## 1 Introduction  
Fucoidan, mostly extracted from brown algae, is a family of fucose-rich sulfated polysaccharides [1; 2]. Fucoidan has been reported to possess a variety of important pharmacological activities, including anticancer [3], immunomodulatory [4], antiviral [5], antithrombotic and anticoagulant [6], antiadhesive [7], neuroprotective [8; 9], and antioxidant effects [10]. Due to the diversity of brown algae species, growing conditions of seaweeds, extraction methods of fucoidan, compositional and structural differences of fucoidan, and varying molecular weights of fucoidan,there is still research interest associated with isolation of fucoidan, identification of potential bioactive components in fucoidan, and explication of the biological mechanisms involved at the molecular level. The occurrence of human cancer cells can be triggered by free radicals [11]. Thus, the application of natural antioxidants as chemopre agents for the treatment of cancer has gained in popularity. Previous investigations have demonstrated that fucoidan acts as a potential ROS scavenger [3] and is capable of preventing oxidative damage [12]. In addition, there is growing evidence showing that fucoidan exhibits anticancer activity in cell models [2; 13] and can induce inhibition of tumor growth in mice [14]. Thus, fucoidan is considered to have potential as a novel and natural agent for auxiliary therapy in the treatment of cancer due to its antioxidant and anticancer properties. The global incidence rates of colorectal cancer have risen steadily in recent years. In Taiwan, dietary habits have gradually become more westernized over the past three decades. The incidence of colon cancer has risen sharply and is currently the third most frequent cause of cancer-related mortality [15; 16]. Previous investigations suggested there are drawbacks such as side effects and toxicity in regularly used anti-colorectal cancer drugs such as cisplatin [17]. Thus, there is a requirement for agents derived from natural sources with no or minimal side effects and no toxicities. Recently, natural bioactive compounds have drawn the attention of researchers due to their possible therapeutic and cancer-preventive activities at non-toxic levels and recent efforts have sought to gain a better understanding of their mechanisms of action, particularly with regard to their chemopre qualities [18]. In addition, both HT-29 cells and Caco-2 cells are considered useful in in vitro models for monitoring anti-colon cancer effects [18; 19]. However, in a study conducted by [PERSON] et al., in general, extract from brown algae _Cystoseira baccata_ or extract containing gold nanoparticles exerted a stronger cytotoxic effect against HT-29 than that against Caco-2 [20]. Moreover, we previously reported the growth inhibitory effect of HT-29 cells exerted by crude and purified fucoidans obtained from _S. cristafeolium_[3]. Thus, in this study, we opted to use HT-29 cells to study the growth inhibitory effects of SG1-SG4 and the related signaling pathways. The present study extends our previous investigation, in which we prepared four fucoidan extracts from _S. glaucescens_ (SG), namely SG1 (without compressional-puffing), SG2 (compressional-puffed at 140 \({}^{\circ}\)C), SG3 (compressional-puffed at 180 \({}^{\circ}\)C), and SG4 (compressional-puffed at 220 \({}^{\circ}\)C) [10]. In this study, the anticancer activity of SG1-SG4 against human colon carcinoma HT-29 cells was examined with respect to cytotoxicity, cell cycle analysis, mitochondrial membrane potential (MMP), cytochrome c, expression of caspase-9 and -3, DNA fragmentation, and annexin V/propidium iodide (PI) staining and the underlying mechanisms involved. This report, to the authors' best knowledge, is the first to evaluate the possible mechanism of anti-colon cancer activity of crude fucoidans extracted from SG by compressional-puffing pretreatment.