Engineers Improve Photodynamic Cancer Therapy

Engineers have created a thin adhesive strip that could greatly improve the effectiveness of photodynamic therapy, a promising cancer treatment with fewer side effects than traditional chemotherapy.

by Lina Zeldovich
October 22, 2018

Inspired by a lowly mollusk, engineers have created a thin adhesive strip that could greatly improve the effectiveness and efficiency of photodynamic therapy, a new and promising cancer treatment that has fewer side effects than traditional chemotherapy.

Also known as light therapy, photodynamic therapy delivers cancer-killing drugs by intravenous injections into the bloodstream.  Once the drugs reach tumor sites, they are activated by shining light on the affected area. Unlike chemotherapy, in which drugs react with and damage other body tissues, light therapy activates the killing agents only at the tumor site, sparing all other organs.

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Some photodynamic therapies are becoming mainstream treatments. One has proved to be effective in treating localized prostate cancer. It is approved for clinical use in South America and is expected to soon gain approved in Europe.

But the method does have its limitations.

Body tissues absorb light, which prevents it from penetrating beyond a certain depth. That makes it difficult to activate light-sensitive compounds in tumors deep within the body, such as in the liver or pancreas.

The ability to regularly apply light therapy to internal organs is also limited. A consistent regimen requires the stable attachment of light-emitting devices to internal tissues. Those types of implantable devices (such as light-emitting diode chips or LED lights) exist and can be activated wirelessly. But they don't affix well to the body organs and have trouble staying securely in place. That decreases therapy efficiency and exposes healthy organs to light, which can cause damage. Surgical suturing, often used to secure internal devices in place, is also limited, particular in the proximity of blood vessels, major nerves or when organs are fragile, change shape or move regularly. Even if the light source shifts slightly away from the malignant growth, the illumination is no longer sufficient for effective treatment.

To overcome those drawbacks, Toshinori Fujie, associate professor of biomedical engineering, and his colleagues at Waseda University in Japan, the National Defense Medical College, and the Japan Science and Technology Agency, developed new ultra-thin adhesive nano-sheets that attach to organs tightly and securely enough to keep the light illumination steady. Their idea was inspired by a mussel foot—an organ mussels use to attach to wet surfaces in the ocean with remarkable stability.

“The idea of the adhesion comes from the natural protein, the protein motif of the mussel, but we synthesized that material,” Fujie said.

The group synthesized a mussel-mimetic protein by polymerizing dopamine, well known for its role as a neurotransmitter. But when dopamine molecules are exposed to oxygen under certain conditions, they form long polymer chains with different qualities and no longer act as neurotransmitters. But they can serve as efficient adhesives.

In their previous studies, Fujie also experimented with another material, polydimethylsiloxane or PDMS, which are very thin silicone films or nano-sheets that are flexible enough to conform well to body organs but lack adhesive properties. So the group used PDMS and the mussel polydopamine together, layering them to get the best of both worlds.

“We essentially used a sandwich structure,” Fujie said. “We put the light-emitting chip on the surface of the PDMS film and covered the PDMS layer with the polydopamine layer.”That polydopamine layer acted as the natural adhesive when affixed to body tissues, and the PDMS layer held the lights in place.

The team tested their implantable device on tumor-bearing mice. The animals were injected with a light-activated medicine end exposed to red and green light for 10 consecutive days. The tumor growth was significantly reduced. The color of the light, determined by its wavelength, made a difference. Under the green light, the tumor in some mice was completely destroyed.

Now that the team successively accomplished the proof of concept, they are examining the efficiency of treatment in a new study. At the same time, they are gearing up to put their invention through the regulatory approvals. They are hoping that once approved the device would help reach cancers hidden deep within the body and improve the overall treatment efficiency.

“Because the device does not require surgical suturing, it can be used for treating cancer near major nerves and blood vessels, as well as for organs that change their shape or move, like liver or pancreas,” Fujie said.

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Lina Zeldovich is an independent technology writer.