Irreversible Electroporation in Eradication of Rabbit VX2 Liver Tumor

Dynamics of Cell Death Due to Electroporation Using Different Pulse Parameters as Revealed by Different Viability Assays

The mechanisms of cell death due to electroporation are still not well understood. Recent studies suggest that cell death due to electroporation is not an immediate all-or-nothing response but rather a dynamic process that occurs over a prolonged period of time. To investigate whether the dynamics of cell death depends on the pulse parameters or cell lines, we exposed different cell lines to different pulses [monopolar millisecond, microsecond, nanosecond, and high-frequency bipolar (HFIRE)] and then assessed viability at different times using different viability assays. The dynamics of cell death was observed by changes in metabolic activity and membrane integrity. In addition, regardless of pulse or cell line, the dynamics of cell death was observed only at high electroporation intensities, i.e., high pulse amplitudes and/or pulse number. Considering the dynamics of cell death, the clonogenic assay should remain the preferred viability assay for assessing viability after electroporation.

Electroporation and Immunotherapy-Unleashing the Abscopal Effect

Simple Summary

Electrochemotherapy and irreversible electroporation are primarily used for treating patients with cutaneous and subcutaneous tumors and pancreatic cancer, respectively. Increasing numbers of studies have shown that the treatments may elicit an immune response in addition to eliminating the tumor cells. The purpose of this review is to give an in-depth introduction to the electroporation-induced immune response and the local and peripheral immune systems, and to describe the various studies investigating the combination of electroporation and immunotherapy. The review may help guide and inspire the design of future clinical trials investigating the potential synergy of electroporation and immunotherapy in cancer treatment.

Abstract

The discovery of electroporation in 1968 has led to the development of electrochemotherapy (ECT) and irreversible electroporation (IRE). ECT and IRE have been established as treatments of cutaneous and subcutaneous tumors and locally advanced pancreatic cancer, respectively. Interestingly, the treatment modalities have been shown to elicit immunogenic cell death, which in turn can induce an immune response towards the tumor cells. With the dawn of the immunotherapy era, the potential of combining ECT and IRE with immunotherapy has led to the launch of numerous studies. Data from the first clinical trials are promising, and new combination regimes might change the way we treat tumors characterized by low immunogenicity and high levels of immunosuppression, such as melanoma and pancreatic cancer. In this review we will give an introduction to ECT and IRE and discuss the impact on the immune system. Additionally, we will present the results of clinical and preclinical trials, investigating the combination of electroporation modalities and immunotherapy.

Combination of natural killer cell-based immunotherapy and irreversible electroporation for the treatment of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is among the most lethal cancer types despite great advancement in overall survival of the patients over the last decades. Surgical resection or partial hepatectomy has been approved as the curative treatment for early-stage HCC patients however only up to 30% of them are eligible for the procedures. Natural killer (NK) cells are cytotoxic lymphocytes recognized for killing virally infected cells and improving immune functions for defending the body against malignant cells. Although autologous NK cells failed to demonstrate significant clinical benefit, transfer of allogeneic adoptive NK cells arises as a promising approach for the treatment of solid tumors. The immunosuppressive tumor microenvironment and inadequate homing efficiency of NK cells to tumors can inhibit adoptive transfer immunotherapy (ATI) efficacy. However, potential of the NK cells is challenged by the transfection efficiency. The local ablation techniques that employ thermal or chemical energy have been investigated for the destruction of solid tumors for three decades and demonstrated promising benefits for individuals not eligible for surgical resection or partial hepatectomy. Irreversible electroporation (IRE) is one of the most recent minimally invasive ablation methods that destruct the cell within the targeted region through non-thermal energy. IRE destroys the tumor cell membrane by delivering high-frequency electrical energy in short pulses and overcomes tumor immunosuppression. The previous studies demonstrated that IRE can induce immune changes which can facilitate activation of specific immune responses and improve transfection efficiency. In this review paper, we have discussed the mechanism of NK cell immunotherapy and IRE ablation methods for the treatment of HCC patients and the combinatorial benefits of NK cell immunotherapy and IRE ablation.

Cell death due to electroporation - A review

Exposure of cells to high voltage electric pulses increases transiently membrane permeability through membrane electroporation. Electroporation can be reversible and is used in gene transfer and enhanced drug delivery but can also lead to cell death. Electroporation resulting in cell death (termed as irreversible electroporation) has been successfully used as a new non-thermal ablation method of soft tissue such as tumours or arrhythmogenic heart tissue. Even though the mechanisms of cell death can influence the outcome of electroporation-based treatments due to use of different electric pulse parameters and conditions, these are not elucidated yet. We review the mechanisms of cell death after electroporation reported in literature, cell injuries that may lead to cell death after electroporation and membrane repair mechanisms involved. The knowledge of membrane repair and cell death mechanisms after cell exposure to electric pulses, targets of electric field in cells need to be identified to optimize existing and develop of new electroporation-based techniques used in medicine, biotechnology, and food technology.

