Charge-reversal-functionalized PLGA nanobubbles as theranostic agents for ultrasonic-imaging-guided combination therapy.

The efficacy of cancer chemotherapy can be generally restrained by the multiple drug resistance (MDR) of tumors, which is typically attributed to the upregulation of ATP-binding cassette (ABC) transporter proteins, such as P-glycoprotein (P-gp). There is an urgent need to present innovative strategies to reverse MDR and enhance the therapeutic efficacy of chemotherapeutic agents in biomedical applications. Here, we report a novel nanosystem of charge-reversal-functionalized PLGA nanobubbles (denoted as Dox-NBs/PPP/P-gp shRNA) for the co-delivery of Dox and P-gp shRNA for the reversal of drug resistance and for ultrasonic-imaging-guided tumor therapy. 1H NMR, FT-IR, SEM, DLS, and UV-vis spectroscopy characterizations were conducted to determine the structure, morphology, and composition of the as-prepared nanobubbles. Dox-NBs/PPP/P-gp shRNA exhibited an average diameter of about 300 nm with good dispersity, biocompatibility, and pH-responsive release properties through the charge-reversal process. The in vitro experiments showed that Dox-NBs/PPP/P-gp shRNA nanobubbles could co-deliver Dox and P-gp shRNA into tumor cells and could effectively suppress P-gp expression, leading to enhanced overall therapeutic effects against MCF-7/MDR cells by restraining the drug efflux. An in vivo antitumor assay revealed an approximately 65% inhibition rate of Dox-NBs/PPP/P-gp shRNA against MCF-7/ADR tumors in tumor-bearing nude mice. Both the in vitro and in vivo toxicity results indicated the Dox-NBs/PPP/P-gp shRNA are highly biocompatible with reducing side-effects and have negligible systemic toxicity in the in vivo therapy of resistant cancers by combining with a chemotherapeutic agent and P-gp knockdown. Furthermore, the in vivo imaging data substantiated that the functionalized nanobubbles could be used as an efficient contrast agent for the ultrasonic imaging of solid tumors. This works highlights the great potential of Dox-NBs/PPP/P-gp shRNA nanobubbles for enhanced imaging-guided combination therapy for overcoming MDR.