Ultrasound-mediated delivery of siESE complexed with microbubbles attenuates HER2+/- cell line proliferation and tumor growth in rodent models of breast cancer.

The highly tunable, noninvasive and spatially targeted nature of microbubble-enhanced, ultrasound-guided (MB+US) drug delivery makes it desirable for a wide variety of therapies. In breast cancer, both HER2 and HER2 type neoplasms pose significant challenges to conventional therapeutics in greater than 40% of breast cancer patients, even with the widespread application of biologics such as trastuzumab. To address this therapeutic challenge, we examined the novel combination of tumor-injected microbubble-bound siRNA complexes and monodisperse size-isolated microbubbles (4-µm diameter) to attenuate tumor growth , as well as MB+US-facilitated shRNA and siRNA knockdown of ESE-1, an effector linked to dysregulated HER2 expression in HER2 cell line propagation. We first screened six variants of siESE and shESE for efficient knockdown of ESE in breast cancer cell lines. We demonstrated efficient reduction of BT-474 (PR, ER, HER2; luminal B) and MDA-MB-468 (PR, ER, HER2; triple-negative) clonogenicity and non-adherent growth after knockdown of ESE-1. A significant reduction in proliferative potential was seen for both cell lines using MB+US to deliver shESE and siESE. We then demonstrated significant attenuation of BT-474 xenograft tumor growth in Nod/SCID female mice using direct injection of microbubble-adsorbed siESE to the tumor and subsequent sonication. Our results suggest a positive effect on drug delivery from MB+US, and highlights the feasibility of using RNAi and MB+US for breast cancer pathologies. RNAi coupled with MB+US may also be an effective theranostic approach to treat other acoustically accessible tumors, such as melanoma, thyroid, parotid and skin cancer.