Evaluation of the VX2 rabbit auricle carcinoma as a model for head and neck cancer in humans

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.

Cell-Free DNA Kinetics in a Pre-Clinical Model of Head and Neck Cancer

In cancer patients, circulating tumour-derived DNA (ctDNA) levels imperfectly reflect disease burden apparent on medical imaging. Further evaluation of ctDNA levels over time is needed to better understand the correlation with tumour growth and therapeutic response. We describe ctDNA kinetics within an orthotopic, immunocompetent preclinical rabbit model of local-regionally advanced head and neck squamous cell carcinoma (HNSCC). Monitoring primary tumour and metastatic lymph node volume by computed tomography (CT), we observed a correlation between ctDNA levels and tumour burden. We found that ctDNA detection could precede evidence of tumour on CT. Sensitivity and specificity of ctDNA detection in this model was 90.2% (95% C.I.: 76.9–97.3%) and 85.7% (95% C.I.: 67.3–96.0%), respectively. Rapid tumour growth followed by auto-necrosis and tumour volume contraction produced a spike in ctDNA levels, suggesting that viable tumour cells may be required for sustained ctDNA release. Following surgical resection, both ctDNA and total plasma DNA were correlated with recurrent tumour volume. Our results reveal the complex kinetic behaviour of ctDNA and total plasma DNA upon tumour growth or surgery. This pre-clinical model could be useful for future studies focused on elucidating mechanisms of ctDNA release into the circulation from primary and metastatic sites.

Spatiotemporal Optoacoustic Mapping of Tumor Hemodynamics in a Clinically Relevant Orthotopic Rabbit Model of Head and Neck Cancer

The purpose of this study was to investigate the usefulness of photoacoustic imaging (PAI) for spatiotemporal mapping of tumor hemodynamics in a rabbit model of head and neck carcinoma. Shope cottontail rabbit papilloma virus associated VX2 carcinomas were established in adult male New Zealand White rabbits (n = 9) by surgical transplantation of tumor tissue in the neck. Noninvasive PAI with co-registered ultrasound (US) was performed to longitudinally monitor tumor growth, oxygen saturation (%sO₂), and hemoglobin concentration (HbT). PAI findings were validated with Doppler sonography measures of percent vascularity (PV). Differences in tumor volumes, %sO₂, HbT, and PV values over time were analyzed using repeated-measures analysis of variance with multiple comparisons. Two-tailed Spearman correlation analysis was performed to determine the correlation coefficient (r) for comparisons between %sO₂, HbT, and tumor volume. US revealed a significant (P < .0001) increase in tumor volume over the 3-week period from 549 ± 260 mm³ on day 7 to 5055 ± 438 mm³ at 21 days postimplantation. Consistent with this aggressive tumor growth, PAI revealed a significant (P < .05) and progressive reduction in %sO₂ from day 7 (37.6 ± 7.4%) to day 21 (9.5 ± 2.1%). Corresponding Doppler images also showed a decrease in PV over time. PAI revealed considerable intratumoral spatial heterogeneity with the tumor rim showing two- to three-fold higher %sO₂ values compared to the core. Noninvasive PAI based on endogenous contrast provides a label-free method for longitudinal monitoring of temporal changes and spatial heterogeneity in thick head and neck tumors.

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.

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.

Intraperitoneal oxidative stress in rabbits with papillomavirus-associated head and neck cancer induces tumoricidal immune response that is adoptively transferable

PURPOSE

How tumors evade or suppress immune surveillance is a key question in cancer research, and overcoming immune escape is a major goal for lengthening remission after cancer treatment. Here, we used the papillomavirus-associated rabbit auricular VX2 carcinoma, a model for studying human head and neck cancer, to reveal the mechanisms underlying the antitumorigenic effects of intraperitoneal oxidative stress following O3/O2-pneumoperitoneum (O3/O2-PP) treatment.

EXPERIMENTAL DESIGN

Solid auricular VX2 tumors were induced in immune-competent adult New Zealand White Rabbits. Animals were O3/O2-PP- or sham-treated, after which they underwent tumor ablation upon reaching no-go criteria. CD3(+) tumor-infiltrating lymphocytes (TIL) were evaluated by immunohistochemistry, and expression levels of 84 immune response genes were measured by quantitative real-time PCR. Adoptive transfer of peripheral blood leukocytes (PBL)-derived from animals with tumor regression-into control animals with progressing tumors was implemented to assess acquired tumor resistance functionally.

