Selectivity and potency of natural product PIM kinase inhibitors identified by in silico docking

PIM3 (Proviral Integration site for Maloney murine leukemia virus kinase 3) is a proto-oncogene with serine/threonine kinase activity that prevents apoptosis, promotes cell survival, and stimulates protein translation. In addition, PIM3 functions in inflammation and immunity pathways. PIM3 inhibitors are being developed to treat cancer and inflammation-related disorders. Here we screen a 98,000 compound virtual library of natural products to identify those that are predicted to fit in the ATP site of PIM3. Since the structure of PIM3 has not been determined experimentally, we performed molecular structure prediction using the SWISS-MODEL tool to generate a PIM3 model structure for in silico screening. Compounds predicted to fit the ATP binding site of PIM3 were validated using biochemical assays, revealing activity against PIM3 for all eight candidates, with potencies mostly in the micromolar range. We tested several analogs of two validated candidates, the diosgenin glycoside dioscin and the biflavonoid hinokiflavone. Among five dioscin analogs, three exhibit similar potency against PIM3, and with some selectivity for PIM3 versus PIM1 and 2. Meanwhile, three of seven biflavonoid analogs exhibit sub-micromolar IC50 potency against PIM3, but with less selectivity for PIM3 versus PIM1 and 2.