Chih-Kai Chao , Joseph Blecha , Ilona Polvoy , Ryan Michael Nillo , Youngho Seo , David M. Wilson , John R. Forsayeth , Henry F. VanBrocklin , John M. Gerdes
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引用次数: 0
Abstract
Objective and background
The objective of this first-in-human study was to investigate the radiosynthesis, and the preliminary safety, biodistribution, and organ radiation dosimetry of the positron emission tomography (PET) imaging tracer methyl N4-([18F]7-fluoro-9H-fluoren-2-yl)asparaginate, known as [18F]RP-115, in a small cohort (n=8) of healthy volunteers. The [18F]RP-115 tracer is a methyl ester prodrug and undergoes metabolic saponification in the central nervous system to generate the corresponding carboxylic acid form that selectively binds to the excitatory amino acid transporter 2 (EAAT2) protein.
Procedures and methods
A multi-step high molar activity tracer radiosynthesis was devised to produce doses. Eight healthy human participants (four male and four female), aged 56–75, received a bolus intravenous injection of [18F]RP-115 (administered activity range: 70.3–355 MBq) prior to a total of 94 min of PET-MR scanning performed as three sequential scanning sessions. Regional tissue volumes of interest were defined, time-integrated activity coefficients (TIAC) were derived, and then estimates of organ and tissue activities and effective doses (whole body) were calculated, with two versions of OLINDA software (1.1 and 2.0) that incorporated two tissue weighting factor sets (ICRP-60 and -103), respectively.
Main findings
Tracer was routinely produced in good radiochemical yields and as suitable high molar activity doses for injection. The [18F]RP-115 injections and PET-MR scans were well-tolerated and no adverse events were reported (≤48 h). Radioactivity was widely biodistributed with good organ uptake. TIACs and estimated radiation organ doses were determined, for which a few statistically significant estimated organ dose differences between males and females were noted. The kidneys were identified as the critical target organ.
Principal conclusions
Injection of [18F]RP-115 was considered safe. The estimated kidney radiation doses relative to administered radioactivity identified a more optimal human [18F]RP-115 tracer injected amount of <211 MBq. This more optimal [18F]RP-115 tracer injected activity definition is similar to the amounts used for other established [18F]labeled clinical PET tracers such as [18F]FDG, and it will be used in future RP-115 clinical PET imaging studies.
期刊介绍：
Nuclear Medicine and Biology publishes original research addressing all aspects of radiopharmaceutical science: synthesis, in vitro and ex vivo studies, in vivo biodistribution by dissection or imaging, radiopharmacology, radiopharmacy, and translational clinical studies of new targeted radiotracers. The importance of the target to an unmet clinical need should be the first consideration. If the synthesis of a new radiopharmaceutical is submitted without in vitro or in vivo data, then the uniqueness of the chemistry must be emphasized.
These multidisciplinary studies should validate the mechanism of localization whether the probe is based on binding to a receptor, enzyme, tumor antigen, or another well-defined target. The studies should be aimed at evaluating how the chemical and radiopharmaceutical properties affect pharmacokinetics, pharmacodynamics, or therapeutic efficacy. Ideally, the study would address the sensitivity of the probe to changes in disease or treatment, although studies validating mechanism alone are acceptable. Radiopharmacy practice, addressing the issues of preparation, automation, quality control, dispensing, and regulations applicable to qualification and administration of radiopharmaceuticals to humans, is an important aspect of the developmental process, but only if the study has a significant impact on the field.
Contributions on the subject of therapeutic radiopharmaceuticals also are appropriate provided that the specificity of labeled compound localization and therapeutic effect have been addressed.
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