Role of sonography for implantation and sequential evaluation of a VX2 rabbit liver tumor model

Intravoxel incoherent motion imaging used to assess tumor microvascular changes after transarterial chemoembolization in a rabbit VX2 liver tumor model

Purpose

To evaluate the correlation between microvascular density (MVD) and intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) parameters and the effect of glycolytic flux after transarterial chemoembolization (TACE) in a rabbit VX2 liver tumor.

Materials and methods

VX2 liver tumor allografts in 15 New Zealand white rabbits were treated with sterile saline (control group, n = 5) or lipiodol-doxorubicin emulsion (experimental group, n = 10). MRI was performed 2 weeks after the procedure to evaluate IVIM parameters, including apparent diffusion coefficient (ADC), pure diffusion coefficient (D), pseudodiffusion coefficient (D*), and perfusion fraction (PF). All animal samples were taken of the tumor and surrounding liver. Immunostaining for CD31, CD34, CD105, and VEGF was used to evaluate MVD. The protein expression of Glut4, HK2, PKM2, LDHA, and MCT1 was determined using western blotting. Pearson correlation tests were used to analyze the relationship between MVD and IVIM parameters.

Results

D* value in the peritumoral region was negatively correlated with CD34 (r = -0.71, P = 0.01). PF value positively correlated with CD34 (r = 0.68, P = 0.015), CD105 (r = 0.76, P = 0.004) and VEGF (r = 0.72, P = 0.008) in the peritumoral region. Glut4, HK2, PKM2, and MCT1 in the peritumoral regions were higher in the experimental group than in the control group (all P < 0.05).

Conclusion

IVIM parameters were correlated with MVD in the intratumoral and peritumoral regions after TACE in a rabbit liver tumor model. The angiogenesis reflected by MVD may be related to changes of glycolytic flux.

Intravoxel incoherent motion diffusion-weighted imaging and shear wave elastography for evaluating peritumoral liver fibrosis after transarterial chemoembolization in a VX2 rabbit liver tumor model

In this study, we sought to evaluate changes in peritumoral fibrosis after transarterial chemoembolization (TACE) in a rabbit VX2 liver tumor model using intravoxel incoherent motion diffusion-weighted imaging (IVIM DWI) and ultrasound shear wave elastography (SWE). A total of 20 rabbits underwent implantation of VX2 tumor tissues in the left lobe of the liver. The rabbits were randomly divided into an experimental group (n = 10) or a control group (n = 10). Those in the experimental group were treated with an emulsion of lipiodol and pirarubicin through a microcatheter 2–3 weeks after implantation; those in the control group were treated with sterile water. Compared with the control group, the true diffusion coefficient (D) and pseudodiffusion coefficient (D*) values in liver tissues were significantly lower (p < 0.05 for all) and liver stiffness values (LSV) (10.58 ± 0.89 kPa) were higher in the experimental group (7.65 ± 0.86 kPa; p < 0.001). The median stage of liver fibrosis based on METAVIR scores was 1 (1,1) in the control group and 2 (2,3) in the experimental group (Z = 4.15, p < 0.001). D, D*, and LSV were significantly correlated with pathologic staining in the assessment of liver fibrosis (r = −0.54 p = 0.015; r = −0.50, p = 0.025; r = 0.91, p < 0.001; respectively). These data suggest that TACE aggravates liver injury and liver fibrosis, especially surrounding the tumor, in a rabbit VX2 liver tumor model. IVIM DWI and SWE can be used to evaluate the change in liver fibrosis.

