"We have demonstrated that the system is feasible in laboratory mice," said Denardo. "The next step will be clinical testing in patients."
Researchers have investigated using heat as a potential treatment for cancer before now, but the problem has always been confining the heat within the tumour and predicting an effective dose. Both these drawbacks have limited the use of heat-based techniques. Now, Denardo and colleagues, together with co-workers at Triton BioSystems in Boston, may have overcome this problem.
The new experiment employs bioprobes, created by welding magnetized iron-oxide nanospheres to radio-labelled monoclonal antibodies found in mice with aggressive breast cancers. The bioprobes are "cloaked" in polymers and sugars, which make them biocompatible with the body's immune system. The researchers infused trillions of the probes into the bloodstreams of laboratory mice bearing human breast tumours. Once inside the bloodstream, the probes seek out and latch onto receptors on the surface of malignant cells.
The UC Davis team then applied an alternating magnetic field to the tumour region three days later. This caused the magnetic nanospheres latched onto the tumour cells to change polarity thousands of times per second, so instantly generating heat. As soon as the applied magnetic field was switched off, the bioprobes cooled back down again. The scientists applied the magnetic field burst in a single 20 minute treatment, and dosing was calculated using an equation that takes into account tumour concentration of bioprobes, heating rate of particles at different amplitudes, and the spacing of magnetic field bursts.
Once the treatment was finished, DeNardo and colleagues observed that tumour growth had slowed down in the mice – a response that correlated closely with heat dose. Moreover, the researchers noted that the nanoprobes were non-toxic.
"Using heat to kill cancer cells isn't a new concept," explained Denardo. "The biggest problems have been how to apply it to the tumour alone, how to predict the amount needed and how to determine its effectiveness. By combining nanotechnology, focused applied magnetic field therapy and quantitative molecular imaging techniques, we have developed a safer technique that could join other modalities as a treatment for breast and other cancers."
The scientists published their work in the Journal of Nuclear Medicine.