RESULTS

Auricular VX2 tumors regressing after O3/O2-PP treatment exhibited increased levels of CD3(+) TILs; they also exhibited enhanced expression of genes that encode receptors involved in pattern recognition, molecules that are required for antigen presentation and T cell activation, and inflammatory mediators. Adoptive cell transfer of PBLs from donor rabbits with regressing tumors to recipient rabbits with newly implanted VX2 carcinoma resulted in acquired tumor resistance of the host and tumor regression.

CONCLUSION

Intraperitoneal oxidative stress effectively converts the immune response against the papillomavirus-associated rabbit VX2 carcinoma from tumor permissive to tumoricidal and leads to a sustainable, adoptively transferable oncolytic immune response.

Risk of lymph node metastases after en bloc cold steel, en bloc laser-, and piecemeal laser surgical resection of auricular VX2 carcinoma

There is some controversy in the literature if lymph vessels are enduring sealed during piecemeal CO2 laser surgery of squamous cell carcinomas of the head and neck or a propagation of tumor cells into the lymphatics occurs. The aim of the present study was to analyze the incidence of lymph node and distant metastases after different methods of resection of a VX2 carcinoma in an animal model. A solid auricular VX2 carcinoma was induced in 200 rabbits. Seven days later, an en bloc cold steel (group A), en bloc laser surgical resection with CO2 laser in continuous wave mode with 2 W (group B), or piecemeal laser surgical resection after transection of the tumor with CO2 laser in continuous wave mode with 2 W (group C) or 20 W (group D) was performed. The animals were killed and the incidence of lymph node and distant metastases was compared between the different groups. Of the rabbits, 21.1 % developed lymph node metastases and 10 % pulmonary metastases. The incidence of lymph node metastases was 17.4 % in group A, 20.4 % in group B, 26 % in group C, and 20 % in group D. These differences were not statistically significant. En bloc cold steel, en bloc laser-, or piecemeal laser surgical resections include similar risk of postoperative metastases. Propagation of tumor cells cannot be excluded with certainty by any of these methods.

Nanocolloidal albumin-IRDye 800CW: a near-infrared fluorescent tracer with optimal retention in the sentinel lymph node

Purpose

At present, the only approved fluorescent tracer for clinical near-infrared fluorescence-guided sentinel node (SN) detection is indocyanine green (ICG), but the use of this tracer is limited due to its poor retention in the SN resulting in the detection of higher tier nodes. We describe the development and characterization of a next-generation fluorescent tracer, nanocolloidal albumin-IRDye 800CW that has optimal properties for clinical SN detection

Methods

The fluorescent dye IRDye 800CW was covalently coupled to colloidal human serum albumin (HSA) particles present in the labelling kit Nanocoll in a manner compliant with current Good Manufacturing Practice. Characterization of nanocolloidal albumin-IRDye 800CW included determination of conjugation efficiency, purity, stability and particle size. Quantum yield was determined in serum and compared to that of ICG. For in vivo evaluation a lymphogenic metastatic tumour model in rabbits was used. Fluorescence imaging was performed directly after peritumoral injection of nanocolloidal albumin-IRDye 800CW or the reference ICG/HSA (i.e. ICG mixed with HSA), and was repeated after 24 h, after which fluorescent lymph nodes were excised.

Results

Conjugation of IRDye 800CW to nanocolloidal albumin was always about 50% efficient and resulted in a stable and pure product without affecting the particle size of the nanocolloidal albumin. The quantum yield of nanocolloidal albumin-IRDye 800CW was similar to that of ICG. In vivo evaluation revealed noninvasive detection of the SN within 5 min of injection of either nanocolloidal albumin-IRDye 800CW or ICG/HSA. No decrease in the fluorescence signal from SN was observed 24 h after injection of the nanocolloidal albumin-IRDye 800CW, while a strong decrease or complete disappearance of the fluorescence signal was seen 24 h after injection of ICG/HSA. Fluorescence-guided SN biopsy was very easy.

Conclusion

Nanocolloidal albumin-IRDye 800CW is a promising fluorescent tracer with optimal kinetic features for SN detection.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-012-2080-5) contains supplementary material, which is available to authorized users.

