Anexo II: Manual de usuario
II.I. Parte pública: Uso del sitio web
Have you ever shined a flashlight through your fi ngers? As the light passes through the tissues, it looks red, but this is not caused just from blood on the inside, but from light passing through the skin. Long wavelength light can pass right through the skin without too much scattering. This method has been used in photodynamic therapy to treat disease within the body.
Light can be used in different ways. If it hits metal in the body, the metal can get hot enough to cook surrounding tissue (e.g., a tumor). If light hits a particle, causing it to give off highly reactive oxygen molecules, these oxygen molecules will react with the surrounding tissue and destroy it (dooming tumors again).
Researchers Jennifer West and Rebekah Drezek at Rice University’s Center for Biological and Environmental Nanotechnology have applied super small particles of gold-coated glass spheres called nanoshells created by Rice professor Naomi Halas to improving both the detection and treatment of diseased tissue. Figure 6-6 illustrates the simplicity of gold nanoshells.
Nanoshells, gold-coated silica particles, have tunable optical properties that are affected by size, geometry, and composition.
Silica
Gold shell
98 Nanotechnology Demystifi ed
Nanoparticles with a silica (glass) core and gold shell have been designed to absorb light wavelengths in the near-infrared (i.e., in the total spectrum of light) where light’s penetration through tissue is greatest. Figure 6-7 shows the different wavelengths of the spectrum. (The visible part of the spectrum is further divided according to color, with red at the long wavelength end and violet at the short wave- length end.)
A new kind of cancer therapy is becoming possible using super small gold nanoshells that travel through a tumor’s “leaky” vessels and are deposited. The blood vessels that supply tumors with nutrients have tiny gaps in them that allow the nanoshells to get in and collect close to the tumor. This is called the enhanced permeability and retention, or EPR, effect. Nanoshells can also be bonded with targeting antibodies and directed, for example, against oncoproteins (cancer pro- teins) or markers, increasing therapy specifi city to the cellular level.
Nanoshells can get to the tumor in two ways: by using a targeting antibody or relying on EPR. Not every cancer has a specifi c known marker for which an anti- body can be designed. Fortunately, EPR means treatment with nanoshells is not limited only to those cancers with specifi c markers.
To treat breast cancer cells with gold-coated nanoparticles, for example, antibod- ies are attached to the gold nanoshells, which latch onto the targeted cancer cells. In tests, mouse cancer cells have been treated by shining an infrared laser beam on an affected area. The gold absorbing the infrared light heats up, but the healthy tissues (with no attached gold nanoparticles) keep cool and are not affected. The rising heat (55°C) fries the tumor cells, leaving healthy cells unharmed.
The beauty of this site-specifi c treatment is that since only the cancerous areas “cook,” the rest of the body’s healthy tissues are not impacted. This offers a huge benefi t over chemotherapy, which kills rapidly growing cells, both friend and foe. (One of the main reasons chemotherapy patients lose their hair is because hair follicle cells divide faster than other cells and are slammed by chemotherapy chemicals.)
Visible Light
Microwave X-rays
Gamma
rays UV Infrared Radio
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CHAPTER 6 Medicine
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In gold nanoshell treatments with mice, scientists achieved a 100 percent effec- tiveness rate in killing breast cancer cells, compared to the untreated mice, which all died within 30 days. Due to this early success, Rice scientists launched human tests in the summer of 2005.
In a mouse colon carcinoma test, after the intravenous (IV) injection of nanoshells, followed six hours later by illumination of the cancerous area, researchers saw complete destruction of the cancer cells. By day 10, all nanoshell treated tumors had entirely disappeared, while tumors in untreated mice grew unaffected.
After the long-term survival of the mice was tracked, scientists found that all mice in the untreated groups died by day 21, while all the nanoshell-treated mice survived for more than 90 days (all are still happily munching on mouse chow at the time of this writing) with no tumor recurrence.
A researcher investigating a potential new therapy has to make sure the treatment isn’t worse than the disease. Problems can arise if these tiny particles don’t get where they are needed (biodistribution), if they hang around in the body forever after the therapy (clearance), or if they prove to be poisonous (toxicity). Therefore, nanoshell biodistribution, clearance, and toxicity have also been evaluated, and the nanoshells pass with fl ying colors.
Such a radically new and improved cancer cure within a body’s tissues through infrared light penetration will nearly eliminate a patient’s experiencing side effects and suffering. In addition, cure rates will rise considerably since the body’s overall defenses won’t have to contend with the severe impact of current chemotherapy that has no proven way of telling bad cells from good ones.