Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine and an upstream regulator of inflammation and cell proliferation. Interestingly, MIF is also an enzyme that functions as a keto-enol tautomerase, though this function is believed to be vestigial in humans. Implicated in the pathogenesis of multiple infectious and autoimmune diseases, including rheumatoid arthritis and cancer, MIF has emerged as an attractive drug target, with the tautomerase active site serving as a convenient binding pocket for small molecule inhibitors. Most MIF inhibitors include a phenol ring, which forms an essential hydrogen bond with an asparagine residue at the back of the binding pocket. While phenol is not an uncommon moiety in approved dugs, it is particularly susceptible to rapid phase 11 metabolic processes and excretion from biological systems, resulting in low oral bioavailability and short half-life. Therefore, potent non-phenolic MIF inhibitors are desirable. Two series of MIF inhibitors lacking the commonly employed phenol group were pursued and are described in this thesis.
The first was a series of benzoxazolone inhibitors. Attempts at lead optimization were stymied by sensitivity of tautomerase assay results to protein source and incubation conditions, inconsistencies between molecular modeling studies and experimental activity data, and the inability to obtain a crystal structure of the protein–inhibitor complex. A binding mode could not be resolved for the scaffold, preventing a rational, structure-based approach to drug development. Nevertheless, a methodical medicinal chemistry strategy was employed to elaborate the structure-activity relationships (SAR) of the series and discover potent inhbitors. A circa 5 µM inhibitor was obtained, but when further attempts to optimize the series proved ineffective, attention was turned to a new scaffold.
The second series of MIF inhibitors pursued involved bioisosteric replacement of phenol with a pyrazole, which is capable of forming dual hydrogen bonds with the asparagine residue at the back of the binding pocket. From a 113-µM virtual screening hit, a structure-based, computer-aided lead optimization strategy was employed. X-ray crystal structures of MIF-inhibitor complexes and molecular modeling results guided effective selection and placement of substituents on the scaffold. Methodical derivitization and expansion of the scaffold to include auxiliary aryl functionality near the rim of the binding pocket and recognition of the benefit of pyrazole fluorination were essential breakthroughs in optimizing this series, resulting in inhibitors with potencies around 60-70 nm. From a metabolic perspective, bioisosteric replacement of a salt bridge-forming carboxylate group on the scaffold with a pharmacologically favorable sulfonamide was found to be well tolerated. Additionally, modification of the solvent-exposed region of the scaffold with solubilizing groups was shown to improve aqueous solubility without affecting activity. The pyrazoles are the only the second series of MIF inhibitors to be optimized from an initial screening hit to give inhibitors with nanomolar potency. With their high potencies and expected favorable metabolism, compounds in this series have the potential to be developed into true MIF-directed therapeutics.
|Advisor:||Jorgensen, William L.|
|School Location:||United States -- Connecticut|
|Source:||DAI-B 80/07(E), Dissertation Abstracts International|
|Subjects:||Chemistry, Organic chemistry|
|Keywords:||Inhibitor, MIF, Macrophage Migration Inhibitory Factor|
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