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.

Renal and hepatic artery embolization with Pickering gel emulsion of lipiodol in rabbit

OBJECTIVE

This research aimed to evaluate the feasibility of a novel liquid embolic agent Pickering gel emulsion of lipiodol (PGEL) for renal and hepatic artery embolization in the rabbit experimental model.

METHODS

Embolization was performed in the right renal artery of 24 adult New Zealand White rabbits and 24 VX2 tumors in the left liver lobe. The rabbits were randomly allocated to four treatment groups (n = 6 per group): (A) normal saline (NS), (B) lipiodol, (C) 180-300 μm polyvinyl alcohol (PVA), and (D) PGEL.

RESULTS

Renal artery embolization in normal rabbits and transarterial embolization (TAE) in VX2 tumor-bearing rabbits indicated that PGEL achieved a better embolization effect for a longer time than lipiodol and PVA. The tumor growth ratio of the PGEL group was significantly lower than that of the NS, lipiodol, and PVA groups at 3 (P < 0.001) and 7 (P < 0.001) days after embolization. In addition, hematoxylin and eosin and immunohistochemical staining revealed that the tumor necrosis ratio was higher in the PGEL group than in the NS, lipiodol, and PVA groups (P < 0.01), and the expression levels of HIF-1α, VEGF, and CD31 decreased after PGEL embolization compared with the lipiodol and PVA treatments.

CONCLUSION

PGEL is an effective embolic material that provides immediate and total occlusion of the renal artery and may be a potential therapeutic embolic agent for TAE of HCC.

Nanoscale CaO2 materials for synergistic transarterial chemoembolization in a VX2 orthotopic rabbit liver cancer model

Transcatheter arterial chemoembolization (TACE) is extensively used in the treatment of hepatocellular carcinoma (HCC), but its efficacy is usually limited to secondary tumor hypoxia and other progressive exacerbation of the abnormal tumor microenvironment (TME). Herein, we synthesized polyvinyl pyrrolidone (PVP)-coated CaO₂ nanoparticles (CaO₂ NPs) and applied them as a synergistic agent to improve the antitumor efficacy of TACE. After injection into the tumor, CaO₂ NPs reacted with water to generate abundant oxygen, hydroxyl ions (OH^-), and calcium ions (Ca²⁺), thereby relieving tumor hypoxia, neutralizing acid, and overloading Ca²⁺ to mediate antitumor effects. Moreover, the effect of chemotherapeutic drugs within the TACE was improved due to the modulated TME. CaO₂ NPs efficiently regulated the TME and improved the antitumor effect of doxorubicin under hypoxia conditions in vitro. Compared to other groups, the TACE+CaO₂ NPs group achieved the lowest tumor growth rate, highest tumor necrosis rate, lowest expression of histological markers associated with hypoxia and angiogenesis (HIF-α, VEGF, and CD31), and highest CD8⁺ T cell recruitment in vivo. Thus, these findings demonstrated that CaO₂ NPs provide synergy for TACE therapy in the VX2 orthotopic rabbit liver cancer model, suggesting that they have a potential broad clinical application. STATEMENT OF SIGNIFICANCE: The efficacy of transcatheter arterial chemoembolization (TACE) for treatment of hepatocellular carcinoma is usually limited to secondary tumor hypoxia and other progressive exacerbation of the abnormal tumor microenvironment (TME). To address this issue, we synthesized CaO₂ nanoparticles (CaO₂ NP_S) which would react with water to generate abundant oxygen, hydroxyl ions (OH^-), and calcium ions (Ca²⁺), thereby relieving tumor hypoxia, neutralizing the acidic TME, and inducing Ca²⁺ overloading. The efficacy of CaO₂ NPs in combination with TACE was investigated in an orthotopic rabbit liver cancer model, and the results showed the great synergetic antitumor effect of TACE and CaO₂ NPs.

Development of a Hepatic VX2 carcinoma model in rabbits using an improved minimally invasive method and evaluation with imaging examinations

Context

The hepatic VX2 carcinoma model in rabbits has been widely used in interventional diagnosis and treatment research for hepatocellular carcinoma (HCC). However, traditional methods for developing this model all have their shortcomings.

Aims

To develop an improved method to construct an animal model of hepatic VX2 carcinoma.

Settings and Design

The puncture technique was used to obtain the VX2 tumor tissue. A tumor puncture-inoculation kit was designed and modified to implant the tumor tissue into the recipient rabbit's liver.

Methods and Material

18 New Zealand white rabbits were implanted with VX2 tumor tissue using the improved tumor puncture-inoculation kit under ultrasound guidance. Ultrasonography, contrast-enhanced computerized tomography, magnetic resonance imaging, and digital subtraction angiography were performed to evaluate tumor formation and imaging characteristics.

Statistical Analysis

Statistical analysis was performed using SPSS software. Two groups were compared using Student's t-test analysis.

Results

All rabbits tolerated VX2 tumor tissue implantation successfully. 17 out of the 18 experimental rabbits developed liver tumors, and one rabbit had abdominal tumor metastasis. The average volume of tumors was 39.47 mm³ and 460.1 mm³ (P < 0.001) on the 7^th and 14^th days after modeling, respectively. Imageological diagnosis showed that all tumors had abundant blood supply and typical imaging characteristics.

Conclusions

This improved modeling method is easy to operate and less traumatic, with a high tumor formation rate, low metastasis rate, prominent tumor imaging characteristics, and high detection rate, which is expected to become a promising method for constructing rabbit liver tumor model.

Development of A 3D-Printed Navigational Template for Establishing Rabbit VX2 Lung Cancer Model

BACKGROUND

The CT-guided percutaneous puncture-inoculation for establishing the rabbit VX2 lung cancer model (LCM) is time-consuming, requires repeated CT scans, and has a high complication rate. Therefore, this study aimed to develop a navigational template using 3D technology to provide an alternative method for establishing the model with improved success and complication rates.

MATERIALS AND METHODS

Ideal pressure was determined using chest CT data from 15 anesthetized rabbits fitted with sphygmomanometer cuff around their chests. Subsequently, a preliminary 3D template with a square window and cross-sign to facilitate precise installation was designed. Using another 20 rabbits fixed with the preliminary template, an ideal common puncture point and parameter were determined, a navigational tunnel was set up on the template surface, and the final puncture navigational template was printed out. Eight-four rabbits (42/group) were assigned to the experimental (template-guided puncture) and control (traditional puncutre) groups and underwent VX2 tumor-fragment inoculation to validate the template. Differences in various parameters between two groups were analyzed.

RESULTS

The ideal pressure was 30 mmHg. All rabbits were inoculated successfully and the template adequately fit the rabbit chest. The experimental group displayed significantly better operation time (198.93±36.64 vs 735.14±91.19 seconds); number of CT scans (0 vs 7.19±1.64); pneumothorax (11.9% vs 35.7%), chest seeding (16.7% vs 35.7%), and mid-lung field tumor-bearing (88.1% vs 59.5%) rates than the control group (all, P <0.05). The groups did not differ in rib injury, tumor volume or survival time (all, P > 0.05).

CONCLUSIONS

We successfully developed a puncture navigational template, providing an alternative method for establishing the rabbit VX2 LCM.

Survival Benefit of Radiofrequency Ablation with Intratumoral Cisplatin Administration in a Rabbit VX2 Lung Tumor Model

PURPOSE

This study evaluated the survival benefit of a combination therapy with radiofrequency ablation (RFA) and intratumoral cisplatin (ITC) administration for lung tumors by using a rabbit VX2 tumor model.

