Gold nanoparticles in chemotherapy and radiotherapy is the use of colloidal gold in therapeutic treatments, often for cancer or arthritis. Gold nanoparticle technology shows promise in the advancement of cancer treatments. Some of the properties that gold nanoparticles possess, such as small size, non-toxicity and non-immunogenicity make these molecules useful candidates for targeted drug delivery systems. 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 along with the chemotherapeutic drug molecules, to allow these molecules to circulate throughout the tumor without being redistributed into the body.
Physical properties
Size Gold nanoparticles range in size depending on which therapy they are being used for. In photothermal cancer therapy, many gold nanoparticle molecules are used in each test and they must all be uniform in size. Including PEG coating, the nanoparticles measured to be ~130 nm in diameter. Gold nanoparticles that act as drug delivery systems in conjugation with chemotherapeutic drugs typically range in size from 10 to 100 nm. Surface area plays a very important role in drug delivery and per mg of gold, as diameters decrease, the surface areas needed to transport drugs increase to the point where a single 1mL volume of 1.8 nm spherical gold nanoparticles have the same surface area as a cell phone. 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.
Color Due to the ability to tune the size and absorption of AuNPs, these molecules can vary in the colors they emit. Colors of AuNP solutions typically range from wine red to pale blue. These colors play a necessary role in the synthesis of AuNPs as indicators of reduction. The color of AuNPs can be modified by the application of pressure which reddish the nanoparticles.
Synthesis For more on synthesis of AuNPs for medical use, see Colloidal gold Other synthesis 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.
Treatments
Photothermal cancer therapy
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. 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. Despite the unquestionable success of gold nanorods or nanoshells as photothermal agents in preclinical research, they have yet to obtain the approval for clinical use because their size is above the renal excretion threshold. In 2019, the first NIR-absorbing plasmonic ultrasmall-in-nano architecture has been reported, and jointly combine: (i) an efficient photothermal conversion suitable for multiple hyperthermia treatments, and (ii) renal excretion of the building blocks after the therapeutic action.
Radiofrequency therapy
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