Characterization of Ablation Thresholds for 3D-Cultured Patient-Derived Glioma Stem Cells in Response to High-Frequency Irreversible Electroporation

Therapeutic perspectives of high pulse repetition rate electroporation

Electroporation, a technique that uses electrical pulses to temporarily or permanently destabilize cell membranes, is increasingly used in cancer treatment, gene therapy, and cardiac tissue ablation. Although the technique is efficient, patients report discomfort and pain. Current strategies that aim to minimize pain and muscle contraction rely on the use of pharmacological agents. Nevertheless, technical improvements might be a valuable tool to minimize adverse events, which occur during the application of standard electroporation protocols. One recent technological strategy involves the use of high pulse repetition rate. The emerging technique, also referred as "high frequency" electroporation, employs short (micro to nanosecond) mono or bipolar pulses at repetition rate ranging from a few kHz to a few MHz. This review provides an overview of the historical background of electric field use and its development in therapies over time. With the aim to understand the rationale for novel electroporation protocols development, we briefly describe the physiological background of neuromuscular stimulation and pain caused by exposure to pulsed electric fields. Then, we summarize the current knowledge on electroporation protocols based on high pulse repetition rates. The advantages and limitations of these protocols are described from the perspective of their therapeutic application.

Involvement of Mitochondria in the Selective Response to Microsecond Pulsed Electric Fields on Healthy and Cancer Stem Cells in the Brain

In the last few years, pulsed electric fields have emerged as promising clinical tools for tumor treatments. This study highlights the distinct impact of a specific pulsed electric field protocol, PEF-5 (0.3 MV/m, 40 μs, 5 pulses), on astrocytes (NHA) and medulloblastoma (D283) and glioblastoma (U87 NS) cancer stem-like cells (CSCs). We pursued this goal by performing ultrastructural analyses corroborated by molecular/omics approaches to understand the vulnerability or resistance mechanisms triggered by PEF-5 exposure in the different cell types. Electron microscopic analyses showed that, independently of exposed cells, the main targets of PEF-5 were the cell membrane and the cytoskeleton, causing membrane filopodium-like protrusion disappearance on the cell surface, here observed for the first time, accompanied by rapid cell swelling. PEF-5 induced different modifications in cell mitochondria. A complete mitochondrial dysfunction was demonstrated in D283, while a mild or negligible perturbation was observed in mitochondria of U87 NS cells and NHAs, respectively, not sufficient to impair their cell functions. Altogether, these results suggest the possibility of using PEF-based technology as a novel strategy to target selectively mitochondria of brain CSCs, preserving healthy cells.

Investigation of lethal thresholds of nanosecond pulsed electric field in rabbit VX2 hepatic tumors through finite element analysis and verification with a single-needle bipolar electrode: A prospective strategy employing three-dimensional comparisons

Pulsed electric field has emerged as a promising modality for the solid tumor ablation with the advantage in treatment planning, however, the accurate prediction of the lesion margin requires the determination of the lethal electric field (E) thresholds. Herein we employ the highly repetitive nanosecond pulsed electric field (RnsPEF) to ablate the normal and VX2 tumor-bearing livers of rabbits. The ultrasound-guided surgery is operated using the conventional double- and newly devised single-needle bipolar electrodes. Finite element analysis is also introduced to simulate the E distribution in the practical treatments. Two- and three-dimensional investigations are performed on the image measurements and reconstructed calcification models on micro-CT, respectively. Specially, an algorithm considering the model surface, volume and shape is employed to compare the similarities between the simulative and experimental models. Blood vessel injury, temperature and synergistic efficacy with doxorubicin (DOX) are also investigated. According to the three-dimensional calculation, the overall E threshold is 4536.4 ± 618.2 V/cm and the single-needle bipolar electrode is verified to be effective in tissue ablation. Vessels are well preserved and the increment of temperature is limited. Synergy of RnsPEF and DOX shows increased apoptosis and improved long-term tumor survival. Our study presents a prospective strategy for the evaluation of the lethal E threshold, which can be considered to guide the future clinical treatment planning for RnsPEF.

High-frequency irreversible electroporation improves survival and immune cell infiltration in rodents with malignant gliomas

Background

Irreversible electroporation (IRE) has been previously investigated in preclinical trials as a treatment for intracranial malignancies. Here, we investigate next generation high-frequency irreversible electroporation (H-FIRE), as both a monotherapy and a combinatorial therapy, for the treatment of malignant gliomas.

Methods

Hydrogel tissue scaffolds and numerical modeling were used to inform in-vivo H-FIRE pulsing parameters for our orthotopic tumor-bearing glioma model. Fischer rats were separated into five treatment cohorts including high-dose H-FIRE (1750V/cm), low-dose H-FIRE (600V/cm), combinatorial high-dose H-FIRE + liposomal doxorubicin, low-dose H-FIRE + liposomal doxorubicin, and standalone liposomal doxorubicin groups. Cohorts were compared against a standalone tumor-bearing sham group which received no therapeutic intervention. To further enhance the translational value of our work, we characterize the local and systemic immune responses to intracranial H-FIRE at the study timepoint.