MATERIALS AND METHODS

Experiments were approved by the institutional animal care committee. VX2 tumor suspension was injected into the lungs of Japanese white rabbits under CT guidance to create a lung tumor model. Thirty-two rabbits bearing a transplanted VX2 lung tumor were randomly assigned to four groups of eight: control (untreated); RFA alone; ITC alone; and RFA with ITC. All treatments were performed one week after tumor transplantation. Kaplan-Meier survival curves were compared by the log-rank test.

RESULTS

The median survival time was 24.5 days (range 17-33 days) in the control group, 40 days (30-80 days) in the RFA alone group, 31.0 days (24-80 days) in the ITC alone group, and not reached (53-80 days) in the RFA with ITC group. The median survival was significantly longer with the RFA/ITC combination compared to the control group (P < 0.001), RFA alone (P = 0.034), and ITC alone (P = 0.004). The survival time after RFA alone was also significantly longer than that of the control group (P < 0.001). There was no significant difference in tumor size or the rate of pneumothorax between each group.

CONCLUSION

RFA prolonged the survival of rabbits with lung VX2 tumors when combined with ITC.

Irreversible electroporation ablation against subcutaneously implanted VX2 tumors in rabbits: findings of shearwave ultrasound elastography

PURPOSE

This study aimed to evaluate stiffness changes of rabbit subcutaneous VX₂ tumors before and after irreversible electroporation (IRE) ablationby shearwave ultrasound elastography (SWE).

METHODS

IRE was performed on 20 subcutaneously implanted VX₂ tumors in rabbits (R-SIVX₂). Tumor stiffness was measured by SWE at different time points (before IRE,120minutes after IRE,7 days after IRE and 14 days after IRE).

RESULTS

Before IRE, the mean stiffness (E_mean) of tumors was (10.45 ± 1.07) KPa. 120 minutes after I RE, the E_mean of tumors obviously rose to (70.53 ± 9.87) KPa. 7 days after IRE, the E_mean of tumors decreased to (40.22 ± 9.01) KPa. 14 days after IRE, the E_mean of tumors was (15.17 ± 1.00) KPa. A clear boundary was observed between the ablation area and the normal tissues in the pathological results.

CONCLUSIONS

The stiffness of the VX₂ tumors experienced a first rise process and tend to be normal in the procedure of IRE. SWE could provide tissue stiffness information of different IRE ablation period as a non-invasive method.

Expression of MMP-2 in residual VX2 liver tumor after transcatheter arterial embolization combined with portal venous embolization in an animal model

Objective

This study aimed to analyze the effects of transcatheter arterial embolization (TAE) combined with portal venous embolization (PVE) on the expression of MMP-2 in residual VX2 liver tumor tissues, liver function and non-embolic lobe regeneration.

Methods

A total of 72 rabbits were randomly divided into Sham, TAE, PVE and TAE ​+ ​PVE groups (n ​= ​18/group). The tissue samples from each group were taken at 6 ​h, 3 days and 7 days after interventional operation, respectively. MMP-2 expression was detected by immunohistochemistry, Real-time PCR, and Western-blotting. The main indicators (such as AST, ATL, and TBIL) of liver function and the volume of non-embolized hepatic lobes were measured in each group after operation. One-way ANOVA and Kruskal-wallis method were used for statistical analysis.

Results

The expression of MMP-2 mRNA and protein remained the highest in the Sham group, and the expression of MMP-2 mRNA and protein in TAE, PVE and TAE ​+ ​PVE groups were successively increased, and the expression of MMP-2 in TAE ​+ ​PVE group was always significantly higher than TAE group. The AST and ALT levels in each group on day 7 after operation showed a significant declination, and all groups have recovered to the preoperative baseline level and TBIL has a slight fluctuation in each group after operation with no statistical difference. On day 7 after operation, the increasing volume of non-embolized liver lobes in TAE ​+ ​PVE group showed a more significant effect than those in PVE group, but there was no statistical significance (37.62 ​± ​1.54 ​ml VS 36.18 ​± ​1.15 ​ml, P ​= ​0.881), and its volume was significantly higher than those in the sham group (27.03 ​± ​1.11 ​ml).

Conclusion

TAE ​+ ​PVE is considered to be an efficient and safe approach for treating rabbit VX2 liver transplantation tumor, but the expression of MMP-2 increased fastest after TAE ​+ ​PVE, which might promote tumor cell invasion and metastasis.

Evaluating the scope of intramedullary invasion of malignant bone tumor by DCE-MRI quantitative parameters in animal study

The purpose was to analyze the value of quantitative parameters of DCE-MRI in evaluating micro-infiltration of malignant bone tumors.

METHODS

Thirty-nine New Zealand white rabbits were used to establish malignant bone tumor models by implanting VX2 tumor fragments into the right tibiae. After three weeks, models were examined by conventional MRI and DCE-MRI; then the right tibiae were cut into sagittal sections and partitioned into histology slices for comparison with microscopic findings. Micro-infiltration groups were selected and the range of infiltration was determined under the microscope, and corresponding DCE images analyzed to obtain the quantitative parameters include Ktrans, Kep, v_e and v_p in parenchyma areas, micro-infiltration areas and simple edema areas. One-way ANOVA was used to compare the differences of the parameters between the three areas. Receiver operating characteristic curves (ROCs) were plotted to determine the accuracy of different parameters by area under curves (AUCs).

RESULTS

22 cases (22/39, 56.4%) were included in the micro-infiltration group and the infiltration depth ranged from 1.3 mm to 4.6 mm, with an average depth of 3.2 mm ± 0.8 mm. The statistical results of quantitative parameters in the three areas were as follows: Ktrans values were (0.494 ± 0.052), (0.403  ±  0.049), (0.173 ± 0.047) min^-1 (p = =0.000), Kep values were (1.959 ± 0.65), (1.528 ± 0.372), (1.174 ± 0.486) min^-1 (p = =0.000), v_e values were (0.247 ± 0.068), (0.283 ± 0.057), (0.168 ± 0.062) min^-1 (p = =0.000), v_p values were (0.125 ± 0.036), (0.108 ± 0.033), (0.098 ± 0.025) min^-1 (p = =0.022), respectively. Ktrans and Kep values had significant difference in the three areas after comparing between-groups, respectively. However, there were no significant difference in v_p values between parenchyma and micro-infiltration areas (p = =0.078), micro-infiltration and simple edema areas (p = =0.315), and v_e values between parenchyma and micro-infiltration areas (p = =0.056). The v_e values were higher in parenchyma and micro-infiltration areas then simple edema areas. Ktrans had highest accuracy in differentiating different areas (AUC > 0.9), respectively.

CONCLUSION

Quantitative parameters Ktrans, Kep and v_e can assess the extent of intramedullary invasion of malignant bone tumors. Ktrans have highest accuracy in differentiating different regions.

Synergism of wt-p53 and synthetic material in local nano-TAE gene therapy of hepatoma: comparison of four systems and the possible mechanism

Background

TAE-gene therapy for hepatoma, incorporating the tumor-targeted therapeutic efficacy of trans-arterial embolization, hydroxyapatite nanoparticles (nHAP) and anti-cancer wild-type p53 gene (wt-p53), was presented in our former studies (Int J Nanomedicine 8:3757-68, 2013, Liver Int 32:998-1007, 2012). However, the incompletely antitumoral effect entails defined guidelines on searching properer materials for this novel therapy.

