Extravesical cryosurgical approach for VX2 bladder tumor in rabbits

Development of a novel castration-resistant orthotopic prostate cancer model in New Zealand White rabbit

BACKGROUND

Prostate cancer (PCa) models in mice and rats are limited by their size and lack of a clearly delineated or easily accessible prostate gland. The canine PCa model is currently the only large animal model which can be used to test new preclinical interventions but is costly and availability is sparse. As an alternative, we developed an orthotopic human prostate tumor model in an immunosuppressed New Zealand White rabbit. Rabbits are phylogenetically closer to humans, their prostate gland is anatomically similar, and its size allows for clinically-relevant testing of interventions.

METHODS

Rabbits were immunosuppressed via injection of cyclosporine. Human PC3pipGFP PCa cells were injected into the prostate via either (a) laparotomy or (b) transabdominal ultrasound (US) guided injection. Tumor growth was monitored using US and magnetic resonance imaging (MRI). Contrast-enhanced ultrasound (CEUS) imaging using nanobubbles and Lumason microbubbles was also performed to examine imaging features and determine the optimal contrast dose required for enhanced visualization of the tumor. Ex vivo fluorescence imaging, histopathology, and immunohistochemistry analyses of the collected tissues were performed to validate tumor morphology and prostate-specific membrane antigen (PSMA) expression.

RESULTS

Immunosuppression and tumor growth were, in general, well-tolerated by the rabbits. Fourteen out of 20 rabbits, with an average age of 8 months, successfully grew detectable tumors from Day 14 onwards after cell injection. The tumor growth rate was 39 ± 25 mm² per week. CEUS and MRI of tumors appear hypoechoic and T2 hypointense, respectively, relative to normal prostate tissue. Minimally invasive US-guided tumor cell injection proved to be a better method compared to laparotomy due to the shorter recovery time required for the rabbits following injection. Among the rabbits that grew tumors, seven had tumors both inside and outside the prostate, three had tumors only inside the prostate, and four had tumors exclusively outside of the prostate. All tumors expressed the PSMA receptor.

CONCLUSIONS

We have established, for the first time, an orthotopic PCa rabbit model via percutaneous US-guided tumor cell inoculation. This animal model is an attractive, clinically relevant intermediate step to assess preclinical diagnostic and therapeutic compounds.

Induction of VX2 para-renal carcinoma in rabbits: generation of animal model for loco-regional treatments of solid tumors

Background

Animal models of para-renal cancer can provide useful information for the evaluation of tumor response to loco-regional therapy experiments in solid tumors. The aim of our study was to establish a rabbit para-renal cancer model using locally implanted VX2 tumors.

Methods

In order to generate a rabbit model of para-renal cancer, we established four hind limb donor rabbits by using frozen VX2 tumor samples. Following inoculation, rabbits were monitored for appetite and signs of pain. Viable tumors appeared as palpable nodules within 2 weeks of inoculation. Tumor growth was confirmed in all rabbits by high-resolution ultrasound analysis and histology. Once tumor growth was established, hind limb tumors extraction was used for tumor line propagation and para-renal tumor creation. Twenty-one rabbit models bearing para-renal cancer were established by implanting VX2 tumor into the para-renal capsula. Tumors developed into discreet 2–3 cm nodules within 1–3 weeks of implantation. Serial renal ultrasonography follow-up, starting 1 week after tumor implantation, was performed. Two weeks after tumor implantation, rabbits were euthanized and tumors and other organs were collected for histopathology.

Results

Tumor growth after VX2 tumor fragment implantation was confirmed in all rabbits by high-resolution ultrasound (US) imaging examinations of the para-renal regions and was measured with digital caliper. The para-renal injection of VX2 tumor fragments, achieved tumor growth in 100% of cases. All data were confirmed by histological analysis.

Conclusions

We generated for the first time, a model of para-renal cancer by surgical tumor implantation of VX2 frozen tumor fragments into rabbit’s para-renal region. This method minimizes the development of metastases and the use of non-necrotic tumors and will optimize the evaluation of tumor response to loco-regional therapy experiments.

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.

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.

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.

Establishment and identification of a rabbit model of peritoneal carcinomatosis from gastric cancer

BACKGROUND

Gastric cancer peritoneal carcinomatosis is a common clinical problem, but there are no suitable large animal models to study this problem. This study was to establish a stable rabbit peritoneal carcinomatosis model of gastric cancer using VX2 tumor, and analyze the clinico-pathological features.

METHODS

VX2 tumor was implanted into 36 New Zealand rabbits by 3 methods: laparotomic orthotopic injection of cancer cells into the submucosal layer of the stomach (Group A), laparotomic implantation of tumor tissue into the greater omentum immediately beneath the gastric antrum (Group B), and percutaneous injection of tumor cells directly into the peritoneal cavity (Group C), 12 rabbits in each group. The animals were closely observed and detailed clinico-pathological studies were conducted.

