Optimization of cutaneous electrically mediated plasmid DNA delivery using novel electrode

The easy accessibility of skin makes it an excellent target for gene transfer protocols. To take advantage of skin as a target for gene transfer, it is important to establish an efficient and reproducible delivery system. Electroporation is an established technique for enhancing plasmid delivery to many tissues in vivo. A critical component of this technique is the electrode configuration. Electroporation parameters were optimized for transgene expression with minimal tissue damage with a novel electrode. The highest transgene expression and efficiency of individual cell transformation with minimal damage was produced with eight 150 ms pulses at field strength of 100 V/cm. This electrode design offers the potential for easier and more reproducible electrically mediated cutaneous plasmid delivery than the simple electrodes currently commercially available. This electrode can be a valuable tool in determining the applicability of electrically mediated cutaneous gene transfer.

In vivo electroporation using an exponentially enhanced pulse: a new waveform

In vivo electroporation is currently accomplished by one of two types of common waveforms: exponential decay or square-wave pulses. The purpose of this report is to present a new electroporation waveform, the exponentially enhanced pulse (EEP). Pulsing protocols including the EEP resulted in high levels of luciferase expression in muscle and skin, equal to or greater than expression resulting from low-voltage, millisecond square-wave pulses. This high level of expression requires fewer pulses when using an EEP protocol. Therefore, similar or greater plasmid DNA expression levels are obtained using fewer pulses with the EEP protocol than with current protocols. This is the first report of this new waveform and shows the success of using protocols employing the EEP to deliver plasmid DNA to various tissue types.

Effects of electrochemotherapy with bleomycin on normal liver tissue in a rat model

Preliminary studies that used electric pulses in vivo to facilitate entry of chemotherapeutic agents into tumour cells resulted in a 69% complete response rate for hepatocellular carcinoma in rats. This success motivated a focused investigation to define the adverse effects of this treatment on normal liver tissue. Bleomycin doses ranging from 0.5 to 2.5 U and electric fields from 500 to 2250 V/cm were investigated. Electrical treatment was administered using an array of six needles arranged in a circular pattern. Necrosis and four other histological parameters were examined 14 and 56 days after treatment. Results indicated that treatment effects were localised to the volume of treated tissue. These parameters, at both time points, were not significantly altered for liver tissue that was treated with all drug doses and electric fields of 1250 V/cm and below. Only the combination of more intense electric pulses with bleomycin produced adverse histological events in the form of localised liver necrosis at day 14. These effects were not visible at day 56. Liver function was normal through all of the treatment except for an elevation of several enzymes 1 day post-treatment.

Treatment of hepatocellular carcinoma in a rat model using electrochemotherapy

The effectiveness of antineoplastic agents has been augmented by applying pulsed electric fields directly to tumours after the administration of the drug. This treatment, known as electrochemotherapy (ECT), has been successful for cutaneous malignancies in animal models and in recent clinical trials. This study was aimed at investigating the applicability of ECT in a surgical setting for hepatocellular carcinomas induced in the livers of rats. Established tumours were injected with bleomycin, and electric pulses were then administered locally. Animals were followed based on tumour volumes and histological samples. Dose response data were obtained for both electric field intensity and bleomycin. Complete response rates for animals treated with electrochemotherapy ranged from 26.67% to 93.33 and were durable. In contrast, tumours that received no treatment, pulses only or drug only responded minimally. This supports the feasibility of using a ECT as a modality for treating hepatocellular carcinoma.

Intradermal delivery of interleukin-12 plasmid DNA by in vivo electroporation

Gene therapy depends on safe and efficient gene delivery. The skin is an attractive target for gene delivery because of its accessibility. Recently, in vivo electroporation has been shown to enhance expression after injection of plasmid DNA. In this study, we examined the use of electroporation to deliver plasmid DNA to cells of the skin in order to demonstrate that localized delivery can result in increased serum concentrations of a specific protein. Intradermal injection of a plasmid encoding luciferase resulted in low levels of expression. However, when injection was combined with electroporation, expression was significantly increased. When performing this procedure with a plasmid encoding interleukin-12, the induced serum concentrations of gamma-interferon were as much as 10 fold higher when electroporation was used. The results presented here demonstrate that electroporation can be used to augment the efficiency of direct injection of plasmid DNA to skin.