Methods

Unmodified nHAP, Ca⁽²⁺⁾ modified nHAP, poly-lysine modified nHAP and liposome were separately used to form U-nanoplex, Ca-nanoplex, Pll-nanoplex, L-nanoplex respectively with wt-p53 expressing plasmid. The four nanoplexs were then applied in vitro for human normal hepacyte L02 and hepatoma HePG2 cell line, and in vivo for rabbits with hepatic VX2 tumor by injection of nanoplexs/lipiodol emulsion into the hepatic artery in a tumor target manner. The distribution, superficial potential, physical structure, morphology and chemical compositions of nanoplexs were evaluated by TEM, SEM, EDS etc., with the objective of understanding their roles in hepatoma TAE-gene therapy.

Results

In vitro, L-nanoplex managed the highest gene transferring efficiency. Though with the second highest transfection activity, Pll-nanoplex showed the strongest tumor inhibition activity while maintaining safe to the normal hepacyte L02. In fact, only Pll-nanoplex can combine both the antitumoral effect to HePG2 and safe procedure to L02 among the four systems above. In vivo, being the only one with successful gene transference to hepatic VX2 tumor, Pll-nanoplex/lipiodol emulsion can target the tumor more specifically, which may explain its best therapeutic effect and hepatic biologic response. Further physical characterizations of the four nanoplexs suggested particle size and proper electronic organic surface may be crucial for nano-TAE gene therapy.

Conclusion

Pll-nanoplex is the most proper system for the combined therapy due to its selectively retention in liver cancer cells, secondary to its morphological and physico-chemical properties of nanometric particle size, steady emulsion, proper organic and electronic surface.

Respiratory motion correction for liver contrast-enhanced ultrasound by automatic selection of a reference image

PURPOSE

Respiratory motion correction is necessary for the quantitative analysis of liver contrast-enhanced ultrasound (CEUS) image sequences. Most respiratory motion correction methods are based on the dual mode of CEUS image sequences, including contrast and grayscale image sequences. Due to free-breathing motion, the acquired two-dimensional (2D) ultrasound cine might show the in-plane and out-of-plane motion of tumors. The registration of an entire 2D ultrasound contrast image sequence based on out-of-plane images is ineffective. For the respiratory motion correction of CEUS sequences, the reference image is usually considered the standard for the deletion of any out-of-plane images. Most methods used for the selection of the reference image are subjective in nature. Here, a quantitative selection method for an optimal reference image from CEUS image sequences in the B mode and contrast mode was explored.

METHODS

The original high-dimensional ultrasound grayscale image data were mapped into a two-dimensional space using Laplacian Eigenmaps (LE), and K-means clustering was adopted. The center image of the larger cluster with a near-peak contrast intensity was considered the optimal ultrasound reference image. In the ultrasound grayscale image sequence, the images with the maximum correlations to the reference image in the same time interval were selected as the corrected image sequence. The effectiveness of this proposed method was then validated on 18 CEUS cases of VX2 tumors in rabbit livers.

RESULTS

Correction smoothed the time-intensity curves (TICs) extracted from the region of interest of the CEUS image sequences. Before correction, the average of the total mean structural similarity (TMSSIM) and the average of the mean correlation coefficient (MCC) from the image sequences were 0.45 ± 0.11 and 0.67 ± 0.16, respectively, and after correction, the average TMSSIM and MCC increased (P < 0.001) by 31% to 0.59 ± 0.11 and by 21% to 0.81 ± 0.11, respectively. The average deviation value (DV) index of the TICs from the image sequences prior to correction was 92.16 ± 18.12, and correction reduced the average to 31.71 ± 7.31. The average TMSSIM and MCC values after correction using the mean frame of the reference image (MBMFRI) were clearly lower than those after correction using the proposed method (P < 0.001). Moreover, the average DV after correction using the MBMFRI was obviously higher than that after correction using the proposed method (P < 0.001).

CONCLUSIONS

The breathing frequency of rabbits is notably faster than that of human beings, but the proposed correction method could reduce the effect of the respiratory motion in the CEUS image sequences. The reference image was selected quantitatively, which could improve the accuracy of the quantitative analysis of rabbit liver CEUS sequences using the reference image method based on the current standard of manual selection and the MBMFRI. This easy-to-operate method can potentially be used in both animal studies and clinical applications.

The efficacy of 99mTc-MIBI imaging in 125I seed implantation treatment of rabbit VX2 transplanted liver cancer

PURPOSE

To evaluate the efficacy of ^99mTc-MIBI imaging in the evaluation of ¹²⁵I radioactive particle implantation for treatment of rabbit VX2 transplanted liver cancer.

METHODS

Twelve New Zealand white rabbit VX2 liver cancer models were successfully prepared by tumor cell suspension method and randomly divided into a control group and treatment group. The treatment group received ¹²⁵I particle implantation according to the TPS plan, and the control group received the same number of hollow particle implantation. ^99mTc-MIBI imaging was performed before and 7 d, 14 d, and 28 d after implantation. The target lesion (target, T) and normal liver tissue (nontarget, N) were determined by region of interest (ROI) technique. Radioactivity count was used to calculate the ^99mTc-MIBI uptake ratio (target-to-nontarget ratio, T/N) between the target lesion and normal liver tissue, thereby obtaining early ratio (ER) and delayed ratio (DR), respectively. The retention index (RI) was calculated. The mice were sacrificed after 28 days for histopathologic observation.

RESULTS

The T/N ratio, ER, and DR showed no statistical changes following the implantation time in the control group. In the treatment group, ER and DR gradually decreased after implantation of ¹²⁵I seeds (P < 0.05). There was no significant difference in RI during different observation times between the treatment group and the control group. Compared with the treatment group, RI exhibited no statistical difference between before and 7 d, 7~14 d, and 14~28 d after implantation (P > 0.05).

CONCLUSION

This method has value in evaluating the efficacy of ¹²⁵I seed implantation treatment of rabbit VX2 transplanted liver cancer. The T/N ratio is independent of the tumor diameter, but is related to the blood perfusion and metabolic state of the tumor. Implantation of ¹²⁵I particles into the rabbit transplanted liver cancer can effectively inhibit tumor growth, thus is a safe and effective method.

Effectiveness of ozonated saline in the treatment of VX2 tumors in rabbits

Objective To investigate the efficacy, safety, and associated mechanisms of injected ozonated saline in the treatment of VX2 tumors. Methods A total of 90 rabbits bearing VX2 tumors on their left hind legs were randomly divided into three groups. The control group (A) received normal saline, while groups B and C received 20 μg/mL and 40 μg/mL O₃/O₂ ozonated saline, respectively. Rabbits were anesthetized and 2 mL of blood was drawn directly from the heart to measure serum concentrations of interleukin (IL-6) and tumor necrosis factor (TNF-α). The skin covering the VX2 tumor was cut in each rabbit and the maximum and vertical diameters of the tumors were measured under direct visualization. Several milliliters of saline, saline pre-treated with 20 μg/mL O₃/O₂, or saline pre-treated with 40 μg/mL O₃/O₂ were directly injected into the tumors of groups A, B, and C, respectively (injection volume (milliliter) =1/2 volume of the tumor, V = 1/2ab²). On days 4, 8 and 12 following treatment, 10 rabbits were randomly selected from each group for blood sample collection, and serum IL-6 and TNF-α were measured. The tumor growth rate was calculated by measuring the maximum and vertical diameters of the VX2 tumors under direct visualization. All selected rabbits were euthanized and the tumors, livers, and lungs were removed for pathological examination. The tumor necrosis rate was calculated by cutting the tumors into half along the longitudinal axis and measuring the maximum diameters of the intratumoral necrotic regions. Results The average tumor volume in the three groups increased to different degrees at each time point; however, the average tumor growth rates in groups B and C were substantially lower than that in group A, exhibiting a statistically significant difference. The difference in the tumor growth rate between group B and group C was not statistically significant. The serum concentrations of IL-6 and TNF-α increased in the three groups at each time point, with larger increases occurring in groups B and C; however, the greater increases did not reach statistical significance. Although the diameters of the necrotic areas were larger in both groups B and C than that in group A, significant differences in necrotic area diameters were only found when comparing groups A and C on days 4 and 12 following treatment. Conclusion Direct injection of different concentrations of ozonated saline into VX2 tumors significantly increased intratumoral necrosis and reduced the tumor growth rate. The associated mechanism may be partially mediated by IL-6 and TNF-α, as the serum concentrations of these molecules increased after the treatment.

