Anti-carcinogenic effects of lemon balm in colon cancer cells.
Colorectal cancer (CRC) is the third most common cancer worldwide with the fourth highest rate of cancer-related mortality. With an increasing incidence of CRC attributed to rapid acquirement of western lifestyle habits such as high caloric nutrition and sedentariness, there is a focus on novel preventative or therapeutic treatments.
Melissa officinalis extracts contain a range of phytochemicals including phenolic acids, flavonoids, sesquiterpenes, monoterpenes and triterpenes with recent reports describing cytotoxic and anti-proliferative effects in various tumour cell lines. The underlying mechanisms however, remain poorly understood. The current study aimed to identify these effects in human colon cancer cells.
Human colon cancer cells were established from two sources, the primary tumour of a 44-year old Caucasian woman with colon adenocarcinoma (HT-29), and from a lung metastasis of a colon carcinoma of a 72-year old male (T84). A standardised hydroethanolic (31% (v/v) 1 : 2.5-3.5) Melissa officinalis L. (lemon balm) leaves extract (LBE) containing 7.48 mg/ml rosmarinic acid was used in the study. Cells were treated with either the LBE or with a corresponding vehicle control in experiments assessing proliferation rate of cancer cells, cell cycle analysis, measurement of extracellular reactive oxygen species (ROS), measurement of intracellular ROS, fluorescence microscopy and immunoblotting.
The study experiments found that LBE inhibited proliferation of both the HT-29 and T84 cancer cells in a concentration-dependant manner. In comparison to optimised anticancer drugs irinotecan, paclitaxel, 5-Fluorouracil and oxaliplatin, the [IC.sub.50] values of LBE was higher, however the LBE treatment led to complete death of the colon cancer cells. In analysing the cell cycles, LBE induced G2/M cell cycle arrest in the HT-29 colon carcinoma cells and reduced the protein expression of cyclin dependant kinases supporting the inhibitory effect of LBE on cell cycle progression. In the HT-29 cells, LBE treatment led to cleavage of caspases 3 and 7, which is a hallmark of apoptosis. Additionally, LBE significantly increased the number of apoptotic cells from 5 to 16% in HT-29 cells and from 43-55% in the T84 model. LBE was observed to induce the formation of ROS (2-fold) both inside and outside of the cells, within the first hours of treatment demonstrating that the M. officinalis extract exerted pro-oxidative effects rather than anti-oxidative effects. To test for specificity of LBE-induced ROS formation, the HT-29 cells were co-treated with LBE and one of the following anti-oxidants, N-acetyl cysteine, glutathione, a-Tocopherol or ascorbic acid, with results demonstrating significant reduction in ROS formation. Finally, the proliferative and apoptotic effects of HT-29 cells were retested with co-treated cells to investigate whether the ROS was the cause or an effect of LBEinduced apoptosis. Interestingly, cells co-treated with an anti-oxidant and the LBE demonstrated significantly diminished anti-proliferative effects and completely or partly protected the cancer cells from LBE-induced apoptosis.
Melissa officinalis has previously been reported to have numerous phytotherapeutic effects including anti-oxidative and free radical scavenging properties. The authors describe the debatable modulating role of phenolic natural products in balancing oxidation and anti-oxidation suggesting that these redox-active molecules may play dual roles and their behaviour to act as prooxidants or anti-oxidants depends on the microoxygen environment of the cells.
The results from these experiments demonstrated that LBE exerted a pro-oxidative rather than anti-oxidative effect due to ROS formation in treated cancer cells and that the increased ROS formation was required for the anti-proliferative and apoptotic effects of M. officinalis. Importantly, it was also demonstrated that these effects were reverted with simultaneous application of strong anti-oxidants such as glutathione and M-acetyl cysteine. Cancer cells are generally characterised by an imbalance of ROS and increasing cellular oxidative stress is a common strategy of current anticancer therapies. This study demonstrates the challenges of combining strong anti-oxidant therapies in the oncology setting, with the potential to disrupt the apoptotic effects of other therapies. Whilst demonstrating a potential role of M. officinalis for anticancer phytotherapies, preclinical in vivo studies as well as human clinical studies will provide further insight.
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|Publication:||Australian Journal of Herbal Medicine|
|Date:||Jun 1, 2015|
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