Qiyong Gong

Manganese ferrite nanoparticle micellar nanocomposites as MRI contrast agent for liver imaging

Iron oxide nanoparticles are effective contrast agents for enhancement of magnetic resonance imaging at tissue, cellular or even molecular levels. In this study, manganese doped superparamagnetic iron oxide (Mn-SPIO) nanoparticles were used to form ultrasensitive MRI contrast agents for liver imaging. Hydrophobic Mn-SPIO nanoparticles are synthesized in organic phase and then transferred into water with the help of block copolymer mPEG-b-PCL. These Mn-SPIO nanoparticles are self-assembled into small clusters (mean diameter approximately 80nm) inside micelles as revealed by transmission electron microscopy. Mn-SPIO nanoparticles inside micelles decrease PCL crystallization temperatures, as verified from differential scanning calorimetry and Fourier transform infrared spectroscopy. The Mn-SPIO based nanocomposites are superparamagnetic at room temperature. At the magnetic field of 1.5T, Mn-SPIO nanoparticle clustering micelles have a T(2) relaxivity of 270 (Mn+Fe)mM(-1)s(-1), which is much higher than single Mn-SPIO nanoparticle containing lipid-PEG micelles. This clustered nanocomposite has brought significant liver contrast with signal intensity changes of -80% at 5min after intravenous administration. The time window for enhanced-MRI can last about 36h with obvious contrast on liver images. This sensitive MRI contrast agent may find applications in identification of small liver lesions, evaluation of the degree of liver cirrhosis, and differential diagnosis of other liver diseases.

Low molecular weight alkyl-polycation wrapped magnetite nanoparticle clusters as MRI probes for stem cell labeling and in vivo imaging.

Superparamagnetic iron oxide (SPIO) nanoparticles are potential probes for noninvasive cell tracking, but the design of safe probes coupled with high labeling efficiency is still an important objective for such application. In this study, an efficient SPIO probe has been developed for mesenchymal stem cells (MSCs) labeling and tracking. Different from many other systems involving high molecular polycations, we chose low molecular weight amphiphilic PEI2k to form stable nanocomplexes with SPIO nanoparticles. The probe can hold multiple SPIO nanoparticles with a controlled clustering structure, leading to much higher T(2) relaxivities compared to single SPIO nanoparticles. Labeled MSCs are unaffected in their viability, proliferation, or differentiation capacity. The iron uptake process in MSCs displays a time- and dose-dependent behavior. Transmission electron microscopy reveals that the nanoprobes are internalized into the cytoplasm of MSCs. Subcutaneous injection of the labeled MSCs dispersed in a collagen type I hydrogel showed strong image contrast against unlabeled cells under a clinical 3T magnetic resonance imaging (MRI) scanner up to 19 days post-transplantation. This study provides an important alternative to label MSCs at optimized low dosages with high efficiency, and the probe may be useful to label other biologically important cells for imaging studies.

Functional L-Lysine Dendritic Macromolecules as Liver-Imaging Probes

Liver-imaging probes are prepared through the conjugation of Gd chelates and galactosyl moieties to peptide dendrimers. The dendritic probes possessing highly controlled structures and a single molecular weight have a two-fold increase in T(1) relaxivity to 9.1 x 10(3) (Gd M)(-1) s(-1) compared to Gd-DTPA. No obvious cytotoxicity of this multifunctional dendritic agent is discovered in vitro. The dendrimer bearing galactosyl moieties leads to a much-higher hepatocyte-cell uptake in vitro and provides good signal-intensity enhancement (35%) of mouse liver in vivo especially at 60 min after intravenous injection. In comparison, non-targeting Gd dendrimers provide only an 11% enhancement of imaging contrast at the same time point. Overall, the dendrimers bearing galactosyl moieties may be used as liver-imaging probes.