Results

The median survival for each cohort are as follows: 31 days (high-dose H-FIRE), 38 days (low-dose H-FIRE), 37.5 days (high-dose H-FIRE + liposomal doxorubicin), 27 days (low-dose H-FIRE + liposomal doxorubicin), 20 days (liposomal doxorubicin), and 26 days (sham). A statistically greater overall survival fraction was noted in the high-dose H-FIRE + liposomal doxorubicin (50%, p = 0.044), high-dose H-FIRE (28.6%, p = 0.034), and the low-dose H-FIRE (20%, p = 0.0214) compared to the sham control (0%). Compared to sham controls, brain sections of rats treated with H-FIRE demonstrated significant increases in IHC scores for CD3+ T-cells (p = 0.0014), CD79a+ B-cells (p = 0.01), IBA-1+ dendritic cells/microglia (p = 0.04), CD8+ cytotoxic T-cells (p = 0.0004), and CD86+ M1 macrophages (p = 0.01).

Conclusions

H-FIRE may be used as both a monotherapy and a combinatorial therapy to improve survival in the treatment of malignant gliomas while also promoting the presence of infiltrative immune cells.

Multifunctional ferromagnetic fiber robots for navigation, sensing, and treatment in minimally invasive surgery

Small-scale robots capable of remote active steering and navigation offer great potential for biomedical applications. However, the current design and manufacturing procedure impede their miniaturization and integration of various diagnostic and therapeutic functionalities. Here, we present a robotic fiber platform for integrating navigation, sensing, and therapeutic functions at a submillimeter scale. These fiber robots consist of ferromagnetic, electrical, optical, and microfluidic components, fabricated with a thermal drawing process. Under magnetic actuation, they can navigate through complex and constrained environments, such as artificial vessels and brain phantoms. Moreover, we utilize Langendorff mouse hearts model, glioblastoma microplatforms, and in vivo mouse models to demonstrate the capabilities of sensing electrophysiology signals and performing localized treatment. Additionally, we demonstrate that the fiber robots can serve as endoscopes with embedded waveguides. These fiber robots provide a versatile platform for targeted multimodal detection and treatment at hard-to-reach locations in a minimally invasive and remotely controllable manner.

Effects of Ultra-Short Pulsed Electric Field Exposure on Glioblastoma Cells

Glioblastoma multiforme (GBM) is the most common brain cancer in adults. GBM starts from a small fraction of poorly differentiated and aggressive cancer stem cells (CSCs) responsible for aberrant proliferation and invasion. Due to extreme tumor heterogeneity, actual therapies provide poor positive outcomes, and cancers usually recur. Therefore, alternative approaches, possibly targeting CSCs, are necessary against GBM. Among emerging therapies, high intensity ultra-short pulsed electric fields (PEFs) are considered extremely promising and our previous results demonstrated the ability of a specific electric pulse protocol to selectively affect medulloblastoma CSCs preserving normal cells. Here, we tested the same exposure protocol to investigate the response of U87 GBM cells and U87-derived neurospheres. By analyzing different in vitro biological endpoints and taking advantage of transcriptomic and bioinformatics analyses, we found that, independent of CSC content, PEF exposure affected cell proliferation and differentially regulated hypoxia, inflammation and P53/cell cycle checkpoints. PEF exposure also significantly reduced the ability to form new neurospheres and inhibited the invasion potential. Importantly, exclusively in U87 neurospheres, PEF exposure changed the expression of stem-ness/differentiation genes. Our results confirm this physical stimulus as a promising treatment to destabilize GBM, opening up the possibility of developing effective PEF-mediated therapies.

Employing Novel Porcine Models of Subcutaneous Pancreatic Cancer to Evaluate Oncological Therapies

Immunocompromised mice are commonly utilized to study pancreatic cancer and other malignancies. The ability to xenograft tumors in either subcutaneous or orthotopic locations provides a robust model to study diverse biological features of human malignancies. However, there is a dire need for large animal models that better recapitulate human anatomy in terms of size and physiology. These models will be critical for biomedical device development, surgical optimization, and drug discovery. Here, we describe the generation and application of immunocompromised pigs lacking RAG2 and IL2RG as a novel model for human xenograft studies. These SCID-like pigs closely resemble NOD scid gamma mice and are receptive to human tumor tissue, cell lines, and organoid xenografts. However, due to their immunocompromised nature, these immunocompromised animals require housing and maintenance under germfree conditions. In this protocol, we describe the use of these pigs in a subcutaneous tumor injection study with human PANC1 cells. The tumors demonstrate a steady, linear growth curve, reaching 1.0 cm within 30 days post injection. The model described here is focused on subcutaneous injections behind the ear. However, it is readily adaptable for other locations and additional human cell types.

