Malignant skin cancer is one of the most dangerous types of cancer. 5000 people are diagnosed with it every year in Austria. The number of cases has risen sharply in recent decades. Thirty years ago, there were only five hundred people suffering from malignant melanomas.
In contrast, mortality rates have risen by only a slight margin. If detected early, the chances for recovery are good. But as soon as metastases start to form, the chances for a cure drop rapidly. This is also due to the fact that there are hardly any long-term effective treatment options (source: Austrian Society for Dermatology (ÖGDV).
Bioactive plant-derived substances
The Institute for Pharmaceutical Sciences at the University of Graz has been conducting research for many years into natural substances that can be used for the treatment of cancer. The team has now achieved a breakthrough which might also make it possible to cure advanced stages of malignant skin cancer. An active substance from the roots of the Onosma paniculata plant, a subspecies of the borage plant (also known as forget-me-not), has been successfully tested on cancer cells and on mice. The researchers also succeeded in modifying the active ingredient and further improving its effect.
The project was carried out in collaboration with the Technical University of Munich and the Helmholtz Institute Munich (the German Research Center for Environmental Health). The group was led by Rudolf Bauer from the Institute of Pharmaceutical Sciences (Pharmacognosy) at the University of Graz. He has been researching medicinal plants that are used in traditional medicine for fifteen years with the aim of identifying bioactive ingredients and discovering new key substances.
The main purpose of the research was to identify the plants that are used in traditional Chinese medicine (TCM) as cures for cancer-related diseases. Cancer-related, because the definition of cancer in TCM differs from that in Western medicine, Nadine Kretschmer explains. She has worked with the project and is a biologist at the Heidelberg University of Medicine. Another goal was to test their suitability as an active substance for a particular medicine. Approximately eighty percent of all Chemotherapeutic drugs are derived from nature, especially from plants. This figure is as high as seventy percent just for cancer therapies. “The active substances on the market are usually synthetically modified even more so that they have an optimal effect. The active substances are then usually produced synthetically or biotechnologically for commercial purposes,” Kretschmer says.
Plants from traditional medicine
The contribution made by the University of Graz to the project was based on a database of several hundred medicinal plants used in traditional medicine which have been accumulated over several years. This project focused on plants from traditional Chinese medicine (TCM). Part of the contribution made by the German partners was the implementation of RNA (ribonucleic acid) sequencing and preliminary evaluations. RNA sequencing serves as a means of determining the nucleotide sequence in the RNA and provides information on how the genetic information of a gene is expressed.
The project included seventy-six of the most promising specimens from the database. These were dried, processed into 253 extracts and tested on various cancer cells. In the end, it was the Onosma Paniculata Bureau & Franch, a type of borage shrub, that offered prospects for further studies. The potent substance β-β-Dimethylacrylshikonin (DMAS) is found in the root of the plant.
No side effects
During the experiments, the substance was tested on cells of malignant melanomas. The substance destroyed the cells thereby confirming their efficacy. In order to test the substance for side effects, the initial in vivo tests were carried out on mice that were afflicted with skin cancer. β-β dimethylacrylshikonin was injected directly into the tumor which caused it to change and die off. Two types of cell death were observed:
- Apoptosis, a regulated death induced by the body
- Necrosis, an uncontrolled death;
There were no side effects.
Two follow-up projects are planned
Subsequent trials were conducted expressly with the aim of modifying the substance in order to improve its efficacy. A specific shikonin derivative proved to be especially effective. This demonstrated that the substance is well suited for the development of pharmaceuticals. In the meantime, two more follow-up projects have been planned. More extensive studies are required and the method of application is still an open question, Kretschmer states.
Kretschmer emphasizes that TCM was purely an inspiration for the active substance. It is still not clear how this works within TCM. Normally no singular plants are used in TCM, instead plant mixtures are used. These are prepared like tea. In an attempt to unravel the effect of TCM, the team cooked up the dried plant according to the TCM method and used it in cell cultivation experiments. However, no anti-tumor effect was observed. Kretschmer sees more potential in an oil-based preparation method that is applied to the affected areas of the skin. This is because shikonins are found in higher concentrations in the oil.
Verifying the identities of plant species
Over the course of the project, the identity of the borage plant species sold as TCM remedies was also tested. “There are roots that look very similar to the plant we are studying and we have found that the species is often sold under fake names in China.” This is problematic because some of the plants that are marketed contain substances that are potentially harmful.
Kretschmer and the research team found a technical solution to the problem: a method which uses thin-layer chromatography for the identification of plants. This innovation is based on a CAMAG system and is simple enough for use in pharmacies.
Thin-layer chromatography (TLC) is a physicochemical separation process that is used to examine the composition of specimens.
The core project was funded by the Austrian Science Fund FWF and was completed in early 2019.
Kretschmer, N.; Deutsch, A.; Durchschein, C.; Rinner, B.; Stallinger, A.; Higareda-Almaraz, J.C.; Scheideler, M.; Lohberger, B.; Bauer, R.: Comparative Gene Expression Analysis in WM164 Melanoma Cells Revealed That β-β-Dimethylacrylshikonin Leads to ROS Generation, Loss of Mitochondrial Membrane Potential, and Autophagy Induction, in: Molecules 2018, 23
Durchschein, C.; Hufner, A.; Rinner, B.; Stallinger, A.; Deutsch, A.; Lohberger, B.; Bauer, R.; Kretschmer, N.: Synthesis of Novel Shikonin Derivatives and Pharmacological Effects of Cyclopropylacetylshikonin on Melanoma Cells, in: Molecules 2018, 23
Jahanafrooz, Z; Stallinger, A; Anders, I; Kleinegger, F; Lohberger, B; Durchschein, C; Bauer, R; Deutsch, A; Rinner, B; Kretschmer, N.: Influence of silibinin and β-β-dimethylacrylshikonin on chordoma cells, in: Phytomedicine 2018, 49
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