Nanothermometers that monitor temperature changes in cells could improve an anticancer heat treatment, say scientists in Puerto Rico. 

Carlos Rinaldi and colleagues from the University of Puerto Rico have been working on improving magnetic fluid hyperthermia cancer treatment (MFH). MFH involves injecting a fluid containing magnetic iron oxide nanoparticles directly into tumours. The temperature of the surrounding cells is then increased from a normal 37 °C to about 42 °C by heat generated when an alternating magnetic field is applied. Whilst healthy cells can survive at 42 °C, tumour cells are destroyed. However, above 42 °C, damage to the healthy tissue can also occur. 

To monitor the temperature of MFH-treated cells, Rinaldi coated the nanoparticles used with a temperature-responsive fluorescent polymer built from N-isopropylacrylamide (NIPAM) and a modified acrylamide. Through the fluorescence change in the polymer, the temperature of the medium surrounding the nanoparticles can be monitored non-invasively, using a spectrofluorometer. And, when the temperature gets too high, the heating can be stopped - the temperature then falls by heat transfer to the surrounding unaffected tissue. 'That is, the body's natural mechanisms bring the temperature down,' explained Rinaldi. 

The work has potential applications in bioengineering, said Rinaldi. He foresees the clinical development of his nanoparticles in MFH treatments, and intends to test this application in vitro in the near future. 'However, there are many challenges to be overcome before these materials can be used in a clinical setting,' Rinaldi warned. 'A major challenge is controlling the transition temperature of the polymer so we can visualise temperature changes relevant to MFH.' 

'Also, NIPAM typically agglomerates at temperatures above a lower critical solution temperature,' added Rinaldi, 'especially in media with high ionic strength. It is actually not clear yet if this will be a problem during treatment, but it would definitely be a problem if the particles are in the bloodstream. We are working on using copolymers and on functionalising the polymer to avoid this.'

Dhirendra Bahadur, at the Indian Institute of Technology Bombay, Mumbai, India, said that the mechanism of cell death - a field of interest to his team - might be 'better understood and monitored through the approach.' He added that 'there are other possibilities, not only for monitoring but also for controlling the temperature in vivo by using tuned materials, which would have the additional advantage that over-heating may be avoided.'

Elinor Richards