# Anticancer Effects of Seaweed-Derived Bioactive Compounds
## 5 Carotenoids  
Carotenoids are lipid-soluble organic compounds pigmented with yellow, orange, and red colors. Carotenoids exert diverse beneficial functions, including the reduction of oxidative stress on the retina [51]. They are synthesized by photosynthetic microorganisms (cyanobacteria, algae, plants), as well as by some fungi and bacteria [52]. In particular, algal carotenoids have various unique structures, such as \(\alpha\)-carotene, \(\beta\)-carotene, chlorophyll, lutein, zeaxanthin, and fucoxanthin. These carotenoids play an important role in human health by providing pro-vitamin A, as well as acting as agents for cerebrovascular disease, photoprotection, and anticancer agents.  
However, animals are unable to synthesize carotenoids endogenously. Animals obtain carotenoids from their diet and modify their structures [53]. Approximately 30 types of carotenoids are found in the algae. Some of these were found in particular algal groups. Figure 3 shows example of seaweed carotenoids. For instance, the unique allene (C=C=C) structure is present in natural products and has been discovered in dinoxanthin (**24**), fucoxanthin (**25**), peridinin (**26**), and pyrrhoxanthin (**27**) [11, 54, 55]. Another unique acetylene (C\(\equiv\)C), commonly found in alloxanthin diterpenoids, monads, dinoxanthin (**24**), and crooxanthin (**29**), was isolated from a variety of algal species, such as _Cryptophyta_, _Haptophyta_, _Dinophyta_, and _Euglenophyta_. Meanwhile, fucoxanthin (**25**), peridinin (**26**), and pyrrhoxanthin (**27**) have an acetylated group (-O-CO-CH\({}_{3}\)) at the hydroxyl position, which is mainly found in _Heterokontophyta_, _Dinophyta_, and _Haptophyta_[11, 56, 57, 58, 59]. Among these seaweed carotenoids, fucoxanthin (**25**) and its deacetylated metabolite fucoxanthin are known for their anticancer potential.  
Figure 2: Structures of phenolic compounds, including chlorotannins and bromophenols.  
In particular, fucoxanthin (**25**) induced apoptosis by modulating various signaling pathways, including downregulation of mitogen-activated protein kinase and B-cell lymphoma 2 (Bcl-2), and activating the poly (ADP-ribose) polymerase (PARP) and caspase-3,-8,-9 [60]. Moreover, fucoxanthin decreased cancer cell metastasis by downregulating the mRNA expression levels of CD44 and CXCR4 and diminished the level of matrix metalloproteinases 9 [61]. Fucoxanthin also induced cell cycle arrest by decreasing the expression levels of cyclin D1, cyclin D2, cyclin-dependent kinase 4 (CDK4), CDK6, and cIAP2 [62,63]. Fucoxanthin (**25**) and fucoxanthiol (**30**) reduced the proliferation of human umbilical vein endothelial cells. Likewise, brown algae fucoxanthin extracts triggered the apoptosis in PC-3 cells via caspase-3 and enhanced the density of hypodiploid cells [64]. Furthermore, BCL2-associated X, apoptosis regulator (Bax), and Bcl-2 apoptosis-associated protein levels, except Bcl-XL, were downregulated by fucoxanthin (**25**) [65]. The macroalgae and microalgae fucoxanthin attenuated cell growth and triggered cell death pathways in diverse cancer cell lines and in vivo models. In addition, it prevents the transition, spread, and invasion of tumor metastasis [66].