ABSTRACT
Antimalarial drug resistance compels the quest for new compounds that target alternative pathways to current drugs. The Plasmodium cyclic GMP-dependent protein kinase (PKG) has essential functions in all of the major life cycle developmental stages. An imidazopyridine PKG inhibitor scaffold was previously shown to clear P. falciparum infection in a rodent model in vivo and blocked transmission to mosquitoes providing proof of concept for this target. To find new classes of PKG inhibitors to serve as alternative chemical starting points, we performed a high-throughput screen of the GSK Full Diversity Collection using recombinant P. falciparum PKG. We developed a robust enzymatic assay in a 1536-well plate format. Promising compounds were then tested for activity against P. falciparum asexual blood stage growth, selectivity and cytotoxicity. By using a scoring system we selected the 66 most promising PKG inhibitors (comprising nine clusters and seven singletons). Among these, thiazoles were the most potent scaffold with mid-nanomolar activity on P. falciparum blood stage and gamete development. Using Kinobeads profiling we identified additional P. falciparum protein kinases targeted by the thiazoles that mediate a faster speed of the kill than PKG-selective compounds. This scaffold represents a promising starting point to develop a new antimalarial.
Subject(s)
Cyclic GMP-Dependent Protein Kinases/metabolism , Plasmodium falciparum/growth & development , Protein Kinase Inhibitors/pharmacology , Thiazoles/pharmacology , Cyclic GMP-Dependent Protein Kinases/antagonists & inhibitors , Erythrocytes/drug effects , Erythrocytes/parasitology , Gene Expression Regulation, Developmental/drug effects , Hep G2 Cells , High-Throughput Screening Assays , Humans , Life Cycle Stages/drug effects , Molecular Structure , Parasitic Sensitivity Tests , Plasmodium falciparum/drug effects , Plasmodium falciparum/enzymology , Protein Kinase Inhibitors/chemistry , Protozoan Proteins/metabolism , Thiazoles/chemistryABSTRACT
One way to speed up the TB drug discovery process is to search for antitubercular activity among compound series that already possess some of the key properties needed in anti-infective drug discovery, such as whole-cell activity and oral absorption. Here, we present MGIs, a new series of Mycobacterium tuberculosis gyrase inhibitors, which stem from the long-term efforts GSK has dedicated to the discovery and development of novel bacterial topoisomerase inhibitors (NBTIs). The compounds identified were found to be devoid of fluoroquinolone (FQ) cross-resistance and seem to operate through a mechanism similar to that of the previously described NBTI GSK antibacterial drug candidate. The remarkable in vitro and in vivo antitubercular profiles showed by the hits has prompted us to further advance the MGI project to full lead optimization.
