Structure-Guided Synthesis of FK506 and FK520 Analogs with Increased Selectivity Exhibit <i>In Vivo</i> Therapeutic Efficacy against Cryptococcus.


Calcineurin is an essential virulence factor that is conserved across human fungal pathogens, including Cryptococcus neoformans, Aspergillus fumigatus, and Candida albicans. Although an excellent target for antifungal drug development, the serine-threonine phosphatase activity of calcineurin is conserved in mammals, and inhibition of this activity results in immunosuppression. FK506 (tacrolimus) is a naturally produced macrocyclic compound that inhibits calcineurin by binding to the immunophilin FKBP12. Previously, our fungal calcineurin-FK506-FKBP12 structure-based approaches identified a nonconserved region of FKBP12 that can be exploited for fungus-specific targeting. These studies led to the design of an FK506 analog, APX879, modified at the C-22 position, which was less immunosuppressive yet maintained antifungal activity. We now report high-resolution protein crystal structures of fungal FKBP12 and a human truncated calcineurin-FKBP12 bound to a natural FK506 analog, FK520 (ascomycin). Based on information from these structures and the success of APX879, we synthesized and screened a novel panel of C-22-modified compounds derived from both FK506 and FK520. One compound, JH-FK-05, demonstrates broad-spectrum antifungal activity in vitro and is nonimmunosuppressive in vivo. In murine models of pulmonary and disseminated C. neoformans infection, JH-FK-05 treatment significantly reduced fungal burden and extended animal survival alone and in combination with fluconazole. Furthermore, molecular dynamic simulations performed with JH-FK-05 binding to fungal and human FKBP12 identified additional residues outside the C-22 and C-21 positions that could be modified to generate novel FK506 analogs with improved antifungal activity. IMPORTANCE Due to rising rates of antifungal drug resistance and a limited armamentarium of antifungal treatments, there is a paramount need for novel antifungal drugs to treat systemic fungal infections. Calcineurin has been established as an essential and conserved virulence factor in several fungi, making it an attractive antifungal target. However, due to the immunosuppressive action of calcineurin inhibitors, they have not been successfully utilized clinically for antifungal treatment in humans. Recent availability of crystal structures of fungal calcineurin-bound inhibitor complexes has enabled the structure-guided design of FK506 analogs and led to a breakthrough in the development of a compound with increased fungal specificity. The development of a calcineurin inhibitor with reduced immunosuppressive activity and maintained therapeutic antifungal activity would add a significant tool to the treatment options for these invasive fungal infections with exceedingly high rates of mortality.





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Publication Info

Hoy, Michael J, Eunchong Park, Hyunji Lee, Won Young Lim, D Christopher Cole, Nicholas D DeBouver, Benjamin G Bobay, Phillip G Pierce, et al. (2022). Structure-Guided Synthesis of FK506 and FK520 Analogs with Increased Selectivity Exhibit In Vivo Therapeutic Efficacy against Cryptococcus. mBio, 13(3). p. e0104922. 10.1128/mbio.01049-22 Retrieved from

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Benjamin Bobay

Assistant Professor in Radiology

I am the Assistant Director of the Duke University NMR Center and an Assistant Professor in the Duke Radiology Department. I was originally trained as a structural biochemist with an emphasis on utilizing NMR and continue to use this technique daily helping collaborators characterize protein structures and small molecules through a diverse set of NMR experiments. Through the structural characterization of various proteins, from both planta and eukaryotes, I have developed a robust protocol of utilizing computational biology for describing binding events, mutations, post-translations modifications (PTMs), and/or general behavior within in silico solution scenarios. I have utilized these techniques in collaborations ranging from plant pathologists at the Swammerdam Institute for Life Sciences department at the University of Amsterdam to biomedical engineers at North Carolina State University to professors in the Pediatrics department at Duke University. These studies have centered around the structural and functional consequences of PTMs (such as phosphorylation), mutation events, truncation of multi-domain proteins, dimer pulling experiments, to screening of large databases of ligands for potential binding events. Through this combination of NMR and computational biology I have amassed 50 peer-reviewed published articles and countless roles on scientific projects, as well as the development of several tutorials concerning the creation of ligand databases and high-throughput screening of large databases utilizing several different molecular dynamic and computational docking programs.


