The strategy of pH-responsive aggregation in tumor micro-environment (TME) provides an intriguing platform for enhancing tumor retention and exerting therapeutic effects sufficiently. In this work, we have designed an intelligent dual pH-responsive self-aggregating nano gold system (Au@PAH-Pt/DMMA) for the combined chemo-radiotherapy, in which a "charge-reversal like" strategy was utilized to realize irreversible stable aggregation and pH-specific release of cisplatin prodrug in TME. Responsive aggregation increases the cellular uptake of Au@PAH-Pt/DMMA by 55%–60%, and the cellular uptake of Pt after X-ray irradiation can be further enhanced by 80%. Additionally, responsive aggregation greatly slows down the rate of efflux from tumor in vivo. This system not only promotes B16 cell apoptosis as a chemotherapeutic agent (30.4%), it also enhances the effect of chemo-radiotheray (CRT) by promoting apoptosis as a radiosensitizer (55.3%). The colony formation assay results were fitted to cell survival curve of B16 cells and the sensitization enhancement ratio (SER) was calculated to be 1.29, which shows a good radiosensitizing ability. When exposed to X-ray, this nanoplatform reached the ideal therapeutic effect, and the tumor inhibition rate of Au@PAH-Pt/DMMA reached 91.6% with low drug administration frequency and dose of X-ray. Overall, the dual pH-responsive nanoparticles Au@PAH-Pt/DMMA could effectively enhance tumor therapeutic efficiency by combined chemo-radiotherapy, which provides a potential method for clinical transformation of cancer treatment.

A major impediment in the development of chitosan nanoparticles (CTS NPs) as effective drug delivery vesicles is their rapid clearance from blood and endosome entrapment. To overcome these problems, a convenient and promising template system was developed by decorating poly(methacrylic acid) (PMAA) to the surface of 10-hydroxy camptothecin (HCPT)-loaded CTS NPs (HCPT-CTS/PMAA NPs). The results show that the presence of negatively charged PMAA significantly elongated the blood circulation time of HCPT-CTS NPs from 12 to 24 h, and reduced the blood clearance (Cl) from 30.57 to 6.72 mL/h in vivo. The calculated area under curve (AUC_0-24h) and terminal elimination half-life (t_1/2) of HCPT-CTS/PMAA NPs were 4.37-fold and 2.48-fold compared with those of HCPT-CTS NPs. Furthermore, the positively charged HCPT-CTS/PMAA NPs triggered by tumor acidic microenvironment (pH 6.5) result in a 453-fold higher cellular uptake than the negatively charged counterparts at pH 7.4. Additionally, HCPT-CTS/PMAA NPs have the ability to escape endosomal entrapment via "proton sponge effect" after incubation with HepG2 cells for 3 h at pH 6.5. Taken together, these findings open up a convenient, low-cost, but effective way to prepare HCPT-CTS/PMAA NPs as a candidate for developing vectors with enhanced long blood circulation and endosomal escape ability in future clinical experiments.