pH-labile artificial natural killer cells for overcoming tumor drug resistance

Natural killer (NK) cells exert cytotoxic effects against infected or stressed cells, such as tumor cells, without the limitation of major histocompatibility complex (MHC) I. NK cells secrete perforins to form tunnels to mediate the entry of granzyme into target cells. This strategy, selected by natural evolution, provides a feasible method for the delivery of antitumor drugs against intracellular targets, and avoids drug-resistant mechanisms in tumor cells, such as the pumping out of drugs mediated by multidrug resistance. We constructed pH-labile artificial NK cells (ANKC) based on nature to mediate high levels of drugs in tumor cells to overcome tumor drug resistance. Mesoporous silicon nanoparticles (MSNs) modified with benzaldehyde were designed to function as scaffolds for ANKC. Doxorubicin (Dox), a model antitumor drug, was loaded into the pores of MSNs. Melittin, a pore-forming peptide, was utilized as the gate for mesopores with an acid-labile Schiff base linkage. pH-labile ANKC released melittin and Dox in slightly acidic tumor microenvironments. Melittin, like perforin, assembled tunnels on the plasma membrane or endosome, ensuring the intracellular transportation of Dox. Dox, similar to granzyme, induced the apoptosis of tumor cells. The combinational treatment partially eased the drug resistance mechanism, such as pumping out of drugs, by continuous intracellular drug accumulation mediated by melittin pores. The pH-labile ANKC demonstrated significant Dox enrichment in drug-resistant MCF-7/Adr cells and MCF-7/Adr-based xenograft tumors in a mouse model, which eventually contributed to efficient inhibition of the proliferation and growth of MCF-7/Adr tumors. PH-labile ANKC provided a potential strategy to treat drug-resistant tumors.