Over the last few decades, the importance of early cancer detection has come to the forefront of the medical field’s attention. Researchers are continuously trying to develop new diagnostic imaging techniques that can better detect cancer. Recently, animals have been of particular interest in this research due to their ability to differentiate between cancerous and healthy cells using their highly sensitive olfactory sense. A study done by zoologist Dr. Giovanni Galizia at the University of Konstanz demonstrates how the receptor cells on a fruit fly’s antennae can be genetically modified so that it glows whenever they detect the odour of cancer cells.
As normal cells differentiate into cancer cells, their metabolism changes and different metabolic products are produced (Strauch et al. 2014). Dr. Galizia experimentally proved that fruit flies can detect these subtle changes by studying how the receptor neurons respond to different odours. A change in calcium concentration is an indication of neuronal activity. For this reason, calcium imaging was a main part of this experiment. Genetically encoded calcium indicators (GECIs) were used to detect these changes in calcium concentrations (Tian et al. 2009). GECIs are used because they can be targeted to specific cell types, consist of a calcium binding domain and fluoresce when bound to a calcium ion, providing visual confirmation for neuronal activity (Tian et al. 2009).
Dr. Galizia inserted a GECI named GCaMP3 into the fruit fly’s antennae to observe any odour-evoked responses. Once the specific neurons have been genetically altered, the fruit flies were fixed onto a podium and subjected to volatile substances emitted from the metabolic products of both normal and cancer cells. In order to obtain the different scents, the healthy and cancer cells were grown in culture flasks containing a specific culture medium. After 24 hours, the specific culture medium was replaced with a nutrient solution and the cells continued to grow for another 96 hours. Finally, the nutrient solution was collected in glass vials to allow the volatile substances to accumulate. Once this was done, the odours of the healthy and cancer cells were extracted from the vials and passed over the antennae using a computer-controlled autosampler. Using a fluorescence microscope, neuronal activity was observed as the GCaMP3 proteins glow in response to calcium influx when exposed to cancer odours (Strauch et al. 2014).
What was even more astonishing was that the study showed the fruit flies were not only able to differentiate between healthy and cancer cells but they were also able to differentiate between various types of breast cancer. The scents of different breast cancer cells created distinct stimulation patterns in the animals as seen in Figure 1 (Strauch et al. 2014).
While this method is still in its early stages of development, it provides a promising approach to diagnose cancer cells using insects’ natural olfactory receptors. This has not only shed light onto the use of fruit flies in medical applications but it also brings forth the possibility of developing artificial sensors that can mimic the biological mechanisms and provide a fast, affordable and easy cancer screening method unmatched by any of the current diagnostic imaging techniques.
Works cited:
Strauch, Martin, Alja Lüdke, Daniel Münch, Thomas Laudes, C Giovanni Galizia, Eugenio Martinelli, Luca Lavra, et al. 2014. “More than Apples and Oranges–Detecting Cancer with a Fruit Fly’s Antenna.” Scientific Reports 4 (January 6): 3576. doi:10.1038/srep03576.
Tian, Lin, S Andrew Hires, Tianyi Mao, Daniel Huber, M Eugenia Chiappe, Sreekanth H Chalasani, Leopoldo Petreanu, et al. 2009. “Imaging Neural Activity in Worms, Flies and Mice with Improved GCaMP Calcium Indicators.” Nature Methods 6 (12) (December): 875–81. doi:10.1038/nmeth.1398.