I am a graduate student interested in drug discovery and the use of small molecules as biochemical tools to investigate biological systems. My current interest is in proteases involved in growth and metabolism of the Apicomplexan parasite Plasmodium.

Education & Certifications

  • Bachelor of Science, University of Wisconsin Madison, Biochemistry and Biology (2008)

Research & Scholarship

Lab Affiliations


Journal Articles

  • Identification of Potent and Selective Non-covalent Inhibitors of the Plasmodium falciparum Proteasome JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Li, H., Tsu, C., Blackburn, C., Li, G., Hales, P., Dick, L., Bogyo, M. 2014; 136 (39): 13562-13565

    View details for DOI 10.1021/ja507692y

    View details for Web of Science ID 000342608800024

  • Assessing subunit dependency of the Plasmodium proteasome using small molecule inhibitors and active site probes. ACS chemical biology Li, H., van der Linden, W. A., Verdoes, M., Florea, B. I., McAllister, F. E., Govindaswamy, K., Elias, J. E., Bhanot, P., Overkleeft, H. S., Bogyo, M. 2014; 9 (8): 1869-1876


    The ubiquitin-proteasome system (UPS) is a potential pathway for therapeutic intervention for pathogens such as Plasmodium, the causative agent of malaria. However, due to the essential nature of this proteolytic pathway, proteasome inhibitors must avoid inhibition of the host enzyme complex to prevent toxic side effects. The Plasmodium proteasome is poorly characterized, making rational design of inhibitors that induce selective parasite killing difficult. In this study, we developed a chemical probe that labels all catalytic sites of the Plasmodium proteasome. Using this probe, we identified several subunit selective small molecule inhibitors of the parasite enzyme complex. Treatment with an inhibitor that is specific for the β5 subunit during blood stage schizogony led to a dramatic decrease in parasite replication while short-term inhibition of the β2 subunit did not affect viability. Interestingly, coinhibition of both the β2 and β5 catalytic subunits resulted in enhanced parasite killing at all stages of the blood stage life cycle and reduced parasite levels in vivo to barely detectable levels. Parasite killing was achieved with overall low host toxicity, something that has not been possible with existing proteasome inhibitors. Our results highlight differences in the subunit dependency of the parasite and human proteasome, thus providing a strategy for development of potent antimalarial drugs with overall low host toxicity.

    View details for DOI 10.1021/cb5001263

    View details for PubMedID 24918547

  • Ferrous iron-dependent drug delivery enables controlled and selective release of therapeutic agents in vivo PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Deu, E., Chen, I. T., Lauterwasser, E. M., Valderramos, J., Li, H., Edgington, L. E., Renslo, A. R., Bogyo, M. 2013; 110 (45): 18244-18249


    The precise targeting of cytotoxic agents to specific cell types or cellular compartments is of significant interest in medicine, with particular relevance for infectious diseases and cancer. Here, we describe a method to exploit aberrant levels of mobile ferrous iron (Fe(II)) for selective drug delivery in vivo. This approach makes use of a 1,2,4-trioxolane moiety, which serves as an Fe(II)-sensitive "trigger," making drug release contingent on Fe(II)-promoted trioxolane fragmentation. We demonstrate in vivo validation of this approach with the Plasmodium berghei model of murine malaria. Malaria parasites produce high concentrations of mobile ferrous iron as a consequence of their catabolism of host hemoglobin in the infected erythrocyte. Using activity-based probes, we successfully demonstrate the Fe(II)-dependent and parasite-selective delivery of a potent dipeptidyl aminopeptidase inhibitor. We find that delivery of the compound in its Fe(II)-targeted form leads to more sustained target inhibition with greatly reduced off-target inhibition of mammalian cathepsins. This selective drug delivery translates into improved efficacy and tolerability. These findings demonstrate the utility of a purely chemical means to achieve selective drug targeting in vivo. This approach may find useful application in parasitic infections and more broadly in any disease state characterized by aberrant production of reactive ferrous iron.

