Microalgal extract from thermotolerant Coelastrella sp. F50 retards the liver tumor progression by targeting hepatic cancer stem cells.

Microalgae extracts have shown antitumor activities. However, the antitumor mechanism of them is not yet completely clear, especially the effect on cancer stem cells (CSCs). This study aimed to elucidate the antitumor activity and mechanism of microalgal extract from thermotolerant Coelastrella sp. F50 (F50) in hepatocellular carcinoma (HCC). Oncogenic behaviors were analyzed using cell proliferation, colony formation, invasion, sphere formation, and side population cells (SPCs) assays in HCC cells after F50 treatment. The molecular mechanism was further studied by quantitative real-time PCR, immunoblot, and immunofluorescence analyses. The chemopreventive efficacy of F50 was evaluated in rat orthotopic hepatoma, and the hepatic pathologies were investigated by immunohistochemical, immunoblot, and immunofluorescence analyses. F50 specifically suppressed hepatic CSCs (tumor spheres, drug efflux, CD133/ABCG2 CSCs markers) with no cytotoxicity in vitro. In the animal experiments, prophylactic F50 administration significantly attenuated tumor progression and improved liver function in HCC-bearing rats. In the mechanistic analysis, F50 potentially inhibited cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2 ) axis in HCC cells and rat hepatoma, and exogenous PGE2 restored CSCs properties in F50-treated HCC cells. In summary, F50 extract inhibits hepatic CSCs by COX-2/PGE2 downregulation and may facilitate a novel phytotherapy for HCC prevention.

Pigment production by a new thermotolerant microalga Coelastrella sp. F50.

Microalgae are good crops to produce natural pigments because of their high growth rates. Tropical zones are better locations than temperate areas for microalgal cultivation because they have longer duration of daylight and more stable temperatures throughout the year, but the high temperatures pose a challenge to microalgal cultivation. A newly isolated thermotolerant microalga produces reddish pigments under environmental stress. Morphological and molecular evidence including meridional ribs on the cell wall, pigment production, and its 18S rDNA sequence suggests that this microalga belongs to the genus Coelastrella. Salt stress and high light intensity accelerated biosynthesis of the pigments, and significant quantities of oil accumulated as the cells experienced stress due to nutrient deficiency. This microalga could withstand temperature of 50°C for more than 8h, which is a necessary trait for outdoor cultivation in tropical areas. The pigments contain astaxanthin, lutein, canthaxanthin, and ß-carotene as analysed by using HPLC.