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Title:Multi-target drug discovery against Staphylococcus aureus and Trypanosoma brucei infections
Author(s):Wang, Yang
Director of Research:Oldfield, Eric
Doctoral Committee Chair(s):Oldfield, Eric
Doctoral Committee Member(s):Hergenrother, Paul J.; Gennis, Robert B.; Zimmerman, Steven C.
Department / Program:Chemistry
Discipline:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):undecaprenyl synthesis
Staphylococcus aureus
Trypanosoma brucei
Abstract:The drug resistance has become a big threat to human health, and there is currently a dearth of new antibiotics being introduced. In order to find novel potent antibiotics against Staphylococcus aureus, a series of amidine and bisamidine compounds were synthesized and investigated against Staphylococcus aureus. The most active compounds are potent inhibitors against undecaprenyl diphosphate synthase (UPPS), an essential enzyme involved in cell wall biosynthesis pathway. Besides, they bound to an AT-rich DNA dodecamer (CGCGAATTCGCG)2 and were found to increase the melting transition by up to 24 °C using differential scanning calorimetry (DSC). Good correlations (R2 = 0.89, S. aureus) were found between experimental and predicted cell growth inhibition by using DNA ΔTm and UPPS IC50 experimental results together with one computed descriptor. We also solved the structures of three bisamidines binding to DNA as well as three UPPS structures. Overall, the results are of general interest in the context of the development of resistance-resistant antibiotics that involve multi-targeting. To extend the potential utility of this class of amidine compound, we tested them against Trypanosoma brucei, the causative agent of human African trypanosomiasis. The most active compound was a biphenyldiamidine which had an EC50 of 7.7 nM against bloodstream form parasites. There was little toxicity against two human cell lines with CC50 > 100 M. There was also good in vivo activity in a mouse model of infection with 100% survival at 3 mg/kg i.p. The most potent lead blocked replication of kinetoplast DNA (k-DNA), but not nuclear DNA, in the parasite. Some compounds also inhibited the enzyme farnesyl diphosphate synthase (FPPS) and some were uncouplers of oxidative phosphorylation. We developed a computational model for T. brucei cell growth inhibition (R2 = 0.76) using DNA ∆Tm values for inhibitor binding, combined with T. brucei FPPS IC50 values. Overall, the results suggest that it may be possible to develop multi-target drug leads against T. brucei that act by inhibiting both k-DNA replication and isoprenoid biosynthesis. In the investigation of other novel inhibitors against T. brucei, we found out that the Mycobacterium tuberculosis cell growth inhibitor SQ109 showed potent activity against T. brucei. Then, I synthesized a library of 48 analogs of SQ109 in which the ethylene diamine linker was replaced by oxa-, thia- or heterocyclic species, and in some cases, the adamantyl group was replaced by a 1,2-carborane or the N-geranyl group by another hydrophobic species. Compounds were tested against Trypanosoma brucei and two human cell lines (human embryonic kidney, HEK293T, and the hepatocellular carcinoma, HepG2). Most potent activity was found with a compound with a fixed positive charge (imidazolium ring), having IC50 values as low as 12 nM (5.5 ng/mL) and a selectivity index of ~300. In the investigation of ways of action, the best compound targeted the mitochondrial membrane potential, exhibiting stronger uncoupling effect and better cell growth inhibition activity compared with SQ109 In another project, we were looking for UPPS inhibitors as anti-infective by in silico screening. 12 UPPS crystal structures were used to validate virtual screening models then 100 virtual hits (from 450,000 compounds) were assayed against UPPS from S. aureus and Escherichia coli. The most promising inhibitors (IC50 ~2 μM) had activity against MRSA, Listeria monocytogenes, Bacillus anthracis and a vancomycin-resistant Enterococcus spp. with MIC or IC50 values in the 0.25-4 μg/mL range. Moreover, one compound, a rhodanine with close structural similarity to the commercial diabetes drug Epalrestat, exhibited good activity as well as a fractional inhibitory concentration index (FICI) of 0.1 with methicillin against the community-acquired MRSA USA300 strain, indicating strong synergism. To further investigate antibacterial agents with novel motifs, I synthesized a series of benzoic acids and phenylphosphonic acids and investigated their effects on the growth of Staphylococcus aureus and Bacillus subtilis. One of the most active compounds acted synergistically with seven antibiotics known to target bacterial cell wall biosynthesis (a fractional inhibitory concentration index, FICI~0.35, on average) but had indifferent effects in combinations with six non cell-wall biosynthesis inhibitors (FICI~1.45, on average). The most active compounds were found to inhibit two enzymes in isoprenoid/bacterial cell wall biosynthesis: undecaprenyl diphosphate synthase (UPPS) and undecaprenyl diphophate phosphatase (UPPP), but not farnesyl diphosphate synthase, and there were good correlations between bacterial cell growth inhibition, UPPS inhibition and UPPP inhibition.
Issue Date:2016-04-18
Type:Thesis
URI:http://hdl.handle.net/2142/90768
Rights Information:Copy right- The Department of Chemistry at the University of Illinois at Urbana-Champaign
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05


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