Folate-conjugated nanobubbles selectively target and kill cancer cells via ultrasound-triggered intracellular explosion.

With the rapid development of cancer-targeted nanotechnology, a variety of nanoparticle-based drug delivery systems have clinically been employed in cancer therapy. However, multidrug resistance significantly impacts the therapeutic efficacy. Physical non-drug therapy has emerged as a new and promising strategy. This study aimed to determine whether novel folate-nanobubbles (F-NBs), combined with therapeutic ultrasound (US), could act as a safe and effective physical targeted cancer therapy. Using folate-conjugated N-palmitoyl chitosan (F-PLCS), we developed novel F-NBs and characterised their physicochemical properties, internalization mechanism, targeting ability, therapeutic effects, and killing mechanism. The results showed that the novel F-NBs selectively accumulated in FR-positive endothelial cells and tumour cells via FR coupled with clathrin- and caveolin-mediated endocytosis in vitro and in vivo. In addition, the F-NBs killed target cells by an intracellular explosion under US irradiation. Hoechst/PI staining demonstrated that apoptosis and necrosis accounted for a large proportion of cell death in vivo. F-NBs combined with US therapy significantly inhibited tumour growth and improved the overall survival of tumour-bearing mice. Under US irradiation, the novel F-NBs selectively killed FR-positive tumour cells in vitro and in vivo via intracellular explosion and therefore is a promising alternative for targeted cancer treatment.