A florescent molecule naturally present in human tissue acts as an indicator of cancer, say bioengineers in the US, who have developed techniques to trace the molecule's concentration, structure and position within a cell. 

NADH, or nicotinamide adenine dinucleotide, is a molecule that resides mostly in a cell's mitochondria, where the vital process of energy production takes place. During this process NADH works with enzymes to produce ATP, a molecule that transports chemical energy around the cell so that it can continue to function. At the onset of cancer, however, the enzymes become disabled, leaving unused NADH to build up. 

Now, Qianru Yu and Ahmed Heikal of Penn State University claim to have developed combined fluorescence and spectroscopy techniques that can exploit this biomarker effect to detect cancer. 'If we are given two live cells, one normal and the other cancerous, we can differentiate between the two with confidence,' says Heikal. 

There are several stages to Yu and Heikal's method. First they use a technique called two-photon fluorescence lifetime imaging to record the level of fluorescence in a cell. Next, using a calibrated microscope, they use these images to construct maps of how the concentration of fluorescent NADH varies throughout the cell. Finally, they developed a technique called rotational diffusion imaging to measure how much NADH is bound to enzymes, as the molecule is unable to rotate when it is bound. 

The researchers discovered that cancerous cells contain on average twice as much NADH than normal cells, and that they contain a higher proportion of NADH that is still in the mitochondria and unbound to enzymes. 

Heikal told Chemistry World he believes their method has advantages over diagnostic tools such as magnetic resonance imaging (MRI) or Computerised (Axial) Tomography (CAT) scans, which do not have single-cell sensitivity, or biopsies, which are destructive and take place outside of the body. 'Our integrated micro-spectroscopy overcomes these challenges by providing molecular information within the context of cell morphology under physiological conditions,' he explains. 

Nevertheless, Paul O'Shea, a biophysicist at the University of Nottingham, is 'not at all surprised' at the findings. He notes that there have been similar studies searching for behavioural differences in cancer cells due to higher NADH levels, which coincide with an oxygen-reducing environment. 'In fact there are several anti-cancer drugs available that only become active in reducing environments to target cancers specifically,' he adds. 

Jon Cartwright 

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