Nanoparticle-mediated Photothermal Therapy

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Gold nanoparticles are injected into host and target the tumor site. Nanoparticles absorb NIR laser radiation and convert it to thermal energy which then selectivity heats the environment, killing cancer cells in the vicinity (Source: Kennedy et.al, 2011) [2].

Current cancer therapies such as chemotherapy and radiation cause damage to healthy cells as well as cancer cells due to a lack of specificity and sensitivity by targeting all highly proliferating cells [4]. Nanoparticle-mediated photothermal therapy (nPTT) utilizes nanometer-sized photothermal agents to actively target and neutralize tumors using thermal energy, decreasing damage to healthy cells and treatment side-effects [1].

When gold nanoparticles (AuNPs) are exposed to a light source at a specific wavelength their conduction band electrons become excited and begin to oscillate, known as surface plasmon resonance (SPR). This oscillation causes light to either be absorbed or scattered. When light is absorbed by the AuNPs it generates thermal energy, killing the tumor cells surrounding it through heat disruption of the cell membrane, protein denaturation, disruption of DNA synthesis, and induction of apoptosis. As nanoparticles have a particularly small optical cross section compared to larger molecules they absorb rather than scatter the majority of light radiation they are exposed to, and have smaller peaks around 520nm [3]. Due to their high absorption potential, AuNPs are ideal for use in thermotherapy, as increased absorption requires less exposure to light radiation during treatment. The small optical cross section of nanoparticles also means that Near-infrared light (NIR) is able to be used as the light source required to achieve SPR in the nanoparticles. While NIR light has the correct wavelength to excite nanoparticles, it will not create resonance in the chromophores (atoms in the cell responsible for color) of healthy cells that could potentially disrupt them, creating a safer treatment that targets only the tumor cells in which the AuNPs have accumulated [2]. Nanoparticles are able to locate the tumor cells using antibodies bound to their surface or specific-binding proteins, and accumulate through openings in the tumor vasculature that are larger than in normal tissue [2]. 

References 

1. Huang, X., Jain, P.K., El-Sayed, I.H., and El-Sayed, M.A. (2008). Plasmonic photothermal therapy (PPTT) using gold nanoparticles. Lasers Med Sci 23, 217–228.

2. Kennedy, L.C., Bickford, L.R., Lewinski, N.A., Coughlin, A.J., Hu, Y., Day, E.S., West, J.L., and Drezek, R.A. (2011). A new era for cancer treatment: gold-nanoparticle-mediated thermal therapies. Small 7, 169–183.

3. "Gold Nanoparticles: Optical Properties." NanoComposix. NanoComposix, n.d. Web. 02 Aug. 2016.

4. Pattani, V.P., Shah, J., Atalis, A., Sharma, A., and Tunnell, J.W. (2015). Role of apoptosis and necrosis in cell death induced by nanoparticle-mediated photothermal therapy. J Nanopart Res 17, 1–11.

5. Wang, L., Yuan, Y., Lin, S., Huang, J., Dai, J., Jiang, Q., Cheng, D., and Shuai, X. (2016). Photothermo-chemotherapy of cancer employing drug leakage-free gold nanoshells. Biomaterials 78, 40–49.

 

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Gold nanoparticle-mediated photothermal therapy is a highly specific cancer therapeutic that reduces unnecessary cell death, decreasing side-effects of cancer treatment. This treatment can also be used to enhance delivery of existing chemotherapy drugs. Vesicles encapsulating doxorubicin (DOX), a medication used in chemotherapy, coated with a layer of gold nanoparticles can also be oscillated using NIR light until the nanoshells rupture and release DOX into tumor cells [5]. 

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While there have been no observed long-term effects of gold nanoparticles remaining in the kidneys or liver, they can persist up to 6 months in the body. Coatings such as poly ethylene glycol (PEG) that are designed to decrease cytotoxicity improve biocompatibility but increase the circulation time of the nanoparticles in the body [2]. 

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