[Development of Molecular Probes for Live Imaging of Cancer and Infectious Diseases]

Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are powerful molecular imaging methods for examining disease-related factors in the whole body using specific imaging probes. Recently, we tried to develop molecular imaging probes that specifically visualize pathological factors associated with cancers and infectious diseases. Although survivin is highly expressed in several cancers, its expression is undetectable in non-dividing tissues. Thus, we developed several small molecular imaging probes that target survivin. These ligands not only showed high affinity for survivin protein, but also showed consistent cellular accumulation with respect to survivin expression levels, thereby indicating the feasibility of their backbones as scaffolds for tumor-specific imaging agents that target survivin. Prion diseases are fatal neurodegenerative diseases characterized by the deposition of amyloid plaques containing abnormal prion protein aggregates (PrP^Sc). Thus, we developed flavonoids, acridines, and benzofurans as PrP^Sc-imaging probes. A styrylchromone derivative ([¹²³I]SC-OMe) appears to be a particularly promising SPECT radioligand for monitoring prion deposit levels in living brains. Gallium-68 is a positron emitter in clinical PET applications that can be produced by a ⁶⁸Ge/⁶⁸Ga generator without a cyclotron. Notably, we developed new adsorbents for ⁶⁸Ge by introducing N-methylglucamine groups into the Sephadex series to serve as a hydrophilic polymer matrix. We also demonstrated that generator-eluted ⁶⁸Ga-citrate could be used for PET imaging of infectious mouse models. Our polysaccharide-based ⁶⁸Ge/⁶⁸Ga generators were shown to be prospectively cost-effective production systems for ⁶⁸Ga radiopharmaceuticals. This Review describes the major findings of these three studies and the future prospect of these fields.