Asterosaponins from the tropical starfish <i>Acanthaster planci</i> and their cytotoxic and anticancer activities <i>in vitro</i>

New asterosaponin, acanthaglycoside G (<b>1</b>), along with three previously known steroidal oligoglycosides (<b>2‒4</b>), were isolated from the ethanolic extract of the starfish <i>Acanthaster planci</i>, collected off the coast of Vietnam. The structure of <b>1</b> was mainly elucidated by extensive NMR and ESIMS techniques as sodium 6-<i>O</i>-{<i>β</i>-D-fucopyranosyl-(1→2)-<i>β</i>-D-quinovopyranosyl-(1→4)-[<i>β</i>-D-quinovopyranosyl-(1→2)]-<i>β</i>-D-quinovopyranosyl-(1→3)-<i>β</i>-D-quinovopyranosyl}-6<i>α</i>-hydroxy-5<i>α</i>-pregn-9(11)-en-20-one-3<i>β</i>-yl sulfate. Compounds <b>3</b> and <b>4</b> showed slight cytotoxic activities against cancer RPMI-7951, HT-29, and MDA-MB-231 cell lines, but effectively inhibited in non-toxic concentrations colony formation of HT-29 and MDA-MB-231 cells and cell migration of MDA-MB-231 cells. Compounds <b>1</b> and <b>2</b> were inactive or less active, respectively.