This present disclosure relates to pharmaceutical compositions for treatingtumors using a polymeric micelle encapsulating an anti-tumor drug. Thepolymericmicelle comprises block copolymers comprising at least one hydrophilic block,at leastone hydrophobic block, and at least one zwitterion. The present disclosurealso relatesto methods of enhancing the solubility of such drugs, methods of increasingthe bloodcirculating time of such drugs, and methods of delivering such drugs to one ormoresolid tumors.