Hyoungsu Kim

Multifunctional Uniform Nanoparticles Composed of a Magnetite Nanocrystal Core and a Mesoporous Silica Shell for Magnetic Resonance and Fluorescence Imaging and for Drug Delivery

During the past two decades, extensive research has been carried out on the biomedical applications of nanostructured materials. Among these various nanomaterials, mesoporous silica materials have been intensively investigated for their potential application as delivery vehicles for small-molecule drugs, DNA, and proteins, owing to their uniform pore size, large surface area, and high accessible pore volume. However, to date, there are only a few reports on the in vivo application of mesoporous silica materials administrated by intravenous injection, because it is difficult to synthesize discrete and monodisperse mesoporous silica particles smaller than around 100 nm that possess high colloidal stability in a physiological environment and small enough size to allow a long blood circulation. In general, bigger nanoparticles (NPs) result in more rapid uptake by the reticuloendothelial system (RES), such as liver and spleen, but smaller NPs can escape from phagocytes in RES and circulate through blood vessels with a long blood half-life. Although there have been several reports on the synthesis of uniform mesoporous silica particles smaller than 200 nm observed in TEM, the particles are not discrete but aggregated. Consequently, it is still a challenge to synthesize discrete, monodisperse, and size-controllable mesoporous silica NPs for in vivo applications. Recently, multifunctional nanostructured materials have been applied to multimodal imaging and simultaneous diagnosis and therapy. In this context, the integration of mesoporous silica with superparamagnetic monodisperse nanocrystals to form uniform core–shell composite particles has great potential for simultaneous bioimaging and drug delivery. Although there have been several reports on composite materials of magnetic nanocrystals and mesoporous silica materials, these materials have not been used for in vivo applications because of their size and aggregation. Herein, we present discrete, monodisperse, and precisely sizecontrollable core–shell mesoporous silica NPs smaller than 100 nm by using single Fe3O4 nanocrystals as cores (designated as Fe3O4@mSiO2). We also demonstrate the multifunctional bioapplications of the core–shell NPs for simultaneous magnetic resonance (MR) and fluorescence imaging, and for drug delivery. The synthetic protocol is represented in Scheme 1. Cetyltrimethylammonium bromide (CTAB) serves not only as the stabilizing surfactant for the transfer of hydrophobic Fe3O4 nanocrystals [10] to the aqueous phase but also as the organic template for the formation of mesopores in the sol– gel reaction. After removing the CTAB templates from the as-synthesized materials by heating them at reflux in acidic ethanol solution (pH 1.4), we collected the Fe3O4@mSiO2 particles. When we decreased the pH value of the extraction solution below 1.0, Fe3O4 nanocrystals as well as CTAB were fully removed from the as-synthesized Fe3O4@mSiO2, resulting in hollow mesoporous silica NPs (designated as H-mSiO2). Finally, for biomedical applications, the surface of the NPs was modified with PEG to render them biocompatible by

Uniform mesoporous dye-doped silica nanoparticles decorated with multiple magnetite nanocrystals for simultaneous enhanced magnetic resonance imaging, fluorescence imaging, and drug delivery.

Highly versatile nanocomposite nanoparticles were synthesized by decorating the surface of mesoporous dye-doped silica nanoparticles with multiple magnetite nanocrystals. The superparamagnetic property of the magnetite nanocrystals enabled the nanoparticles to be used as a contrast agent in magnetic resonance (MR) imaging, and the dye molecule in the silica framework imparted optical imaging modality. Integrating a multitude of magnetite nanocrystals on the silica surface resulted in remarkable enhancement of MR signal due to the synergistic magnetism. An anticancer drug, doxorubicin (DOX), could be loaded in the pores and induced efficient cell death. In vivo passive targeting and accumulation of the nanoparticles at the tumor sites was confirmed by both T2 MR and fluorescence imaging. Furthermore, apoptotic morphology was clearly detected in tumor tissues of mice treated with DOX loaded nanocomposite nanoparticles, demonstrating that DOX was successfully delivered to the tumor sites and its anticancer activity was retained.

Large-Scale Synthesis of Uniform and Extremely Small-Sized Iron Oxide Nanoparticles for High-Resolution T1 Magnetic Resonance Imaging Contrast Agents

