Only constraint I'm aware is the right to refusal should another pharma come along. This was discussed briefly by dr Seymour some time ago. Might have been last spring. Anyway, I think that might be enough to keep other pharmas from bothering with approaching.
Still, nearly every mother big pharma has a current policy of no interest before the ind is filed. Before 2008, the we a bunch of deals negotiated for promising tech in late animal trials similar to where nnvc is right now, but that all changed with the economic crisis.
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