Recent advances of sonodynamic therapy in cancer treatment

Corroles and corrole/transferrin nanoconjugates as candidates for sonodynamic therapy

We report corroles as good agents for utilizing the otherwise harmless sonication of aqueous solutions as a tool for creating highly cytotoxic singlet oxygen, and demonstrate cancer cell killing via this approach.

Influence of Magnetic Nanoparticles on the Focused Ultrasound Hyperthermia

Ultrasound hyperthermia is a medical treatment used to increase temperature of tissues. It can be used independently or as a supportive method for an anticancer treatment. The therapeutic efficacy of focused ultrasound hyperthermia can be improved using sonosensitizers, nanoparticles enhancing the attenuation and dissipation of acoustic energy. As sonosensitizers, we propose magnetic nanoparticles owing to their biodegradability, biocompatibility, and simple positioning in tissues using a magnetic field. Focused ultrasound hyperthermia studies were performed using tissue-mimicking phantoms. Temperature changes were measured at various ultrasound powers and distances from the center of the ultrasound focus. Specific absorption rate (SAR) values, describing the power deposition in the tissues during the hyperthermia treatment, were evaluated for the center of the focus point and for various distances from it. The results show that the addition of nanoparticles increases the SAR almost two times compared to that for the pure phantom. The highest SAR is obtained in the ultrasound focus; it decreases with the increase of the distance from the focus.

Insight into ultrasound-mediated reactive oxygen species generation by various metal-porphyrin complexes

Ultrasound is used to trigger the cytotoxicity of chemical compounds, known as sonosensitisers, in an approach called sonodynamic therapy (SDT), which is under investigation herein. The generation of reactive oxygen species (ROS) has been proposed as the main biological occurrence that leads to the cytotoxic effects, which are achieved via the synergistic action of two components: the energy-absorbing sonosensitiser and ultrasound (US), which are both harmless per se. Despite some promising results, a lack of investigation into the mechanisms behind US sonosensitiser-mediated ROS generation has prevented SDT from reaching its full potential. The aim of this work is to investigate the US-responsiveness of a variety of metal-porphyrin complexes, free-base porphyrin and Fe(III), Zn(II) and Pd(II) porphyrin, by analyzing their ROS generation under US exposure and related bio-effects. All experiments were also carried out under light exposure and the results were used as references. Our results show that porphyrin ultrasound-responsiveness depends on the metal ion present, with Zn(II) and Pd(II) porphyrin being the most efficient in generating singlet oxygen and hydroxyl radicals. ROS production efficiency is lower after ultrasound exposure than after light exposure, because of the various physico-chemical mechanisms involved in sensitiser activation. US and porphyrin-mediated ROS generation is oxygen-dependent and the activation of porphyrin by US appears to be more compatible with sonoluminescence-based photo-activation rather than a radical path process that occurs via the homolytic bond rupture of water. Notably, the cytotoxicity results reported herein, which are mirrored by ex-cellulo data, confirm that the type of ROS generation achieved by the US activation of intracellular porphyrins is pivotal to the effectiveness of cancer cell killing.

Nanoparticle-assisted ultrasound: A special focus on sonodynamic therapy against cancer

At present, ultrasound radiation is broadly employed in medicine for both diagnostic and therapeutic purposes at various frequencies and intensities. In this review article, we focus on therapeutically-active nanoparticles (NPs) when stimulated by ultrasound. We first introduce the different ultrasound-based therapies with special attention to the techniques involved in the oncological field, then we summarize the different NPs used, ranging from soft materials, like liposomes or micro/nano-bubbles, to metal and metal oxide NPs. We therefore focus on the sonodynamic therapy and on the possible working mechanisms under debate of NPs-assisted sonodynamic treatments. We support the idea that various, complex and synergistics physical-chemical processes take place during acoustic cavitation and NP activation. Different mechanisms are therefore responsible for the final cancer cell death and strongly depends not only on the type and structure of NPs or nanocarriers, but also on the way they interact with the ultrasonic pressure waves. We conclude with a brief overview of the clinical applications of the various ultrasound therapies and the related use of NPs-assisted ultrasound in clinics, showing that this very innovative and promising approach is however still at its infancy in the clinical cancer treatment.

