Very late antigen-4 (α(4)ß(1) Integrin) targeted PET imaging of multiple myeloma.

Biomedical imaging techniques such as skeletal survey and (18)F-fluorodeoxyglucose (FDG)/Positron Emission Tomography (PET) are frequently used to diagnose and stage multiple myeloma (MM) patients. However, skeletal survey has limited sensitivity as it can detect osteolytic lesions only after 30-50% cortical bone destruction, and FDG is a marker of cell metabolism that has limited sensitivity for intramedullary lesions in MM. Targeted, and non-invasive novel probes are needed to sensitively and selectively image the unique molecular signatures and cellular processes associated with MM. Very late antigen-4 (VLA-4; also called α(4)ß(1) integrin) is over-expressed on MM cells, and is one of the key mediators of myeloma cell adhesion to the bone marrow (BM) that promotes MM cell trafficking and drug resistance. Here we describe a proof-of-principle, novel molecular imaging strategy for MM tumors using a VLA-4 targeted PET radiopharmaceutical, (64)Cu-CB-TE1A1P-LLP2A. Cell uptake studies in a VLA-4-positive murine MM cell line, 5TGM1, demonstrated receptor specific uptake (P<0.0001, block vs. non-block). Tissue biodistribution at 2 h of (64)Cu-CB-TE1A1P-LLP2A in 5TGM1 tumor bearing syngeneic KaLwRij mice demonstrated high radiotracer uptake in the tumor (12±4.5%ID/g), and in the VLA-4 rich organs, spleen (8.8±1.0%ID/g) and marrow (11.6±2.0%ID/g). Small animal PET/CT imaging with (64)Cu-CB-TE1A1P-LLP2A demonstrated high uptake in the 5TGM1 tumors (SUV 6.6±1.1). There was a 3-fold reduction in the in vivo tumor uptake in the presence of blocking agent (2.3±0.4). Additionally, (64)Cu-CB-TE1A1P-LLP2A demonstrated high binding to the human MM cell line RPMI-8226 that was significantly reduced in the presence of the cold targeting agent. These results provide pre-clinical evidence that VLA-4-targeted imaging using (64)Cu-CB-TE1A1P-LLP2A is a novel approach to imaging MM tumors.

Comparison of two cross-bridged macrocyclic chelators for the evaluation of 64Cu-labeled-LLP2A, a peptidomimetic ligand targeting VLA-4-positive tumors.

Integrin α(4)ß(1) (also called very late antigen-4 or VLA-4) plays an important role in tumor growth, angiogenesis and metastasis, and there has been increasing interest in targeting this receptor for cancer imaging and therapy. In this study, we conjugated a peptidomimetic ligand known to have good binding affinity for α(4)ß(1) integrin to a cross-bridged macrocyclic chelator with a methane phosphonic acid pendant arm, CB-TE1A1P. CB-TE1A1P-LLP2A was labeled with (64)Cu under mild conditions in high specific activity, in contrast to conjugates based on the "gold standard" di-acid cross-bridged chelator, CB-TE2A, which require high temperatures for efficient radiolabeling. Saturation binding assays demonstrated that (64)Cu-CB-TE1A1P-LLP2A had comparable binding affinity (1.2 nM vs 1.6 nM) but more binding sites (B(max)=471 fmol/mg) in B16F10 melanoma tumor cells than (64)Cu-CB-TE2A-LLP2A (B(max)=304 fmol/mg, p<0.03). In biodistribution studies, (64)Cu-CB-TE1A1P-LLP2A had less renal retention but higher uptake in tumor (11.4±2.3 %ID/g versus 3.1±0.6 %ID/g, p<0.001) and other receptor-rich tissues compared to(64)Cu-CB-TE2A-LLP2A. At 2h post-injection, (64)Cu-CB-TE1A1P-LLP2A also had significantly higher tumor:blood and tumor:muscle ratios than (64)Cu-CB-TE2A-LLP2A (CB-TE1A1P=19.5±3.0 and 13.0±1.4, respectively, CB-TE2A=4.2±1.4 and 5.5±0.9, respectively, p<0.001). These data demonstrate that (64)Cu-CB-TE1A1P-LLP2A is an excellent PET radiopharmaceutical for the imaging of α(4)ß(1) positive tumors and also has potential for imaging other α(4)ß(1) positive cells such as those of the pre-metastatic niche.

