Novel and safe therapeutics that block infection by variola, the causative agent of smallpox, are essential for a rapid response to bioterrorism. Therapeutics can prevent smallpox spread when vaccine delivery is delayed and protect individuals with conditions for whom the vaccine is contraindicated. Polymerase- Processivity complexes are ideal therapeutic targets in that they have the potential to select for both Specific (processivity) and Broad-Spectrum (polymerase) inhibitors. Processivity factors tether DMA polymerase to DMA, enabling the enzyme to synthesize long strands. We have now established that processive DMA synthesis of vaccinia virus (W) requires three proteins, an E9 DMA polymerase and the A20, D4R processivity factors. Because these three vaccinia proteins are at least 97% homologous to the corresponding proteins of variola virus, W therapeutics are predicted to target the same function in variola. We recently completed High Throughput Screen (HTS) of 52,000 compounds from small chemical libraries using our Rapid Plate Assay. We identified 21 LEAD inhibitors that effectively block vaccinia virus DNA synthesis and prevent infection with negligible cell cytotoxicity. A second HTS will add additional LEADS. Our goals are to define which protein of the triad (E9/A20/D4) is targeted by each LEAD inhibitor using an in vitro selectivity assay, employing SPR technology and analyzing therapeutic resistant viruses. Additional new analogs will be obtained by in silico Compound Mining. Medicinal Chemistry of select LEAD compounds will generate inhibitors of superior anti-viral potency and safety. Excitingly, we will also employ Rational Drug Design based on the crystal D4-A20 association to identify highly specific inhibitors of poxviruses. LEAD compounds will be tested for inhibition of variola virus at the CDC. We will evaluate the efficacy of LEAD compounds to protect mice against challenge by poxviruses. We will also continue to define Broad-Spectrum inhibitors that prevent infection of other medically important viruses. Our studies are intended to produce excellent therapeutics that can, in the future, be taken to the pharmokinetic stages of testing. Our hope is to develop a unique class of inhibitors that protect against pox and other viral diseases.

Public Health Relevance

These studies are aimed at discovering therapeutics that will prevent the spread of smallpox, if it becomes used as a bio-terror weapon. The Broad-Spectrum action of certain of these therapeutics will hopefully generate new anti-virals that can be used to prevent current infections that are of medical significance as well as block other important agents of bioterrorism.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project--Cooperative Agreements (U01)
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Special Emphasis Panel (ZAI1-MMT-M (J2))
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Challberg, Mark D
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University of Pennsylvania
Schools of Medicine
United States
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Druck Shudofsky, Abigail M; Silverman, Janice Elaine Y; Chattopadhyay, Debasish et al. (2010) Vaccinia virus D4 mutants defective in processive DNA synthesis retain binding to A20 and DNA. J Virol 84:12325-35