The research in my group can be summarized as investigations of the molecular mechanisms of action, rational design, and syntheses of potential medicinal agents, particularly for neurodegenerative diseases. Numerous drugs are known to function as specific inhibitors of particular enzymes. When little is known about the enzyme's molecular mechanism of action, chemical model studies are designed to determine reasonable nonenzymatic pathways applicable to the enzyme. On the basis of the proposed mechanism of enzyme action, inhibitors are designed and synthesized. Organic synthesis is a primary tool for this work. The enzymes are isolated from either mammalian tissue or from overexpressed cells containing recombinant enzymes. Active‑site labeling studies utilize MALDI‑TOF and electrospray ionization mass spectrometry as well as radiolabeled inactivators and peptide mapping. We also are synthesizing compounds to act as receptor antagonists for important receptors related to neurodegenerative diseases.
One enzyme in which we are interested is nitric oxide synthase, the enzyme that generates the important second messenger nitric oxide. This enzyme exists in three isozymic forms, one in brain (nNOS), in macrophage (iNOS, the inducible form), and in endothelial cells (eNOS). Inhibitors of the brain isoform may be important in the treatment of a variety of neurodegenerative problems, such as Parkinson’s disease, Alzheimer’s disease, cerebral palsy, and stroke, but only if selective inhibition of this isoform can be accomplished to avoid blockage of NO production in cells where it is needed. We have synthesized several new classes of compounds that are highly selective for nNOS. In collaboration with a crystallographer at UC Irvine, we have many high resolution crystal structures (see the figure for one of our inhibitors bound to nNOS) of all of the isozymes with some of our inhibitors bound and are using these structures for the design of new classes of inhibitors. Two of these compounds have been shown to be very effective in the prevention of cerebral palsy in a rabbit model.
Another enzyme inhibition project is related to g‑aminobutyric acid (GABA) aminotransferase. Compounds that inhibit this enzyme exhibit anticonvulsant activity and are important in the treatment of addiction and epilepsy. We are synthesizing compounds that can act as inactivators of this enzyme and are studying their mechanisms of inactivation. One of our inactivators is currently in clinical trials.
The group also has receptor antagonism projects in collaboration with groups at our medical school as well as at other universities dealing with potential treatments for Parkinson’s disease, amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD). We have run high throughput screens (HTS) at the Northwestern HTS facility and have collaborated with other groups running HTS in search of lead compounds for these diseases. A collaborator at our medical school has demonstrated the involvement of a brain calcium channel in the onset of Parkinson’s disease (PD) and showed that a high blood pressure calcium channel blocker drug slows the progression of PD. This drug is in clinical trials for PD, but the patient has to have hypertension to use it. We have identified and modified a class of compounds that selectively antagonizes the brain calcium channel over the heart calcium channel (responsible for the lowering of the blood pressure), which should have little effect on blood pressure. For the ALS and HD projects we have modified the lead to make potent compounds, have studied microsomal and plasma stability of the compounds, have modified the compounds to avoid the metabolic problems, and produced compounds being studied (in collaboration) in animal models for ALS and HD.
My group does the organic synthesis, enzyme isolation, enzyme inhibition studies, structure-based design, and some pharmacokinetics studies. We collaborate with other groups for crystallography and animal studies.