Emerging technologies in therapeutic ultrasound: thermal ablation to gene delivery

Low-intensity ultrasound inhibits melanoma cell proliferation in vitro and tumor growth in vivo

PURPOSE

To determine the effect of low-intensity ultrasound on cancer cell proliferation in vitro and tumor growth in vivo.

METHODS

In vitro, several cancer cell lines were exposed to low-intensity ultrasound at 0.11 W/cm² for 2 min. Of the cell lines screened, melanoma C32 is one of the cell lines that showed sensitivity to growth inhibition by ultrasound and was therefore used in succeeding experiments. In vivo, under the same ultrasound conditions used in vitro, C32 tumors in mice were exposed to ultrasound daily for 2 weeks, and the tumor volumes were monitored weekly using sonography.

RESULTS

In vitro, C32 cell growth was inhibited, attaining 43.2% inhibition on the 3rd day. In vivo, tumor growth was significantly inhibited, with the treated tumors exhibiting 2.7-fold slowed tumor growth vs. untreated tumors at week 2. Such inhibition was not associated with increased cell death. Several genes related to the cell cycle and proliferation were among those significantly regulated.

CONCLUSION

These findings highlight the potential of low-intensity ultrasound to inhibit tumor growth in a noninvasive, safe, and easy-to-administer way. In addition, this may suggest that the mechanical stress induced by ultrasound on C32 cells may have affected the intrinsic biomolecular mechanism related to the cell growth of this particular cell line. Further research is needed to identify which of the regulated genes played key roles in growth inhibition.

Framework for Personalized Real-Time Control of Hidden Temperature Variables in Therapeutic Knee Cooling

The paper formalizes, implements and evaluates a framework for personalized real-time control of inner knee temperature during cryotherapy after knee surgery. Studies have shown that the cryotherapy should be controlled depending on the individual patient's feedback on the cooling, which raises the need for smart personalized therapy. The framework is based on the feedback control loop that uses predicted instead of measured inner temperatures because measurements are not feasible or would introduce invasiveness into the system. It uses machine learning to construct a predictive model for estimation of the controlled inner temperature variable based on other variables whose measurement is more feasible - temperatures on the body surface. The machine learning method uses data generated from computer simulation of the therapeutic treatment for different input simulation parameters. A fuzzy proportional-derivative controller is designed to provide adequate near real-time control of the inner knee temperature by controlling the cooling temperature. The framework is evaluated for robustness and controllability. The results show that controlled cooling is essential for small-sized (and large-sized) knees that are significantly more (less) sensitive to the cooling compared to average-sized knees. Moreover, the framework recognizes dynamic physiological changes and potential changes in the system settings, such as extreme changes in the blood flow or changed target inner knee temperature, and consequently adapts the cooling temperature to reach the target value.

Sonodynamic therapy-derived multimodal synergistic cancer therapy

Sonodynamic therapy (SDT) represents a promising modality that provides the possibility of non-invasively eliminating solid tumors in a site-directed manner. In light of the complexity and heterogeneity of tumors, more and more studies are attempting to combine SDT with other therapeutic methods so as to achieve better tumor treatment effect, which sheds new light on the potential of SDT-based synergistic therapeutics. Herein, the representative studies of SDT-instructed multimodal synergistic cancer therapy are comprehensively presented, such as sono-chemotherapy, sono-radiotherapy, sono-immunotherapy, and sono-chemodynamic therapy, etc., and their incorporate mechanisms are discussed in detail. The current challenges and future prospects to promote the advanced development of SDT-based nanomedicines in this burgeoning research field are highlighted. It is believed that such an emerging synergistic therapeutic modality based on SDT will play a more significant role in the field of tumor precision treatment medicine.

Cell penetrating peptide-modified nanoparticles for tumor targeted imaging and synergistic effect of sonodynamic/HIFU therapy

Background

Theranostics based on multifunctional nanoparticles (NPs) is a promising field that combines therapeutic and diagnostic functionalities into a single nanoparticle system. However, the major challenges that lie ahead are how to achieve accurate early diagnosis and how to develop efficient and noninvasive treatment. Sonodynamic therapy (SDT) utilizing ultrasound combined with a sonosensitizer represents a novel noninvasive modality for cancer therapy. Different ultrasound frequencies have been used for SDT, nevertheless, whether the effect of SDT can enhance synergistic HIFU ablation remains to be investigated.

