*Article* **Cytotoxic Effect of** *Rosmarinus officinalis* **Extract on Glioblastoma and Rhabdomyosarcoma Cell Lines**

**Eleni Kakouri 1, Olti Nikola 2, Charalabos Kanakis 1, Kyriaki Hatziagapiou 2,3, George I. Lambrou 2, Panayiotis Trigas 4, Christina Kanaka-Gantenbein <sup>2</sup> and Petros A. Tarantilis 1,\***


**Abstract:** *Rosmarinus officinalis* is a well-studied plant, known for its therapeutic properties. However, its biological activity against several diseases is not known in detail. The aim of this study is to present new data regarding the cytotoxic activity of a hydroethanolic extract of *Rosmarinus officinalis* on glioblastoma (A172) and rhabdomyosarcoma (TE671) cancer cell lines. The chemical composition of the extract is evaluated using liquid chromatography combined with time-of-flight mass spectrometry, alongside its total phenolic content and antioxidant activity. The extract showed a promising timeand dose-dependent cytotoxic activity against both cell lines. The lowest IC50 values for both cell lines were calculated at 72 h after treatment and correspond to 0.249 ± 1.09 mg/mL for TE671 cell line and 0.577 ± 0.98 mg/mL for A172 cell line. The extract presented high phenolic content, equal to 35.65 ± 0.03 mg GAE/g of dry material as well as a strong antioxidant activity. The IC50 values for the antioxidant assays were estimated at 12.8 ± 2.7 μg/mL (DPPH assay) and 6.98 ± 1.9 μg/mL (ABTS assay). The compound detected in abundance was carnosol, a phenolic diterpene, followed by the polyphenol rosmarinic acid, while the presence of phenolic compounds such as rhamnetin glucoside, hesperidin, cirsimaritin was notable. These preliminary results suggest that *R. officinalis* is a potential, alternative source of bioactive compounds to further examine for abilities against glioblastoma and rhabdomyosarcoma.

**Keywords:** *Rosmarinus officinalis*; phenolic compounds; chemical analysis; glioblastoma; rhabdomyosarcoma; cancer