An in vivo study of a custom-made high-frequency irreversible electroporation generator on different tissues for clinically relevant ablation zones

PURPOSE

To examine the ablation zone, muscle contractions, and temperature increases in both rabbit liver and kidney models in vivo for a custom-made high-frequency irreversible electroporation (H-FIRE) generator.

MATERIALS AND METHODS

A total of 18 New Zealand white rabbits were used to investigate five H-FIRE protocols (n = 3 for each protocol) and an IRE protocol (n = 3) for the performance of the designed H-FIRE device in both liver and kidney tissues. The ablation zone was determined by using histological analysis 72 h after treatment. The extent of muscle contractions and temperature change during the application of pulse energy were measured by a commercial accelerometer attached to animals and fiber optic temperature probe inserted into organs with IRE electrodes, respectively.

RESULTS

All H-FIRE protocols were able to generate visible ablation zones without muscle contractions, for both liver and kidney tissues. The area of ablation zone generated in H-FIRE pulse protocols (e.g., 0.3-1 μs, 2000 V, and 90-195 bursts) appears similar to that of IRE protocol (100 μs, 1000 V, and 90 pulses) in both liver and kidney tissues. No significant temperature increase was noticed except for the protocol with the highest pulse energy (e.g., 1 μs, 2000 V, and 180 bursts).

CONCLUSION

Our work serves to complement the current H-FIRE pulse waveforms, which can be optimized to significantly improve the quality of ablation zone in terms of precision for liver and kidney tumors in clinical setting.

Combination of Irreversible Electroporation and STING Agonist for Effective Cancer Immunotherapy

Recently, cancer immunotherapy has received attention as a viable solution for the treatment of refractory tumors. However, it still has clinical limitations in its treatment efficacy due to inter-patient tumor heterogeneity and immunosuppressive tumor microenvironment (TME). In this study, we demonstrated the triggering of anti-cancer immune responses by a combination of irreversible electroporation (IRE) and a stimulator of interferon genes (STING) agonist. Optimal electrical conditions inducing damage-associated molecular patterns (DAMPs) by immunogenic cell death (ICD) were determined through in vitro 2D and 3D cell experiments. In the in vivo syngeneic lung cancer model, the combination of IRE and STING agonists demonstrated significant tumor growth inhibition. We believe that the combination strategy of IRE and STING agonists has potential for effective cancer immunotherapy.

Differential Cell Death and Regrowth of Dermal Fibroblasts and Keratinocytes After Application of Pulsed Electric Fields

Background: High-powered pulsed electric fields (PEF) may be used for tissue debridement and disinfection, while lower PEF intensities may stimulate beneficial cellular responses for wound healing. We investigated the dual effects of nonuniform PEF on cellular death and stimulation. Methods: Dermal fibroblast or keratinocyte monolayers were exposed to PEF induced by two needle electrodes (2 mm apart). Voltages (100-600 V; 1 Hz; 70 micros pulse width; 90 pulses/cycle) were applied between the two electrodes. Controls consisted of similar monolayers subjected to a scratch mechanical injury. Results: Cell growth and closure of the cell-free gap was faster in PEF-treated cell monolayers versus scratched ones. Media conditioned from cells pre-exposed to PEF, when applied to responder cells, stimulated greater proliferation than media from scratched monolayers. Conclusions: PEF treatment causes the release of soluble factors that promote cell growth, and thus may play a role in the accelerated healing of wounds post PEF.

Temporal Characterization of Blood-Brain Barrier Disruption with High-Frequency Electroporation

Treatment of intracranial disorders suffers from the inability to accumulate therapeutic drug concentrations due to protection from the blood–brain barrier (BBB). Electroporation-based therapies have demonstrated the capability of permeating the BBB, but knowledge of the longevity of BBB disruption (BBBD) is limited. In this study, we quantify the temporal, high-frequency electroporation (HFE)-mediated BBBD in an in vivo healthy rat brain model. 40 male Fisher rats underwent HFE treatment; two blunt tipped monopolar electrodes were advanced into the brain and 200 bursts of HFE were delivered at a voltage-to-distance ratio of 600 V/cm. BBBD was verified with contrast enhanced T1W MRI (gadopentetate dimeglumine) and pathologically (Evans blue dye) at time points of 1, 24, 48, 72, and 96 h after HFE. Contrast enhanced T1W scans demonstrated BBBD for 1 to 72 h after HFE but intact BBB at 96 h. Histologically, tissue damage was restricted to electrode insertion tracks. BBBD was induced with minimal muscle contractions and minimal cell death attributed to HFE. Numerical modeling indicated that brief BBBD was induced with low magnitude electric fields, and BBBD duration increased with field strength. These data suggest the spatiotemporal characteristics of HFE-mediated BBBD may be modulated with the locally applied electric field.