DEVELOPMENT OF NEW LIPID A BINDING AGENTS

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DESCRIPTION: Sepsis affects the lives of hundreds of thousands of people each in the U.S. Sepsis caused by Gram-negative bacteria results from adverse host immune response to the Lipid A (LA) portion of endotoxin. Compounds with high affinity for LA, including polymyxin B (PMB) and derivatives, are capable of detoxifying LA nd protection a host against sepsis. By binding LA, these compounds also sensitize Gram-negative bacteria to hydrophobic antibiotics. However, therapeutic use of PMB is limited due to its toxicity. The aim of this research is to develop small molecules capable of strong and selective associating with LA for use in treatment of sepsis and as means of fighting bacterial infection. Taking the interactions of PMB with LA as a model, this research focuses on the preparation of simple compounds, based on cholic acid scaffolding, capable of mimicking the LA-binding behavior of PMB but lacking the toxicity of the antibiotic. Simple cholic-acid based LA binders will present many advantages over reported LA binding molecules including: ease of preparation and derivatization, greater control over biological stability, and potential oral bioavailablity. Cholic acid derivatives were designed to mimic a conformation of PMB believed to be important in its association with LA. Preliminary experiments with cholic acid derivatives demonstrate their ability to sensitize Gram- negative bacteria to hydrophobic antibiotics, a behavior of LA binding agents. Optimization of LA-binding characteristics will be achieved by preparing libraries of compounds made up by amino acids linked to cholic acid scaffold. The libraries will be screened for LA binding using affinity chromatography. The affinity chromatography stationary phase will be made up of LA immobilized through hydrophobic interactions of C18- silica particles or polystyrene beads. The types of amino acids in effective LA binders will be determined via mass spectroscopy. New LA-binding agents will be tested for the ability to sensitize Gram- negative bacteria to hydrophobic antibiotics and/or inhibit the effects of LA on human monocytes (specifically interleukin 1b production). Association of PMB and the new LA-binders with LA and LA derivatives will be compared using microtitration calorimetry.