In the battle against cancer, which kills nearly 8 million people worldwide each year, doctors have in their arsenal many powerful weapons, including various forms of chemotherapy and radiation. What they lack, however, is good reconnaissance — a reliable way to obtain real-time data about how well a particular therapy is working for any given patient.
Magnetic resonance imaging and other scanning technologies can indicate the size of a tumor, while the most detailed information about how well a treatment is working comes from pathologists’ examinations of tissue taken in biopsies. Yet these methods offer only snapshots of tumor response, and the invasive nature of biopsies makes them a risky procedure that clinicians try to minimize.
Now, researchers at MIT’s Koch Institute for Integrative Cancer Research are closing that information gap by developing a tiny biochemical sensor that can be implanted in cancerous tissue during the initial biopsy.
The sensor then wirelessly sends data about telltale biomarkers to an external “reader” device, allowing doctors to better monitor a patient’s progress and adjust dosages or switch therapies accordingly. Making cancer treatments more targeted and precise would boost their efficacy while reducing patients’ exposure to serious side effects.
Their research is featured in a paper in the journal Lab on a Chip that has been published online.
The sensors developed by the researchers provide real-time, on-demand data concerning two biomarkers linked to a tumor’s response to treatment: pH and dissolved oxygen.
When cancerous tissue is under assault from chemotherapy agents, it becomes more acidic. In fact, some therapies will trigger an immune system reaction, and the inflammation will make the tumor appear to be growing, even while the therapy is effective.
Oxygen levels, meanwhile, can help doctors gauge the proper dose of a therapy such as radiation, since tumors thrive in low-oxygen (hypoxic) conditions. “It turns out that the more hypoxic the tumor is, the more radiation you need”. “So, these sensors, read over time, could let you see how hypoxia was changing in the tumor, so you could adjust the radiation accordingly.”
The sensor housing, made of a biocompatible plastic, is small enough to fit into the tip of a biopsy needle. It contains 10 microliters of chemical contrast agents typically used for magnetic resonance imaging (MRI) and an on-board circuit to communicate with the external reader device.
Four years ago, they built a similar implantable sensor that could be read by an MRI scanner. “MRI scans are expensive and not easy to make part of routine care”.
For power, these new sensors rely on the reader. Specifically, there’s a metal coil inside the reader and a much smaller coil in the sensor itself. An electric current magnetizes the coil inside the reader, and that magnetic field creates a voltage in the sensor’s coil when the two coils are close together — a process called mutual inductance.
The reader sends out a series of pulses, and the sensor “rings back”. The variation in this return signal over time is interpreted by a computer to which the reader is wired, revealing changes in the targeted biomarkers.
The team successfully tested the sensors in lab experiments, including implanting them in rodents. While the sensors were only implanted for a few weeks, the researchers believed they could be used to monitor a person’s health over many years.
These initial experiments showed that the sensors could quickly, reliably, and accurately detect pH and oxygen concentration in tissue. The researchers next want to see how well the sensors do measuring changes in pH over an extended period of time.