Quantitative MRI for Assessment of Treatment Outcomes in a Rabbit VX2 Hepatic Tumor Model

Globally, primary and secondary liver cancer is one of the most common cancer types, accounting 8.2% of deaths worldwide in 2018. One of the key strategies to improve the patient's prognosis is the early diagnosis, when liver function is still preserved. In hepatocellular carcinoma (HCC), the typical wash-in/wash-out pattern in conventional magnetic resonance imaging (MRI) reaches a sensitivity of 60% and specificity of 96-100%. However, in recent years functional MRI sequences such as hepatocellular-specific gadolinium-based dynamic-contrast enhanced MRI, diffusion-weighted imaging (DWI), and magnetic resonance spectroscopy (MRS) have been demonstrated to improve the evaluation of treatment success and thus the therapeutic decision-making and the patient's outcome. In the preclinical research setting, the VX2 liver rabbit tumor, which once originated from a virus-induced anaplastic squamous cell carcinoma, has played a longstanding role in experimental interventional oncology. Especially the high tumor vascularity allows assessing the treatment response of locoregional interventions such as radiofrequency ablation (RFA) and transcatheter arterial embolization (TACE). Functional MRI has been used to monitor the tumor growth and viability following interventional treatment. Besides promising results, a comprehensive overview of functional MRI sequences used so far in different treatment setting is lacking, thus lowering the comparability of study results. This review offers a comprehensive overview of study protocols, results, and limitations of quantitative MRI sequences applied to evaluate the treatment outcome of VX2 hepatic tumor models, thus generating a unique basis for future MRI studies and potential translation into the clinical setting. Level of Evidence: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2019. J. Magn. Reson. Imaging 2020;52:668-685.

Dual-Energy CT-Derived Volumetric Iodine Concentration for the Assessment of Therapeutic Response after Microwave Ablation in a Rabbit Model with Intrahepatic VX2 Tumor

PURPOSE

To evaluate whether changes in volumetric iodine concentration (VIC) could serve as a suitable predictor of therapeutic response to microwave (MW) ablation in a rabbit intrahepatic VX2 tumor model.

MATERIALS AND METHODS

Sixteen intrahepatic VX2 tumors were transplanted in 8 New Zealand White rabbits treated with MW ablation. Contrast-enhanced dual-energy CT scans were obtained at baseline and follow-up. Therapeutic response assessment by modified Response Evaluation Criteria In Solid Tumors (mRECIST), Choi criteria, and VIC changes was performed. An intraclass correlation coefficient (ICC) was used to characterize consistency of assessment results among the criteria used. Technical success was evaluated with explant pathologic findings as a reference. Correlations between technical success and variations in diameter, CT density, and VIC were analyzed.

RESULTS

Disease control was observed in 4, 8, and 10 of the 16 tumors per mRECIST, Choi criteria, and VIC changes, respectively. VIC exhibited strong consistency (ICC = 0.807, P < .0001) with Choi criteria. According to explant pathology, technical success was achieved in 10 of the 16 tumors. There was a moderate correlation between VIC changes and technical success (r = 0.532, P = .034), and no correlation was found between technical success and variations in diameter or CT density.

CONCLUSIONS

Compared with mRECIST and Choi criteria, dual-energy CT-derived VIC allowed for better prediction of therapeutic response after MW ablation and could provide a potential imaging biomarker of tumor response to MW ablation in patients with hepatocellular carcinoma.

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.

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.

Perfusion CT estimates photosensitizer uptake and biodistribution in a rabbit orthotopic pancreatic cancer model: a pilot study

RATIONALE AND OBJECTIVES

It was hypothesized that perfusion computed tomography (CT), blood flow (BF), blood volume (BV), and vascular permeability surface area (PS) product parameters would be predictive of therapeutic anticancer agent uptake in pancreatic cancer, facilitating image-guided interpretation of human treatments. The hypothesis was tested in an orthotopic rabbit model of pancreatic cancer, by establishing the model, imaging with endoscopic ultrasound (EUS) and contrast CT, and spatially comparing the perfusion maps to the ex vivo uptake values of the injected photosensitizer, verteporfin.

MATERIALS AND METHODS

Nine New Zealand white rabbits underwent direct pancreas implantation of VX2 tumors, and CT perfusion or EUS was performed 10 days postimplantation. Verteporfin was injected during CT imaging, and the tissue was removed 1 hour postinjection for frozen tissue fluorescence scanning. Region-of-interest comparisons of CT data with ex vivo fluorescence and histopathologic staining were performed.

