Low-intensity continuous ultrasound triggers effective bisphosphonate anticancer activity in breast cancer.

Ultrasound (US) is a non-ionizing pressure wave that can produce mechanical and thermal effects. Bisphosphonates have demonstrated clinical utility in bone metastases treatment. Preclinical studies suggest that bisphosphonates have anticancer activity. However, bisphosphonates exhibit a high affinity for bone mineral, which reduces their bioavailability for tumor cells. Ultrasound has been shown to be effective for drug delivery but in interaction with gas bubbles or encapsulated drugs. We examined the effects of a clinically relevant dose of bisphosphonate zoledronate (ZOL) in combination with US. In a bone metastasis model, mice treated with ZOL+US had osteolytic lesions that were 58% smaller than those of ZOL-treated animals as well as a reduced skeletal tumor burden. In a model of primary tumors, ZOL+US treatment reduced by 42% the tumor volume, compared with ZOL-treated animals. Using a fluorescent bisphosphonate, we demonstrated that US forced the release of bisphosphonate from the bone surface, enabling a continuous impregnation of the bone marrow. Additionally, US forced the penetration of ZOL within tumors, as demonstrated by the intratumoral accumulation of unprenylated Rap1A, a surrogate marker of ZOL antitumor activity. Our findings made US a promising modality to trigger bisphosphonate anticancer activity in bone metastases and in primary tumors.

Low-Intensity Ultrasound Promotes Clathrin-Dependent Endocytosis for Drug Penetration into Tumor Cells.

Ultrasound-mediated drug delivery is a field of research with promising results, although the exact mechanisms underlying intracellular delivery of therapeutic compounds remain to be elucidated. Many studies use drug carriers and cavitation to enhance drug uptake into tumor cells. However, cavitation could induce cell lysis and remain difficult to control and predict in vivo. In this study, low-intensity ultrasound was delivered using two transducers working at 2.9 and 1.3 MHz. The maximal peak negative pressure was 0.29 MPa to avoid cavitation. Low-intensity ultrasound induced clathrin-mediated endocytosis and forced the penetration of a bisphosphonate (zoledronic acid) into MCF-7 human breast cancer cells potentially as a result of mechanical stresses. When sonication parameters were adjusted to create mild hyperthermia in addition to the mechanical stress, further significant accumulation of ZOL was observed. These results provide better insight into the role of acoustic parameters in drug uptake.