Mechanisms implicated in the enhanced sensitivity of MDA-MB-231 breast cancer cells to anti-neoplastic agents post sub-lethal HIFU exposure -

Abstract

High Intensity Focused Ultrasound (HIFU) is an ex-corporeal medical device that was first introduced in the 1940s for the treatment of neurological disorders and has been subjected to several improvements since then. It is a non-invasive and non-ionizing therapeutic method that is now utilized to destroy a wide variety of tumors including breast cancer. At the focal point where the acoustic waves are intensified, cell death can result from cavitation and-or thermal ablation effects. However, the effects of sub-lethal HIFU exposure on cell function are not clearly understood. Previous work from our laboratory showed that sub-lethal HIFU exposure of MDA-MB-231 breast cancer cells in vitro results in significant alterations in transcript expression of a number of mechanosensitive genes, including Cav-1 gene which encodes for caveolin-1 protein. Moreover, there was enhanced cellular sensitivity to suboptimal cytotoxic doses of Paclitaxel and Doxil. Therefore, we hypothesized that sonoporation and-or caveolin-dependent endocytosis are among the mechanisms involved in this enhanced in vitro sensitivity of MDA-MB-231 cells post sub-lethal HIFU. For the purpose of this study, we utilized a commercial HIFU setup that operates at the fundamental resonance of 0.5MHz. To examine if sonoporation is implicated in the enhanced drug uptake post sub-lethal HIFU, we assessed the uptake of FITC-dextran by two methods: cell fixation followed by flow cytometry or laser confocal microscopic imaging and analysis. To determine if caveolin-dependent endocytosis is implicated as a mechanism of enhanced drug uptake, we pre-treated the cells with Genistein, a specific potent inhibitor of this pathway. Cellular viability was quantified using trypan blue vital stain exclusion assay. We found no significant change in FITC-dextran uptake in MDA-MB-231 cells post sub-lethal HIFU exposure at 30hr prior to the in vitro addition of agents by flow cytometry and laser confocal microscopy. Similarly, no significant change in FITC-dextran uptake was