RESULTS

Dynamic contrast-enhanced CT showed enhanced BF, BV, and PS in the tumor rim and decreased BF, BV, and PS in the tumor core. Significant correlations were found between ex vivo verteporfin concentration and each of BF, BV, and PS.

CONCLUSIONS

The efficacy of verteporfin delivery in tumors is estimated by perfusion CT, providing a noninvasive method of mapping photosensitizer dose.

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.

Early treatment response to sorafenib for rabbit VX2 orthotic liver tumors: evaluation by quantitative contrast-enhanced ultrasound

The aim of our study was to investigate the application of contrast-enhanced ultrasound (CEUS) and its quantification analysis for the prediction of early treatment response of sorafenib on rabbit VX2 liver tumor model. Rabbits were implanted VX2 tumor mass to establish a liver tumor model. Fourteen days after tumor implantation, rabbits presented with single liver tumor were randomly divided into two groups. Rabbits in treatment group were given by gavage once a day for 14 days with sorafenib suspension at a dose of 30 mg/kg, whereas rabbits in control group were given saline by gavage of the same volume. CEUS was performed before treatment and 3, 7, 14 days after treatment for the analysis of tumor size, enhancement pattern, and necrosis range. The time intensity curve (TIC) was used to obtain quantitative parameters of enhancement patterns. Before sorafenib administration, tumor volumes ranged from 0.24 to 0.75 cm(3) (mean 0.49 ± 0.18 cm(3)) in treatment group and 0.24 to 0.44 cm(3) (mean 0.30 ± 0.12 cm(3)) in control group. The dynamic enhancement patterns of tumors were homogeneous hyper-enhancement (n = 8), heterogeneous hyper-enhancement (n = 4), and peripheral rim-like enhancement (n = 2). All tumors of the treatment group presented with peripheral rim-like enhancement with large necrotic area after sorafenib administration, whereas tumors of the control group showed heterogeneous hyper-enhancement (n = 5) and peripheral rim-like enhancement (n = 2). There was a significant difference in area under the curve (AUC) before and after sorafenib treatment (P = 0.045). CEUS may be of value in the evaluation of early therapeutic response after sorafenib administration.

Ultrasound-mediated gene and drug delivery using a microbubble-liposome particle system

Theranostic agents present a promising clinical approach for cancer detection and treatment. We herein introduce a microbubble and liposome complex (MB-Lipo) developed for ultrasound (US) imaging and activation. The MB-Lipo particles have a hybrid structure consisting of a MB complexed with multiple Lipos. The MB components are used to generate high echo signals in US imaging, while the Lipos serve as a versatile carrier of therapeutic materials. MB-Lipo allows high contrast US imaging of tumor sites. More importantly, the application of high acoustic pressure bursts MBs, which releases therapeutic Lipos and further enhances their intracellular delivery through sonoporation effect. Both imaging and drug release could thus be achieved by a single US modality, enabling in situ treatment guided by real-time imaging. The MB-Lipo system was applied to specifically deliver anti-cancer drug and genes to tumor cells, which showed enhanced therapeutic effect. We also demonstrate the clinical potential of MB-Lipo by imaging and treating tumor in vivo.

Intraoperative detection of liver tumors aided by a fluorescence goggle system and multimodal imaging

Real-time image guidance in the operating room is needed to improve instantaneous surgical decisions. Toward this goal, we utilized a new fluorescence goggle system and a near-infrared fluorescent dye approved for human use, indocyanine green, to demonstrate the feasibility of detecting liver tumors intraoperatively. The fluorescence goggle provided successful imaging of multifocal breast cancer metastases in mouse liver. Diffused tumor deposits as small as 0.8 mm in diameter were detected, which were not obvious without the fluorescence goggle. A combination of surface-weighted fluorescence imaging and deep tissue-sensitive ultrasound imaging allowed comprehensive image guidance with the fluorescence goggle system for tumor resection in a rabbit VX2 liver metastasis model. This multimodal detection and guided surgical intervention strategy using ultrasonic imaging and real-time intraoperative fluorescence guidance is a promising and innovative technology platform for improving surgical outcome of human patients with primary or metastatic liver cancer.