89Zr-nanocolloidal albumin-based PET/CT lymphoscintigraphy for sentinel node detection in head and neck cancer: preclinical results

Identifying sentinel nodes near the primary tumor remains a problem in, for example, head and neck cancer because of the limited resolution of current lymphoscintigraphic imaging when using (99m)Tc-nanocolloidal albumin. This study describes the development and evaluation of a nanocolloidal albumin-based tracer specifically dedicated for high-resolution PET detection.

METHODS

(89)Zr was coupled to nanocolloidal albumin via the bifunctional chelate p-isothiocyanatobenzyldesferrioxamine B. Quality control tests, including particle size measurements, and in vivo biodistribution and imaging experiments in a rabbit lymphogenic metastasis model were performed.

RESULTS

Coupling of (89)Zr to nanocolloidal albumin appeared to be efficient, resulting in a stable product with a radiochemical purity greater than 95%, without affecting the particle size. PET showed distinguished uptake of (89)Zr-nanocolloidal albumin in the sentinel nodes, with visualization of lymphatic vessels, and with a biodistribution comparable to (99m)Tc-nanocolloidal albumin.

CONCLUSION

(89)Zr-nanocolloidal albumin is a promising tracer for sentinel node detection by PET.

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.

Establishment and characterization of a rabbit oral squamous cell carcinoma cell line as a model for in vivo studies

The incidence of oral squamous cell carcinoma (SCC) is increasing but the long-term survival rate remains low. An animal model would therefore be helpful for evaluation of new treatment modalities for oral SCC. Hamster is small animal, therefore, the cancer of hamster cheek pouch is not optimal for tumor imaging. The VX2 cell line has been used in many carcinoma-related studies, including oral SCC research, but it is derived from cutaneous tissue and not mucosa. We chemically induced tongue squamous cell carcinoma in rabbits and subsequently established a rabbit squamous cell line. The cells grew in multiple layers without contact inhibition for 60 passages over 2 years and were positive for cytokeratin (CK). Electron microscopy revealed that cells were polygonal with rich microvilli on the surface, and there were desmosomes between cells and bundles of tonofibril beside the cell membrane. The chromosome number ranged from 71 to 272, with a modal value of 145 (12.4%). The cells were transplantable into nude mice subcutaneously or rabbit submucosally and produced carcinomas in all the animals. The cell line should be a useful tool for the study of the biological characteristics of oral SCC, especially tongue SCC.

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.

Localization of the sentinel lymph node in tongue VX2 carcinoma via indirect CT lymphography combined with methylene blue dye injection

CONCLUSIONS

Indirect computed tomography lymphography (CT-LG) combined with blue dye injection can locate the sentinel lymph node (SLN) in tongue carcinoma.

OBJECTIVE

To localize the SLN in tongue VX2 carcinoma using indirect CT-LG combined with methylene blue injection.

METHODS

Eighteen rabbits were placed into three groups: metastasis, hyperplasia, and control. Indirect CT-LG was performed with an iohexol injection into the tongue submucosa. CT images were acquired at 1, 5, and 15 min after injection. Methylene blue was injected into the same area 24 h after indirect CT-LG, followed by SLN identification and histopathological examination.

RESULTS

SLNs were visualized with an identification rate of 100%. SLN location identified using CT lymphography was confirmed by methylene blue dye. Control and hyperplastic enhanced SLNs were round or oval without any filling defects. Control rabbits had enhanced SLN attenuation values of 689.2 +/- 55.4 HU, 278.4 +/- 33.5 HU, and 71.7 +/- 9.2 HU at 1, 5, and 15 min after injection, respectively. Hyperplastic rabbits had values of 877.4 +/- 69.4 HU, 352.5 +/- 43.3 HU, and 80.2 +/- 11.5 HU. Filling defects were only observed in the ipsilateral metastatic SLNs of the metastasis group. CT attenuation values of the metastatic SLNs were 687.4 +/- 55.6 HU, 535.1 +/- 86.6 HU, and 282.3 +/- 19.4 HU at 1, 5, and 15 min, respectively, after iohexol injection. Metastatic lymph node attenuation values were significantly greater than those of the control or hyperplastic nodes at 5 (p < 0.001) and 15 min (p < 0.001) after injection.

Conductive interstitial thermal therapy (CITT) inhibits recurrence and metastasis in rabbit VX2 carcinoma model

PURPOSE

To investigate the potential of conductive interstitial thermal therapy (CITT) to inhibit recurrence and metastasis in a partially resected tumour model.

