Non-Contact High-Frequency Ultrasound Microbeam Stimulation: A Novel Finding and Potential Causes of Cell Responses

Invasiveness research is an essential step in breast cancer metastasis. The application of high-frequency ultrasound microbeam stimulation (HFUMS) offers a manner of determining the invasion potential of human breast cancer cells by eliciting the elevation of transient cytoplasmic calcium ions (Ca²⁺). The fluorescent index (FI), which is a composite parameter reflecting calcium elevations elicited by HFUMS, was shown to be higher in invasive breast cancer cells (MDA-MB-231) compared to weakly invasive breast cancer cells (MCF-7) using the low-intensity 50-MHz HFUMS. This novel finding shows significant difference from the reported studies in which MCF-7 cells showed no response to HFUMS. In addition to the negligible response of normal human breast cells (MCF-10A), HFUMS shows the potential to be capable of differentiating the normal cells from the cancer cells. To understand the mechanism of HFUMS worked on mechanotransduction in cells, different channel blockers were used to investigate the roles of specific channels during HFUMS. It was found that GsMTx4 (30 μM), a selective blocker of mechanosensitive Piezo channels, reduces the FI values significantly in MDA-MB-231 cells, while SKF-96365 (40 μM), a general TRP channel blocker, cannot induce the significant inhibition of FI values. The results indicate that Piezo channels may play the main role in invasion and metastatic propagation of cells.