## 3 Results and Discussion
### Evaluation of Cytotoxicity
It also promotes apoptosis by interfering with the S phase of the cell cycle and blocks the activity of topoisomerase I due to its antioxidant activity [49]. Natural products have also been studied for their efficacy against rhabdomyosarcoma and they have been found to inhibit cancer cell proliferation via various mechanisms [50; 51]. However, as regards the extract examined in this study, literature data are limited and besides neither data of only rutin activity are available. Nevertheless, as it is previously mentioned, rutin is a quercetin glucoside bearing a rhamnose and a glucose moiety attached to position 3 of the aglycon. Studies of rutin metabolism demonstrated that the flavonoid is metabolized by various microorganisms and enzymes of the gut microbiota to quercetin and quercetin 3-O-glucose [52; 53]. Thus, in the present study, we discuss the effect of quercetin, a compound used against various types of sarcomas. Quercetin is a flavonoid and its cytotoxic effect has been examined against various osteosarcoma cell lines, followed by different mechanisms. For example, in the study of [54], quercetin was examined for its capacity to inhibit the proliferation of a highly metastatic cancer cell line, the 143B osteosarcoma cell line. It was observed that quercetin at a dose of 10 \(\upmu\)M decreases cell proliferation while at higher doses induces apoptosis, disrupts the cell cycle at the G2/M phase and inhibits the migration of cancer cells. Similarly, another osteosarcoma cell line, i.e., HOS and MG63, was evaluated for their sensitivity against quercetin. Similar results were observed regarding quercetin activity on cancer cells viability and cell cycle arrest [55]. Methotrexate at high doses is a basic treatment approach for children suffering from osteosarcoma. However multi-drug resistance in cancer chemotherapy is a quite common phenomenon and some patients come across methotrexate resistance. For this reason, [56] examined the effect of quercetin against U2-OS and U2-OS/MTX300 cell lines, sensitive and resistant respectively to methotrexate treatment. According to their results, quercetin inhibited cancer cell viability via apoptosis as it diminishes mitochondria activity. Similar to quercetin, luteolin has also been proven as a potential candidate against sarcomas. Uterine sarcoma cells, MES-SA/Dx5, were susceptible to luteolin as the flavonoid inhibited their proliferation in a dose-dependent manner. Taken together, these data demonstrate the important role of natural compounds in cancer-fighting. In our study, an A172 glioblastoma and a TE671 rhabdomyosarcoma cell line were used to investigate the cytotoxic effect of _S. aspera_ extract. Since the presence of rutin and luteolin was dominant, emphasis was given to the above-mentioned flavonoids or their metabolites. For both compounds, the concentrations that inhibited cancer cells growth and proliferation were calculated at 3.46 \(\upmu\)M for rutin and 3.39 \(\upmu\)M for luteolin. Considering that both flavonoids can cross the blood-brain barrier, it is important to extensively study these compounds. Our results are in accordance with the literature data presented herein and highlight de novo the very important role of natural products for cancer research. Although the exact mechanism by which the extract induces cytotoxicity is to be clarified, its strong antioxidant activity as estimated by the DPPH and ABTS assays, is possibly the key to the extract activity.