Direct visualization of electroporation-assisted in vivo gene delivery to tumors using intravital microscopy - spatial and time dependent distribution

Gene Electrotransfer of Canine Interleukin 12 into Canine Melanoma Cell Lines

A gene electrotransfer (GET) of interleukin 12 (IL-12) had already given good results when treating tumors in human and veterinary clinical trials. So far, plasmids used in veterinary clinical studies encoded a human or a feline IL-12 and an ampicillin resistance gene, which is not recommended by the regulatory agencies to be used in clinical trials. Therefore, the aim of the current study was to construct the plasmid encoding a canine IL-12 with kanamycin antibiotic resistance gene that could be used in veterinary clinical oncology. The validation of the newly constructed plasmid was carried out on canine malignant melanoma cells, which have not been used in GET studies so far, and on human malignant melanoma cells. Canine and human malignant melanoma cell lines were transfected with plasmid encoding enhanced green fluorescence protein at different pulse parameter conditions to determine the transfection efficiency and cell survival. The IL-12 expression of the most suitable conditions for GET of the plasmid encoding canine IL-12 was determined at mRNA level by the qRT-PCR and at protein level with the ELISpot assay. The obtained results showed that the newly constructed plasmid encoding canine IL-12 had similar or even higher expression capacity than the plasmid encoding human IL-12. Therefore, it represents a promising therapeutic plasmid for further IL-12 gene therapy in clinical studies for spontaneous canine tumors. Additionally, it also meets the main regulatory agencies' (FDA and EMA) criteria.

Biological properties of melanoma and endothelial cells after plasmid AMEP gene electrotransfer depend on integrin quantity on cells

The data on the biological responsiveness of melanoma and endothelial cells that are targeted by Antiangiogenic MEtargidin Peptide (AMEP) are limited; therefore, the antiproliferative, antimetastatic and antiangiogenic effects of AMEP were investigated in murine melanoma and human endothelial cells after plasmid AMEP gene electrotransfer into the cells in vitro. Plasmid AMEP, a plasmid coding for the disintegrin domain of metargidin targeting specific integrins, had cytotoxic and antiproliferative effects on murine melanoma and human endothelial cells. Among the metastatic properties of cells, migration, invasion and adhesion were investigated. Plasmid AMEP strongly affected the migration of murine melanoma and human endothelial cell lines and also affected the invasion of highly metastatic murine melanoma B16F10 and human endothelial cell lines. There was no effect on cell adhesion on Matrigel(TM) or fibronectin in all cell lines. The antiangiogenic effect was shown with tube formation assay, where human microvascular endothelial cell line (HMEC-1) proved to be more sensitive to plasmid AMEP gene electrotransfer than the human umbilical vein endothelial cell line (HUVEC). The study indicates that antiproliferative and antimetastatic biological responses to gene electrotransfer of plasmid AMEP in murine melanoma cells were dependent on the integrin quantity on melanoma cells and not on the expression level of AMEP. The strong antiangiogenic effect expressed in human endothelial cell lines was only partly dependent on the quantity of integrins and seemed to be plasmid AMEP dose dependent.

Protective effect of heme oxygenase-1 on hepatic ischemia-reperfusion injury through inhibition of platelet adhesion to the sinusoids

BACKGROUND AND AIM

Heme oxygenase-1 (HO-1) acts as a protector against hepatic inflammatory injury. HO-1 catalyzes the conversion of heme protein to biliverdin, free iron, and carbon monoxide. Pro-inflammatory responses play critical roles in hepatic ischemia-reperfusion (I/R) injury, and carbon monoxide effectively downregulates I/R injury. The aim of this study was to evaluate the mechanism by which HO-1 reduces warm I/R injury.

METHODS

Sprague-Dawley rats were divided into two groups: the 20-min ischemia group (control group; n = 6) and the 20-min ischemia with cobalt protoporphyrin (CoPP group; n = 6). CoPP is an inducer of HO-1 in the sinusoids. Kupffer cells were labeled using the liposome entrapment method, and platelets were labeled with rhodamine-6G. The adherent platelets were observed for up to 120 min after reperfusion by intravital microscopy.

RESULTS

In the control group, the number of adherent platelets significantly increased than in the CoPP group. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive cells were observed after 120 min of reperfusion in the control group. They were not observed in the CoPP group. In the CoPP group, serum alanine transaminase and interleukin-6 levels reduced after reperfusion. Moreover, the flow velocity of platelets in the hepatic sinusoid markedly increased.

