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Gold Nanoparticles

This article is about gold nanoparticles in chemotherapy. For colloidal gold, see Colloidal gold.

Gold Nanoparticles in Chemotherapy is the use of collodial gold in therapeutic treatments, often for cancer or arthritis. Gold nanoparticle technology shows promise in the advancement of cancer treatments. With tumor-targeting delivery vectors becoming smaller, the ability to by-pass the natural barriers and obstacles of the body becomes more probable. To increase specificity and likelihood of drug delivery, tumor specific ligands may be grafted onto the particles to circulate throughout the tumor without being redistributed into the body.

Obstacles may include cell type targeting. A tumor consists of a multitude of cell types, and thus targeting a single type of cell is ineffective and potentially dangerous. At most, this type of targeting would only have a minor effect on killing the tumor. Tumors are constantly changing and thus phenotype targeting is rendered useless. Two main problems persist: how to get to the target and how to destroy a variety of cells.

Physical Properties

Solutions of gold nanoparticles of various sizes. The size difference causes the difference in colors.

Size

Gold nanoparticles range in size depending on which therapy it is being used for. In photothermal cancer therapy, the sizes of the required molecules must be uniform. Including PEG coating, the nanoparticles measured to be ~130 nm in diameter.

Drug vectorization requires greater specificity, and are synthesized within the single digit measurements ranging from 3-7 nm.

Antibacterial treatments are testing different sizes for cell type targeting; 10, 20 and 40 nm.

Colour

Due to the ability to tune the size and absorption of AuNPs, the various colours it emits can range from a vibrant red to a pale blue. These colours play a necessary role in the synthesis of AuNPs, as indicators of reduction.

Synthesis

For more on synthesis of AuNPs for medical use, see Colloidal Gold

The Turkevich Method – Sodium Citric Acid Gold: Used specifically for production of uniform sizes. A solution of chloroauric acid and citric acid were boiled with virgorous stirring. Colour changes were apparent, starting from a faint grayish-pink/blue and darkened over time, indicating a reduction from Au(III) to Au(I). The particles that were noted when examined under an electron microscope were spherical. Particle size ranged from 200±15 Å. Gold conjugates with anti-EFGR were prepared by mixing the reduced Au with the anti-EFGR solution.

Mechanism

The gold particles provide a surface for self-assembly of its shell (PEG, antibodies, etc.) for biocompatibility. AuNPs bind to EFGR on the surface and act as photoabsorbers, absorbing a wavelength of 530 nm without damaging benign cells. Power densities of 76, 64, 50, 38, 25 and 19 W/cm² were used on benign cells. After trypan blue staining to detect dead tissue, the test was negative for any blue cells. Thus these power densities were chosen as the magnitude to expose the AuNP incubated, malignant HSC cells.

Treatments

Photothermal Cancer Therapy

Main Article: Photothermal therapy[[|alt=http://nanohybrids.net/pages/molecular-targeting-in-imaging%7Cthumb%7C(Left) Overexpression of EFGR emitting from cancerous cells. (Right) AuNP conjugation by use of EFGR targeting. Reprinted with permission of NanoHybrids. |319x319px]] A direct method of accessing and destroying tumour cells can be accomplished by photothermal cancer therapy or photodynamic therapy (PDT). This procedure is known to treat small tumours that are difficult to access and avoids the drawbacks (adverse effects) of conventional methods, including the unnecessary destruction of healthy tissues. The cells are destroyed by exposure to light, rupturing membranes causing the release of digestive enzymes. AuNPs have high absorption cross sections requiring only minimal input of irradiation energy. Human breast carcinoma cells infused with metal nanoparticles in vitro have been shown to have an increase in morbidity with exposure to near infrared (NIR). Short term exposure in vivo (4–6 minutes) to NIR had undergone the same effect. Hirsch et al observed that extreme heating in tumours would cause irreversible tissue damage including coagulation, cell shrinkage and loss of nuclear straining. Results of their in vivo nanoshell therapy of mice revealed penetration of the tumor ~5mm.The metal particles were tuned to high absorption and scattering, resulting in effective conversion of light into heat covering a large surface area. [[|alt=http://nanohybrids.net/pages/molecular-targeting-in-imaging%7Cleft%7Cthumb%7CA spherical gold nanoparticle conjugated with various biomarkers for masking and binding. Reprinted with permission of Nanohyrids. |347x347px]] The El-Sayed group studied AuNP effects in vitro and in vivo. They determined that the NIR wavelengths were converted into heat on the picosecond timescale, allowing for short exposure of CW to minimize possible exposure to healthy cells. In vitro, photothermal therapy was used in oral epithelial cell lines, (HSC 313 and HOC 3 Clone 8) and one benign epithelial cell line (HaCaT). El-Sayed et al found that the malignant cells that had undergone incubation in AuNPs conjugated with anti-epithelial growth factor receptor (EGFR) required half the energy to destroy a cell than a benign cell. Their material included gold coated silica nanoshells that could selectively absorb NIR waves. The particles were tuned by varying the thickness of the Au shell and changing the size of the silica core. In exposing these particles to NIR, the efficacy of Au was measured through the decrease of EFGR in oral squamous carcinoma cells.