In vivo electroporation of plasmids encoding GM-CSF or interleukin-2 into existing B16 melanomas combined with electrochemotherapy induces long-term antitumour immunity

When cancer cells, including melanoma cells, are genetically altered to secrete cytokines, irradiated and injected into subjects, long-term antitumour immunity is induced. Optimally, existing melanomas induced to produce cytokines in vivo could stimulate this same immune response. Although in vivo electroporation enhances plasmid expression, electroporation of plasmids encoding granulocyte-monocyte colony stimulating factor (GM-CSF) and interleukin-2 (IL2) into B16 mouse melanomas did not significantly alter tumour growth at the concentration tested. Electrochemotherapy, which causes short-term, complete regressions of treated tumour but no resistance to challenge, was combined with plasmid delivery. The combination treatment resulted in the induction of long-term immunity to recurrence and resistance to challenge in up to 25% of mice.

Theory and in vivo application of electroporative gene delivery

Efficient and safe methods for delivering exogenous genetic material into tissues must be developed before the clinical potential of gene therapy will be realized. Recently, in vivo electroporation has emerged as a leading technology for developing nonviral gene therapies and nucleic acid vaccines (NAV). Electroporation (EP) involves the application of pulsed electric fields to cells to enhance cell permeability, resulting in exogenous polynucleotide transit across the cytoplasmic membrane. Similar pulsed electrical field treatments are employed in a wide range of biotechnological processes including in vitro EP, hybridoma production, development of transgenic animals, and clinical electrochemotherapy. Electroporative gene delivery studies benefit from well-developed literature that may be used to guide experimental design and interpretation. Both theory and experimental analysis predict that the critical parameters governing EP efficacy include cell size and field strength, duration, frequency, and total number of applied pulses. These parameters must be optimized for each tissue in order to maximize gene delivery while minimizing irreversible cell damage. By providing an overview of the theory and practice of electroporative gene transfer, this review intends to aid researchers that wish to employ the method for preclinical and translational gene therapy, NAV, and functional genomic research.

Electrically mediated plasmid DNA delivery to hepatocellular carcinomas in vivo

Gene therapy by direct delivery of plasmid DNA has several advantages over viral gene transfer, but plasmid delivery is less efficient. In vivo electroporation has been used to enhance delivery of chemotherapeutic agents to tumors in both animal and human studies. Recently, this delivery technique has been extended to large molecules such as plasmid DNA. Here, the successful delivery of plasmids encoding reporter genes to rat hepatocellular carcinomas by in vivo electroporation is demonstrated.

Toxicity of anticancer agents mediated by electroporation in vitro

Electroporation is a physical event that temporarily reduces cell membrane barrier properties. Diminished membrane barrier properties are achieved by exposing cells to pulsed electric fields. When a cell has been treated with electric fields it is possible for extracellular agents to gain access to the cell interior. This process has been used in vivo to increase the uptake of chemotherapeutic agents by tumor cells which results in dramatically higher response rates than when drug is used alone. This type of treatment is called electrochemotherapy (ECT); bleomycin is most often used as the drug for this type of treatment. It was hypothesized that electroporation could be used to augment the cytotoxicity of other anticancer agents. Therefore, this study was performed in order to screen 44 different combinations of drug and cell type in vitro to identify drugs that may have higher cytotoxicity when combined with electroporation. Results from seven cell types indicate that the IC50 of bleomycin can be reduced by a factor of 100-5000 when electroporation is used to facilitate internalization. The IC50 values of cisplatin and carboplatin could be reduced by factors ranging from 3 to 13 in six different cell lines as a result of electroporation. These IC50 reductions in multiple cell lines suggest that cisplatin and carboplatin may be effective in vivo as part of ECT treatment.

Delivery of genes in vivo using pulsed electric fields

The first research that focused on the effects of pulsed electric fields on living cells described the phenomena of reversible and irreversible membrane breakdown in an in vitro environment in the 1960s and 1970s (1-6). This early research led to the current understanding that exposing cells to intense electric fields induces a transmembrane potential that is superposed on the resting potential. Induced potentials of sufficient magnitude cause a dielectric breakdown of the membrane. This physical phenomenon was termed electroporation, or electropermeabilization, because it was observed that molecules that do not normally pass through the membrane gain intracellular access after the cells were treated with electric fields.

