A new anti-cancer strategy wields light as a precision weapon. Unlike traditional light therapy — which is limited to the skin and areas accessible with an endoscope — this technique can target and attack cancer cells that have spread deep inside the body, according to researchers at Washington University School of Medicine in St. Louis.

Light emitted as part of traditional cancer-imaging techniques, to locate metastatic tumors, also can trigger light-sensitive drugs, according to the new study. In addition, the research shows that when such drugs are packaged into nanoparticles that target lit-up cancer cells, the light-sensitive drug produces toxic free radicals that kill the tumor cells. The researchers showed that the technique worked effectively in mice with multiple myeloma, a cancer of white blood cells, and aggressive metastatic breast cancer.

The study is published online in Nature Communications.
“Cancer that has spread remains the major reason patients die,” said senior author Samuel Achilefu, PhD, the Michel M. Ter-Pogossian Professor of Radiology at the School of Medicine. “Our study shows that this phototherapeutic technology is particularly suited to attacking small tumors that spread to different parts of the body, including deep in the bone marrow.”

The technology harnesses a chemotherapy drug called titanocene. As a chemotherapy agent alone, titanocene has not worked well in clinical trials, even at relatively high doses. But when exposed to the radiation emitted by visible light, titanocene produces reactive particles that are toxic to cells, even at low doses.

Achilefu and his colleagues packaged low doses of titanocene inside nanoparticles they targeted to proteins known to sit on the surface of cancer cells. They found that when the nanoparticles make contact with cancer cells, their membranes fuse together, releasing the titanocene into the cells.

The investigators then deliver a common cancer imaging agent called fluorodeoxyglucose (FDG), a type of sugar. Energy-hungry cancer cells take up the FDG at high rates, causing tumors to glow in a positron emission tomography (PET) scan. This glow also triggers the titanocene, releasing free radicals and killing the cells.

Since the titanocene and the light-emitting FDG are targeted to the same place at the same time only in tumors, the technique is believed to be less toxic than standard radiation and chemotherapy. Research also shows that the body rids itself of titanocene through the liver, while FDG is cleared through the kidneys. That the two components are disposed of separately minimizes damage to other organs. When separated, the two components are not toxic, according to the investigators.

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