Predicting electrotransfer in ultra-high frequency sub-microsecond square wave electric fields

Basic Principles of RNA Interference: Nucleic Acid Types and In Vitro Intracellular Delivery Methods

Since its discovery in 1989, RNA interference (RNAi) has become a widely used tool for the in vitro downregulation of specific gene expression in molecular biological research. This basically involves a complementary RNA that binds a target sequence to affect its transcription or translation process. Currently, various small RNAs, such as small interfering RNA (siRNA), micro RNA (miRNA), small hairpin RNA (shRNA), and PIWI interacting RNA (piRNA), are available for application on in vitro cell culture, to regulate the cells' gene expression by mimicking the endogenous RNAi-machinery. In addition, several biochemical, physical, and viral methods have been established to deliver these RNAs into the cell or nucleus. Since each RNA and each delivery method entail different off-target effects, limitations, and compatibilities, it is crucial to understand their basic mode of action. This review is intended to provide an overview of different nucleic acids and delivery methods for planning, interpreting, and troubleshooting of RNAi experiments.

Improving NonViral Gene Delivery Using MHz Bursts of Nanosecond Pulses and Gold Nanoparticles for Electric Field Amplification

Gene delivery by the pulsed electric field is a promising alternative technology for nonviral transfection; however, the application of short pulses (i.e., nanosecond) is extremely limited. In this work, we aimed to show the capability to improve gene delivery using MHz frequency bursts of nanosecond pulses and characterize the potential use of gold nanoparticles (AuNPs: 9, 13, 14, and 22 nm) in this context. We have used bursts of MHz pulses 3/5/7 kV/cm × 300 ns × 100 and compared the efficacy of the parametric protocols to conventional microsecond protocols (100 µs × 8, 1 Hz) separately and in combination with nanoparticles. Furthermore, the effects of pulses and AuNPs on the generation of reactive oxygen species (ROS) were analyzed. It was shown that gene delivery using microsecond protocols could be significantly improved with AuNPs; however, the efficacy is strongly dependent on the surface charge of AuNPs and their size. The capability of local field amplification using AuNPs was also confirmed by finite element method simulation. Finally, it was shown that AuNPs are not effective with nanosecond protocols. However, MHz protocols are still competitive in the context of gene delivery, resulting in low ROS generation, preserved viability, and easier procedure to trigger comparable efficacy.

Does the shape of the electric pulse matter in electroporation?

Electric pulses are widely used in biology, medicine, industry, and food processing. Numerous studies indicate that electroporation (EP) is a pulse-dependent process, and the electric pulse shape and duration strongly determine permeabilization efficacy. EP protocols are precisely planned in terms of the size and charge of the molecules, which will be delivered to the cell. In reversible and irreversible EP applications, rectangular or sine, polar or bipolar pulses are commonly used. The usage of pulses of the asymmetric shape is still limited to high voltage and low voltage (HV/LV) sequences in the context of gene delivery, while EP-based applications of ultra-short asymmetric pulses are just starting to emerge. This review emphasizes the importance and role of the pulse shape for membrane permeabilization by EP.

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

This work focuses on bleomycin electrochemotherapy using new modality of high repetition frequency unipolar nanosecond pulses. 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 L 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 s x 8 protocol was used. It was shown that it is possible to manipulate the efficacy of unipolar sub-microsecond electrochemotherapy solely by the time delay between the pulses. Also, 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 s pulses.

Sub-microsecond electrotransfection using new modality of high frequency electroporation

Micro-millisecond range electric field pulses have been used for decades to facilitate DNA transfer into cells and tissues, while the growing number of clinical trials underline the strong potential of DNA electroporation. In this work, we present new sub-microsecond range protocols and methodology enabling successful electrotransfection in the sub-microsecond range. To facilitate DNA transfer, a 3 kV/60 A and high frequency (1 MHz) sub-microsecond range square wave generator was applied in the study. As a model, Chinese hamster ovary (CHO-K1) cells were used. Sub-microsecond range (300-700 ns) high frequency pulsed electric fields of 2-15 kV/cm were applied. The efficiency of electrotransfection was evaluated using two green fluorescent protein encoding plasmids of different size (3.5 kbp and 4.7 kbp). It was shown that transfection efficiency cannot be effectively improved with increase of the number of pulses after a certain threshold, however, independently on the plasmid size, the proposed sub-microsecond range pulsing methodology (2-5 kV/cm; n = 250) efficiency-wise was equivalent to 1.5 kV/cm × 100 μs × 4 electroporation procedure. The results of the study are useful for further development of in vitro and in vivo methods for effective electrotransfer of DNA using shorter pulses.