About 14.1 million people, each year, around the world receives possibly the most dreadful message in their life; cancer. Despite decades of advancement of cancer research, development and cancer therapy, more than 8.2 million die from it, which amounts to a percentage of more than 50%. Current most widely employed conventional treatment methods including surgery, chemotherapy or radiation prove to be effective yet with severe side effects. Also, there is great potential for improvement, both in terms of the effectively and side effects. One of the most promising and latest cancer treatment method is called photothermal therapy, where nanoparticles like nanogold are employed to infiltrate and kill cancer cells from within using the heat.
Cancer, the challenges and opportunities
Cancer is characterized by uncontrolled growth of abnormal cells which is caused by a DNA damage that may be inherited or caused by environmental reasons. The disease form tumors, typically in tissues or in body flow system. Surgical operation is quite effective in extirpation of tumors in primary stage yet limited significantly in terms of accessibility and unique identification of the maligned cells. Chemotherapy uses drugs to attack maligned cells that divide rapidly, which include cancer cells. Usually this has significant side effects and known as the most distressful phase any cancer patient has to go through. This is mainly due to the toxicity of the drugs to the normal cells. Unfortunately, cancer cells also can develop resistance to these drugs that always leaves patient under a cloud of uncertainty about his or her life. Surgery and chemotherapy are usually followed by radiotherapy where the cells are subjected to high energy ionizing radiation such as X-Rays, gamma rays and electrons to damage cells and tissue at the molecular level and primarily used to complementary technique to kill remaining cancer cells. However, the radiotherapy also kill healthy cells and drastically affect immunity particularly if it’s directed at the bones. These limitations and disadvantages both medical and psychological has driven the need of alternative cancer treatment methods mainly through the use of nanotechnology to address the limitations of the current approaches.
Nanotechnology cancer treatment approach
Metals such as gold and silver have free electrons surrounding the surface. These so called electron plasma can interact with incoming light by collectively oscillating upon light absorption. When the particle diameter is in the nanoscale; smaller than the wavelength of the light, surface plasmon keep on oscillating around the particle giving rise to a phenomenon known as localized surface plasmon resonance. At this point, most of the light at the resonance wavelength is absorbed or scattered by the nanoparticle. The photon energy absorbed in this way is dissipated as heat and strong absorption would make it possible to reach temperatures in the range of thousands even with low a power laser source.
The centerpiece of photothermal therapy is a nanoparticle typically consisting of a noble metal like gold. The particles are typically covered by a protective coating which is typically modified to have specific affinity towards cancer cells. This helps the therapy by which the particles are absorbed in to the cancer cells more favorably than healthy cells. Small size of the particle is decisive for this nanotechnology cancer treatment and typically the nanoparticles are so small that they are 500 times smaller than the smallest cell in the body. This also means that even in a small drop of nanoparticle solution, trillions of light absorbing nanoparticle exist, making the whole process more efficient. At the beginning of the treatment, nanoparticles are injected directly or to the surrounding area of the tumor. After being injected, nanoparticles spread across the tissue and favorably absorbed by the tumor. Then the tumor is subjected to photo-excitation through a laser typically in the range of 650 to 1350 nm. This wavelength range is known as the near-infrared window in biological tissue as light within this wavelength range has highest penetration depth in tissue. Plasmonic absorption of the nanogold particles are tuned specifically to absorb at this wavelength thus highest amount of energy possible is transferred. With continuous photon energy absorption, particles begin to oscillate and kill cancer cells either through self-destruction due to heat generated or burst due to swelling caused by the heat. This can significantly reduce the growth and initiate shrinkage of the tumor, making it possible to remove it through surgical operation. Nanoparticles are then discharged by the body through natural processes.
Nanogold structures comprising, nanospheres, nanorods, nanocages and nanoshells are experimented to tune the plasmonic absorption to be within the near-infrared window. The procedure is still experimented at the animal testing stage and expected to enter in to the human trial stage very soon.
- Dickerson EB, Dreaden EC, Huang X, et al. Gold nanorod assisted near-infrared plasmonic photothermal therapy (PPTT) of squamous cell carcinoma in mice. Cancer letters. 2008;269(1):57-66. doi:10.1016/j.canlet.2008.04.026.
- Huang, X., Jain, P. K., El-Sayed, I. H., & El-Sayed, M. A. (2008). Plasmonic photothermal therapy (PPTT) using gold nanoparticles. Lasers Med Sci, 23(3), 217-228.
- Terry B Huff, Ling Tong, Yan Zhao, Matthew N Hansen, Ji-Xin Cheng & Alexander Wei “Hyperthermic effects of gold nanorods on tumor cells.” (2007): 125-132.