Phenolic compounds originated from one of the main class of secondary metabolites in plants, are natural phytochemicals derived mostly from phenylalanine and less often from tyrosine, and are widely present in food and nutraceuticals. They attract peoples’ attention owing to their strong antioxidant activity and potentially protective effects against oxidative damage diseases including cancers. Recently, evidence suggesting phenolic compounds to possess an effective inhibitory effect on cancer invasion and metastasis is also increasingly reported in the scientific literature.
Among these phenolic compounds, curcumin and its derivatives have been extensively studied and evaluated.
Curcumin [bis(4-hydroxy-3-methoxy-phenyl)-1,6-heptadiene-3,5-dione] is naturally a phenolic compound isolated as a yellow pigment from turmeric (Curcuma longa), which is commonly used as a spice, a food colourant, and also as a food preservative. Furthermore, curcumin is well documented for its medicinal properties in Chinese and Indian medicines and has been used in Ayurvedic medicine for over 6000 years. Several studies report that it is one agent that possesses a variety of biological and pharmacological activities including anti-proliferation, anti-apoptosis , anti-angiogenesis and inhibition of cell invasion and metastasis. Previous studies demonstrated the potential antimetastatic activities of curcumin and its derivatives on a variety of cancers including lung cancer, breast cancer, colorectal cancer in vitro as well as in vivo. However, the exact molecular mechanisms by which curcumin exerts its effects is still to be determined.
Fig. 1. Chemical structure of curcumin and its analogues derived from turmeric
Fig. 2. Curcumin inhibits proliferation, invasion, angiogenesis and metastasis of different cancers through interaction with multiple targets.
Thyroid cancer is the most common type of endocrine malignancy and its incidence is rapidly growing worldwide. The most prevalent thyroid cancer is that of papillary origin (PTC; account for about 60–80%) which differs from follicular (FTC; 15–25%) and anaplastic carcinomas (ATC; 2–5%). In addition, about 3–10% of thyroid tumours derived from parafollicular C-cells are termed as medullary thyroid carcinoma (MTC). However, well differentiated cancers such as PTC may undergo dedifferentiation and progression to anaplastic carcinoma, a formidable disease characterized by widespread invasion, early distant metastasis.
Anti Metastasis Effects of Curcumin
Previous works strongly indicate that curcumin is a novel anti-metastasis agent used for treatment of thyroid cancer. curcumin could induce apoptosis in K1 papillary thyroid cancer cells via inducing intracellular formation of Reactive Oxygen Species followed by the collapse of MMP and the intracellular Ca2+ influx amount and affecting the expression of Bcl-2 and PARP. However, whether curcumin also plays a crucial role on metastasis of papillary thyroid cancer cells is still on question.
There Exist many investigations which have been shown that curcumin has inhibitory effects of metastasis toward a wide range of tumours, but its effect on thyroid cancer is not completely clarified. Curcumin dose-dependently suppressed cell viability of K1 as well as its cell attachment, spreading, migration and invasion abilities. Moreover, curcumin can also down-regulate the expression and activity of matrix metalloproteinase-9 (MMP-9).
Metastasis is a complex, multistep process made up of a cascade of interrelated, sequential steps including invasion, migration, adhesion, infiltration, colonization at a distant site, and the subsequent formation of new capillaries. To identify possible sites to prohibit cells treated with curcumin from metastasis.
It has been investigated the cytotoxicity of curcumin on papillary thyroid cancers. Curcumin dose-dependently inhibits the cell viability of K1 cells. (Fig. 3) then Among a series of crucial steps involved in initiating metastasis, invasion is the initial step and even the most essential one. An agent that could efficiently inhibit the ability of cancer cells to form secondary metastatic foci would be an ideal candidate to suppress cancer progression.
Fig 3.Effects of curcumin on K1 cell viability. Cells were incubated with or without
curcumin (12.5, 25, 50 and 100 lM) for 24 h at 37 C. After incubation, the effects of
curcumin on cell viability were determined by MTT assay. All data represent as the
means ± SEM of five independent experiments. SC, solvent control. ⁄P < 0.05 vs SC,
⁄⁄P < 0.01 vs SC (Student’s two tailed t-test).
