Researchers Develop New Photosensitizers For Cancer Therapy

by George Zamora

SOCORRO, N.M., May 11, 2007 – New Mexico Tech researchers have developed a new agent to treat certain cancers by using the unique light-emitting properties of specific nanoparticles to deliver tiny, yet therapeutic, dosages of antibodies and reactive oxygen to individual tumor cells or clusters of cells, without affecting surrounding tissue.

The newly developed photosensitizers, which work as light-sensitive drugs when used with established photodynamic therapy procedures, are described in a research paper published in a recent issue of the Journal of the American Chemical Society (JACS).

Unlike previous photosensitizers which have been used in photodynamic therapy for cancers, the new design of these versatile photosensitizers uses infrared light as an irradiation source, a technique that is being touted as “the biggest advancement in photodynamic therapy in the last ten years.”

New Mexico Tech chemistry assistant professors Peng Zhang and Wim Steelant, along with Tech students Manoj Kumar and Matthew Scholfield, are the university researchers cited as co-authors of the JACS article, titled “Versatile Photosensitizers for Photodynamic Therapy at Infrared Excitation.”

The design of the novel photosensitizers is based on using nanoparticles, or materials in the nanometer (10 to the negative 9th power) range, with unique “photon upconversion” properties.

Specifically, the photon upconverting nanoparticles (PUNPs) developed by the Tech researchers convert lower-energy light to higher-energy light after being exposed to infrared wavelengths of light.

In addition, antibody molecules specific to the cancer cells were attached to the nanoparticles’ surfaces, serving as a guide to direct the PUNPs toward the target cancer cells.

“Infrared has the ability to penetrate human tissue three to five times deeper than other wavelengths of visible light typically used in photodynamic therapy, which is a highly desirable feature for applying photodynamic therapy to many cancer treatments,” says Zhang. “However, the photo-sensitive drugs being used in the previous experiments, unlike the new photosensitizers we’ve developed, usually could not be excited by infrared light.”

“The use of these photosensitizers is a very big advancement in photodynamic therapy,” adds Steelant. “With this new technology, we can target specific cancer cells, down to a very small, but well-defined spot. . . . Our only limiting factor encountered so far is our lack of ultra-high-powered microscopes which would allow us to see down to the individual lipids or proteins in the cancer cells themselves.”

In their ongoing research, the New Mexico Tech scientists have successfully used PUNPs to detect and kill breast cancer cells, and they plan on expanding their study to include prostrate cancer cells as well.

Zhang and Steelant are joined in their promising oncology study by Séverine van Slambrouck, a post-doctoral researcher at New Mexico Tech who has become adept at culturing breast cancer cells in the university’s Laboratory of Biochemical and Biomedical Research.

“Severine’s work is crucial to our study, since she can pinpoint cancer cells from a tumor that’s localized to the metastasizing phase, where the cancer begins to spread,” Steelant points out. “Therefore, we are able to see in great detail where the cancer is, and where and how fast it’s spreading.”

The photosensitizer research study being conducted by Zhang and his colleagues at New Mexico Tech is funded through start-up financial and logistical support provided by the research university in Socorro, as well as by a research grant from the National Center for Research Resources of the National Institutes of Health.