Targeted and ultrasound-triggered drug delivery using liposomes co-modified with cancer cell-targeting aptamers and a thermosensitive polymer

In this study, we demonstrated the feasibility of targeted and ultrasound-triggered drug delivery using liposomes co-modified with single stranded DNA aptamers that recognized platelet-derived growth factor receptors (PDGFRs) as targeting ligands for breast cancer cells and poly(NIPMAM-co-NIPAM) as the thermosensitive polymer (TSP) to sensitize these liposomes to high temperature. TSP-modified liposomes (TSP liposomes) released encapsulated calcein under 1 MHz ultrasound irradiation for 30 s at 0.5 W/cm² as well as the case under incubation for 5 min at 42 °C. Ultrasound-triggered calcein release from TSP liposomes was due to an increased local temperature, resulting from cavitation bubble collapse induced by ultrasound, and not due to an increase in the bulk medium temperature. Liposomes modified with PDGFR aptamers (APT liposomes) bound to MDA-MB-231 human breast cancer cells through PDGFR aptamers; however, they did not bind to primary human mammary epithelial cells (HMECs). The binding of APT liposomes was greatest for MDA-MB-231 cells, followed by MCF-7, WiDr, and HepG2 cancer cells. In a cell injury assay using doxorubicin (DOX)-loaded APT/TSP liposomes and ultrasound irradiation, cell viability of MDA-MB-231 at 24 h after ultrasound irradiation (1 MHz for 30 s at 0.5 W/cm²) with DOX-loaded APT/TSP liposomes was 60%, which was lower than that with ultrasound irradiation and DOX-loaded TSP liposomes or with DOX-loaded APT/TSP liposomes alone.