Irreversible Electroporation (IRE) in Locally Advanced Pancreatic Cancer: A Review of Current Clinical Outcomes, Mechanism of Action and Opportunities for Synergistic Therapy

Locally advanced pancreatic cancer (LAPC) accounts for 30% of patients with pancreatic cancer. Irreversible electroporation (IRE) is a novel cancer treatment that may improve survival and quality of life in LAPC. This narrative review will provide a perspective on the clinical experience of pancreas IRE therapy, explore the evidence for the mode of action, assess treatment complications, and propose strategies for augmenting IRE response. A systematic search was performed using PubMed regarding the clinical use and safety profile of IRE on pancreatic cancer, post-IRE sequential histological changes, associated immune response, and synergistic therapies. Animal data demonstrate that IRE induces both apoptosis and necrosis followed by fibrosis. Major complications may result from IRE; procedure related mortality is up to 2%, with an average morbidity as high as 36%. Nevertheless, prospective and retrospective studies suggest that IRE treatment may increase median overall survival of LAPC to as much as 30 months and provide preliminary data justifying the well-designed trials currently underway, comparing IRE to the standard of care treatment. The mechanism of action of IRE remains unknown, and there is a lack of data on treatment variables and efficiency in humans. There is emerging data suggesting that IRE can be augmented with synergistic therapies such as immunotherapy.

Novel Ablation Therapy Using Endoscopic Irreversible Electroporation in the Bile Duct: A Pilot Animal Study

Background/Aims

Irreversible electroporation (IRE) is a relatively new ablation method. However, the application of IRE ablation in the treatment of biliary disease has not been attempted. A minimally invasive approach using endoscopic retrograde cholangiopancreatography (ERCP) can be a novel therapeutic modality for IRE ablation. In this study, we aimed to investigate the feasibility of endoscopic IRE for the biliary tract using an animal model.

Methods

A new catheter-type electrode was developed for endoscopic IRE ablation of the biliary tract. We performed ERCP and endoscopic IRE ablations in the normal common bile duct of Yorkshire pigs. The experimental setting of IRE was 500 V/cm (50 pulses, 100-µs length). The animals were sacrificed after 24 hr, and the ablated bile duct was examined.

Results

Well-demarcated focal color changes were observed on the mucosa of the common bile duct. The depth of change after IRE was confined to the mucosal and submucosal layers. Apoptotic changes in the bile duct were observed only around the IRE ablation area. Immunohistochemistry assay showed cell death in the bile duct along the electrode.

Conclusions

Endoscopic IRE ablation using ERCP was successfully performed in the common bile duct. It can be a potential option for the treatment of biliary tumors.

Analysis of damage-associated molecular pattern molecules due to electroporation of cells in vitro

Background Tumor cells can die via immunogenic cell death pathway, in which damage-associated molecular pattern molecules (DAMPs) are released from the cells. These molecules activate cells involved in the immune response. Both innate and adaptive immune response can be activated, causing a destruction of the remaining infected cells. Activation of immune response is also an important component of tumor treatment with electrochemotherapy (ECT) and irreversible electroporation (IRE). We thus explored, if and when specific DAMPs are released as a consequence of electroporation in vitro. Materials and methods In this in vitro study, 100 μs long electric pulses were applied to a suspension of Chinese hamster ovary cells. The release of DAMPs - specifically: adenosine triphosphate (ATP), calreticulin, nucleic acids and uric acid was investigated at different time points after exposing the cells to electric pulses of different amplitudes. The release of DAMPs was statistically correlated with cell permeabilization and cell survival, e.g. reversible and irreversible electroporation. Results In general, the release of DAMPs increases with increasing pulse amplitude. Concentration of DAMPs depend on the time interval between exposure of the cells to pulses and the analysis. Concentrations of most DAMPs correlate strongly with cell death. However, we detected no uric acid in the investigated samples. Conclusions Release of DAMPs can serve as a marker for prediction of cell death. Since the stability of certain DAMPs is time dependent, this should be considered when designing protocols for detecting DAMPs after electric pulse treatment.

