Exogenous vitamin C triggered surface charge-conversion of pH/reduction responsive micelles for enhanced tumor specific activity of loaded doxorubicin.

The effective accumulation at tumor sites and endocytosis by tumor cells for anticancer agents in carriers are essential in successful cancer therapy, and both of the processes are affected by the surface charge of drug carriers. In this study, vitamin C (VC) was employed as an "exogenous switch" to trigger the surface charge conversion of DOX-loaded micelles to obtain a better antitumor effect. T micelles formed by poly(epsilon-caprolactone)-b-poly(N,N-diethylaminoethyl methacrylate)-ss-b-poly(2-methacryloy-loxyethyl phosphorylcholine) (PCL-PDEA-ss-PMPC) turned their zeta potentials from +1 mV to +18 mV under treatment of 20 mM VC, while the zeta potentials of control R micelles formed by PCL-ss-P(DEA-r-MPC) almost remained unchanged under the same condition. DOX-loaded T@DOX and R@DOX had high DLCs of 12% and 13.8%, respectively, and both showed an accelerated drug release in a reductive environment (10 mM GSH or 20 mM VC) at pH 5.0. Notably, due to the surface charge conversion and fast drug release triggered by VC, T@DOX/VC (T@DOX was pretreated by VC) showed an enhanced cytotoxicity and cellular uptake superior to T@DOX, R@DOX, and R@DOX/VC. T@DOX/VC also displayed the in vivo antitumor effect well, which was comparable to DOX center dot HCL but with less toxic side effects than DOX center dot HCL. In summary, VC as an exogenous trigger can induce a better antitumor effect of drug-loaded micelles with a suitable polymer structure by charge conversion, and T@DOX/VC has shown to be as a promising approach to achieve potent treatment of tumors.