On the Viability of Tadalafil-Based 18F-Radiotracers for In Vivo Phosphodiesterase 5 (PDE5) PET Imaging

Development and Initial Characterization of the First 18F-CXCR2-Targeting Radiotracer for PET Imaging of Neutrophils

The interleukin-8 receptor beta (CXCR2) is a highly promising target for molecular imaging of inflammation and inflammatory diseases. This is due to its almost exclusive expression on neutrophils. Modified fluorinated ligands were designed based on a squaramide template, with different modification sites and synthetic strategies explored. Promising candidates were then tested for affinity to CXCR2 in a NanoBRET competition assay, resulting in tracer candidate 16b. As direct 18F-labeling using established tosyl chemistry did not yield the expected radiotracer, an indirect labeling approach was developed. The radiotracer [18F]16b was obtained with a radiochemical yield of 15% using tert-butyl (S)-3-(tosyloxy)pyrrolidine carboxylate and a pentafluorophenol ester. The subsequent time-dependent uptake of [18F]16b in CXCR2-negative and CXCR2-overexpressing human embryonic kidney cells confirmed the radiotracer's specificity. Further studies with human neutrophils revealed its diagnostic potential for functional imaging of neutrophils.

The action of phosphodiesterase-5 inhibitors on β-amyloid pathology and cognition in experimental Alzheimer's disease: A systematic review

Alzheimer's disease (AD) is the most frequent cause of dementia worldwide. The etiology of AD is partially explained by the deposition of β-amyloid in the brain. Despite extensive research on the pathogenesis of AD, the current treatments are ineffective. Here, we systematically reviewed studies that investigated whether phosphodiesterase 5 inhibitors (PDE5i) are efficient in reducing the β-amyloid load in hippocampi and improving cognitive decline in rodent models with β-amyloid accumulation. We identified ten original studies, which used rodent models with β-amyloid accumulation, were treated with PDE5i, and β-amyloid was measured in the hippocampi. PDE5i was efficient in reducing the β-amyloid levels, except for one study that exclusively used female rodents and the treatment did not affect β-amyloid levels. Interestingly, PDE5i prevented cognitive decline in all studies. This study supports the potential therapeutic use of PDE5i for the reduction of the β-amyloid load in hippocampi and cognitive decline. However, we highlight the importance of conducting additional experimental studies to evaluate the PDE5i-related molecular mechanisms involved in β-amyloid removal in male and female animals.