Sudden Cell Death Induced by Ca2+ Delivery via Microbubble Cavitation

Ca2+ sonotransfer into breast cancer cells in a suspension, 3-D spheroid and subcutaneous tumor models

Calcium-based treatments have gained considerable attention in the field of electroporation, primarily, due to their comparable efficacy to conventional electro-chemotherapy. However, their applications in sonoporation remain under-investigated, despite its high potential for site-specific and temporally-controlled drug delivery. Current study examines the curative potential of calcium sonoporation across multiple experimental models, including: i) cell suspension, ii) 3-D spheroid culture and iii) subcutaneous murine breast cancer tumors. Murine breast cancer is an established analogue of stage IV human breast cancer. For comparison, parallel experiments, using classical anticancer drug bleomycin were performed. Ca2+ sonoporation efficiently enhanced 4 T1 cell death in a suspension in the absence of microbubbles, under relatively low acoustic pressure (100-200 kPa). In contrast, efficient spheroid growth reduction required microbubble-mediated inertial cavitation at higher (700 kPa) acoustic pressure. In vivo, Ca2+ sonoporation demonstrated similar tumor growth reduction as bleomycin sonoporation. Both treatments reduced tumor growth from the third day after the onset of treatment. Successful cancer treatment was achieved even at lower values of cavitation dose metrics. Our study presents a multi-level validation of Ca2+ sonoporation as an effective treatment strategy for murine breast cancer. Importantly, complete tumor eradication and prolonged animal survival up to one month were observed even at significantly reduced cavitation activity, indicating clinical safety of the treatment.

Breaking through with ultrasound: TP53-driven efficacy of calcium sonoporation in pediatric rhabdomyosarcoma cells

Ultrasound-mediated sonoporation is a promising technique that temporarily permeabilizes cell membranes to enhance delivery of therapeutic agents directly to tumor sites while minimizing systemic side effects. Calcium, a critical regulator of cell death and proliferation, can be introduced into cells by ultrasound, offering a novel therapeutic approach. This study investigates calcium sonoporation (CaSP), which combines ultrasound with calcium ions and microbubbles, to target pediatric rhabdomyosarcoma A204 and RD cells. Our findings showed that CaSP disrupted cellular homeostasis by facilitating the controlled influx of calcium, leading to oxidative stress, mitochondrial dysfunction, cell cycle arrest and activation of apoptotic pathways. The study revealed that the TP53 mutational status significantly influences the cellular response to CaSP. TP53-wild-type A204 cells were particularly susceptible to CaSP, exhibiting marked increases in apoptosis and oxidative damage. In contrast, TP53-mutated RD cells exhibited a reduced oxidative stress and apoptotic response, highlighting the critical role of TP53 in mediating the effects of CaSP. This differential response underscored the potential of TP53 gene as a biomarker for predicting the efficacy of CaSP, offering a pathway toward more personalized cancer therapies. Furthermore, the study demonstrated that CaSP can selectively target cancer cells while sparing healthy tissue. The research laid the groundwork for future studies to optimise sonoporation parameters and explore its integration with existing cancer treatments. The insights gained from this study pave the way for developing more personalized cancer treatment strategies, particularly for tumors influenced by specific genetic contexts, such as TP53 mutations.

Calcium ion delivery by microbubble-assisted sonoporation stimulates cell death in human gastrointestinal cancer cells