Potential involvement of the 18 kDa translocator protein and reactive oxygen species in apoptosis of THP-1 macrophages induced by sonodynamic therapy

Sonodynamic therapy (SDT) with exogenous protoporphyrin IX (PpIX) or endogenous PpIX derived from 5-aminolevulinic acid (ALA) has been carried out to produce apoptotic effects on macrophages, indicating a potential treatment methodology for atherosclerosis. Our previous studies have found that mitochondria damage by reactive oxygen species (ROS) plays a major role in the SDT-induced apoptosis. This study aimed at investigating the potential involvement of the mitochondrial 18 kDa translocator protein (TSPO) and ROS in the pro-apoptotic effects of SDT on THP-1 macrophages. THP-1 macrophages were divided into control and SDT groups, and went through pretreatment of the specific TSPO ligand PK11195 and ROS scavengers N-Acetyl Cysteine (NAC), then compared with groups without pretreatment. Application of PK11195 reduced intracellular accumulation of endogenous PpIX. PK11195 and NAC reduced the generation of intracellular ROS and oxidation of cardiolipin induced by SDT, respectively. PK11195 and NAC also reduced SDT-induced mitochondrial membrane potential (ΔΨ_m) loss, the translocation of cytochrome c and cell apoptosis. PpIX accumulation, ROS generation and cell apoptosis were also attenuated by siTSPO. Our findings indicate the pivotal role of TSPO and ROS in SDT-induced cardiolipin oxidation, ΔΨ_m collapse, cytochrome c translocation and apoptosis in THP-1 macrophages.

Heating Induced by Therapeutic Ultrasound in the Presence of Magnetic Nanoparticles

The efficiency of ultrasound hyperthermia for anti-cancer treatments such as radiotherapy or chemotherapy can be improved by using sonosensitizers, which are materials that enhance the attenuation and dissipation of acoustic energy. We propose the use of magnetic nanoparticles as sonosensitizers because of their biocompatibility, nontoxicity, and common use in several medical applications. A magnetic material was synthetized and then incorporated in the form of a magnetic fluid in agar tissue-mimicking phantoms. Ultrasound hyperthermia studies were conducted at various ultrasound frequencies and concentrations of magnetic nanoparticles in the phantoms. The theoretical modeling based on a heat transfer equation and the experimental results show good agreement and confirm that the temperature rise during ultrasound heating in tissue-mimicking phantoms doped with sonosensitizers is greater than that in a pure agar phantom. Furthermore, on the basis of Pennes' bio-heat equation, which takes into consideration the blood perfusion and metabolic heat, the thermal dose and lesion shapes after sonication were determined for a hypothetical tissue.

Sonodynamic Therapy Mediated by Emodin Induces the Oxidation of Microtubules to Facilitate the Sonodynamic Effect

In previous studies, sonodynamic therapy mediated by emodin (emodin-SDT) induced cytoskeletal filament disruption and apoptosis of THP-1-derived macrophages. In this research, we investigated the underlying mechanism. THP-1-derived macrophages were incubated with emodin and exposed to ultrasound irradiation. After emodin-SDT, we measured the production of reactive oxygen species (ROS) and analyzed the level of amino acid oxidation in microtubules, the cleavage of microtubules and the mitochondrial membrane potential (MMP). We found that intracellular emodin accumulated mainly on microtubules. After emodin-SDT, generation of ROS was evident. Analysis of the carbonyl content of proteins suggested oxidation of microtubules. Microtubules were disrupted after emodin-SDT, and the antioxidant N-acetyl-L-cysteine prevented this disruption. MMP decreased after emodin-SDT, and this effect could be prevented by N-acetyl-L-cysteine. We conclude that emodin-SDT induces the generation of ROS. The oxidation of microtubules leads to its cleavage and the subsequent decline in MMP.

