Enzymatic Analysis of Novel Giardia intestinalis MTA Nucleosidase Inhibitors

Giardia intestinalis is a parasitic protozoan that is one of the most common causes of intestinal illness, with hundreds of millions of cases every year. Increasingly, drug resistant strains of Giardia intestinalis have been discovered. Thus there is an urgent need to develop novel antiparasitic therapies. A potential target is the parasite specific enzyme 5’ methylthioadenosine nucleosidase (MTN). MTN plays a central role in the methionine/purine salvage pathways, which G. intestinalis requires to survive. An initial in silico computational study identified 33 small molecule inhibitors (SMIs) from the NCI diversity set II chemical library that potentially bound tightly to the E. coli MTN enzyme. Homology models of E. coli MTN to the MTNs of Entamoeba histolytica and Giardia intestinalis suggested these inhibitors would also work against the parasite enzymes. For this project, we used a UV spectrophotometric assay to screen the 33 compounds for inhibitory effects against Giardia MTN (798) and have identified novel structural motifs for the best inhibitors, which showed low micromolar Ki values. In addition, we developed a new high throughput screening (HTS) assay to examine multiple drugs and drug concentrations at one time with the goal of improving our rate of drug discovery for treating these parasitic infections.