Antitumor Effects of Intra-Arterial Delivery of Albumin-Doxorubicin Nanoparticle Conjugated Microbubbles Combined with Ultrasound-Targeted Microbubble Activation on VX2 Rabbit Liver Tumors

Image-guided intra-arterial therapies play a key role in the management of hepatic malignancies. However, limited clinical outcomes suggest the need for new multifunctional drug delivery systems to enhance local drug concentration while reducing systemic adverse reactions. Therefore, we developed the albumin-doxorubicin nanoparticle conjugated microbubble (ADMB) to enhance therapeutic efficiency by sonoporation under exposure to ultrasound. ADMB demonstrated a size distribution of 2.33 ± 1.34 µm and a doxorubicin loading efficiency of 82.7%. The echogenicity of ADMBs was sufficiently generated in the 2–9 MHz frequency range and cavitation depended on the strength of the irradiating ultrasound. In the VX2 rabbit tumor model, ADMB enhanced the therapeutic efficiency under ultrasound exposure, compared to free doxorubicin. The intra-arterial administration of ADMBs sufficiently reduced tumor growth by five times, compared to the control group. Changes in the ADC values and viable tumor fraction supported the fact that the antitumor effect of ADMBs were enhanced by evidence of necrosis ratio (over 70%) and survival tumor cell fraction (20%). Liver toxicity was comparable to that of conventional therapies. In conclusion, this study shows that tumor suppression can be sufficiently maximized by combining ultrasound exposure with intra-arterial ADMB administration.

Feasibility of hyperspectral analysis for discrimination of rabbit liver VX2 tumor

BACKGROUND

Hepatocellular carcinoma is one of the most common malignant tumors worldwide. Currently, the most accurate diagnosis imaging modality for hepatocellular carcinoma is enhanced magnetic resonance imaging. However, it is still difficult to distinguish cirrhosis lesions, and novel diagnosis modalities are still needed.

AIM

To investigate the feasibility of hyperspectral analysis for discrimination of rabbit liver VX2 tumor.

METHODS

In this study, a rabbit liver VX2 tumor model was established. After laparotomy, under direct view, VX2 tumor tissue and normal liver tissue were subjected to hyperspectral analysis.

RESULTS

The spectral signature of the liver tumor was clearly distinguishable from that of the normal tissue, simply from the original spectral curves. Specifically, two absorption peaks at 600-900 nm wavelength in normal tissue disappeared but a new reflection peak appeared in the tumor. The average optical reflection at the whole waveband of 400-1800 nm in liver tumor was higher than that of the normal tissue.

CONCLUSION

Hyperspectral analysis can differentiate rabbit VX2 tumors. Further research will continue to perform hyperspectral imaging to obtain more information for differentiation of liver cancer from normal tissue.

Intravoxel Incoherent Motion Diffusion-weighted MR Imaging for Early Evaluation of the Effect of Radiofrequency Ablation in Rabbit Liver VX2 Tumors

RATIONALE AND OBJECTIVES

This study aims to investigate the value of intravoxel incoherent motion (IVIM)-derived parameters for early evaluation of the efficiency of radiofrequency ablation (RFA) treatment for rabbit liver VX2 tumor.

MATERIALS AND METHODS

Eighteen rabbit liver VX2 tumor models were constructed, and computed tomography-guided RFA was performed. One day before and 7 days after RFA, 18 models underwent magnetic resonance imaging, including contrast-enhanced imaging and IVIM diffusion-weighted imaging with 16 b-factors (0-1000 s/mm²). Post-RFA liver tumors were segmented into viable tumor, inflammatory reaction, and ablation necrotic regions according to gross and histopathologic examinations. Parameters derived from IVIM were calculated. One-way analysis of variance and least significant difference test were used for comparisons among the three regions. The diagnostic performance of parameters was evaluated using receiver operating characteristic (ROC) analysis.

RESULTS

ADC_total, D, and f values were significantly lower in viable tumor than in inflammatory reaction regions (all P < .05), but D* showed no significant difference between the two regions. ADC_total values of viable tumor regions were significantly lower than that of ablation necrotic regions (P = .007), but D* values of necrotic regions were significantly lower than that of viable tumor regions (P = .045). In ROC analysis, ADC showed the highest area under the ROC curve for differentiating inflammatory reaction from viable tumor region.

CONCLUSIONS

ADC_total, D, and f were valuable discriminating markers for differentiation between regions of viable tumor and inflammatory reaction in post-RFA tumor, especially ADC_total outperformed the other two parameters with higher diagnostic performance.

Mesenchymal Stem Cells Promote Tumor Progression via Inducing Stroma Remodeling on Rabbit VX2 Bladder Tumor Model

Background and aim: Mesenchymal stem cells (MSCs) are capable of impacting tumor progression but its role in tumor stroma remodeling still remains unclear. This present study was aimed to evaluate the potential function of MSCs on tumor stroma remodeling using rabbits VX2 bladder tumor model. Methods: The VX2 bladder tumor models were established by injecting mixed cell suspensions (10⁶ of VX2 tumor cells and 0/10⁶/10⁷ of autologous MSCs in group A, B, C, respectively) into the bladder mucosa using thirty male New Zealand white rabbits. The tumor volume was measured by ultrasound at the time points of 1st, 2nd, 3rd and 4th week after inoculation. At the end of the fourth week, the tumor tissue expressions of basic fibroblast growth factor (bFGF), transforming growth factor beta 1 (TGFβ-1), hepatocyte growth factor (HGF), matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9) were determined using Real-time quantitative PCR and immunohistochemistry. Masson trichrome staining and Cy3-FITC double-labelled immunofluorescence staining were used to determine the MSCs distribution in tumor tissue in another two rabbits implanted with a cell suspension of 10⁶ VX2 tumor cells and 10⁶ autologous MSCs. Results: MSCs were homogeneously distributed in tumor tissues after 7 days of inoculation, which were not consistent with the distribution of tumor stroma. After 21 days of inoculation, MSCs have been integrated into tumor interstitial tissue and mainly distributed in the mesenchyma around the tumor nest. At the 1st, 2nd, 3rd and 4th week time point, tumor volume in group A < group B < group C, and the difference has statistical significance (all p<0.001).The relative mRNA and protein levels of bFGF, TGFβ-1 and HGF were significantly higher in group B and C compared with group A (all p<0.05), as well as the mRNA levels of bFGF, HGF were higher in group C than group B (p<0.05), and the protein levels of bFGF, TGFβ-1 were higher in group C than group B (p<0.05). The mRNA and protein levels of MMP2 were significantly higher in group B, C than group A (p<0.05). MMP9 was increasingly over expressed along with the growing amount of MSCs inoculated within tumor, both at the level of mRNA and protein (all p<0.05). Conclusion: MSCs participate in tumor stroma remodeling via inducing overexpression of some important growth factors and MMPs.