Materials and methods

We prepared a nanosystem for codelivery of a sonosensitizer (methylene blue, MB) and a magnetic resonance contrast agent (gadodiamide, Gd-DTPA-BMA) based on hydrophilic biodegradable polymeric NPs composed of poly (lactic-co-glycolic acid) (PLGA). To enhance accumulation and penetration of the NPs at the tumor site, the surface of PLGA NPs was decorated with a tumor-homing and penetrating peptide-F3 and polyethylene glycol (PEG). The physicochemical, imaging and therapeutic properties of F3-PLGA@MB/Gd and drug safety were thoroughly evaluated both in vitro and in vivo. F3-PLGA@MB/Gd was evaluated by both photoacoustic and resonance imaging.

Results

F3-PLGA@MB/Gd NPs exhibited higher cellular association than non-targeted NPs and showed a more preferential enrichment at the tumor site. Furthermore, with good drug safety, the apoptosis triggered by ultrasound in the F3-PLGA@MB/Gd group was greater than that in the contrast group.

Conclusion

F3-PLGA@MB/Gd can work as a highly efficient theranostic agent, and the incorporation of targeted multimodal and combined therapy could be an encouraging strategy for cancer treatment.

Review of ultrasound image guidance in external beam radiotherapy part II: intra-fraction motion management and novel applications

Imaging has become an essential tool in modern radiotherapy (RT), being used to plan dose delivery prior to treatment and verify target position before and during treatment. Ultrasound (US) imaging is cost-effective in providing excellent contrast at high resolution for depicting soft tissue targets apart from those shielded by the lungs or cranium. As a result, it is increasingly used in RT setup verification for the measurement of inter-fraction motion, the subject of Part I of this review (Fontanarosa et al 2015 Phys. Med. Biol. 60 R77-114). The combination of rapid imaging and zero ionising radiation dose makes US highly suitable for estimating intra-fraction motion. The current paper (Part II of the review) covers this topic. The basic technology for US motion estimation, and its current clinical application to the prostate, is described here, along with recent developments in robust motion-estimation algorithms, and three dimensional (3D) imaging. Together, these are likely to drive an increase in the number of future clinical studies and the range of cancer sites in which US motion management is applied. Also reviewed are selections of existing and proposed novel applications of US imaging to RT. These are driven by exciting developments in structural, functional and molecular US imaging and analytical techniques such as backscatter tissue analysis, elastography, photoacoustography, contrast-specific imaging, dynamic contrast analysis, microvascular and super-resolution imaging, and targeted microbubbles. Such techniques show promise for predicting and measuring the outcome of RT, quantifying normal tissue toxicity, improving tumour definition and defining a biological target volume that describes radiation sensitive regions of the tumour. US offers easy, low cost and efficient integration of these techniques into the RT workflow. US contrast technology also has potential to be used actively to assist RT by manipulating the tumour cell environment and by improving the delivery of radiosensitising agents. Finally, US imaging offers various ways to measure dose in 3D. If technical problems can be overcome, these hold potential for wide-dissemination of cost-effective pre-treatment dose verification and in vivo dose monitoring methods. It is concluded that US imaging could eventually contribute to all aspects of the RT workflow.

Engineered porphyrin loaded core-shell nanoparticles for selective sonodynamic anticancer treatment

AIM

Porphyrin-loaded core-shell nanoparticles have been engineered for use as in vivo sonosensitizing systems, radio-tracers or magnetic resonance (MR) imaging agents, which may be suitable for the selective treatment of solid tumors and imaging analyses.

MATERIALS & METHODS

Polymethyl methacrylate nanoparticles (PMMANPs) have been either loaded with meso-tetrakis (4-sulphonatophenyl) porphyrin (TPPS) for sonodynamic anticancer treatment, with (64)Cu-TPPS for positron emission tomography biodistribution studies or with Mn(III)-TPPS for MR tumor accumulation evaluation.