Uniform and extremely small-sized iron oxide nanoparticles (ESIONs) of < 4 nm were synthesized via the thermal decomposition of iron-oleate complex in the presence of oleyl alcohol. Oleyl alcohol lowered the reaction temperature by reducing iron-oleate complex, resulting in the production of small-sized nanoparticles. XRD pattern of 3 nm-sized nanoparticles revealed maghemite crystal structure. These nanoparticles exhibited very low magnetization derived from the spin-canting effect. The hydrophobic nanoparticles can be easily transformed to water-dispersible and biocompatible nanoparticles by capping with the poly(ethylene glycol)-derivatized phosphine oxide (PO-PEG) ligands. Toxic response was not observed with Fe concentration up to 100 μg/mL in MTT cell proliferation assay of POPEG-capped 3 nm-sized iron oxide nanoparticles. The 3 nm-sized nanoparticles exhibited a high r(1) relaxivity of 4.78 mM(-1) s(-1) and low r(2)/r(1) ratio of 6.12, demonstrating that ESIONs can be efficient T(1) contrast agents. The high r(1) relaxivities of ESIONs can be attributed to the large number of surface Fe(3+) ions with 5 unpaired valence electrons. In the in vivo T(1)-weighted magnetic resonance imaging (MRI), ESIONs showed longer circulation time than the clinically used gadolinium complex-based contrast agent, enabling high-resolution imaging. High-resolution blood pool MR imaging using ESIONs enabled clear observation of various blood vessels with sizes down to 0.2 mm. These results demonstrate the potential of ESIONs as T(1) MRI contrast agents in clinical settings.

Large-Scale Synthesis of Bioinert Tantalum Oxide Nanoparticles for X-ray Computed Tomography Imaging and Bimodal Image-Guided Sentinel Lymph Node Mapping

Ever since Au nanoparticles were developed as X-ray contrast agents, researchers have actively sought alternative nanoparticle-based imaging probes that are not only inexpensive but also safe for clinical use. Herein, we demonstrate that bioinert tantalum oxide nanoparticles are suitable nanoprobes for high-performance X-ray computed tomography (CT) imaging while simultaneously being cost-effective and meeting the criteria as a biomedical platform. Uniformly sized tantalum oxide nanoparticles were prepared using a microemulsion method, and their surfaces were readily modified using various silane derivatives through simple in situ sol-gel reaction. The silane-modified surface enabled facile immobilization of functional moieties such as polyethylene glycol (PEG) and fluorescent dye. PEG was introduced to endow the nanoparticles with biocompatibility and antifouling activity, whereas immobilized fluorescent dye molecules enabled simultaneous fluorescence imaging as well as X-ray CT imaging. The resulting nanoparticles exhibited remarkable performances in the in vivo X-ray CT angiography and bimodal image-guided lymph node mapping. We also performed an extensive study on in vivo toxicity of tantalum oxide nanoparticles, revealing that the nanoparticles did not affect normal functioning of organs.

Total Synthesis and Molecular Target of Largazole, a Histone Deacetylase Inhibitor

Full details of the concise and convergent synthesis (eight steps, 19% overall yield), its extension to the preparation of a series of key analogues, and the molecular target and pharmacophore of largazole are described. Central to the synthesis of largazole is a macrocyclization reaction for formation of the strained 16-membered depsipeptide core followed by an olefin cross-metathesis reaction for installation of the thioester. The biological evaluation of largazole and its key analogues, including an acetyl analogue, a thiol analogue, and a hydroxyl analogue, suggested that histone deacetylases (HDACs) are molecular targets of largazole and largazole is a class I HDAC inhibitor. In addition, structure-activity relationship (SAR) studies revealed that the thiol group is the pharmacophore of the natural product. Largazoles HDAC inhibitory activity correlates with its antiproliferative activity.

Magnetosome-like ferrimagnetic iron oxide nanocubes for highly sensitive MRI of single cells and transplanted pancreatic islets

For ultrasensitive magnetic resonance imaging (MRI), magnetic nanoparticles with extremely high r2 relaxivity are strongly desired. Magnetosome-like nanoparticles were prepared by coating polyethylene glycol-phospholipid (PEG-phospholipid) onto ferrimagnetic iron oxide nanocubes (FIONs). FIONs exhibited a very high relaxivity (r2) of 324 mM-1 s-1, allowing efficient labeling of various kinds of cells. The magnetic resonance (MR) imaging of single cells labeled with FIONs is demonstrated not only in vitro but also in vivo. Pancreatic islet grafts and their rejection could be imaged using FIONs on a 1.5 T clinical MRI scanner. The strong contrast effect of FIONs enabled MR imaging of transplanted islets in small rodents as well as in large animals. Therefore, we expect that MR imaging of pancreatic islet grafts using FIONs has the potentials for clinical applications. Furthermore, FIONs will enable highly sensitive noninvasive assessment after cell transplantation.

