Excess 17β estradiol (E2) is a risk factor of breast cancer. Previously, we have reported that E2 through influencing mitochondria by unknown mechanism contribute to the estrogen induced breast carcinogenesis. The aim of this study was to evaluate the mitotoxic and cytotoxic effects of normal O. Majorana organic extract (OME) as well as PEGylated nanoconjugate of OME with triphenylphosphonium (P-OME) against human breast epithelial and cancer cell lines. Origanum majorana, commonly known as marjoram, is a perennial herb, which is widely used in the Middle East as a spice. It has been shown to possess extensive range of biological activity, including antioxidant, anti-inflammatory, and anti-tumor growth effects. Interestingly, the anticancer potential of O. Majorana against breast cancer remains largely unexplored. Here, we investigated the anticancer effect of O. Majorana on three breast cell lines. We also used triphenylphosphonium (TPP) cation to check whether an imbalance in mitochondrial bioenergetics, in part, may be responsible for estrogen induced growth of breast cancer. Determination of cell density (cell survival) by SRB and mitochondrial metabolic activity by MTT assays showed that both OME and P-OME reduced growth of MDA-MB-231 and MCF-7 cells, but no effect on normal breast epithelial MCF-10A cells. OME and TPP blocked E2-induced increases of cell survival, metabolic activity and proliferation of breast cancer MCF-7 cells. E2 treatment increased MitoTracker® Red 580 labeling, indicating E2 treatment increased MCF7 cells mitochondrial mass. We observed a several fold increase in mitochondrial transcription factor A (TFAM) DNA binding activity as early as 3 hrs in treated MCF7 cells. DNA synthesis was inhibited in E2-exposed MCF7 cells by the silencing of TFAM. To discern whether a decrease in ATP production may be responsible for the E2-induced growth signaling, we measured the ATP present in the MCF7 cells. Our data showed that the ATP levels in E2 treated cells were very similar to control cells. E2 treatment of MCF-7 cells increased mRNA and protein levels of BNIP3 involved in mitophagy/autophagy. Together these data suggest that a carcinogenic concentration of E2 may modify mitochondrial dynamics, mitophagy, biogenesis and metabolism. In summary, our results demonstrated for the first time that OME was able to inhibit estrogen-induced growth of MCF-7 cells in a time- and concentration-dependent manner. Our results also demonstrated that P-OME nanoconjugate compared to OME was far more effective in exerting its cytotoxic effect through the induction of growth arrest, mitochondrial metabolic activity, senescence, apoptosis and autophagic cell death in the highly metastatic triple negative MDA-MB-231 cells. Our findings offer a new perspective on the utility of O. Majorana plant extract to be developed as a new alternative medicinal therapy against breast tumors.

Citation Format: Mohannad Garoub, Jayanta Das, Stanislaw Wnuk, Deodutta Roy. Origanum majorana organic extract induces senescence and autophagic cell death in breast cancer cells through influencing mitochondrial metabolism. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4061.