RESULTS

PMMANPs are easily functionalized with negatively charged molecules and show favorable biodistribution. In vivo TPPS-PMMANPs have demonstrated shock wave responsiveness in a Mat B III syngeneic rat breast cancer model as measured by MR analyses of pre- and post-treatment tumor volumes.

CONCLUSION

TPPS-PMMANPs are a multimodal system which can efficiently induce in vivo sonodynamic anticancer activity.

Non-invasive real-time prediction of inner knee temperatures during therapeutic cooling

The paper addresses the issue of non-invasive real-time prediction of hidden inner body temperature variables during therapeutic cooling or heating and proposes a solution that uses computer simulations and machine learning. The proposed approach is applied on a real-world problem in the domain of biomedicine - prediction of inner knee temperatures during therapeutic cooling (cryotherapy) after anterior cruciate ligament (ACL) reconstructive surgery. A validated simulation model of the cryotherapeutic treatment is used to generate a substantial amount of diverse data from different simulation scenarios. We apply machine learning methods on the simulated data to construct a predictive model that provides a prediction for the inner temperature variable based on other system variables whose measurement is more feasible, i.e. skin temperatures. First, we perform feature ranking using the RReliefF method. Next, based on the feature ranking results, we investigate the predictive performance and time/memory efficiency of several predictive modeling methods: linear regression, regression trees, model trees, and ensembles of regression and model trees. Results have shown that using only temperatures from skin sensors as input attributes gives excellent prediction for the temperature in the knee center. Moreover, satisfying predictive accuracy is also achieved using short history of temperatures from just two skin sensors (placed anterior and posterior to the knee) as input variables. The model trees perform the best with prediction error in the same range as the accuracy of the simulated data (0.1°C). Furthermore, they satisfy the requirements for small memory size and real-time response. We successfully validate the best performing model tree with real data from in vivo temperature measurement from a patient undergoing cryotherapy after ACL reconstruction.

Hypocrellin B in hepatocellular carcinoma cells: Subcellular localization and sonodynamic damage

PURPOSE

To study subcellular localization of hypocrellin B in hepatocellular carcinoma cells, and hypocrellin B-mediated sonodynamic action-induced cell damage.

MATERIALS AND METHODS

After incubation with 2.5 μM of hypocrellin B, human hepatocellular carcinoma HepG2 cells were exposed to ultrasound waves for 8 sec at an intensity of 0.46 W/cm(2). Clonogenic survival of HepG2 cells was measured using a colony forming assay and light microscope. Ultrastructural morphology was observed using transmission electron microscope (TEM) and mitochondrial membrane potential (MMP) was assessed using confocal laser scanning microcope (CLSM) after rhodamine 123 staining. Additionally, subcellular localization of hypocrellin B in HepG2 cells with organelle probe staining was also observed using CLSM.

RESULTS

The colony forming units of HepG2 cells decreased substantially after sonodynamic treatment. The results of TEM showed microvilli disappearance, apoptotic body formation, swollen mitochondria with loss of cristae and mitochondrial myelin-like features (or membrane whorls). Collapse of MMP was found in the treated cells. Hypocrellin B was distributed in mitochondria and lysosomes as well as in endoplasmic reticulum and Golgi apparatus.

CONCLUSIONS

The findings demonstrated that sonodynamic action of hypocrellin B induced mitochondrial damage, survival inhibition, and apoptosis of HepG2 cells. Additionally, other subcellular organelles such as endoplasmic reticulum, Golgi apparatus and lysosomes were also the targets of hypocrellin B-mediated sonodynamic action as well as mitochondria.

