Identification of a cell-penetrating peptide applicable to a protein-based transcription activator-like effector expression system for cell engineering.

Cellular reprogramming is a promising technology in regenerative medicine, but most studies have been performed by using expression vectors. For future clinical applications, it is necessary to establish a system in which cell engineering can be manipulated without any risk of damaging the genome. Here, we identified a cell-penetrating peptide composed of 10 amino acids (RIFIHFRIGC) with nuclear trafficking activity and found that it was significantly more potent than a Tat-derived peptide or polyarginine peptide (R11). We named the peptide "nuclear trafficking peptide" (NTP) and applied it to a protein-based artificial transcription factor (NTP-ATF), which was composed of a transcription activator-like effector and transcription domain (VP64). An NTP-ATF designed to the proximal promoter region of the microRNA-302/367 cluster efficiently induced endogenous RNA expression at an extremely low concentration (0.25 nM), and repetitive treatment of mouse embryonic fibroblasts with NTP-ATF generated induced pluripotent stem-like cells, which gave chimeric mice. Together with the observation that recombinant NTP-ATF protein did not induce any apparent cytotoxicity, we propose that NTP-ATF is a promising system for cellular reprogramming applicable to regenerative medicine.

Evaluation of selective tumor detection by clinical magnetic resonance imaging using antibody-conjugated superparamagnetic iron oxide.

Active targeting by monoclonal antibodies (mAbs) combined with nanosize superparamagnetic iron oxide (SPIO) is a promising technology for magnetic resonance imaging (MRI) diagnosis. However, the clinical applicability of this technology has not been investigated using appropriate controls. It is important to evaluate the targeting technology using widely used clinical 1.5-Tesla MRI in addition to the high-Tesla experimental MRI. In this study, we measured mAb-conjugated dextran-coated SPIO nanoparticles (CMDM) in vivo using clinical 1.5-Tesla MRI. MRI of tumor-bearing mice was performed using a simple comparison between positive and negative tumors derived from the same genetic background in each mouse. The system provided significant tumor-targeting specificity of the target tumor. To the best of our knowledge, this is the first report on the specific detection of target tumors by mAb-conjugated SPIO using clinical 1.5-Tesla MRI. Our observations provide clues for reliable active targeting using mAb-conjugated SPIO in clinical applications.