Porphyrin-Loaded Pluronic Nanobubbles: A New US-Activated Agent for Future Theranostic Applications

Sonodynamic therapy (SDT) has become a promising noninvasive approach for cancer therapy. The treatment exploits the ability of particular molecules (i.e., porphyrins) to be excited by ultrasound and produce reactive oxygen species (ROS) during their decay process. These reactive species, in turn, result in cell death. To capitalize on the real-time visualization and on-demand delivery of ultrasound contrast agents, this study aims to combine porphyrins with nanobubbles (NBs) to obtain an ultrasound-activated theranostic agent that exploits the SDT activity in vitro. Two porphyrin classes, exposing different hydrophobic side chains, were synthesized. NB size and encapsulation efficiency were markedly dependent on the porphyrin structure. The combination of these porphyrin and NBs resulted in a significant reduction in cell viability upon sonication in pilot studies performed on the LS 174T colorectal cancer cell line.

The Combination of Glycolytic Inhibitor 2-Deoxyglucose and Microbubbles Increases the Effect of 5-Aminolevulinic Acid-Sonodynamic Therapy in Liver Cancer Cells

Sonodynamic therapy (SDT) overcomes the shortcoming of photodynamic therapy in the treatment of cancer. Previous studies indicated that the glycolysis inhibitor 2-deoxyglucose (2-DG) potentiated photodynamic therapy induced tumor cell death and microbubbles (MBs) improved the SDT performance. We hypothesized that the combination of 2-DG and MBs will increase the effect of 5-aminolevulinic acid (ALA)-SDT in HepG2 liver cancer cells. When cells were treated with 5-min ALA-SDT and 2-mmol/L 2-DG, the cell survival rate decreased to 73.0 ± 7.1% and 75.2 ± 7.9%, respectively. Furthermore, 2 mmol/L 2-DG increased 5-min ALA-SDT induced growth inhibition and augmented ALA-SDT induced cell apoptotic rate from 9.8 ± 0.7% to 17.4 ± 2.2%. In the combination group (2-DG and ALA-SDT group), HepG2 cells possessed typical apoptotic characters. 2-DG also increased ALA-SDT associated intracellular reactive oxygen species generation and loss of mitochondrial membrane potential. Moreover, SonoVue MBs had stimulatory function on cell viability inhibition, apoptosis, reactive oxygen species production and mitochondrial membrane potential loss for combination treatment. This study suggests a promising therapeutic strategy using a combination of 2-DG, MBs and ALA-SDT for treating liver cancer.

NIRF Heptamethine Cyanine Dye Nanocomplexes for Multi Modal Theranosis of Tumors

Heptamethine cyanine dyes are categorized as a class of near infrared fluorescent (NIRF) dyes which have been discovered to have tumor targeting and accumulation capability. This unique feature of NIRF dye makes it a promising candidate for imaging, targeted therapy and also as a drug delivery vehicle for various types of cancers. The favored uptake of dyes only in cancer cells is facilitated by several factors which include organic anion-transporting polypeptides, high mitochondrial membrane potential and tumor hypoxia in cancer cells. Currently nanotechnology has opened possibilities for multimodal or multifunctional strategies for cancer treatment. Including heptamethine cyanine dyes in nanoparticle based delivery systems have generally improved its theranostic ability by several fold owing to the multiple functionalities and structural features of heptamethine dyes. For this reason, nanocomplexes with NIRF heptamethine cyanine dye probe are preferred over non-targeting dyes such as indo cyanine green (ICG). This review sums up current trends and progress in NIRF heptamethine cyanine dye, including dye properties, multifunctional imaging and therapeutic applications in cancer.