Electrically mediated drug delivery for treating subcutaneous and orthotopic pancreatic adenocarcinoma in a hamster model

BACKGROUND

Current therapies for pancreatic adenocarcinoma only benefit a fraction of those diagnosed with this disease. New strategies for improving treatment are clearly needed. This study investigated the use of electrically mediated drug delivery for the treatment of pancreatic adenocarcinoma in a hamster model.

MATERIALS AND METHODS

Hamster PC-1 pancreatic adenocarcinoma cells and Golden Syrian hamsters were used as a model.

RESULTS

In vitro testing indicated that bleomycin was more effective than Cisplatin and Doxorubicin when delivered using pulsed electric fields. Treatment of subcutaneous tumors with bleomycin and electric fields resulted in a 100 percent complete response rate. No effect was observed when either drug or pulses were used alone. Treatment of tumors induced in the gland resulted in a 25 percent complete response rate.

CONCLUSIONS

Electrochemotherapy was highly effective for subcutaneous tumors. There was also a significant antitumor effect for the more complex and clinically relevant intraoperative treatment of tumors in the pancreas.

Fundamentals of flow cytometry

Flow cytometers are instruments that are used primarily to measure the physical and biochemical characteristics of biological particles. This technology is used to perform measurements on whole cells as well as prepared cellular constituents, such as nuclei and organelles. Flow cytometers are investigative tools for a broad range of scientific disciplines because they make measurements on thousands of individual cells/particles in a matter of seconds. This is a unique advantage relative to other detection instruments that provide bulk particle measurements. Flow cytometry is a complex and highly technical field; therefore, a basic understanding of the technology is essential for all users. The purpose of this article is to provide fundamental information about the instrumentation used for flow cytometry as well as the methods used to analyze and interpret data. This information will provide a foundation to use flow cytometry effectively as a research tool.

Electrically enhanced drug delivery for the treatment of soft tissue sarcoma

BACKGROUND

Pulsed electric fields have been shown to increase the effectiveness of antineoplastic agents by temporarily increasing the permeability of cell membranes. This type of drug delivery is called electrochemotherapy, and it has been successful in the treatment of patients with cutaneous malignancies in clinical trials. This study focused on determining the applicability of electrochemotherapy to the treatment of soft tissue sarcoma, using an animal model bearing human sarcomas. The antitumor effects of single and multiple electrochemotherapy treatments were investigated using small (250 mm3) and large (4000 mm3) tumors.

METHODS

Established tumors were injected with bleomycin, then electric pulses were administered to the tumor site. Animals were followed based on periodic tumor volume determinations, which were used to categorize treatment of each tumor as a complete response, a partial response, stable disease, or progressive disease. Histologic analysis was used to confirm response data.

RESULTS

Animals were randomly assigned to one of four different treatment groups. These groups received no treatment, drug only, electric pulses only, or drug combined with electric pulses. A single electrochemotherapy treatment protocol for small tumors resulted in a 100% complete response rate and a 41.7% cure rate. Multiple treatments of small and large tumors resulted in complete response rates of 83.3% and 100%, respectively. These responses were identical to the cure rates. In contrast, tumors in the groups that received no treatment, electric pulses only, and drug only progressed for both single treatment and multiple treatment scenarios, regardless of tumor size.

CONCLUSIONS

In this study, a single electrochemotherapy treatment had a strong cytoreductive effect on small tumors that lasted approximately 35 days, until recurrences began. Multiple treatment of small and large tumors resulted in high complete response rates that lasted at least 100 days after treatment. This indicates the feasibility of electrochemotherapy as a modality of limb-preserving treatment for patients with sarcoma of the extremities.