    View details for DOI 10.1073/pnas.1312782110

    View details for Web of Science ID 000326550800056

    View details for PubMedID 24145449

  • Validation of the Proteasome as a Therapeutic Target in Plasmodium Using an Epoxyketone Inhibitor with Parasite-Specific Toxicity CHEMISTRY & BIOLOGY Li, H., Ponder, E. L., Verdoes, M., Asbjornsdottir, K. H., Deu, E., Edgington, L. E., Lee, J. T., Kirk, C. J., Demo, S. D., Williamson, K. C., Bogyo, M. 2012; 19 (12): 1535-1545


    The Plasmodium proteasome has been suggested to be a potential antimalarial drug target; however, toxicity of inhibitors has prevented validation of this enzyme in vivo. We report a screen of a library of 670 analogs of the recent US Food and Drug Administration-approved inhibitor, carfilzomib, to identify compounds that selectively kill parasites. We identified one compound, PR3, that has significant parasite killing activity in vitro but dramatically reduced toxicity in host cells. We found that this parasite-specific toxicity is not due to selective targeting of the Plasmodium proteasome over the host proteasome, but instead is due to a lack of activity against one of the human proteasome subunits. Subsequently, we used PR3 to significantly reduce parasite load in Plasmodium berghei infected mice without host toxicity, thus validating the proteasome as a viable antimalarial drug target.

    View details for DOI 10.1016/j.chembiol.2012.09.019

    View details for Web of Science ID 000313087300007

    View details for PubMedID 23142757

  • Proteases as regulators of pathogenesis: Examples from the Apicomplexa BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS Li, H., Child, M. A., Bogyo, M. 2012; 1824 (1): 177-185


    The diverse functional roles that proteases play in basic biological processes make them essential for virtually all organisms. Not surprisingly, proteolysis is also a critical process required for many aspects of pathogenesis. In particular, obligate intracellular parasites must precisely coordinate proteolytic events during their highly regulated life cycle inside multiple host cell environments. Advances in chemical, proteomic and genetic tools that can be applied to parasite biology have led to an increased understanding of the complex events centrally regulated by proteases. In this review, we outline recent advances in our knowledge of specific proteolytic enzymes in two medically relevant apicomplexan parasites: Plasmodium falciparum and Toxoplasma gondii. Efforts over the last decade have begun to provide a map of key proteotolyic events that are essential for both parasite survival and propagation inside host cells. These advances in our molecular understanding of proteolytic events involved in parasite pathogenesis provide a foundation for the validation of new networks and enzyme targets that could be exploited for therapeutic purposes. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

    View details for DOI 10.1016/j.bbapap.2011.06.002

    View details for Web of Science ID 000298715900018

    View details for PubMedID 21683169

  • Total Synthesis and Biological Evaluation of the Fab-Inhibitory Antibiotic Platencin and Analogues Thereof EUROPEAN JOURNAL OF ORGANIC CHEMISTRY Leung, G. Y., Li, H., Toh, Q., Ng, A. M., Sum, R. J., Bandow, J. E., Chen, D. Y. 2011: 183-196
  • Templated Chemistry for Sequence-Specific Fluorogenic Detection of Duplex DNA CHEMBIOCHEM Li, H., Franzini, R. M., Bruner, C., Kool, E. T. 2010; 11 (15): 2132-2137


    We describe the development of templated fluorogenic chemistry for detection of specific sequences of duplex DNA in solution. In this approach, two modified homopyrimidine oligodeoxynucleotide probes are designed to bind by triple-helix formation at adjacent positions on a specific purine-rich target sequence of duplex DNA. One fluorescein-labeled probe contains an ?-azidoether linker to a fluorescence quencher; the second (trigger) probe carries a triarylphosphine group that is designed to reduce the azide and cleave the linker. The data showed that at pH 5.6 these probes yielded a strong fluorescence signal within minutes on addition to a complementary homopurine duplex DNA target. The signal increased by a factor of about 60, and was completely dependent on the presence of the target DNA. Replacement of cytosine in the probes with pseudoisocytosine allowed the templated chemistry to proceed readily at pH 7. Single nucleotide mismatches in the target oligonucleotide slowed the templated reaction considerably; this demonstrated high sequence selectivity. The use of templated fluorogenic chemistry for detection of duplex DNAs has not been previously reported and could allow detection of double-stranded DNA, at least for homopurine-homopyrimidine target sites, under native and nondenaturing conditions.