Perfusion Computer Tomography Assessment of the Effect of Angiotensin II On Blood Flow Distribution in Rabbits with Intrarenal VX2 Tumors

BACKGROUND/AIMS

Unlike other organs, which only have one set of capillary network, the renal microvasculature consists of two sets of capillary network series connected by efferent arterioles. Angiotensin II constricts the efferent glomerular artery. Hence, renal tumor blood flow (BF) distribution may be different from tumors in other organs. This study aims to investigate the effects of angiotensin II on the hemodynamics of intrarenal VX2 tumors using perfusion computed tomography(CT).

METHODS

Twenty-four male New Zealand white rabbits were randomly divided into three groups: groups A (blank controls), group B (negative controls), and group C (angiotensin II-treated animals). Group B and C were established to the model of intrarenal VX2 tumors. Furthermore, perfusion CT of the kidney was performed in each group. Prior to perfusion CT scan in group C, the mean arterial blood was elevated to 150-160 mmHg by angiotensin II. The BF, blood volume (BV), mean transit time (MTT), capillary permeability-surface area product (PS), and relative permeability-surface area product (RPS) of tumors and renal tissues were calculated.

RESULTS

Compared with normal renal cortex tissues in group A, the BF, BV and PS values of tumors in group B were significantly lower, MTT was prolonged and RPS increased. Compared with group B, only the RPS of these tumors increased from 83.23 ± 29.17% to 120.94 ± 31.84% by angiotensin II infusion. Angiotensin II significantly increased the RPS value of the renal cortex distant from the tumor (CDT) and the right renal cortex (RRC).

CONCLUSIONS

Perfusion CT can accurately observe the influence of angiotensin II on normal and tumor BF in kidneys. This clarifies the effect of angiotensin II on intrarenal tumor hemodynamics.

Combination therapy involving radiofrequency ablation and targeted chemotherapy with bevacizumab plus paclitaxel and cisplatin in a rabbit VX2 lung tumor model

Objective

Radiofrequency ablation (RFA) is less effective for large tumors > 3 cm in diameter. Various studies of combination therapy using RFA and other treatments have been conducted to improve the results of RFA treatment of lung tumors, survival was extended in a tumor model when RFA was followed by concomitant use of systemic chemotherapy. Bevacizumab (BCM) is a one of molecular target drugs. Numerous clinical trials and reports have shown BCM’s effect when used in combination with cisplatin (CDDP) in lung tumor. Our objective is to evaluate the survival of concurrent, combined use of radiofrequency ablation and BCM, and platinum-doublet chemotherapy [CDDP/paclitaxel (PTX)] in a rabbit VX2 lung tumor.

Results

Survival times of the RFA alone, CDDP/PTX, CDDP/PTX/BCM, RFA/CDDP/PTX, and RFA/CDDP/PTX/BCM groups were significantly prolonged compared to that of the control group (P = 0.0055, P = 0.0055, P = 0.0004, P = 0.0002, P = 0.0019, respectively). Survival of the RFA/CDDP/PTX/BCM group was not significantly prolonged compared to the RFA alone (P = 0.53) and CDDP/PTX/BCM group (P = 0.68), while showing a significantly shorter survival time than that of the RFA/CDDP/PTX group (P = 0.017). The addition to BCM with combination RFA and systemic therapy with CDDP/PTX did not have a positive effect on survival.

Dynamics of angiogenesis and cellularity in rabbit VX2 tumors using contrast-enhanced magnetic resonance imaging and diffusion-weighted imaging

A number of studies have demonstrated that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may be used to evaluate microvessel density (MVD), and may quantitatively reflect tumor angiogenesis. To investigate the dynamics, including angiogenesis and tumor cellularity, of rabbit VX2 tumors during the 4 weeks following tumor implantation, the present study used DCE-MRI combined with diffusion-weighted imaging (DWI) to scan the tumors at 3 days, and then at 1, 2, 3 and 4-week intervals, following tumor implantation. The dynamics, volume transfer coefficient (K^trans) and apparent diffusion coefficient (ADC) of the tumor parenchyma were analyzed. Furthermore, the associations between K^trans and MVD at 4 weeks after tumor implantation were analyzed. Tumor K^trans was positively correlated with MVD at 4 weeks (r=0.674, P<0.001). Following tumor implantation, the tumor K^trans level rose for 2 weeks and then began to decline, reaching its lowest point at 4 weeks (P<0.001). ADC values at 1 week were higher than at 3 days, but declined thereafter (P<0.001). Tumor necrosis appeared by 1 week after tumor implantation. The necrosis degree of tumor was gradually increased from the occurrence of necrosis within the 4-week time span of the present study (1 vs. 2 weeks, P=0.008; 2 vs. 3 weeks, P<0.001; 3 vs. 4 weeks, P<0.001). The present study identified that tumor angiogenesis is a dynamic process that serves a function in tumor growth, and that DCE-MRI may reflect tumor parenchymal MVD and be useful in evaluating angiogenesis.

Spiral computed tomography evaluation of rabbit VX2 hepatic tumors treated with 20 kHz ultrasound and microbubbles

The aim of the present study was to explore the therapeutic effect of 20 kHz ultrasound (US) and microbubbles (MBs) on rabbit VX2 liver tumors by spiral computed tomography (CT) scanning. A total of 16 New Zealand rabbits with hepatic VX2 tumors were divided into four groups: Control, MB, low-frequency US and US + MB. The treatment effect was evaluated by spiral CT scanning prior to, during and following treatment (at 0 weeks and the end of 1 and 2 weeks). The tumor growth rate was recorded. The specimens of VX2 tumors were collected for histological examination and transmission electron microscopy (TEM). No significant differences were observed between tumor areas measured by CT and pathology after 2-week treatment (P>0.05). The mean tumor growth rates in the control, MB, US and US + MB groups after 2 weeks of treatment were 385±21, 353±12, 302±14 and 154±9%, respectively (P<0.05, US + MB vs. the other three groups). Hematoxylin and eosin staining in the US + MB group revealed coagulation necrosis, interstitial hemorrhage and intravascular thrombosis. In the control, MB and US groups, tumor cells exhibited clear nuclear hyperchromatism. TEM of US + MB revealed vascular endothelial cell wall rupture, widened endothelial cell gaps, interstitial erythrocyte leakage and microvascular thrombosis, while intact vascular endothelial cells and normal erythrocytes in the tumor vessels were observed in the control, MB and US groups. A combination of 20 kHz US and MBs may effectively inhibit rabbit VX2 tumors. Spiral CT scanning is an ideal method to evaluate the US treatment on rabbit tumors.

Enhancing tissue permeability with MRI guided preclinical focused ultrasound system in rabbit muscle: From normal tissue to VX2 tumor

High Intensity Focused Ultrasound (HIFU) is an emerging noninvasive, nonionizing physical energy based modality to ablate solid tumors with high power, or increase local permeability in tissues/tumors in pulsed mode with relatively low power. Compared with traditional ablative HIFU, nondestructive pulsed HIFU (pHIFU) is present in the majority of novel applications recently developed for enhancing the delivery of drugs and genes. Previous studies have demonstrated the capability of pHIFU to change tissue local permeability for enhanced drug delivery in both mouse tumors and mouse muscle. Further study based on bulk tissues in large animals and clinical HIFU system revealed correlation between therapeutic effect and thermal parameters, which was absent in the previous mouse studies. In this study, we further investigated the relation between the therapeutic effect of pHIFU and thermal parameters in bulky normal muscle tissues based on a rabbit model and a preclinical HIFU system. Correlation between therapeutic effect and thermal parameters was confirmed in our study on the same bulk tissues although different HIFU systems were used. Following the study in bulky normal muscle tissues, we further created bulky tumor model with VX2 tumors implanted on both hind limbs of rabbits and investigated the feasibility to enhance tumor permeability in bulky VX2 tumors in a rabbit model using pHIFU technique. A radiolabeled peptidomimetic integrin antagonist, 111In-DOTA-IA, was used following pHIFU treatment in our study to target VX2 tumor and serve as the radiotracer for follow-up single-photon emission computed tomography (SPECT) scanning. The results have shown significantly elevated uptake of 111In-DOTA-IA in the area of VX2 tumors pretreated by pHIFU compared with the control VX2 tumors not being pretreated by pHIFU, and statistical analysis revealed averaged 34.5% enhancement 24h after systematic delivery of 111In-DOTA-IA in VX2 tumors pretreated by pHIFU compared with the control VX2 tumors.

