Gd-based upconversion nanocarriers with yolk–shell structure for dual-modal imaging and enhanced chemotherapy to overcome multidrug resistance in breast cancer

Multidrug resistance (MDR) of cancers is still a major challenge, and it is very important to develop visualized nanoprobes for the diagnosis and treatment of drug resistant cancers. In this work, we developed a multifunctional delivery system based on DOX-encapsulated NaYF4:Yb/Er@NaGdF4 yolk–shell nanostructures for simultaneous dual-modal imaging and enhanced chemotherapy in drug resistant breast cancer. Using the large pore volume of the nanostructure, the delivery system had a high loading efficiency and excellent stability. Also, an in vitro and in vivo toxicity study showed the good biocompatibility of the as-prepared yolk–shell nanomaterials. Moreover, by nanocarrier delivery, the uptake of DOX could be greatly increased in drug resistant MCF-7/ADR cells. Compared with free DOX, the as-prepared delivery system enhanced the chemotherapy efficacy against MCF-7/ADR cells, indicating the excellent capability for overcoming MDR. Furthermore, core–shell NaYF4:Yb/Er@NaGdF4 improved the upconversion luminescence (UCL) performance, and the designed delivery system could also be applied for simultaneous UCL and magnetic resonance (MR) imaging, which could be a good candidate as a dual-modal imaging nanoprobe. Therefore, we developed a multifunctional yolk–shell delivery system, which could have potential applications as a visualized theranostic nanoprobe to overcome MDR in breast cancer.