A dendronized heparin–gadolinium polymer self-assembled into a nanoscale system as a potential magnetic resonance imaging contrast agent

We reported the preparation and characterization of a dendronized heparin–gadolinium polymer (Dendronized-heparin–Gd) based nanoscale system as a potential MRI contrast agent, which combined the advantages of heparin and the peptide dendron. The dendronized polymer self-assembled into a compact nanoscale system, which was confirmed by dynamic light scattering (DLS) and scanning electron microscopy (SEM) results, and a negative charge was observed. The content of gadolinium (Gd(III)) was 6% as a weight percentage, determined by inductively coupled plasma mass spectrometry (ICP-MS) analysis. The in vitro and in vivo toxicity studies demonstrated that the Dendronized-heparin–Gd polymeric nanoscale system exhibited good biocompatibility – no obvious side effects to normal cells and organs of healthy mice were observed by a cytotoxicity assay, body weight shift and histological analysis. The polymeric nanoscale system showed a 7-fold increase in the T1 relaxivity compared to the clinical agent Magnevist (Gd-DTPA). In vivo MR imaging studies on the mice bearing 4T1 breast tumors showed that the nanoscale system had a much higher contrast enhancement in the tumor than Gd-DTPA. The distribution of Gd(III) in the tissues at different times after administration indicated a higher Gd(III) accumulation in the tumor for the nanoscale system compared to Gd-DTPA. Overall, the dendronized heparin polymer based nanoscale system with a high contrast enhancement in tumors and low side effects may be used as a MRI contrast agent for disease diagnosis.

Multivalent manganese complex decorated amphiphilic dextran micelles as sensitive MRI probes

T1 contrast agents based on Mn(II) were conjugated on amphiphilic dextran micelles via click chemistry. The obtained paramagnetic nanomicelle contrast agent has a higher T1 relaxivity (13.3 Mn mmol-1 s-1) and better sensitivity than those of free Mn(II) complexes. Studies carried out in vivo suggest that this contrast agent has a better and long-acting vascular enhancement effect at a lower manganese dosage (0.1 Mn mmol kg-1 BW).

Enzyme/pH-sensitive polyHPMA–DOX conjugate as a biocompatible and efficient anticancer agent

In this study, to enhance the therapeutic function and reduce the side-effects of doxorubicin (DOX), a biodegradable N-(2-hydroxypropyl) methacrylamide (HPMA) polymer-DOX conjugate has been prepared through reversible addition fragmentation chain transfer (RAFT) polymerization and conjugation chemistry, and the anticancer agent DOX was covalently linked to the polymeric vehicle through a pH-responsive hydrazone bond. The cellular mechanisms of the conjugate were explored, and the therapeutic indexes were studied as well. The high molecular weight (MW) polymeric conjugate (94 kDa) was degraded into products with low MW (45 kDa) in the presence of lysosomal cathepsin B and also showed pH-responsive drug release behavior. In vitro cellular mechanism studies revealed that the polymeric conjugate was uptaken by the 4T1 cells, leading to cell apoptosis and cytotoxicity to cancer cells, while the polymeric conjugate demonstrated excellent in vivo biosafety even at a high dose. Compared to free DOX, the conjugate has a much longer half-life in pharmacokinetics and accumulates in tumors with a much higher amount. The conjugate therefore has a much greater in vivo anticancer efficacy against 4T1 xenograft tumors and shows subtle side-effects, which were confirmed via tumor size and weight, immunohistochemistry and histological studies. Overall, this polymeric conjugate may be used as an enzyme/pH-sensitive anticancer agent.

