Tiny device may one day track cancer from inside

Researchers at the Massachusetts Institute of Technology have created prototypes for cancer monitors the size of a grain of rice, small enough to fit easily into the bore of a biopsy needle. Tiny coated particles inside the devices can bind with molecules linked to cancer at the site, creating minuscule clumps that can be detected by a noninvasive scan like an MRI, said Michael J Cima, a professor of materials science and engineering.

Cima tested the tiny monitors in mice. He said: “We were able to show that in mice that had the cancer, we could detect it with the change in the MRI.” “The biopsy is the gold standard for diagnosis,” he said. “But the downside is that you only get a measurement at the time you take the tissue.” By contrast, the monitors can offer continuous information.

Cima’s monitors could have many applications, said W Mark Saltzman, chairman of the department of biomedical engineering at Yale. “The idea of being able to monitor cancer in situ is very appealing,” he said of Cima’s devices. In the future, the devices may hold possibilities not only for sensing trouble, but also for remedying it, Saltzman said.

“What if you could link these devices that can detect a change in the tumour to some other device?” he asked. That second device might then release the appropriate drug for treatment.

Cima’s monitor is a small plastic container with a reservoir to sequester the magnetic nanoparticles so they cannot get out. The particles are of the same material as those currently given to patients intravenously to improve contrast in MRIs. On the top is a membrane through which fluids diffuse into the chamber arid make contact with the particles.

The magnetic nanoparticle technology used in the device was developed by Ralph Weissleder, a professor at Harvard Medical School. He has collaborated with Cima on many projects. The particles can detect substances, called biomarkers, that are shed by tumour cells as they develop or respond to therapy, Weissleder said.

“My lab focuses primarily on detecting these markers on the outside” of the body by, for example, analysing a drop of blood, he said. Cima’s focus, by contrast, “is on detecting them inside the body, through his implantable devices.” Weissleder says the technologies could help doctors when patients ask whether a tumour will respond to a particular therapy.

“Hopefully biomarkers will deliver answers and make cancer treatments a little more rational than they are today,” he said. In the future, Cima’s device may not have to be read by a large, doughnut-shaped MRI, machine. The group is working on another version of the implantable device, made with a metal coil that acts as a kind of antenna. That version can be read by a hand-held magnetic resonance detector.
Cima is planning a variety of devices, each set up to monitor a different metabolic activity of tissue near a tumour.

“Things as simple as pH and dissolved oxygen are known to be very good indicators of responses to therapy,” he said. “If the therapy is having an impact on the survival of that tumour, you’ll see it in the local metabolites.” But testing on human patients is years away. He hopes that the devices will eventually lead to a stream of diagnostic information.