In vitro activity: Staurosporine, a microbial alkaloid, significantly inhibits protein kinase C from rat brain with IC50 of 2.7 nM. Staurosporine displays strong inhibitory effect against HeLa S3 cells with IC50 of 4 NM. Staurosporine also inhibits a variety of other protein kinases, including PKA, PKG, phosphorylase kinase, S6 kinase, Myosin light chain kinase (MLCK), CAM PKII, cdc2, v-Src, Lyn, c-Fgr, and Syk with IC50 of 15 nM, 18 nM, 3 nM, 5 nM, 21 nM, 20 nM, 9 nM, 6 nM, 20 nM, 2 nM, and 16 nM, respectively. Staurosporine (1 μM) induces>90% apoptosis in PC12 cells. Consistently, Staurosporine treatment induces a rapid and prolonged elevation of intracellular free calcium levels [Ca2+]i, accumulation of mitochondrial reactive oxygen species (ROS), and subsequent mitochondrial dysfunction. The apoptosis of MCF7 cells induced by Staurosporine can be enhanced by the expression of functional caspase-3 via caspase-8 activation and Bid cleavage. Staurosporine treatment at 1 μM only partially inhibits IL-3-stimulated Bcl2 phosphorylation but completely blocks PKC-mediated Bcl2 phosphorylation. Staurosporine induces apoptosis of human foreskin fibroblasts AG-1518, depending on the lysosomal cathepsins D mediated cytochrome c release and caspase activation. In addition to activating the classical mitochondrial apoptosis pathway, Staurosporine triggers a novel intrinsic apoptosis pathway, relying on the activation of caspase-9 in the absence of Apaf-1.

Kinase Assay: Protein kinase C is assayed in a reaction mixture (0.25 mL) containing 5 μmol of Tris/HCl, pH 7.5, 2.5 μmol of magnesium acetate, 50 μg of histone II S, 20 μg of phosphatidylserine, 0.88 μg of diolein, 125 nmol of CaCl2, 1.25 nmol of [γ-32]ATP (5-10 × 104 cpm/nmol) and 5 μg of partially purified enzyme. The binding of [3H]PDBu to protein kinase C is determined: Reaction mixture (200 μL contained 4 μmo1 of Tris/malate, pH 6.8, 20 μmol of KCl, 30 nmol of CaC12, 20 μg of phosphatidylserine, 5 μg of partially purified protein kinase C, 0.5% (final concentration) of DMSO,10 pmol of [3H]PDBu (l-3 × 104 cpm/pmol) and 10 μL of various amounts of Staurosporine.

Cell Assay: Cells are exposed to Staurosporine for ~32 hours. Cells are fixed in 4% paraformaldehyde and stained with the DNA-binding dye Hoechst 33342. Cells are visualized under epifluorescence illumination, and the percentage of apoptotic cells (cells with condensed and fragmented DNA) is determined.

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