A cell-permeable pyrazolidinedione compound that is shown to target RhoGEF DH-PH domain junction with high affinity (Kd = 65nM) and effetively prevent RhoGEFs LARG, p115, and PDZ from interacting with RhoA, while displaying little potency against DBL-RhoA, LBC-RhoA, intersectin-Cdc42, or TrioN-Cdc42 interaction. Shown to completely prevent serum-induced activation of cellular RhoA, but not Cdc42 or Rac1, in NIH-3T3 cultures (10uM) and RhoA downstream signaling events. Greatly synergizes with Rho GEF-binding domain blocker Rhosin in blocking RhoA-LARG interaction and in preventing cellular RhoA activation (both drug at 5uM).