Study of Histotripsy With Subsequent Heating on In Vitro VX2 Cancer Cells

OBJECTIVE: Focused ultrasound has emerged as a precise and minimally invasive modality for effective cancer treatment. In this study, we propose a novel method that integrates the mechanical effects of focused ultrasound, known as histotripsy, with heating to enhance both the immediate and sustained cytotoxic effects on cancer cells. METHODS: Our investigation focused on VX2 cancer cells in suspension, examining five experimental groups: blank control, negative control, heating alone, histotripsy alone, and histotripsy with subsequent heating. B-mode ultrasound imaging was utilized to visualize cavitation bubble cloud formation and its motion during histotripsy. The suspension was contained in individually sealed compartments obtained from bubble wrap (referred to as bubble wrap compartments) embedded within the agarose phantom. Residual living cells were examined immediately after treatment and cultured for 96 hours to analyze the growth patterns. Additionally, CFDA SE staining was employed to assess cell proliferation. Furthermore, both intracellular and extracellular heat shock protein 70 (HSP70) levels were measured to investigate the potential initiation of an immune response. RESULTS: The combination of histotripsy and subsequent heating significantly reduced the normalized concentration of living cells immediately after treatment. It also decreased the proliferation rate of residual cells compared with the other experimental groups. Histotripsy with subsequent heating also increased the generation and release of HSP70, which might potentially enhance an innate anti-tumor immune response in vivo. CONCLUSION: Histotripsy and subsequent heating improved the immediate lethal impact on VX2 cancer cells and curtailed the proliferation of residual cancer cells in suspension. This study presents a promising strategy for cancer therapy in the future.