Irreversible Electroporation: Background, Theory, and Review of Recent Developments in Clinical Oncology

Irreversible electroporation (IRE) has established a clinical niche as an alternative to thermal ablation for the eradication of unresectable tumors, particularly those near critical vascular structures. IRE has been used in over 50 independent clinical trials and has shown clinical success when used as a standalone treatment and as a single component within combinatorial treatment paradigms. Recently, many studies evaluating IRE in larger patient cohorts and alongside other novel therapies have been reported. Here, we present the basic principles of reversible electroporation and IRE followed by a review of preclinical and clinical data with a focus on tumors in three organ systems in which IRE has shown great promise: the prostate, pancreas, and liver. Finally, we discuss alternative and future developments, which will likely further advance the use of IRE in the clinic.

Does Drug-Eluting Bead TACE Enhance the Local Effect of IRE? Imaging and Histopathological Evaluation in a Porcine Model

OBJECTIVES

We conducted an in vivo trial on swine to compare the ablation volumes of irreversible electroporation (IRE) followed by drug-eluting beads transarterial chemoembolization (DEB-TACE) versus IRE only.

MATERIALS AND METHODS

Nine swine underwent CT-guided IRE in one liver lobe and IRE immediately followed by DEB-TACE in a different liver lobe. For DEB-TACE, 100-300 µm beads (DC-Beads^®) were loaded with 50 mg doxorubicin. For IRE, the NanoKnife^® was used employing two electrodes according to the vendor's protocol. Imaging follow-up was performed including CT-based lesion volume assessment using contrast-enhanced CT (venous phase) on days 1, 3, and 7 after the procedure. Three animals were killed for histopathological analysis after each follow-up.

RESULTS

Ablation volumes in CT in the IRE + DEB-TACE group were 15.4 ± 10.5 ml on day 1, 8.7 ± 5.6 ml on day 3, and 1.6 ± 0.7 ml on day 7. In the IRE group, the corresponding values were 5.2 ± 5.2 ml on day 1, 1.0 ± 1.2 ml on day 3, and 0.1 ± 0.1 ml on day 7. On day 1 and day 3, ablation volumes of IRE + TACE group were significantly larger than in the IRE group (p < 0.05). 96% of beads were depicted in or around ablative lesions. 69% of these beads were found in the surrounding hemorrhagic infiltration and 31% within the ablative lesion itself.

CONCLUSIONS

Combination of IRE immediately followed by DEB-TACE resulted in larger ablation volumes compared to IRE alone, suggesting that local efficacy of IRE can be enhanced by post-IRE DEB-TACE.

Irreversible electroporation in the eradication of rabbit VX2 cervical tumors

The aim of this study was to evaluate the effects of irreversible electroporation (IRE) on the eradication of rabbit VX2 cervical tumors. A VX2 cervical cancer model was first made in 20 New Zealand rabbits. IRE ablation was performed for the cervical cancers of 15 rabbits when the diameter of the tumor was about 1.0-1.5 cm. The control group (n = 5) did not receive IRE ablation. The gross pathology, ultrasound, computed tomography, hematoxylin and eosin, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, and proliferating cell nuclear antigen immunohistochemical staining were performed to evaluate the efficacy of IRE on cervical cancer. All the rabbits tolerated the IRE ablation without serious complications. The tumors treated by IRE slightly increased in size during the first two days, but decreased gradually. IRE caused tumor cell death efficiently, mainly through cell apoptosis; however, it did not induce complete tumor ablation in our study. The results suggested that IRE could eradicate rabbit VX2 cervical tumors efficiently. However, the optimal IRE parameters remain to be determined.

Breast tissue ablation with irreversible electroporation in rabbits: A safety and feasibility study

Background and aim

Irreversible electroporation (IRE) was confirmed to control several solid tumors effectively in vivo. Our preclinical study aimed to assess the feasibility and safety of IRE in the breast of rabbit.

Methods

Thirty New Zealand white rabbits were randomly divided into 3 groups of 10 rabbits (control group, IRE group A, and B). Two mono-electrode needles were inserted into the breast tissue by percutaneous puncture. Electrocardiogram and vital signs were monitored before, during, and after ablation. Histopathology, immunohistochemistry, and transmission electron microscopy were examined at 0 hours, 12 hours, 24 hours, 4 days, 7 days, 14 days, and 28 days after ablation.

Results

All the rabbits survived the procedure with no significant adverse effects. Intra-operative ventricular arrhythmias occurred in 1 rabbit from IRE group B and was immediately relieved after ablation. Reversible subcutaneous hemorrhage was observed in 8 rabbits from IRE group A and 7 rabbits from IRE group B. No skin was burnt, however, pectoralis major muscle injuries were found in all rabbits. Histopathological and ultrastructural examination revealed the coexistence of cell necrosis and apoptosis. HE, TUNEL, and Masson staining revealed breast tissue injury and the recovery of damage by fibrous tissue and granulation tissue. Notably, the structures of mammary gland lobules and interstitial components of the breasts were well preserved.

Conclusions

Our study suggests that IRE destroys breast cancer while effectively preserving the skin, the structure of mammary gland lobules, and interstitial components. IRE may be a promising technique to locally control breast cancer and to maintain the esthetic of the breast.

Irreversible electroporation in primary and metastatic hepatic malignancies: A review

BACKGROUND

Liver cancer makes up a huge percentage of cancer mortality worldwide. Irreversible electroporation (IRE) is a relatively new minimally invasive nonthermal ablation technique for tumors that applies short pulses of high frequency electrical energy to irreversibly destabilize cell membrane to induce tumor cell apoptosis.

METHODS

This review aims to investigate the studies regarding the use of IRE treatment in liver tumors and metastases to liver. We searched PubMed for all of IRE relevant English language articles published up to September 2016. They included clinical trials, experimental studies, observational studies, and reviews. This review manuscript is nothing with ethics issues and ethical approval is not provided.

RESULTS

In recent years, increasingly more studies in both preclinical and clinical settings have been conducted to examine the safety and efficacy of this new technique, shedding light on the crucial advantages and disadvantages that IRE possesses. Unlike the current leading thermal ablation techniques, such as radiofrequency ablation (RFA), microwave ablation (MWA), and cryoablation, IRE requires shorter ablation time without damaging adjacent important vital structures.

CONCLUSION

Although IRE has successfully claimed its valuable status in the field of hepatic cancer treatment both preclinical and clinical settings. In order to systemically test and establish its safety and efficacy for clinical applications, more studies still need to be conducted.

Long-term effectiveness of irreversible electroporation in a murine model of colorectal liver metastasis

Irreversible electroporation (IRE) has recently gained in popularity as an ablative technique, however little is known about its oncological long-term outcomes. To determine the long-time survival of animals treated with a high dose of IRE and which histological changes it induces in tumoral tissue, IRE ablation was performed in forty-six athymic-nude mice with KM12C tumors implanted in the liver by applying electric current with different voltages (2000 V/cm, 1000 V/cm). The tumors were allowed to continue to grow until the animals reached the end-point criteria. Histology was harvested and the extent of tumor necrosis was semi-quantitatively assessed. IRE treatment with the 2000 V/cm protocol significantly prolonged median mouse survival from 74.3 ± 6.9 days in the sham group to 112.5 ± 15.2 days in the 2000 V/cm group. No differences were observed between the mean survival of the 1000 V/cm and the sham group (83.2 ± 16.4 days, p = 0.62). Histology revealed 63.05% ± 23.12 of tumor necrosis in animals of the 2000 V/cm group as compared to 17.50% ± 2.50 in the 1000 V/cm group and 25.6% ± 22.1 in the Sham group (p = 0.001). IRE prolonged the survival of animals treated with the highest electric field (2000 V/cm). The animals in this group showed significantly higher rate of tumoral necrosis.

Magnetic Resonance Imaging Findings After Percutaneous Irreversible Electroporation of Liver Metastases: A Systematic Longitudinal Study

Objective

The aim of this study was to systematically investigate the course of magnetic resonance (MR) signal intensity (SI) changes that occur in noncirrhotic livers after irreversible electroporation (IRE) of liver metastases.

Methods

This study is an institutional review board–approved prospective longitudinal follow-up study on 27 patients with 37 liver metastases who underwent computed tomography–guided percutaneous IRE and a standardized follow-up protocol by serial hepatic MR imaging studies that consisted of a gadobutrol-enhanced dynamic series, axial T2-weighted (T2w) turbo spin echo, and diffusion-weighted imaging (b = 0/50/800), acquired before, within 2, and at 24 hours after IRE; at 1, 2, 4, 6, 8, and 12 weeks after IRE; and every 3 months thereafter for a follow-up of at least 12 months.

Results

The ablated target lesion remained visible within the ablation zone in 23 (62%) of 37 of cases for a mean time of 21 ± 20 weeks (median, 12 weeks). The ablation zone appeared homogeneously hyperintense on T2w turbo spin echo images on the day of IRE in 37 of 37 cases. By 24 hours after IRE, the ablation zone inverted its SI in 35 of 37 cases to intermediately hypointense, with a rim of T2w bright SI that exhibited arterial phase enhancement; this persisted for 7 ± 5 weeks (median, 4 weeks). The rim resolved in 35 (95%) of 37 cases within 3 months. The ablation zone increased slightly over the first 48 hours, then shrank progressively. Complete healing of the ablation zone was observed in 57% (21/37) after an average of 14 ± 15 (median, 8 weeks).

Average apparent diffusion coefficient values of the ablation zone decreased from 0.74 ± 0.36 × 10⁻³ mm²/s pre-IRE to 0.63 ± 0.27 × 10⁻³ mm²/s within the first 24 hours (P < 0.05), followed by a progressive normalization to 0.91 ± 0.30 × 10⁻³ mm²/s at 2 months.

Conclusions

Knowledge of the broad spectrum of MR imaging findings after IRE is important to avoid diagnostic errors in the follow-up of patients after IRE.

Irreversible electroporation of the liver: is there a safe limit to the ablation volume?

Irreversible electroporation is a fast-growing liver ablation technique. Although safety has been well documented in small ablations, our aim is to assess its safety and feasibility when a large portion of liver is ablated. Eighty-seven mice were subjected to high voltage pulses directly delivered across parallel plate electrodes comprising around 40% of mouse liver. One group consisted in 55 athymic-nude, in which a tumor from the KM12C cell line was grown and the other thirty-two C57-Bl6 non-tumoral mice. Both groups were subsequently divided into subsets according to the delivered field strength (1000 V/cm, 2000 V/cm) and whether or not they received anti-hyperkalemia therapy. Early mortality (less than 24 hours post-IRE) in the 2000 V/cm group was observed and revealed considerably higher mean potassium levels. In contrast, the animals subjected to a 2000 V/cm field treated with the anti-hyperkalemia therapy had higher survival rates (OR = 0.1, 95%CI = 0.02–0.32, p < 0.001). Early mortality also depended on the electric field magnitude of the IRE protocol, as mice given 1000 V/cm survived longer than those given 2000 V/cm (OR = 4.7, 95%CI = 1.8–11.8, p = 0.001). Our findings suggest that ionic disturbances, mainly due to potassium alterations, should be warned and envisioned when large volume ablations are performed by IRE.

Electric Ablation with Irreversible Electroporation (IRE) in Vital Hepatic Structures and Follow-up Investigation

Irreversible electroporation (IRE) with microsecond-pulsed electric fields (μsPEFs) can effectively ablate hepatocellular carcinomas in animal models. This preclinical study evaluates the feasibility and safety of IRE on porcine livers. Altogether, 10 pigs were included. Computed tomography (CT) was used to guide two-needle electrodes that were inserted near the hilus hepatis and gall bladder. Animals were followed-up at 2 hours and at 2, 7 and 14 days post-treatment. During and after μsPEF ablation, electrocardiographs found no cardiovascular events, and contrast CT found no portal vein thrombosis. There was necrosis in the ablation zone. Mild cystic oedema around the gall bladder was found 2 hours post-treatment. Pathological studies showed extensive cell death. There was no large vessel damage, but there was mild endothelial damage in some small vessels. Follow-up liver function tests and routine blood tests showed immediate liver function damage and recovery from the damage, which correlated to the pathological changes. These results indicate that μsPEF ablation affects liver tissue and is less effective in vessels, which enable μsPEFs to ablate central tumour lesions close to the hilus hepatis and near large vessels and bile ducts, removing some of the limitations and contraindications of conventional thermal ablation.

Colorectal liver metastatic disease: efficacy of irreversible electroporation--a single-arm phase II clinical trial (COLDFIRE-2 trial)

Background

Irreversible electroporation (IRE) is a novel image-guided tumor ablation technique that has shown promise for the ablation of lesions in proximity to vital structures such as blood vessels and bile ducts. The primary aim of the COLDFIRE-2 trial is to investigate the efficacy of IRE for unresectable, centrally located colorectal liver metastases (CRLM). Secondary outcomes are safety, technical success, and the accuracy of contrast-enhanced (ce)CT and ¹⁸F-FDG PET-CT in the detection of local tumor progression (LTP).

Methods/design

In this single-arm, multicenter phase II clinical trial, twenty-nine patients with ¹⁸F-FDG PET-avid CRLM ≤ 3,5 cm will be prospectively included to undergo IRE of the respective lesion. All lesions must be unresectable and unsuitable for thermal ablation due to vicinity of vital structures. Technical success is based on ceMRI one day post-IRE. All complications related to the IRE procedure are registered. Follow-up consists of ¹⁸F-FDG PET-CT and 4-phase liver CT at 3-monthly intervals during the first year of follow-up. Treatment efficacy is defined as the percentage of tumors successfully eradicated 12 months after the initial IRE procedure based on clinical follow-up using both imaging modalities, tumor marker and (if available) histopathology. To determine the accuracy of ¹⁸F-FDG PET-CT and ceCT, both imaging modalities will be individually scored by two reviewers that are blinded for the final oncologic outcome.

Discussion

To date, patients with a central CRLM unsuitable for resection or thermal ablation have no curative treatment option and are given palliative chemotherapy. For these patients, IRE may prove a life-saving treatment option. The results of the proposed trial may represent an important step towards the implementation of IRE for central liver tumors in the clinical setting.

Trial registration

Trial registration number: NCT02082782.

Development, growth, propagation, and angiographic utilization of the rabbit VX2 model of liver cancer: a pictorial primer and "how to" guide

The VX2 tumor is a leporine anaplastic squamous cell carcinoma characterized by rapid growth, hypervascularity, and facile propagation in the skeletal muscle. Since its introduction over 70 years ago, it has been used to model a variety of malignancies, and is commonly employed by interventional radiologists in preclinical investigations of hepatocellular carcinoma. However, despite the widespread and lasting popularity of the model, there are few technical resources detailing its use. Herein, we present a comprehensive pictorial outline of the technical methodology for development, growth, propagation, and angiographic utilization of the rabbit VX2 liver tumor model.

Irreversible Electroporation of Malignant Hepatic Tumors--Alterations in Venous Structures at Subacute Follow-Up and Evolution at Mid-Term Follow-Up

Purpose

To evaluate risk factors associated with alterations in venous structures adjacent to an ablation zone after percutaneous irreversible electroporation (IRE) of hepatic malignancies at subacute follow-up (1 to 3 days after IRE) and to describe evolution of these alterations at mid-term follow-up.

Materials and Methods

43 patients (men/women, 32/11; mean age, 60.3 years) were identified in whom venous structures were located within a perimeter of 1.0 cm of the ablation zone at subacute follow-up after IRE of 84 hepatic lesions (primary/secondary hepatic tumors, 31/53). These vessels were retrospectively evaluated by means of pre-interventional and post-interventional contrast-enhanced magnetic resonance imaging or computed tomography or both. Any vascular changes in flow, patency, and diameter were documented. Correlations between vascular change (yes/no) and characteristics of patients, lesions, and ablation procedures were assessed by generalized linear models.

Results

191 venous structures were located within a perimeter of 1.0 cm of the ablation zone: 55 (29%) were encased by the ablation zone, 78 (41%) abutted the ablation zone, and 58 (30%) were located between 0.1 and 1.0 cm from the border of the ablation zone. At subacute follow-up, vascular changes were found in 19 of the 191 vessels (9.9%), with partial portal vein thrombosis in 2, complete portal vein thrombosis in 3, and lumen narrowing in 14 of 19. At follow-up of patients with subacute vessel alterations (mean, 5.7 months; range, 0 to 14 months) thrombosis had resolved in 2 of 5 cases; vessel narrowing had completely resolved in 8 of 14 cases, and partly resolved in 1 of 14 cases. The encasement of a vessel by ablation zone (OR = 6.36, p<0.001), ablation zone being adjacent to a portal vein (OR = 8.94, p<0.001), and the usage of more than 3 IRE probes (OR = 3.60, p = 0.035) were independently associated with post-IRE vessel alterations.

Conclusion

Venous structures located in close proximity to an IRE ablation zone remain largely unaffected by this procedure, and thrombosis is rare.

Update on treatment of liver metastases: focus on ablation therapies

There is substantial and growing interest in the use of local therapies to treat patients with metastatic cancer, especially those deemed to have "oligometastatic" disease. Much of the literature to date consists of reports on metastasectomy for liver and lung metastases. Non-surgical minimally or non-invasive treatments including thermal ablation, irreversible electroporation, and high-dose radiation therapy (stereotactic ablative radiation therapy) can also be used in the treatment of primary and secondary tumors, including in the treatment of liver metastases. In this review, we discuss the rationale for using these ablative treatments in the treatment of liver metastases including similarities and differences between them.

Combination of interventional adenovirus-p53 introduction and ultrasonic irradiation in the treatment of liver cancer

The aim of the present study was to investigate the effect of the combination of interventional adenovirus-p53 (Ad-p53) introduction and ultrasonic irradiation (CIAIUI) treatment for liver cancer, including evaluating the Ad-p53 transfection efficiency and the impact of the p53 gene on vascular endothelial growth factor (VEGF) and matrix metalloprotein 2 (MMP2) protein expression levels. Ad-p53 was arterially infused into the hepatic carcinoma via the interventional introduction of the hepatic tumor-bearing artery (IIHTBA) or the CIAIUI. Serum VEGF levels were determined by performing an enzyme-linked immunosorbent assay; immunohistochemical analysis was used to identify the expression levels of intratumoral p53, MMP2 and VEGF; and western blot analysis was used to determine the impact of different Ad-p53 administration methods on the expression of wild-type p53. The wild-type p53 expression level was significantly higher in the p53-treated group compared with the control group, and the p53 expression level in the CIAIUI group was significantly higher compared with the non-irradiation group. The CIAIUI could significantly reduce the serum VEGF levels. The two delivery methods caused a reduction in the intratumoral VEGF and MMP2 expression levels, and the effects of CIAIUI were most obvious. Ad-p53 infusion via IIHTBA promoted the protein expression levels of p53, however, it inhibited the protein expression levels of MMP2 and VEGF, indirectly indicating that the gene may inhibit the growth of liver cancer. Therefore, CIAIUI therapy exhibited an overall improved therapeutic effect compared with the more simple IIHTBA therapy.

Irreversible electroporation ablation of malignant hepatic tumors: subacute and follow-up CT appearance of ablation zones

PURPOSE

To describe findings on contrast-enhanced computed tomography (CT) images of malignant hepatic tumors 24-72 hours after percutaneous ablation by irreversible electroporation (IRE) and at midterm follow-up.

MATERIALS AND METHODS

Retrospective analysis of 52 malignant liver tumors-30 primary hepatic tumors and 22 hepatic metastases-in 34 patients (28 men and 6 women, mean age 64 y) treated by IRE ablation was performed. Ablation zones were evaluated by two examiners in a consensus reading by means of a dual-phase CT scan (consisting of a hepatic arterial and portal venous phase) performed 24-72 hours after IRE ablation and at follow-up.

RESULTS

During the portal venous phase, ablation zones either were homogeneously hypoattenuating (n = 36) or contained heterogeneously isoattenuating or hyperattenuating (n = 16) foci, or both, in a hypoattenuating area. Of 52 lesions, 38 included gas pockets. Peripheral contrast enhancement of the ablation defect was evident in 23 tumors during the arterial phase and in 36 tumors during the portal venous phase. Four tumors showed intralesional abscesses after the intervention. At follow-up (mean, 4.7 mo), the mean volume of the ablation defects was reduced to 29% of their initial value.

CONCLUSIONS

Because normal findings on contrast-enhanced CT images after IRE ablation may be very similar to the typical characteristics of potential complications following ablation, such as liver abscesses, CT scans must be carefully analyzed to distinguish normal results after intervention from complications requiring further treatment.

Irreversible electroporation: ready for prime time?

Image-guided ablation has evolved rapidly in the past decade into a competitive technique for treating focal solid malignancies. However, as they rely mainly on thermal energy, such as radiofrequency or microwave, many tumors close to sensitive organs, such as ducts, bowel, and nerves, still remain nonablatable owing to the risk of thermal injury. Irreversible electroporation is a novel ablation modality that relies largely on a nonthermal mechanism to induce cell death, and therefore may overcome many of the shortcomings of thermal ablation. Emerging preclinical data as well as early clinical experience is showing promise for this technique in treating a variety of tumors including periportal liver masses, pancreatic cancer, perihilar renal tumors, prostate cancer, and other soft tissue tumors. However, practical limitations remain for irreversible electroporation, and its complete cancer and location-specific safety and efficacy profiles are still largely unknown. We therefore review what is known for this new ablation modality based on preclinical and preliminary clinical data, and discuss its emerging indications as well as technical challenges.

CT-guided irreversible electroporation in an acute porcine liver model: effect of previous transarterial iodized oil tissue marking on technical parameters, 3D computed tomographic rendering of the electroporation zone, and histopathology

PURPOSE

To evaluate the effect of previous transarterial iodized oil tissue marking (ITM) on technical parameters, three-dimensional (3D) computed tomographic (CT) rendering of the electroporation zone, and histopathology after CT-guided irreversible electroporation (IRE) in an acute porcine liver model as a potential strategy to improve IRE performance.

METHODS

After Ethics Committee approval was obtained, in five landrace pigs, two IREs of the right and left liver (RL and LL) were performed under CT guidance with identical electroporation parameters. Before IRE, transarterial marking of the LL was performed with iodized oil. Nonenhanced and contrast-enhanced CT examinations followed. One hour after IRE, animals were killed and livers collected. Mean resulting voltage and amperage during IRE were assessed. For 3D CT rendering of the electroporation zone, parameters for size and shape were analyzed. Quantitative data were compared by the Mann-Whitney test. Histopathological differences were assessed.

RESULTS

Mean resulting voltage and amperage were 2,545.3 ± 66.0 V and 26.1 ± 1.8 A for RL, and 2,537.3 ± 69.0 V and 27.7 ± 1.8 A for LL without significant differences. Short axis, volume, and sphericity index were 16.5 ± 4.4 mm, 8.6 ± 3.2 cm(3), and 1.7 ± 0.3 for RL, and 18.2 ± 3.4 mm, 9.8 ± 3.8 cm(3), and 1.7 ± 0.3 for LL without significant differences. For RL and LL, the electroporation zone consisted of severely widened hepatic sinusoids containing erythrocytes and showed homogeneous apoptosis. For LL, iodized oil could be detected in the center and at the rim of the electroporation zone.

CONCLUSION

There is no adverse effect of previous ITM on technical parameters, 3D CT rendering of the electroporation zone, and histopathology after CT-guided IRE of the liver.

Irreversible electroporation for nonthermal tumor ablation in the clinical setting: a systematic review of safety and efficacy

PURPOSE

To provide an overview of current clinical results of irreversible electroporation (IRE), a novel, nonthermal tumor ablation technique that uses electric pulses to induce cell death, while preserving structural integrity of bile ducts and vessels.

METHODS

All in-human literature on IRE reporting safety or efficacy or both was included. All adverse events were recorded. Tumor response on follow-up imaging from 3 months onward was evaluated.

RESULTS

In 16 studies, 221 patients had 325 tumors treated in liver (n = 129), pancreas (n = 69), kidney (n = 14), lung (n = 6), lesser pelvis (n = 1), and lymph node (n = 2). No major adverse events during IRE were reported. IRE caused only minor complications in the liver; however, three major complications were reported in the pancreas (bile leak [n = 2], portal vein thrombosis [n = 1]). Complete response at 3 months was 67%-100% for hepatic tumors (93%-100% for tumors o 3 cm). Pancreatic IRE combined with surgery led to prolonged survival compared with control patients (20 mo vs 13 mo) and significant pain reduction.

CONCLUSIONS

In cases where other techniques are unsuitable, IRE is a promising modality for the ablation of tumors near bile ducts and blood vessels. This articles gives an extensive overview of the available evidence, which is limited in terms of quality and quantity. With the limitations of the evidence in mind, IRE of central liver tumors seems relatively safe without major complications, whereas complications after pancreatic IRE appear more severe. The available limited results for tumor control are generally good. Overall, the future of IRE for difficult-to-reach tumors appears promising.

Multimodality imaging to assess immediate response to irreversible electroporation in a rat liver tumor model

PURPOSE

To compare changes on ultrasonographic (US), computed tomographic (CT), and magnetic resonance (MR) images after irreversible electroporation (IRE) ablation of liver and tumor tissues in a rodent hepatoma model.

MATERIALS AND METHODS

Studies received approval from the institutional animal care and use committee. Forty-eight rats were used, and N1-S1 tumors were implanted in 24. Rats were divided into groups and allocated for studies with each modality. Imaging was performed in normal liver tissues and tumors before and after IRE. MR imaging was performed in one group before and after IRE after hepatic vessel ligation. US images were graded to determine echogenicity changes, CT attenuation was measured (in Hounsfield units), and MR imaging signal-to-noise ratio (SNR) was measured before and after IRE. Student t test was used to compare attenuation and SNR measurements before and after IRE (P < .05 indicated a significant difference).

RESULTS

IRE ablation produced greater alterations to echogenicity in normal tissues than in tumors. Attenuation in ablated liver tissues was reduced compared with that in control tissues (P < .001), while small attenuation differences between ablated (42.11 HU ± 2.11) and control (45.14 HU ± 2.64) tumors trended toward significance (P = .052). SNR in ablated normal tissues was significantly altered after IRE (T1-weighted images: pre-IRE, 145.95 ± 24.32; post-IRE, 97.80 ± 18.03; P = .004; T2-weighted images, pre-IRE, 47.37 ± 18.31; post-IRE, 90.88 ± 37.15; P = .023). In tumors, SNR differences before and after IRE were not significant. No post-IRE signal changes were observed after hepatic vessel ligation.

CONCLUSION

IRE induces rapid changes on gray-scale US, unenhanced CT, and MR images. These changes are readily visible and may assist a performing physician to delineate ablation zones from the unablated surrounding parenchyma.