As reported everywhere today, Sen. Ted Kennedy died Tuesday night after a year-plus fight with malignant glioma, a type of brain cancer. The condition, in which tumor cells arise from glia cells of the brain, is known to be especially deadly and hard to treat – only about 16 percent of patients diagnosed with the condition survive five years. Treatment involves radiation, surgery and chemotherapy, but long-term survival is a challenge.
In this case, the nanoparticle being tested as a potential cancer treatment is titanium dioxide, an unusual compound currently used for everything from treating wastewater to self-cleaning windows to movie snow. The special thing about titanium dioxide (or TiO2 in chemistry shorthand) is that it’s a photocatalyst – expose it to light and it generates free radicals, unstable atoms, that can destroy dirt on a window or, potentially, kill off a cell.
The problem for the latter use is how to get TiO2 into the cells you want to kill, the ones in the tumor, without taking out a lot of innocent bystanders along the way. Argonne researchers solved this issue by attaching titanium dioxide to an antibody for the interleukin receptor, a molecule expressed on the cell surface of tumor cells. Essentially, the antibody in this case is a key that only works in certain locks (the interleukin receptor), and when it finds the right cell, it is brought inside along with its TiO2 party guest.
At first, that TiO2 doesn’t cause any trouble – it’s kind of a sleeper agent inside the tumor cell. But when the cell is exposed to UV light, it begins producing free radicals, which wreak havoc with the cell’s internal organs and cause it to self-destruct.
Experiments conducted by the research team at Argonne proved that this set-up could work, at least in the artificial environment of the laboratory. The modified TiO2 trojan horses successfully attached themselves to cancer cells that were grown in the lab, and even to the “invadopodia” of those cells – tendrils used by cancer cells to attack neighboring cells. When these cells were exposed to UV light for 6 hours, 80% of the tumor cells died off.
“When exposed to light, these nanoparticles actually cause the death of cancer cells,” Lesniak said. “There are many scenarios where this could work. For example, during surgery while resecting a tumor, you could inject these nanoparticles, target the tumor and expose it to a source of light.”
However, about 15% of normal cells were also bound by TiO2 particles and died after UV light, collateral damage that Lesniak said would be a potential concern, though it’s comparable to side effects of existing treatments.
“You have to offset against the certainty of death when you’re dealing with this kind of aggressive cancer,” he said.