Antitumour Potential of Gigartina pistillata Carrageenans against Colorectal Cancer Stem Cell-Enriched Tumourspheres

Abstract

Gigartina pistillata is a red seaweed common in Figueira da Foz, Portugal. Here, the antitumour potential of G. pistillata carrageenan, with a known variable of the life cycle, the female gametophyte (FG) and tetrasporophyte (T) was evaluated against colorectal cancer stem cell (CSC) -enriched tumourspheres. FTIR-ATR analysis of G. pistillata carrageenan extracts indicated differences between life cycle phases, being FG a κ/ι hybrid carrageenan and T a ʎ/ξ hybrid. Both carrageenan extracts presented IC₅₀ values inferior to 1 μg/mL in HT29-derived CSC-enriched tumourspheres, as well as reduced tumoursphere area. The two extracts were also effective at reducing cellular viability in SW620- and SW480-derived tumourspheres. These results indicate that carrageenans extracted from two G. pistillata life cycle phases have antitumour potential against colorectal cancer stem-like cells, specially the T carrageenan.

Keywords: antitumour activity; cancer stem cells; carrageenan; colorectal cancer.

Figure 1

Idealized structure of the chemical units of different types of carrageenan [8].

Figure 2

G. pistillata in nature, fixed in a rocky platform in Praia do Cabo Mondego, Figueira da Foz, Portugal.

Figure 3

FTIR-ATR spectra of the carrageenan extracted from FG (Female gametophyte) (a) and T (tetrasporophyte) (b) G. pistillata life cycle.

Figure 4

Carrageenan extracts reduce cellular viability in cancer stem cell (CSC)-enriched tumourspheres derived from HT29 colorectal cancer cell line. (a) Strategy for CSC-enriched tumoursphere formation; (b) IC₅₀ determination for salinomycin, T and FG carrageenans in HT29 CSC-enriched tumourspheres. Cell viability was determined by ATP (adenosine triphosphate) metabolism assays. Results are depicted as mean ± SD, n = 3.

Figure 5

Carrageenan extracts have broad anti-CSC action. Both T and FG carrageenans impact at different extents in CSC-enriched tumourspheres derived from SW620, SW480, and HCT116 cell lines, in a dose-independent manner. Cell viability was determined by ATP metabolism assays. Results are depicted as mean ± SEM, n = 3.

Figure 6

Carrageenan extracts impact on HT29-derived CSC-enriched tumoursphere formation when incubated at their respective IC₅₀ dose (FG carrageenan: 0.6572 µg/mL; T carrageenan: 0.7050 µg/mL; salinomycin: 0.1450 µg/mL). (a) A significant reduction on tumoursphere size is observed, however tumoursphere number is not significantly altered. Results are depicted as mean ± SEM, n = 3. ** p < 0.005; *** p < 0.001. Sal—salinomycin. (b) Representative images of seven-day tumourspheres at 10× magnification. Scale bar, 275 µm.