Transfection by Electroporation of Cancer and Primary Cells Using Nanosecond and Microsecond Electric Fields.

Gene transfer into primary immune cells as well as into cell lines is essential for scientific and therapeutical applications. One of the methods used for gene transfer is electroporation (EP). EP is a method where a pulsed electric field (PEF) causes a highly transient permeability of the targeted cell membrane. In this work, we present the electrotransfection of CHO-K1, 4T1 cell lines, and primary murine DCs with detectable protein-encoding plasmids in the sub-microsecond range. Microsecond (µs)- and nanosecond (ns)-range pulsed electric field transfection protocols were used. The efficiency of electrotransfection was evaluated using green fluorescent protein (GFP)-encoding plasmids (4.7 kbp; p-EGFP-N1) and plasmids expressing a firefly luciferase and red fluorescent protein (tdTomato) (8.5 kbp; pcDNA3.1(+)/Luc2 = tdT)). It was shown that the used nsPEFs protocol (7 kV/cm × 300 ns × 100, 1 MHz) ensured a better transfection efficiency than µsPEFs (1.2 kV/cm × 100 µs × 8, 1 Hz). Plasmid size and concentration had a strong impact on the cell transfection efficiency too. We also showed that there were no significant differences in transfection efficiency between immature and mature DCs. Finally, the nsPEF protocols were successfully applied for the stable transfection of the CHO-K1 cell line with the linearized pcDNA3.1(+)/Luc2 = tdT plasmid. The results of the study are applicable in gene therapy and DNA vaccination studies for the derivation of optimal electrotransfection conditions.

Nanosecond electrochemotherapy using bleomycin or doxorubicin: Influence of pulse amplitude, duration and burst frequency.

Electroporation is a pulsed electric field (PEF) induced phenomenon, which effectiveness varies dependent on pulse parameters. This work focuses on nano-electrochemotherapy with bleomycin and doxorubicin to derive protocols as effective as European Standard Operating Procedures on Electrochemotherapy (ESOPE), which employ conventional microsecond range pulses. As a model, murine Lewis lung carcinoma (LLC1) cell line was used. The effects of pulse duration (100-500 ns), PEF amplitude (6-10 kV/cm) and pulse repetition frequency (10 kHz, 100 kHz, 1 MHz) were studied. A total of 75 ns protocol variations have been used. For detection of cell permeabilization, Yo-Pro-1 and flow cytometry were employed. Cell viability was evaluated 24-, 48-, or 72-hours post-electroporation. Nanosecond parametric protocols resulting in comparable treatment efficiency as ESOPE (1.3 kV/cm × 100 µs × 8) have been proposed. It was shown that high-frequency nanosecond electrochemotherapy with bleomycin or doxorubicin could be an alternative for established ESOPE protocols.

Bioluminescent calcium mediated detection of nanosecond electroporation: Grasping the differences between 100 ns and 100 µs pulses.

Electroporation is a phenomenon of transient or irreversible permeabilization of the cell membrane after pulsed electric field treatment. Fluorescent probes are frequently used to assess the extent of permeabilization, however, as an alternative, a D-luciferin oxidation-based method can be used. In this work, we have used sequences of a microsecond (1.3 kV/cm × 100 µs) and nanosecond (12.5 kV/cm × 100 ns) pulses to trigger various levels of cell permeabilization and assessed the differences in the response using a conventional fluorescent probe (YO-PRO-1 (YP)) and D-luciferin oxidation methodology. The nanosecond pulses (n = 5-100) have been delivered with 1 kHz repetition frequency, and the results were compared with 1 MHz protocols. Additionally, the effects of extracellular Ca2+ have been assessed. Various concentrations of CaCl2 (2, 5, and 10 mM) have been used, and it was shown that the bioluminescence of the cells after electroporation depends on extracellular calcium concentration. It was shown that the changes in bioluminescence signal could be used as a marker of cell membrane permeabilization on par with YP assay when calcium is added and thus, effectively employed for analysis of electroporation phenomenon in vitro both for nanosecond and microsecond pulses.

High-Frequency Nanosecond Bleomycin Electrochemotherapy and its Effects on Changes in the Immune System and Survival.

In this work, a time-dependent and time-independent study on bleomycin-based high-frequency nsECT (3.5 kV/cm × 200 pulses) for the elimination of LLC1 tumours in C57BL/6J mice is performed. We show the efficiency of nsECT (200 ns and 700 ns delivered at 1 kHz and 1 MHz) for the elimination of tumours in mice and increase of their survival. The dynamics of the immunomodulatory effects were observed after electrochemotherapy by investigating immune cell populations and antitumour antibodies at different timepoints after the treatment. ECT treatment resulted in an increased percentage of CD4+ T, splenic memory B and tumour-associated dendritic cell subsets. Moreover, increased levels of antitumour IgG antibodies after ECT treatment were detected. Based on the time-dependent study results, nsECT treatment upregulated PD 1 expression on splenic CD4+ Tr1 cells, increased the expansion of splenic CD8+ T, CD4+CD8+ T, plasma cells and the proportion of tumour-associated pro inflammatory macrophages. The Lin- population of immune cells that was increased in the spleens and tumour after nsECT was identified. It was shown that nsECT prolonged survival of the treated mice and induced significant changes in the immune system, which shows a promising alliance of nanosecond electrochemotherapy and immunotherapy.

Effects of Time Delay Between Unipolar Pulses in High Frequency Nano-Electrochemotherapy.

OBJECTIVE: this work focuses on bleomycin electrochemotherapy using new modality of high repetition frequency unipolar nanosecond pulses. METHODS: As a tumor model, Lewis lung carcinoma (LLC1) cell line in C57BL mice (n = 42) was used. Electrochemotherapy was performed with intertumoral injection of bleomycin (50 µL of 1500 IU solution) followed by nanosecond and microsecond range electrical pulse delivery via parallel plate electrodes. The 3.5 kV/cm pulses of 200 and 700 ns were delivered in a burst of 200 at frequencies of 1 kHz and 1 MHz. For comparison of treatment efficiency, a standard 1.3 kV/cm x 100 µs x 8 protocol was used. RESULTS: It was shown that it is possible to manipulate the efficacy of unipolar sub-microsecond electrochemotherapy solely by the time delay between the pulses. SIGNIFICANCE: the results suggest that the sub-microsecond range pulses can be as effective as the protocols in European Standard Operating Procedures on Electrochemotherapy (ESOPE) using 100 µs pulses.