Stereoselective Synthesis of 2,6‐cis‐Tetrahydropyrans through a Tandem Allylic Oxidation/Oxa‐Michael Reaction Promoted by the gem‐Disubstituent Effect: Synthesis of (+)‐Neopeltolide Macrolactone

Structurally complex tetrahydropyrans (THPs) are found in a wide range of biologically interesting natural products. Although considerable effort has been devoted to the development of synthetic routes to THPs, there still exists a great need for a synthetic approach to these classes of molecules that enables rapid and easy access to substrates, proceeds with excellent stereoselectivity in excellent yield, and requires mild reaction conditions compatible with various functional groups. Surprisingly, despite considerable progress in the Michael reaction of carbon nucleophiles, there has been far less interest in the analogous Michael reaction of oxygen nucleophiles (oxa-Michael reaction). The slow development of the oxa-Michael reaction is mainly due to major drawbacks such as the low reactivity of oxygen nucleophiles and the reversibility issue, as well as a lack of control over stereoselectivity. Owing to the poor nucleophilicity of oxygen atoms in the oxaMichael reaction, alcohols must be deprotonated by strong bases to enhance their nucleophilicity, or the conjugate acceptor must be activated by Lewis or Brønsted acids, amines, or transition-metal complexes. These harsh reaction conditions are often incompatible with other functional groups of the substrate. In particular, as a result of competitive acetal formation, instability, and the enolizability of aldehydes, the oxa-Michael reaction of alcohols to a,b-unsaturated aldehydes has been elusive. Herein, we report the stereoselective and efficient synthesis of 2,6-cis-THPs through an unprecedented tandem allylic oxidation/oxa-Michael addition of alcohols to a,bunsaturated aldehydes promoted by the gem-disubstituent effect and its application to the concise synthesis of (+)-neopeltolide macrolactone. To overcome the low reactivity of oxygen nucleophiles, we envisioned the introduction of a structural element that would promote preorganization of the conformation of a substrate for an intramolecular oxa-Michael reaction. We also anticipated that this structural element could help decrease the reversibility of the reaction to form the oxa-Michael product. We hypothesized that a 1,3-dithiane group at the C4 position of an alcohol nucleophile could satisfy these requirements on the basis of the gem-disubstituent effect. Furthermore, the 1,3-dithiane group would serve as a latent functional group for a carbonyl, hydroxy, or olefinic group, or a hydrogen atom. To test this hypothesis, we prepared substrate 4 for the oxa-Michael reaction as follows (Scheme 1): The 1,3-dithiane coupling of 1 with allyl bromide 2, followed by THP deprotection, provided 3. The coupling of 3 with ( )-glycidyl benzyl ether then proceeded smoothly to afford the allylic alcohol 4. As expected, the chemoselective oxidation of 4 with MnO2 and subsequent intramolecular oxa-Michael reaction of the resulting a,b-unsaturated aldehyde 5 provided the desired 2,6-cis-THP 6a with excellent stereoselectivity (d.r.>20:1, 93 %; tandem allylic oxidation/oxa-Michael reaction).

Synthesis and activity of largazole analogues with linker and macrocycle modification.

To characterize largazoles structural requirements for histone deacetylase (HDAC) inhibitory and antiproliferative activities, a series of analogues with modifications to the side chain or 16-membered macrocycle were prepared and biologically evaluated. Structure-activity relationships suggested that the four-atom linker between the macrocycle and octanoyl group in the side chain and the (S)-configuration at the C17 position are critical to repression of HDAC activity. However, the valine residue in the macrocycle can be replaced with alanine without significant loss of activity.

The anti-inflammatory effect of bee venom stimulation in a mouse air pouch model is mediated by adrenal medullary activity.

Cutaneous electrical or chemical stimulation can produce an anti‐inflammatory effect, which is dependent on adrenal medullary‐sympathetic activation. We have previously shown that peripheral injection of bee venom (BV) also produces a significant anti‐inflammatory effect that is neurally mediated. In the present study, we examined whether this anti‐inflammatory effect is also dependent on the adrenal gland using the mouse inflammatory air pouch model. Subcutaneous (s.c.) BV injection produced a marked suppression of leucocyte migration and tumour necrosis factor (TNF)‐α concentration induced by zymosan injection into the air pouch. The role of the adrenal gland in this suppression was evaluated in adrenalectomized mice. Adrenalectomy significantly reversed the suppression of leucocyte migration and TNF‐α elevation caused by BV. Serum concentrations of corticosteroid were increased in mice with zymosan‐induced air‐pouch inflammation and this increase was reduced by BV administration, suggesting that adrenal corticosteroid release is not involved in mediating the anti‐inflammatory effects of BV. To test this hypothesis, the corticosteroid receptor antagonist (RU486) was administered and found not to affect the BV‐induced inhibition of leucocyte migration. By contrast, pretreatment with the β‐adrenergic antagonist propranolol reversed the BV‐induced inhibitory effect on leucocyte migration. These results suggest that the anti‐inflammatory effect of s.c. BV administration is mediated in part by the release of catecholamines from the adrenal medulla.

Total synthesis of cyanolide A and confirmation of its absolute configuration.

The tandem allylic oxidation/oxa-Michael reaction promoted by the gem-disubstituent effect and the 2-methyl-6-nitrobenzoic anhydride (MNBA)-mediated dimerization were explored for the efficient and facile synthesis of cyanolide A.