High intensity focused ultrasound-induced gene activation in sublethally injured tumor cells in vitro

Abstract

Cultured human cervical cancer (HeLa) and rat mammary carcinoma (R3230Ac) cells were transfected with vectors encoding green fluorescent protein (GFP) under the control of hsp70B promoter. Aliquots of 10-μl transfected cells (5 × 10 7 cells/ml) were placed in 0.2-ml thin-wall polymerase chain reaction tubes and exposed to 1.1-MHz high intensity focused ultrasound (HIFU) at a peak negative pressure P − =2.68 MPa. By adjusting the duty cycle of the HIFU transducer, the cell suspensions were heated to a peak temperature from 50 to 70 °C in 1-10 s. Exposure dependent cell viability and gene activation were evaluated. For a 5-s HIFU exposure, cell viability dropped from 95% at 50 °C to 13% at 70 °C. Concomitantly, gene activation in sublethally injured tumor cells increased from 4% at 50 °C to 41% at 70 °C. A similar trend was observed at 60 °C peak temperature as the exposure time increased from 1 to 5 s. Further increase of exposure duration to 10 s led to significantly reduced cell viability and lower overall gene activation in exposed cells. Altogether, maximum HIFU-induced gene activation was achieved at 60 °C in 5 s. Under these experimental conditions, HIFU-induced gene activation was found to be produced primarily by thermal rather than mechanical stresses.

Ultrasound mediated delivery of drugs and genes to solid tumors

“…Liu et al [72] used tumors cells transfected with a bioluminescent reporter gene that was controlled by an HSP70B promoter. Their in vitro experiments used HIFU exposures to create relatively high temperatures (60 °C) for short durations (5 sec), where the thermal dose was just below that for inducing coagulative necrosis.…”

Ultrasound-Directed Drug Delivery

“…High-intensity focused ultrasound (HIFU) is a new noninvasive modality of cancer therapy using the thermal effects of ultrasound to ablate tumors [1][2][3]110]. The ultrasound energy is focused in a small region inside the body, increasing the local temperature at which cell death occurs, whereas the temperature outside the focal region is low enough to prevent tissue damage [110].…”

“…At acoustic pulse lengths and pressures much higher then allowed in diagnostic imaging, ultrasound has therapeutic applications, such as tumor treatment [1][2][3], hemostasis [4], and lithotripsy [5,6]. But also at clinical diagnostic settings, ultrasound may be used in therapy.…”

Superparamagnetic iron oxide nanoparticle-labeled cells as an effective vehicle for tracking the GFP gene marker using magnetic resonance imaging

“…GFP is appealing as a marker gene because of its ease of use in different types of in vitro and in vivo studies. In vivo grafting of GFP cells has revealed the usefulness of GFP as a marker gene for macroscopic and cellular analyzes of graft performance [19,20]. For our experimental design we used SPIO-labeled GFP cells for confocal microscopy and MRI detection.…”