pH-responsive polymer–drug conjugates: Design and progress

Polymer-drug conjugates are becoming established as a shining platform for drug delivery. Incorporation of pH-responsive linker between drug and polymer is expected to realize triggered release of bioactive agents from conjugates in specific sites, either in mildly acidic extracellular matrices of tumor tissues or, after cellular internalization, in acidic endosomes and lysosomes. As an emerging drug delivery system, such pH-responsive polymer-drug conjugates are able to selectively deliver and activate drug molecules while reducing their systemic side-effects. In this review, we present the recent advances in pH-responsive polymer-drug conjugates with different chemical structures and architectures, and attempt to clarify their mechanism of action, synthesis and characterization technology. Furthermore, several promising approaches for the future will also be suggested.