K-252a, a metabolite isolated from the culture broth of Nocardiopsis sp. K-252a, was found to exhibit an extremely potent inhibitory activity on protein kinase C. The IC50 value was 32.9 nM. K252a is a potent inhibitor of various protein kinases including Protein kinase A, Protein kinase C and Protein kinase G. It acts by competition with the ATP binding site with Ki values of 18-25 nM. K252a also acts as a specific and potent inhibitor (IC50 = 3 nM) of Trk receptors and thus selectively blocks the effects of nerve growth factor (NGF) on PC12 cells. At lower concentrations, K252a can act as a neuroprotective compound, promoting survival of primary neuronal cultures. This alkaloid induces apoptosis and cell cycle arrest by inhibiting Cdc2 and Cdc25.4 Recently, K252a was found to improve psoriasis in a SCID mouse-human skin model and to suppress referred mechanical hypersensitivity and neuropeptide up-regulation associated with acute pancreatitis.

Staurosporine is an alkaloid isolated from the culture broth of Streptomyces staurosporesa. It exerts antimicrobial, hypotensive, and cytotoxic activity. The main biological activity of staurosporine is the inhibition of protein kinases through the prevention of ATP binding to the kinase. This is achieved through the stronger affinity of staurosporine to the ATP-binding site on the kinase. Staurosporine is a prototypical ATP-competitive kinase inhibitor in that it binds to many kinases with high affinity, though with little selectivity. It is a potent, cell permeable protein kinase C inhibitor with an IC50 of 0.7 nM. At higher concentration (1-20 nM), staurosporine also inhibits other kinases such as PKA, PKG, CAMKII and Myosin light chain kinase (MLCK). At 50-100 nM, it is a functional neurotrophin agonist, promoting neurite outgrowth in neuroblastoma, pheochromocytoma and brain primary neuronal cultures. At 0.2- 1 uM, staurosporine induces cell apoptosis. Staurosporine is also a potent GSK-3β inhibitor with a reported IC50 value of 15 nM. In research, staurosporine is used to induce apoptosis. It has been found that one way in which staurosporine induces apoptosis is by activating caspase-3. Staurosporine was discovered to have biological activities ranging from anti-fungal to anti-hypertensive. The interest in these activities resulted in a large investigative effort in chemistry and biology and the discovery of the potential for anti-cancer treatment. Staurosporine induces apoptosis by multiple pathways and that the inhibition of more than one kinase is responsible for its potent activity. Because the mechanism of action of staurosporine is distinct from traditional anticancer drugs, this may warrant further preclinical evaluations of the antitumor potential of new staurosporine derivatives either alone or in combination with death ligands or conventional chemotherapeutic drugs.

3-Amino-N-(2,6-difluorophenyl)-5-(4-sulfamoylanilino)-1,2,4-triazole-1-carbothioamide (CDK1/2 INHIBITOR III) is potent inhibitor of Cyclin-dependent kinase 1/2 (IC50=0.6nM and 0,5nM) with marked antiproliferative activity.