Timothy Larson

Multiwavelength Photoacoustic Imaging and Plasmon Resonance Coupling of Gold Nanoparticles for Selective Detection of Cancer

Gold nanoparticles targeting epidermal growth factor receptor via antibody conjugation undergo molecular specific aggregation when they bind to receptors on cell surfaces, leading to a red shift in their plasmon resonance frequency. Capitalizing on this effect, we demonstrate the efficacy of the molecular specific photoacoustic imaging technique using subcutaneous tumor-mimicking gelatin implants in ex-vivo mouse tissue. The results of our study suggest that highly selective and sensitive detection of cancer cells is possible using multiwavelength photoacoustic imaging and molecular specific gold nanoparticles.

Preventing Protein Adsorption and Macrophage Uptake of Gold Nanoparticles via a Hydrophobic Shield

Polyethylene glycol (PEG) surface coatings are widely used to render stealth properties to nanoparticles in biological applications. There is abundant literature on the benefits of PEG coatings and their ability to reduce protein adsorption, to diminish nonspecific interactions with cells, and to improve pharmacokinetics, but very little discussion of the limitations of PEG coatings. Here, we show that physiological concentrations of cysteine and cystine can displace methoxy-PEG-thiol molecules from the gold nanoparticle (GNP) surface that leads to protein adsorption and cell uptake in macrophages within 24 h. Furthermore, we address this problem by incorporating an alkyl linker between the PEG and the thiol moieties that provides a hydrophobic shield layer between the gold surface and the hydrophilic outer PEG layer. The mPEG-alkyl-thiol coating greatly reduces protein adsorption on GNPs and their macrophage uptake. This has important implications for the design of GNP for biological systems.

Photoacoustic imaging and temperature measurement for photothermal cancer therapy.

Photothermal therapy is a noninvasive, targeted, laser-based technique for cancer treatment. During photothermal therapy, light energy is converted to heat by tumor-specific photoabsorbers. The corresponding temperature rise causes localized cancer destruction. For effective treatment, however, the presence of photoabsorbers in the tumor must be ascertained before therapy and thermal imaging must be performed during therapy. This study investigates the feasibility of guiding photothermal therapy by using photoacoustic imaging to detect photoabsorbers and to monitor temperature elevation. Photothermal therapy is carried out by utilizing a continuous wave laser and metal nanocomposites broadly absorbing in the near-infrared optical range. A linear array-based ultrasound imaging system is interfaced with a nanosecond pulsed laser to image tissue-mimicking phantoms and ex-vivo animal tissue before and during photothermal therapy. Before commencing therapy, photoacoustic imaging identifies the presence and spatial location of nanoparticles. Thermal maps are computed by monitoring temperature-induced changes in the photoacoustic signal during the therapeutic procedure and are compared with temperature estimates obtained from ultrasound imaging. The results of our study suggest that photoacoustic imaging, augmented by ultrasound imaging, is a viable candidate to guide photoabsorber-enhanced photothermal therapy.

Small multifunctional nanoclusters (Nanoroses) for targeted cellular imaging and therapy

The ability of 20-50 nm nanoparticles to target and modulate the biology of specific types of cells will enable major advancements in cellular imaging and therapy in cancer and atherosclerosis. A key challenge is to load an extremely high degree of targeting, imaging, and therapeutic functionality into small, yet stable particles. Herein we report approximately 30 nm stable uniformly sized near-infrared (NIR) active, superparamagnetic nanoclusters formed by kinetically controlled self-assembly of gold-coated iron oxide nanoparticles. The controlled assembly of nanocomposite particles into clusters with small primary particle spacings produces collective responses of the electrons that shift the absorbance into the NIR region. The nanoclusters of approximately 70 iron oxide primary particles with thin gold coatings display intense NIR (700-850 nm) absorbance with a cross section of approximately 10(-14) m(2). Because of the thin gold shells with an average thickness of only 2 nm, the r(2) spin-spin magnetic relaxivity is 219 mM(-1) s(-1), an order of magnitude larger than observed for typical iron oxide particles with thicker gold shells. Despite only 12% by weight polymeric stabilizer, the particle size and NIR absorbance change very little in deionized water over 8 months. High uptake of the nanoclusters by macrophages is facilitated by the dextran coating, producing intense NIR contrast in dark field and hyperspectral microscopy, both in cell culture and an in vivo rabbit model of atherosclerosis. Small nanoclusters with optical, magnetic, and therapeutic functionality, designed by assembly of nanoparticle building blocks, offer broad opportunities for targeted cellular imaging, therapy, and combined imaging and therapy.

Molecular specific optoacoustic imaging with plasmonic nanoparticles

Gold nanoparticles functionalized with antibodies can specifically bind to molecular biomarkers such as epithelial growth factor receptor (EGFR). The molecule specific nature of the antibody-functionalized gold nanoparticles forms the basis for the developed optoacoustic imaging technique to detect cancer at an asymptotic stage. Optoacoustic imaging was performed with 532 nm and 680 nm pulsed laser irradiation on three-dimensional tissue phantoms prepared using a human keratinocyte cell line. The results of our study demonstrate that the combination of anti-EGFR gold ioconjugates and optoacoustic imaging can allow highly sensitive and selective detection of human epithelial cancer cells.

