NSC 23766 trihydrochloride is a specific inhibitor of the binding and activation of Rac GTPase, used for cancer treatment. In Vitro: NSC 23766 (100 μM) treatment effectively inhibits polar body emission in a dose-dependent manner. NSC 23766 (200 μM) increases the percentage of morphologically abnormal spindles of oocytes. In NSC 23766-treated oocytes, the p-MAPK protein expression is significantly decreased^[2]. NSC23766 (50 μM) plus 100 ng/mL Jagged1, GDF9 and BMP15, reduces the number of germLine cell cysts and increases the number of primordial follicles^[3]. NSC23766 significantly inhibits GTP-Rac1 activity and phosphorylation of Rac1-PAK, ERKs and p38 MAPK in the spinal dorsal horn neurons^[4]. In Vivo: NSC23766 (2.5 mg/kg/day, i.p.) significantly attenuates the onset of spontaneous diabetes in NOD mice, without significant effects on the growth (body weights) of the mice. NSC23766 significantly increases the expression of Rac1 and CHOP, a marker for ER-stress, in islets from NOD mice^[1].