Michael D. Shultz

Encapsulation of a Radiolabeled Cluster Inside a Fullerene Cage, 177LuxLu(3−x)N@C80: An Interleukin-13-Conjugated Radiolabeled Metallofullerene Platform

In this communication, we describe the successful encapsulation of (177)Lu into the endohedral metallofullerene (177)Lu(x)Lu(3-x)N@C(80) (x = 1-3) starting with (177)LuCl(3) in a modified quartz Kraschmer-Huffman electric generator. We demonstrate that the (177)Lu (beta-emitter) in this fullerene cage is not significantly released for a period of up to at least one-half-life (6.7 days). We also demonstrate that this agent can be conjugated with an interleukin-13 peptide that is designed to target an overexpressed receptor in glioblastoma multiforme tumors. This nanoparticle delivery platform provides flexibility for a wide range of radiotherapeutic and radiodiagnostic multimodal applications.

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.

Metallofullerene-based Nanoplatform for Brain Tumor Brachytherapy and Longitudinal Imaging in a Murine Orthotopic Xenograft Model

PURPOSE To demonstrate in an orthotopic xenograft brain tumor model that a functionalized metallofullerene (f-Gd₃N@C₈₀) can enable longitudinal tumor imaging and, when radiolabeled with lutetium 177 (¹⁷⁷Lu) and tetraazacyclododecane tetraacetic acid (DOTA) (¹⁷⁷Lu-DOTA-f-Gd₃N@C₈₀), provide an anchor to deliver effective brachytherapy. MATERIALS AND METHODS All experiments involving the use of mice were carried out in accordance with protocols approved by the institutional animal care and use committee. Human glioblastoma U87MG cells were implanted by using stereotactic procedures into the brains of 37 female athymic nude-Foxn1nu mice and allowed to develop into a tumor for 8 days. T1- and T2-weighted magnetic resonance (MR) imaging was performed in five mice. Biodistribution studies were performed in 12 mice at four time points over 7 days to evaluate gadolinium content. Survival studies involved 20 mice that received infusion of a nanoplatform by means of convection-enhanced delivery (CED) 8 days after tumor implantation. Mice in survival studies were divided into two groups: one comprised untreated mice that received f-Gd₃N@CC₈₀ alone and the other comprised mice treated with brachytherapy that received 1.11 MBq of ¹⁷⁷Lu-DOTA-f-Gd₃N@CC₈₀. Survival data were evaluated by using Kaplan-Meier statistical methods. RESULTS MR imaging showed extended tumor retention (25.6% ± 1.2 of the infused dose at 52 days, confirmed with biodistribution studies) of the f-Gd₃N@CC₈₀ nanoplatform, which enabled longitudinal imaging. Successful coupling of ¹⁷⁷Lu to the f-Gd₃N@CC₈₀ surface was achieved by using a bifunctional macrocyclic chelator. The extended tumor retention allowed for effective brachytherapy, as indicated by extended survival time (> 2.5 times that of the untreated group) and histologic signs of radiation-induced tumor damage. CONCLUSION The authors have developed a multimodal nanoplatform and have demonstrated longitudinal tumor imaging, prolonged intratumoral probe retention, biodistribution, and extended survival in an orthotopic xenograft brain tumor model.

In Vitro and in Vivo Studies of Single-Walled Carbon Nanohorns with Encapsulated Metallofullerenes and Exohedrally Functionalized Quantum Dots

Single-walled carbon nanohorns (SWNHs) are new carbonaceous materials. In this paper, we report the first successful preparation of SWNHs encapsulating trimetallic nitride template endohedral metallofullerenes (TNT-EMFs). The resultant materials were functionalized by a high-speed vibration milling method and conjugated with CdSe/ZnS quantum dots (QDs). The successful encapsulation of TNT-EMFs and external functionalization with QDs provide a dual diagnostic platform for in vitro and in vivo biomedical applications of these new carbonaceous materials.

Metallofullerenes: a new class of MRI agents and more?

Metallofullerenes have incited research endeavors across many disciplines owing to their wide range of properties obtainable by altering the metal component inside the fullerene cage or by a variety of surface functionalities. With a metal component of gadolinium, gadofullerenes have particularly shown promise in MRI applications owing to their high proton relaxivity and isolation of the metal from the biological environment. This article aims to give a perspective on the development of metallofullerenes as MRI contrast agents and further applications that distinguish them as a new class of imaging agent.

Probing the role of interfacial residues in a dimerization inhibitor of HIV-1 protease.

The importance of each side chain of a cross-linked interfacial peptide inhibitor of HIV-1 protease was evaluated using an alanine scanning approach. Whereas the parent inhibitor has an IC50 value of 350 nM, values for the mutations reported here range from 280-9200 nM. The relative importance or each residue was thus assigned and correlated to the solvent accessible surface area (SASA) exposed upon mutation.

Hydrophobicity versus activity in crosslinked interfacial peptide inhibitors of HIV-1 protease

Abstract Crosslinked peptides with amino functionality incorporated within the tethering moiety 2a-c , 3a-c were synthesized and tested as interfacial inhibitors of HIV-1 protease As part of a strategy to develop the novel method of dissociative inhibition as a viable pharmacological approach, compounds were made to test hydrophobicity and size requirements of the tethering moiety. In the case of crosslinked interfacial peptide inhibitors of HIV-1 protease, hydrophilic 2a-c and bulky hydrophobic 3a-c tethers decreased effectiveness by approximately 10- and 2-fold, respectively.

Dimerization inhibitors of HIV-1 protease: Effective inhibition requires the cross-linking of non-identical peptides

Since the first discovery that cross-linked peptides corresponding to the dimerization interface of HIV-1 PR (1) can effectively inhibit the formation of the active homodimer of HIV-1 protease [1], extensive work to improve upon this class of inhibitors has been done leading to smaller inhibitors such as 2. In the absence of structural data, questions of the binding locus of each peptide remain. Do the peptides bind differentially and would the use of identical peptides cross-linked to mimic the dimerization interface be more beneficial than a more tedious synthesis of differentially substituted inhibitors? To answer these questions and to gain further insight into the use of dimerization inhibitors a series of Identically Substituted Cross-linked Protease Inhibitors (ISCPIs) were synthesized and evaluated against Non-Identical Cross-linked Protease Inhibitors (NISCPIs). In all of the cases investigated (17) except for one, all ISCPIs were less potent than their corresponding NISCPIs. The one exception yielded a compound with similar potency as judged by the value, but one that did not inhibit HIV-1 PR through a dissociative mechanism.