Sipholenol A is a natural sipholane
triterpenoid isolated from the Red Sea sponge, Callyspongia siphonella. Previous studies showed the antimigratory and antiproliferative activities of the semisynthetic
sipholenol A esters against
breast cancer cell lines. This study investigated the effects of sipholenol A-4-O-3',4'-dichlorobenzoate (SPA) on the growth, migration and invasion of diverse human
breast cancer cells. Results showed that SPA inhibited the growth of the human
breast cancer cells, MDA-MB-231, MCF-7, BT-474 and T-47D, in a dose-dependent manner. Immunofluorescent analysis showed that SPA significantly reduced Ki-67-positive cells in MDA-MB-231 cells. Flow cytometry and Western blot analyses revealed that SPA treatment suppressed MDA-MB-231 cell growth by inducing cell cycle arrest at the G1 phase. In addition, SPA suppressed
breast cancer cell migration, invasion and decreased Brk and FAK activation in a dose-dependent manner. Molecular docking study suggested a perfect fitting at the FAK's FERM domain, inhibiting the main autophosphorylation site, Y397, which was further confirmed by Western blot analysis. Most known small molecule FAK inhibitors target the
kinase domain, creating several off-target side effects. The in vivo studies showed that SPA treatment suppressed
breast tumor growth and Ki-67, CD31, p-Brk and p-FAK expression in orthotopic
breast cancer in nude mice. In conclusion, SPA inhibited the growth, invasion and migration of
breast cancer cells possibly via deactivating Brk and FAK signaling, suggesting good potential for
therapeutic use to control invasive
breast cancer.