A Simple Dual-pH Responsive Prodrug-Based Polymeric Micelles for Drug Delivery

To precisely deliver drug molecules at a targeted site and in a controllable manner, there has been great interest in designing a synergistical drug delivery system that can achieve both surface charge-conversion and controlled release of a drug in response to different stimuli. Here we outline a simple method to construct an intelligent drug carrier, which can respond to two different pH values, therefore achieving charge conversion and chemical-bond-cleavage-induced drug release in a stepwise fashion. This drug carrier comes from the self-assembly of a block copolymer-DOX conjugate synthesized through a Schiff base reaction between poly(2-(diisopropylamino)ethyl methacrylate-b-poly-(4-formylphenyl methacrylate-co-polyethylene glycol mono methyl ether methacrylate) (PDPA-b-P(FPMA-co-OEGMA)) and DOX. The surface charge of the BCP-DOX micelles reversed from negative to positive when encountering a weakly acidic environment due to the protonation of PDPA segments. In vitro cellular uptake measurement shows that the cellular uptake and internalisation of the BCP-DOX micelles can be significantly enhanced at pH similar to 6.5. Moreover, this drug carrier exhibits a pH-dependent drug release owing to the cleavage of the imine bond at pH < 5.5. With this dual-pH responsive feature, these micelles may have the ability to precisely deliver DOX to the cancer cells.