Carbon nanotubes target cancer cells

A new noninvasive laser therapy that uses the strong optical absorbance of single-walled carbon nanotubes in the 700- to 1100-nm wavelength range has been shown to selectively destroy cancer cells while leaving healthy ones unharmed.

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A new noninvasive laser therapy that uses the strong optical absorbance of single-walled carbon nanotubes in the 700- to 1100-nm wavelength range has been shown to selectively destroy cancer cells while leaving healthy ones unharmed.1 According to Hongjie Dai, associate professor of chemistry at Stanford University (Stanford, CA), the carbon nanotubes turn into miniature thermal scalpels when placed inside a living cell and irradiated with near-IR energy.

“Near-IR light holds particular promise in nanotechnology-enabled cancer therapy,” he said. “Because neither biological molecules nor water can absorb light in this frequency range, near-IR light can pass through tissues to reach tumor-targeted nanostructures such as carbon nanotubes.”

Carbon nanotubes can be targeted to cancer cells growing in culture and used to either deliver DNA to the cell nucleus or kill the cell with high temperature. The key to either of these actions is that carbon nanotubes naturally absorb light in the near-IR.

An 808-nm-emitting diode-laser bar was coupled into a 1-m-long, 200-µm-core fiber with a numerical aperture of 0.22, providing a 1.4-W/cm2 intensity in the experimental region. Dai and his colleagues placed a solution containing carbon nanotubes inside cancer cells; upon laser irradiation, the solution was heated to 70°C in two minutes, quickly destroying the cancer cells. Healthy cells without nanotubes showed no effects when placed under the same near-IR light.

Dai has applied for a patent on the procedure through Stanford’s Office of Technology Licensing and has patented another technique that uses near-IR pulses to “shake” the DNA molecule loose from the carbon nanotube after both have entered the cell. The objective is to use the nanotube to deliver therapeutic molecules of DNA, RNA, or protein directly into the cell nucleus to fight various infections and diseases.

For example, an antibody can be attached to a carbon nanotube to target a particular kind of cancer cell, such as lymphoma. As is the case with many cancers, lymphoma cells have well-defined surface receptors that recognize unique antibodies. When attached to a carbon nanotube, the antibody would play the role of a Trojan horse.

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Carbon nanotubes penetrate folate-overexpressing cells via receptor binding and are then heated with near-IR (NIR) 808‑nm laser radiation (left, top). The folate-overexpressing cells are killed (left, bottom); higher-magnification inset image shows details of the killed cells). Normal (non-folate-overexpressing) cells do not allow carbon nanotubes inside them (right, top). Normal cells with no internalized nanotubes are unharmed by the same laser irradiation (right, bottom; inset image shows a live normal cell in stretched shape).
Click here to enlarge image

Relying on biochemical properties to selectively deliver carbon nanotubes into cancer cells and not into healthy ones, Dai and lymphoma researchers at the Stanford School of Medicine are using laboratory mice with lymphoma to determine whether shining near-IR light on the animal’s skin would destroy lymphatic tumors while leaving normal cells intact. Because cancer cells contain numerous receptors for the vitamin folate, the researchers coated the nanotubes with folate molecules, which would only be attracted to diseased cells with folate receptors.

Direct injection

Carbon nanotubes also can be delivered to diseased cells by direct injection. This benign therapy could potentially eliminate months of debilitating chemotherapy and radiation treatment. “In breast cancer, for example, there might come a time when we inject nanotubes into the tumor and expose the breast to near-IR light,” Dai said.

The researchers have also used nanotubes to transport molecules inside cells. They conjugated DNA to the nanotubes, allowed cells to take up the nanotubes by endocytosis, and used a pulsed near-IR laser to break the membrane around the nanotube and detach the DNA. Pulsing the laser enabled it to release the DNA without heating the cell sufficiently to cause its death. The result was delivery of the DNA to the cell nucleus.

“Carbon nanotubes are proving to be a versatile tool for ferrying biological compounds into cells,” Dai said. “Delivering therapeutic molecules of DNA, RNA, or protein directly into the cell nucleus could help fight various infections and diseases, in addition to cancer.”

Ilene Schneider

REFERENCE

1. N. W. Shi Kam et al., Proc. Nat’l. Academy of Sciences, 102(33)(Aug. 8, 2005).

ILENE SCHNEIDER is a freelance writer living in Irvine, CA; e-mail: ischnei440@aol.com.

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