Maria Ciofani

Associate Professor of Integrative Immunobiology

Transcriptional Regulation of Proinflammatory Lymphocytes

IL-17-expressing CD4 T helper (Th17) cells are important members of the intestinal immune cell community that contribute to protection against bacterial and fungal infections, and maintenance of intestinal homeostasis.  Although central to immunity, dysregulted Th17 cell function has been implicated in tissue inflammation and autoimmune disease (e.g. Inflammatory bowel disease, arthritis, and multiple sclerosis).  In order to understand this balance between healthy and pathogenic responses, we are interested in defining the transcriptional regulatory mechanisms that govern (1) Th17 cell specification from naive T cell precursors and, (2) Th17 cell effector plasticity during inflammation.  Combining genome-wide interrogation of regulatory information (transcription factor occupancy, chromatin accessibility, and transcriptional output) with gene-deficiency models in mice, we can dissect the contribution of key transcriptional regulators in proinflammatory T cell function.

We currently have open positions for students, postdoctoral fellows and a research technician.


Jiyong Hong

Professor of Chemistry

Research in the Hong group focuses on using chemical tools, in particular small molecules, to understand the signaling pathways in biology. We synthesize biologically interesting natural products and screen small molecule libraries to identify modulators of biological processes. Then, we explore their modes of action in order to investigate intracellular signaling pathways and identify novel targets for drug design. In addition, we design and develop unique and efficient synthetic strategies that will allow rapid access to molecular complexity and structural diversity. Through multidisciplinary approaches, including organic synthesis, molecular biology, and cell biology, the cellular components and molecular events that embody cancer, immune response, and GPCR signaling have systematically been explored. Compounds employed in these studies could also advance the development of novel therapeutics for the treatment of human diseases.

  1. Synthesis of Natural Products and Study of Mode of Action: We synthesize biologically interesting natural products and explore the modes of action in order to investigate intracellular signaling pathways and identify novel targets for drug design. Completed target molecules include largazole (a marine natural product with HDAC inhibitory activity), brasilibactin A (a cytotoxic siderophore), manassantins A and B (natural products with anti-HIF-1 activity), and subglutinols A and B (natural products with immunosuppressive activity).
  2. Development of Novel Synthetic Methodology: We design and develop unique and efficient synthetic strategies which will allow rapid access to molecular complexity and structural diversity. A specific area of interest includes the development of novel methods for the stereoselective synthesis of substituted tetrahydrofurans and tetrahydropyrans.
  3. Screen of Small Molecule Libraries for Identification of Small Molecule Modulators of Biological Processes: With the advent of combinatorial chemistry and other synthetic technologies, it is feasible to prepare large collections of synthetic organic molecules. These libraries are useful in providing molecules that can be used to probe relevant biological pathways. We are interested in identification of modulators of biological processes, including drug abuse and neurodegenerative diseases.

Through multidisciplinary approaches, the cellular components and molecular events that embody cancer, immune response, and neurodegenerative diseases are systematically explored. Compounds employed in these studies could also advance the development of novel therapeutics for the treatment of human diseases.

Joseph Heitman

Chair, Department of Molecular Genetics and Microbiology

Joseph Heitman was an undergraduate at the University of Chicago (1980-1984), graduating from the BS-MS program with dual degrees in chemistry and biochemistry with general and special honors. He then matriculated as an MD-PhD student at Cornell and Rockefeller Universities and worked with Peter Model and Norton Zinder on how restriction enzymes recognize specific DNA sequences and how bacteria respond to and repair DNA breaks and nicks. Dr. Heitman moved as an EMBO long-term fellow to the Biocenter in Basel Switzerland where, in studies with Mike Hall and Rao Movva, pioneered the use of yeast as a model for studies of immunosuppressive drug action. Their studies elucidated the central role of FKBP12 in forming complexes with FK506 and rapamycin that inhibit cell signaling and growth, discovered Tor1 and Tor2 as the targets of rapamycin, and contributed to the appreciation that immunosuppressive drugs inhibit signal transduction cascades that are conserved from yeasts to humans.

