Described are charge reversible polymers, peptides and their resulting colloidal particles, comprising polymers and peptides having primary and secondary amines that are protected as easily hydrolysable amides. The amides are charge-reversible such that at neutral pH they are negatively charged but become positively charged at pH less than 6 and thus are relatively stable at neutral pH but quickly hydrolyze at pH below 6. Incorporating a drug in a micelle or a polymer comprised of the charge-reversible polymers or peptides provides a drug carrier for delivering the drug preferentially to the solid tumor or other targeted cells.
