An ultrasonic microscope is a useful tool for observing living tissue without chemical fixation or histochemical processing. Two-dimensional (2D) acoustic impedance microscopy developed in our previous study for living cell observation was employed to visualize intracellular changes. We proposed a brain tumor model by cocultivating rat glial cells and C6 gliomas to quantitatively analyze the effects of two types of anticancer drugs, cytochalasin B (CyB) and temozolomide (TMZ), when they were applied. We reported that CyB treatment (25 µg/ml, T = 90 min) significantly reduced the acoustic impedance of gliomas and has little effect on glial cells. Meanwhile, TMZ treatment (2 mg/ml, T = 90 min) impacted both cells equally, in which both cells’ acoustic impedances were decreased. As CyB targets the actin filament polymerization of the cells, we have concluded that the decrease in acoustic impedance was in fact due to actin filament depolymerization and the data can be quantitatively assessed for future studies in novel drug development.

The mechanical properties of living cells are known to be associated with disease states and cell function. In this study, acoustic impedance microscopy using a sapphire lens transducer with a center frequency of 320 MHz was employed to characterize the elasticity of the C127I cell line against an anticancer drug, nimustine hydrochloride (ACNU), and an anticancer agent, betulinic acid (BA). Confocal laser scanning microscopy was also used to investigate the drug affecting actin filaments, the nucleus, and mitochondria structures. Breast cancer cells were found to have significantly lower acoustic impedance after treatment with ACNU and BA than intact cells. Confocal images showed a significant difference in the localization of actin filaments and mitochondria structures, which suggested a difference in cell elasticity. An important insight emerging from this work is that the acoustic impedance of cells may potentially serve as a useful biomarker for anticancer drug efficacy tests, as diseases such as cancer have their own particular mechanical properties.

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Scanning acoustic microscope (SAM) is a useful observational tool in cellular study as living observation which is non-invasive is feasible compared to conventional optical microscope. In previous study, the cell morphological change by acoustic impedance measurement were successfully visualized. These acoustic impedance changes correspond with cell elasticity mainly reflects the changes of the cytoskeleton. In this study, we evaluate the elastic change of murine breast cancer cell, C127I during mitosis. C127I cells were cultured to ~75% confluency before measurement, using a transducer with a central frequency of 320 MHz. Dynamic changes during mitosis were successfully mapped using SAM and confirmed by laser confocal microscopy. Cells in prometaphase, anaphase and telophase which can only be confirmed through immunostaining before were successfully visualized using SAM. This suggests that SAM is capable to distinguish cell in different mitotic phase based on the changes of acoustic impedance.