Identification of Small Molecule Inhibitors of Staphylococcus aureus RnpA.

Staphylococcus aureus RnpA is thought to be a unique dual functional antimicrobial target that is required for two essential cellular processes, precursor tRNA processing and messenger RNA degradation. Herein, we used a previously described whole cell-based mupirocin synergy assay to screen members of a 53,000 compound small molecule diversity library and simultaneously enrich for agents with cellular RnpA inhibitory activity. A medicinal chemistry-based campaign was launched to generate a preliminary structure activity relationship and guide early optimization of two novel chemical classes of RnpA inhibitors identified, phenylcarbamoyl cyclic thiophene and piperidinecarboxamide. Representatives of each chemical class displayed potent anti-staphylococcal activity, limited the protein's in vitro ptRNA processing and mRNA degradation activities, and exhibited favorable therapeutic indexes. The most potent piperidinecarboxamide RnpA inhibitor, JC2, displayed inhibition of cellular RnpA mRNA turnover, RnpA-depletion strain hypersusceptibility, and exhibited antimicrobial efficacy in a wax worm model of S. aureus infection. Taken together, these results establish that the whole cell screening assay used is amenable to identifying small molecule RnpA inhibitors within large chemical libraries and that the chemical classes identified here may represent progenitors of new classes of antimicrobials that target RnpA.

Crystal structure of the ribonuclease-P-protein subunit from Staphylococcus aureus.

Staphylococcus aureus ribonuclease-P-protein subunit (RnpA) is a promising antimicrobial target that is a key protein component for two essential cellular processes, RNA degradation and transfer-RNA (tRNA) maturation. The first crystal structure of RnpA from the pathogenic bacterial species, S. aureus, is reported at 2.0 Šresolution. The structure presented maintains key similarities with previously reported RnpA structures from bacteria and archaea, including the highly conserved RNR-box region and aromatic residues in the precursor-tRNA 5'-leader-binding domain. This structure will be instrumental in the pursuit of structure-based designed inhibitors targeting RnpA-mediated RNA processing as a novel therapeutic approach for treating S. aureus infections.

Synthesis and Biological Evaluation of Scutellaria Flavone Cyclaneaminol Mannich Base Derivatives as Novel CDK1 Inhibitors.

Cyclin-dependent kinase 1 (CDK1) is the only necessary CDK in the cell proliferation process and a new target in the research and development of anti-cancer drugs. Natural flavones are selective CDK1 inhibitors which can suppress the proliferation of cancer cells. However, their bioavailability is poor. To solve these problems, 6 Scutellaria flavones were isolated from hydrolyzed products of Scutellaria baicalensis and used as lead compounds, 18 Scutellaria flavones cyclane-aminol Mannich base derivatives were semi-synthesized and their biological activity as novel CDK1 inhibitors was evaluated. Results indicated that the biological activity of 8-Hydroxypiperidinemethyl-baicalein (BA-j) is the highest among these compounds. BA-j is a selective CDK1 inhibitor, and has broad-spectrum anti-proliferative activity in human cancer cells (IC50 12.3µM). BA-j can capture oxygen free radicals (.O2(-)) and selectively increase intracellular H2O2 level in cancer cells and activated lymphocytes, thus inducing their apoptosis rather than in normal cells. These findings suggest that BA-j selectively induces apoptosis in cancer and activated lymphocyte by controlling intracellular H2O2 level, and can be developed into a novel anti-proliferative agent for the treatment of cancer, AIDS, and some immune diseases.

BA-j as a novel CDK1 inhibitor selectively induces apoptosis in cancer cells by regulating ROS.

Cyclin-dependent kinase 1 (CDK1) is the only necessary CDK in cell proliferation and a novel target in the development of anticancer drugs. 8-Hydroxypiperidinemethyl-baicalein (BA-j) is a novel selective CDK1 inhibitor with broad spectrum anti-cancer activity (IC50 12.3 µM) and 2 tumor xenografts. Because of the differential mechanisms controlling redox-states in normal and cancer cells, BA-j can capture oxygen free radicals ((·)O2(-)) and selectively increase the level of H2O2 in cancer cells, thereby specifically oxidize and activate the intrinsic apoptosis pathway bypassing the extrinsic death receptor pathway, thus inducing apoptosis in cancer cells rather than in normal cells. BA-j is different from cytotoxic anticancer drugs which can activate both the intrinsic apoptosis pathway and the extrinsic death receptor pathway, and therefore harm normal cells while killing cancer cells. The molecular and biochemical mechanisms of reactive oxygen species (ROS) regulation suggest that BA-j may be developed into a novel anticancer agent.

Cyclane-aminol 10-hydroxycamptothecin analogs as novel DNA topoisomerase I inhibitors induce apoptosis selectively in tumor cells.

A novel series of cyclane-aminol 10-hydroxycamptothecin (HCPT) analogs was designed and synthesized through the Mannich reaction using HCPT as the lead compound, such as 10-hydroxyl-9-L-prolinol (+) methylcamptothecin (PRPT), 10-hydroxyl-9-(4'-hydroxy) piperidinylmethylcamptothecin (PPPT), and 10-hydroxy-9-(4'-hydroxyethyl)-piperazinylmethycamptothecin (QPPT). Three kinds of new cyclane-aminols were introduced into the structure of HCPT, which modified strong cytotoxic HCPT into cyclane-aminol HCPT analogs with moderate cytotoxicity and improved selectivity toward DNA topoisomerase I inhibition in tumor cells. Special metabolic pathways for cyclane-aminol HCPT analogs in rats were discovered, which differed from other HCPT analogs. Cyclane-aminol HCPT analogs can capture O2 and cause an increase in intracellular hydrogen peroxide levels with selective induction of apoptosis in tumor cells rather than in normal peripheral blood mononuclear cells. Among them, PPPT has a much better druggability than topotecan (TPT) and has the potential to be developed into an antitumor agent.