The present invention relates to a polyplex for use in the treatment of castration resistant prostate cancer (CRPC) comprising a double stranded RNA (dsRNA) and a polymeric conjugate, wherein said polymeric conjugate consists of a linear polyethyleneimine (LPEl), one or more polyethylene glycol (PEG) moieties, one or more linkers and one or more targeting moieties, wherein said LPEl is covalently bound to one or more PEG moieties and each of said one or more PEG moieties is conjugated via one of the one or more linkers to one of the one or more targeting moieties, wherein each of said one or more targeting moieties is capable of binding to a cancer antigen, and wherein said cancer antigen is prostate surface membrane antigen (PSMA). Further, the invention relates to a pharmaceutical composition for use in the treatment of CRPC.
