Our research spans from mechanistic study of biological phenomena, development of novel methodologies, to applications of the mechanistic understanding and methodologies to discover novel therapeutic agents and chemical probes. It is estimated that ~80% of all disease relevant human proteins are undruggable by current drug modalities, which include small molecules (molecular weight <500) and biologics (molecular weight >5000). Prominent examples of undruggable proteins are those involved in intracellular protein-protein interactions (PPIs) and the defective/missing proteins caused by genetic mutations. The ultimate goal of our research is to find a general strategy for drugging these challenging targets. The following projects are under current investigation in our group.
  • Macrocycles as Protein-Protein Interaction Inhibitors. Protein-protein interactions (PPIs) represent an exciting but also very challenging class of drug targets, because they usually have large, flat binding sites, to which conventional small molecules do not bind with high affinity or specificity. We and others have demonstrated that macrocycles in the molecular-weight range of 500-2000 serve as effective PPI inhibitors. We have developed a powerful technology to chemically synthesize and screen large libraries of cyclic and bicyclic peptides (up to 10exp8 different compounds) against essentially any protein of interest. We are currently applying this technology to discover macrocyclic peptide inhibitors against PPIs involved in human diseases (e.g., cancer, cystic fibrosis, inflammation, and autoimmunity). We are also developing new methodologies to synthesize and screen combinatorial libraries of non-peptidic, natural product-like macrocycles. Read More…
  • Cell-Penetrating Molecules for Drug Delivery. A major obstacle in drug discovery is that drug candidates often cannot cross the cell membrane to reach an intracellular target. This is particularly problematic for peptide-, protein-, and nucleic acid-based drugs (e.g., siRNA), which are mostly entrapped inside endosomes and subsequently digested inside lysosomes. We have discovered a family of small, amphipathic cyclic peptides such as cyclo(phe-Nal-Arg-arg-Arg-arg-Gln) as powerful cell-penetrating peptides, which are capable of efficiently delivering small molecules, peptides, proteins, and nucleic acids into the cytosol of mammalian cells. We discovered that the cyclic CPPs enter cells by endocytic mechanisms and efficiently exit the early endosome by a novel vesicle budding and collapse mechanism. We have also discovered non-peptidic cell-penetrating motifs (CPMs) that specifically deliver cargo molecules into the mitochondrial matrix. Current studies in this area include discovery of additional CPPs/CPMs with improved properties (e.g., selectivity for cancer cells) and further investigation of their molecular mechanisms of action. Read More…
  • Development of Intracellular Biologics and Chemical Probes. Biologic drugs (e.g., monoclonal antibodies) have transformed the drug industry over the past several decades, but are so far limited to targeting extracellular targets. We are leveraging the cyclic CPP technology to develop intracellular biologics as the next-generation therapeutics and chemical probes. First, we are developing innovative strategies to use cyclic CPPs to deliver proteins, nucleic acids, and protein-nucleic acid complexes into the cell. Second, the ligand discovery and cyclic CPP technologies from above are being integrated to develop macrocyclic peptides as potent, specific, cell-permeable, and metabolically stable inhibitors against medicinally important but previously challenging PPI targets, such as calcineurin (inflammation and organ transplantation), CAL PDZ domain (cystic fibrosis), MDM2 (cancer), NEMO (cancer and inflammation), K-Ras (cancer), and TNFa (autoimmunity and inflammation). Read More…

Major Techniques in Research:

  • Solid-phase synthesis of peptide and non-peptidic libraries.
  • Solution-phase synthesis of library building blocks and other small molecules.
  • High-throughput library screening and peptide sequencing by mass spectrometry.
  • Molecular cloning, expression and purification of proteins.
  • Biophysical characterization of proteins (e.g., fluorescence polarization and surface plasmon resonance).
  • Enzyme kinetics and inhibition.
  • Mammalian tissue culture, transfection, co-immunoprecipitation, and western blotting.
  • Confocal microscopy, flow cytometry.

Current Sources of Research Funding:

Image result for National Institute of General Medical Sciences                      Image result for National Institute of Allergy and Infectious Diseases                                  Image result for Cystic Fibrosis Foundation