Y16

Y16 binds to the junction site of the DH-PH domains of LARG with a ∼80 nM Kd and suppresses LARG catalyzed RhoA activation dose dependently. It is active in blocking the interaction of LARG and related G-protein–coupled Rho GEFs with RhoA without a detectable effect on other DBL family Rho GEFs, Rho effectors, or a RhoGAP. In cells, Y16 selectively inhibits serum-induced RhoA activity and RhoA-mediated signaling, effects that can be rescued by a constitutively active RhoA or ROCK mutant. By suppressing RhoA activity, Y16 inhibits mammary sphere formation of MCF7 breast cancer cells but does not affect the nontransforming MCF10A cells. Y16 works synergistically with Rhosin/G04, a Rho GTPase activation site inhibitor, in inhibiting LARG–RhoA interaction, RhoA activation, and RhoA-mediated signaling functions. Y16 effectively inhibits the growth, migration, and invasion activities of breast cancer cells^[1].

PC-3 cells were quiesced in RPMI1640 containing 0.5% FBS for 24 hr. Cells were then trypsinized, resuspended in RPMI1640 containing 0.5% FBS, and counted. A total of 2.5 × 10⁴ cells were loaded into the upper chamber. The lower chamber was filled with RPMI1640 supplemented with 10% FCS. A13 (10 μM), A2 (10 μM), Y16 (10 μM), or DMSO was added both in the upper and lower chambers. The concentration of DMSO in the medium was 0.1% for all experimental conditions. After a 36 hr incubation period, the cell suspension was aspirated, and the membranes were fixed in 70% ethanol at -20℃ for 20 min. Cells that had attached but not migrated were removed, the membranes were rinsed in water, and migrated cells on the underside of the membrane were visualized with staining in 2% crystal violet. Cells were counted on three independent transwell membranes using a light microscope.