Novel Small Molecule Therapeutics and Mechanisms of Action for the Treatment of Filovirus Diseases

Filoviruses are among the deadliest diseases known to mankind with mortality rates up to 90%. Furthermore, new filoviruses are being discovered in areas such as China where they had not previously been reported. Currently there are no FDA-approved vaccines or therapeutics to treat these diseases. The lack of therapeutics, the high mortality rates and discovery of new filoviruses highlights the need to urgently identify pan-filovirus antivirals. To that end we set out to characterize the mechanisms of action for previously identified filovirus antivirals and to identify novel inhibitors with potential for pan-filovirus application. Our efforts focused on identifying viral entry inhibitors as the entirety of filovirus entry is mediated by a single glycoprotein making it an attractive target. The results presented in this thesis provide evidence of two distinct mechanisms of action that work in tandem providing the observed anti-filovirus properties of small molecules across numerous drug classes. Drug classes including antihistamines, antimuscarinics, selective-serotonin reuptake inhibitors, selective estrogen receptor modulators, calcium-channel blockers, and topical anesthetics. One mechanism involves direct binding to the EBOV-GP in a cavity associated with the fusion-loop leading to protein destabilization in the late-endosome, which provides Ebola specific protection. The target for the second mechanism remains to be elucidated but is intracellular, dependent upon the presence of a terminal amine, and provides protection against both Ebolavirus and Marburgvirus. Furthermore, we identified the selective estrogen receptor modulator, Ridaifen-B, as a potent entry inhibitor of both Ebolavirus and Marburgvirus entry. Using the mechanistic findings of this thesis, we modified Ridaifen-B’s terminal amines to synthesize novel analogs with increased potency for both Ebolavirus and Marburgvirus. The most potent of these compounds, YF-1-147-1, inhibits both viruses in the nanomolar range making it the most potent entry inhibitor to date. Overall, we believe the work presented in this thesis provides invaluable insight into a potentially broadly-protective mechanism of action and a novel entry inhibitor significantly more effective than previously published anti-filovirus agents.