Numerically, the most successful strategy in antibacterial drug discovery has been the synthetic modification of natural products to produce new semisynthetic antibiotics. However, this approach has only been successfully applied to a few select scaffolds. Revisiting this approach, we have focused on examining the low molecular weight antibiotic spectinomycin, which we felt had been neglected, in spite of its safe pharmacological profile. Spectinomycin is an aminocyclitol antibiotic that specifically inhibits bacterial protein synthesis by binding to 30S ribosome at a unique site that is highly conserved across bacterial pathogens. Although, spectinomycin is potent in cell free assays its clinical use it restricted to second line treatment for Neisseria gonorrhoeae infections. Previous attempts to develop spectinomycin analogs, in the 1980s, led to the discovery of trospectinomycin, which showed improved activity against different bacterial pathogens and progressed into late stage clinical trials before being withdrawn for commercial reasons, validating the potential to modify this core to obtain more potent generations of drug. In view of the recent rise in multi-drug resistant bacteria that were not present when semi-synthetic broad spectrum spectinomycin analogs were last examined, we reinvestigated the potential for developing novel spectinomycin analogs as treatments for drug resistant organisms. In recent work we have found spectinomycin core tractable for advanced synthetic modifications producing several series of analogs that maintain the excellent ribosomal affinity of spectinomycin and access a unique binding pocket at the interface of 30S ribosome Helix 34 and a loop of ribosomal protein RpsE. These compounds have an excellent safety profile and far superior chemical stability to spectinomycin. In these efforts, we have recently discovered a novel series of aryl substituted aminospectinomycins with good antibacterial activities. The most potent of our compounds in our initial set demonstrate: good broad spectrum anti-bacterial activity including activity against NIAID priority biodefense pathogens;on target inhibition of protein synthesis;good pharmacokinetic profiles;and excellent anti-S. pneumoniae activity in vivo. We believe the aminospectinomycins represent an important rediscovery of a neglected chemotype that can be used for the treatment of drug resistant and biodefense infections. The further development of this series will be pursued in three aims to: (i) Perform further structure based design and synthesis of novel aminospectinomycins with high antibacterial potency in seven targeted subseries;(ii) Confirm the mode of action of emerging leads and study the potential for cross resistance and inactivation;(iii) Perform lead development through five stages of detailed tests that include a full antimicrobial assessment, in vitro ADME, pharmacokinetic testing, toxicologic and in vivo efficacy experiments. After each stage, the data will be used to guide the design and synthesis of future generations of compounds and to select the best compounds to move on to the next stage such that viable, well characterized drug candidates will emerge from this study suitable for preclinical development.
There is an urgent medical need to develop new antibacterial agents to treat drug resistant and biodefense pathogens. In this proposal we aim to explore and develop a novel series of semisynthetic aminomethyl spectinomycin analogs and advance this class of compounds towards preclinical testing.
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