The transition from a non-invasive to an invasive phenotype is an essential step in tumor metastasis. The Snail family of transcription factors (TFs) is known to play a significant role in this transition. These TFs are zinc fingers that bind to the CAGGTG Ebox consensus sequence. Co^III-Ebox is a cobalt(III) complex attached to an Ebox oligonucleotide that confers specificity towards Snail TFs. Co^III-Ebox has been shown to inhibit Snail-mediated embryonic neural crest development in Xenopus laevis, but its efficacy in inhibiting Snail-induced cancer cell invasiveness has not been explored. Here, we describe the efficacy of Co^III-Ebox in inhibiting the invasive aspects of heregulin-β1(HRG)-treated breast cancer cells. Co^III-Ebox was found to inhibit the capacity of Snail to repress target genes after HRG induction. Snail inhibition by Co^III-Ebox reduced the invasive propensity of cells in 2D and 3D, thereby demonstrating promise in inhibiting metastasis.

Oligomers of the Aβ42 peptide are significant neurotoxins linked to Alzheimer's disease (AD). Histidine (His) residues present at the N terminus of Aβ42 are believed to influence toxicity by either serving as metal–ion binding sites (which promote oligomerization and oxidative damage) or facilitating synaptic binding. Transition metal complexes that bind to these residues and modulate Aβ toxicity have emerged as therapeutic candidates. Cobalt(III) Schiff base complexes (Co–sb) were evaluated for their ability to interact with Aβ peptides. HPLC-MS, NMR, fluorescence, and DFT studies demonstrated that Co–sb complexes could interact with the His residues in a truncated Aβ16 peptide representing the Aβ42 N terminus. Coordination of Co–sb complexes altered the structure of Aβ42 peptides and promoted the formation of large soluble oligomers. Interestingly, this structural perturbation of Aβ correlated to reduced synaptic binding to hippocampal neurons. These results demonstrate the promise of Co–sb complexes in anti-AD therapeutic approaches.

Transcription factors are key regulators in both normal and pathological cell processes. Affecting the activity of these proteins is a promising strategy for understanding gene regulation and developing effective therapeutics. Co^III Schiff base complexes ([Co(acacen)(L)₂]⁺ where L=labile axial ligands) have been shown to be potent inhibitors of a number of zinc metalloproteins including Cys₂His₂ zinc finger transcription factors. Inhibition by [Co(acacen)(L)₂]⁺ of the target protein is believed to occur through a dissociative exchange of the labile axial ligands for histidine (His) residues essential for function. Here, we report a series of spectroscopic investigations with model peptides of zinc fingers that elucidate the interaction between [Co(acacen)(L)₂]⁺ complexes and zinc finger transcription factors. Observed changes in NMR chemical shifts and 2D ¹H-¹H NOESY NMR spectra demonstrate the preference of [Co(acacen)(L)₂]⁺ complexes to coordinate His residues over other amino acids. The conformation of [Co(acacen)(L)₂]⁺ upon His coordination was characterized by ¹H NMR spectroscopy, near-UV CD, and electronic absorption. These studies reveal that the resulting His-coordinated [Co(acacen)(L)₂]⁺ complex possesses an octahedral structure. The effects of [Co(acacen)(L)₂]⁺ complexes on the zinc-finger structure were assessed by the degree of hydrogen bonding (probed by 2D NMR spectroscopy) and secondary-structure profiles measured by far-UV CD. These structural studies demonstrate the ability of [Co(acacen)(L)₂]⁺ complexes to disrupt the ββα structure of zinc fingers, resulting in primarily random-coil conformations. A mechanism is described wherein [Co(acacen)(L)₂]⁺ complexes inhibit zinc finger transcription factor activity through selectively coordinating His residues in the zinc finger by dissociative ligand exchange and disrupting the ββα structural motif required for gene regulation.