METHOD

Fifteen New Zealand white rabbits were implanted with VX2 tumour intramuscularly in the rear thigh. Once the tumour size reached 20-25 mm in diameter, three animals were randomly selected to serve as controls, while the remaining animals were designated as the study group and treated with CITT. In the CITT group, the partially resected tumour and margins were thermally ablated. In the control group the tumour was partially resected to simulate positive margins. The animals were monitored for up to 12 weeks. At the endpoint, the animals were sacrificed, and whole-body diagnostic necropsy was conducted immediately.

RESULTS

Recurrences and metastatic lesions were observed in iliac and popliteal lymph nodes and abdomens of all control animals. In contrast, the observed rate of recurrence and metastatic lesion was 0% among CITT-treated animals, significantly less than the >or=50% null-hypothesis rate expected upon treatment failure (exact binomial P = 0.0002). Complete histopathological healing was obtained in 2 of 12 rabbits, and residual inflammation remained at the ablation site up to 12 weeks post-ablation in 10 of 12 rabbits. This pattern of necrosis and inflammatory response was not observed in any of the control rabbits.

CONCLUSIONS

The CITT device effectively ablated partially resected VX2 carcinoma in a rabbit model, and inhibited recurrence and metastasis in this model. CITT evoked an inflammatory response that may be linked to the mechanism involved in reduced metastatic spread.

Rabbit VX2 tumors as an animal model of uterine fibroids and for uterine artery embolization

PURPOSE

To determine the suitability of the rabbit VX2 tumor animal model for uterine fibroids and uterine artery embolization (UAE).

MATERIALS AND METHODS

The authors implanted and grew one uterine VX2 tumor per rabbit in six rabbits. UAE was performed by using 100-300 microm embolic particles and confirmed with x-ray digital subtraction angiography, magnetic resonance (MR) imaging, and necropsy. Unenhanced and contrast medium-enhanced MR images of VX2 tumors were obtained before and after UAE. Relative MR signal-to noise-ratio (SNR) was measured in the uterine VX2 tumor and in normal uterine tissue before and after UAE and compared by using a paired t-test (P = .05).

RESULTS

VX2 uterine tumors were successfully grown, and both VX2 tumor presence in the uterus and UAE were seen angiographically and confirmed with necropsy in all six rabbits. Statistically significant reductions in relative SNRs were measured in tumors (SNR before UAE, 15.3 +/- 5.15; SNR after UAE, 3.84 +/- 3.94; P < .0001). No statistically significant decrease in SNR was measured in normal uterine tissue before and after UAE (P = .63 for the right uterine horn and P = .93 for the left uterine horn).

CONCLUSION

Rabbit VX2 uterine tumors may be a suitable animal model of uterine fibroids and UAE.

Treatment with ozone/oxygen-pneumoperitoneum results in complete remission of rabbit squamous cell carcinomas

Head and neck squamous cell carcinomas (HNSCC) represent a group of metastasizing tumors with a high mortality rate in man and animals. Since the biomolecule ozone was found to inhibit growth of various carcinoma cells in vitro we here applied the highly aggressive and lethal VX2 carcinoma HNSCC tumor model of the New Zealand White rabbit to test whether ozone exerts antitumorous effects in vivo. Therapeutic insufflation of medical ozone/oxygen (O(3)/O(2)) gas mixture into the peritoneum (O(3)/O(2)-pneumoperitoneum) at an advanced stage of tumor disease led to a survival rate of 7/14 rabbits. Six of the seven surviving rabbits presented full tumor regression and the absence of local or distant lung metastases. Insufflation of pure oxygen (O(2)) resulted in a survival rate of 3/13 animals accompanied by full tumor remission in 2 of the 3 surviving animals. Of the 14 sham-treated animals only 1 had spontaneous tumor remission and survived. No adverse effects or changes in standard blood parameters were observed after repeated intraperitoneal insufflations of the O(3)/O(2) or O(2) gas. Animals with O(3)/O(2)-induced tumor eradication developed tolerance against reimplantation of the VX2 tumor. This could be reversed by immune suppression with a combination of dexamethasone and cyclosporin A suggesting an antitumorous effect of O(3)/O(2)-mediated activation of the body's own immunosurveillance. Although the exact mechanisms of action are still unclear the present data point to O(3)/O(2)-pneumoperitoneum as a promising new strategy in anticancer therapy.