Ultrasound-mediated cell membrane permeabilization - sonoporation, enhances drug delivery directly to tumor sites while reducing systemic side effects. The potential of ultrasound to augment intracellular calcium uptake - a critical regulator of cell death and proliferation - offers innovative alternative to conventional chemotherapy. However, calcium therapeutic applications remain underexplored in sonoporation studies. This research provides a comprehensive analysis of calcium sonoporation (CaSP), which combines ultrasound treatment with calcium ions and SonoVue microbubbles, on gastrointestinal cancer cells LoVo and HPAF-II. Initially, optimal sonoporation parameters were determined: an acoustic wave of 1 MHz frequency with a 50 % duty cycle at intensity of 2 W/cm2. Subsequently, various cellular bioeffects, such as viability, oxidative stress, metabolism, mitochondrial function, proliferation, and cell death, were assessed following CaSP treatment. CaSP significantly impaired cancer cell function by inducing oxidative and metabolic stress, evidenced by increased mitochondrial depolarization, decreased ATP levels, and elevated glucose uptake in a Ca2+ dose-dependent manner, leading to activation of the intrinsic apoptotic pathway. Cellular response to CaSP depended on the TP53 gene's mutational status: colon cancer cells were more susceptible to CaSP-induced apoptosis and G1 phase cell cycle arrest, whereas pancreatic cancer cells showed a higher necrotic response and G2 cell cycle arrest. These promising results encourage future research to optimize sonoporation parameters for clinical use, investigate synergistic effects with existing treatments, and assess long-term safety and efficacy in vivo. Our study highlights CaSP's clinical potential for improved safety and efficacy in cancer therapy, offering significant implications for the pharmaceutical and biomedical fields.

The comparison of the dynamics of Ca2+ and bleomycin intracellular delivery after cell sonoporation and electroporation in vitro

Ca2+, in combination with SP or EP, induces cell cytotoxicity much faster compared to BLM. The application of BLM in combination with, SP or EP, reaches the level of cell death, induced by similar combination with Ca2+, only after 72 h. The methods of SP and EP were calibrated according to the level of differential cytotoxicity, determined after 6 days (using cell clonogenic assay). The combination of Ca2+ SP induces cell death faster than Ca2+ EP - after Ca2+ SP it increases to a maximum level after 15 min and remains constant for up to 6 days, while the cytotoxic efficiency after Ca2+ EP increases to the level of Ca2+ SP only after 72 h. The combination of BLM SP shows a very similar dynamics to BLM EP - both reach maximal level of cytotoxicity after 48-72 h. Ca2+ and BLM in combination with SP have shown similar levels of cytotoxicity at higher acoustic pressures (≥250 kPa); therefore, Ca2+ SP can be used to induce immediate and maximal level of cytotoxic effect. The faster cytotoxic efficiency of Ca2+ in combination with SP than EP was determined to be due to the involvement of microbubble inertial cavitation.

The Assessment of Calcium and Bleomycin Cytotoxic Efficiency in Relation to Cavitation Dosimetry

Microbubble (MB)- and ultrasound (US)-facilitated intracellular Ca²⁺ delivery, known as sonoporation (SP), is a promising anticancer treatment modality, since it allows a spatio-temporally controllable and side-effect-free alternative to conventional chemotherapy. The current study provides extensive evidence that a 5 mM concentration of Ca²⁺ in combination with US alone or US and Sonovue MBs can be an alternative to the conventional 20 nM concentration of the anticancer drug bleomycin (BLM). Ca²⁺ application together with SP induces a similar level of death in Chinese hamster ovary cells to the combination of BLM and SP but does not cause systemic toxicity, as is inherent to conventional anticancer drugs. In addition, Ca²⁺ delivery via SP alters three vital characteristics essential for viable cells: membrane permeability, metabolic activity and proliferation ability. Most importantly, Ca²⁺ delivery via SP elicits sudden cell death-occurring within 15 min-which remains similar during 24-72 h and 6 d periods. The extensive study of US waves side-scattered by MBs led to the quantification of the cavitation dose (CD) separately for subharmonics, ultraharmonics, harmonics and broadband noise (up to 4 MHz). The CD was suitable for the prognostication of the cytotoxic efficiency of both anticancer agents, Ca²⁺ and BLM, as was indicated by an overall high (R² ≥ 0.8) correlation (22 pairs in total). These extensive analytical data imply that a broad range of frequencies are applicable for the feedback-loop control of the process of US-mediated Ca²⁺ or BLM delivery, successively leading to the eventual standardization of the protocols for the sonotransfer of anticancer agents as well as the establishment of a universal cavitation dosimetry model.