CONCLUSIONS

This study suggests that HO-1 inhibits platelet adhesion to sinusoids. Such inhibition leads to the prevention of hepatic I/R injury.

Interaction between Kupffer cells and platelets in the early period of hepatic ischemia-reperfusion injury--an in vivo study

BACKGROUND

Hepatic ischemia-reperfusion (I/R) leads to activation of Kupffer cells (KCs). The activated KCs cause platelet and leukocyte adhesion to the sinusoidal endothelium. Previously, we reported that platelet-endothelium interactions occur earlier than leukocyte responses. The aim of this study was to evaluate the interaction between platelets and KCs in the hepatic microcirculation after I/R.

MATERIALS AND METHODS

Sprague-Dawley rats were divided into three groups: the no-ischemia group (control group; n = 6); the 20-min ischemia group (I/R group; n = 6); and the 20-min ischemia + anti-rat platelet serum group (APS group; n = 6). KCs were labeled using the liposome entrapment method. The number of adherent platelets was observed for up to 120 min after reperfusion by intravital microscopy. To investigate the effects of platelets on I/R injury, rats were injected intravenously with rabbit APS for platelet depletion.

RESULTS

In the I/R group, the number of adherent platelets increased significantly after I/R. More than 50% of the adherent platelets adhered to KCs. Electron microscopy indicated that the platelets attached to the KCs after hepatic ischemia. The histologic findings indicated liver damage and apoptosis of hepatocytes in zone 1. In the I/R group, but not in the control and APS groups, serum ALT increased immediately after reperfusion.

CONCLUSIONS

We succeeded in visualizing the dynamics of both KCs and platelets in the hepatic sinusoids. Liver ischemia induced the adhesion of platelets to KCs in the early period, which could play a key role in reperfusion injury of the liver.

Molecular delivery to cells facilitated by corona ion deposition

A novel method of inducing the delivery of nonpermeant molecules to the cytosol of cells is presented in this paper. Corona discharge in air was utilized to produce ions that in turn were deposited onto the liquid surface of media containing cultured cells. Murine B16 melanoma cells were used to demonstrate the molecular delivery of fluorescent dye calcein, the drug bleomycin, and a nucleic acid stain SYTOX-green. None of these molecules penetrate cells with intact membranes. Following the corona treatment, cells were observed to admit significant quantities of these molecules from the culture media, relative to control samples. Further, greater than 95% viability of treated cells was observed by Trypan Blue assay. This method may provide an attractive alternative to electroporation where a physical contact between electrodes and cells is needed to deliver molecules to the cytosol.

Gene electrotransfer into murine skeletal muscle: a systematic analysis of parameters for long-term gene expression

Skeletal muscle is an attractive target tissue for delivery of therapeutic genes, since it is well vascularized, easily accessible, and has a high capacity for protein synthesis. For efficient transfection in skeletal muscle, several protocols have been described, including delivery of low voltage electric pulses and a combination of high and low voltage electric pulses. The aim of this study was to determine the influence of different parameters of electrotransfection on short-term and long-term transfection efficiency in murine skeletal muscle, and to evaluate histological changes in the treated tissue. Different parameters of electric pulses, different time lags between plasmid DNA injection and application of electric pulses, and different doses of plasmid DNA were tested for electrotransfection of tibialis cranialis muscle of C57Bl/6 mice using DNA plasmid encoding green fluorescent protein (GFP). Transfection efficiency was assessed on frozen tissue sections one week after electrotransfection using a fluorescence microscope and also noninvasively, followed by an in vivo imaging system using a fluorescence stereo microscope over a period of several months. Histological changes in muscle were evaluated immediately or several months after electrotransfection by determining infiltration of inflammatory mononuclear cells and presence of necrotic muscle fibers. The most efficient electrotransfection into skeletal muscle of C57Bl/6 mice in our experiments was achieved when one high voltage (HV) and four low voltage (LV) electric pulses were applied 5 seconds after the injection of 30 microg of plasmid DNA. This protocol resulted in the highest short-term as well as long-term transfection. The fluorescence intensity of the transfected area declined after 2-3 weeks, but GFP fluorescence was still detectable 18 months after electrotransfection. Extensive inflammatory mononuclear cell infiltration was observed immediately after the electrotransfection procedure using the described parameters, but no necrosis or late tissue damage was observed. This study showed that electric pulse parameters, time lag between the injection of DNA and application of electric pulses, and dose of plasmid DNA affected the duration of transgene expression in murine skeletal muscle. Therefore, transgene expression in muscle can be controlled by appropriate selection of electrotransfection protocol.

