Singlet oxygen generation by sonication using a water-soluble fullerene (C60) complex: a potential application for sonodynamic therapy

From 2D to 3D In Vitro World: Sonodynamically-Induced Prooxidant Proapoptotic Effects of C60-Berberine Nanocomplex on Cancer Cells

OBJECTIVES

The primary objective of this research targeted the biochemical effects of SDT on human cervix carcinoma (HeLa) and mouse Lewis lung carcinoma (LLC) cells grown in 2D monolayer and 3D spheroid cell culture.

METHODS

HeLa and LLC monolayers and spheroids were treated with a 20 µM C60-Ber for 24 h, followed by irradiation with 1 MHz, 1 W/cm2 US. To evaluate the efficacy of the proposed treatment on cancer cells, assessments of cell viability, caspase 3/7 activity, ATP levels, and ROS levels were conducted.

RESULTS

Our results revealed that US irradiation alone had negligible effects on LLC and HeLa cancer cells. However, both monolayers and spheroids irradiated with US in the presence of the C60-Ber exhibited a significant decrease in viability (32% and 37%) and ATP levels (42% and 64%), along with a notable increase in ROS levels (398% and 396%) and caspase 3/7 activity (437% and 246%), for HeLa monolayers and spheroids, respectively. Similar tendencies were observed with LLC cells. In addition, the anticancer effects of C60-Ber surpassed those of C60, Ber, or their mixture (C60 + Ber) in both cell lines.

CONCLUSIONS

The detected intensified ROS generation and ATP level drop point to mitochondria dysfunction, while increased caspase 3/7 activity points on the apoptotic pathway induction. The combination of 1 W/cm2 US with C60-Ber showcased a promising platform for synergistic sonodynamic chemotherapy for cancer treatment.

Singlet oxygen detection in vivo is hindered by nonspecific SOSG staining

Singlet oxygen is considered an important cell damaging agent due to its propensity to react with organic compounds. This drives the interest in developing methods for determination of 1O2. Simplicity of application and high sensitivity makes fluorescent probes a popular choice for in vivo 1O2 detection. Despite its proclaimed cell-impermeability, the commercially available Singlet Oxygen Sensor Green (SOSG) is widely applied to support assertions of 1O2 involvement in cell and tissue damage. Our investigation, however, demonstrate that different microbial species and cancer cells become fluorescent when exposed to SOSG under conditions which exclude generation of 1O2. Cells, permeabilized with chlorhexidine or by heat exposure under anaerobic conditions, exhibited SOSG fluorescence. Permeabilized cells could be stained with SOSG even 24 h post-permeabilization. Since SOSG is cell impermeable, the main factor that led to fluorescent staining was plasma membrane damage. Spectral analyses of different batches of SOSG revealed that SOSG endoperoxide (SOSG-EP) did not increase even after prolonged storage under the recommended conditions. The commercial preparations of SOSG, however, were not SOSG-EP free, which can produce erroneous results when SOSG staining is used as a proof of singlet oxygen production in vivo.

Silent Death by Sound: C60 Fullerene Sonodynamic Treatment of Cancer Cells

The acoustic pressure waves of ultrasound (US) not only penetrate biological tissues deeper than light, but they also generate light emission, termed sonoluminescence. This promoted the idea of its use as an alternative energy source for photosensitizer excitation. Pristine C₆₀ fullerene (C₆₀), an excellent photosensitizer, was explored in the frame of cancer sonodynamic therapy (SDT). For that purpose, we analyzed C₆₀ effects on human cervix carcinoma HeLa cells in combination with a low-intensity US treatment. The time-dependent accumulation of C₆₀ in HeLa cells reached its maximum at 24 h (800 ± 66 ng/10⁶ cells). Half of extranuclear C₆₀ is localized within mitochondria. The efficiency of the C₆₀ nanostructure's sonoexcitation with 1 MHz US was tested with cell-based assays. A significant proapoptotic sonotoxic effect of C₆₀ was found for HeLa cells. C₆₀'s ability to induce apoptosis of carcinoma cells after sonoexcitation with US provides a promising novel approach for cancer treatment.

Enhancing Penetration Ability of Semiconducting Polymer Nanoparticles for Sonodynamic Therapy of Large Solid Tumor

Sonodynamic therapy (SDT) holds growing promise in deep-seated or large solid tumor treatment owing to its high tissue penetration depth ability; however, its therapeutic efficacy is often compromised due to the hypopermeable and hypoxic characteristics in the tumor milieu. Herein, a semiconducting polymer nanoparticle (SPNC) that synergistically enhances tumor penetration and alleviates tumor hypoxia is reported for sonodynamic therapy of large solid tumors. SPNC comprises a semiconducting polymer nanoparticle core as a sonodynamic converter coated with a poly (ethylene glycol) corona. An oxygen-modulating enzyme, catalase, is efficiently conjugated to the surface of nanoparticles via the coupling reaction. Superior to its counterpart SPNCs (SPNC2 (84 nm) and SPNC3 (134 nm)), SPNC with the smallest size (SPNC1 (35 nm)) can efficiently penetrate throughout the tumor interstitium to alleviate whole tumor hypoxia in a large solid tumor model. Upon ultrasound (US) irradiation, SPNC1 can remotely generate sufficient singlet oxygen to eradicate tumor cells at a deep-tissue depth. Such a single treatment of SPNC1-medicated sonodynamic therapy effectively inhibits tumor growth in a large solid tumor mouse model. Therefore, this study provides a generalized strategy to synergistically overcome both poor penetration and hypoxia of large tumors for enhanced cancer treatment.