The influence of blood supply on high intensity focused ultrasound a preliminary study on rabbit hepatic VX2 tumors of different ages

RATIONALE AND OBJECTIVES

The aim of this study was to explore the effects of blood supply on high-intensity focused ultrasound (HIFU) applied to rabbit hepatic VX2 tumors of different ages.

MATERIALS AND METHODS

Eighteen rabbits with VX2 hepatic tumors were randomly divided into three groups according to the time of sacrifice after tumor implantation: 10, 15, or 20 days. Contrast-enhanced ultrasound was performed immediately before HIFU ablation. The same settings for HIFU dose parameters were used to ablate the central tumor area in each group, and the real-time temperature of the targeted site of the tumor was measured. After HIFU, the coagulation necrosis volumes of tumor tissue and the microvascular density of residual tumor tissue were determined.

RESULTS

Histopathologic analysis showed that the extent of a tumor's blood supply followed the order 10-day group > 15-day group > 20-day group (P < .01). Contrast-enhanced ultrasound showed the same results. There was no statistically significant difference among the three groups in terms of temperature-increase parameters during HIFU treatment (P > .05). However, there were statistically significant differences between the groups in terms of temperature-decrease parameters during HIFU treatment and in terms of necrosis volumes after HIFU treatment (P < .05). Necrosis volume was inversely related to absolute enhanced intensity (r = -0.823, P < .001).

CONCLUSIONS

The extent of a tumor's blood supply had a significant effect on the temperature-decrease phase but not on the temperature-increase phase during HIFU treatment. The longer the temperature-decrease phase, the more slowly heat dissipated after HIFU, resulting in larger coagulation necrosis volumes.

DMBA-induced hamster buccal pouch carcinoma and VX2-induced rabbit cancer as a model for human oral carcinogenesis

In this article, we have described and compared the advantages and disadvantages of two potential animal cancer models (the hamster buccal pouch cancer model and the VX2-induced rabbit cancer model) for human squamous cell carcinomas of the oral mucosa. Currently, no animal cancer model is perfectly applicable to human oral squamous cell carcinomas. This is because the hamster buccal pouch cancer model has a different etiology and genetic constitution compared with human oral carcinomas. In addition, the VX2-induced rabbit cancer model is not produced in situ and, consequently, its natural behavior is totally reliant on the location of transplantation. Nonetheless, with the use of these two animal cancer models together, researchers could evaluate different aspects of the cellular and molecular biological characteristics or assess potential novel treatment regimens for squamous cell carcinomas of the human oral mucosa.

Biodistribution and acute toxicity of naked gold nanoparticles in a rabbit hepatic tumor model

There is a paucity of data regarding the safety of administering solid gold nanoparticles (AuNPs) in large animal tumor models. We assessed the acute toxicity and biodistribution of 5 nm and 25 nm solid AuNPs in New Zealand White rabbits (n = 6 in each) with implanted liver Vx2 tumors 24 h after intravenous injection. Gold concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP) and imaged with transmission electron microscopy (TEM). There was no clinico-pathologic evidence of renal, hepatic, pulmonary, or other organ dysfunction. After 25 nm AuNP administration, the concentration of white blood cells increased after treatment (p = 0.001). Most other blood studies were unchanged. AuNPs were distributed to the spleen, liver, and Vx2 tumors, but not to other tissues. The urinary excretion of AuNPs was bimodal as measured by ICP. 25 nm AuNPs were more evenly distributed throughout tissues and may be better tools for medical therapy.