Oliveria decumbens vent is a valuable plant in Iran, used as a vegetable. Traditionally, the aerial parts of this plant are used to treat the cancer-related symptoms, inflammation, pain, and feverish conditions. However, the scientific evidence related to its traditional effects especially the possible cellular and molecular mechanisms needs to be illuminated.The main objectives of our study were to explore in-vitro anti-cancer properties of OEO in 2D and 3D conditions, to understand the mechanism of OEO in the induction of death in cancer cells, and to identify in-vivo anti-tumor effect of OEO and induced immunomodulatory effects.OEO was extracted by hydrodistillation and analyzed by GC-MS method. To evaluate the cytotoxic effect of OEO on 4T1 cancer monolayer cells (2D culture) and spheroids (3D cultures), MTT (3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay was used. Fluorescence staining, various flow cytometry techniques, colorimetric assay, electrophoresis, and comet assay were performed to understand the anti-cancer mechanisms of OEO and determine the death mode in treated 4T1 cells. In animal studies, mouse mammary tumor model was established, the anti-tumor effect of OEO was investigated and ultimately by using the ELISA cytokine assay, immunostimulatory of OEO was studied.According to GC/MS analysis, thymol, carvacrol, p-cymene, and γ-terpinene were identified as main components of OEO. Based on MTT assay, OEO inhibited viability in 4T1 cancer cell without any significant effect on L929 normal cells in 2D, also the anti-proliferative effects of OEO on 4T1 spheroids (3D) was significant but less extent. Our results revealed that OEO induces apoptosis through ROS generation, mitochondrial membrane potential (ΔΨm) disruption, caspase3 activation, and DNA damage. Evaluating the effectiveness of OEO on 4T1 tumor-challenging mice and cytokine assay confirmed anti-tumor effects of OEO and development of an immune response related to Th1 expansion.These data shed light on the apoptotic mechanisms related to OEO cytotoxicity and introduced this compound as a candidate in cancer therapy.
