Molecular imaging of breast cancer: present and future directions

Medical imaging technologies have undergone explosive growth over the past few decades and now play a central role in clinical oncology. But the truly transformative power of imaging in the clinical management of cancer patients lies ahead. Today, imaging is at a crossroads, with molecularly targeted imaging agents expected to broadly expand the capabilities of conventional anatomical imaging methods. Molecular imaging will allow clinicians to not only see where a tumor is located in the body, but also to visualize the expression and activity of specific molecules (e.g., proteases and protein kinases) and biological processes (e.g., apoptosis, angiogenesis, and metastasis) that influence tumor behavior and/or response to therapy. Breast cancer, the most common cancer among women and a research area where our group is actively involved, is a very heterogeneous disease with diverse patterns of development and response to treatment. Hence, molecular imaging is expected to have a major impact on this type of cancer, leading to important improvements in diagnosis, individualized treatment, and drug development, as well as our understanding of how breast cancer arises.

Fluorescent nanoparticle imaging allows noninvasive evaluation of immune cell modulation in esophageal dysplasia

Esophageal tumors provide unique challenges and opportunities for developing and testing surveillance imaging technology for different tumor microenvironment components, including assessment of immune cell modulation, with the ultimate goal of promoting early detection and response evaluation. In this context, accessibility through the lumen using a minimally invasive approach provides a means for repetitive evaluation longitudinally by combining fluorescent endoscopic imaging technology with novel fluorescent nanoparticles that are phagocytized by immune cells in the microenvironment. The agent we developed for imaging is synthesized from Feraheme (ferumoxytol), a Food and Drug Administration-approved monocrystaline dextran-coated iron oxide nanoparticle, which we conjugated to a near-infrared fluorochrome, CyAL5.5. We demonstrate a high level of uptake of the fluorescent nanoparticles by myeloid-derived suppressor cells (MDSCs) in the esophagus and spleen of L2Cre;p120ctnflox/flox mice. These mice develop esophageal dysplasia leading to squamous cell carcinoma; we have previously demonstrated that dysplastic and neoplastic esophageal lesions in these mice have an immune cell infiltration that is dominated by MDSCs. In the L2Cre;p120ctnflox/flox mice, evaluation of the spleen reveals that nearly 80% of CD45+ leukocytes that phagocytized the nanoparticle were CD11b+Gr1+ MDSCs. After dexamethasone treatment, we observed concordant decreased fluorescent signal from esophageal lesions during fluorescent endoscopy and decreased CyAL5.5-fluorescent-positive immune cell infiltration in esophageal dysplastic lesions by fluorescence-activated cell sorting analysis. Our observations suggest that this translatable technology may be used for the early detection of dysplastic changes and the serial assessment of immunomodulatory therapy and to visualize changes in MDSCs in the esophageal tumor microenvironment.

Fluorochrome-functionalized nanoparticles for imaging DNA in biological systems

Attaching DNA binding fluorochromes to nanoparticles (NPs) provides a way of obtaining NPs that bind to DNA through fluorochrome mediated interactions. To obtain a nanoparticle (NP) that bound to the DNA in biological systems, we attached the DNA binding fluorochrome, TO-PRO 1 (TO), to the surface of the Feraheme (FH) NP, to obtain a fluorochrome-functionalized NP denoted TO-FH. When reacted with DNA in vitro, TO-FH formed microaggregates that were characterized by fluorescence, light scattering, and T2 changes. The formation of DNA/TO-FH microaggregates was also characterized by AFM, with microaggregates exhibiting a median size of 200 nm, and consisting of DNA and multiple TO-FH NPs whose individual diameters were only 25-35 nm. TO-FH failed to bind normal cells in culture, but treatment with chemotherapeutic agents or detergents yielded necrotic cells that bound TO-FH and vital fluorochromes similarly. The uptake of TO-FH by HT-29 xenografts (treated with 5-FU and oxaliplatin) was evident by surface fluorescence and MRI. Attaching multiple DNA binding fluorochromes to magnetic nanoparticles provides a way of generating DNA binding NPs that can be used to detect DNA detection by microaggregate formation in vitro, for imaging the DNA of necrotic cells in culture, and for imaging the DNA of a tumor treated with a chemotherapeutic agent. Fluorochrome functionalized NPs are a multimodal (magnetic and fluorescent), highly multivalent (n ≈ 10 fluorochromes/NP) nanomaterials useful for imaging the DNA of biological systems.