A bacteria-targeted MR contrast agent, Zn-1, consisting of two Zn-dipicolylamine (Zn-dpa) groups conjugated to a Gd^III chelate has been synthesized and characterized. In vitro studies with S. aureus and E. coli show that Zn-1 exhibits a significant improvement in bacteria labeling efficiency vs. control. Studies with a structural analogue, Zn-2, indicate that removal of one Zn-dpa moiety dramatically reduces the agent's affinity for bacteria. The ability of Zn-1 to significantly reduce the T₁ of labeled vs. unlabeled bacteria, resulting in enhanced MR image contrast, demonstrates its potential for visualizing bacterial infections in vivo.

In vivo iron load must be monitored to prevent complications from iron overload diseases such as hemochromatosis or transfusion-dependent anemias. While liver biopsy is the gold standard for determining in vivo iron load, MRI offers a noninvasive approach. MR phantoms have been reported that estimate iron concentration in the liver and mimic relaxation characteristics of in vivo deposits of hemosiderin. None of these phantoms take into account the size distribution of hemosiderin, which varies from patient to patient based on iron load. We synthesized stable and reproducible microsphere-ferritin conjugates (ferribeads) of different sizes that are easily characterized for several parameters that are necessary for modeling such as iron content and bead fraction. T₁s and T₂s were measured on a 1.41-T low-resolution NMR spectrometer and followed a size-dependent trend. Ferribeads imaged at 4.7 and 14.1 T showed that signal intensities are dependent on the distribution of ferritin around the bead rather than the iron concentration alone. These particles can be used to study the effects of particle size, ferritin distribution, and bead fraction on proton relaxation and may be of use in mimicking hemosiderin in a phantom for estimating iron concentration. Magn Reson Med, 2011. © 2010 Wiley-Liss, Inc.

Despite recent advances in tissue engineering to regenerate biological function by combining cells with material supports, development is hindered by inadequate techniques for characterizing biomaterials in vivo. Magnetic resonance imaging is a tomographic technique with high temporal and spatial resolution and represents an excellent imaging modality for longitudinal noninvasive assessment of biomaterials in vivo. To distinguish biomaterials from surrounding tissues for magnetic resonance imaging, protein polymer contrast agents were developed and incorporated into hydrogels. In vitro and in vivo images of protein polymer hydrogels, with and without covalently incorporated protein polymer contrast agents, were acquired by magnetic resonance imaging. T₁ values of the labeled gels were consistently lower when protein polymer contrast agents were included. As a result, the protein polymer contrast agent hydrogels facilitated fate tracking, quantification of degradation, and detection of immune response in vivo. For the duration of the in vivo study, the protein polymer contrast agent-containing hydrogels could be distinguished from adjacent tissues and from the foreign body response surrounding the gels. The hydrogels containing protein polymer contrast agent have a contrast-to-noise ratio 2-fold greater than hydrogels without protein polymer contrast agent. In the absence of the protein polymer contrast agent, hydrogels cannot be distinguished by the end of the gel lifetime. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.

We report the synthesis and characterization of polyvinyl alcohol (PVA) embolic particles modified with a clinically approved magnetic resonance (MR) contrast agent. PVA particles are used during transcatheter arterial embolization (TAE) procedures and this minimally invasive technique is a widely employed treatment for inoperable tumors. The PVA particles are injected into tumor vessels and prevent blood flow which results in tumor attenuation. An accurate assessment of the endpoint of embolization is critical to successful TAE procedures. Recent reports suggest that 20% of endpoint determination of TAE procedures by angiographic techniques are erroneous. Real time, in vivo imaging of the embolic particles would overcome this limitation. The contrast-modified PVA particles described here show an 80% decrease in T₁ relaxation times compared to unmodified particles. Images of particles in capillary tubes of similar size to catheters used in TAE procedures are clearly visible by MRI. Magn Reson Med 59:898–902, 2008. © 2008 Wiley-Liss, Inc.