Intra-articular electrotransfer of plasmid encoding soluble TNF receptor variants in normal and arthritic mice

BACKGROUND

Anti-inflammatory gene therapy is promising in inflammatory diseases such as rheumatoid arthritis (RA). We have previously demonstrated that intra-muscular (i.m.) electrotransfer (ET) of plasmids encoding three different human tumor necrosis factor-alpha-soluble receptor I variants (hTNFR-Is) exert protective effects in an experimental RA model. However, such a systemic approach could be responsible for side effects. The present study aimed at performing an intra-articular (i.a.) gene therapy by electrotransfer using the hTNFR-Is plasmids.

METHODS AND RESULTS

We evaluated targeting of mice joints by CCD optical imaging after i.a. ET of a luciferase-encoding plasmid and we showed that ET led to strongly increased transgene expression in a plasmid dose-dependent manner. Moreover, articular and seric hTNFR-Is was detectable for 2 weeks. As expected, systemic hTNFR-Is rates were lower after i.a. ET than after i.m. ET. A longer protein secretion could be achieved with several i.a. ETs. Also, we observed that hTNFR-Is expression within arthritic joints was slightly higher than in normal joints.

CONCLUSIONS

In collagen-induced arthritis (CIA), a mouse model for RA, we demonstrated that hTNFR-Is/mIgG1-encoding plasmid i.a. ET decreased joint destruction in the ankles. In conclusion, our results suggest that local TNFR-Is gene therapy may play a role in decreasing joint destruction in CIA.

Ultrasound-based nonviral gene delivery induces bone formation in vivo

Nonviral gene delivery is a promising, safe, therapeutic tool in regenerative medicine. This study is the first to achieve nonviral, ultrasound-based, osteogenic gene delivery that leads to bone tissue formation, in vivo. We hypothesized that direct in vivo sonoporation of naked DNA encoding for the osteogenic gene, recombinant human bone morphogenetic protein-9 (rhBMP-9) would induce bone formation. A luciferase plasmid (Luc), encoding rhBMP-9 or empty pcDNA3 vector mixed with microbubbles, was injected into the thigh muscles of mice. After injection, noninvasive sonoporation was applied. Luc activity was monitored noninvasively, and quantitatively using bioluminescence imaging in vivo, and found for 14 days with a peak expression on day 7. To examine osteogenesis in vivo, rhBMP-9 plasmid was sonoporated into the thigh muscles of transgenic mice that express the Luc gene under the control of a human osteocalcin promoter. Following rhBMP-9 sonoporation, osteocalcin-dependent Luc expression lasted for 24 days and peaked on day 10. Bone tissue was formed in the site of rhBMP-9 delivery, as was shown by micro-computerized tomography and histology. The sonoporation method was also compared with previously developed electrotransfer-based gene delivery and was found significantly inferior in its efficiency of gene delivery. We conclude that ultrasound-mediated osteogenic gene delivery could serve as a therapeutic solution in conditions requiring bone tissue regeneration after further development that will increase the transfection efficiency.

The effect of the histological properties of tumors on transfection efficiency of electrically assisted gene delivery to solid tumors in mice

Uniform DNA distribution in tumors is a prerequisite step for high transfection efficiency in solid tumors. To improve the transfection efficiency of electrically assisted gene delivery to solid tumors in vivo, we explored how tumor histological properties affected transfection efficiency. In four different tumor types (B16F1, EAT, SA-1 and LPB), proteoglycan and collagen content was morphometrically analyzed, and cell size and cell density were determined in paraffin-embedded tumor sections under a transmission microscope. To demonstrate the influence of the histological properties of solid tumors on electrically assisted gene delivery, the correlation between histological properties and transfection efficiency with regard to the time interval between DNA injection and electroporation was determined. Our data demonstrate that soft tumors with larger spherical cells, low proteoglycan and collagen content, and low cell density are more effectively transfected (B16F1 and EAT) than rigid tumors with high proteoglycan and collagen content, small spindle-shaped cells and high cell density (LPB and SA-1). Furthermore, an optimal time interval for increased transfection exists only in soft tumors, this being in the range of 5-15 min. Therefore, knowledge about the histology of tumors is important in planning electrogene therapy with respect to the time interval between DNA injection and electroporation.