Molecular imaging of very late antigen-4 (α4ß1 integrin) in the premetastatic niche.

UNLABELLED: Despite advances in cancer treatment over the past few decades, metastatic disease remains the primary cause of morbidity and mortality. Recent reports suggest the formation of a "premetastatic niche" before the metastatic cascade, where niche is defined as the microenvironment for tumor cells to be able to engraft and proliferate at secondary sites. Bone marrow-derived (BMD) cells that express vascular endothelial growth factor receptor-1 and very late antigen-4 (VLA-4) have been shown to arrive at sites of metastasis to form a receptive environment for tumor cells. Here we describe experiments toward imaging of VLA-4-positive BMD cells using a high-affinity PET probe, (64)Cu-labeled 11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2] hexadecane (CB-TE2A)-LLP2A. METHODS: VLA-4-negative MDA-MB-231/firefly luciferase (fluc) human breast tumor cells were injected intraarterially in the left ventricle in nude mice. Tumor metastasis in mice was monitored for 30 d by bioluminescence imaging and small-animal PET/CT. Small-animal PET images were collected 2 h after mice were injected in the tail vein with (64)Cu-CB-TE2A-LLP2A (5.6-11.1 MBq [150-300 µCi; specific activity, 400 µCi/µg]). Cellular uptake of (64)Cu-CB-TE2A-LLP2A was determined in VLA-4-positive B16F10 mouse melanoma cells and VLA-4-negative MDA-MB-231/fluc human breast cancer tumor cells. Biodistribution experiments in nude mice bearing VLA-4-positive B16F10 subcutaneous tumors in the flank were conducted to validate targeting of VLA-4-positive cells in vivo. RESULTS: Uptake of (64)Cu-CB-TE2A-LLP2A was higher in VLA-4-positive human melanoma B16F10 cells than in VLA-4-negative MDA-MB-231 cells (P < 0.05). In B16F10 tumor-bearing mice, (64)Cu-CB-TE2A-LLP2A had high uptake in the VLA-4-rich organs marrow, spleen, and tumor (11.26% ± 2.59%, 8.36% ± 2.15%, and 3.09% ± 0.58% injected dose/g, respectively). Cumulative standardized uptake value data from 2 independent studies (n = 7 and 8 mice) on nude mice implanted with VLA-4-negative MDA-MB-231/fluc human breast tumor cells suggested an influx of VLA-4-positive BMD cells that corresponded to metastasis (P < 0.05). Immunohistochemical analysis and flow cytometry also showed upregulation of VLA-4-positive cell clusters and BMD cells at the metastatic sites, providing evidence for noninvasive imaging of BMD cells in the premetastatic niche. CONCLUSION: The results of the study demonstrated the potential of PET with VLA-4-targeted (64)Cu-CB-TE2A-LLP2A to visualize BMD cell reorganization and expansion noninvasively in vivo.

Epitaxial overgrowth of platinum on palladium nanocrystals.

This paper describes a systematic study on the epitaxial overgrowth of Pt on well-defined Pd nanocrystals with different shapes (and exposed facets), including regular octahedrons, truncated octahedrons, and cubes. Two different reducing agents, i.e., citric acid and L-ascorbic acid, were evaluated and compared for the reduction of K2PtCl4 in an aqueous solution in the presence of Pd nanocrystal seeds. When citric acid was used as a reducing agent, conformal overgrowth of octahedral Pt shells on regular and truncated octahedrons of Pd led to the formation of Pd-Pt core-shell octahedrons, while non-conformal overgrowth of Pt on cubic Pd seeds resulted in the formation of an incomplete octahedral Pt shell. On the contrary, localized overgrowth of Pt branches was observed when L-ascorbic acid was used as a reducing agent regardless of the facets expressed on the surface of Pd nanocrystal seeds. This work shows that both the binding affinity of a reducing agent to the Pt surface and the reduction kinetics for a Pt precursor play important roles in determining the mode of Pt overgrowth on Pd nanocrystal surface.