RESULTS

The success rates of peritoneal carcinomatosis formation were 100% (12/12), 91.7% (11/12) and 58.3% (7/12), respectively, for Groups A, B and C (P = 0.019, A versus C; P = 0.077, B versus C; P = 0.500, A versus B, Fisher's exact test). Two weeks after submucosal cancer cells injection in Group A, ulcerative gastric cancer with peritoneal carcinomatosis showed typical VX2 tumor pathology, with widespread intraperitoneal metastatic nodules, bloody ascites and perspicuous pulmonary metastases. The clinico-pathological progression pattern was very similar to patients of advanced gastric cancer with peritoneal carcinomatosis. Groups B and C showed similar pattern of cancer progression, but less aggressive.

CONCLUSIONS

First large animal model of peritoneal carcinomatosis from gastric cancer has been established by laparotomic orthotopic injection of VX2 cancer cells into the submucosal layer of the stomach, providing a more suitable model for surgical interventional studies. The clinico-pathological features of this model resemble human peritoneal carcinomatosis.

MRI and hybrid PET/CT for monitoring tumour metastasis in a metastatic breast cancer model in rabbit

OBJECTIVE

To study tumour growth and metastasis in a rabbit metastatic breast cancer (MBC) model and find the most sensitive screening modality in monitoring tumour metastasis.

METHODS

The MBC model was established by injecting a VX2 tumour mass suspension into the mammary glands of 23 rabbits and was monitored by using physical examination, X-ray, MRI and hybrid PET/CT.

RESULTS

Of all 23 rabbits, axillary lymph node metastasis was detected in 21 (91%) at day 33 after tumour inoculation, mediastinal node metastasis in five (22%) at day 42, abdominal node metastasis in two (9%) at day 48, lung metastasis in six (26%) at day 39, liver metastasis in three (13%) at day 48, and lumbar spine metastasis in one (4%) at day 51. Tumour invasion of pleura was found in one, stomach wall in one, and pleura and stomach concurrently in one rabbit. Sensitivity for detection of lymph node metastases was 78.6% (22/28) and 67.9% (19/28) with MRI and PET/CT, respectively; and sensitivity for detection of metastases in distant organs was 85.7% (12/14) and 71.4% (10/14), respectively.

CONCLUSIONS

The MBC model used here exhibits fast tumour growth and extensive metastasis in a relatively short period. Its metastatic pattern is quite similar to that of human MBC and hence could be potentially used as a model for testing imaging modalities and translational research, e.g., MBC management. MRI is superior to PET/CT in monitoring tumour metastasis.

Transurethral bladder cryoablation in the porcine model

OBJECTIVES

To examine the feasibility of transurethral, focal, full-thickness bladder wall cryoablation in the porcine model using a novel 38-cm cryoablation probe.

METHODS

A total of 18 pigs were divided into three groups. Groups 1 (n = 6) and 2 (n = 6) underwent transurethral bladder wall cryoablation in a saline environment with two freeze-thaw cycles. The pigs in groups 1 and 2 were killed after 1 and 3 weeks, respectively. The pigs in group 3 (n = 6) underwent transurethral cryoablation after the bladder had been insufflated with carbon dioxide gas. The pigs in group 3 were killed after 1 week. In all groups, laparoscopic access was obtained to protect the abdominal contents from the transmural cryoablation process. Bladder integrity was evaluated with cystography and laparoscopic visualization, and each cryolesion was excised en bloc for extensive histopathologic evaluation.

RESULTS

All 18 pigs successfully underwent bladder wall cryoablation. For all groups, the preoperative, postoperative, and sacrifice cystograms were without evidence of extravasation. No urinomas, hematomas, or adhesions were present in groups 1 and 2. Minimal adhesions were identified in 3 (50%) of 6 pigs in group 3. For groups 1, and 2, the mean length and width of the area of complete necrosis on histopathologic evaluation was 6.5 and 3.0 mm and 2.3 and 1.3 mm, respectively. For group 3, the mean diameter of the cryolesion was 8.2 mm. Full-thickness necrosis was confirmed in all groups.

CONCLUSIONS

The results of our study have shown that, in this model, complete full-thickness transurethral bladder wall cryoablation, with maintenance of bladder wall integrity, is feasible.

Percutaneous Bladder Cryoablation in Porcine Model

PURPOSE

To demonstrate the morphologic changes of full-thickness bladder cryoablation utilizing contemporary percutaneous technology.

MATERIALS AND METHODS

Cryoablation of the bladder wall was conducted in 24 pigs. The bladders were exposed laparoscopically and inspected cystoscopically. The animals underwent either extravesical (serosal) or transvesical (mucosal) approaches for the creation of the cryoablation lesion. Single or double freeze/thaw cycles were applied, and no bladder drainage was used. The bladder was evaluated for perforation, and histologic examination was undertaken to assess the extent of acute, subacute (2 weeks), or chronic (1 month) lesions.

RESULTS

Cryoablation reliably produced a controlled transmural area of necrosis (both serosa and mucosa) by both techniques. The size and extent of the lesion were directly proportional to the duration of freezing and the type of cryoprobe used. The pathology report confirmed the full-thickness coagulative necrosis of muscle. Bladder perforation was not detected clinically or at autopsy.

CONCLUSION

Cryoablation produces reliable zones of tissue destruction without bladder perforation. These preliminary data show the safety and feasibility for trials in the treatment of bladder tumors by laparoscopic, cystoscopic, or image-guided techniques.