Rapid and simplified synthesis of [ 18 F]Fluoromisonidazole and its use in PET imaging in an experimental model of subarachnoid hemorrhage

Multimodal imaging of the role of hyperglycemia following experimental subarachnoid hemorrhage

Hyperglycemia has been linked to worsening outcomes after subarachnoid hemorrhage (SAH). Nevertheless, the mechanisms involved in the pathogenesis of SAH have been scarcely evaluated so far. The role of hyperglycemia was assessed in an experimental model of SAH by T2 weighted, dynamic contrast-enhanced magnetic resonance imaging (T2W and DCE-MRI), [18F]BR-351 PET imaging and immunohistochemistry. Measures included the volume of bleeding, the extent of cerebral infarction and brain edema, blood brain barrier disruption (BBBd), neutrophil infiltration and matrix metalloprotease (MMP) activation. The neurofunctional outcome, neurodegeneration and myelinization were also investigated. The induction of hyperglycemia increased mortality, the size of the ischemic lesion, brain edema, neurodegeneration and worsened neurological outcome during the first 3 days after SAH in rats. In addition, these results show for the first time the exacerbating effect of hyperglycemia on in vivo MMP activation, Intercellular Adhesion Molecule 1 (ICAM-1) expression and neutrophil infiltration together with increased BBBd, bleeding volume and fibrinogen accumulation at days 1 and 3 after SAH. Notably, these data provide valuable insight into the detrimental effect of hyperglycemia on early BBB damage mediated by neutrophil infiltration and MMP activation that could explain the worse prognosis in SAH.

Synthesis of [18F]FMISO, a hypoxia-specific imaging probe for PET, an overview from a radiochemist's perspective

BACKGROUND

[¹⁸F]fluoromisonidazole ([¹⁸F]FMISO, 1H-1-(3-[¹⁸F]fluoro-2-hydroxypropyl)-2-nitroimidazole) is a commonly used radiotracer for imaging hypoxic conditions in cells. Since hypoxia is prevalent in solid tumors, [¹⁸F]FMISO is in clinical application for decades to explore oxygen demand in cancer cells and the resulting impact on radiotherapy and chemotherapy.

RESULTS

Since the introduction of [¹⁸F]FMISO as positron emission tomography imaging agent in 1986, a variety of radiosynthesis procedures for the production of this hypoxia tracer has been developed. This paper gives a brief overview on [¹⁸F]FMISO radiosyntheses published so far from its introduction until now. From a radiopharmaceutical chemist's perspective, different precursors, radiolabeling approaches and purification methods are discussed as well as used automated radiosynthesizers, including cassette-based and microfluidic systems.

CONCLUSION

In a GMP compliant radiosynthesis using original cassettes for FASTlab we produced [¹⁸F]FMISO in 49% radiochemical yield within 48 min with radiochemical purities > 99% and molar activities > 500 GBq/µmol. In addition, we report an easy and efficient radiosynthesis of [¹⁸F]FMISO, based on in-house prepared FASTlab cassettes, providing the radiotracer for research and preclinical purposes in good radiochemical yields (39%), high radiochemical purities (> 99%) and high molar activity (> 500 GBq/µmol) in a well-priced option.

An improved one-pot preparation of [18 F]FMISO based on solid phase extraction purification: Pitfalls on the analytical method reported in the Ph.Eur.'s monograph

By adapting previously reported reaction conditions, [¹⁸ F]FMISO was synthesized using a TracerLab FX-FDG module in 31 min from no carrier added [¹⁸ F]fluoride in 56% radiochemical yield. A novel and simple purification setup based on disposable cartridges was developed allowing the radiopharmaceutical to be obtained in high radiochemical purity (>99.5%) and with chemical impurities far below the Ph.Eur.'s thresholds. Moreover, the study pinpointed some shortcomings of the high-performance liquid chromatography (HPLC) method reported in the dedicated Ph.Eur's monograph.

Effects of 18F-fluorinated neopentyl glycol side-chain on the biological characteristics of stilbene amyloid-β PET ligands

INTRODUCTION

The 2,2-dihydroxymethyl-1-[¹⁸F]fluoropropane group, also called ¹⁸F-labelled neopentyl glycol side-chain, is a novel ¹⁸F-labelling group for positron emission tomography (PET) imaging agents. The aim of using this group is to develop simple purification with solid-phase extraction without high-performance liquid chromatography. However, the effects of the neopentyl ¹⁸F-labelling group on the characteristics of brain imaging agents are unknown. Here, we added this side-chain to compounds with an aminostilbene structure to evaluate their effects on the biological properties of aminostilbene as an amyloid-β (Aβ) radioligand.

METHODS

Biodistributions of four novel ¹⁸F-labelled stilbene compounds with different lengths of polyethylene glycol (PEG) linkers, called [¹⁸F]Cpd-0, -1, -2, and -4, (PEG = 0, 1, 2, and 4), and [¹⁸F]AV-1 in normal mice were evaluated. Metabolite analysis of [¹⁸F]Cpd-0 and -1 was performed with mouse plasma and brain. A competitive binding assay of [¹⁸F]AV-1 binding to Aβ_1-42 fibrils was performed to determine the binding properties of the compounds.

RESULTS

[¹⁸F]Cpd-0, -1, and -2 demonstrated moderate initial brain uptake in mice (3.1-4.2% injected dose/g at 2 min post-injection) followed by fast clearance, and in vivo defluorination of these compounds was negligible. [¹⁸F]Cpd-4 exhibited low brain uptake and high bone uptake. Compared with [¹⁸F]Cpd-1, the percentage of [¹⁸F]Cpd-0 in mouse brain was high at 10 min post-injection. A competitive binding assay revealed partial interference effects by the neopentyl glycol side-chain on binding of stilbene compounds to Aβ_1-42 fibrils.

CONCLUSIONS

Aminostilbene compounds with two or fewer PEG linkers containing an ¹⁸F-labelled neopentyl glycol side-chain demonstrated preferable pharmacokinetic properties as a brain imaging radioligand in normal mice. These side-chains can be used as an alternative labelling group for imaging agents targeting the brain.

[18F]-FMISO PET/MRI Imaging Shows Ischemic Tissue around Hematoma in Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH), being the most severe cerebrovascular disease, accounts for 10-15% of all strokes. Hematoma expansion is one of the most important factors associated with poor outcome in intracerebral hemorrhage (ICH). Several studies have suggested that an "ischemic penumbra" might arise when the hematoma has a large expansion, but clinical studies are inconclusive. We performed a preclinical study to demonstrate the presence of hypoxic-ischemic tissue around the hematoma by means of longitudinal [¹⁸F]-fluoromisonidazole ([¹⁸F]-FMISO) PET/MRI studies over time in an experimental ICH model. Our results showed that all [¹⁸F]-FMISO PET/MRI images exhibited hypoxic-ischemic tissue around the hematoma area. A significant increase of [¹⁸F]-FMISO uptake was found at 18-24 h post-ICH when the maximum of hematoma volume is achieved and this increase disappeared before 42 h. These results demonstrate the presence of hypoxic tissue around the hematoma and open the possibility of new therapies aimed to reduce ischemic damage associated with ICH.