Fluorochrome-functionalized magnetic nanoparticles for high-sensitivity monitoring of the polymerase chain reaction by magnetic resonance

Easy to find: magnetic nanoparticles bearing fluorochromes (red) that intercalate with DNA (green) form microaggregates with DNA generated by the polymerase chain reaction (PCR). These aggregates can be detected at low cycle numbers by magnetic resonance (MR).

A magnetofluorescent nanoparticle for ex-vivo cell labeling by covalently linking the drugs protamine and Feraheme

We synthesized a nanoparticle (NP) for ex-vivo cell labeling and MRI tracking by covalently coupling the C-terminus of a rhodamine-labeled protamine (ProRho) to Feraheme (FH) in order to yield the nanoparticle denoted ProRho-FH. Since protamine can adsorb to certain charged surfaces, we confirmed a covalent interaction between ProRho and FH by heparin affinity chromatography. ProRho-FH lacks a net charge (zeta potential approximately 0) due to the combination of negative FH and positive ProRho charges. ProRho-FH was readily internalized by U87 cells and mouse mesenchymal stem cells as determined by FACS and MR relaxometry. Finally, some 4,000 stem cells were implanted in a mouse brain and imaged by MRI. Due to its lack of net surface charge, ProRho-FH relies on the internalizing properties of the surface guanidinium groups present in the arginine-rich protamine to induce NP uptake. ProRho-FH is a unique cell-labeling agent due to its synthesis using two approved drugs, magnetofluorescence, site-specific covalent attachment chemistry, and lack of surface charge.

Supramolecular self-assembled arrangements of maltose glyconanoparticles

Our group previously reported the preparation of water-soluble Au-Fe(x)O(y) nanoparticles functionalized with a maltose neoglycoconjugate. A fraction soluble in methanol was also separated and originated a new supramolecular polymeric aggregate. We report here the full characterization of this novel material by transmission electron microscopy (TEM), fluorescence emission, and atomic force microscopy. By means of noncontact dynamic atomic force microscopy, we have been able to obtain information about the organization of the organic components of the polymers, which eluded TEM analysis. We have observed that polymers packed in units about 65 nm in length and 40 nm in width on Au surfaces. The nanoparticles seem to be encapsulated by the organic material. We propose interactions between the sugar residues and the amphiphilic character of the maltose neoglycoconjugate (with a lipophilic undecane spacer) as responsible for the origin of these amazing supramolecular arrangements.

Kinetic approach for the study of noncovalent interaction between [Ru(NH3)5pz]2+ and gold nanoparticles

Gold nanoparticles (AuNPs) capped with N-(2-mercaptopropionyl)glycine have been used to study the strength and character of the binding of a cationic metal complex, [Ru(NH3)5pz]2+ (pz = pyrazine), at pH = 8, to these nanoparticles. The strength of the binding has been studied using a kinetic approach consisting of the study of the kinetics of the oxidation of this ruthenium complex by S2O82- at different NaCl concentrations. When the ionic strength increases, the strength of the binding decreases, as a consequence of the partial neutralization of the charge on the AuNPs which, at pH = 8, has the tiopronin residue negatively charged. The increase of the ionic strength also produces a change in the character of the binding, which changes from anticooperative to noncooperative when the ionic strength increases. The nonelectrostatic and electrostatic components of the free energy of binding are determined. From the latter, we have obtained the values of the electrostatic potential differences at the AuNPs/solutions interface.