An antibody is an agent of the immune system that attaches to an antigen. Usually antibodies recognize antigens on a virus or bacteria and attach to the invader to mark it for destruction by other immune cells.

In a new study,  University of Colorado Anschutz researchers engineered an antibody to recognize and attach to a protein called EGFR. Bladder tumors (but not healthy cells) are often covered in EGFR. Other researchers have hooked molecules of chemotherapy to antibodies that recognize EGFR and have used this antibody-antigen system to micro-target the delivery of chemotherapy. In this case, researchers used nifty chemistry to attach gold nanoparticles to antibodies.

Once they had a gold nanoparticle attached to an antibody that seeks out and binds to EGFR on the surface of bladder tumors, they used plasmon resonance, the process that makes nanoparticles vibrate in certain frequencies of light, to "tune" nanoparticles to a chosen frequency. Resulting energy transfer from the light to the particle creates heat in a very small area. In this study, researchers tuned their gold nanoparticles to experience plasmon resonance in near infrared light -- a wavelength of light that is generally safe by itself. Finally, when they shined a laser's near infrared light on the nanoparticle-antibody conjugate, it aggravated the nanoparticles, which heated up and fried the nearby tumor tissue.

Test tumors were very small bumps on the bladders of mice. The tumors were grown using cells that express the enzyme luciferase, which makes them glow, like fireflies. The more a mouse bladder glowed, the more cancer was present. And conversely, the less it glowed, the more cancer had been killed by  nanoparticles.

The study compared mice injected with EGFR-directed nanoparticles and laser light to mice only treated with laser light and found that, indeed, tumors in mice with targeted gold nanoparticles glowed less than their counterparts in the control group. In fact, these tumors glowed less than they had before treatment, implying that the technique had successfully slowed and even reversed tumor growth. Side effects were minimal.