In vivo gene delivery by electroporation

The physical phenomenon of electroporation has been successfully exploited in vitro for the delivery of genes, drugs, and other molecules with increasing frequency over the past two decades. This type of electrically mediated delivery has been translated into an in vivo setting in more recent years with a focus on therapeutic molecules. One promising area is the delivery of genes as a therapy.Advances in molecular medicine have produced a very large amount of information about genes that translate to therapeutic molecules when expressed in living cells. Current standard methods for transferring genes utilize viruses to deliver DNA into cells. These viral methods have not yielded optimal results in most cases. Therefore, there is an increasing interest in nonviral methods for gene delivery. In vivo electrically mediated gene delivery is an attractive alternative because of the site specific nature of delivery as well as the universal applicability of electroporation. A review of the studies performed to investigate and develop this new gene delivery technology is presented.

Basics of flow cytometry

In summary, a beginner requires fundamental knowledge about flow cytometric instrumentation in order to effectively use this technology. It is important to remember that flow cytometers are very complex instruments that are composed of four closely related systems. The fluidic system transports particles from a suspension through the cytometer for interrogation by an illumination system. The resulting light scattering and fluorescence is collected, filtered, and converted into electrical signals by the optical and electronics system. The data storage and computer control system saves acquired data and is also the user interface for controlling most instrument functions. These four systems provide a very unique and powerful analytical tool for researchers and clinicians. This is because they analyze the properties of individual particles, and thousands of particles can be analyzed in a matter of seconds. Thus, data for a flow cytometric sample are a collection of many measurements instead of a single bulk measurement. Basic knowledge of instrumentation is a tremendous aid to designing experiments that can be successfully analyzed using flow cytometry. For example, it is important to know the emission wavelength of the laser in the instrument that will be used for analysis. This wavelength is critical knowledge for selecting probes. It is also important to understand that a different range of wavelengths is detected for each fluorescent channel. This will aid selection of probes that are compatible with the flow cytometer. Understanding the complication that emission spectra overlap contributes to detection can be used to guide fluorochrome selections for multicolor analysis. All of these experiment design considerations that rely on knowledge of how flow cytometers work are a very practical and effective means of avoiding wasted time, energy, and costly reagents. Data analysis is a paramount issue in flow cytometry. Analysis includes interpreting as well as presenting data that has been stored in list-mode files. Data analysis is very graphically oriented. There are a number of types of graphic representation that are available to visually aid data analysis. Two standard types of displays are used. These data plots are one-parameter histograms and bivariate plots. A user must be familiar with these two fundamental types of display in order to effectively analyze data. Histograms are the most simple modes of data representation. Histograms allow visualization of a single acquired parameter. Mean fluorescence and distributional statistics can be obtained based on markers that the user can graphically set on the plot. Percentages of positively expressing particles relative to a control sample can also obtained in a similar manner. In addition, multiple histograms can be overlayed on one another to depict qualitative and quantitative differences in two or more samples. Two-parameter data plots are somewhat more complicated than histograms; however, they can yield more information. Two-parameter dot plots of FSC vs SSC allow visualization of both light-scattering parameters that are important for identifying populations of interest. Bivariate fluorescent plots allow discrimination of dual-labeled populations that might remain hidden if histograms were used to display fluorescent data. Two-parameter plots that combine one light-scattering parameter and a fluorescent parameter are useful for analyzing control samples to elucidate the origin of nonspecific binding. Data analysis is very graphically oriented. Experience and pattern recognition become important when using two-parameter data plots for qualitative as well as quantitative analysis. The technique of gating or drawing regions on dual parameter light-scatter plots allows one to exclude information and examine the population of interest by disallowing particles that might confound or interfere with analysis. This is one of the fundamental uses for gating. (ABSTRACT TRUNCATED)

Treatment of cutaneous and subcutaneous tumors with electrochemotherapy using intralesional bleomycin

BACKGROUND

Electrochemotherapy (ECT) is performed by locally administering a chemotherapeutic agent in combination with electric pulses. Previous clinical studies have demonstrated the effectiveness of ECT. In these initial trials, the drug was administered intravenously, followed by administration of electric pulses directly to the tumor. This study was initiated to determine whether an intralesional injection of the drug in combination with electric pulses could provide an improved result. A group of 34 patients was studied.

