Aggregation of hyperphosphorylated tau is a major hallmark of many neurodegenerative diseases, including Alzheimer disease (AD). In vivo imaging with PET may offer important insights into pathophysiologic mechanisms, diagnosis, and disease progression. We describe different strategies for quantification of F-AV-1451 (T807) tau binding, including models with blood sampling and noninvasive alternatives. Fifteen subjects (4 controls, 6 AD, 3 progressive supranuclear palsy, 2 cortico basal syndrome) underwent 180-min PET with F-AV-1451 and arterial blood sampling. Modeling with arterial input functions included 1-, 2-, and 3-tissue-compartment models and the Logan plot. Using the cerebellum as reference region, we applied the simplified reference tissue model 2 and Logan reference plot. Finally, simplified outcome measures were calculated as ratio, with reference to cerebellar concentrations (SUV ratio [SUVR]) and SUVs. Tissue compartment models were not able to describe the kinetics of F-AV-1451, with poor fits in 33%-53% of cortical regions and 80% in subcortical areas. In contrast, the Logan plot showed excellent fits and parameter variance (total volume of distribution SE< 5%). Compared with the 180-min arterial-based Logan model, strong agreement was obtained for the Logan reference plot also for a reduced scan time of 100 min ( = 0.91) and SUVR 100-120 min ( = 0.94), with 80-100 min already representing a reasonable compromise between duration and accuracy ( = 0.93). Time-activity curves and kinetic parameters were equal for cortical regions and the cerebellum in control subjects but different in the putamen. Cerebellar total volumes of distribution were higher in controls than patients. For these methods, increased cortical binding was observed for AD patients and to some extent for cortico basal syndrome, but not progressive supranuclear palsy. The Logan plot provided the best estimate of tau binding using arterial input functions. Assuming that the cerebellum is a valid reference region, simplified methods seem to provide robust alternatives for quantification, such as the Logan reference plot with 100-min scan time. Furthermore, SUVRs between target and cerebellar activities obtained from an 80- to 100-min static scan offer promising potential for clinical routine application.

Aliphatic nucleophilic substitution (S N 2) with [ 18 F]fluoride is the most widely applied method to prepare 18 F-labeled positron emission tomography (PET) tracers. Strong basic conditions commonly used during 18 F-labeling procedures inherently limit or prohibit labeling of base-sensitive scaffolds. The high basicity stems from the tradition to trap [ 18 F]fluoride on anion exchange cartridges and elute it afterward with basic anions. This sequence is used to facilitate the transfer of [ 18 F]fluoride from an aqueous to an aprotic organic, polar reaction medium, which is beneficial for S N 2 reactions. Furthermore, this sequence also removes cationic radioactive contaminations from cyclotron-irradiated [ 18 O]water from which [ 18 F]fluoride is produced. In this study, we developed an efficient elution procedure resulting in low basicity that permits S N 2 18 F-labeling of base-sensitive scaffolds. Extensive screening of trapping and elution conditions (>1000 experiments) and studying their influence on the radiochemical yield (RCY) allowed us to identify a suitable procedure for this. Using this procedure, four PET tracers and three synthons could be radiolabeled in substantially higher RCYs (up to 2.5-fold) compared to those of previously published procedures, even from lower precursor amounts. Encouraged by these results, we applied our low-basicity method to the radiolabeling of highly base-sensitive tetrazines, which cannot be labeled using state-of-art direct aliphatic 18 F-labeling procedures. Labeling succeeded in RCYs of up to 20%. We believe that our findings facilitate PET tracer development by opening the path toward simple and direct S N 2 18 F fluorination of base-sensitive substrates.

This work studied self-reports from adolescents on how the COVID-19 pandemic has changed their behaviors, relationships, mood, and victimization. Data collection was conducted between September 2020 and February 2021 in five countries (Sweden, the USA, Serbia, Morocco, and Vietnam). In total, 5114 high school students (aged 15 to 19 years, 61.8% females) responded to our electronic survey. A substantial proportion of students reported decreased time being outside (41.7%), meeting friends in real life (59.4%), and school performance (30.7%), while reporting increased time to do things they did not have time for before (49.3%) and using social media to stay connected (44.9%). One third of the adolescents increased exercise and felt that they have more control over their life. Only a small proportion of adolescents reported substance use, norm-breaking behaviors, or victimization. The overall COVID-19 impact on adolescent life was gender-specific: we found a stronger negative impact on female students. The results indicated that the majority of adolescents could adapt to the dramatic changes in their environment. However, healthcare institutions, municipalities, schools, and social services could benefit from the findings of this study in their work to meet the needs of those young people who signaled worsened psychosocial functioning, increased stress, and victimization.

Activated factor VII blocked in the active site with Phe-Phe-Arg-chloromethyl ketone (active site inhibited factor VII (ASIS)) is a 50-kDa protein that binds with high affinity to its receptor, tissue factor (TF). TF is a transmembrane glycoprotein that plays an important role in, for example, thrombosis, metastasis, tumor growth, and tumor angiogenesis. The aim of this study was to develop an (18)F-labeled ASIS derivative to assess TF expression in tumors. Active site inhibited factor VII was labeled using N-succinimidyl-4-[(18)F]fluorobenzoate, and the [(18)F]ASIS was purified on a PD-10 desalting column. The radiochemical yield was 25 ± 6%, the radiochemical purity was >97%, and the pseudospecific radioactivity was 35 ± 9 GBq/µmol. The binding efficacy was evaluated in pull-down experiments, which monitored the binding of unlabeled ASIS and [(18)F]ASIS to TF and to a specific anti-factor VII antibody (F1A2-mAb). No significant difference in binding efficacy between [(18)F]ASIS and ASIS could be detected. Furthermore, [(18)F]ASIS was relatively stable in vitro and in vivo in mice. In conclusion, [(18)F]ASIS has for the first time been successfully synthesized as a possible positron emission tomography tracer to image TF expression levels. In vivo positron emission tomography studies to evaluate the full potential of [(18)F]ASIS are in progress.