Dihydrofolate reductase (DHFR) has been a validated drug target for anticancer, antiprotozoal and antibacterial therapeutics for at least 60 years. We use DHFR as a target for several pathogenic organisms. Using structures of the pathogenic and human enzyme, we design compounds that are potent and selective. We have developed a novel design for DHFR inhibitors that allows us to make hundreds of variants of these compounds that are biologically effective. All synthetic chemistry work is conducted in collaboration with Dr. Dennis Wright at UConn.

Compounds are tested in vitro using enzyme assays and in culture. The cell culture inhibition studies are in collaboration with Dr. Nigel Priestley at the University of Montana.

Targeting infectious disease

Iterative cycles of structure-based drug design for these pathogenic species of DHFR have led to compounds that are potent and selective and that inhibit the growth of the organism in culture.

Fungal disease: Candida glabrata and Candida albicans

We have designed new inhibitors for Candida glabrata DHFR and are solving the crystal structure of the enzyme bound to one of these inhibitors. The inhibitors have picomolar enzyme inhibition and potently inhibit the growth of the fungus in culture.

Work is underway to develop dual Candida albicans/Candida glabrata inhibitors. To do this, we will use modeling, crystal structures and synthesis.

Bacterial disease: Bacillus anthracis

We have designed a number of new DHFR inhibitors and found that several inhibit DHFR from B. anthracis and promote bacterial cell death while maintaining low mammalian cell toxicity. A crystal structure of the most potent of these compounds iwth the enzyme has been determined to 2.25 Angstroms, allowing us to elucidate key interactions. Work is underway to increase the potency and selectivity of these compounds. We are also working to determine a solution structure by NMR of a complex of the protein with one of these ligands bound. The NMR work is a collaboration with Dr. Olga Vinogradova at UConn.

Bacterial disease: Staphylococcus aureus

In order to develop new therapeutics that will be effective against trimethoprim-resistant methicillin-resistant S. aureus (MRSA), we are designing new DHFR inhibitors based on the propargyl-linked scaffold. Crystal structures of the wild-type S. aureus and resistant S. aureus have been determined and will be used to develop potent and selective inhibitors.

Protozoal disease: Cryptosporidium hominis

Cryptosporidia are water-borne parasites that cause gastrointestinal disease. Using the crystal structure of the bifunctional DHFR-TS (dihydrofolate reductase-thymidylate synthase) determined in our lab in 2003, we originated the DHFR ligand design project.

Structure-based drug design

New methods in docking and scoring

Accurate ranking during in silico lead optimization is critical to drive the generation of new ligands with higher affinity, yet it is especially difficult because of the subtle changes between analogs. We have found that ensembles of receptor structures represent protein flexibility and that docking to ensembles improves ligand ranking.