A potent anticancer agent

What is cancer?

Cancer cells proliferate at an increased rate compared to normal healthy cells and are resistant to apoptosis. The ability for cancer cells to evade elimination by the immune system and grow uncontrollably is caused by mutations to key signalling molecules, which regulate pathways controlling proliferation and cell survival (1). Normal healthy cells tightly regulate the production and release of the growth factors that regulate the growth and proliferation rate, this ensures that homeostasis and tissue maintenance are achieved. In cancerous cells, this signalling has become deregulated and homeostasis is lost, leading to uncontrollable growth and proliferation.

Cancer cell proliferation can be enhanced in a number of different ways. They can produce increased levels of growth factors leading to faster rates of growth. The level of receptor proteins on the surface of cancer cells can also be increased, this then causes these cells to become hyperresponsive to growth factors. A similar situation can occur due to alterations to the receptor modules that regulate activation of downstream signalling pathways independent to the binding of growth factors. Cancer cells can also signal nearby healthy cells causing alterations in their signalling pathways, these alterations then stimulate the release of growth facts which are then supplied back to the cancer cells increasing their proliferation (2-3).

The hallmarks of cancer

Cancer development is divided into three distinct stages: initiation, promotion and progression. Initiation involves damage or mutation of the cell DNA which primes the cell to become cancerous. The next stage is promotion where a number of factors allow a mutated cell to resist apoptosis and replicate thus promoting the growth of a tumor. Finally, as the cancer cell forms a tumor we get disease progression.

The six proposed hallmarks of cancer by Hanahan and Weinberg include sustaining proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, and activating invasion and metastasis (1). As tumors progress they begin to display more of these hallmarks as part of disease progression. Anticancer therapies are classed as either chemopreventive or chemotherapeutic depending which stage of cancer development they focus on. Therapies that focus on the initiation and promotion stages of cancer are chemopreventive. The therapies that focus on cancer progression are chemotherapeutic.

Solutions in nature

The search for compounds and news drugs to combat these rogue cells has lead to researchers exploring the natural world searching for plants and herbs that might contain anticancer agents. Many pharmaceutical agents have been discovered by screening natural products from plants. For example, drugs like the chemotherapeutics etoposide, isolated from the mandrake plant and Queen Anne’s lace, and paclitaxel and docetaxel, isolated from the bark of the Nyssaceae tree, are all examples of drugs sourced from natural resources (4).

Rosemary extract and rosmarinic acid have both been reported to have antioxidant, anti-inflammatory and anticancer properties. Rosemary extract contains a variety of polyphenols with carnosic acid and rosmarinic acid being present in high concentrations (5). Rosemary extract and its polyphenols carnosic acid and rosmarinic acid have been found to exert strong anticancer effects (6-7).

Today we are going to take a look at some of the in vitro and in vivo studies that have focused on the anticancer effects of rosemary extract and in particular the polyphenol rosmarinic acid.

A multitude of in vitro studies

There have been a host of studies looking at rosmarinic acid and its anticancer properties in a wide range of cancer cell lines.

HT29 colon cancer cells treated with rosmarinic acid lead to a reduction of COX2 levels (8). COX2 in excessive levels is linked to inflammation and is expressed by cancer cells. HCT15 and CO115 colon cancer cells saw an increased level of apoptosis when exposed to rosmarinic acid as well as a decrease of phosphorylated-ERK which regulates cell proliferation (9).

MCF-7 and MDA-MB-231 breast cancer cells treated with rosmarinic acid saw decreased cell vaibility (10-12). Rosmarinic acid also reduced cell viability in DU145 and PC3 prostate cancer cell lines (13). A2780 and A2790CP70 ovarian cancer cell lines exposed to rosmarinic acid saw a reduction of cell proliferation and also an increased sensitivity to chemotherapy drug cisplatin (14).

SCG7901/Adr gastric cancer cells treated with rosmarinic acid also saw a fall in cell viability, drug and resistance (15). MKN45 gastric cancer cells also saw similar reduction of cell viability and a reduction of pro-inflammatory cytokines when treated with rosmarinic acid (16). We also see in HepG2 cells also experienced an increase in apoptosis when treated with rosmarinic acid via a reduction of Bcl-2 (a pathway that allows the cell to resist apoptosis) levels (17). In Hep-3B liver cancer cells we also see a reduction of cell viability when the cells are exposed to rosmarinic acid (18).

Rosmarinic acid treatment of U937 leukemia cells resulted in an increased rate of apopotosis and a decreased level of inflammatory TNF-α induced-NF-κB activation and a reduction of free radicals (19). CCRF-CEM, CEM/ADR5000 leukemia cell lines exposed to rosmarinic acid experienced increased cytotoxicity, apoptosis, necrosis, and cell cycle arrest (20). HL-60 leukemia cells also experienced an anticancer effect from treatment with rosmarinic acid (21).

In Vivo Studies

Ok so the amount of in vitro data for rosmarinic acid is very impressive with multiple cell lines affected but what about studies in vivo? Well there have also been a number of studies in animal cancer models, let’s take a look at some of them.

Rosmarinic acid administration at a dosage of 1-4 mg/kg in a mouse model of lung cancer lead to a decrease in the growth rate of tumor (22). In another study treatment with rosmarinic acid reduced induced tumor formation in hamsters (23). A mouse study showed that treatment with 360 mg/kg from weeks 4-12 decreased the frequency of adenomas (24). Researchers showed that the administration of 100 m/kg of rosmarinic acid 1 week prior to inducing cancer in mice reduced skin tumors (25).

A research team found that a dosage of 2.5 – 10 mg/kg of rosmarinic acid given to rats for 4 weeks resulted in decreased colon tumor formation and the number of polyps present (26). Rosmarinic acid administered at a dosage of 2 mg/kg for 2 weeks to mice had an anti-Warburg effect, mediated through decreased glucose uptake (27). Finally another rat study showed that rosmarinic acid at just 5 mg/kg for 30 weeks was able to decrease induced colon tumor formation through decreased TNF-α, IL-6 and COX2 levels (28).

Conclusion

Taken together, this large number of studies provides support the the anticancer effects of rosmarinic acid and also suggests several different mechanisms that may be responsible for its ability to inhibit tumor growth, cell proliferation and cancer progression.

 

Literature
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