Combination of bubble liposomes and high-intensity focused ultrasound (HIFU) enhanced antitumor effect by tumor ablation

Ultrasound (US) is used in the clinical setting not only for diagnosis but also for therapy. As a therapeutic US technique, high-intensity focused ultrasound (HIFU) can be applied to treat cancer in a clinical setting. Microbubbles increased temperature and improved the low therapeutic efficiency under HIFU; however, microbubbles have room for improvement in size, stability, and targeting ability. To solve these issues, we reported that "Bubble liposomes" (BLs) containing the US imaging gas (perfluoropropane gas) liposomes were suitable for ultrasound imaging and gene delivery. In this study, we examined whether BLs and HIFU could enhance the ablation area of the tumor and the antitumor effect. First, we histologically analyzed the tumor after BLs and HIFU. The ablation area of the treatment of BLs and HIFU was broader than that of HIFU alone. Next, we monitored the temperature of the tumor, and examined the antitumor effect. The temperature increase with BLs and HIFU treatment was faster and higher than that with HIFU alone. Moreover, treatment with BLs and HIFU enhanced the antitumor effect, which was better than with HIFU alone. Thus, the combination of BLs and HIFU could be efficacious for cancer therapy.

Classification of stimuli-responsive polymers as anticancer drug delivery systems

Although several anticancer drugs have been introduced as chemotherapeutic agents, the effective treatment of cancer remains a challenge. Major limitations in the application of anticancer drugs include their nonspecificity, wide biodistribution, short half-life, low concentration in tumor tissue and systemic toxicity. Drug delivery to the tumor site has become feasible in recent years, and recent advances in the development of new drug delivery systems for controlled drug release in tumor tissues with reduced side effects show great promise. In this field, the use of biodegradable polymers as drug carriers has attracted the most attention. However, drug release is still difficult to control even when a polymeric drug carrier is used. The design of pharmaceutical polymers that respond to external stimuli (known as stimuli-responsive polymers) such as temperature, pH, electric or magnetic field, enzymes, ultrasound waves, etc. appears to be a successful approach. In these systems, drug release is triggered by different stimuli. The purpose of this review is to summarize different types of polymeric drug carriers and stimuli, in addition to the combination use of stimuli in order to achieve a better controlled drug release, and it discusses their potential strengths and applications. A survey of the recent literature on various stimuli-responsive drug delivery systems is also provided and perspectives on possible future developments in controlled drug release at tumor site have been discussed.

Gas-filled phospholipid nanoparticles conjugated with gadolinium play a role as a potential theragnostics for MR-guided HIFU ablation

To develop a long-circulating theragnostics, meaning therapeutics and diagnostics for MR-guided HIFU ablation, we designed and prepared Gd-C₅F₁₂-phospholipid nanobubbles (PLNs) 30–100 nm in diameter. The biochemical and physical characterization of Gd-C₅F₁₂-PLNs were performed. Since Gd-C₅F₁₂-PLN-50 (Φ = 50 nm) and Gd-C₅F₁₂-PLN-100 (Φ = 100 nm) enhanced the hyperthermal effect of HIFU size- and concentration-dependently in a tissue-mimicking phantom, its circulation, distribution, tumor accumulation and tumor ablation were examined in tumor-bearing mice. The plasma-half life of Gd-C₅F₁₂-PLNs was longer than 1.5 hrs. Gd-C₅F₁₂-PLNs mainly accumulated in the liver and the spleen, suggesting that they are slowly secreted through the hepatobiliary pathway. Monitored by the T1 signal intensity of MR, Gd-C₅F₁₂-PLNs accumulated in tumor tissues for 8 hours in mice. HIFU with Gd-C₅F₁₂-PLN-100 showed the increased tumor ablation area as compared with HIFU alone. The results suggest that Gd-C₅F₁₂-PLNs exhibit a potential theragnostics for MR-guided HIFU ablation.

Calibration of the 1-MHz Sonitron ultrasound system

Successful drug and gene delivery across cellular membranes can lead to improved therapeutic outcomes. Recent studies have suggested that sonoporation may enhance drug and gene delivery across cellular membranes. The enhancement may be a result of transient permeation of the membrane from cavitation or microstreaming effects of microbubbles exposed to ultrasound. Given limited acoustic pressure calibration and beam profile characterization of the Sonitron ultrasound systems in cellular bioeffects studies previously published, the objective of this work was to calibrate the acoustic output and explore the potential for standing waves in a cell-well plate. In this study, three 1-MHz transducers driven by Sonitron ultrasound systems, which have been used in a number of sonoporation studies, were calibrated. Transducers with 10-mm, 6-mm and 20-mm-diameter apertures (Sonitron 1000 and 2000, Rich-Mar, Inola, OK, USA) were calibrated using polyvinylidene fluoride (PVDF) needle hydrophones. Axial and transverse beam profiles were obtained, and the pressures were measured as a function of Sonitron intensity dial setting and duty cycle. The acoustic intensity was calculated and compared with the Sonitron intensity dial setting for duty cycles from 10-100%. Standing waves caused by reflections from the hydrophone holder were detected for each transducer. This observation may also have implications for in vitro sonoporation studies. Acoustic field characterization is an important first step in understanding the mechanisms of sonoporation and drug delivery across biomembranes.

