Inspired by natural porphyrins – synthetic porphyrins in melanoma cells (“Porphyrins 1”) and in fibroblasts (“Porphyrins 2”)
Text written by: Nela Malatesti, Faculty of Biotechnology and Drug Development, University of Rijeka
The inspiration in our research are natural porphyrins. Porphyrins are organic compounds that are usually purple (that is how they got their name), and natural porphyrins are often referred to as ‘colours of life’, as many of them participate in important biological processes. For example, heme is an extremely important natural porphyrin that is a non-protein part of hemoglobin, a protein in red blood cells, and which is responsible for binding oxygen in the process of breathing. Because of the heme, the blood is red. Heme belongs to metalloporphyrins, porphyrins that have some metal ion in their structure, so heme contains iron. However, the same porphyrin, but without iron is a well-known photosensitiser. Photosensitisers are molecules that can absorb visible light, and transfer that ‘captured’ energy to oxygen molecules nearby. In this way, reactive oxygen species are formed, the most important of which is the so-called singlet oxygen. As their name suggests, these are highly reactive species that can oxidise various biological molecules (e.g., proteins and lipids) that are close enough to react with them. In this case, porphyrins can damage the cell in which they are located and lead to its death. Scientists have called this phenomenon photodynamic action and use it in photodynamic therapy to destroy unwanted cells and tissues, for example, various types of tumors, but also against pathogenic microbes.
In our research group at the Faculty of Biotechnology and Drug Development, we deal with the synthesis of porphyrins and test them on tumour and healthy human cells for applications in photodynamic therapy. The porphyrins we synthesise are, therefore, inspired by natural porphyrins. They are also most often purple, and in addition to absorbing light, they can also emit light in the form of fluorescence. This fluorescence is usually bright red and we use it to observe porphyrins under a fluorescent microscope. With this we can examine whether our porphyrins, for example, enter the tumour cells that we want to destroy, and with the help of other cell tracking dyes that mark certain organelles in the cell, we can also find out where exactly in the cell our porphyrins are located. This is important because the photodynamic action will be more powerful in destroying tumors if enough porphyrin has entered the tumour cells, and if it is located close to important parts of the cell whose damage can lead to cell death. On the other hand, it is important to us that porphyrins do not enter the nucleus (in pictures dyied blue) so as not to be dangerous to healthy cells. That is why we always tests our porphyrins also on healthy cells such as the cells from the skin – fibroblasts shown here. The tumour cells shown here are melanoma (MeWo) cells and are globular in shape as opposed to elongated, spindle-shaped fibroblast cells. Green fluorescence marks the endoplasmic reticulum, and porphyrins, you guessed it – are red.
Our research group consists of PhD student Martina Mušković, mag.med.chem., and her mentors, professors, dr.sc. Ivana Ratkaj who leads the biological part of the research, and dr. sc. Nela Malatesti who takes care of porphyrin synthesis. In our research, cooperation with other scientists is very important, as well as numerous hardworking students who make their graduate and final theses with this topic in our laboratories. These pictures were made as part of her doctoral thesis by Martina Mušković who synthesised porphyrins, and then microscopy determined how porphyrins enter cells and where they can be found in them.