There are various biotechnological advances for in vivo delivery of drugs.To effectively target the malignant cells, the AuNPs were conjugated by polyethylene glycol, a process known as PEGylation. This masks the foreign particles from the immune system such that it arrives at its destination and increases circulation time in the system. Antibody conjugation lines the surface of the nanoparticle with cell markers to limit spread only to malignant cells.

In vivo testing of mice that developed murine colon carcinoma tumour cells. They were injected with the solution of AuNPs that were allowed to spread after 6 hours. Surrounding cells were swabbed with PEG and exposed to laser treatment for detection of abnormal heating indicating areas where Au nanoshells may have gathered. The injected area was also swabbed with PEG to maximize light penetration.

Radio frequency therapy

Main article: Radiofrequency Ablation

X-ray radiography procedures involve the diagnosis of cancer cells through the process of image acquisition. These techniques rely on the absorption of x-rays on the exposed tissue in order to improve image quality. In certain radiological procedures such as Radio Frequency Therapy, a contrast agent can be injected into the targeted cancer tissue and result in increased x-ray attenuation.

Radiofrequency therapy treatment involves the destruction of tumor cancer tissue cells through the differential heating of cancer tissue by radio-frequency diathermy. This differential heating is a result of the blood supply in the body carrying away the heat and cooling the heated tissue.

Gold nanoparticles are excellent absorbers of x-rays, due to its high atomic number of ⁷⁹Au. This allows for a higher mass of the element, providing for a greater area of x-ray absorption. By acting as a contrast agent and injected into cancerous tumor cells, it would result in a higher dose of the cancerous tissue being exposed during radiotherapy treatment.

Anti-Angiogenesis Therapy

Main article: Therapeutic angiogenesis

Angiogenesis is the formation of new blood vessels from pre-existing vessels. It is said to play a large part in the growth and spread of cancer cells. AuNPs have the ability to inhibit angiogenesis by directly coordinating to heparin binding growth factors. They are able to inhibit phosphorylation of proteins responsible for angiogenesis in a dose dependent matter. At concentrations 335-670 nm, almost complete inhibition of phosphorylation was observed. Development of this technology has been found to reduce the effects of rheumatoid arthritis due to a decrease in blood vessels for inflammatory proteins to travel.

In addition, angiogenic inhibitors have a critical limitation due to the instability of biological conditions and high dosage required. To counter this, an emerging strategy for the development of therapies targeting tumor-associated angiogenesis through the use of nanotechnology and anti-angiogenic agents was developed. This approach solved the limitation instability by speeding up the delivery of angiogenesis inhibitors.

Gold nanoparticles display anti-angiogenic properties by inhibiting the function of pro-angiogenic heparin-binding growth factors (HG – GFs), with prime examples being the vascular endothelial growth factor 165 (VEGF165) and the basic fibroblast growth factor (bFGF). Studies by Rochelle R. Arvizo, et al have shown that the use of AuNPs of various size and surface charge plays an important role in its inhibitory effects.

In today’s biological fields, the use of nanotechnology has allowed for the indirect use of AuNPs to deliver DNA to mammalian cells; thereby reducing tumor agents and increasing efficiency of electron transfer by modulating the activity of glucose oxidase. Current ongoing research by the Mayo Clinic Laboratories includes the examination of AuNPs as messengers to deliver reagents capable of manipulating the angiogenic response in vivo.

Anti-bacterial Therapy

Gold nanoparticles can be used as bacteria targeting particles, in antibacteria therapy. The therapy would target bacteria with light absorbing gold nanoparticles conjugated with specific antibodies, thus selectively kill bacteria using laser.

Studies has shown the effectiveness of this method on killing Staphylococcus aureus, which is significant human pathogen responsible for a wide range of diseases such as skin and wound infections, toxic shock syndrome, septic arthritis, endocarditis, and osteomyelitis. In this system, the bacteria damage is caused by inducing strong laser which leads to overheating effects accompanied by the bubble-formation phenomena around clustered gold nanoparticles.