Microbubble Compositions, Properties and Biomedical Applications

Over the last decade, there has been significant progress towards the development of microbubbles as theranostics for a wide variety of biomedical applications. The unique ability of microbubbles to respond to ultrasound makes them useful agents for contrast ultrasound imaging, molecular imaging, and targeted drug and gene delivery. The general composition of a microbubble is a gas core stabilized by a shell comprised of proteins, lipids or polymers. Each type of microbubble has its own unique advantages and can be tailored for specialized functions. In this review, different microbubbles compositions and physiochemical properties are discussed in the context of current progress towards developing novel constructs for biomedical applications, with specific emphasis on molecular imaging and targeted drug/gene delivery.

Augmentation of targeted delivery with pulsed high intensity focused ultrasound

This paper reviews the enhanced delivery of genes, drugs and therapeutics using ultrasound. It begins with a general overview of the field and the various techniques associated with it, including sonophoresis, hyperthermia (with ultrasound), sonoporation, and microbubble assisted transvascular and targeted delivery. Particular attention is then paid to pulsed high intensity focused ultrasound drug delivery without the use of ultrasound contrast agents. Feasibility and mechanistic studies of this technique are described in some detail. Conclusions are then drawn regarding possible mechanisms of this treatment, and to contrast with the better known treatments relying on injection of ultrasound contrast agents.

Therapeutic potential of low-intensity ultrasound (part 1): thermal and sonomechanical effects

In this first part of the review, we will focus on and discuss various aspects of low-intensity ultrasound (US), with emphasis on mild thermal effects, apoptosis induction, and sonomechanical effects. Mild thermal effects of US have been commonly applied to physical therapy. Though US has clear beneficial effects, the advantage of using US over other heating modalities remains unclear. US has also been used in vivo and clinically in the treatment of wounds and fractures, with promising results. On the biomolecular level, studies have shown that US can induce apoptosis and that certain conditions can provide optimal apoptosis induction. As to potential therapeutic applications, in addition to the thermal and other physical effects, apoptosis induction by US may offer direct and rapid treatment of tumors or cancer tissues. Technological advances and rapidly accelerating research in this field are providing an ever-increasing array of therapeutic options for lowintensity US.

Ultrasound-enhanced chemotherapy and gene delivery for glioma cells

Treatment of brain cancer is limited in part by inefficient intracellular delivery of drugs and DNA for chemotherapy and gene therapy, respectively. This study tested the hypothesis that ultrasound may be used to enhance intracellular delivery and efficacy of chemotherapeutics and genes in glioma cells in vitro. First, suitable ultrasound conditions were identified by measuring intracellular uptake of calcein and viability of GS 9L rat gliosarcoma cells after a range of different ultrasound exposures. We selected sonication at 10 J/cm2, which achieved intracellular delivery of approximately 10(6) molecules/cell. Next, glial cells were sonicated with varying concentrations of model chemotherapeutics: BCNU and bleomycin. For both drugs, cytotoxicity was increased in a synergistic manner when accompanied by ultrasound exposure. Finally, expression of a plasmid DNA encoding a GFP reporter was increased up to 30-fold when exposed to ultrasound. Altogether, these findings suggest that ultrasound may be useful to increase the efficacy of chemotherapy and gene therapy of glioma cells.

