4.5.4. Data Analysis

The GraphPad Prism (version 8.4.2, GraphPad Software for Windows, San Diego, CA, USA) was used to calculate the IC50 value according to a four-parameter logistic model. Dose- and time-dependent effect of the tested extract with respect to the control group were also calculated with GraphPad Prism (version 8.4.2). All data were presented as mean ± standard error of the mean (SEM). Statistical differences between untreated and treated cells were evaluated with the Student *t*-test. *p* values < 0.05 were considered statistically significant and confidence intervals were at ±95% (±95% CI). Normalized results are presented as log10 concentration.

#### **5. Conclusions**

In conclusion, the extract examined in this study highlights, for the first time, the cytotoxic effect of *R. officinalis* against TE671 and A172 cancer cell lines. The extract inhibited cancer cell proliferation in a dose- and time-dependent manner, with TE671 cells being more susceptible to the treatment with the extract. A further approach of this study would be to determine the mechanism by which *R. officinalis* exhibited its cytotoxic activity. However, our results are a first approach to the use of the plant as a candidate therapeutic agent. As expected, the extract presented notable antioxidant activity, high total phenolic content and a rich chemical profile. Given the importance of phenolic compounds as potent antioxidant molecules and the connection of antioxidant activity with cancer treatment, this Mediterranean plant is certainly worth further investigation.

**Supplementary Materials:** The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/molecules27196348/s1, File S1: Detailed description of the ms/ms fragmentation process.

**Author Contributions:** Conceptualization, E.K., G.I.L. and P.A.T.; methodology, E.K., O.N., C.K. and K.H.; investigation, E.K., C.K., G.I.L., P.T., C.K.-G. and P.A.T.; data curation, E.K. and C.K.; writing—original draft preparation, E.K.; writing—review and editing, E.K.; O.N., C.K., K.H., G.I.L., P.T., C.K.-G. and P.A.T.; supervision, P.A.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Samples of *R. officinalis* extract are available from the authors.
