In vitro activity: NSC23766 is identified to fit into a surface groove of Rac1 known to be critical for GEF specification. NSC23766 effectively inhibits Rac1 binding and activation by the Rac-specific GEF Trio or Tiam1 in a dose-dependent manner without interfering with the closely related Cdc42 or RhoA binding or activation by their respective GEFs or with Rac1 interaction with BcrGAP or effector PAK1. NSC 23766 is active in regulating Rac GTPase functions on cytoskeleton and many cell functions including cell cycle, cell growth, adhesion, migration and gene transcription. NSC 23766 (50 μM) potently blocks serum or platelet-derived growth factor-induced Rac1 activation and lamellipodia formation without affecting the activity of endogenous Cdc42 or RhoA in NIH 3T3 cells. NSC 23766 reduces Trio or Tiam1 but not Vav, Lbc, Intersectin, or a constitutively active Rac1 mutant-stimulated NIH 3T3 cells growth and suppresses Trio, Tiam1, or Ras-induced cell transformation. NSC23766 dose-dependently inhibits PC-3 cells proliferation and anchorage-independent growth. 25 μM NSC23766 inhibits the PC-3 cell invasion through Matrigel by 85%. [1] 50 μM NSC 23766 inhibits thrombin-induced activation of Rac1 an d Rac2 in human platelets, as well as platelet aggregation. NSC23766 prevents Aβ40 and Aβ42 production in swAPP-HEK293cells without affecting Notch and sAPPα. NSC23766 prevents γ-secretase activity in cell, but not act as a direct γ-secretase inhibitor. NSC23766 dose-dependently reduces levels of secreted and intracellular Aβ40 with IC50 of 48.94 μM. 50 μM NSC 23766 inhibits release of Aβ42 by 57.97%. NSC23766 regulates endothelial nitric oxide synthase expression and endothelial function. 100 μM NSC23766 represses the eNOS promoter activity by 60% in bovine aortic ECs and by 30% to 35% in bEND.3 cells. Inhibition of Rac1 with NSC23766 destabilizes eNOS mRNA and shortens its half-life to 17 hours. NSC23766 dose-dependently attenuates ACh-induced relaxation of wild-type mice aortic rings. NSC23766 inhibits cell growth and induces apoptosis. NSC23766 decreases MDA-MB-468 and MDA-MB-231 cells viability in a dose-dependent manner with IC50 of ~10 μM, which is not correlated with the status of estrogen receptor (ER), progesterone receptor (PR), Her2, and p53 mutation. NSC23766 has little effect on the survival of the MCF12A normal mammary epithelial cells. After 24 hours expose to NSC 23766, MDA-MB-231 cells showes an increase from 41% to 65% in G1 phase and a concomitant decrease in S and G2-M phases. 100 μM NSC23766 induces a six-fold increase of apoptotic MDA-MB-468. The inhibition of NSC23766 on cell cycle arrest or apoptosis in breast cancer cells is mediated by downregulation of cyclin D1, survivin, and X-linked inhibitor of protein apoptosis.

Kinase Assay: Cells are grown in log phase in a 10-cm dish, and are starved in 0.5% serum medium or indicated otherwise for 24 h before lysis in a buffer containing 20 mM Tris HCl (pH 7.6), 100 mM NaCl, 10 mM MgCl2, 1% Nonidet P-40, 10% glycerol, and 1× protease inhibitor mixture. Lysates are clarified, the protein concentrations are normalized, and the GTP-bound Rac1 in the lysates is measured by an effector domain pull-down assay. For the His6-PAK1 PBD pull-down assay, cell lysates are incubated with Ni2+-agarose-immobilized His6-PAK1 PBD domain (~1 μg each) purified from E. coli for 30 min. The Ni2+-agarose co-precipitates are washed twice in the wash buffer and analyzed by immunoblotting with anti-Rac1 monoclonal antibody.

Cell Assay: Cells (1.5 × 104/mL Human breast cancer cells MDA-MB-468) are seeded in each well of 96-well tissue culture plates with 200 μL of medium. After 24 hours of plating, the medium is replaced with 200 μL of fresh medium containing NSC23766 at the indicated concentrations. At the end of the treatment period 20 μL of MTS solution are added to each well and incubated at 37 ℃ for 2 hours. Absorbance at 490 nm is read on a 96-well plate reader.