To my knowledge, no inhibitor has been reported to directly inhibit DICER1 enzymatic domain. However, Xanthone derivatives were shown to block secondary structures of pre-miRNA from DICER1's digestion (http://www.sciencedirect.com/science/article/pii/S0960894X12014102). Complete depletion of DICER1 is lethal to many cell types, but some cells can tolerate. If you could provide more details about your studies, people may give you better suggestion.