Go6976 is a Protein Kinase C (PKC) inhibitor, with an IC₅₀ of 20 nM. IC50 & Target: IC50: 20 nM (PKC)^[1]. In Vitro: Go6976 is a potent inhibitor of PKC in vitro (IC₅₀ is 20 nM. This compound is structurally related to staurosporine, which is the most potent PKC inhibitor^[1]. UCN-01 is originally identified as a PKC inhibitor. Surprisingly, Go6976 is found to abrogate S and G₂ arrest. Dose-response studies reveal that 30 nM Go6976 is sufficient to cause abrogation of S-phase arrest in 6 h and abrogation of G₂ arrest followed by lethal mitosis in 24 h. Incubation of cells with 100 nM Go6976 is sufficient to cause complete abrogation of S and G₂ arrest at 6 and 24 h, respectively, which is only slightly less potent than in bovine serum. Incubation of cells with UCN-01 or Go6976 alone do not decrease viability compared with control at the concentrations used. Incubation of cells with 5 ng/mL SN38 result in cytostasis, and addition of 50 nM UCN-01 or 100 nM Go6976 to arrested MDA-MB-231 cells cause a dramatic decrease in viable cell number by 96 h^[2].