To: micdundee2 who wrote (32834 ) 1/19/2007 10:27:50 AM From: George Burdell Respond to of 48461 The meat from the WHO report: Candidate antiviral drugs 7.1 Dr Dennis Hruby reviewed data available on the discovery and development of ST-246, a new candidate antiviral drug. The drug is 8000 times more potent than Cidofovir, can be delivered orally and is relatively easy to synthesize. It is effective against all tested orthopoxviruses, preventing the wrapping of intracellular mature virus (IMV) by intracellular membranes and thereby the formation of extracellular virus particles. The target of the drug is F13 (according to the nomenclature used for the vaccinia Copenhagen strain), a protein essential for the production of extracellular enveloped virus. 7.2 ST-246 is highly effective when given 4–72 hours post infection with a range of orthopoxviruses in small rodents. It can be used prophylactically and therapeutically and can even be given simultaneous with vaccination, without interfering with the immune response to the vaccine. 7.3 Studies for gaining regulatory approval of the drug are now in progress. The drug has a long biological half life of approximately 18 hours which suggests that a once-a-day oral regimen might be sufficient. Current information suggests that its bioavailability is good and that there are no adverse side effects. In vitro tests show that the antiviral effects of ST-246 are reproducible across different variola virus strains. Drug resistance to ST-246 can occur with an estimated frequency of 2.5 x 10-6. ST-246 is considered superior to Cidofovir preparations, which are in a more advanced state of drug approval. 7.4 Initial studies indicate that ST-246 is inherently stable and so strategies for creating stockpiles can be developed. 7.5 Dr John Huggins then gave an overview of the current status of antiviral drug development using the current monkeypox and non-human primate variola virus disease models. ST-246 was clearly seen as the drug of choice but Cidofovir could be used as the test case for licensure issues, particularly because its safety in humans did not need to be established. Cidofovir had a proven efficacy with respect to orthopoxvirus infections and protocols had been submitted to the US FDA for consideration under the Special Protocol Assessment Provision. If successful, this will enable the drug manufacturer (Gilead Sciences) to submit a proposal for regulatory approval for this indication. This will be done in parallel with further work on ST-246. 7.6 It was noted that ST-246 was a non-toxic inhibitor of variola virus spread that can be given orally. Clinical safety will be determined in humans and efficacy studies will be performed in non-human primate models of variola virus and monkeypox virus to support an application for orphan drug status of the compound. However, oral drugs may not be well tolerated in severely ill individuals and hence alternative formulations of ST-246 may need to be developed, which can be administered via different routes. The fact that ST-246 was highly specific in inhibiting the spread of orthopoxviruses was emphasized, as was that this could result in its wider deployment as a potent antiviral compound. Overall, ST-246 looked like an excellent drug candidate that has provided solid protection against challenge by different orthopoxviruses, including variola virus, in all models examined.