Preclinical models of regional lymph node tumor metastasis

Animal models have produced vital information regarding the mechanisms of RLN metastasis. Modern imaging and molecular techniques have made it clear that growing tumors secrete cytokines that induce invasion, angiogenesis, lymphangiogenesis, increased intratumoral IFV and IFP, increased fluid flow from the tumor to the surrounding tissues, increased lymphatic flow, an increase in the rate of entry of tumor cells into lymphatic capillaries, and an increased number of tumor cells reaching the RLN(s). This is important knowledge that will help direct translational research in human patients. We can look forward to continued improvement in the management of human tumors that metastasize to the RLNs.

Animal models in oral cancer research

Biologically and clinically relevant animal models are essential in investigation of the progression of diseases and the elaboration of diagnostic or therapeutic protocols. The several rodent models used for in vivo evaluation for oral cancer employ chemical, transplantation and genetic (knockout and transgenic) induction methods. These models are described together with their advantages and disadvantages. Their optimization and application in future research may improve the early detection and treatment of oral cancer.

Lymph node metastasis in an animal model: Effect of piecemeal laser surgical resection

BACKGROUND AND OBJECTIVES

Endoscopic laser surgical resection of advanced squamous cell carcinoma (SCC) often requires division of the tumor into several pieces. It is unknown if this approach influences the incidence of regional and distant metastases.

STUDY DESIGN/MATERIALS AND METHODS

In 143 rabbits VX2 SCC was induced. Eight days later the tumor was resected by two different methods. In the first group en bloc cold steel resection was performed. In the second group piecemeal laser resection was performed. On the 51th day the animals were sacrificed and examined for lymph node and distant metastases.

RESULTS

After piecemeal laser resection 47.7% of the animals had lymph node metastases compared to 24.6% after en bloc resection (P = 0.01). The incidence of distant metastases did not differ for the two groups.

CONCLUSIONS

In our model narrow margin piecemeal laser resection was associated with a higher incidence of metastases compared to wide en bloc surgical resection. The exact mechanism responsible for this increase is unclear.

Tumour embolization of the Vx2 rabbit head and neck cancer model with Dextran hydrogel and Holmium-poly(L-lactic acid) microspheres: a radionuclide and histological pilot study

INTRODUCTION

Intra-arterial embolization of unresectable malignant tumours with biodegradable microspheres is an effective way of selective anti-tumour therapy. Promising candidates are Dextran hydrogel (Dex) microspheres for chemo-embolization and Holmium-166 poly(L-lactic acid) (166HoPLA) microspheres for radio-embolization. This study was performed to investigate the distribution of intra-arterially injected microspheres both in vivo and histologically in order to establish an optimal size of particles for embolization of head and neck tumours.

MATERIAL

Twenty rabbits with Vx2 auricular tumours were embolized via the caudal auricular artery with 4 different batches of microspheres: Radioactive (166)HoPLA microspheres sieved between 20 and 50 microm and Dextran hydrogel microspheres sieved between 20 and 100 microm (Dex20), 30 and 100 microm (Dex30) or 50 and 100 microm (Dex50). Dex20 and Dex50 microspheres were labelled with 99mTechnetium in six cases.

METHODS

The average particle size of the microspheres was determined. The proportion of microspheres entrapped in the tumour was measured with a gamma camera. The distribution of microspheres around the primary tumour and spill of particles over into lungs or other organs was analysed from histological sections.

RESULTS

The mean particle diameter varied from 19 to 66 microm: (166)HoPLA 19+/-11 microm, Dex20 40+/-19 microm, Dex30 50+/-19 microm, Dex50 66+/-21 microm. The 19 microm(166)HoPLA particles proved inadequate for embolization as 51% spilled over into the lungs, whereas over 95% of the 40-66 microm Dex microspheres were retained within the primary tumour area. Particle density in lung tissues proved significantly lower for the Dex50 group. Stray emboli to the brain occurred in two rabbits.

CONCLUSION

The results of this investigation show that both Dextran hydrogel and holmium-166 poly(L-lactic acid) microspheres are potential candidates for embolization of head and neck cancer. In future studies, arterio-arteriolar anastomoses which might confound treatment should be identified and occluded. Particles with a number weighted mean diameter of at least 40 microm and a volume weighted mean size up to 70 microm should be used.