Methylerythritol Phosphate Pathway-Specific Natural Products as Antibacterials

The long-term objective of this project is to identify a new class of antibiotics targeting the methylerythritol phosphate (MEP) pathway, a novel pathway essential for the viability of all Gram-negative and many Gram- positive bacteria. Gram-negative bacteria are responsible for more than half of hospital acquired (nosocomial) infections which cost an estimated $5 billion dollars per year with >60% caused by resistant bacteria. Every bacterial pathogen (Gram-negative and Gram-positive) described by the CDC and NIAID as Category A, B or C biological agents require the MEP pathway for survival. The overuse/misuse of many antibiotics has resulted in a concurrent rise in resistance to dangerous levels. Additionally, several nations are known or suspected to have developed bacterial agents for use in a biological attack with some of these agents engineered to be antibiotic resistant. Future generations of existing antibiotics are expected to have shorter periods of utility than an entirely new class as bacteria will not have been subjected to selective pressure leading to resistance. The ability to engineer resistance to as of yet unknown antibiotics is also unlikely. The MEP pathway for isoprenoid biosynthesis represents a novel target for developing antibiotics with greater potential for increased utility over existing antibiotic classes. Isoprenoid biosynthesis is an essential process of all living organisms. Representing one of the most diverse classes of natural products, isoprenoids range in size from ten-carbon monoterpenes to natural rubber (molecular weight 1.5 million), yet they are constructed from two five-carbon precursors: isopententyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). For the biosynthesis of IPP and DMAPP, humans use the mevalonate (MVA) pathway while all Gram-negative and many Gram-positive bacteria require the unrelated MEP pathway. This natural pathway distribution and a dearth of agents specifically targeting the MEP pathway make it an ideal new target for antibacterials. Only one compound targeting the MEP pathway has undergone clinical evaluation. Therefore, any chemical entity targeting this pathway represents an entirely new class of antibiotics. <P> Echelon Biosciences will utilize a novel, proprietary whole-cell screening platform to identify natural products that specifically target the MEP pathway which could potentially lead to compounds as pre-clinical development candidates. This will be accomplished by the following aims. <P> First, in vitro biochemical assays to determine mechanism of action for the last steps in the pathway will be completed; <P> Second, a natural product library will be screened for MEP pathway inhibitors using a modification of a validated screening platform; <P> Third, characterizing the inhibition observed as a result of hits; Fourth, synthesizing fragment-based libraries of compounds around natural products identified in the screen. <P>PUBLIC HEALTH RELEVANCE: Resistance of bacteria to current therapeutics is of paramount importance in community and hospital settings as well as for biodefense. This project will identify natural products specifically blocking a novel bacterial pathway not found in humans. The pathway is not the target of any currently prescribed therapeutic, therefore these compounds and their derivatives are expected to have prolonged utility relative to subsequent generations of antibiotics presently in use.