Brachytherapy with Iodine-125 seeds strand for treatment of main portal vein tumor thrombi: an experimental study in a rabbit model

This study aims to establish an animal model of implanted main portal vein tumor thrombus (MPVTT) and to evaluate safety and efficacy of brachy therapy with Iodine-125 ((125)I) seeds strand to treat MPVTT of rabbit. VX2 tumor thrombus was implanted in main portal vein (MPV) of 32 New Zealand white rabbits. These rabbits were randomly divided into treatment group (Group T, T1-T16) and control group (Group C, C1-C16). (125)I seeds and blank seeds strand were implanted in MPV of rabbits in Group T and C, respectively. Changes of general condition, body weight and blood laboratory examination were monitored at every time point after procedure. 2 weeks later, 8 rabbits of each group were sacrificed for pathologic examination. The rest of rabbits were dissected postmortem, and therapeutic effects were evaluated on basis of multi-detector computed tomography and histopathology. Ki-67 labeling index (Ki-67 LI) and apoptosis index (AI) were compared between two groups. Overall survival period was recorded. At every time point after brachytherapy, more serious weight loss were detected in Group C. Results of liver function tests and blood cells counts showed no significant difference between two groups. Mean volume of tumor tissue within MPV were 565.40 ± 220.90 mm(3) in Group T and 2269.90 ± 437.00 mm(3) in Group C (P < 0.001). (Ki-67 LI) and AI were (4.14 ± 1.84)% and (6.51 ± 1.92)% in Group T, compared with (33.82 ± 6.07)% and (0.91 ± 0.26)% in Group C, respectively (P < 0.001). Media survival time of rabbits were 39.50 ± 2.37 days in Group T and 27.38 ± 1.22 days in Group C, respectively (P = 0.001). In conclusion, injecting and suspensory fixing VX2 tumor strip into MPV is a reliable method to establish MPVTT animal model. Brachytherapy with (125)I seeds strand was safe and effective to treat VX2 tumor strand inoculated in the MPV of rabbit.

Relevance of Rabbit VX2 Tumor Model for Studies on Human Hepatocellular Carcinoma: A MicroRNA-Based Study

MicroRNAs are small (~22 nt), noncoding RNA molecules that have critical cellular functions in proliferation, differentiation, angiogenesis and apoptosis. miRNA expression profiling has been used to create signatures of solid tumors and, in many cases, it has been shown to correlate with the severity of the disease. The rabbit VX2 tumor model has been used widely to study a number of human cancers. Our objective in this study is to generate an miRNA signature of the VX2 tumor and to identify miRNAs that are highly expressed in this aggressive tumor. In this study, we performed miRNA profiling of the rabbit VX2 tumor using a microarray that has probes for 1292 unique miRNAs. Their expression in tumor samples was quantified and analyzed. We found that 35 miRNAs were significantly up-regulated in the VX2 tumor. Among these, 13 human miRNAs and eight members of the let-7 family were previously identified in cancers. In addition, we show that the expression of three miRNAs (miR-923, miR-1275, and miR-1308) is novel for the rabbit VX2 tumor, and their expression was not previously shown to be associated with any type of cancer. For the first time, we show the miRNA signature profile for a solid tumor in a rabbit model. miRNAs highly expressed in the VX2 tumor may serve as novel candidates for molecular biomarkers and as potential drug targets.

The effects of percutaneous ethanol injection followed by 20-kHz ultrasound and microbubbles on rabbit hepatic tumors

OBJECTIVE

Low-frequency ultrasound (US) in combination with microbubbles (MBs) is able to inhibit the growth of VX2 rabbit liver tumors. In this study, we investigated the feasibility of using percutaneous ethanol injection (PEI) followed by low-frequency ultrasound and microbubbles (USMB) to inhibit VX2 tumor growth.

METHODS

Eighteen New Zealand rabbits with hepatic VX2 tumors were divided into three groups: PEI, low-frequency ultrasound and MBs followed by PEI (USMB + PEI), and PEI followed by USMB (PEI + USMB). PEI was performed by ultrasound-guided injection of 95% anhydrous alcohol into internal liver tumors in rabbits twice a week for 2 weeks. The US parameters were 20 kHz, 2 W/cm(2), 40% duty cycle, 5 min, and once every other day for 2 weeks. Magnetic resonance imaging (MRI) was used to observe tumors before and after treatment, to examine changes in the tumors, and to measure the diameters of the tumors. All animals were followed up for 180 days after tumor implantation. Autopsy was performed at the end of the scheduled follow-up or immediately after death. Anatomically observed metastatic sites included the liver, lung, abdomen, and pelvic cavity. The survival time of all rabbits was recorded.

RESULTS

After 4 weeks of treatment, on MRI, the tumor diameters in the PEI, USMB + PEI, and PEI + USMB groups were 8.33 ± 1.83, 19 ± 2.61, and 4.5 ± 1.22 mm, respectively. There was a significant difference in tumor size indicated by MRI in the three groups. Tumor size was smaller in the PEI + USMB group than in the PEI and USMB + PEI groups, with t = 4.54, p = 0.0062, and t = 16.38, p < .0001, respectively. The PEI + USMB group showed the fewest metastasis sites (χ(2) = 11.7333, p = 0.0194) and the longest survival period (χ(2) = 7.448, p = 0.0241).

CONCLUSION

Percutaneous ethanol injection followed by low-frequency ultrasound and microbubbles can be effective in inhibiting rabbit liver tumors and prolonging survival time.

Percutaneous Tumor Ablation: Cryoablation Facilitates Targeting of Free Epirubicin-Ethanol-Ioversol Solution Interstitially Coinjected in a Rabbit VX2 Tumor Model

This acute study was aimed at exploring the ability of a cryoablative lesion to drive the distribution of a concomitant in situ injection of a free epirubicin-ethanol-ethiodol-methylene blue mixture. We report the feasibility and safety of this new percutaneous computed tomography-guided combinatorial ablative procedure on VX2 tumors. Eight New Zealand white rabbits bearing 16 tumors on both side of the back muscle were randomly selected and treated on the same day with the following procedures: (1) 8 concomitant cryoablation and interstitial chemotherapy and (2) 8 intratumor marginal chemotherapy. For the latter, an injection needle was positioned at the inner distal margin of a first selected tumor side, where the chemotherapy was delivered during 5 serial sequences. For the concomitant therapy, a single cryoneedle maintained the ice front at the tumor margin, where a needle delivered the drug dose during 5 freeze-injection-thaw sequences. Enhanced computed tomography scans on days 3, 7, and 10 assessed the tumor contours and the tracer localization. Two rabbits were killed on days 0, 3, 7, and 10 for gross and histopathological analyses. During the concomitant therapy, ioversol was distributed at the tumor and iceball margins along with the methylene blue. Enhanced computed tomography on days 3, 7, and 10 showed a focal enlarging defect of the tumor marginal enhancing rim. The rim coincided with focal necrosis at histopathology. During the intratumor chemotherapy procedure, computed tomography showed that the tracers distributed mostly over the tumor mass. No marginal necrosis was detected at histopathology. On day 10, the tumor size for the intratumor chemotherapy group was twice that of the concomitant therapy group. No adverse events were observed. In this VX2 tumor model, our image-guided concomitant therapy is feasible and may enhance the effectiveness of a free epirubicin tracer mixture at the tumor margin.