Enhancement of ultrasound contrast agent in high-intensity focused ultrasound ablation

High-intensity focused ultrasound (HIFU) is becoming an increasingly attractive modality for ablation. Enhancement of HIFU is an important issue that has been discussed and investigated worldwide. Ultrasound contrast agents are considered to constitute an efficient medium for changing acoustic characteristics and improving energy deposition in the focal region. The role of microbubbles in inducing enhanced heating, cavitation, and other related events in HIFU ablation has been investigated, with the goal of improving coagulation necrosis volume or decreasing acoustic power and exposure duration. Consequently, with the use of ultrasound contrast agents, applications of HIFU are expected to become more efficient, safe, and accurate and to produce fewer adverse effects. This paper reviews studies that have been conducted to investigate the enhancement of ultrasound contrast agents in HIFU ablation through experiments that were carried out in vitro and in vivo; an analysis of results of this enhancement mechanism is provided.

Mechanism of intracellular delivery by acoustic cavitation

Using conditions different from conventional medical imaging or laboratory cell lysis, ultrasound has recently been shown to reversibly increase plasma membrane permeability to drugs, proteins and DNA in living cells and animals independently of cell or drug type, suggesting a ubiquitous mechanism of action. To determine the mechanism of these effects, we examined cells exposed to ultrasound by flow cytometry coupled with electron and fluorescence microscopies. The results show that cavitation generated by ultrasound facilitates cellular incorporation of macromolecules up to 28 nm in radius through repairable micron-scale disruptions in the plasma membrane with lifetimes >1 min, which is a period similar to the kinetics of membrane repair after mechanical wounding. Further data suggest that cells actively reseal these holes using a native healing response involving endogenous vesicle-based membrane resealing. In this way, noninvasively focused ultrasound could deliver drugs and genes to targeted tissues, thereby minimizing side effects, lowering drug dosages, and improving efficacy.

Combination of HIFU therapy with contrast-enhanced sonography for quantitative assessment of therapeutic efficiency on tumor grafted mice

The objective was to evaluate treatment efficiency of a new high-intensity focused ultrasound (HIFU) prototype combining a therapeutic transducer with a sonographic probe. The optimal HIFU sequence was defined on ex vivo samples before in vivo evaluation of tumor ablation was performed by perfusion quantification after contrast agent injection. The original feature of this prototype is a 9-MHz sonographic probe in a HIFU device and connected to an Aplio (Toshiba) sonograph. Acoustical power and treatment time were determined on ex vivo livers to generate 1-cm-long lesions. Lesion reproducibility was assessed for the power and treatment time selected. The gap between lesions and HIFU displacement shot procedures were optimized to ablate a 1-cm3 volume. The optimized protocol was applied to five murine tumors in vivo. Tumor ablation was quantified according to (1) contrast uptake (CU) after HIFU using perfusion software (Toshiba) in "vascular recognition imaging" mode and Sonovue (Bracco) contrast agent, and (2) the percentage of necrosis quantified on histologic slides. Ex vivo results: optimized settings, at 442 W/cm2 applied during three cycles (3 s on/5 s off) generated 10 identical elementary lesions measuring 9.78 (+/-0.66) * 2.11 (+/-0.33) mm2. A 4-mm gap between adjacent lesions and a 2-min pause between shot lines were found optimal. In vivo results: 60 % (+/-22) mean reduction in CU after HIFU and tumor necrosis histologically estimated at 58 % (+/-5.7) were quantified for the five animals. The therapeutic potential of this HIFU prototype was demonstrated in vivo through objective quantification of tumor ablation based on CU.

Effect of solution composition of plasmid DNA on gene transfection following liver surface administration in mice

We investigated the effect of plasmid DNA (pDNA) solution composition on gene transfection following liver surface administration in mice. Gene transfection experiments in situ and in vivo were performed using the following pDNA solutions: dextrose solution, NaCl solution, phosphate buffer, phosphate-buffered saline, Tris/HCl buffer with EDTA, Tris/HCl buffer with EDTA and Triton X-100, and water. In in situ experiments, we used a glass cylindrical diffusion cell that limited the contact area between the liver surface and the naked pDNA solution. The gene transfection at the site of diffusion cell attachment increased in hypotonic solution, and decreased in hypertonic solution, compared with isotonic solution. In in vivo experiments, instillation of naked pDNA solution onto the liver surface using a micropipette caused no significant differences in gene transfection in the applied lobe. These results suggest that it is important to select the optimal pDNA solution composition to control the gene transfection.