…VRUS feels their dual nuke compound has the potential to be moved forward as a DAA. They haven't even picked which guanine nuke (either PSI-938 or PSI-661) they will pair with PSI-7977.
My understanding is that PSI-938 and PSI-661 resolve to the same active metabolite but use a different prodrug. If this is the case, it probably doesn’t matter much which of these purine nukes is used as long as the metabolism of the prodrug is not affected by the other drug(s) in the cocktail.