New approach for local cancer treatment using pulsed high-intensity focused ultrasound and phase-change nanodroplets

Novel treatment system using endoscopic ultrasound-guided high-intensity focused ultrasound: A proof-of-concept study

AIM

High-intensity focused ultrasound (HIFU) is a novel minimally invasive local treatment of solid tumors. Endoscopic ultrasound-guided HIFU (EUS-HIFU) using mechanical effects would have potential benefits, including precise detection of target lesions and enhance drug delivery. The aim of this study is to develop EUS-HIFU device and to prove our concept in porcine model using a locally injected phase change nano droplet (PCND) as the sensitizer.

METHOD

A phospholipid PCND contained volatile perfluoro-carbon liquids. The prototype HIFU apparatus comprised a small (20 × 20 mm) transducer with center frequency of 2.1 MHz, attachable to a linear EUS transducer. Under general anesthetic, a single porcine received EUS-guided injection of PCND. The HIFU transducer was placed laparotomically in the stomach, and the liver was ablated through the gastric wall.

RESULTS

PCND was injected successfully and a distinct lesion was generated at the HIFU transducer focus only in injected areas that received HIFU exposure at 4.7 kW/cm2 at a duty cycle of 5 % (mean temporal intensity, 0.245 kW/cm2) for 30 s. The generated lesions were mechanically fractionated in macroscopic view.

CONCLUSION

The concept of transluminal HIFU ablation using novel EUS-HIFU system was proved in a porcine animal model. This novel treatment system has great potential for future cancer treatment although further investigation in more animals and different organs are warranted.

Cellular and Molecular Targeted Drug Delivery in Central Nervous System Cancers: Advances in Targeting Strategies

Central nervous system (CNS) cancers are among the most common and treatment-resistant diseases. The main reason for the low treatment efficiency of the disorders is the barriers against targeted delivery of anticancer agents to the site of interest, including the blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB). BBB is a strong biological barrier separating circulating blood from brain extracellular fluid that selectively and actively prevents cytotoxic agents and majority of anticancer drugs from entering the brain. BBB and BBTB are the major impediments against targeted drug delivery into CNS tumors. Nanotechnology and its allied modalities offer interesting and effective delivery strategies to transport drugs across BBB to reach brain tissue. Integrating anticancer drugs into different nanocarriers improves the delivery performance of the resultant compounds across BBB. Surface engineering of nanovehicles using specific ligands, antibodies and proteins enhances the BBB crossing efficacy as well as selective and specific targeting to the target cancerous tissues in CNS tumors. Multifunctional nanoparticles (NPs) have brought revolutionary advances in targeted drug delivery to brain tumors. This study reviews the main anatomical, physiological and biological features of BBB and BBTB in drug delivery and the recent advances in targeting strategies in NPs-based drug delivery for CNS tumors. Moreover, we discuss advances in using specific ligands, antibodies, and surface proteins for designing and engineering of nanocarriers for targeted delivery of anticancer drugs to CNS tumors. Finally, the current clinical applications and the perspectives in the targeted delivery of therapeutic molecules and genes to CNS tumors are discussed.

Selective intracellular delivery of perfluorocarbon nanodroplets for cytotoxicity threshold reduction on ultrasound-induced vaporization

BACKGROUND

Phase-change nanodroplets (PCNDs), which are liquid perfluorocarbon nanoparticles, have garnered much attention as ultrasound-responsive nanomedicines. The vaporization phenomenon has been employed to treat tumors mechanically. However, the ultrasound pressure applied to induce vaporization must be low to avoid damage to nontarget tissues.

AIMS

Here, we report that the pressure threshold for vaporization to induce cytotoxicity can be significantly reduced by selective intracellular delivery of PCNDs into targeted tumors.

METHODS AND RESULTS

In vitro experiments revealed that selective intracellular delivery of PCNDs induced PCND aggregation specifically inside the targeted cells. This close-packed configuration decreased the pressure threshold for vaporization to induce cytotoxicity. Moreover, following ultrasound exposure, significant decrease was observed in the viability of cells that incorporated PCNDs (35%) but not in the viability of cells that did not incorporate PCNDs (88%).