Electric Fields in Tumors Exposed to External Voltage Sources: Implication for Electric Field-Mediated Drug and Gene Delivery

The intratumoral field, which determines the efficiency of electric field-mediated drug and gene delivery, can differ significantly from the applied field. Therefore, we investigated the distribution of the electric field in mouse tumors and tissue phantoms exposed to a large range of electric stimuli, and quantified the resistances of tumor, skin, and electrode-tissue interface. The samples used in the study included 4T1 and B16.F10 tumors, mouse skin, and tissue phantoms constructed with 1% agarose gel with or without 4T1 cells. When pulsed electric fields were applied to samples using a pair of parallel-plate electrodes, we determined the electric field and resistances in each sample as well as the resistance at the electrode-tissue interface. The electric fields in the center region of tissue phantoms and tumor slices ex vivo were macroscopically uniform and unidirectional between two parallel-plate electrodes. The field strengths in tumor tissues were significantly lower than the applied field under both ex vivo and in vivo conditions. During in vivo stimulation, the ratio of intratumoral versus applied fields was approximately either 20% or 55%, depending on the applied field. Meanwhile, the total resistance of skin and electrode-tissue interface was decreased by approximately 70% and the electric resistance at the center of both tumor models was minimally changed when the applied field was increased from 50 to 400 V/cm. These results may be useful for improving electric field-mediated drug and gene delivery in solid tumors.

Determination of the lipid bilayer breakdown voltage by means of linear rising signal

Electroporation is characterized by formation of structural changes within the cell membrane, which are caused by the presence of electrical field. It is believed that "pores" are mostly formed in lipid bilayer structure; if so, planar lipid bilayer represents a suitable model for experimental and theoretical studies of cell membrane electroporation. The breakdown voltage of the lipid bilayer is usually determined by repeatedly applying a rectangular voltage pulse. The amplitude of the voltage pulse is incremented in small steps until the breakdown of the bilayer is obtained. Using such a protocol each bilayer is exposed to a voltage pulse many times and the number of applied voltage pulses is not known in advance. Such a pre-treatment of the lipid bilayer affects its stability and consequently the breakdown voltage of the lipid bilayer. The aim of this study is to examine an alternative approach for determination of the lipid bilayer breakdown voltage by linear rising voltage signal. Different slopes of linear rising signal have been used in our experiments (POPC lipids; folding method for forming in the salt solution of 100 mM KCl). The breakdown voltage depends on the slope of the linear rising signal. Results show that gently sloping voltage signal electroporates the lipid bilayer at a lower voltage then steep voltage signal. Linear rising signal with gentle slope can be considered as having longer pre-treatment of the lipid bilayer; thus, the corresponding breakdown voltage is lower. With decreasing the slope of linear rising signal, minimal breakdown voltage for specific lipid bilayer can be determined. Based on our results, we suggest determination of lipid bilayer breakdown voltage by linear rising signal. Better reproducibility and lower scattering are obtained due to the fact that each bilayer is exposed to electroporation treatment only once. Moreover, minimal breakdown voltage for specific lipid bilayer can be determined.

In vitro and in vivo imaging of cell migration: Two interdepending methods to unravel metastasis formation

Metastasis development requires the migratory activity of tumor cells. It is therefore important to understand the molecular mechanisms of this migration in order to prevent metastasis development, which is the pernicious step in most solid tumor diseases. A lot of methods have been invented to investigate tumor cell migration, but not all are equally suited and no method alone is able to deliver a complete picture of tumor cell migration. We herein suggest a combination of three-dimensional in vitro and in vivo methods for the investigation of tumor cell migration and summarize the knowledge, which has been reached so far.

Analysis methods of human cell migration

The autonomous migration of specialized cells is an essential characteristic in both physiological and pathological functions in the adult human organism. Leukocytes, fibroblasts, and stem cells, but also tumor cells, are thus the subject of intense investigation in a broad range of research fields. A wide spectrum of methods have therefore been established to analyze chemokinetic and chemotactic cell migration, ranging from easy-to-handle two-dimensional surface migration assays to highly specialized three-dimensional and intravital analysis methods. It is now manifest that the results obtained with these various migration assays substantially differ. This review therefore gives an overview of the migration assays which are currently in use, describes the methods, and critically enlightens the particular advantages and disadvantages of each method.