Plasmonic Intravascular Photoacoustic Imaging for Detection of Macrophages in Atherosclerotic Plaques

To detect macrophages in atherosclerotic plaques, plasmonic gold nanoparticles are introduced as a contrast agent for intravascular photoacoustic imaging. The phantom and ex vivo tissue studies show that the individual spherical nanoparticles, resonant at 530 nm wavelength, produce a weak photoacoustic signal at 680 nm wavelength while photoacoustic signal from nanoparticles internalized by macrophages is very strong due to the plasmon resonance coupling effect. These results suggest that intravascular photoacoustic imaging can assess the macrophage-mediated aggregation of nanoparticles and therefore identify the presence and the location of nanoparticles associated with macrophage-rich atherosclerotic plaques.

Hybrid plasmonic magnetic nanoparticles as molecular specific agents for MRI/optical imaging and photothermal therapy of cancer cells

Nanoparticles which consist of a plasmonic layer and an iron oxide moiety could provide a promising platform for development of multimodal imaging and therapy approaches in future medicine. However, the feasibility of this platform has yet to be fully explored. In this study we demonstrated the use of gold-coated iron oxide hybrid nanoparticles for combined molecular specific MRI/optical imaging and photothermal therapy of cancer cells. The gold layer exhibits a surface plasmon resonance that provides optical contrast due to light scattering in the visible region and also presents a convenient surface for conjugating targeting moieties, while the iron oxide cores give strong T2 (spin?spin relaxation time) contrast. The strong optical absorption of the plasmonic gold layer also makes these nanoparticles a promising agent for photothermal therapy. We synthesized hybrid nanoparticles which specifically target epidermal growth factor receptor (EGFR), a common biomarker for many epithelial cancers. We demonstrated molecular specific MRI and optical imaging in MDA-MB-468 breast cancer cells. Furthermore, we showed that receptor-mediated aggregation of anti-EGFR hybrid nanoparticles allows selective destruction of highly proliferative cancer cells using a nanosecond pulsed laser at 700?nm wavelength, a significant shift from the peak absorbance of isolated hybrid nanoparticles at 532?nm.

Directed evolution of gold nanoparticle delivery to cells

A newly selected anti-receptor (anti-EGFR) aptamer was conjugated to gold nanoparticles via a facile hybridization method and was found to specifically and quantitatively direct the delivery of gold nanoparticles to cells expressing EGFR through receptor-mediated endocytosis.

EGFR-Targeted Hybrid Plasmonic Magnetic Nanoparticles Synergistically Induce Autophagy and Apoptosis in Non-Small Cell Lung Cancer Cells

Background The epidermal growth factor receptor (EGFR) is overexpressed in 80% of non-small cell lung cancer (NSCLC) and is associated with poor survival. In recent years, EGFR-targeted inhibitors have been tested in the clinic for NSCLC. Despite the emergence of novel therapeutics and their application in cancer therapy, the overall survival rate of lung cancer patients remains 15%. To develop more effective therapies for lung cancer we have combined the anti-EGFR antibody (Clone 225) as a molecular therapeutic with hybrid plasmonic magnetic nanoparticles (NP) and tested on non-small cell lung cancer (NSCLC) cells. Methodology/Principal Findings Cell viability was determined by trypan-blue assay. Cellular protein expression was determined by Western blotting. C225-NPs were detected by electron microscopy and confocal microscopy, and EGFR expression using immunocytochemistry. C225-NP exhibited a strong and selective antitumor effect on EGFR-expressing NSCLC cells by inhibiting EGFR-mediated signal transduction and induced autophagy and apoptosis in tumor cells. Optical images showed specificity of interactions between C225-NP and EGFR-expressing NSCLC cells. No binding of C225-NP was observed for EGFR-null NSCLC cells. C225-NP exhibited higher efficiency in induction of cell killing in comparison with the same amount of free C225 antibody in tumor cells with different levels of EGFR expression. Furthermore, in contrast to C225-NP, free C225 antibody did not induce autophagy in cells. However, the therapeutic efficacy of C225-NP gradually approached the level of free antibodies as the amount of C225 antibody conjugated per nanoparticle was decreased. Finally, attaching C225 to NP was important for producing the enhanced tumor cell killing as addition of mixture of free C225 and NP did not demonstrate the same degree of cell killing activity. Conclusions/Significance We demonstrated for the first time the molecular mechanism of C225-NP induced cytotoxic effects in lung cancer cells that are not characteristic for free molecular therapeutics thus increasing efficacy of therapy against NSCLC.

Increased optical contrast in imaging of epidermal growth factor receptor using magnetically actuated hybrid gold/iron oxide nanoparticles

We describe a new approach for optical imaging that combines the advantages of molecularly targeted plasmonic nanoparticles and magnetic actuation. This combination is achieved through hybrid nanoparticles with an iron oxide core surrounded by a gold layer. The nanoparticles are targeted in-vitro to epidermal growth factor receptor, a common cancer biomarker. The gold portion resonantly scatters visible light giving a strong optical signal and the superparamagnetic core provides a means to externally modulate the optical signal. The combination of bright plasmon resonance scattering and magnetic actuation produces a dramatic increase in contrast in optical imaging of cells labeled with hybrid gold/iron oxide nanoparticles.