis, which can serve as indices of pathological status. Biomarkers are critical for the targeted identification of specific molecules, cells, tissues, or proteins that dramatically alter throughout the progression of brain conditions. There has been tremendous progress with biomarkers in acute conditions and chronic diseases affecting the central nervous system.

Alteration of neuroinflammation detected by 18F-GE180 PET imaging in place-conditioned rats with morphine withdrawal

BACKGROUND

Accumulating evidence indicates that neuroinflammation (NI) significantly contributes to drug addiction, but the conversion of NI after drug withdrawal is not clear. Here, we conducted ¹⁸F-flutriciclamide (GE180) positron emission tomography (PET) imaging to investigate the conversion of NI during drug withdrawal and conditioning-induced aversion by measuring the change in microglial activation with ¹⁸F-GE180.

METHODS

Twelve male adult Sprague-Dawley rats were subjected to morphine withdrawal by the administration of naloxone, and six of them were used to model conditioned place aversion (CPA). ¹⁸F-GE180 PET imaging was performed for 11 rats on the last day of the morphine treatment phase and for 10 rats on the response assessment phase of the behavior conditioning procedure. A ¹⁸F-GE180 template was established for spatial normalization of each individual image, and the differential ¹⁸F-GE180 uptakes between the drug withdrawal (DW) group and the drug addiction (DA) group, the CPA group and the DA group, and the CPA group and the DW group were compared by a voxel-wise two-sample t test using SPM8.

RESULTS

Both the DW group and the CPA group spent less time in the conditioning cage during the post-test phase compared with the pretest phase, but only the difference in the CPA group was significant (63.2 ± 34.6 vs. - 159.53 ± 22.02, P < 0.005). Compared with the DA group, the uptake of ¹⁸F-GE180 increased mainly in the hippocampus, visual cortex, thalamus and midbrain regions and decreased mainly in the sensory-related cortices after the administration of naloxone in both the DW and CPA groups. Increased ¹⁸F-GE180 uptake was only observed in the mesolimbic regions after conditioned aversion compared with the DW group.

CONCLUSION

In morphine-dependent rats, Neuroinflammation (NI) became more severe in the addiction-involved brain regions but remitted in the sensory-related brain regions after the administration of naloxone, and this NI induced by withdrawal was further aggravated after conditioned aversion formation thus may help to consolidate the withdrawal memory.

[18F]PBR146 and [18F]DPA-714 in vivo Imaging of Neuroinflammation in Chronic Hepatic Encephalopathy Rats

Neuroinflammation is an important pathogenesis of hepatic encephalopathy (HE). The upregulation of translocator protein (TSPO) during neuroinflammation provides an imaging molecular target to evaluate the severity of neuroinflammation in chronic HE rats. [18F]DPA-714 and [18F]PBR146 targeting TSPO are often used for neuroinflammation imaging. This study performed bile duct ligation (BDL) in rats to simulate chronic HE model, tested the behavioral experiments, and conducted [18F]PBR146 and [18F]DPA-714 micro-PET/CT scans followed analyzing the average %ID/g values of the whole brain, brain regions and main organs of subjects. After sacrifice the rats, the blood plasma samples were taken for blood biochemical indexes and plasma inflammatory factor levels examination, the liver and brain specimens were obtained for pathological analysis. The BDL rats showed chronic liver failure with defects in cognition, motor coordination ability and mental state. [18F]PBR146 and [18F]DPA-714 micro-PET/CT imaging results were similar in whole brain of BDL group and Sham group. Besides, some regional brain areas in BDL rats were found abnormal uptakes mainly located in basal ganglia area, auditory cortex, motor cortex, cingulate gyrus, somatosensory cortex, hippocampus, thalamus, midbrain, and medulla oblongata, and these regions also correlated with behavioral alterations. In conclusion, both [18F]PBR146 and [18F]DPA-714 had the similar imaging effects in hepatic encephalopathy models could quantitatively evaluate neuroinflammation load and distribution. The difference brain regions with higher uptake values of radiotracers in BDL rats were correlated with behavioral alterations.

The Cerebellar Dopaminergic System

In the central nervous system (CNS), dopamine (DA) is involved in motor and cognitive functions. Although the cerebellum is not been considered an elective dopaminergic region, studies attributed to it a critical role in dopamine deficit-related neurological and psychiatric disorders [e.g., Parkinson's disease (PD) and schizophrenia (SCZ)]. Data on the cerebellar dopaminergic neuronal system are still lacking. Nevertheless, biochemical studies detected in the mammalians cerebellum high dopamine levels, while chemical neuroanatomy studies revealed the presence of midbrain dopaminergic afferents to the cerebellum as well as wide distribution of the dopaminergic receptor subtypes (DRD1-DRD5). The present review summarizes the data on the cerebellar dopaminergic system including its involvement in associative and projective circuits. Furthermore, this study also briefly discusses the role of the cerebellar dopaminergic system in some neurologic and psychiatric disorders and suggests its potential involvement as a target in pharmacologic and non-pharmacologic treatments.

Supplemental taurine during adolescence and early adulthood has sex-specific effects on cognition, behavior and neurotransmitter levels in C57BL/6J mice dependent on exposure window

The mammalian brain goes through final maturation during late adolescence and early adulthood with sex differences in timing. The key cellular processes, including changes in neurotransmitter receptor density and synaptic pruning, make this age uniquely vulnerable to neurotoxic insults. Teenagers and young adults are the major consumers of energy drinks, which contain high levels of taurine and caffeine. Taurine is one of the most abundant amino acids in the central nervous system, but the effects of supplemental taurine consumption during adolescence has not been well studied. We conducted an initial short-term exposure study with 0.12% taurine in drinking water and a long-term exposure dose-response study using 0.06 and 0.12% taurine in male and female C57BL/6J mice. We examined a broad range of cognitive functions and behaviors and measured neurotransmitter levels. We found no significant differences in anxiety, open field locomotor activity, or sensorimotor gating. However, we found impairments in novel object recognition and sex differences in Morris water maze. When taurine treatment stopped before behavioral experiments began, male mice had significant impairments in spatial learning and memory. In the dose-response study when taurine treatment continued throughout behavioral experiments, females had significant impairments. We also found sex differences in neurotransmitter levels with females having higher levels of glutamate, DOPAC and 5-HIAA. We conclude that both females and males are at risk from excess taurine consumption during final brain maturation.