Project Summary
Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality worldwide and the fastest growing
malignancy in the United States. The use of radioembolization or external beam radiation are frequently used
for HCC treatment. However, both these techniques demonstrate a treatment response of only 25-89%
depending on the evaluation criteria used and progression free survival of roughly 13 months. Consequently,
additional strategies for HCC radiosensitization are greatly needed. Contrast-enhanced ultrasound is a well-
established technique for HCC imaging and employs ultrasound-sensitive microbubbles to better visualize tumor
vascularity. Ultrasound-triggered microbubble destruction (UTMD) and nanobubble destruction has been shown
to sensitize tumors to radiotherapy by inducing vascular endothelial cell apoptosis and increasing ceramide
production. Our group has demonstrated the feasibility, safety, and preliminary efficacy of using UTMD for
sensitizing HCC to radiotherapy in animal models and, more recently, in a randomized clinical trial. However, we
believe the magnitude of these bioeffects is limited by the size of UCAs (1-8 µm in diameter), which restricts their
extravasation into the tumor tissue and limits the shear forces generated during cavitation. One attractive
alternative to UCAs is acoustic droplets, which are composed of liquid perfluorocarbons encapsulated above
their boiling point. The smaller size of these agents (< 200 nm) and stability relative to nanobubbles permits
greater penetration into the tumor interstitium compared to ultrasound-sensitive bubbles. Acoustic droplets can
be locally vaporized and destroyed using diagnostic ultrasound equipment, thereby generating larger local forces
on the surrounding tissue than can be achieved with UTMD. Consequently, this proposal will investigate the use
of acoustic droplets to improve HCC radiosensitivity relative to UCA. Two specific droplet formulations will be
used, prioritizing either efficient clinical translation or droplet stability in vivo. In aim 1 we will characterize acoustic
droplets made via condensation of a commercially approved UCA and by benchtop fabrication of phospholipid-
coated perfluorobutane droplets, and evaluate their ability to initiate ceramide production, cellular apoptosis, and
radiosensitivity relative to micro- and nanobubbles following ultrasound-triggering in vitro. Aim 2 will evaluate the
ability of the two acoustic droplet formulations to generate ceramide production and vascular disruption relative
to micro- and nanobubbles in a subcutaneous syngeneic model of HCC as well as explore the effects on tumor
immune response. Finally, aim 3 will assess the potential improvement of the two acoustic droplet formulations
relative to ultrasound-sensitive gas bubbles to act as a radiosensitizer in an orthotopic model of human HCC. At
the conclusion of this work, we will have evaluated the mechanisms and potential therapeutic advantages of
using acoustic droplet vaporization for HCC radiosensitization. These approaches are clinically translatable and
may ultimately improve HCC patient survival by improving radiotherapy response.