Structure Based Drug Design Targeting Bacterial Antibiotic Resistance and Alzheimer's Disease
Eric M. Lewandowski · Digital Commons - University of South Florida (University of South Florida) · 2015
Structure based drug design is a rapidly advancing discipline that examines how protein targets structurally interact with small molecules, or known inhibitors, and then uses this information to lead inhibitor optimization efforts. In the case of novel inhibitors, protein structural information is first obtained via X-ray crystallography, NMR studies, or a combination of both approaches. Then, computational molecular docking is often used to screen, in silico, millions of small molecules and calculate the potential interactions they may have with the target protein’s binding pocket, in hopes of identifying novel low affinity inhibitors. By examining the interactions these small, low affinity, inhibitors have with the binding pocket, optimization efforts can be focused on maximizing interactions with “hot spots” within the pocket, thus leading to larger, high affinity inhibitors. A similar optimization technique can also be applied to known inhibitors. By examining the interactions of a known inhibitor with the binding site, new compounds can be designed to target “hot spots” in the binding pocket using the known inhibitors core structure as a starting point. The affinity of the newly designed compounds can then be compared to the affinity of the original inhibitor, and further rounds of optimization can be carried out. While simple in design, there are many challenges associated with structure based drug design studies, and there is no guarantee novel inhibitors will be found, but ultimately, it is an extremely powerful methodology that results in a much higher hit rate than other, similar, techniques. The work herein describes the use of structure based drug design to target several different proteins involved in bacterial antibiotic resistance, and a protein that has been implicated in the development of Alzheimer’s disease. The goal of the first project was to design a new PBP inhibitor based upon an existing scaffold, and to better understand the binding mechanism and molecular interactions between penicillin binding proteins and their inhibitors. PBPs are a group of proteins that catalyze the last steps of bacterial cell wall formation, and are the targets of the β-lactam antibiotics. Two compounds were designed which conjugated a ferrocene or ruthenocene group to 6-aminopenicillinic acid, and their antibiotic properties were tested against a range of bacterial strains. To get a better understanding of how the 6-APA organometallic compounds interacted with the PBP active site, a CTX-M-14 β-lactamase model system was used for X-ray crystallographic studies. CTX-M-14 was chosen as its active site shares many key catalytic features with PBPs, and it easily, and reproducibly, yields crystals capable of diffracting to sub-atomic ( 10μM. However, three compounds were found to be exceptionally active, and could prevent Cofilin dephosphorylation at both 1 and 10 μM. One of these three compounds was tested directly against purified SSH1 and found to inhibit its activity, and reduce Aβ production. Crystallization of purified SSH1, and SSH2, was attempted in order to get complex structures with the three best compounds. SSH2 crystals were obtained which diffracted to 1.91 Å, and several initial hits were found for SSH1. Optimization of crystals for both proteins is currently ongoing. The SSH1 inhibitor, along with the two other highly active compounds, provides an excellent starting point for the development of highly potent SSH1 inhibitors.