Daniel Appella, Ph.D.

Research Goal

Through our research, we hope to develop the next generation of diagnostics and therapeutics to detect and treat human diseases.

Current Research

Our research uses synthetic organic chemistry to create new molecules with unique biological activity. Each project has the potential to evolve into a new strategy for diagnosing or treating a disease. We spend most of our time synthesizing molecules, but we also use molecular modeling to design our molecules and employ biophysical and cell biology techniques to study the molecules we make. We collaborate with other NIH scientists as well as outside research organizations to study the biological effects of our molecules in vivo. Specific projects of our group are summarized below.

We have invented a new class of molecules called thyclotides. These new molecules contain chiral tetrahydrofuran (THF) rings in a peptidic backbone, and display different types of sidechains from this backbone. Thyclotides tend to have good cellular uptake properties, and we are carefully investigating this effect to improve the bioavailability of therapeutic molecules. Thyclotides with nucleobases as sidechains overlap with another class of molecules called peptide nucleic acids (PNAs). We have developed chemical strategies that can be used to functionalize and/or pre-organize PNAs while preserving the binding properties to complementary nucleic acids. Specifically, we developed methods to incorporate cyclopentane rings into the PNA backbone to enhance the nucleic acid binding properties of PNA. Using this modification, we have shown that detection of nucleic acids derived from pathogens is greatly improved. We are engaged in developing new diagnostic techniques based on this chemically-modified version of PNA and also incorporating thyclotides into these designs. PNAs on their own do not enter cells. We have shown that thyclotide versions of PNAs are able to enter cells without assistance from other cell-penetrating molecules, and we are further exploring this property of thyclotides for biological and therapeutic applications.

We are also developing new types of small molecules that interact with biological targets considered to be challenging for drug development. The goal is to develop new types of therapeutic compounds that take advantage of unique mechanisms of action. In this area, we are examining small molecules that inactivate the nucleocapsid protein (NC) of HIV. We have found that 2-mercaptobenzamides with simple sidechains inactivate NC of HIV via an acyl transfer mechanism that is catalytic within the intracellular environment. The molecules we have developed have good antiviral activity and work very well in combination with an experimental HIV vaccine. We are also developing molecules that inhibit a phosphatase enzyme called PPM1D (or Wip1), which is an enzyme that is over expressed in many different cancers. Inhibitors of Wip1 could lead to new therapies to treat cancer, however developing inhibitors of phosphatases is very difficult. We are investigating the structural aspects of Wip1 and using this information to design new chemical inhibitors for this enzyme.

Applying our Research

We hope to provide more reliable methods to detect human disease and provide therapeutic strategies for treatment.

Need for Further Study

Our research can develop diagnostics based on genetic signatures of diseases, so new nucleic acid sequences that are markers of disease would help move our diagnostic area forward. Developing new therapies requires large investments in organic chemists making new molecules and the associated infrastructure to test the molecules for biological activity and toxicity. Additional funds to support such efforts are certainly needed.

Research in Plain Language

Our lab designs and makes new molecules that may help diagnose or treat human diseases. We use organic chemistry to create new types of molecules with interesting biological activity. With other scientists, we study how these molecules function in living organisms.

We focus on a few specific classes of molecules. We mainly design and make a type of molecule called a thyclotide. This is a synthetic molecule that helps other molecules to enter cells. We hope to use thyclotides to enhance the bioavailability of therapeutic molecules. We are also exploring new types of small molecules with unique biological activities that could evolve into new treatments for HIV and cancer.