Docking and Virtual Screening to Identify PKC Agonists: Potentials in Anticancer Therapeutics

Protein kinase C (PKC) is down-stream to most of the G-protein coupled receptor or tyrosine kinase receptors mediated signaling events from the cell surface. PKC C1 domain has a hydrophobic region with a polar groove to facilitate 1,2-diacyl-glycerol (DAG) binding or other agonist molecule for PKC activation. Post activation, a partial or complete blocking of hydrophilic groove makes the DAG binding site completely hydrophobic and facilitates easier penetration of the PKC into the membrane. Phorbol ester, a strong PKC agonist, uses this mechanism to induce tumor formation. A total of 300 heterocyclic compounds with 70% similarity to phorbol 12-myristate 13-acetate (PMA) were selected, and virtual docking was performed with PKC-α as target. An initial screening indicated that most of the molecules fit well into the C1 domain and had better binding energy than PMA. Further analysis in a PMA competition experiment identified five molecules, Zc 67913417, Zc 68601770, Zc 25726447, Zc 35376386 and Zc 49785214 as potent PKC agonists. In addition, as these compounds showed better binding than PMA, more interaction with PKC residues (hydrogen bonding and hydrophobic), and the top five hit molecules was potent enough to abolish carcinogenic effects of PMA. Searching the top heterocyclic compounds into the drug database gave a number of approved drugs. Testing two candidate drugs, nandrolone decanoate and budesonide, reduced cellular viability of HT1080 in a dose-dependent manner with an IC50 values of 96.8 nM and 200nM respectively. An in silico toxicity analysis indicated that top hit molecules are non-toxic, non-mutagenic in cellular and bacterial system, and have no tumorigenic potentials in a single cell or animal model. Hence, a virtual screening, agonist competition assay, and in silico toxicity assessment allowed us to identify five new PKC agonist molecules for future drug discovery against cancer. Keywords: Agonist, Cancer, Docking, Heterocyclic, Protein kinase C, PMA, Toxicity.