Metastasis is the main cause of death in cancer, and current treatments against it are ineffective. But new research may have found a way to slow down, and perhaps even halt, the spread of cancer cells.
Metastasis is the process by which cancer spreads throughout the body. During this process, cancer cells may either invade nearby healthy tissue, penetrate the walls of lymph nodes, or enter the surrounding blood vessels.
But new research may have found a way to control metastasis by inhibiting the migration of cancer cells. Stopping the cells from migrating is key in stopping metastasis.
What enables cancer cells to migrate is a set of protrusions that help them to move. The team of researchers - led by Mostafa El-Sayed, Julius Brown Chair and Regents Professor of Chemistry and Biochemistry at Georgia Tech's School in Atlanta, GA - managed to successfully cut off these protrusions using a special technique.
The findings were published in the journal PNAS.
Breaking cancer cells' 'legs'
The long, thin protrusions that help cancer cells to move are called filopodia. They are an extension of a set of "broad, sheet-like" fibers called lamellipodia, which can be found around the edges of the cell.
The suffix "-podia" (or "-podium," singular) comes from the Greek language and means "something footlike."
Essentially, lamellipodia and filopodia are tiny "legs" that help healthy cells to move within the tissue. But in cancerous cells, lamellipodia and filopodia are produced in excess.
The researchers used so-called nanorods, made of gold nanoparticles, to obstruct these tiny legs.
With the help of nanotechnology, scientists are able to reduce the size of certain materials to a nanoscale - with "nano" meaning the billionth part of a meter - at which point these materials start to show new chemical and physical properties.
Prof. El-Sayed and colleagues introduced the nanorods locally. The nanorods were covered with a coating of molecules, called RGD peptides, that made them attach to a specific kind of protein called integrin.
"The targeted nanorods tied up the integrin and blocked its functions, so it could not keep guiding the cytoskeleton to overproduce lamellipodia and filopodia," explains co-author Yan Tang, a postdoctoral assistant in computational biology.
A cytoskeleton is the support structure of a cell, responsible for giving it a shape. It also has additional functions, with one of them being to form the filopodia protrusions.
Method could kill cancer cells
The experiments revealed that simply binding the nanorods to the integrin delayed the migration of the cancer cells.
Importantly, this method avoided healthy cells, which could make this therapy drastically less damaging for patients who undergo toxic chemotherapy treatment.
"There are certain, specific integrins that are overproduced in cancerous cells," explains Moustafa Ali, one of the study's first authors. "And you don't find them so much in healthy cells."
In the second stage of the experiment, Prof. El-Sayed and team heated the gold nanoparticles with a laser of near-infrared light. This effectively stopped the migration of the malignant cells.
"The light was not absorbed by the cells, but the gold nanorods absorbed it, and as a result, they heated up and partially melted cancer cells they are connected with, mangling lamellipodia and filopodia."
In this experiment, not all cancer cells were killed, as this would have prevented the researchers from examining whether or not they successfully stopped them from migrating. However, the researchers say that the method could be adjusted to kill the malignant cells.
Prof. El-Sayed and his colleagues have previously conducted similar experiments in mice, in which they applied the same method. The former research found no toxicity from the gold for up to 15 months after the treatment.
The laser could reach the gold nanorods at 4 to 5 centimeters deep inside the tissue, and deeper tumors could be treated with deeper nanorods injections, the authors say.