[Development of Radiolabeled Molecular Imaging Probes for in Vivo Analysis of Biological Function]

Molecular imaging is a newly emerging field aimed at advancing our understanding of biology and medicine through the noninvasive in vivo investigation of cellular molecular events involved in normal and pathologic processes. In this field, researchers and/or clinicians are combining modern tools of molecular and cell biology with state of the art technology in order to noninvasively image living subjects. Various imaging modalities such as optics (fluorescence and luminescence), nuclear magnetic resonance imaging, ultrasound, and radiation are being used to visually capture and study molecular and cellular events in living organisms. Among these modalities, nuclear medical molecular imaging uses radionuclides [i.e., positron emission tomography (PET) and single-photon emission computed tomography (SPECT)], and has characteristic properties that allow researchers and/or clinicians to obtain functional images of living subjects with high sensitivity. Translational molecular imaging, a research step between animal experiments and the clinical setting, has been successful when using nuclear medical molecular imaging. This approach leads to better methods for studying biological processes, as well as for diagnosing and managing diseases. In this review, two topics associated with our research on nuclear medical molecular imaging are summarized: (1) the development of a nuclear medical molecular imaging probe that targets cerebral nicotinic acetylcholine receptors (nAChRs), and the translational molecular imaging research conducted using this nAChR imaging probe; and (2) the development of oxygen-dependent degradable nuclear medical molecular imaging probes that target hypoxia-inducible factor-1-active tumor microenvironments.