Rabbit VX2 Liver Tumor Model: A Review of Clinical, Biology, Histology, and Tumor Microenvironment Characteristics.

The rabbit VX2 is a large animal model of cancer used for decades by interventional radiologists to demonstrate the efficacy of various locoregional treatments against liver tumors. What do we know about this tumor in the new era of targeted therapy and immune-oncology? The present paper describes the current knowledge on the clinics, biology, histopathology, and tumor microenvironment of VX2 based on a literature review of 741 publications in the liver and in other organs. It reveals the resemblance with human cancer (anatomy, vascularity, angiogenic profile, drug sensitivity, immune microenvironment), the differences (etiology, growth rate, histology), and the questions still poorly explored (serum and tissue biomarkers, genomic alterations, immune checkpoint inhibitors efficacy).

Vandetanib-eluting Radiopaque Beads: Pharmacokinetics, Safety, and Efficacy in a Rabbit Model of Liver Cancer.

Background Transarterial chemoembolization with cytotoxic drugs is standard treatment for unresectable intermediate-stage hepatocellular carcinoma but achieves suboptimal outcomes because of hypoxic stress and the production of detrimental proangiogenic factors. An alternative approach using radiopaque embolization beads loaded with the antiangiogenic drug vandetanib may provide improved anticancer efficacy. Purpose To evaluate the pharmacokinetics, safety, and efficacy of vandetanib-eluting radiopaque bead (VERB) chemoembolization of rabbit liver tumors. Materials and Methods Between April 2015 and March 2016, 60 New Zealand white rabbits with VX2 liver tumors were randomly treated with VERBs at different doses, with nonloaded radiopaque beads (ROBs), or with intra-arterial vandetanib suspension (VS) or were not treated. Vandetanib plasma concentration and tumor growth at US were evaluated. Animals were euthanized after 3 days or 3 weeks. Assessment included bead distribution at x-ray imaging and histologic examination, tumor viability at histologic examination, and vandetanib tissue concentration. Group comparison analysis (Mann-Whitney, Kruskal-Wallis, and χ2 tests) and predictive factor analysis for tumor growth and viability were performed. Results Vandetanib plasma concentration was lower with VERBs than with VS (P < .01), while concentration in tumor was higher for VERBs (than for VS) at 3 days (median, 29.2 vs 2.74 ng/mg; P = .48). Tumor growth was lower with VERBs than with ROBs and with VS at both time points, with median values of +114%, +192%, and +466% at 3 weeks, respectively. Tumor viability was lower at 3 days for VERBs than for ROBs and for VS (3%, 18%, and 38%, respectively) but was not significantly different at 3 weeks. The volume of bead in tumor was a significant predictive factor for lower tumor growth in multivariable analysis at 3 days (P = .03). Drug tumor concentration was a significant predictive factor for lower tumor growth at 3 weeks (P = .04). Conclusion Vandetanib-eluting radiopaque bead chemoembolization showed a pharmacokinetic advantage over intra-arterial drug administration in a preclinical model of liver cancer. High deposition of beads and high vandetanib concentration in tumor led to stronger antitumor effects. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Kim and Van den Abbeele in this issue.

Midterm Recanalization after Arterial Embolization Using Hydrogel-Coated Coils versus Fibered Coils in an Animal Model.

