four u.s. senators ask senate judiciary committee launch investigation deal drugmaker allergan plc agn.n strike native american tribe protect patent generic challenge accord letter see reuters democrats maggie hassan sherrod brown bob casey richard blumenthal letter judiciary committee chairman chuck grassley rank member dianne feinstein wednesday call allergan deal blatantly anti-competitive attempt shield patent review keep drug price high allergan say sept. transfer patent dry eye medication restasis upstate new york saint regis mohawk tribe agree exclusively license back company exchange ongoing payments allergan say email response reuters request comment meet last week staff senators brown hassan provide detail brief agreement would welcome opportunity provide additional brief senators well opportunity brief senators casey blumenthal answer question may allergan say email tribe company say tribe sovereign status shield patent review u.s. patent trial appeal board administrative court empower invalidate patent friday tribe assert immunity ongoing administrative proceed bring generic drugmakers lead mylan nv myl.o seek invalidate allergan patent introduce cheap versions restasis market mylan call allergan deal tribe sham transaction say tribe allow invoke immunity prevent administrative review patent lawyers note patent board recognize immunity state entities like public universities tribal immunity consider even strong shield generic drug company often seek challenge brand-name drug patent administrative proceed cheap fast federal court litigation allergan say would invoke tribe immunity federal court senators want probe allergan transfer deal tribe letter