oa Editorial [Hot topic: The Medicinal Chemistry of Targeted Tumor Imaging (II) (Guest Editor: Xiaoyuan (Shawn) Chen)]

This issue (volume 10, number 12) and the previous issue (volume 10, number 11) of Current Topics in Medicinal Chemistry, dedicated to “The Medicinal Chemistry of Targeted Tumor Imaging,” are aimed at describing and highlighting the state-of-the-art of current research and development in the field of molecular imaging probe development. Last issue contained a total of 5 review articles covering the chemistry of positron emission tomography (PET), single-photon emission computed tomography (SPECT), and activatable optical fluorescence imaging. The remaining 7 review articles on quantum dot based fluorescence imaging, T1 and T2 weighted MR contrast agents, gas microbubbles for contrast-enhanced ultrasound, theranostic nanoparticles, general design of cancer imaging probe and strategies to label cells for cancer are discussed in this issue. This issue starts by a review article from Jinhao Gao et al. summarizing recent advances of quantum dot (QD) nanoparticlebased near-infrared fluorescence (NIR) optical imaging probes. Compared with the organic dyes and fluorescent proteins, QDs show many unique optical properties, such as symmetrical, narrow, and tunable emission spectra, superior photostability, high quantum yields, and the capacity of simultaneous excitation of multiple fluorescence colors. Based on the availability of various Cd and non-Cd based quantum dots, how the physicochemical properties, surface chemistry and bioconjugation chemistry of QDs profoundly affect the absorption, distribution, metabolism, excretion, toxicity, and tumor targeting efficiency were elaborated in this article. The next review article by Nazila Kamaly et al. talked about the development and implementation of tumor targeted T1 MRI contrast agents, with an emphasis on the chemistry used to modify pre-existing clinical MRI contrast agents for targeted tumor imaging. MRI is capable of producing three dimensional images of tissues containing water with a high degree of spatial resolution. MRI contrast agents provide reliable means to enhance images and play a key role in clinical investigations. MRI contrast agents consist of molecules which incorporate a paramagnetic metal ion, most commonly Gd or iron (Fe). Image improvement arises from the modulation of longitudinal (T1) or transverse (T2) relaxation times of the surrounding bulk water protons by the coordinated metal ions. Both small molecules that carry single and nanoparticles (NPs) carrying multiple paramagnetic metal ions were discussed. The third review article by Lise-Marie Lacroix et al. described the synthesis of iron based magnetic nanoparticle (MNP) contrast agents for T2-weighted MRI or as heaters for magnetic fluid hyperthermia (MFH). It first introduced the nanomagnetism and elucidated the critical parameters to optimize the superparamagnetic NPs for MRI and ferromagnetic NPs for MFH. It then further outlined the new chemistry developed for making monodisperse MNPs with controlled magnetic properties. The review finally highlighted the NP functionalization with biocompatible molecules and biological targeting agents for tumor diagnosis and therapy. The fourth review article by Francesca Cavalieri et al. described the use of gas-filled microbubbles for ultrasound imaging guided cancer therapy. Combining diagnostic and therapeutic ultrasound for tumor imaging and treatment is especially attractive for reasons of simplicity and cost-effectiveness. The development of microbubbles acting as targeted and smart drug carriers is however a very challenging goal as these systems present difficult and inherent problems of stability. The methods of preparation, mechanism of action, in vitro and in vivo stability, structural/functional characterization of microbubbles were described in details. New mechanisms for ultrasound-enhanced local drug and gene delivery were also reviewed. Different strategies used to target microbubbles to regions of disease and some of the recent experiences in ultrasound image-guided therapy were illustrated. The fifth review article by Debatosh Majumdar et al. summarized the current status and future prospects of using nanotechnology for targeted cancer imaging. Theragnostics (or sometimes called theranostics) is an approach based on the fusion of diagnostics and therapeutics. In theragnostics, the results of diagnostic tests are used to design and decide the appropriate targeted therapy, in which an anti-cancer drug is delivered specifically to the targeted cancer site with the help of appropriate targeting ligands. Theragnostics is also aimed to monitor the treatment response, increase the drug efficacy and safety. This review provided a number of nanoparticle platforms for multimodality imaging and simultaneous imaging and therapy applications....