Sonoporation based on repeated vaporization of gold nanodroplets

Background

Gold nanodroplets (AuNDs) have been proposed as agents for photothermal therapy and photoacoustic imaging. Previously, we demonstrated that the sonoporation can be more effectively achieved with synchronized optical and acoustic droplet vaporization. By applying a laser pulse at the rarefactional phase of the ultrasound (US) pulse, the vaporization threshold can be reached at a considerably lower laser average power. However, a large loading quantity of the AuNDs may increase the risk of air embolism. The destruction of phase‐shifted AuNDs at the inertial cavitation stage leads to a reduced drug delivery performance. And it also causes instability of echogenicity during therapeutic monitoring.

Purpose

In this study, we propose to further improve the sonoporation effectiveness with repeated vaporization. In other words, the AuNDs repeatedly undergo vaporization and recondensation so that sonoporation effects are accumulated over time at lower energy requirements. Previously, repeated vaporization has been demonstrated as an imaging contrast agent. In this study, we aim to adopt this repeated vaporization scheme for sonoporation.

Methods

Perfluoropentane NDs with a shell made of human serum albumin were used as the US contrast agents. Laser pulses at 808 nm and US pulses of 1 MHz were delivered for triggering vaporization and inertial cavitation of NDs. We detected the vaporization and cavitation effects under different activation firings, US peak negative pressures (PNPs), and laser fluences using 5‐ and 10‐MHz focused US receivers. Numbers of calcein‐AM and propidium iodide signals uptake by BNL hepatocarcinoma cancer cells were used to evaluate the sonoporation and cell death rate of the cells.

Results

We demonstrate that sonoporation can be realized based on repeatable vaporization instead of the commonly adopted inertial cavitation effects. In addition, it is found that the laser fluence and the acoustic pressure can be reduced. As an example, we demonstrate that the acoustic and optical energy for achieving a similar level of sonoporation rate can be as low as 0.44 MPa for the US PNP and 4.01 mJ/cm² for the laser fluence, which are lower than those with our previous approach (0.53 MPa and 4.95 mJ/cm², respectively).

Conclusion

We demonstrated the feasibility of vaporization‐based sonoporation at a lower optical and acoustic energy. It is an advantageous method that can enhance drug delivery efficiency, therapeutic safety and potentially deliver an upgraded gene therapy strategy for improved theragnosis.

Radioimmunotherapy Combined With Low-Intensity Ultrasound and Microbubbles: A Potential Novel Strategy for Treatment of Solid Tumors

The prognosis of advanced malignant tumors is very poor, and effective treatment is limited. Radioimmunotherapy (RIT) is a novel treatment method. However, its anti-tumor effect is relatively low in solid tumors, which is mainly due to the blood-tumor barrier preventing RIT from penetrating the tumor, resulting in an insufficient dose. Low-intensity ultrasound with microbubbles (USMB) has proven capable of opening the blood-tumor barrier. The combination of the two technologies may overcome the poor anti-tumor effect of RIT and promote the clinical application of RIT in solid tumors. In this article, we reviewed the current research status of RIT in the treatment of solid tumors and the opportunities and challenges of USMB combined with RIT.

Ca2+ roles in electroporation-induced changes of cancer cell physiology: From membrane repair to cell death

The combination of Ca²⁺ ions and electroporation has gained attention as potential alternative to electrochemotherapy. Ca²⁺ is an important component of the cell membrane repair system and its presence directly influences the dynamics of the pore cycle after electroporation which can be exploited for cancer therapies. Here, the influence of Ca²⁺ concentration is investigated on small molecule electrotransfer and release of Calcein from 4T1, MX-1, B16F10, U87 cancer cells after cell exposure to microsecond electric pulses. Moreover, we investigated simultaneous molecule electrotransfer and intracellular calcium ion influx when media was supplemented with different Ca²⁺ concentrations. Results show that increased concentrations of calcium ions reduce the electrotransfer of small molecules to different lines of cancer cells as well as the release of Calcein. These effects are related with an enhanced membrane repair mechanism. Overall, we show that the efficiency of molecular electrotransfer can be controlled by regulating Ca²⁺ concentration in the electroporation medium. For the first time, the cause of cancer cell death in vitro from 1 mM CaCl₂ concentrations is related to the irreversible loss of Ca²⁺ homeostasis after cell electroporation. Our findings provide fundamental insight on the mechanisms of Ca²⁺ electroporation that might lead to improved therapeutic outcomes.