Implant Measures Tumor Growth, Therapy Progress

A tiny implant now being developed could soon help doctors quickly track the growth of tumors and the progress of chemotherapy in cancer patients.

The implant contains nanoparticles that can be modified to test for different substances, including metabolites such as glucose and oxygen that are associated with tumor growth. It can also track the effects of cancer drugs. Once inside a patient, the implant could reveal how much of a specific cancer drug has reached the tumor, helping clinicians determine whether a treatment is working in a particular patient.

"You really want to have some sort of rapid measure of whether it's working or not, or whether you should go on to the next [drug],” said Dr. Michael Cena, professor of engineering in the department of materials science and engineering at the Massachusetts Institute of Technology (MIT; Cambridge, MA, USA), and the lead investigator of the project.

Such nanoparticles have been used before, but for the first time, the MIT researchers have encased the nanoparticles in a silicone delivery device, allowing them to remain in patients' bodies for an extended period of time. The device can be implanted directly into a tumor, allowing researchers to get a more precise look at what is happening in the tumor over time.

With blood testing, which is now commonly used to track chemotherapy progress, it is difficult to determine if cancer drugs are reaching their intended targets, according to Grace Kim, a graduate student in the Harvard (Cambridge, MA, USA)-MIT Division of Health Sciences and Technology, and one of the researchers working on the implant. The reason is because of the complicated nature of the system of blood vessels surrounding tumors, and one has to be certain that drugs present in the blood have also reached the tumor, according to Ms. Kim.

The new technique, known as implanted magnetic sensing, makes use of detection nanoparticles composed of iron oxide and coated with a glucose compound called dextran. Antibodies specific to the target molecules are attached to the surface of the particles. When the target molecules are present, they bind to the particles and cause them to clump together. That clumping can be detected by magnetic resonance imaging (MRI).

The nanoparticles are trapped inside the silicone device, which is sealed off by a porous membrane. The membrane allows molecules smaller than 30 nm to penetrate, but the detection particles are too big to get out.

The device can be engineered to test for many things at the same time, leading Ms. Kim to offer a cooking-based analogy. "When you're cooking a turkey, you can take the temperature with a thermometer,” she said. "But with something like this, instead of just taking the temperature, you can find out about the moisture, the saltiness, and whether there's enough rosemary.”

In addition to monitoring the presence of chemotherapy drugs, the device could also be used to determine whether a tumor is growing or shrinking, or whether it has spread to other locations, by sensing the amount and location of tumor markers.

The next phase for the research group is to begin more extensive preclinical testing. They will be looking for human chorionic gonadotropin (hCG) hormone, which can be considered a marker for cancer because it is produced by tumors but not typically found in healthy individuals (unless they are pregnant).



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