Slipping through cell walls, nanotubes deliver high-potency punch to cancer tumors in mice
Now researchers at Stanford University have addressed that problem using single-walled carbon nanotubes as delivery vehicles. The new method has enabled the researchers to get a higher proportion of a given dose of medication into the tumor cells than is possible with the "free" drug—that is, the one not bound to nanotubes—thus reducing the amount of medication that they need to inject into a subject to achieve the desired therapeutic effect.
"That means you will also have less drug reaching the normal tissue," said Hongjie Dai, professor of chemistry and senior author of a paper, which will be published in the Aug. 15 issue of Cancer Research. So not only is the medication more effective against the tumor, ounce for ounce, but it greatly reduces the side effects of the medication.
Graduate student Zhuang Liu is first author of the paper.
Dai and his colleagues worked with paclitaxel, a widely used cancer chemotherapy drug, which they employed against tumors cells of a type of breast cancer that were implanted under the skin of mice. They found that they were able to get up to 10 times as much medication into the tumor cells via the nanotubes as when the standard formulation of the drug, called TaxolŽ, was injected into the mice.
The tumor cells were allowed to proliferate for about two weeks prior to being treated. After 22 days of treatment, tumors in the mice treated with the paclitaxel-bearing nanotubes were on average less than half the size of those in mice treated with Taxol.
Critical to achieving those results were the size and surface structure of the nanotubes, which governed how they interacted with the walls of the blood vessels through which they circulated after being injected. Though a leaky vessel—nautical or anatomical—is rarely a good thing, in this instance the relatively leaky walls of blood vessels in the tumor tissue provided the opening that the nanotubes needed to slip into the tumor cells.
"The results are actually highly dependent on the surface chemistry," Dai said. "In other words, you don't get this result just by attaching drugs to any nanotubes."