PURPOSE: To compare angiographic and pathologic effects (ie, occlusion, recanalization) after embolization with Hydrogel-coated coils (HydroCoils) and fibered coils in the renal and internal iliac arteries after 7 days and 1 and 4 months in an animal model. MATERIALS AND METHODS: Twelve sheep had 1 internal iliac and 1 renal artery randomly embolized with HydroCoils or fibered coils. Renal and internal iliac arteries were embolized with detachable 0.018-inch coils and pushable 0.035-inch coils, respectively. All animals had control angiography performed at 7 days, and 1 and 4 months to assess recanalization before euthanasia. Recanalization and inflammation were evaluated via pathologic examination. RESULTS: At 1 month, 100% of arteries embolized with HydroCoils were occluded vs 50% of those embolized with fibered coils (P = .004). At 4 months, 80% of arteries embolized with HydroCoils were occluded vs 25% of those embolized with fibered coils (P = .01). Surface of vessel occlusion was significantly greater for iliac arteries (96.7% ± 8.9) than for renal arteries (94.2% ± 5.3; P = .0076). Surface of occlusion of the renal arteries (92.2% ± 5.1) was lower for fibered coils than for HydroCoils (96.8% ± 4.7; P = .0287). Surface percentage of thrombus was significantly lower for HydroCoils than for fibered coils (P < .0001). Surface percentage of thrombus was correlated with surface percentage of recanalization (P = .0181). CONCLUSIONS: After 4 months, 75% of arteries embolized with fibered coils were recanalized vs 20% of those embolized with HydroCoils (P = .01). Reduced amount of thrombus after embolization with HydroCoils accounted for a reduced rate of arterial recanalization.

Lymphatic Transport and Lymph Node Location of Microspheres Subcutaneously Injected in the Vicinity of Tumors in a Rabbit Model of Breast Cancer.

PURPOSE: To assess the lymphatic transport of microparticles of 100 nm, 1 µm and 10 µm subcutaneously injected into the breast area of healthy and tumor-bearing rabbits, and to analyze their location in lymph node (LN) in relation to malignant cells. METHODS: Female rabbits (n = 9) bearing a VX2 tumor in one thoracic mammary gland were subcutaneously injected at D15 with polystyrene fluorescent particles around the nipple, on the tumor and on the healthy sides. The tumor and the LN measured by ultrasound at D9, D15 and D20 were explanted at D20. The LN metastases were evaluated by cytokeratin staining. LN uptake of the particles was measured by quantifying the green fluorescence surface in hot spot regions of healthy and pathologic LN. RESULTS: All animals developed mammary tumors. Metastases were found in 39% of LN from the tumor side. LN invasion was significantly lower for the 10 µm group versus the 100 nm group (p < 0.0348). The fully invaded area of metastatic LN contained significantly less 100 nm and 1 µm particles compared to the low and non-invaded regions and to the healthy LN. In the invaded LN, the 1 µm MS occupied more surface than the 100 nm particles. CONCLUSIONS: 1 µm MS arrived numerously into the areas low-invaded and non-invaded by the tumoral cells of the pathologic LN, but they were very rare in the fully invaded regions. Compared to the 100 nm nanospheres, the 1 µm were better retained (20 times) into the sentinel LN, showing the advantage of micrometric particles for lymph-targeted chemotherapy when injected before complete invasion by metastases.

Peripheral Embolization Using Hydrogel-Coated Coils Versus Fibered Coils: Short-Term Results in an Animal Model.

OBJECTIVES: To angiographically compare the occlusive effects of hydrocoils and fibered coils in the renal and internal iliac arteries at 24 h and 7 days in the sheep model. To determine the occlusive mechanism by hydrocoils and fibered coils by pathological examination. MATERIALS AND METHODS: Two types of peripheral hydrogel-coated and fibered coils similar in diameter and length were compared. The right and left renal arteries were embolized with 0.018-inch detachable hydrocoils or fibered coils in six sheep. Then, the right and left internal iliac arteries were embolized with 0.035-inch pushable hydrocoils or fibered coils. Arterial recanalization was evaluated at 24 h and at 7 days with angiography. At pathology, the surface percentage of thrombus and embolic material (platinum, Dacron fibers and hydrogel) and the presence of inflammation were assessed. RESULTS: No difference was found between the coils for recanalization at 24 h or 7 days. For hydrocoils, the surface of occlusion corresponded to thrombus for 42% and coil for 58% including 42% of platinum and 16% of hydrogel, respectively. For fibered coils, the surface of occlusion was composed of thrombus for 69% and of platinum and fibers for 31%. The surface percentage occupied by thrombus was significantly lower for hydrocoils than for fibered coils (p = 0.0047). The surface percentage of embolic was also different between the two products (p = 0.049). No degradation of hydrogel was found at any time points. CONCLUSION: The percentage of thrombus was significantly less with hydrocoils as compared to fibered coils, which may account for reduced long-term recanalization.

