I think it's falling because it will be deleted from the Russell 3000 index at end June 2011. The Russell indices are 'reconstituted' once a year at the end of every June. Russell published the proposed 2011 additions and deletions to their funds on 10 June - NuPathe was on the deletions list. In addition, traders can second guess the likely additions and deletions a couple of weeks in advance as Russell publish the technical rules behind their reconstitution technique.
Deletion from the Russell index is a real technical hit - index trackers have to unload it & many institutional fund mandates require stocks to be on Russell indices. I suspect the price will drift down 'til end June - probably with a nasty fall around the reconstitution date.
In my view, this would be a perfect buying opportunity for the upcoming NDA catalyst.
Very thinly traded and easily manipulated with little volume. It appears to be having stop losses cleared out for progressively lower entry points. I doubt much will change until volume pick up in July or early August. GL