The advancement of nanotechnology in the past decade has driven the development of numerous medical applications. None of them is as promising as the use of targeted nanoparticles aimed to improve the treatment of cancer, which has serious side effects.
Targeted nanoparticles act as a sophisticated Trojan horse (see how it works in the above video): they take advantage of the physical and chemical processes in the body to camouflage and slip into the cancer cells, where they release their anti-cancer arsenal. Moreover, this “cell war strategy” allows nanoparticles to circumvent the body’s defenses and to reduce collateral damage to healthy tissues.
The benefit will be a more effective and less toxic chemotherapy, if this nanotechnique succeeds in clinical trials. Results have been encouraging in Phase I trials, showing a regression of tumors even when using lower doses of anti-cancer drugs than conventional chemotherapy.
Researchers at MIT and at Brigham and Women’s Hospital in Boston designed nanoparticles that for the first time were able to simultaneously meet with these requirements:
- Prolonged circulation: a polyethylene glycol (PEG) coating makes nanoparticles look like tiny water droplets. So for a while they can go under the radar of the human body’s defenses: staying much longer within the bloodstream, nanoparticles are more likely to reach a tumor before being eliminated.
- Tumor targeting: with a size of 50 to 100 nanometers, they are too large to reach healthy tissue through their finest capillaries. However tumors grow very fast and their blood vessels are defective, with large gaps through which nanoparticles can sneak in. In addition, nanoparticles “recognize” cancer cells because they carry embedded molecules that bind to a specific protein. This protein (PSMA) is abundant on the surface of cancer cells found in different kinds of tumors.
- Controlled drug release: these nanoparticles are hollow capsules carrying molecules of docetaxel, a drug commonly used in chemotherapy to treat breast, lung or prostate cancer. Nanoparticles are “programmed” to release their therapeutic payload inside cancer cells and to do it at an effective rate.
The great challenge of this technique is to find the right combination of these three properties. To succeed in clinical trials researchers must refine the design of nanoparticles, trying to match the ideal situation described in the above video. Balancing these factors is complicated in practical applications. I.e. increasing the size of nanoparticles prevents them from affecting healthy tissue, but if they are too big they can neither attack cancer cells nor avoid the human body’s defenses.
There is still a long way to go. The first tests have proven these treatments with nanoparticles to be more specific than conventional chemotherapy, but still there are times when not enough of the drug reaches the tumor site or times when the drug affects healthy tissues too. In practice targeted nanoparticles are not so good at distinguishing healthy cells from cancer cells.
To further reduce these side effects in healthy tissues, scientists can design nanoparticles to be better at targeting cancer cells. However, this more focused nanoparticles are a less technically viable option and they are more expensive to produce. Another challenge of these clinical trials is controlling the toxicity of the remaining products. Tests will continue during this decade, before the great promise of anti-cancer nanoparticles becomes a reality.
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