Core–shell H-MSNs enable sequential release of Dox and siRNA for tumor treatment. a) Schematic illustration of mesopore surface modification with PEI for the subsequent loading of P-gp siRNA. b) Mechanism scheme demonstrating the therapeutic functions of H-MSNs in suppressing MDR of cancer cells and enhancing chemotherapeutic efficiency. c) Confocal laser scanning microscope images of MCF7-ADR cancer cells after co-incubation with free Dox, H-MSNs-Dox, and H-MSNs-Dox/siRNA for 2 and 24 h. d) Quantitative mean fluorescence intensity (MFI) analysis of Dox uptake in MCF7-ADR cancer cells after incubation for 2, 12, and 24 h by employing flow-cytometry measurement. e) Photographic images of tumors from MCF7-ADR cancer-bearing mice sacrificed after being treated with different agents for 14 days. f) Tumor masses of MCF7-ADR cancer-bearing mice sacrificed after being treated with different agents for 14 days. g) Tumor-volume changes over time after the administration of different agents until mice sacrificing on the 14th day. Reproduced with permission.[143] Copyright 2017, Elsevier.