Enzyme/pH-sensitive dendritic polymer-DOX conjugate for cancer treatment

It is in a great demand to design a biodegradable, tumor microenvironment-sensitive drug delivery system to achieve safe and highly efficacious treatment of cancer. Herein, a novel pH/enzyme sensitive dendritic pdiHPMADOX conjugate was designed. diHPMA dendritic copolymer with GFLG segments in the branches which are sensitive to the intracellular enzyme of the tumor was prepared through RAFT polymerization. DOX was attached to dendritic diHPMA polymer through a pH-sensitive hydrazone bond. The dendritic pdiHPMA-DOX conjugate self-assembled into nanoparticles with an ideal spherical shape at a mean size of 103 nm. The DOX attached to the polymeric carrier was released in an acidic environment, and the GFLG linker for synthesizing the dendritic vehicle with a high molecular weight (MW, 220 kDa) was cleaved to release low MW segments (<40 kDa) in the presence of cathepsin B. The dendritic polymeric conjugate was internalized via an endocytic pathway, and then released the anticancer drug, which led to significant cytotoxicity for tumors. The blood circulation time was profoundly prolonged, resulting in high accumulation of DOX into tumors. In vivo anti-tumor experiments with 4T1 tumor bearing mice demonstrated that the conjugate had a better antitumor efficacy in comparison with free DOX. Additionally, body weight measurements and histological examinations indicated that the conjugate showed low toxicities to normal tissues. This dendritic polymeric drug carrier in a response to intracellular enzyme and acidic pH of tumor tissue or cells holds great promise in tumor-targeted therapy.摘要本文设计了一种可生物降解的、肿瘤环境敏感的药物释放系统, 以达到安全、高效治疗癌症的目的. 我们利用单体N-(1,3-二羟基- 2-丙基)甲基丙烯酰胺, 通过可逆加成−断裂链转移聚合方法制备了含有对肿瘤细胞内组织蛋白酶B敏感的GFLG肽段的支化聚合物–药物 偶联物. 阿霉素通过pH敏感的腙键偶联到支化聚合物骨架上. 支化聚合物药物偶联物可自组装形成纳米粒, 平均粒径约为103 nm. 连接到 聚合物载体的阿霉素可在酸性环境中释放. 较高分子量(MW, 220 kDa) 的含有GFLG连接的支化聚合物—阿霉素偶联物可在组织蛋白酶B 的作用下降解为低分子量聚合物片段(<40 kDa). 支化偶联物通过内吞途径进入细胞, 然后释放抗癌药物, 进而对肿瘤细胞引起明显的细胞 毒性。偶联物的血液循环时间显著延长, 使得阿霉素在肿瘤部位大量蓄积. 4T1荷瘤小鼠体内抗肿瘤实验表明, 支化偶联物的抗肿瘤效果 优于游离阿霉素. 此外, 体重测量和组织形态学检查的结果表明支化偶联物对正常组织的毒性很低. 因此, 这种对细胞内的酶和肿瘤组织 或细胞内的酸性pH具有响应性的支化聚合物给药系统在肿瘤靶向治疗中具有一定的前景.

Control of the interparticle spacing in superparamagnetic iron oxide nanoparticle clusters by surface ligand engineering

Polymer-mediated self-assembly of superparamagnetic iron oxide (SPIO) nanoparticles allows modulation of the structure of SPIO nanocrystal cluster and their magnetic properties. In this study, dopamine-functionalized polyesters (DA-polyester) were used to directly control the magnetic nanoparticle spacing and its effect on magnetic resonance relaxation properties of these clusters was investigated. Monodisperse SPIO nanocrystals with different surface coating materials (poly(e-caprolactone), poly(lactic acid)) of different molecular weights containing dopamine (DA) structure (DA-PCL2k, DA-PCL1k, DA-PLA1k)) were prepared via ligand exchange reaction, and these nanocrystals were encapsulated inside amphiphilic polymer micelles to modulate the SPIO nanocrystal interparticle spacing. Small-angle x-ray scattering (SAXS) was applied to quantify the interparticle spacing of SPIO clusters. The results demonstrated that the tailored magnetic nanoparticle clusters featured controllable interparticle spacing providing directly by the different surface coating of SPIO nanocrystals. Systematic modulation of SPIO nanocrystal interparticle spacing can regulate the saturation magnetization (M s) and T 2 relaxation of the aggregation, and lead to increased magnetic resonance (MR) relaxation properties with decreased interparticle spacing.