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Medical News Today: Implantable biosensor could monitor progress of cancer therapy

You stand a better chance of winning a war when you have good intelligence that keeps you informed from behind enemy lines. This is also true of the fight against cancer. Here, an invaluable tool would be an implantable biosensor that sends up-to-date information about the current state of a tumor and how it is responding to treatment.
MIT biosensor
The sensor fits into the tip of a biopsy needle.

Image credit: C. C. Vassiliou et al./MIT

This is the aim of a team from MIT in Cambridge, MA, that has developed such a device and discusses it in the journal Lab on a Chip.

To monitor a cancer’s response to treatment, doctors currently rely on the results of magnetic resonance imaging (MRI) and other scanning technologies, plus tissue analysis of biopsies.

But these methods can only offer a snapshot that is already history by the time the results are analyzed. Also, in the case of biopsies, there is a limit to how many times you can invade the body with a risky procedure to take a sample.

Now researchers from MIT’s Koch Institute for Integrative Cancer Research have developed an implantable device that promises to provide readings about the state of a tumor as it happens. Such a device would give doctors a chance to change therapy dosing, and potentially reduce unnecessary side effects.

One of the developers, Michael Cima, a professor in engineering and senior author of the study, says:

“We wanted to make a device that would give us a chemical signal about what’s happening in the tumor. Rather than waiting months to see if the tumor is shrinking, you could get an early read to see if you’re moving in the right direction.”

Biosensor monitors pH and dissolved oxygen

The biosensor works by monitoring two biomarkers: pH (a measure of acidity) and dissolved oxygen. These are valuable indicators of how well the tumor is responding to treatment. When chemotherapy begins to take effect, the tumor tissue becomes more acidic.

“Many times, you can see the response chemically before you see a tumor actually shrink,” Prof. Cima says. In fact, he explains, some therapies can even trigger an immune response that causes inflammation, which in turn can make it look like the tumor is growing when in fact the therapy is taking effect.

By measuring dissolved oxygen, the biosensor helps doctors determine the appropriate dose for treatment, since tumors thrive in low-oxygen (hypoxic) conditions.

The tiny biosensor is so small it fits into the tip of a biopsy needle. It is made of a biocompatible plastic shell enclosing 10 ml of chemical contrast agents typically used in MRI scans, and some electronics for sending readings to an external device.

The power to the device relies on the external reader. There is a small metal coil in the device and a larger one in the reader. An electric current magnetizes the coil in the reader which, by a process called mutual inductance, sets up a voltage in the sensor’s coil when it is near it.

To obtain a reading, the reader sends out a series of pulses that causes the sensor to “ring back” with signals that are interpreted by a computer connected to the reader. The computer turns the signals from the sensor into readings that reveal changes in the levels of the biomarkers.

Tests showed the biosensor is fast, accurate and reliable

To test the device, the team implanted it in rats. The tests showed the sensors could send quick, accurate, reliable signals about pH and oxygen concentration in tissue.

The team now want to see how well the sensor measures changes in pH over longer periods. “I want to push these probes so we can use them to monitor tumor response,” Prof. Cima says. “We did a little bit of that in these experiments, but we need to make that really robust.”

He foresees the sensors being used to monitor patients’ health over many years.

“There are thousands of people alive today, because they have implantable electronics, like pacemakers and defibrillators,” Prof. Cima notes. “We’re making these sensors out of materials that are in these kinds of long-term implants, and given that they’re so small, I don’t think there will be a problem.”

While cancer care is the main focus of their work, the researchers also see other uses for the biosensor and would like to work with researchers in other fields, such as environmental science, as Prof. Cima explains:

“For example, you could use these to measure dissolved oxygen or pH from a lot of different sites all over a pond or a lake. I’m excited about using these sensors to bring big data to environmental monitoring.”

In October 2014, Medical News Today learned how another group of scientists is working on a “lab on a chip” that promises to detect lung cancer much earlier than is currently possible using only a small drop of the patient’s blood. This would be a great improvement on the present method of lung cancer diagnosis requiring an invasive biopsy that is only effective after tumors are bigger than 3 cm and may already have started spreading.

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