The potential for photodynamic therapy to treat cancer is limited by the fact that light cannot penetrate deep inside tissue. Now, a new approach that uses microwaves to activate nanoparticles could overcome this problem and shows promise as a way to safely kill cancer cells in deeply situated tumors.
Nanoparticles are tiny particles - between 1-100 nm - that have unusual properties compared with the same substance at the larger scale. These unusual properties and their tiny size - comprising just a few hundred atoms - makes them useful for working at the cellular and sub-cellular level in biology.
In a paper published in the Journal of Biomedical Nanotechnology, physicists at the University of Texas at Arlington (UTA) describe how, using microwaves, they activated photosensitive nanoparticles to generate a highly reactive form of oxygen to kill cells within solid tumors.
Lead author Wei Chen, a professor of physics at UTA, says by using microwaves, their approach could be used to target deeply situated tumors in all types of tissue.
Each activated nanoparticle generates a singlet oxygen molecule - a highly reactive version of oxygen that damages cell mitochondria, the compartments inside cells that produce the energy the cell needs. Eventually, this leads to cell death.
Current treatments based on photodynamic therapy use visible, ultraviolet, or near infrared light. At these wavelengths, electromagnetic radiation cannot penetrate deep inside tissue, limiting the therapy to the treatment of skin cancers or tumors close to the skin surface.
New type of nanoparticle generates singlet oxygen
In previous work, the team discovered that using X-rays, they could activate a new type of nanoparticle - copper-cysteamine or Cu-Cy - to generate singlet oxygen to slow tumor growth. However, X-ray radiation can harm healthy tissue and poses significant risks to patients.
In the new study, the researchers show it is possible to activate Cu-Cy nanoparticles with microwaves, which can be targeted directly at the tumor without harming surrounding healthy tissue.
Using a bone cancer cell line (osteosarcoma), the team tested the new method in cell cultures and live animals. In both cases, microwave activated Cu-Cy nanoparticles caused significant cell destruction.
Upon being heated up by the microwaves, the nanoparticles release copper ions, which in turn generate the reactive oxygen needed for cancer cell destruction.
While increased safety is an obvious benefit of such an approach, Prof. Chen also lists other advantages. These include the fact the Cu-Cy nanoparticles have very low toxicity, are easy and cheap to make, and they emit an intense luminescence, offering potential use as an imaging agent.
Prof. Chen says they have a patent pending on the new photosensitizer nanoparticles.
Alex Weiss, UTA chair of the Physics Department, says Prof. Chen's work on nanoparticle activation could "transform cancer treatment." The latest findings show how these new types of therapy could play an important role in finding safe, effective, and inexpensive treatments for cancer.
"Our new concept combining microwaves with photodynamic therapy opens up new avenues for targeting deeper tumors and has already proven effective in rapidly and safely reducing tumor size."
Prof. Wei Chen