Comparative Study of Pulsed Versus Continuous High-Intensity Focused Ultrasound Ablation Using In Vitro and In Vivo Models

US/PA/MR multimodal imaging-guided multifunctional genetically engineered bio-targeted synergistic agent for tumor therapy

Focused ultrasound ablation surgery (FUAS) is a minimally invasive treatment option that has been utilized in various tumors. However, its clinical advancement has been hindered by issues such as low safety and efficiency, single image guidance mode, and postoperative tumor residue. To address these limitations, this study aimed to develop a novel multi-functional gas-producing engineering bacteria biological targeting cooperative system. Pulse-focused ultrasound (PFUS) could adjust the ratio of thermal effect to non-thermal effect by adjusting the duty cycle, and improve the safety and effectiveness of treatment.The genetic modification of Escherichia coli (E.coli) involved the insertion of an acoustic reporter gene to encode gas vesicles (GVs), resulting in gas-producing E.coli (GVs-E.coli) capable of targeting tumor anoxia. GVs-E.coli colonized and proliferated within the tumor while the GVs facilitated ultrasound imaging and cooperative PFUS. Additionally, multifunctional cationic polyethyleneimine (PEI)-poly (lactic-co-glycolic acid) (PLGA) nanoparticles (PEI-PLGA/EPI/PFH@Fe3O4) containing superparamagnetic iron oxide (SPIO, Fe3O4), perfluorohexane (PFH), and epirubicin (EPI) were developed. These nanoparticles offered synergistic PFUS, supplementary chemotherapy, and multimodal imaging capabilities.GVs-E.coli effectively directed the PEI-PLGA/EPI/PFH@Fe3O4 to accumulate within the tumor target area by means of electrostatic adsorption, resulting in a synergistic therapeutic impact on tumor eradication.In conclusion, GVs-E.coli-mediated multi-functional nanoparticles can synergize with PFUS and chemotherapy to effectively treat tumors, overcoming the limitations of current FUAS therapy and improving safety and efficacy. This approach presents a promising new strategy for tumor therapy.

Therapeutic Ultrasound for Enhanced Corneal Permeability to Macromolecules

OBJECTIVES

Topically applied macromolecules have the potential to provide vision-saving treatments for many of the leading causes of blindness in the United States. The aim of this study was to determine if ultrasound can be applied to increase transcorneal drug delivery of macromolecules without dangerously overheating surrounding ocular tissues.

METHODS

Dissected corneas of adult rabbits were placed in a diffusion cell between a donor compartment filled with a solution of macromolecules (40, 70 kDa, or 150 kDa) and a receiver compartment. Each cornea was exposed to the drug solution for 60 minutes, with the experimental group receiving 5 minutes of continuous ultrasound or 10 minutes of pulsed ultrasound at a 50% duty cycle (pulse repetition frequency of 500 ms on, 500 ms off) at the beginning of treatment. Unfocused circular ultrasound transducers were operated at 0.5 to 1 W/cm2 intensity and at 600 kHz frequency.

RESULTS

The greatest increase in transcorneal drug delivery seen was 1.2 times (P < .05) with the application of pulsed ultrasound at 0.5 W/cm2 and 600 kHz for 10 minutes with 40 kDa macromolecules. Histological analysis revealed structural damage mostly in the corneal epithelium, with most damage occurring at the epithelial surface.

CONCLUSIONS

This study suggests that ultrasound may be used for enhancing transcorneal delivery of macromolecules of lower molecular weights. Further research is needed on the long-term effects of ultrasound parameters used in this study on human ocular tissues.

