Isaac O. Donkor, Ph. D.
- B. Pharm. (Hons.), University of Science and Technology (Ghana), 1978
- M.S.(Medicinal Chemistry), Duquesne University, 1984.
- Ph.D. (Medicinal Chemistry), Duquesne University, 1988.
- Postdoctoral Training, The University of North Carolina, Chapel Hill, 1988-1989.
RESEARCH IN THE DONKOR'S LAB
Proteases play pivotal roles in various pathological conditions hence they serve as attractive targets for drug discovery. We are interested in the biochemical roles and molecular architecture of proteases as the first step to developing specific inhibitors for this important class of enzymes. Our current goal is to discover calpain isoform-specific inhibitors as biochemical tools for studying calpain function and as potential therapeutic agents. Calpains are intracellular cysteine proteases regulated by the second messenger, Ca2+. Several calpain isoforms have been reported of which m-calpain and m-calpain are the most ubiquitous in mammalian cells. Calpains have been proposed to be important modulators of a number of physiologic and pathologic events in cells. For example, calpains are believed to play a role in signal transduction, apoptosis, cell cycle regulation and cytoskeletal reorganization. Overactivation of calpains may have pathologic consequences via inappropriate proteolysis of target proteins such as occurs in cardiac ischemia (heart attack), cerebral ischemia (stroke), brain trauma, spinal cord injury, Alzheimer’s disease, muscular dystrophy, platelet aggregation, and cataract. Calpain inhibitors are therefore of interest as therapeutic agents. We have adopted two approaches in our effort to discover novel potent and selective calpain inhibitors as biochemical tools and as potential therapeutic agents. Our first approach involves probing the subsites of calpain to determine the structural requirements for selective inhibitor binding to the different calpain isoforms. Our second approach aims at discovering novel allosteric site(s) on calpain that will allow the development of nonpeptide allosteric inhibitors of the enzyme.
Anti-infective Agents Research
The laboratory is involved in the design, synthesis, and evaluation of anti-infective agents for the treatment of AIDs associated opportunistic infections as well as agents that target parasitic pathogens such as Trypanosoma brucei, Trypanosoma rhodesiense, Leishmania donovani, and Plasmodium falciparum.
Nucleic Acid Research
A fundamental element of gene regulation is the sequence specific DNA affinity binding of cellular molecules. Affinity binding also plays a pivotal role in the biological activity of a variety of chemotherapeutic agents including anticancer, antibacterial, and antiprotozoal agents. DNA sequence specific binding is influenced by van der Waals contacts, hydrophobic interactions, H-bonding, and electrostatic interactions. The binding can involve ligand-DNA interactions in the major and/or minor grooves of DNA, or via intercalation where the ligand is sandwiched into the DNA base pair stack. Our goal is to better understand the structural basis of DNA affinity binding and to exploit this knowledge to design molecules that can recognize specific DNA sequences for the purposes of gene regulation and/or antineoplastic, antibacterial or antiprotozoal action.
Techniques Employed in the Laboratory
- Inhibitor design: Classical and contemporary approaches to drug design including computer-aided inhibitor design methodologies are employed.
- Organic synthesis: Classical and combinatorial chemistry approaches are employed to synthesize novel peptides, peptidomimetics and heterocyclic compounds.
- Chromatographic techniques: Flash chromatography and/or HPLC are employed in the resolution of stereoisomers; purification of reaction intermediates and final products; and determination of purity and/or enantiomeric excess of reaction products.
- Spectroscopic techniques: NMR (300 MHz and 500 MHz); UV/VIS; FT-IR; and LC-MS are employed in the characterization of reaction intermediates and final products.
- Polarimetry: A DigiPol 781 automatic polarimeter is available for the determination of specific rotations of optically active compounds.
- Determination of melting temperatures: The melting temperature of DNA ligand complexes are evaluated using UV-VIS spectrophotometry.
- Enzymology: Kinetic experiments are routinely performed to determine IC50 values; Ki values; second order rate constants; and to investigate the type of inhibition.
- Cell culture studies: Cell cultures are used to study the biology of the compounds synthesized in the laboratory.