[In vivo imaging of Alzheimer's disease lesion]

In the development of Alzheimer's disease (AD) therapeutics, positron emission tomography (PET) imaging techniques play an important role in the selection of patients for administration and objective evaluation of treatment effects. The clinical implementation of amyloid-β (Aβ) and tau PET agents is progressing, with the aim of noninvasively visualizing brain lesions in AD. Furthermore, the development of PET agents for imaging neuroinflammation is advancing. Near-infrared fluorescence (NIRF) imaging has attracted attention as an alternative technology to nuclear imaging. Near-infrared light in the wavelength range of 650-900 nm, known as the optical window, is absorbed less by living tissue compared to visible light. Therefore, by using probes that emit NIRF, it is possible to noninvasively measure the distribution of probes within the body. Indocyanine green (ICG), a non-specific NIRF probe, is already being used in surgical procedures, but NIRF probes specifically for AD lesions are still in the developmental stage. The characteristics required for NIRF Aβ probe include high binding affinity and selectivity for Aβ, excitation and fluorescence wavelengths in the optical window, and blood-brain barrier permeability. Numerous NIRF probes for Aβ have been developed, reaching levels suitable for use in animal experiments. In recent years, research has also progressed on the development of multi-target fluorescence imaging probes that can identify multiple targets with a single probe by utilizing differences in fluorescence wavelengths according to the binding targets.