Low contrast medium and radiation dose for hepatic computed tomography perfusion of rabbit VX2 tumor

AIM: To evaluate the feasibility of low contrast medium and radiation dose for hepatic computed tomography (CT) perfusion of rabbit VX2 tumor.

METHODS: Eleven rabbits with hepatic VX2 tumor underwent perfusion CT scanning with a 24-h interval between a conventional tube potential (120 kVp) protocol with 350 mgI/mL contrast medium and filtered back projection, and a low tube potential (80 kVp) protocol with 270 mgI/mL contrast medium with iterative reconstruction. Correlation and agreement among perfusion parameters acquired by the conventional and low dose protocols were assessed for the viable tumor component as well as whole tumor. Image noise and tumor-to-liver contrast to noise ratio during arterial and portal venous phases were evaluated.

RESULTS: A 38% reduction in contrast medium dose (360.1 ± 13.3 mgI/kg vs 583.5 ± 21.5 mgI/kg, P < 0.001) and a 73% decrease in radiation dose (1898.5 mGy • cm vs 6951.8 mGy • cm) were observed. Interestingly, there was a strong positive correlation in hepatic arterial perfusion (r = 0.907, P < 0.001; r = 0.879, P < 0.001), hepatic portal perfusion (r = 0.819, P = 0.002; r = 0.831, P = 0.002), and hepatic blood flow (r = 0.945, P < 0.001; r = 0.930, P < 0.001) as well as a moderate correlation in hepatic perfusion index (r = 0.736, P = 0.01; r = 0.636, P = 0.035) between the low dose protocol with iterative reconstruction and the conventional protocol for the viable tumor component and the whole tumor. These two imaging protocols provided a moderate but acceptable agreement for perfusion parameters and similar tumor-to-liver CNR during arterial and portal venous phases (5.63 ± 2.38 vs 6.16 ± 2.60, P = 0.814; 4.60 ± 1.27 vs 5.11 ± 1.74, P = 0.587).

CONCLUSION: Compared with the conventional protocol, low contrast medium and radiation dose with iterative reconstruction has no significant influence on hepatic perfusion parameters for rabbits VX2 tumor.

Using semi-quantitative dynamic contrast-enhanced magnetic resonance imaging parameters to evaluate tumor hypoxia: a preclinical feasibility study in a maxillofacial VX2 rabbit model

PURPOSE

To test the feasibility of semi-quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) parameters for evaluating tumor hypoxia in a maxillofacial VX2 rabbit model.

METHODS

Eight New Zealand rabbits were inoculated with VX2 cell solution to establish a maxillofacial VX2 rabbit model. DCE-MRI were carried out using a 1.5 Tesla scanner. Semi-quantitative DCE-MRI parameters, maximal enhancement ratio (MER) and slope of enhancement (SLE), were calculated and analyzed. The tumor samples from rabbits underwent hematoxylin-eosin (HE), pimonidazole (PIMO) and vascular endothelial growth factor (VEGF) immunohistochemistry (IHC) staining, and the PIMO area fraction and VEGF IHC score were calculated. Spearman's rank correlation analysis was used for statistical analysis.

RESULTS

The MER values of eight VX2 tumors ranged from 1.132 to 1.773 (1.406 ± 0.258) and these values were negatively correlated with the corresponding PIMO area fraction (p = 0.0000002), but there was no significant correlation with the matched VEGF IHC score (p = 0.578). The SLE values of the eight VX2 tumors ranged from 0.0198 to 0.0532 s(-1) (0.030 ± 0.011 s(-1)). Correlation analysis showed that there was a positive correlation between SLE and the corresponding VEGF IHC score (p = 0.0149). However, no correlation was found between SLE and the matched PIMO area fraction (p = 0.662). The VEGF positive staining distribution predominantly overlapped with the PIMO adducts area, except for the area adjacent to the tumor blood vessel.

CONCLUSIONS

The semi-quantitative parameters of DCE-MRI, MER and SLE allowed for reliable measurements of the tumor hypoxia, and could be used to noninvasively evaluate hypoxia during tumor treatment.

Rabbit hepatic arterial anatomy variations: implications on experimental design

BACKGROUND

The VX2 rabbit model of liver cancer is commonly used to evaluate the efficacy of locoregional anticancer therapy and knowledge of the hepatic arterial anatomy in the rabbit is important for catheter-directed experiments.

PURPOSE

To describe the normal anatomy and anatomic variations of the celiac axis and hepatic artery in the rabbit.

MATERIAL AND METHODS

Angiograms of 222 rabbits were retrospectively reviewed. The branching pattern of the celiac axis was classified and the diameters of the major branches were measured. Paired t-tests were used to compare the difference between the average sizes of arteries.

RESULTS

Variant celiac axis or hepatic artery anatomy was noted in 25.9% of angiograms, with the gastric branches arising from the proper hepatic artery in 23.3% of cases. The celiac axis could be successfully classified into one of five distinct branching patterns in 193 (86.9%) cases. The mean diameters of the right and left hepatic arteries were 0.67 mm (95% CI [0.64, 0.7]) and 1.25 mm (95% CI [1.19, 1.31]), respectively. The mean diameters of the medial and lateral branches of the left hepatic artery were 0.63 mm (95% CI [0.6, 0.67]) and 0.91 mm (95% CI [0.86, 0.96]), respectively. The right hepatic artery was significantly smaller than the left hepatic artery and the lateral branch of the left hepatic artery (all P values <0.0001).

CONCLUSION

Arterial variants in the rabbit are not uncommon. The proper hepatic artery often gives origin to gastric artery branches. To facilitate superselective intra-arterial intervention, the left lateral lobe of the liver should be targeted for tumor implantation because of the significant size difference between the right and left hepatic arteries.

Experimental study of image-guided percutaneous microwave ablation in rabbit lung VX2 tumor model

PURPOSE

To investigate the efficacy and safety of percutaneous microwave ablation.

METHODS

Twenty-six rabbits with lung VX2 tumor were randomly divided into experimental and control group. In the experimental group, microwave ablation guided by ultrasound or CT was performed based on location of the tumor. Enhanced CT scan was carried out immediately before and after the ablation for all animals. Two animals from each group were sacrificed immediately or 1 week after the ablation respectively and the others were followed for the rest of their lives.

RESULTS

CT scan revealed that the tumor was greatly reduced or ablated after ablation. Pathological examination immediately after ablation also confirmed the tumor reduction or ablation. The survival time of the animals in the experimental group was significantly longer than that in the control group.

CONCLUSIONS

Microwave ablation is a safe and effective method for treating lung cancer in rabbits, showing potential clinical applicability.