CONCLUSIONS

Intracellular delivery of PCNDs reduced ultrasound pressure applied for vaporization to induce cytotoxicity. Confocal laser scanning microscopy and flow cytometry revealed that prolonged PCND-cell incubation increased PCND uptake and aggregation. This aggregation effect might have contributed to the cytotoxicity threshold reduction effect.

Ultrasound and microbubble mediated therapeutic delivery: Underlying mechanisms and future outlook

Beyond the emerging field of oncological ultrasound molecular imaging, the recent significant advancements in ultrasound and contrast agent technology have paved the way for therapeutic ultrasound mediated microbubble oscillation and has shown that this approach is capable of increasing the permeability of microvessel walls while also initiating enhanced extravasation and drug delivery into target tissues. In addition, a large number of preclinical studies have demonstrated that ultrasound alone or combined with microbubbles can efficiently increase cell membrane permeability resulting in enhanced tissue distribution and intracellular drug delivery of molecules, nanoparticles, and other therapeutic agents. The mechanism behind the enhanced permeability is the temporary creation of pores in cell membranes through a phenomenon called sonoporation by high-intensity ultrasound and microbubbles or cavitation agents. At low ultrasound intensities (0.3-3 W/cm²), sonoporation may be caused by microbubbles oscillating in a stable motion, also known as stable cavitation. In contrast, at higher ultrasound intensities (greater than 3 W/cm²), sonoporation usually occurs through inertial cavitation that accompanies explosive growth and collapse of the microbubbles. Sonoporation has been shown to be a highly effective method to improve drug uptake through microbubble potentiated enhancement of microvascular permeability. In this review, the therapeutic strategy of using ultrasound for improved drug delivery are summarized with the special focus on cancer therapy. Additionally, we discuss the progress, challenges, and future of ultrasound-mediated drug delivery towards clinical translation.

Endoscopic ultrasonography and small-bowel endoscopy: Present and future

Over the last decade, impressive technological advances have occurred in ultrasonography and small-bowel endoscopy. Nowadays, endoscopic ultrasonography is an essential diagnostic tool and a therapeutic weapon for pancreatobiliary disorders. Capsule endoscopy and device-assisted enteroscopy have quickly become the reference standard for the diagnosis of small-bowel luminal diseases, thereby leading to radical changes in diagnostic and therapeutic pathways. We herein provide an up-to-date overview of the latest advances in endoscopic ultrasonography and small-bowel endoscopy, focusing on the emerging paradigms and technological innovations that might improve clinical practice in the near future.

Observing Bubble Cavitation by Back-Propagation of Acoustic Emission Signals

Temporal- and spatial-resolved observations of microbubble cavitation generated through high-intensity ultrasound irradiation are key in improving both the efficiency and efficacy of ultrasound-assisted drug delivery systems. A method of measuring bubble cavitation applying an image-reconstruction technique of back-propagation of an acoustic cavitation emission (ACE) signal is proposed. A high-intensity focused ultrasound wave (pump wave) irradiates the bubble synchronously using ultrasound recording equipment to acquire the timing of the RF signal, which is produced when the bubble radiates a secondary wave during bubble cavitation. The ACE signal source is reconstructed through ultrasound-wave back-propagation followed by amplitude deconvolution. The proposed method was applied to microbubbles of an ultrasound contrast agent by changing the sound pressure of the pump wave. The method reliability of the temporal resolution was verified by simulating the amplitude-modulated signal of the virtual sound source. The temporal transition of the ACE signal exhibited sub-microsecond-order fluctuations in the signal intensity. From the amplitude signal image and the instantaneous frequency image reconstruction of the proposed method, two different ACE phenomena were visualized. One is the periodic pattern by the beat signals from the harmonic and ultraharmonic component of nonlinear oscillation under low-intensity ultrasound conditions. The other is the nonperiodic temporal and spatial distributions of this irradiation under high-intensity ultrasound conditions.