Dr. Heitman moved to Duke University in 1992, and is a member of the Department of Molecular Genetics and Microbiology where his studies focus on microorganisms addressing fundamental biological questions and unmet medical needs.  Dr. Heitman and colleagues focus on model and pathogenic yeasts including Cryptococcus neoformans and other diverse species from the fungal kingdom. Their studies with fungi as genetic models have revealed biological and genetic principles that can be generalized as models for eukaryotic cell and organism function. These include discovering FKBP12 and Tor1/2 as the targets of the immunosuppressive anti-proliferative natural product rapamycin, elucidating central roles of the calcium activated phosphatase calcineurin governing fungal virulence and morphogenesis and antifungal drug action, deciphering how cells sense and respond to nutrients via permeases, G protein coupled receptors, and the Tor signaling cascade, and illustrating how both model and pathogenic fungi sense both the environment and the infected host. In parallel, their studies address the evolution, structure, and function of fungal mating type loci as models for gene cluster and sex chromosome evolution.  The discovery of an ancestral sex determining locus in the basal fungal lineages involving two HMG domain proteins, SexM and SexP, homologous to the mammalian Sry sex determinant provides insights into both the origins of sex specification and its plasticity throughout the radiation of the fungal and metazoan kingdoms from their last shared common ancestor.  Their discovery of unisexual mating in fungi and subsequent analysis of its impact on the evolution of eukaryotic microbial pathogens provides insights into both microbial evolution and pathogenesis and how sexual reproduction may have first evolved.  Recent studies have unveiled novel mechanisms of antimicrobial drug resistance involving epimutations that silence drug-target genes via RNAi, functions of RNAi in genomic integrity of microbial pathogens, and loss of RNAi in hypervirulent outbreak lineages.

Dr. Heitman is a recipient of the Burroughs Wellcome Scholar Award in Molecular Pathogenic Mycology (1998-2005), the 2002 ASBMB AMGEN award for significant contributions using molecular biology to our understanding of human disease, and the 2003 Squibb Award from the Infectious Diseases Society of America (IDSA) for outstanding contributions to infectious disease research, the 2018 Korsmeyer Award from the American Society for Clinical Investigation, and the 2018 Rhoda Benham Award from the Medical Mycological Society of the Americas.  He is the recipient of an NIH/NIAID MERIT award 2011-2021 in support of studies on fungal unisexual reproduction in microbial pathogen evolution, a Duke University translational research mentoring award in 2012, and a Dean’s Award for Excellence in Mentoring from the Duke Graduate School in 2018.  He has served as an instructor in residence since 1998 for the Molecular Mycology Course at the Marine Biological Laboratory at Woods Hole, MA. Dr. Heitman is an editor for the journals PLOS GeneticsGenetics (2012-2017)PLOS Pathogens (Pearls review editor), Current Genetics (2001-2014)mBio, and Fungal Genetics and Biology; a member of the editorial boards of PLOS BiologyCurrent BiologyCell Host and Microbe, and PeerJ; former editor for PLOS Pathogens (mycology section editor, 2008-2011) and Eukaryotic Cell (2002-2012); an advisory board member for the Fungal Genome Initiative at the Broad Institute, the Fungal Kingdom Genome Project at the Department of Energy Joint Genome Institute, the NIAID Genomic Sequencing Centers for Infectious Diseases, and for the Integrated Microbial Biodiversity Program at the Canadian Institute for Advanced Research (CIFAR); co-chair for the Duke Chancellor’s Science Advisory Council (2009-2010); and co-chair/chair for the FASEB summer conference on Microbial Pathogenesis: Mechanisms of Infectious Disease (2011, 2013).  He was elected a member of the American Society for Clinical Investigation (ASCI) in 2003, a fellow of the Infectious Diseases Society of America (IDSA) in 2003, a fellow of the American Academy of Microbiology in 2004, a fellow of the American Association for the Advancement of Science (AAAS) in 2004, a member of the Association of American Physicians (AAP) in 2006, and a member of the American Academy of Arts & Sciences in 2020.  Dr. Heitman was an investigator with the Howard Hughes Medical Institute from 1992 to 2005. Dr. Heitman served as the director for the Duke University Program in Genetics and Genomics (UPGG) from 2002-2009 (including writing two funded competitive renewals for the T32 NIH training grant and establishing the annual program retreat). He was the founding director for the Center for Microbial Pathogenesis (now called the Center for Host-Microbial Interactions, CHoMI) and served in this capacity January 2002-October 2014.  He is currently the director of the Tri-institutional (Duke, UNC-CH, NC State) Molecular Mycology and Pathogenesis Training Program (MMPTP) (since July 1, 2012), and Chair of the Department of Molecular Genetics and Microbiology (since September 1, 2009).

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