METHODS

The dose of intralesional bleomycin was based on tumor volume. This was followed 10 minutes later by 6 or 8 99-microsec pulses of electricity at an amplitude of 1.3 kV/cm. Both the bleomycin and the electric pulses were administered after 1% lidocaine with epinephrine solution was injected around the treatment site.

RESULTS

All patients responded to the treatment. Responses were observed in 142 (99%) of 143 metastatic nodules or primary tumors within 12 weeks, with complete responses observed in 130 (91%) of the nodules. No complete responses were observed in nodules treated with bleomycin only or electric pulses only. Random biopsies confirmed the clinical findings. All patients tolerated the procedure well, and no significant side effects were noted. Muscle contraction was evident during administration of each electric pulse but promptly subsided after the pulse.

CONCLUSIONS

ECT was shown to be an effective local treatment for cutaneous malignancies. The results suggest that ECT may have a tissue-sparing effect and result in minimal scarring. ECT may be a suitable alternative therapy for the treatment of basal cell carcinoma, local or regional recurrent melanoma, and other skin cancers.

Effective treatment of cutaneous and subcutaneous malignant tumours by electrochemotherapy

Electrochemotherapy (ECT) enhances the effectiveness of chemotherapeutic agents by administering the drug in combination with short intense electric pulses. ECT is effective because electric pulses permeabilize tumour cell membranes and allow non-permeant drugs, such as bleomycin, to enter the cells. The aim of this study was to demonstrate the anti-tumour effectiveness of ECT with bleomycin on cutaneous and subcutaneous tumours. This article summarizes results obtained in independent clinical trials performed by five cancer centres. A total of 291 cutaneous or subcutaneous tumours of basal cell carcinoma (32), malignant melanoma (142), adenocarcinoma (30) and head and neck squamous cell carcinoma (87) were treated in 50 patients. Short and intense electric pulses were applied to tumours percutaneously after intravenous or intratumour administration of bleomycin. The tumours were measured and the response to the treatment evaluated 30 days after the treatment. Objective responses were obtained in 233 (85.3%) of the 273 evaluable tumours that were treated with ECT. Clinical complete responses were achieved in 154 (56.4%) tumours, and partial responses were observed in 79 (28.9%) tumours. The application of electric pulses to the patients was safe and well tolerated. An instantaneous contraction of the underlying muscles was noticed. Minimal adverse side-effects were observed. ECT was shown to be an effective local treatment. ECT was effective regardless of the histological type of the tumour. Therefore, ECT offers an approach to the treatment of cutaneous and subcutaneous tumours in patients with minimal adverse side-effects and with a high response rate.

In vivo antitumor effects of electrochemotherapy in a hepatoma model

The use of in vivo electroporation in combination with a chemotherapeutic agent (electrochemotherapy) for the treatment of liver tumors was examined. Induced rat hepatomas were treated with a 0.5 unit intratumor bleomycin dose followed by rectangular direct current pulses. Six pulses were administered during treatment using a needle array electrode that rotated the applied electric field around the tumors. A 84.6% objective response rate resulted for tumors that received both bleomycin and electric pulses. Control groups that received partial or no treatment showed less than 10% objective response rates. These results indicate that electrochemotherapy can be translated from the treatment of cutaneous cancers to the treatment of liver tumors and other internal tumors.

Novel electrode designs for electrochemotherapy

Direct current pulses for electrochemotherapy treatment are typically administered using two parallel plate electrodes that are placed on either side of the tumor. This simple design has produced high response rates (70 to 85%) in animal studies and in clinical trials. However, parallel plate electrodes are not suitable for all situations. This study describes five novel electrode designs and compares their effectiveness to a parallel plate design for treating melanoma tumors in mice. Results for the 2 x 2 needle array design showed 50% increases in doubling time and in complete response rate compared to the standard parallel plate electrode.