    View details for DOI 10.1002/cbic.201000329

    View details for Web of Science ID 000284050000013

    View details for PubMedID 20859985

  • Directed Evolution of Ionizing Radiation Resistance in Escherichia coli JOURNAL OF BACTERIOLOGY Harris, D. R., Pollock, S. V., Wood, E. A., Goiffon, R. J., Klingele, A. J., Cabot, E. L., Schackwitz, W., Martin, J., Eggington, J., Durfee, T. J., Middle, C. M., Norton, J. E., Popelars, M. C., Li, H., Klugman, S. A., Hamilton, L. L., Bane, L. B., Pennacchio, L. A., Albert, T. J., Perna, N. T., Cox, M. M., Battista, J. R. 2009; 191 (16): 5240-5252


    We have generated extreme ionizing radiation resistance in a relatively sensitive bacterial species, Escherichia coli, by directed evolution. Four populations of Escherichia coli K-12 were derived independently from strain MG1655, with each specifically adapted to survive exposure to high doses of ionizing radiation. D(37) values for strains isolated from two of the populations approached that exhibited by Deinococcus radiodurans. Complete genomic sequencing was carried out on nine purified strains derived from these populations. Clear mutational patterns were observed that both pointed to key underlying mechanisms and guided further characterization of the strains. In these evolved populations, passive genomic protection is not in evidence. Instead, enhanced recombinational DNA repair makes a prominent but probably not exclusive contribution to genome reconstitution. Multiple genes, multiple alleles of some genes, multiple mechanisms, and multiple evolutionary pathways all play a role in the evolutionary acquisition of extreme radiation resistance. Several mutations in the recA gene and a deletion of the e14 prophage both demonstrably contribute to and partially explain the new phenotype. Mutations in additional components of the bacterial recombinational repair system and the replication restart primosome are also prominent, as are mutations in genes involved in cell division, protein turnover, and glutamate transport. At least some evolutionary pathways to extreme radiation resistance are constrained by the temporally ordered appearance of specific alleles.

    View details for DOI 10.1128/JB.00502-09

    View details for Web of Science ID 000268386600023

    View details for PubMedID 19502398

  • Defective dissociation of a "Slow" RecA mutant protein imparts an Escherichia coli growth defect JOURNAL OF BIOLOGICAL CHEMISTRY Cox, J. M., Li, H., Wood, E. A., Chitteni-Pattu, S., Inman, R. B., Cox, M. M. 2008; 283 (36): 24909-24921


    The RecA and some related proteins possess a simple motif, called (KR)X(KR), that (in RecA) consists of two lysine residues at positions 248 and 250 at the subunit-subunit interface. This study and previous work implicate this RecA motif in the following: (a) catalyzing ATP hydrolysis in trans,(b) coordinating the ATP hydrolytic cycles of adjacent subunits, (c) governing the rate of ATP hydrolysis, and (d) coupling the ATP hydrolysis to work (in this case DNA strand exchange). The conservative K250R mutation leaves RecA nucleoprotein filament formation largely intact. However, ATP hydrolysis is slowed to less than 15% of the wild-type rate. DNA strand exchange is also slowed commensurate with the rate of ATP hydrolysis. The results reinforce the idea of a tight coupling between ATP hydrolysis and DNA strand exchange. When a plasmid-borne RecA K250R protein is expressed in a cell otherwise lacking RecA protein, the growth of the cells is severely curtailed. The slow growth defect is alleviated in cells lacking RecFOR function, suggesting that the defect reflects loading of RecA at stalled replication forks. Suppressors occur as recA gene alterations, and their properties indicate that limited dissociation by RecA K250R confers the slow growth phenotype. Overall, the results suggest that recombinational DNA repair is a common occurrence in cells. RecA protein plays a sufficiently intimate role in the bacterial cell cycle that its properties can limit the growth rate of a bacterial culture.

    View details for DOI 10.1074/jbc.M803934200

    View details for Web of Science ID 000258820000054

    View details for PubMedID 18603529

Stanford Medicine Resources: