Electroporation-mediated transcatheter arterial chemoembolization in the rabbit VX2 liver tumor model

A Novel Coacervate Embolic Agent for Tumor Chemoembolization

Transcatheter arterial chemoembolization (TACE) has proven effective in blocking tumor-supplied arteries and delivering localized chemotherapeutic treatment to combat tumors. However, traditional embolic TACE agents exhibit certain limitations, including insufficient chemotherapeutic drug-loading and sustained-release capabilities, non-biodegradability, susceptibility to aggregation, and unstable mechanical properties. This study introduces a novel approach to address these shortcomings by utilizing a complex coacervate as a liquid embolic agent for tumor chemoembolization. By mixing oppositely charged quaternized chitosan (QCS) and gum arabic (GA), a QCS/GA polymer complex coacervate with shear-thinning property is obtained. Furthermore, the incorporation of the contrast agent Iohexol (I) and the chemotherapeutic doxorubicin (DOX) into the coacervate leads to the development of an X-ray-opaque QCS/GA/I/DOX coacervate embolic agent capable of carrying drugs. This innovative formulation effectively embolizes the renal arteries without recanalization. More importantly, the QCS/GA/I/DOX coacervate can successfully embolize the supplying arteries of the VX2 tumors in rabbit ear and liver. Coacervates can locally release DOX to enhance its therapeutic effects, resulting in excellent antitumor efficacy. This coacervate embolic agent exhibits substantial potential for tumor chemoembolization due to its shear-thinning performance, excellent drug-loading and sustained-release capabilities, good biocompatibility, thrombogenicity, biodegradability, safe and effective embolic performance, and user-friendly application.

Single-session transarterial chemoembolization combined with percutaneous thermal ablation in liver metastases 3 cm or larger

PURPOSE

The purpose of this study was to evaluate the safety and efficacy of transarterial chemoembolization (TACE) combined with percutaneous thermal ablation in patients with liver metastases 3 cm in diameter or larger.

MATERIALS AND METHODS

This retrospective study included 39 patients with a total of 46 liver metastases treated. There were 14 men and 25 women, with a mean age of 55 ± 13.3 (SD) (age range: 28-77 years). All patients were treated with a combination of TACE and thermal ablation in a single session. Primary outcome was local tumor progression. Secondary outcomes were procedure related complications and systemic disease progression.

RESULTS

Mean tumor size was 3.6 ± 0.6 (SD) cm (range: 3-5 cm). Conventional TACE was performed in 32 liver metastases (32/46; 70%) and drug-eluting beads-TACE in 14 liver metastases (14/46; 30%) followed by radiofrequency ablation in 34 (34/46; 74%), microwave ablation in 11 (11/46; 24%) and cryoablation in one (1/46; 2%) metastasis. Four grade 2 (4/39; 10%) complications were observed. After a mean follow up of 31.9 ± 26.1 (SD) months (range: 2-113 months) overall local tumor progression rate was 15% (7/46). Local tumor progression rate at 12 months was 13% (6/46). Overall systemic disease progression was seen in 29 patients (29/39; 74%) with a systemic disease progression rate at 12 months of 59% (23/39).

CONCLUSION

Treatment of large liver metastases with TACE and thermal ablation in a single session is safe and achieves high local control rate.

Combination of irreversible electroporation with sustained release of a synthetic membranolytic polymer for enhanced cancer cell killing

Irreversible electroporation (IRE) is used clinically as a focal therapy to ablate solid tumors. A critical disadvantage of IRE as a monotherapy for cancer is the inability of ablating large tumors, because the electric field strength required is often too high to be safe. Previous reports indicate that cells exposed to certain cationic small molecules and surfactants are more vulnerable to IRE at lower electric field strengths. However, low-molecular-weight IRE sensitizers may suffer from suboptimal bioavailability due to poor stability and a lack of control over spatiotemporal accumulation in the tumor tissue. Here, we show that a synthetic membranolytic polymer, poly(6-aminohexyl methacrylate) (PAHM), synergizes with IRE to achieve enhanced cancer cell killing. The enhanced efficacy of the combination therapy is attributed to PAHM-mediated sensitization of cancer cells to IRE and to the direct cell killing by PAHM through membrane lysis. We further demonstrate sustained release of PAHM from embolic beads over 1 week in physiological medium. Taken together, combining IRE and a synthetic macromolecular sensitizer with intrinsic membranolytic activity and sustained bioavailability may present new therapeutic opportunities for a wide range of solid tumors.

Ablation plus Transarterial Embolic Therapy for Hepatocellular Carcinoma Larger than 3 cm: Science, Evidence, and Future Directions

Thermal ablation is widely regarded as definitive therapy for early-stage hepatocellular carcinoma, but its efficacy decreases in tumors greater than 3 cm. Extensive clinical studies have supported improved outcomes provided through combining transarterial embolic therapy with ablation in the treatment of larger tumors. This article will provide a survey of the science and data for combination therapy in both thermal and nonthermal ablation modalities, as well as describe emerging applications.

Evaluation of lymph node metastasis in a rabbit tumor model: correlations between contrast-enhanced ultrasound and pathologic findings

Purpose

The purpose of this study was to evaluate the ability of contrast-enhanced ultrasonography (CEUS) with microbubbles to detect metastatic lymph nodes (LNs) for treatment planning and prognosis.

Methods

For the metastatic LN model, ground VX₂ tumor tissues were injected subcutaneously in 12 rabbits, just below the right hind limb. The rabbits were classified into three groups based on the LN area: group A (n=4, >1.9 cm² ), group B (n=4, 1-1.9 cm² ), and group C (n=4, <1 cm² ). The LNs were monitored on CEUS for 10 seconds after injecting 2.5 mL of microbubbles. The percent area of metastatic LNs was calculated on pathologic images and compared with CEUS images.

Results

In group A, the mean percent area of metastasis was 40.7%±19.4%. In all cases of metastasis, round-shaped perfusion defects were clearly observed in CEUS images. The metastatic areas were strongly correlated with pathologic findings. The mean percent area in group B was 21.5%±14.4%. The CEUS findings showed multiple nodular perfusion defects, clearly revealing the metastatic areas. In group B, the CEUS and pathologic findings were concordant for three of the four cases. The mean percent area in group C was 9.1%±6.4%. However, in this group, CEUS only detected a small perfusion defect in one case.

Conclusion

CEUS has the potential to depict characteristic imaging features of metastatic LNs but still has limitations in early detection.

Image-Based Analysis of Tumor Localization After Intra-Arterial Delivery of Technetium-99m-Labeled SPIO Using SPECT/CT and MRI

The aim of this study is to evaluate the localization of ^99mTc-labeled dextran-coated superparamagnetic iron oxide (SPIO) nanoparticles to the liver tumor using image-based analysis. We delivered ^99mTc-SPIO intravenously or intra-arterially (IA) with/without Lipiodol to compare the tumor localization by gamma scintigraphy, single-photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI) in a rabbit liver tumor. The gamma and SPECT image-based analysis shows that the uptake ratio of the tumor to the normal liver parenchyma is highest after delivery of ^99mTc-SPIO with Lipiodol IA and that well correlates with the trend of the signal decrease in the liver MRIs. Intra-arterial delivery of SPIO with Lipiodol might be a good drug delivery system targeting the hepatic tumors, as confirmed by image-based analysis.

Radio-frequency ablation-based studies on VX2rabbit models for HCC treatment

Hepatocellular carcinoma (HCC) is the fifth most frequent cancer worldwide with high morbidity, mortality and increasing incidence. It is of note that the main curative therapies for HCC are hepatic resection and transplantation although the majority of patients at the time of presentation are not eligible for resection or orthotopic liver transplantation (OLT) due to the underlying cirrhosis. Currently, a variety of loco-regional therapies, including radiofrequency ablation (RFA), percutaneous ethanol injection (PEI), microwave coagulation therapy (MCT), transarterial chemoembolization (TACE) and others, have been developed as alternative treatment options for HCC. Among these techniques, RFA is currently the most widely used treatment, due to its several advantages, such as safety and efficacy. To date, the effectiveness of RFA for HCC is reduced by the presence of residual tumor as a consequence of insufficient treatment. In order to ameliorate the effects of RFA on HCC, several in vivo studies, have been performed on its application as single or in combination treatment with drugs or others loco-regional therapies, by using rabbit VX2 liver model. This represents an ideal model of liver cancers and is widely used for imaging and other experimental studies due to the rapid growth of these tumors and their similarity to human hepatocellular carcinoma. In order to elucidate the therapeutic potential of RFA with adjuvant treatments for HCC, we reviewed the latest findings on the RFA-based studies in rabbit VX2 hepatocarcinoma models.

CT spectral imaging for monitoring the therapeutic efficacy of VEGF receptor kinase inhibitor AG-013736 in rabbit VX2 liver tumours

PURPOSE

The aim of this study was to evaluate the value of computed tomography (CT) spectral imaging in assessing the therapeutic efficacy of a vascular endothelial growth factor (VEGF) receptor inhibitor AG-013736 in rabbit VX2 liver tumours.

METHODS

Twenty-three VX2 liver tumour-bearing rabbits were scanned with CT in spectral imaging mode during the arterial phase (AP) and portal phase (PP). The iodine concentrations(ICs)of tumours normalized to aorta (nICs) at different time points (baseline, 2, 4, 7, 10, and 14 days after treatment) were compared within the treated group (n = 17) as well as between the control (n = 6) and treated groups. Correlations between the tumour size, necrotic fraction (NF), microvessel density (MVD), and nICs were analysed.

RESULTS

The change of nICs relative to baseline in the treated group was lower compared to the control group. A greater decrease in the nIC of a tumour at 2 days was positively correlated with a smaller increase in tumour size at 14 days (P < 0.05 for both). The tumour nIC values in AP and PP had correlations with MVD (r = 0.71 and 0.52) and NF (r = -0.54 and -0.51) (P < 0.05 for all).

CONCLUSIONS

CT spectral imaging allows for the evaluation and early prediction of tumour response to AG-013736.

KEY POINTS

• AG-013736 treatment response was evaluated by CT in a rabbit tumour model. • CT spectral imaging allows for the early treatment monitoring of targeted anti-tumour therapies. • Spectral CT findings correlated with vascular changes after anti-tumour therapies. • Spectral CT is a promising method for assessing clinical treatment response.

Transcatheter intra-arterial infusion of doxorubicin loaded porous magnetic nano-clusters with iodinated oil for the treatment of liver cancer

A promising strategy for liver cancer treatment is to deliver chemotherapeutic agents with multifunctional carriers into the tumor tissue via intra-arterial (IA) transcatheter infusion. These carriers should release drugs within the target tissue for prolonged periods and permit intra-procedural multi-modal imaging of selective tumor delivery. This targeted transcatheter delivery approach is enabled via the arterial blood supply to liver tumors and utilized in current clinical practice which is called chemoembolization or radioembolization. During our study, we developed Doxorubicin (Dox) loaded porous magnetic nano-clusters (Dox-pMNCs). The porous structure and carboxylic groups on the MNCs achieved high-drug loading efficiency and sustained drug release, along with magnetic properties resulting in high MRI T2-weighted image contrast. Dox-pMNC within iodinated oil, Dox-pMNCs, and Dox within iodinated oil were infused via hepatic arteries to target liver tumors in a rabbit model. MRI and histological evaluations revealed that the long-term drug release and retention of Dox-pMNCs within iodinated oil induced significantly enhanced liver cancer cell death.

Electrochemical Effects after Transarterial Chemoembolization in Combination with Percutaneous Irreversible Electroporation: Observations in an Acute Porcine Liver Model

PURPOSE

To evaluate the effects of combined use of transarterial chemoembolization and irreversible electroporation (IRE) for focal tissue ablation in an acute porcine liver model.

MATERIALS AND METHODS

Two established interventional techniques were combined: IRE with zones of irreversible and reversible electroporation and chemoembolization with microspheres, iodized oil, and doxorubicin. IRE was performed before chemoembolization in two pigs (pigs 1 and 2; IRE/chemoembolization group), chemoembolization was performed before IRE in two pigs (pigs 3 and 4; chemoembolization/IRE group), and only IRE was performed in two pigs (pigs 5 and 6). Five study groups were defined: IRE/chemoembolization (pigs 1 and 2), chemoembolization/IRE (pigs 3 and 4), IRE only (pigs 5 and 6), chemoembolization only (tissue outside the IRE zones in pigs 1-4), and control (untreated liver tissue outside the IRE zones in pigs 5 and 6). Animals were euthanized 2 hours after intervention. Size and shape of IRE zones on contrast-enhanced computed tomography, cell death on light microscopy, and doxorubicin tissue concentrations on chromatography and fluorescence microscopy were analyzed.

RESULTS

Size and shape of IRE zones were not significantly different (eg, P = .067 for volume). A histologic marker for irreversible cell death was positive in IRE/chemoembolization, chemoembolization/IRE, and IRE groups only in the macroscopically visible IRE zones. Doxorubicin tissue concentrations were not significantly different (P = .873). However, in the reversible electroporation (RE) zones, broad areas with intense intranuclear doxorubicin accumulation were observed in IRE/chemoembolization but not in chemoembolization/IRE and chemoembolization groups.

CONCLUSIONS

IRE before chemoembolization enhances the intranuclear accumulation of doxorubicin in the RE zone.

Percutaneous ultrasound guided implantation of VX2 for creation of a rabbit hepatic tumor model

Creation of a VX2 tumor model has traditionally required a laparotomy and surgical implantation of tumor fragments. Open surgical procedures are invasive and require long procedure times and recovery that can result in post-operative morbidity and mortality. The purpose of this study is to report the results of a percutaneous ultrasound guided method for creation of a VX2 model in rabbit livers. A total of 27 New Zealand white rabbits underwent a percutaneous ultrasound guided approach, where a VX2 tumor fragment was implanted in the liver. Magnetic resonance imaging was used to assess for tumor growth and necropsy was performed to determine rates of tract seeding and metastatic disease. Ultrasound guided tumor implantation was successful in all 27 rabbits. One rabbit died 2 days following the implantation procedure. Two rabbits had no tumors seen on follow-up imaging. Therefore, tumor development was seen in 24/26 (92%) rabbits. During the follow-up period, tract seeding was seen in 8% of rabbits and 38% had extra-hepatic metastatic disease. Therefore, percutaneous ultrasound guided tumor implantation safely provides reliable tumor growth for establishing hepatic VX2 tumors in a rabbit model with decreased rates of tract seeding, compared to previously reported methods.

Improved drug targeting to liver tumors after intra-arterial delivery using superparamagnetic iron oxide and iodized oil: preclinical study in a rabbit model

PURPOSE

The purpose of this study was to evaluate the feasibility and the therapeutic efficacy of a novel drug-delivery system that uses superparamagnetic iron oxide (SPIO) and iodized oil (IO) to improve the selective intra-arterial (IA) drug delivery to an experimentally induced hepatic tumor.

MATERIALS AND METHODS

This animal study was approved by our institutional animal care and use committee. Fifteen rabbits with hepatic VX2 carcinomas were treated with IA delivery of 4 different agents: doxorubicin alone (group A, n = 3), doxorubicin/IO (group B, n = 3), a doxorubicin/SPIO complex (group C, n = 4), and a doxorubicin/SPIO/IO complex (group D, n = 5). The infused doxorubicin dose was 1 mg for all groups. The serum doxorubicin concentration was measured at 0, 5, 30, 60, and 120 minutes after the delivery. To assess the distribution of the SPIO, magnetic resonance (MR) scans were performed at day 7 after the delivery, when computed tomographic scans were performed in addition to MR in group B and D to assess the distribution of IO. After the completion of follow-up imaging, all the animals were euthanized to measure the intratumoral doxorubicin concentration and to assess tumor viability through pathologic examination.

RESULTS

Groups C and D demonstrated significantly lower MR signal intensities, which inversely corresponded to SPIO deposition, in the tumor areas than did groups A and B. Group D exhibited the lowest serum doxorubicin concentration at all time points up to 180 minutes after the delivery, suggesting minimal passage of doxorubicin into the systemic circulation. The intratumoral doxorubicin concentrations were 72.4 ng/g for group A, 142.0 ng/g for group B, 264.1 ng/g for group C, and 679.6 ng/g for group D. The proportion of viable tumor cells were 65.3% for group A, 1.3% for group B, 17.0% for group C, and 0.1% for group D.

CONCLUSIONS

The drug-delivery system developed using SPIO and IO can result in better drug targeting when it is used for IA delivery to liver cancer. The results of this study warrant further investigation of this potential clinical treatment of advanced liver cancer.

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.

Dynamic contrast-enhanced and diffusion-weighted magnetic resonance imaging noninvasive evaluation of vascular disrupting treatment on rabbit liver tumors

Evaluation of vascular disrupting treatment (VDT) is generally based on tumor size and enhancement on conventional magnetic resonance imaging (MRI) which, unfortunately, may be limited in providing satisfactory information. The purpose of the study is to evaluate consecutive changes of 20 rabbit VX2 liver tumors after VDT by dynamic contrast-enhanced MRI (DCE-MRI) and diffusion-weighted imaging (DWI) at a 3.0 T MR unit. Twenty four hours after intravenous injection of Combretastatin A-4-phosphate (CA4P) at 20 mg/kg, DCE-MRI derived Maximum Slope of Increase (MSI) and Positive Enhancement Integral (PEI) decreased sharply due to sudden shutting down of tumor feeding vessels. DWI derived Apparent Diffusion Coefficient (ADC) in tumor periphery decreased because of ischemic cell edema. On day 4, an increase of MSI was probably caused by the recovery of blood supply. A remarkable increase of ADC represented a large scale of necrosis among tumors. On day 8, the blood perfusion further decreased and the extent of necrosis further increased, reflected by lower MSI and PEI values and higher ADC value. On day 12, a second decrease of ADC was noticed because the re-growth of periphery tumor. The experimental data indicate that the therapeutic effects of VDT may be noninvasively monitored with DCE-MRI (reflecting tumor blood perfusion) and DWI (reflecting the changes of histology), which provide powerful measures for assessment of anticancer treatments.

The effect of blood flow on magnetic resonance imaging of non thermal irreversible electroporation

To generate an understanding of the physiological significance of MR images of Non-Thermal Irreversible Electroporation (NTIRE) we compared the following MR imaging sequences: T1W, T2W, PD, GE, and T2 SPAIR acquired after NTIRE treatment in a rodent liver model. The parameters that were studied included the presence or absence of a Gd-based contrast agent, and in vivo and ex-vivo NTIRE treatments in the same liver. NTIRE is a new minimally invasive tissue ablation modality in which pulsed electric fields cause molecularly selective cell death while, the extracellular matrix and large blood vessels remain patent. This attribute of NTIRE is of major clinical importance as it allows treatment of undesirable tissues near critical blood vessels. The presented study results suggest that MR images acquired following NTIRE treatment are all directly related to the unique pattern of blood flow after NTIRE treatment and are not produced in the absence of blood flow.

