Fucoidan, a type of complex carbohydrate called a polysaccrharide, is found in many forms of brown seaweed. Fucoidan has a variety of biological activities, including anticancer, antiviral, neuroprotective, and immune-modulating effects. It has been reported that fucoidan enhances the activities of natural killer (NK) cells which play a vital role in anti-cancer activity.

In vitro: Fucoidan triggered apoptosis of PC-3 cells, human prostate cancer cells, via evoking intrinsic and extrinsic signaling pathways in a dose-dependent fashion, which indicated that fucoidan could dose-dependently block the growth of PC-3 cells. The activation of apoptosis induced by fucoidan was involved in the inactivation of p38 MAPK and phosphatidylinositol 3-kinase (PI3K) /Akt, and the activation of extracellular signal-regulated kinase mitogen-activated protein kinase (ERK1/2 MAPK) [1].

In vivo: Female Balb/c mice bearing breast cancer were intraperitoneally injected with fucoidan at 10 mg/kg body weight every two days for 20 days. Fucoidan decreased the tumor volume and the tumor weight in Balb/c mice. Additionally, fucoidan triggered apoptosis, which indicated that fucoidan could exert a strong antitumor effect on breast cancer model. Compared with control group, fucoidan dampened angiogenesis in tumor tissue via inducing a remarkable decrease in intratumoral vascular endothelial growth factor expression and inhibited lung metastasis of breast cancer [2].

References:
[1].  Boo, H., Hong, J., Kim, S., Kang, J., Kim, M., & Kim, E. et al. The Anticancer Effect of Fucoidan in PC-3 Prostate Cancer Cells. Marine Drugs. 2013; 11(8): 2982-2999.
[2].  Xue, M., Ge, Y., Zhang, J., Wang, Q., Hou, L., & Liu, Y. et al. Anticancer Properties and Mechanisms of Fucoidan on Mouse Breast Cancer In Vitro and In Vivo. Plos ONE. 2012; 7(8). e43483.