Comparing CT perfusion with oxygen partial pressure in a rabbit VX2 soft-tissue tumor model

The aim of this study was to evaluate the oxygen partial pressure of the rabbit model of the VX2 tumor using a 64-slice perfusion CT and to compare the results with that obtained using the oxygen microelectrode method. Perfusion CT was performed for 45 successfully constructed rabbit models of a VX2 brain tumor. The perfusion values of the brain tumor region of interest, the blood volume (BV), the time to peak (TTP) and the peak enhancement intensity (PEI) were measured. The results were compared with the partial pressure of oxygen (PO2) of that region of interest obtained using the oxygen microelectrode method. The perfusion values of the brain tumor region of interest in 45 successfully constructed rabbit models of a VX2 brain tumor ranged from 1.3-127.0 (average, 21.1 ± 26.7 ml/min/ml); BV ranged from 1.2-53.5 ml/100g (average, 22.2 ± 13.7 ml/100g); PEI ranged from 8.7-124.6 HU (average, 43.5 ± 28.7 HU); and TTP ranged from 8.2-62.3 s (average, 38.8 ± 14.8 s). The PO2 in the corresponding region ranged from 0.14-47 mmHg (average, 16 ± 14.8 mmHg). The perfusion CT positively correlated with the tumor PO2, which can be used for evaluating the tumor hypoxia in clinical practice.

Cellular Imaging Using Equivalent Cross-Relaxation Rate Technique in Rabbit VX-2 Tumor Model

Purpose:

Equivalent cross-relaxation rate (ECR) imaging (ECRI) is a measurement technique that can be used to quantitatively evaluate changes in structural organization and cellular density by MRI. The aim of this study was to evaluate the correlation between the ECR value and cellular density in the rabbit VX2 tumor model.

Materials and methods:

Five rabbits implanted with 10 VX2 tumors in the femur muscles were included in this study. We adopted the off-resonance technique with a single saturation transfer pulse frequency of 7 ppm downfield from water resonance. The ECR value was defined as the percentage of signal loss between the unsaturated and saturated images. ECR images were constructed based on the percentage of the ECR value. Pathological specimens were divided into 34 areas and classified into two groups: the viable group and the necrotic group. ECR values were measured and compared between groups. The correlation between the ECR value and cellular density was then determined.

Results:

The mean ECR value was significantly higher in the viable group than in the necrotic group (61.2% vs. 35.8%). The area under the curve that calculated by receiver operating characteristic curve was 0.991 at 7 ppm. The regression graph showed a linear relationship between the ECR value and cellular density; the correlation coefficient (r) was 0.858.

Conclusion:

There is a strong association between the ECR value and cellular density in VX2 tumors and so ECRI could be a potentially useful technique for accurately depicting viable and necrotic areas.

Technology of in vivo two-dimension multi-voxel 1H magnetic resonance spectroscopy for rabbit liver VX2 tumor

AIM: To investigate the best techniques of in vivo two-dimension multi-voxel ¹H magnetic resonance spectroscopy (2D ¹H-MRS) for rabbit liver VX2 tumor.

METHODS: The liver of 8 New Zealand white rabbits was implanted directly and respectively with VX2 tumor lump after abdominal cavity was opened. 2D ¹H-MRS acquisition in vivo and unenhanced MRI was performed respectively from the 2^nd week to 4^th week after VX2 tumor was implanted. With knee coil, in vivo 2D ¹H-MRS acquisitions were performed respectively with different TR, different TE and different NEX at 1.5 T MR scanner when other parameters were the same. The distinction between groups was analyzed by SPSS11.0 with baseline and signal-noise ratio (SNR).

RESULTS: From the qualified MRS spectrum, there were up to 6 peaks which could be identified: methyl lipids (Lip1), methylene lipids (Lip2), methylene lipids with double carbon bond (Lip3), glutamine and glutamate complex (Glx), Choline (Cho), and glycogen and glucose complex (Glyu). Baseline and SNR had no significant differences between TR = 1000 ms, 2000 ms and 3000 ms. Baseline had no significant difference between TE = 30 ms and 144 ms. Except that SNR of Glx with 30 ms in TE was higher than that with 144 ms in TE (1.95 ± 0.36 vs 1.24 ± 0.26, P < 0.05), SNR of other metabolites were similar. With NEX increasing, the distinctions of baseline between NEX = 4, 8 and 16 were significant (χ² = 10.000, P < 0.01). SNR of all metabolites increased when NEX was increased gradually. Both of baseline and SNR were the best when NEX was 16.

CONCLUSION: It's practical of in vivo two-dimension multi-voxel ¹H-MRS on the rabbit liver VX2 tumor by a 1.5 T MR scanner. Immobilization, pre-scan (reaching FWHM ≤ 10 Hz and WS ≥ 98%), knee coil, TR = 1000 ms, TE = 30 ms and NEX = 16 may be the best to acquire highly qualified spectra.

Establishing models of portal vein occlusion and evaluating value of multi-slice CT in hepatic VX2 tumor in rabbits

AIM: To establish models of portal vein occlusion of hepatic VX2 tumor in rabbits and to evaluate the value of multi-slice CT.

METHODS: Forty New Zealand rabbits were divided into 4 groups according to digital table: Immediate group (group A; transplantation of tumor immediately after the portal vein occlusion), 3-wk group (group B; transplantation of tumor at 3 wk after the portal vein occlusion), negative control group (group C) and positive control group (group D), 10 rabbits in each group. Hepatic VX2 tumor was transplanted with abdominal-embedding innoculation immediately after the portal vein occlusion and at 3 wk after the portal vein occlusion. Meanwhile, they were divided into negative control group (Left external branch of portal vein was occluded by sham-operation, and left exite was embedded and inoculated pseudoly) and positive control group (Transplanted tumor did not suffer from the portal vein occlusion). All rabbits were scanned with multi-slice CT.

RESULTS: All 40 animals were employed in the final analysis without death. Tumor did not grow in both immediate group and 3-wk group. In 3-wk group, left endite was atrophied and growth of tumor was inhibited. The maximal diameter of tumor was significantly smaller than that in positive control group (2.55 ± 0.46 vs 3.59 ± 0.37 cm, t = 5.57, P < 0.001). Incidences of metastasis in the liver and lung were lower in 3-wk group than those in positive control group (10% vs 40%, and 90% vs 100%, respectively). The expression intensities of the vascular endothelium growth factor (VEGF) in groups A, B, C and D were 0.10 ± 0.06, 0.66 ± 0.21, 0.28 ± 0.09 and 1.48 ± 0.32, respectively. VEGF expression level in the test group A was significantly lower than that in the negative control group C (t = 5.07; P < 0.001). In addition, VEGF expression in the test group B was significantly lower than that in the positive control group D (t = 6.38; P < 0.001). Scanning with multi-slice CT showed that displaying rate of hepatic artery branches was obviously lower in grade III (40%) than that in gradeI(70%) and II (100%) (P < 0.05); but there was no significant difference in displaying rate of the portal vein at various grades. Values of blood flow (BF) of the liver, blood volume (BV), mean transit time (MTT) and permeability of vascular surface (PS) were lower in the immediate group and 3-wk group than those in control groups, but values of hepatic arterial fraction (HAF) were increased. Significant positive correlations were existed between BF and BV (r = 0.905, P < 0.01), and between BF and PS (r = 0.967, P < 0.01), between BV and PS (r = 0.889, P < 0.01). A significant negative correlation existed between PV and HAF (r = -0.768, P < 0.01), between PS and HAF (r = -0.557, P < 0.01). The values of BF, BV and PS had a positive correlation with VEGF (r_BF = 0.842, r_BV = 0.579, r_PS = 0.811, P < 0.01) . However, there was no significant correlation between the values of MTT and HAF and the VEGF expression (r_MTT = 0.066, r_HAF = -0.027).

CONCLUSION: Ligating the left external branch of portal vein is an ideal way to establish models of portal vein occlusion in rabbits with hepatic VX2 tumor. Multi-slice CT plays a key role in evaluating effect of portal vein occlusion.