While doing research for security-related radiation detection, University of Texas at Arlington physics professor Wei Chen discovered unexplained decreases in the luminescence of a copper-cysteamine complex over a time-lapse exposure to x-rays. He found that the nanoparticles, called Cu-Cy, were losing energy as they emitted singlet oxygen—a toxic byproduct that is used to damage cancer cells in photodynamic therapy (PDT). Chen, also a federally funded cancer researcher, found through further testing that the nanoparticles, combined with x-ray exposure, significantly slowed tumor growth in lab studies.1
PDT kills cancer when a photosensitizer, introduced into tumor tissue, produces toxic singlet oxygen after being exposed to light. Some PDT methods use visible or near-infrared (NIR) light, others introduce luminescent nanoparticles into the tumor. Researchers activate the luminescent nanoparticle with NIR light or x-rays, which in turn activates the photosensitizer. Both approaches have limited ability to treat deep-tissue cancers: Either they are inefficient or the light source needed to activate them doesn't penetrate deep enough. Chen said that x-ray-inducible Cu-Cy particles surpass current photosensitizers because the x-rays can penetrate deep into tissue. Also, Cu-Cy nanoparticles don't need other photosensitizers to be effective, so the treatment is more convenient, efficient, and lower in cost.
Chen's team tested the Cu-Cy on human breast and prostate cancer cells in the lab, and found it to be effective when combined with x-ray exposure. In one test, for example, a tumor treated with Cu-Cy injection and x-ray exposure stayed virtually the same size over a 13-day period while a tumor without the full treatment tripled in size.
Another advantage of the new nanoparticle is its low toxicity to healthy cells: In fact, its intense photoluminescence and x-ray luminescence can also be used for cell imaging.2
Chen continues to pursue PDT research under a grant from the Department of Defense Congressionally Directed Medical Research Programs and with collaborations from industry. He says that further research would include reducing the size of the Cu-Cy nanoparticle to make it more easily absorbed in the tumor tissue.
1. L. Ma, X. Zou, and W. Chen, J. Biomed. Nanotechnol., 10, 8, 1501–1508 (2014).
2. L. Ma et al., J. Mater. Chem. C, doi:10.1039/c4tc00114a (2014).