The selective targeting of S. aureus was performed using a monoclonal antibody to one of the major surface-clustered proteins, protein A (spa), which is linked to the peptidoglycan portion of the cell wall. Killing efficiency depends on local overheating effects accompanied by the bubble-formation phenomena, a new photothermal (PT) imaging technique was developed using a thermolens mode on a technical platform of the Olympus BX51 microscope (Olympus, Melville, NY).

Drug Vectorization

• Vectorization to cancer cells

• “Magic bullet” idealy target the tumor cell by itself. But this has not been discovered yet.
• Nanovector should contains anticancer drug as its core, nanoparticles in which can protect normal cells by pack anticancer drug inside, and a targeting molecule which direct the drug to and can be recognized by tumor cells.

1. Research shows that 80~90% of breast cancer’s tumor cells have estrogen receptors and 60~70% of prostate cancer’s tumor cells have androgen receptors.
2. These significant amount of hormone receptors are play a role in intermolecular actions. This role is now used by targeting and therapeutic ligands on gold nanoparticles to target tissue-selective anti-tumor drug delivery.
3. In order to have multiple targeting and therapeutic ligands bind with gold nanoparticles, the gold nanoparticles has undergo polymer stabilization. For example, anti-estrogen molecules are bind with thiolated PEG to bind with gold nanoparticles via Au-S bonds, this process forms thiolate protected gold nanoparticles.

   

   PEGylated gold nanoparticles

• Gold nanoparticle's advantages in drug vectorization

1. It can pack several different sizes and types of dendrimer(branched molecules)
2. Several different types of ligand can be added to gold nanoparticles, in order to gain different functions, for example, targeting tumor cells.

• Pack Docetaxel in to PEGylated Gold nanoparticles (Encapsulation of Docetaxel into PEGylated Gold Nanoparticles for Vectorization to Cancel Cells)

1. Docetaxel is an anti-mitotic chemotherapy medicine which showing great performance in clinical trial. (anti-mitotic medicine interfering cell division)
2. Docetaxel was approved by FDA, to treat several different kinds of cancer. i.e. breast cancer(include locally advanced or metastatic).

Market Approval

No human clinical trials are being conducted as of current. Thus gold nanoparticles on the market are purely for synthesis of nanoparticle complexes in research. Nanocomposix specializes in the production of various sizes of nanoparticles, controlled by varying the concentrations of reducing reagent and HAuCl4.

Sigma Aldrich offers six different sizes of spherical gold nanoparticles and have developed gold nanourchins for similar usage. The surface causes a red shift in the surface plasmon peak as compared to spherical gold nanoaprticles.

Limitations

Heating is non-specific; thus the energy source is essentially the heat source which causes a maximal temperature to be insufficient. Large tumours must have long exposure to laser induced thermal therapy. Metals may undergo aggregation to result in a reduced absorbance.

Other Uses

The ligand used to decrease aggregation of gold nanorods.

Gold nanoparticles may be used in an indirectly therapeutic way. The issue of angiogenesis describes the formation of new blood vessels, which not only increased spread of cancerous cells, but may proliferate the spread of proteins responsible for rheumatoid arthritis. As AuNPs reduce angiogenesis, rheumatoid arthritis is reduced as a result. Chamberland et al studied the use of anti-TNF conjugated gold nanorods (AuNRs) ex vivo in rat tail joints to reduce the effect of rheumatoid arthritis. They observed the effects of the drug delivery system via PAT technology. The properties of the AuNRs found to be the most efficient had measurements of 45 x 15 nm with an absorption peak of 660 nm. This tuning allowed for better contrast between the targeted areas and intra-articular tissue. Thus, the etanercept conjugated AuNRs were seen to increase the light sensitivity. The imaging technique provides greater opportunities for sensitive in vivo drug tracking in biothechnology.

HIV

Several valences of AuNPs were found to inhibit HIV fusion. 2-nm AuNP-mercaptobenzoic acid were conjugated to a derivative of a known CCR5 antagonist, which is a small molecule that antagonize CCR5 receptor, and CCR5 is commonly used by HIV to enter the cell. This will ultimately lead to an effect that restrict HIV infection.

Hepatitis B

Prepared AuNPs-Hepatitis B virus (HBV) DNA gene probes could be used to detect HBV DNA directly. The detection-visualized fluorescence-based method is highly sensitive, simple, low cost, which could potentially apply to multi-gene detection chips.

Tuberculosis

A successful application of the AuNP-nanoprobe colorimetric method to clinical diagnosis reported by Baptista et al. was the sensitive detection in clinical samples of Mycobacterium tuberculosis, the human tuberculo nanoprobe sis etiologic agent.