Screening of Bioactive Microalgae from Freshwaters, Collected in Hue, Vietnam: Cytotoxic Constituents from HU04.

[BACKGROUND/OBJECTIVES] Microalgae are recognized as prolific producers of bioactive metabolites with pharmaceutical potential. This study aimed to isolate and characterize cytotoxic constituents from selected cytotoxic microalgae, collected in Hue city, Vietnam.

[METHODS] Microalgal samples were collected from freshwater bodies, morphologically identified, and maintained in laboratory culture. Thirteen strains were successfully isolated and cultivated in BG11, Z8, and BBM media to determine optimal growth conditions. Cytotoxic effects of extracts/compounds were determined using the sulforhodamine B assay on human lung cancer (SK-LU-1) and human liver cancer (HepG2) cell lines. The methanol extract was partitioned with -hexane and CHCl, followed by extensive chromatographic separation and HPLC purification to afford twelve compounds, including two new and ten known compounds. The structures were elucidated by HR-ESI-MS and NMR spectra, chemical methods, and comparing compounds in the literature.

[RESULTS] From the phytoplankton samples collected across six freshwater bodies in Hue city, Vietnam, thirteen microalgal strains were successfully isolated and purified under laboratory conditions. These strains were morphologically and taxonomically identified to be HU05, HU13, HU08, HU02, HU04, HU14, HU12, HU11, HU03, HU15, HU16, HU06, and HU07. All methanol extracts of those microalgae were evaluated for cytotoxic activity. The MeOH extracts of (HU13) and (HU04) exhibited significant cytotoxic effects, with IC values of 6.19 ± 0.80 and 4.89 ± 0.76 µg/mL for , and 9.51 ± 0.84 and 8.32 ± 0.94 µg/mL for against SK-LU-1 and HepG2 cell lines, respectively. Furthermore, chemical studies of HU04 led to the isolation of two new compounds, smithioside A () and smithioside B () and ten known ones, 3,4,5-trimethoxyphenyl-1--β-D-glucopyranoside (), 4'-hydroxy-3'-methoxyphenol-β-D-[6--(4″-hydroxy-3″,5″-dimethoxylbenzoate)]-glucopyranoside (), 4'-hydroxy-2',6'-dimethoxyphenol 1--β-D-(6--syringoyl)glucopyranoside (), mallophenol B (), pisoninol II (), guaiacylglycerol (), ()-asarone (), deacetylsarmentamide B (), ()-2-hexenyl-β-D-glucopyranoside (), and 5,6-dihydropyridin-2(1)-one (). The cytotoxic activity of all isolated compounds was also evaluated against SK-LU-1 and HepG2 cancer cell lines. Compound showed the strongest activity, with IC values of 9.13 ± 0.89 µM (SK-LU-1) and 7.64 ± 0.46 µM (HepG2). Compounds and exhibited moderate cytotoxic activity on both human cancer cell lines with IC values ranging from 25.99 to 51.47 µM.

[CONCLUSIONS] These results highlight the potential of HU04 as a source of bioactive compounds, particularly in anticancer applications. These findings suggest that HU04 extracts could be developed for therapeutic purposes targeting cancer.