Michelle S. Bradbury

Multimodal silica nanoparticles are effective cancer-targeted probes in a model of human melanoma

Nanoparticle-based materials, such as drug delivery vehicles and diagnostic probes, currently under evaluation in oncology clinical trials are largely not tumor selective. To be clinically successful, the next generation of nanoparticle agents should be tumor selective, nontoxic, and exhibit favorable targeting and clearance profiles. Developing probes meeting these criteria is challenging, requiring comprehensive in vivo evaluations. Here, we describe our full characterization of an approximately 7-nm diameter multimodal silica nanoparticle, exhibiting what we believe to be a unique combination of structural, optical, and biological properties. This ultrasmall cancer-selective silica particle was recently approved for a first-in-human clinical trial. Optimized for efficient renal clearance, it concurrently achieved specific tumor targeting. Dye-encapsulating particles, surface functionalized with cyclic arginine-glycine-aspartic acid peptide ligands and radioiodine, exhibited high-affinity/avidity binding, favorable tumor-to-blood residence time ratios, and enhanced tumor-selective accumulation in αvβ3 integrin-expressing melanoma xenografts in mice. Further, the sensitive, real-time detection and imaging of lymphatic drainage patterns, particle clearance rates, nodal metastases, and differential tumor burden in a large-animal model of melanoma highlighted the distinct potential advantage of this multimodal platform for staging metastatic disease in the clinical setting.

Fluorescent Silica Nanoparticles with Efficient Urinary Excretion for Nanomedicine

The development of molecularly targeted probes that exhibit high biostability, biocompatibility, and efficient clearance profiles is key to optimizing biodistribution and transport across biological barriers. Further, coupling probes designed to meet these criteria with high-sensitivity, quantitative imaging strategies is mandatory for ensuring early in vivo tumor detection and timely treatment response. These challenges have often only been examined individually, impeding the clinical translation of fluorescent probes. By simultaneously optimizing these design criteria, we created a new generation of near-infrared fluorescent core-shell silica-based nanoparticles (C dots) tuned to hydrodynamic diameters of 3.3 and 6.0 nm with improved photophysical characteristics over the parent dye. A neutral organic coating prevented adsorption of serum proteins and facilitated efficient urinary excretion. Detailed particle biodistribution studies were performed using more quantitative ex vivo fluorescence detection protocols and combined optical-PET imaging. The results suggest that this new generation of C dots constitutes a promising clinically translatable materials platform which may be adapted for tumor targeting and treatment.

Derivation of engraftable skeletal myoblasts from human embryonic stem cells

Human embryonic stem cells (hESCs) are a promising source for cell therapy in degenerative diseases. A key step in establishing the medical potential of hESCs is the development of techniques for the conversion of hESCs into tissue-restricted precursors suitable for transplantation. We recently described the derivation of multipotent mesenchymal precursors from hESCs. Nevertheless, our previous study was limited by the requirement for mouse feeders and the lack of in vivo data. Here we report a stroma-free induction system for deriving mesenchymal precursors. Selective culture conditions and fluorescence-activated cell sorting (FACS)-mediated purification yielded multipotent mesenchymal precursors and skeletal myoblasts. Skeletal muscle cells undergo in vitro maturation resulting in myotube formation and spontaneous twitching. We found that hESC-derived skeletal myoblasts were viable after transplantation into the tibialis anterior muscle of SCID/Beige mice, as assessed by bioluminescence imaging. Lack of teratoma formation and evidence of long-term myoblast engraftment suggests considerable potential for future therapeutic applications.

Clinical translation of an ultrasmall inorganic optical-PET imaging nanoparticle probe

