Zhi-Jian Chen

High Relaxivity Trimetallic Nitride (Gd3N) Metallofullerene MRI Contrast Agents with Optimized Functionality

Water-soluble poly(ethylene glycol) (PEG) functionalized and hydroxylated endohedral trimetallic nitride metallofullerene derivatives, Gd(3)N@C(80)[DiPEG(OH)(x)], have been synthesized and characterized. The (1)H MRI relaxivities in aqueous solution were measured for the derivatives with four different molecular weights of PEG (350-5000 Da) at 0.35, 2.4, and 9.4 T. The 350/750 Da PEG derivatives have the highest relaxivities among the derivatives, 237/232 mM(-1) s(-1) for r(1) and 460/398 mM(-1) s(-1) for r(2) (79/77 mM(-1) s(-1) and 153/133 mM(-1) s(-1) based on Gd(3+) ion), respectively, at a clinical-range magnetic field of 2.4 T. These represent some of the highest relaxivities reported for commercial or investigational MRI contrast agents. Dynamic light scattering results confirm a larger average size for 350/750 Da PEGs derivatives (95/96 nm) relative to longer chain length derivatives, 5000 Da PEG derivatives (37 nm). Direct infusion of the optimized 350 Da PEG derivatives into live tumor-bearing rat brains demonstrated an initial uniform distribution, and hence, the potential for effective brachytherapy applications when the encapsulated Gd(3+) ions are replaced with radioactive (177)Lu.

Facile Preparation of a New Gadofullerene-Based Magnetic Resonance Imaging Contrast Agent with High 1H Relaxivity

A new magnetic resonance imaging (MRI) contrast agent based on the trimetallic nitride templated (TNT) metallofullerene Gd(3)N@C(80) was synthesized by a facile method in high yield. The observed longitudinal and transverse relaxivities r(1) and r(2) for water hydrogens in the presence of the water-soluble gadofullerene 2 Gd(3)N@C(80)(OH)(approximately 26)(CH(2)CH(2)COOM)(approximately 16) (M = Na or H) are 207 and 282 mM(-1) s(-1) (per C(80) cage) at 2.4 T, respectively; these values are 50 times larger than those of Gd(3+) poly(aminocarboxylate) complexes, such as commercial Omniscan and Magnevist. This high (1)H relaxivity for this new hydroxylated and carboxylated gadofullerene derivative provides high signal enhancement at significantly lower Gd concentration as demonstrated by in vitro and in vivo MRI studies. Dynamic light scattering data reveal a unimodal size distribution with an average hydrodynamic radius of ca. 78 nm in pure water (pH = 7), which is significantly different from other hydroxylated or carboxylated fullerene and metallofullerene derivatives reported to date. Agarose gel infusion results indicate that the gadofullerene 2 displayed diffusion properties different from those of commercial Omniscan and those of PEG5000 modified Gd(3)N@C(80). The reactive carboxyl functionality present on this highly efficient contrast agent may also serve as a precursor for biomarker tissue-targeting purposes.

Intraparenchymal drug delivery via positive-pressure infusion: experimental and modeling studies of poroelasticity in brain phantom gels

We have used agarose gel to develop a robust model of the intraparenchymal brain tissues for the purpose of simulating positive-pressure infusion of therapeutic agents directly into the brain. In parallel with that effort, we have synthesized a mathematical description of the infusion process on the basis of a poroelastic theory for the swelling of the tissues under the influence of the infusates penetration into the interstitial space. Infusion line pressure measurements and video microscopy determinations of infusate volume of distribution within the gel demonstrate a good match between theory and experiment over a wide range of flow rates (0.5-10.0 microliters/min) and have clinical relevance for the convection-enhanced delivery of drugs into the brain without hindrance by the blood-brain barrier. We have put the brain phantom gel and the infusion measurement system into routine use in determining performance characteristics of novel types of neurosurgical catheters. This approach simplifies the catheter design process and helps to avoid some of the costs of in vivo testing. It also will allow validation of the elementary aspects of treatment planning systems that predict infusion distribution volumes on the basis of theoretical descriptions such as those derived from the poroelastic model.

Distribution of macromolecular dyes in brain using positive pressure infusion: a model for direct controlled delivery of therapeutic agents

BACKGROUND Direct infusion of therapeutic agents into the brain is a novel technique that has the potential for bypassing the blood-brain barrier and delivering high concentrations of therapeutic agents into the brain parenchyma. We have developed a model to characterize the distribution of Evans Blue (MW 960) and Blue Dextran (MW 2 x 10(6)) in rat brain using a positive pressure infusion system. METHODS Evans Blue and Blue Dextran were infused in volumes of 20, 40, 60, 100, 140, and 180 microL into the caudate putamen of female Fischer rats over a period of 2 h with rates of infusion varying between 0.167 microL and 1.5 microL/min. During the infusions, the pressure generated in the infusion system and intracranial pressure were measured using a fiberoptic pressure monitoring system. After infusions, the volumes of distribution of the dye molecules were measured from 3-mm thick sections using video microscopy and computer image analysis. Histologic changes during the infusion were studied using snap freezing and hematoxylin/eosin staining of cryosections. RESULTS Volumes of distribution for Evans Blue were greater than those for Blue Dextran. There was extensive spread of each dye in the ipsilateral hemisphere and also across the corpus callosum to the opposite hemisphere. Infusion/interstitial pressures peaked during the first 5 min of the infusion period, after which pressures dropped to a plateau value that remained relatively constant during the remainder of the infusion. Histologic findings suggest that this phenomenon is an important transition process that is likely to play a role in the pattern of distribution of macromolecules infused by this technique. No marked changes in intracranial pressure were noted during the infusion procedure. CONCLUSIONS Direct positive pressure infusion into the brain has great potential in the treatment of brain tumors and other central nervous system disorders using both high and low molecular weight compounds (immunotoxins, protein conjugates, pharmacologic agents, oligonucleotides, and viral vectors).

