Compositions and methods for efficient delivery of therapeutic agents in vivo are provided. Typically, the compositions are in the form of polymeric particles formed from one or more therapeutic agent complexed with a polycationic polymer which is further encapsulated in one or more amphiphilic polymers, preferably diblock copolymer of a polyalkylene oxide and a polyester such as poly(D,L-lactide)-poly(ethylene glycol) (PLA-PEG). In the preferred embodiments, the chemotherapeutic agent reduces, or inhibits N-glycosylation of one or more receptor tyrosine kinases of cancer cells. Methods of using the particles to treat cancer are also provided.