Cancer stem cells refer to a small subpopulation of cells that can be found in tumors. As their name implies, cancer stem cells are capable of self-renewal and of transforming into any cell type. But what makes these cells dangerous is that they also have the same characteristics as cancer cells. Cancer stem cells are responsible not just for the development of tumors, but also for their progression, metastasis, and drug resistance. Cancer stem cells are not affected by chemotherapy and radiotherapy; in fact, some studies have reported that these treatments actually increase their number and malignancy.
The existence of cancer stem cells was a random discovery. Researchers were investigating the cause of a common form of blood cell cancer known as acute myeloid leukemia (AML) when they noticed a small fraction of the cell population that was different from the rest. These cells were still capable of dividing while the majority of the leukemic cells had already lost this ability. When they transferred some of these curious cells to a mouse, they initiated a new incidence of leukemia. The cells also showed resistance to chemotherapy and rapidly replenished the leukemic cell population right after therapy. This caused the recurrence of AML.
Today, researchers know these cells as cancer stem cells. They also know that these cells have the same DNA mutations as ordinary cancer cells but behave differently due to their stem cell-like nature. As for the origin of these cells, researchers believe they are most likely the product of cell reprogramming, which has been observed in a variety of tumors. However, the mechanisms that drive this process are still unclear, and research on this subject is still ongoing.
The pomegranate plant (Punica granatum) is a fruit-bearing shrub native to Asian countries. It has been cultivated in the Mediterranean region since ancient times and is widely known for its fruit. The plant has attracted scientific interest for decades due to its medicinal properties, its history as a natural remedy, and its effectiveness against various pathogens. According to studies, nearly every part of the plant possesses antimicrobial, antioxidant, and anti-inflammatory properties. Pomegranates are also rich in beneficial compounds, such as ellagic acid, anthocyanins, punicalagin, and other hydrolyzable tannins. Pomegranate juice, peel, and oil are known for their anti-cancer activities.
For their study, the American researchers investigated the effects of pomegranate extract on two different breast cancer cell lines. They took particular note of the cells' ability to form mammospheres or clumps of mammary gland cells – a hallmark of breast cancer stem cells. They reported that pomegranate extract reduced the formation of mammospheres in both breast cancer cell lines, suggesting that it can affect the ability of cancer stem cells to self-renew. When the researchers incubated mammospheres with the pomegranate extract, they observed that the cells broke formation and became adherent cultures. This suggested that the extract can cause cancer stem cells to differentiate into a specific mature cell type. Differentiation robs stem cells of their ability to proliferate rapidly and renew themselves.
The researchers also tested the effects of pomegranate extracts on epithelial-to-mesenchymal transition (EMT), a reprogramming process associated with the formation of cancer stem cells and the maintenance of their characteristics. The researchers reported that pomegranate extract reduced the ability of breast cancer stem cells to migrate. It also reduced the expression of genes involved in EMT, including a transcription factor that induces EMT. Based on these findings, the researchers concluded that the anti-tumor activity of pomegranate is due in part to its ability to stop EMT from happening. Because of this, they believe that pomegranates can be used in the prevention of breast cancer.