Conjugation of functionalized gadolinium metallofullerenes with IL-13 peptides for targeting and imaging glial tumors.

BACKGROUND Glioblastoma multiforme is the most common and most lethal primary brain tumor in humans, with median survival of approximately 1 year. Owing to the ability of glioma cells to aggressively infiltrate normal brain tissue and survive exposure to current adjuvant therapies, there is a great need for specific targeted nanoplatforms capable of delivering both therapeutic and imaging agents directly to invasive tumor cells. METHOD Gadolinium-containing endohedral fullerenes, highly efficient contrast agents for MRI, were functionalized and conjugated with a tumor-specific peptide and assessed for their ability to bind to glioma cells in vitro. RESULTS We report the successful conjugation of the carboxyl functionalized metallofullerene Gd(3)N@C(80)(OH)(-26)(CH(2)CH(2)COOH)(-16) to IL-13 peptides and the successful targeting ability towards brain tumor cells that overexpress the IL-13 receptor (IL-13Rα2). CONCLUSION These studies demonstrate that IL-13 peptide-conjugated gadolinium metallofullerenes could serve as a platform to deliver imaging and therapeutic agents to tumor cells.

Intratumoral Administration and Convection-Enhanced Delivery

ABSTRACT: Convection-enhanced delivery is a means of localized drug delivery to the central nervous system. The therapeutic agent, infused via a catheter, is carried (convectus, latin) by bulk flow though the interstitial space. This method has proved to be a useful laboratory technique for targeted, wide-spread distribution of a broad range of agents including small molecules and gene therapy vectors, such as viruses and liposomes. The success in the lab has translated into a significant number of clinical studies which combine the use of convection-enhanced delivery and elegantly devised molecular strategies. Additionally, several studies suggest that convection-enhanced delivery can be accurately predicted with mathematical models, allowing precise planning of dosage and distribution in the clinical setting. Taken together the results of these investigations hint at the promise of an expanded armantarium against brain tumors.

Distribution and stability of antisense phosphorothioate oligonucleotides in rodent brain following direct intraparenchymal controlled-rate infusion.

OBJECT High-flow microinfusion is a novel technique for delivery of compounds directly into brain parenchyma, bypassing the blood-brain barrier. The feasibility of this technique has been demonstrated with low-molecular-weight compounds, macromolecular dyes, and proteins. Delivery of antisense oligonucleotides into brain parenchyma represents an additional potential application of this technique not previously described. In this report the authors sought to examine the distribution and disposition of phosphorothioate oligodeoxynucleotide (PS-ODN) for this reason. METHODS An 18-mer 35S-PS-ODN (Mr approximately 6000) was infused over 1 hour into the caudate putamen of Fischer 344 rats. At 1, 6, 12, 24, and 48 hours after beginning the infusion, the brains were extracted and analyzed using quantitative autoradiographic techniques. Cerebrospinal fluid (CSF) was also aspirated from the cisterna magna and was analyzed to determine the radioactivity and stability of the 35S-PS-ODN. At 1 hour, the infused ODN was uniformly distributed in brain tissue, with a maximum average concentration of 4806.5 +/- 210.5 nCi/g. This represents a tissue concentration of 19.2 +/- 0.84 microM. Extensive spread into surrounding parenchyma was observed over the ensuing 47 hours. The 35S-PS-ODN radioactivity peaked in the CSF at the end of the 1-hour infusion, containing 1% (50 +/- 20 nCi) of the infused radioactivity. Activity then decayed exponentially over 11 hours, but stabilized at a lower CSF content of 0.2% (1 +/- 0.1 nCi) thereafter. The volume of distribution was 105 +/- 7.9 mm3 at 1 hour, representing a volume of distribution/volume of infusion ratio of 5.2. The volume of distribution increased to 443 +/- 62.3 mm3 at the end of 48 hours, whereas the average minimum tissue concentration decreased from 15.2 microM to 3.2 microM. Undegraded 18-mer was observed throughout the 48-hour period by means of 20% polyacrylamide/7 M urea gel electrophoresis. The animals tolerated the infusion without evidence of toxicity and minimal structural changes in tissue were observed on histological investigation. CONCLUSIONS The authors found that PS-ODNs can be safely delivered in high concentrations to wide areas of rat brain by using high-flow microinfusion and are stable even after 48 hours in situ.