Nanoparticle-Mediated Acoustic Cavitation Enables High Intensity Focused Ultrasound Ablation Without Tissue Heating

While thermal ablation of various solid tumors has been demonstrated using high intensity focused ultrasound (HIFU), the therapeutic outcomes of this technique are still unsatisfactory because of common recurrence of thermally ablated cancers and treatment side effects due to the high ultrasound intensity and acoustic pressure requirements. More precise ablation of tumors can be achieved by generating cavitating bubbles in the tissue using shorter pulses with higher acoustic pressures, which induce mechanical damage rather than thermal. However, it has remained as a challenge to safely deliver the acoustic pressures required for mechanical ablation of solid tumors. Here, we report a method to achieve mechanical ablation at lower acoustic pressures by utilizing phospholipid-stabilized hydrophobic mesoporous silica nanoparticles (PL-hMSN). The PL-hMSNs act as seeds for nucleation of cavitation events and thus significantly reduce the peak negative pressures and spatial-average temporal-average HIFU intensities needed to achieve mechanical ablation. Substantial mechanical damage was observed in the red blood cell or tumor spheroid containing tissue mimicking phantoms at PL-hMSN concentrations as low as 10 μg mL^-1, after only 5 s of HIFU treatment with peak negative pressures ∼11 MPa and duty cycles ∼0.01%. Even the application of HIFU (peak negative pressure of 16.8 MPa and duty cycle of 0.017%) for 1 min in the presence of PL-hMSN (200 μg mL^-1) did not cause any detectable temperature increase in tissue-mimicking phantoms. In addition, the mechanical effects of cavitation promoted by PL-hMSNs were observed up to 0.5 mm from the center of the cavitation events. This method may thus also improve delivery of therapeutics or nanoparticles to tumor environments with limited macromolecular transport.

Efficient and controllable thermal ablation induced by short-pulsed HIFU sequence assisted with perfluorohexane nanodroplets

A HIFU sequence with extremely short pulse duration and high pulse repetition frequency can achieve thermal ablation at a low acoustic power using inertial cavitation. Because of its cavitation-dependent property, the therapeutic outcome is unreliable when the treatment zone lacks cavitation nuclei. To overcome this intrinsic limitation, we introduced perfluorocarbon nanodroplets as extra cavitation nuclei into short-pulsed HIFU-mediated thermal ablation. Two types of nanodroplets were used with perfluorohexane (PFH) as the core material coated with bovine serum albumin (BSA) or an anionic fluorosurfactant (FS) to demonstrate the feasibility of this study. The thermal ablation process was recorded by high-speed photography. The inertial cavitation activity during the ablation was revealed by sonoluminescence (SL). The high-speed photography results show that the thermal ablation volume increased by ∼643% and 596% with BSA-PFH and FS-PFH, respectively, than the short-pulsed HIFU alone at an acoustic power of 19.5 W. Using nanodroplets, much larger ablation volumes were created even at a much lower acoustic power. Meanwhile, the treatment time for ablating a desired volume significantly reduced in the presence of nanodroplets. Moreover, by adjusting the treatment time, lesion migration towards the HIFU transducer could also be avoided. The SL results show that the thermal lesion shape was significantly dependent on the inertial cavitation in this short-pulsed HIFU-mediated thermal ablation. The inertial cavitation activity became more predictable by using nanodroplets. Therefore, the introduction of PFH nanodroplets as extra cavitation nuclei made the short-pulsed HIFU thermal ablation more efficient by increasing the ablation volume and speed, and more controllable by reducing the acoustic power and preventing lesion migration.

Endoscopic Ultrasound and Related Technologies for the Diagnosis and Treatment of Pancreatic Disease - Research Gaps and Opportunities: Summary of a National Institute of Diabetes and Digestive and Kidney Diseases Workshop

A workshop was sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases to address the research gaps and opportunities in pancreatic endoscopic ultrasound (EUS). The event occurred on July 26, 2017 in 4 sessions: (1) benign pancreatic diseases, (2) high-risk pancreatic diseases, (3) diagnostic and therapeutics, and (4) new technologies. The current state of knowledge was reviewed, with identification of numerous gaps in knowledge and research needs. Common themes included the need for large multicenter consortia of various pancreatic diseases to facilitate meaningful research of these entities; to standardize EUS features of different pancreatic disorders, the technique of sampling pancreatic lesions, and the performance of various therapeutic EUS procedures; and to identify high-risk disease early at the cellular level before macroscopic disease develops. The need for specialized tools and accessories to enable the safe and effective performance of therapeutic EUS procedures also was discussed.