Rapid dramatic alterations to the tumor microstructure in pancreatic cancer following irreversible electroporation ablation

AIM

NanoKnife(®) (Angiodynamics, Inc., NY, USA) or irreversible electroporation (IRE) is a newly available ablation technique to induce the formation of nanoscale pores within the cell membrane in targeted tissues. The purpose of this study was to elucidate morphological alterations following 30 min of IRE ablation in a mouse model of pancreatic cancer.

MATERIALS & METHODS

Immunohistochemistry markers were compared with diffusion-weighted MRI apparent diffusion coefficient measurements before and after IRE ablation.

RESULTS

Immunohistochemistry apoptosis index measurements were significantly higher in IRE-treated tumors than in controls. Rapid tissue alterations after 30 min of IRE ablation procedures (structural and morphological alterations along with significantly elevated apoptosis markers) were consistently observed and well correlated to apparent diffusion coefficient measurements.

DISCUSSION

This imaging assay offers the potential to serve as an in vivo biomarker for noninvasive detection of tumor response following IRE ablation.

Postnatal testicular development in the Chinchilla rabbit

The Chinchilla rabbit is a breed with high commercial value and nowadays is increasingly used in various fields of biomedical research, however, its postnatal reproductive biology has been little studied. The aim of the present study was to investigate the postnatal development of the testis in this rabbit breed to determine both the proliferative periods and apoptosis. 30 rabbits aged 3-100 days old were used in the study. Determination of the period of differentiation of gonocytes to spermatogonia (50dpp), the periods of proliferation and apoptosis of their cells, as well as the beginning of spermatogenesis (60dpp) and the different stages of the seminiferous epithelium cycle were made. We found that these testicular developments were closer to that of humans when compared with rats, a species commonly employed in reproductive research. On comparing these results with those obtained from other breeds, there are clear differences favoring the use of this species as a research model in the field of male reproductive biology.

Chemical shift MR imaging methods for the quantification of transcatheter lipiodol delivery to the liver: preclinical feasibility studies in a rodent model

PURPOSE

To demonstrate the feasibility of using chemical shift magnetic resonance (MR) imaging fat-water separation methods for quantitative estimation of transcatheter lipiodol delivery to liver tissues.

MATERIALS AND METHODS

Studies were performed in accordance with institutional Animal Care and Use Committee guidelines. Proton nuclear MR spectroscopy was first performed to identify lipiodol spectral peaks and relative amplitudes. Next, phantoms were constructed with increasing lipiodol-water volume fractions. A multiecho chemical shift-based fat-water separation method was used to quantify lipiodol concentration within each phantom. Six rats served as controls; 18 rats underwent catheterization with digital subtraction angiography guidance for intraportal infusion of a 15%, 30%, or 50% by volume lipiodol-saline mixture. MR imaging measurements were used to quantify lipiodol delivery to each rat liver. Lipiodol concentration maps were reconstructed by using both single-peak and multipeak chemical shift models. Intraclass and Spearman correlation coefficients were calculated for statistical comparison of MR imaging-based lipiodol concentration and volume measurements to reference standards (known lipiodol phantom compositions and the infused lipiodol dose during rat studies).

RESULTS

Both single-peak and multipeak measurements were well correlated to phantom lipiodol concentrations (r(2) > 0.99). Lipiodol volume measurements were progressively and significantly higher when comparing between animals receiving different doses (P < .05 for each comparison). MR imaging-based lipiodol volume measurements strongly correlated with infused dose (intraclass correlation coefficients > 0.93, P < .001) with both single- and multipeak approaches.

CONCLUSION

Chemical shift MR imaging fat-water separation methods can be used for quantitative measurements of lipiodol delivery to liver tissues.