During the process of invasion, the adhesion of cancer cells to their surrounding interstitium and basement membrane composition is the first step; in the process of invading to the blood vessels and then spilling out, the adhesion of cancer cells to vascular endothelialium and the basement membrane heterogeneity is the key step of metastasis. These all highlight the important role of adhesion in the cells attachment to tissue and finally spreading. The interaction and adhesion of cells with different biological surface is a dynamic process of invasion and metastasis of cancer cells. The adhesion process includes three steps: adhesion factors secret, cells attachment to tissue and finally spreading. The interaction and adhesion of cells with different biological surface is a dynamic process that requires specific cell surface receptors, structural proteins, signalling proteins and the intracellular cytoskeleton to participate in.
Fig. 4. Effects of curcumin on cell spreading.
As integrins are the principle cell surface adhesion receptors and Extracellular Cell Matrix is a complex mixture of matrix molecules including the glycoproteins, fibronectin, collagens, laminins, proteoglycans, and non-matrix proteins including growth factors . curcumin is able to inhibit metastasis via blocking the steps of integrin-mediated cell adhesion. Many researchers also reported curcumin dramatically inhibits cell adhesion ability in a great deal of cancers, such as breast cancer.
Afterwards invasive tumour cells must induce local degradation of ECM via proteolysis and then migrate through the modified matrix.Matrix metalloproteinases (MMPs), the major class of proteinases, play an important role in cell tumour invasion and metastasis.
MMPs, a family of zinc dependent endopeptidases, are key enzymes involved in these processes. Two members of the MMP family, the 72-kDa type IV collagenase MMP-2 (gelatinase A) and the 92- kDa type IV collagenase MMP-9 (gelatinase B), have been shown to be highly expressed and to play a significant role in the pathogenesis of thyroid cancers. Moreover, it was reported that they have been implicated in the invasion, metastasis, and tumour-mediated angiogenesis of many subtypes of thyroid cancers, including PTC, FTC and ATC. Expression of these extracellular matrix-degrading enzymes correlates positively with the presence of metastasis and disease progression in thyroid cancer patients. Thus, both gelatin zymography and Western blot assays were used to verify if curcumin could modulate the activity and expression of MMPs in thyroid cancer cells. the result show in figure 1 revealed that the activity and expression of MMP-9 were visibly downgraded by curcumin in a dose-dependent manner, while the same treatment of curcumin had no apparent effect on the activity of MMP-2 (data not shown). These results suggest that curcumin inhibits thyroid cancer cells metastasis at least in part through down-regulation of the expression and activity of MMP-9. It was reported that curcumin could also inhibit MMP-9 activity in osteosarcoma cells . While Lin et al. reported that curcumin suppressed invasion and metastasis of human lung cancer cells A549 in vitro by inhibition both of MMP-2 and -9 . In all of these cases, there may be a selective inhibitory effect of curcumin on the member of MMPs in different cell types.
Fig. 5. Effects of curcumin on the activity and expression of MMP-9. (A) Gelatin
zymography analysis of the activity of MMP-9 of cells pretreated with or without
curcumin (12.5, 25, 50 and 100 lM) for 24 h. (B) Western blot analysis of the
expression level of MMP-9 of cells pretreated with or without curcumin (12.5, 25,
50 and 100 lM) for 24 h. b-actin was monitored as a loading control. All data
represent as the means ± SEM of three independent experiments. SC, solvent
control. ⁄P < 0.05 vs control, ⁄⁄P < 0.01 vs control (Student’s two tailed t-test).
To successfully invade, cells must acquire the ability of migration.
Migration of cells is based on cycles of lamellipodial extension, attachment, cell body translocation, and retraction of the cell. The results showed that curcumin could reduce cell migration rate in a dose-dependent manner, and especially, up to 25 lM of curcumin treatment could completely suppress the migration of K1 cells. In other words, curcumin inhibits the ability of cell migration, consequently suppresses metastasis of thyroid cancer partially.
Cell migration is an important event that depends on efficient coordination between cell attachment and detachment on extracellular matrix. In summary, curcumin inhibits thyroid cancer cell attachment, spread, migration, invasion as well as the expression and activity of essential proteolytic enzymes, mainly MMP-9. Overall, these findings open a new avenue and clinical utility for curcumin that can be used for therapeutic and preventive purposes of thyroid proliferative diseases by not only suppressing the proliferation of thyroid cancer cells but also inhibiting metastasis-associated events.