The acquisition of multidrug resistance (MDR) is a major hurdle for the successful chemotherapy of tumors. Herein, a novel hybrid micelle with pH and near‐infrared (NIR) light dual‐responsive property is reported for reversing doxorubicin (DOX) resistance in breast cancer. The hybrid micelles are designed to integrate the pH‐ and NIR light‐responsive property of an amphiphilic diblock polymer and the high DOX loading capacity of a polymeric prodrug into one single nanocomposite. At physiological condition (i.e., pH 7.4), the micelles form compact nanostructure with particle size around 30 nm to facilitate blood circulation and passive tumor targeting. Meanwhile, the micelles are quickly dissociated in weakly acidic environment (i.e., pH ≤ 6.2) to release DOX prodrug. When exposed to NIR laser irradiation, the hybrid micelles can trigger notable tumor penetration and cytosol release of DOX payload by inducing tunable hyperthermia effect. In combination with localized NIR laser irradiation, the hybrid micelles significantly inhibit the growth of DOX‐resistant MCF‐7/ADR breast cancer in an orthotopic tumor bearing mouse model. Taken together, this pH and NIR light‐responsive micelles with hyperthermia‐triggered tumor penetration and cytoplasm drug release can be an effective nanoplatform to combat cancer MDR.

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The combination of chemotherapy and RNA interference is a promising approach for efficient cancer therapy. However, the success of such a strategy is hampered by the lack of suitable vectors to coordinate small interfering RNA (siRNA) and chemotherapeutic drug into one single platform. We herein report a novel triple-layered pH-responsive micelleplex loading siRNA and alkylated cisplatin prodrug for NF-Kappa B targeted treatment of metastatic breast cancer. The micelles were self-assembled from poly(ethylene glycol)-block-poly(aminolated glycidyl methacrylate)-block-poly(2-(diisopropyl amino) ethyl methacrylate) (PEG-b-PAGA-b-PDPA) triblock copolymers. At pH 7.4, the cisplatin prodrug was encapsulated in the hydrophobic PDPA core and siRNA was loaded on the positively charged PAGA interlayer to form the micelleplexes. The PEG corona can prevent protein absorption during blood circulation, minimize non-specific interaction with the reticuloendothelial system, and prolong the systemic circulation of the micelleplexes. The positively charged PAGA interlayer can facilitate deep tumor penetration of the micelleplexes, which, upon cellular uptake, are dissociated in the early endosomes to release anticancer drug payload due to protonation of the PDPA core. Using a 4T1 breast cancer model, we demonstrate that this novel micelleplex co-loaded with cisplatin prodrug and siRNA-p65 is able to simultaneously inhibit tumor growth and suppress distant metastasis of the cancer cells by downregulating NF-kappa B expression. The results reported in this study suggest that siRNA and anticancer drug co-delivery using pH-responsive micelleplexes is a promising strategy for efficient treatment of metastatic cancer.