Metal-polymer hybrid colloidal particles with an eccentric structure.

We have synthesized metal-polymer hybrid colloidal particles characterized by an eccentric structure by precipitation polymerization in the presence of metal colloids. The key to the formation of an eccentric core-shell structure was to introduce metal colloids a few minutes after (rather than before) starting the polymerization. The hybrid particles were uniform in size, and each one of them contained only one metal nanoparticle at its surface after the experimental procedures had been optimized. This method could be extended to a number of different metal colloids stabilized by small molecules, and the yield was found to be more or less independent of the size of the metal nanoparticles. In addition, the position of the metal nanoparticle in the hybrid particle could be controlled by changing the concentration of cross-linker, and the overall size of the hybrid particles could be altered by solvent treatment. Because of the simplicity of this procedure, it should be possible to use it for the large-scale production of colloidal particles having a hybrid, complex structure.

Pd-Pt bimetallic nanodendrites with high activity for oxygen reduction.

Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. We synthesized Pd-Pt bimetallic nanodendrites consisting of a dense array of Pt branches on a Pd core by reducing K2PtCl4 with L-ascorbic acid in the presence of uniform Pd nanocrystal seeds in an aqueous solution. The Pt branches supported on faceted Pd nanocrystals exhibited relatively large surface areas and particularly active facets toward the oxygen reduction reaction (ORR), the rate-determining step in a proton-exchange membrane fuel cell. The Pd-Pt nanodendrites were two and a half times more active on the basis of equivalent Pt mass for the ORR than the state-of-the-art Pt/C catalyst and five times more active than the first-generation supportless Pt-black catalyst.

Facile synthesis of highly faceted multioctahedral Pt nanocrystals through controlled overgrowth.

Highly faceted Pt nanocrystals with a large number of interconnected arms in a quasi-octahedral shape were synthesized simply by reducing H2PtCl6 precursor with poly(vinyl pyrrolidone) in aqueous solutions containing a trace amount of FeCl3. The iron species (Fe(3+) or Fe(2+)) play a key role in inducing the formation of the multioctahedral structure by decreasing the concentration of Pt atoms and keeping a low concentration for the Pt seeds during the reaction. This condition favors the overgrowth of Pt seeds along their corners and thus the formation of multiarmed nanocrystals. Electron microscopy studies revealed that the multioctahedral Pt nanocrystals exhibit a large number of edge, corner, and surface step atoms. The size of the multioctahedral Pt nanocrystals can be controlled by varying the concentration of FeCl3 added to the reaction and/or the reaction temperature. These multioctahedral Pt nanocrystals were tested as electrocatalysts for the oxygen reduction reaction in a proton exchange membrane fuel cell and exhibited improved specific activity and durability compared to commercial Pt/C catalyst.

Facile synthesis of bimetallic nanoplates consisting of Pd cores and Pt shells through seeded epitaxial growth.

Pd-Pt core-shell nanoplates with hexagonal and triangular shapes were synthesized through the heterogeneous, epitaxial growth of Pt on Pd nanoplates. The Pd nanoplates were synthesized by reducing Na2PdCl4 precursor with PVP as a reducing agent, which then served as seeds for the nucleation of Pt atoms formed by reducing H2PtCl6 with citric acid. Characterization of the as-prepared Pd-Pt nanoplates by scanning transmission electron microscopy and high-resolution transmission electron microscopy reveals that a thin, uniform Pt shell was formed around the Pd nanoplate, demonstrating the layer-by-layer epitaxial growth of Pt on Pd surface in this approach. The close lattice match between Pd and Pt (lattice mismatch of only 0.77%) and the slow reduction rate associated with the mild reducing power of citric acid play key roles in achieving the epitaxial growth of Pt shells on Pd nanoplates.