Ultrasmall inorganic hybrid optical-PET imaging particles were found to be safe and physiologically stable in patients with melanoma. First-in-Human Nanoparticles for Molecular Cancer Imaging Molecular targeting and nanotechnology together have a promising future in cancer imaging. Tiny particles can be coated with antibodies or peptides to target a molecule specific to cancer, improving diagnostic accuracy and patient stratification. Yet, these decorated nanoparticles have been slow in making it to clinical trials. Now, Phillips and colleagues describe the translation of ultrasmall (<10 nm) inorganic nanoparticles, called “C dots,” from animals to patients. The C dots comprised a silica shell encapsulating the fluorescent Cy5 dye, coated with a polymer called poly(ethylene glycol) (PEG), and then decorated with the integrin-targeting, radiolabeled peptide 124I-cRGDY. With the Cy5 and 124I, the particle could be imaged by optical methods (fluorescence) and by positron emission tomography (PET). The goal of this first-in-human study was to evaluate pharmacokinetics and biodistribution of the 124I-cRGDY–PEG–C dots when injected systemically, with molecular targeting and cancer imaging as a secondary effort. The authors found that the nanoparticles were not toxic in a small group of five patients with metastatic melanoma and that the particles were excreted intact via the kidneys and bladder (by contrast, larger or uncoated particles often get lodged in the liver). In some patients, the C dots were visible in the tumor region by PET imaging. Many more patients will need to be studied to confirm lack of toxicity and to optimize tumor targeting, but this first demonstration in people suggests that such ultrasmall nanoparticles can be tested in people, heralding in a new era of molecular cancer imaging. A first-in-human clinical trial of ultrasmall inorganic hybrid nanoparticles, “C dots” (Cornell dots), in patients with metastatic melanoma is described for the imaging of cancer. These renally excreted silica particles were labeled with 124I for positron emission tomography (PET) imaging and modified with cRGDY peptides for molecular targeting. 124I-cRGDY–PEG–C dot particles are inherently fluorescent, containing the dye, Cy5, so they may be used as hybrid PET-optical imaging agents for lesion detection, cancer staging, and treatment management in humans. However, the clinical translation of nanoparticle probes, including quantum dots, has not kept pace with the accelerated growth in minimally invasive surgical tools that rely on optical imaging agents. The safety, pharmacokinetics, clearance properties, and radiation dosimetry of 124I-cRGDY–PEG–C dots were assessed by serial PET and computerized tomography after intravenous administration in patients. Metabolic profiles and laboratory tests of blood and urine specimens, obtained before and after particle injection, were monitored over a 2-week interval. Findings are consistent with a well-tolerated inorganic particle tracer exhibiting in vivo stability and distinct, reproducible pharmacokinetic signatures defined by renal excretion. No toxic or adverse events attributable to the particles were observed. Coupled with preferential uptake and localization of the probe at sites of disease, these first-in-human results suggest safe use of these particles in human cancer diagnostics.

Associations among Magnetic Resonance Spectroscopy, Apparent Diffusion Coefficients, and Image-guided Histopathology with Special Attention to Radiation Necrosis

OBJECTIVE:In patients with malignant glioma previously treated with surgery, radiation, and chemotherapy, clinical and radiographic signs of recurrent disease often require differentiation between radiation necrosis and recurrent tumor. Published work suggests that although magnetic resonance spectroscopy (MRS) can reliably differentiate pure tumor, pure necrosis, and spectroscopically normal tissues, it may not be particularly helpful because most patients have mixed histological findings comprised of necrosis and tumor. To improve our clinical ability to discriminate among these histological entities, we have analyzed MRS in conjunction with apparent diffusion coefficient (ADC) sequences derived from magnetic resonance imaging. METHODS:In 18 patients, spectroscopic and diffusion-weighted images were obtained before surgery for suspected recurrent neoplastic disease. Spectral data for pure tumor, pure necrosis, and mixed tumor and necrosis were derived from 65 spectroscopic observations in patients with previously treated gliomas (n = 16) and metastatic tumors (n = 2). Spectral data for choline (Cho), N-acetylaspartate (NAA), creatine (Cr), and lipid-lactate were analyzed separately and in conjunction with ADCs in all patients (15 observations of pure tumor, 33 observations of pure necrosis, and 13 observations of mixed tumor and necrosis). Histological specimens were obtained stereotactically at the time of surgery (<48 h after image acquisition) for recurrent disease and digitally co-registered with MRS data. RESULTS:ADC values for pure tumor, pure necrosis, and mixed tumor and necrosis were 1.30, 1.60, and 1.42, respectively. Cho/NAA less than 0.20, NAA/normal Cr greater than 1.56, and NAA/Cho greater than 1.32 increase the odds that a tissue biopsy will be pure necrosis versus mixed tumor and necrosis. Although various values of all MRS ratios analyzed may provide positive correlations for histopathological differentiation of tissue between that of pure tumor and that of pure necrosis, the addition of ADC values to only NAA/Cho and NAA/normal Cr increases the odds of correct differentiation between pure tumor and pure necrosis. The addition of ADC values does not provide additional information beyond that of MRS in distinguishing specimens of mixed tumor and necrosis from either pure tumor or pure necrosis. CONCLUSION:It has been demonstrated that MRS ratio analysis may allow for the clinical discrimination between specimens of pure tumor and pure necrosis, and the addition of ADC data into this analysis may enhance this specific differentiation. However, although a trend toward correlation between ADC values and the various histopathological features was noted, the direct addition of ADC data does not seem to allow further discrimination, beyond that provided by MRS, among specimens of mixed tumor and necrosis and either pure tumor or pure necrosis.

Long-Term Impact of Radiation on the Stem Cell and Oligodendrocyte Precursors in the Brain

