In the second century A.D., during the Han dynasty, a Chinese author and alchemist known as Wei Boyang is believed to have written: “Gold is the most valuable thing in all the world because it is immortal and never gets rotten. Alchemists eat it, and they enjoy longevity.” Nearly two millennia later, the precious metal may live up to the hype: It’s part of a cutting-edge approach to prolong the lives of cancer patients.
Though they didn’t quite capture the details, Wei Boyang and other ancients who associated gold’s long-lasting luster with good health were surprisingly prescient. Gold’s immortality—the fact that it doesn’t interact with most compounds and thus doesn’t corrode—makes it essentially nontoxic to the body. This characteristic gives it huge potential value in medicine, for mundane procedures like dental fillings and, in the era of nanotechnology, for diagnosing and treating deadly diseases.
“There are an enormous number of people using gold nanoparticles,” says Chad Mirkin, a chemist at Northwestern University whose own studies focus on how the particles could help turn off genes that cause disease. “We’re talking hundreds and hundreds of researchers around the world.”
One surprising approach comes out of research conducted at Rice University in Texas, along with the MD Anderson Cancer Center and other institutes. Oncologists are now injecting cancer patients with ultra-tiny, gold-wrapped spheres. The nanoparticles, each smaller than a red blood cell, accumulate in a tumor after slipping out of the bloodstream through little holes in the tumor’s rapidly growing vessels. Once there, the gold waits—until an oncologist blasts it with near-infrared light.
Despite gold’s shiny quality, the spheres are made to absorb rather than reflect certain wavelengths of light, a property used against the cancer cells. “We artificially contaminate the tumor,” says Sunil Krishnan of MD Anderson. The nanoparticles convert the light into heat, and as temperatures in the tumor climb above 104 degrees Fahrenheit, the cancer cells deform, shrivel and then disintegrate.
In experiments in mice, Krishnan is zapping the scraps of pancreatic cancer remaining after a tumor is removed surgically. But clinical trials in people, including for cancers of the head, neck and lungs, are targeting tumors without surgery.
Although gold can be expensive, some potential therapies use as little as 3 percent of the amount in a typical wedding band. Instead, the main obstacle will probably be rigorous safety tests. “One of the tenets of nano is that everything that is miniaturized is different,” says Mirkin. So researchers need to confirm that new gold-based treatments are friendly to the body.
If so, a sly little ditty written by a 17th-century herbalist who also recognized the curative powers of gold may prove true today: “For gold is cordial, And that’s the reason, Your raking misers live so long a season.”