Enhanced effects of multiple treatment electrochemotherapy

Electrochemotherapy has been demonstrated to be an effective treatment for cutaneous cancers. The treatment includes administering a chemotherapeutic agent followed by electric pulses which are applied directly to the tumour. The pulses facilitate delivery of drug through the plasma membrane. Enhanced delivery is restricted to the area that has been electrically treated. Currently, electrochemotherapy is administered as a single treatment. Complete response rates are high; however, partial responses are obtained in a fraction of the treated tumours. An issue associated with this is whether or not multiple treatments would result in an improved therapy for these partially responding tumours. A multiple treatment electrochemotherapy study was implemented in order to address this issue. The study utilized subcutaneously induced murine B16 melanoma tumours in C57B1/6 mice. Results showed large tumour volume reductions in multiple treatment groups. In addition, a twofold increase in tumour doubling time and greater percentages of complete responses were found as a result of multiple treatment. These results will be utilized to augment existing clinical trials with respect to retreating tumours that have partially responded to a single electrochemotherapy treatment.

Phase I/II trial for the treatment of cutaneous and subcutaneous tumors using electrochemotherapy

BACKGROUND

Electroporation is a process that causes a transient increase in the permeability of cell membranes. It can be used to increase the intracellular concentration of chemotherapeutic agents in tumor cells (electrochemotherapy; ECT). A clinical study was initiated to determine if this mode of treatment would be effective against certain primary and metastatic cutaneous malignancies. A group of six patients, three with malignant melanoma, two with basal cell carcinoma, and one with metastatic adenocarcinoma, were enrolled in the study. the treatment was administered in a two-step process.

METHODS

Each patient received a 10 unit/m2 dose of bleomycin administered intravenously at 1 to 1.5 units/minute. This was followed by eight 99 microsecond pulses at an amplitude of 1.3 kV/cm administered directly to the tumors 5 to 15 minutes after the bleomycin was completely infused. Pulses were administered after the injection of 1% lidocaine solution around the treatment site.

RESULTS

Two of three melanoma patients had objective responses. In these two patients, five of six treated tumors decreased in size, and three completely responded. Untreated tumors displayed continued growth. Objective responses were observed in both basal cell carcinoma (BCC) patients. One patient had partial responses in both treated tumors. The other patient had one of four primary BCCs respond completely, and the remaining three respond partially. Patients with metastatic breast adenocarcinoma showed complete responses in both treated nodules after ECT. All patients tolerated the treatment well with no residual effects from the electric pulses.

CONCLUSIONS

ECT was an effective local treatment in the majority of nodules treated. The results thus far are very encouraging and the study is being continued.

Mechanically facilitated cell-cell electrofusion

Apparatus and methods were developed to enable mechanically facilitated cell-cell electrofusion to be performed. The apparatus and methods mechanically place cells in contact before fusion. The key component of this fusion system was a newly developed fusion chamber. The chamber was composed of two functionally identical electrodes that were housed in a multi-layer structure. The layers functioned as support for the electrodes. They also allowed adjustment of the distance between opposing electrode faces. The electrodes were constructed in a manner that allowed cells to be deposited, by vacuum, onto each face. Electrode faces were positioned at a predetermined distance from each other to mechanically force cell-cell contact between the deposited cells. Fusion was induced by delivering direct current pulses to the juxtaposed cells. Fusion products were detected and quantitated by flow cytometry. Details of the chamber design and a protocol for using the fusion chamber are given. Mechanically facilitated cell-cell electrofusion was demonstrated by using the chamber to produce fusion products from like fusion partners. The practical applicability of the chamber was demonstrated by fusing unlike cell types. Mechanically facilitated cell-cell electrofusion is not specific to the cells used in this study; the chamber can be adapted for use with other cell types.

Detection and quantitation of cell-cell electrofusion products by flow cytometry

A cytometric method for detecting and quantitating hybrid cells that resulted from cell-cell electrofusion was developed. Cells from two different lines and two vital fluorescent dyes were used in conjunction with a flow cytometer to demonstrate the method. Each dye was used to stain one cell type prior to electrofusion. Hybrid cells exhibited dual fluorescence while unfused cells retained their single fluorescence. Flow cytometry was used to detect dual fluorescing hybrid cells that resulted from electrofusion. Fluorescent microscopy was used to confirm that 92% of the cytometrically detected cells were hybrids. Flow cytometry was also used to quantitatively show differences in hybrid yields for samples fused using different electrical conditions. These results demonstrate that the method can be used for detection and quantitation of electrofusion products. The methodologies presented are not specific to the cell types used; they can be adapted for use with other cell types.