There are six specific subprojects for this Program of Excelence in Nanotechnology:

Project 1: Novel metal and semiconductor nanoparticles for improved in vivo sensing and targeting
The overall goal of this project is to advance our understanding of newer types of metal nanoparticles to optimize them for in vivo use. We will pursue detailed characterization of several such novel nanoparticles to identify those that are suitable as a platform for molecularly targeted delivery, while also being biodegradable and minimally toxic/immunogenic. Furthermore, to optimize target delivery (and therefore minimize accumulation in non-target tissues), we will seek nanoparticle preparations that exhibit a pharmacokinetic pattern of long blood half-life (> 6 hours in a mouse) and low hepatic uptake (< 50% injected dose in liver). Three recent discoveries in our laboratories form the basis of the proposed experiments: a) the observation that hybrid small molecule monolayers can result in highly functionalized materials with vastly improved physicochemical properties) the observation that nanostructuring of ligand shells can reduce nonspecific protein absorption) the synthesis and in vivo use of non-toxic silicon quantum dots.

Project 2: Nanoparticle libraries for targeting
To date, considerable effort has been directed toward surface modifications and coatings to modulate pharmacokinetic properties (e.g. blood half-life, elimination, biodegradation), toxicity and immunogenicity. Based on such biocompatible materials, targeting has generally been achieved by conjugating antibodies to nanoparticle surfaces. While this approach has been very successful for in vitro sensing 111,112, its in vivo application has proved more challenging because of immunogenicity, pharmacokinetics, cost, and shelf halflife. Another recent approach has been the conjugation of affinity peptides to nanoparticles. Recent advances in diversity-oriented synthesis and high throughput small molecule screening have led to the discovery of novel small molecules that specifically modulate protein function (among other macromolecules) by site-specific binding. The application of these small molecule approaches to the creation of nanomaterials offers the promise of a generalizable, higher throughput method to make novel nanomaterials and screen them for use in the diagnosis and treatment of disease. This project will synthesize the expertise of the Weissleder laboratory in medically useful nanoparticles, and the Schreiber laboratory in small molecule chemistry and technology to create and test the first diversity-oriented synthetic magnetofluorescent nanoparticle library.

Project 3: Perturbational profiling of toxicity and biological activity of novel nanomaterials
Our long-term goal is the development of novel nanomaterials that are useful as in vivo biological probes and therapies while having acceptable safety profiles. The safety of certain nanomaterials has been called into question by recent studies, but the extent of this problem is unknown. For instance, exposure to fullerenes resulted in increased brain lipid peroxidation in a fish model. Minimizing cellular toxicity and optimizing tissue specificity are important avenues towards the overall goal of clinically safe and effective nanomaterials. Current toxicity testing is largely based on laborious histologic or survival studies in animal models, or simple in vitro toxicologic measures such as LD50 (the dose at which 50% of the cells are killed); both approaches yield limited insights into the cellular mechanisms of toxicity. Furthermore, while tissuespecific targeting of nanomaterials has been reported, a systematic approach to evaluate the effects of nanomaterials in different cellular contexts is lacking. A recent report examined a variant of this problem, using a high throughput format to study the growth and differentiation of a single cell type (human embryonic stem cells) in the presence of hundreds of different polymers.

Project 4: Novel nanofabricated NO sensors
This project will develop, test and validate novel polymeric approaches to sensing analytes and biomarkers of relevance in cardiovascular disease. The concept is based on novel electrochemical and fluorescent polymers developed by the Swager lab. Specifically, we will develop NO sensors as well as enzyme sensors (e.g. proteases, esterases in macrophages). Nitric oxide (NO) regulates vascular tones and local blood flow, platelet aggregation and adhesion, and leukocyte-endothelial dysfunction, which occurs in hypertension, diabetes, aging and as a prelude to atherosclerosis. The common feature of endothelial dysfunction is a decrease in the amount of bioavailable NO. Despite the fact that NO has emerged as vital biological signaling agents with a multitude of roles in regulating cardiovascular systems, central nervous systems, blood flow, and immune response, the ability to precisely monitor the levels of NO in real-time in clinical settings remains a challenge.

Project 5: Nanosensing of Oxidative Stress in Atherosclerosis
Contemporary concepts of the pathogenesis of atherosclerosis accord a major role to oxidative stress. The vast majority of the literature regarding oxidation in atherosclerosis has revolved around lipoproteins 152,153. Oxidatively modified lipoprotein particles, particularly low density lipoproteins (LDL) can evoke many functions from vascular wall cells linked to atherogenesis. Oxidized phospholipids extracted from modified lipoproteins may account for many of these effects observed in vitro. Most of the protocols for producing oxidatively modified LDL for laboratory studies use transition-metal catalysis. in vivo, experimental and human atherosclerotic lesions contain abundant markers of oxidative modification of macromolecules. Oxidatively modified lipoproteins exist in atherosclerotic plaques. Circulating levels of oxidized LDL, measured by assays of varying validity and standardization, may correlate with atherosclerotic burden and events. Many animal experiments have shown reductions in atherosclerosis with antioxidant interventions. Yet, despite numerous attempts, clinical trials have thus far produced no convincing evidence for a benefit of antioxidant vitamins in reducing atherosclerosis or its complications.

Project 6: Protease nanosensors for pulmonary disease
Pulmonary emphysema is a major component of the morbidity and mortality of chronic obstructive pulmonary disease (COPD), a condition that afflicts more than 16 million persons in the US and has become the fourth leading cause of death. Furthermore, COPD accounts for 13% of hospital admissions in our country, and recent evidence suggests that its incidence is rising, particularly in women. Given the large increase in smoking in many countries COPD will become a major worldwide problem in the ensuing years. COPD is defined as fixed airflow obstruction in response to exposure to a noxious agent, which is most commonly long-term cigarette smoke exposure. COPD is comprised of emphysema and small airway obstruction. COPD encompasses both chronic bronchitis, a symptom of excessive mucous production, and emphysema, defined "as a condition of the lung characterized by abnormal, permanent enlargement of airspaces distal to the terminal bronchiole, accompanied by destruction of their walls. In fact, most patients have an admixture of large airway changes (accounting for symptoms of chronic bronchitis), small airway changes, and parenchymal lung involvement. One can dissect the pathogenesis of emphysema into four stages, each of which may be influenced by genetic factors. First, chronic exposure to cigarette smoke leads to inflammatory cell recruitment into the terminal airspaces of the lung. Second, these inflammatory cells release proteinases that damage the extracellular matrix of the lung. Third, structural cells are lost (likely secondary to loss of matrix attachment from proteinase activity, but possibly as a primary event). Fourth, damage coupled with ineffective repair of extracellular matrix and cellular components results in the loss of alveolar units and airspace enlargement that defines pulmonary emphysema.

Project 7: F13 targeted nanoassemblies for high efficiency thrombolytic delivery to thrombi
This project will utilize naturally occurring amino acids to form self-assembly nanoparticles to deliver tPA or UK to the clot by targeting F13. F13 is a tissue transglutaminase that covalently crosslinks certain peptide substrates into growing thrombi. We hypothesize, on the basis of our previous studies, that once injected into the body, the nanoparticles would accumulate in clot over time. There they would achieve high local concentrations and release tPA or UK in a controlled manner over an extended period of time. This hypothesis derivedderives from our recent work where we have shown that a F13 fluorogenic sensor can be used to: a) locally assess clot formation and b) measure the efficacy of F13-mediated retention of polymers in thrombi.