Background The cellular basis of long term radiation damage in the brain is not fully understood. Methods and Findings We administered a dose of 25Gy to adult rat brains while shielding the olfactory bulbs. Quantitative analyses were serially performed on different brain regions over 15 months. Our data reveal an immediate and permanent suppression of SVZ proliferation and neurogenesis. The olfactory bulb demonstrates a transient but remarkable SVZ-independent ability for compensation and maintenance of the calretinin interneuron population. The oligodendrocyte compartment exhibits a complex pattern of limited proliferation of NG2 progenitors but steady loss of the oligodendroglial antigen O4. As of nine months post radiation, diffuse demyelination starts in all irradiated brains. Counts of capillary segments and length demonstrate significant loss one day post radiation but swift and persistent recovery of the vasculature up to 15 months post XRT. MRI imaging confirms loss of volume of the corpus callosum and early signs of demyelination at 12 months. Ultrastructural analysis demonstrates progressive degradation of myelin sheaths with axonal preservation. Areas of focal necrosis appear beyond 15 months and are preceded by widespread demyelination. Human white matter specimens obtained post-radiation confirm early loss of oligodendrocyte progenitors and delayed onset of myelin sheath fragmentation with preserved capillaries. Conclusions This study demonstrates that long term radiation injury is associated with irreversible damage to the neural stem cell compartment in the rodent SVZ and loss of oligodendrocyte precursor cells in both rodent and human brain. Delayed onset demyelination precedes focal necrosis and is likely due to the loss of oligodendrocyte precursors and the inability of the stem cell compartment to compensate for this loss.

Effect of brain tumor neovasculature defined by rCBV on BOLD fMRI activation volume in the primary motor cortex.

We utilized blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) and MR perfusion imaging methods to study the influence of brain tumor neovascularity on the BOLD fMRI activation volume in the primary motor cortex (PMC). The results from 57 brain tumor cases demonstrated that, for grade IV gliomas only, decreases in the BOLD fMRI activation volumes within the ipsilateral PMC, when compared with that observed in the contralateral PMC, correlated with increases in the relative regional cerebral blood volume (rCBV) in the PMC. In addition, relative increases in the activation volumes, corresponding to decreases in the rCBV, exhibited a linear dependence on the distance between the grade IV glioma and PMC. These findings lend support to the hypothesis that decreases in the fMRI activation volumes adjacent to a GBM may, in part, be due to the increased contribution of aberrant tumor neovascularity, with the resultant de-coupling of blood flow from neuronal activity. The nature of the relationship between the resulting activation volumes and adjacent tumor characteristics is complex, but is found to be dependent on the tumor grade and type, as well as the distance of the tumor to the PMC.

Highly Aminated Mesoporous Silica Nanoparticles with Cubic Pore Structure

Mesoporous silica with cubic symmetry has attracted interest from researchers for some time. Here, we present the room temperature synthesis of mesoporous silica nanoparticles possessing cubic Pm3n symmetry with very high molar ratios (>50%) of 3-aminopropyl triethoxysilane. The synthesis is robust allowing, for example, co-condensation of organic dyes without loss of structure. By means of pore expander molecules, the pore size can be enlarged from 2.7 to 5 nm, while particle size decreases. Adding pore expander and co-condensing fluorescent dyes in the same synthesis reduces average particle size further down to 100 nm. After PEGylation, such fluorescent aminated mesoporous silica nanoparticles are spontaneously taken up by cells as demonstrated by fluorescence microscopy.

Multicompartment Mesoporous Silica Nanoparticles with Branched Shapes: An Epitaxial Growth Mechanism

Tuning Mesopores Porous materials are of interest for catalysis and filtration because the open channels lend themselves to separating materials or function. Suteewong et al. (p. 337) report on a method to make branched mesoporous silica nanoparticles that contain cubic (core) and hexagonally structured (branch) parts within one particle. Controlling the extent of the branched structure is achieved by tuning the concentration of additives in a simple, one-pot reaction system. A one-pot synthesis method furnishes mesoporous silica nanoparticles with both cubic and hexagonally structured compartments. Mesoporous nanomaterials have attracted widespread interest because of their structural versatility for applications including catalysis, separation, and nanomedicine. We report a one-pot synthesis method for a class of mesoporous silica nanoparticles (MSNs) containing both cubic and hexagonally structured compartments within one particle. These multicompartment MSNs (mc-MSNs) consist of a core with cage-like cubic mesoporous morphology and up to four branches with hexagonally packed cylindrical mesopores epitaxially growing out of the cubic core vertices. The extent of cylindrical mesostructure growth can be controlled via a single additive in the synthesis. Results suggest a path toward high levels of architectural complexity in locally amorphous, mesostructured nanoparticles, which could enable tuning of different pore environments of the same particle for specific chemistries in catalysis or drug delivery.

Ultrasmall nanoparticles induce ferroptosis in nutrient-deprived cancer cells and suppress tumour growth

The design of cancer-targeting particles with precisely-tuned physiocochemical properties may enhance delivery of therapeutics and access to pharmacological targets. However, molecular level understanding of the interactions driving the fate of nanomedicine in biological systems remains elusive. Here, we show that ultrasmall (< 10 nm in diameter) poly(ethylene glycol) (PEG)-coated silica nanoparticles, functionalized with melanoma-targeting peptides, can induce a form of programmed cell death known as ferroptosis in starved cancer cells and cancer-bearing mice. Tumor xenografts in mice intravenously injected with nanoparticles using a high-dose multiple injection scheme exhibit reduced growth or regression, in a manner that is reversed by the pharmacological inhibitor of ferroptosis, liproxstatin-1. These data demonstrate that ferroptosis can be targeted by ultrasmall silica nanoparticles and may have therapeutic potential.