In vivo molecular imaging has become a key technology for pathophysiological science and drug development. We are mostly utilizing PET(positron emission tomography) as a first-choice modality, because of its ultra-high sensitivity for molecules, adequate temporal and spatial resolution, and especially broad spectrum of target molecules. In vivo molecular imaging could bring the high-quality information about: 1. Molecular diagnosis for living patients with symptoms 2. Closer approach for etiology and differential diagnosis 3. Direct follow-up of key molecules as disease markers 4. Pharmacokinetics/Pharmacodynamics in primates/human 5. Dose finding information for individuals, corresponding to SNPs 6. Direct evidence for accumulation in non-target organs related to adverse effects 7. Drug effects with surrogate markers 8. Early decision of dropout substances (drug candidates) Here, the examples are shown as beta-amyloid imaging for Alzheimer's and mild cognitive impairment, serotonin transporter imaging for chronic fatigue, and dopaminergic components imaging for evaluation of drug for autistic spectrum disorder. In 2005, RIKEN and National Institute of Radiological Science were selected as the key centers for development of All-Japan research network to further promote mutual international and multi -disciplinary collaboration on in vivo molecular imaging.

Molecular imaging for drug development

Gold nanoparticles and cancer: Detection, diagnosis and therapy.

Background Paclitaxel (PTX) has interesting anticancer activity. However, it is insoluble in water, which seriously hinders its use in clinical. Superparamagnetic iron oxide nanoparticles (SPIONs) are used as an ideal drug delivery system. Therefore, we proposed a folic acid (FA) targeting drug-loaded SPIONs to reduce its adverse reaction. Methods To improve the hydrophilicity of PTX, the structure of PTX was modified by succinic anhydride to obtain 2'-succinate paclitaxel (SPTX). FA conjugated Polyethylene glycol (PEG)/polyethyleneimine (PEI)-SPIONs SPTX-loaded nanoparticles (SPTX@FA@PEG/PEI-SPIONs) were prepared by solvent volatilization and hydrogen bond adsorption, and the nano-formulation was optimized by response surface methodology (RSM). The characteristics, antitumor effect in vitro, pharmacokinetics, and biodistribution of SPTX@FA@PEG/PEI-SPIONs were evaluated. Results SPTX was successfully loaded on the surface of FA@PEG/PEI-SPIONs. The formation of SPTX@FA@PEG/PEI-SPIONs was exhibited water-dispersive monodispersity with high stability by RSM, and dynamic light scattering (DLS) was 178.1±3.12 nm, particle size observed in the transmission electron microscope (TEM) was 13.01±1.10 nm, and the encapsulation efficiency (EE) and loading efficiency (LE) were 81.1±1.66% and 14.8±1.46%, respectively. It enhanced the stability in normal physiological condition, accelerated drug release at tumorous pH, and preferentially prolonged the circulation time. In vitro, the SPTX@FA@PEG/PEI-SPIONs significantly targeted to folate receptor (FR) positive cancers cell (HNE-1) via the receptor-ligand mediated pathway, resulting in effective cytotoxic activity. Pharmacokinetic results demonstrated that SPTX@FA@PEG/PEI-SPIONs (t1/2=3.41 h) had longer than free SPTX or PTX (t1/2=1.67 h) in rats in vivo. Tissue distribution studies showed that SPTX@FA@PEG/PEI-SPIONs were present at high levels in the liver and help in targeting the folate receptors present on the kidneys. Conclusion These results suggest that SPTX@FA@PEG/PEI-SPIONs offer a highly promising approach to control drug release, improve drug pharmacokinetics and actively target the nasopharyngeal carcinoma.

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Dheeraj Kumar

Papers

Development of technetium-99m labeled ultrafine gold nanobioconjugates for targeted imaging of folate receptor positive cancers