Tumor-homing bacterium-adsorbed liposomes encapsulating perfluorohexane/doxorubicin enhance pulsed-focused ultrasound for tumor therapy

Objective: To make up for the insufficient ultrasound ablation of tumors, the energy output or synergist is increased but faces the big challenge of normal tissue damage. In this study, we report a tumor-homing bacterium, Bifidobacterium bifidum (B. bifidum), adsorbing liposomes that encapsulate perfluorohexane (PFH) and doxorubicin (DOX) to enhance the pulsed-focused ultrasound (PFUS) for tumor therapy, so as to improve the efficacy, safety and controllability of ultrasound treatment. Methods: The PFH and DOX co-loaded cationic liposomal nanoparticles (CL-PFH-DOX-NPs) were prepared for ultrasound (US) imaging, cell-killing, and B. bifidum adsorption for the reactive oxygen species (ROS) testing. The aggregation of B. bifidum and CL-PFH-DOX-NPs is called tumor-homing aggregation (B. bifidum@CL-PFH-DOX-NPs) in this study, and the synergistic effects of B. bifidum@CL-PFH-DOX-NPs were analyzed in vivo. Results: Comprehensive studies validated that CL-PFH-DOX-NPs can enhance US imaging and cell-killing and B. bifidum can promote ROS, and B. bifidum@CL-PFH-DOX-NPs achieve PFUS synergism in vivo. Importantly, active homing of B. bifidum facilitated the delivery and retention of CL-PFH-DOX-NPs in tumors, reducing dispersion in normal tissues, achieving the targeting ability of B. bifidum@CL-PFH-DOX-NPs. The best sonication time was chosen according to the distribution of CL-PFH-DOX-NPs in vivo to achieve efficient therapy. Especially, B. bifidum@CL-PFH-DOX-NPs amplified cavitation and the immune-boosting effects. Conclusion: Multifunctional B. bifidum@CL-PFH-DOX-NPs were successfully constructed with well targeting, which not only realized US imaging monitoring, strong cavitation and complementary killing during PFUS, but also achieved immunity enhancement after PFUS. The combination of PFUS, B. bifidum and CL-PFH-DOX-NPs provides a new idea for the potential application of ultrasound therapy in solid tumors.

Phase-shift Perfluoropentane Nanoemulsions Enhance Pulsed High-intensity Focused Ultrasound Ablation in an Isolated Perfused Liver System and Their Potential Value for Cancer Therapy

PURPOSE

To investigate whether phase-shift perfluoropetane (PFP) nanoemulsions can enhance pulsed high-intensity focused ultrasound (HIFU) ablation.

METHODS

PFP was encapsulated by poly(lactic-co-glycolic acid) (PLGA) to form a nanometer-sized droplet (PLGA-PFP), which was added to an isolated perfused liver system. Meanwhile, phosphate-buffered saline (PBS) was used as a control. The perfused liver was exposed to HIFU (150 W, t = 3/5/10 s) at various duty cycles (DCs). The ultrasound images, cavitation emissions, and temperature were recorded. Rabbits with subcutaneous VX2 tumors were exposed to HIFU (150 W) at various DCs with or without PLGA-PFP. After ablation, necrosis volume and energy efficiency factor were calculated. Pathologic characteristics were observed.

RESULTS

Compared to the PBS control, PLGA-PFP nanoemulsions markedly enhanced HIFU-induced necrosis volume in both perfused livers and subcutaneous VX2 tumor-bearing rabbits (P <.05). Inertial cavitation was much stronger in the pulsed-HIFU exposure at 10% than that in the continuous-wave HIFU exposure (P <.01). Peak temperature at 100% DC was significantly higher than that at 10% (P <.05). Compared to 100% DC HIFU exposure, the mean necrosis volume induced by 10 s exposure at 50% DC was significantly larger (P <.005) but lower at 10% DC in the isolated perfused livers (P <.05). In addition, the mean necrosis volume in subcutaneous VX2 tumor-bearing rabbits was significantly increased after HIFU exposure at 10% DC when compared to those at 100% DC (P <.05). Histopathologic analysis showed liquefaction necrosis in pulsed HIFU.

CONCLUSION

PLGA-PFP nanoemulsions can enhance HIFU ablation in the isolated perfused livers and promote tumor ablation in the subcutaneous xenograft rabbit model. Appropriate pulsed HIFU exposure may increase the necrosis volume and reduce total ultrasound energy required for HIFU ablation.