Laparoscopic subperitoneal injection of chemo-loaded particles lowers tumor growth on a rabbit model of peritoneal carcinomatosis.

The purpose of our study was to assess the effect of controlled-release chemotherapy on the growth and viability of peritoneal carcinomatosis treated by subperitoneal injection in a rabbit VX2 model. A model of peritoneal carcinomatosis was created by laparoscopic injection of VX2 tumor in the left and right broad ligaments of 12 White New Zealand rabbits. At day 12, each tumor was randomly treated with a peritumoral injection of 0.5 mL microspheres loaded with doxorubicin (DEM-DOX) or unloaded (DEM-BLAND). Seven days after treatment, tumor volume, tumor viability in histology, local tumor necrosis in contact with DEM, and doxorubicin concentration profile around the drug eluting microspheres (DEM) were measured. Tumor volume was significantly lower in the DEM-DOX group (3.6 ± 3.2 cm3) compared with the DEM-BLAND group (8.9 ± 5.4 cm3) (p = 0.0425). The percentage of viable tumor tissue was significantly lower in the DEM-DOX group (38% ± 17%) compared with the DEM-BLAND group (56% ± 20%) (p = 0.0202). Tissue necrosis was observed around all DEM-DOX up to a distance of 1.094 ± 0.852 mm and never observed around DEM-BLAND. Drug concentration was above the therapeutic level of 1.0 µM up to a distance of 1.4 mm from the DEM to the tumor. Laparoscopic subperitoneal injection of chemo-loaded particles is feasible and lowers tumor growth and viability in a rabbit model of peritoneal carcinomatosis after 1 week.

bFGF Up-regulation Reduces Spontaneous Necrosis of VX2 Tumors Without Increasing Tumoral Microvascular Density.

AIM: To determine whether up-regulation of basic fibroblast growth factor (bFGF) in VX2 cells reduces tumor necrosis. MATERIALS AND METHODS: VX2 cells were transfected with expression vector containing cDNA of rabbit bFGF. Stable clones producing rabbit bFGF (bFGF-VX2) were selected. bFGF-VX2 (n=5) or non-transfected VX2 (control) (n=5) cells were implanted into leg muscle of 10 rabbits. The tumors were characterized 21 days after grafting. RESULTS: Overexpression of bFGF by VX2 tumors significantly reduced necrosis (p<0.0223) and increased cell viability (p<0.0223), without effect on the mean vascular density. bFGF concentration was significantly higher in bFGF-VX2 tumors (p<0.0062) and negatively correlated with tumor volume at day 21 (ρ=-0.927, p<0.0034). Vascular endothelial growth factor concentration was significantly lower in bFGF-VX2 tumors (p<0.0105) and negatively correlated with the bFGF concentration of tumors (ρ=-0.903, p<0.0067). CONCLUSION: The overexpression of bFGF in VX2 cells increased tumor viability and reduced necrosis, making the evaluation of long-term anticancer therapies possible in this model.

Antitumoral Effect of Sunitinib-eluting Beads in the Rabbit VX2 Tumor Model.

Purpose To measure plasmatic sunitinib concentration (PSC) and intratumoral sunitinib concentration (ITSC) after transcatheter arterial chemoembolization (TACE) with two different sizes of sunitinib-eluting beads (SEBs) in rabbits with VX2 hepatic allografts and to investigate treatment effects on vascular endothelial growth factor receptor type 2 (VEGFR2) phosphorylation, tumor volume, and histopathologic changes. Materials and Methods The protocol was approved by the French Ethics Committee for Animal Experiments (Comité d'Ethique en Expérimentation Animale du Centre INRA de Jouy-en-Josas et AgroParisTech, or COMETHEA, approval no. 11/028). Two experiments were performed. In the first, seven animals received 0.05 mL of 100-300-µm SEBs (1.5 mg of sunitinib) in the hepatic artery, and six animals received saline injections. In the second, eight animals received 0.05 mL of 70-150-µm SEBs (1.5 mg of sunitinib), seven received 0.05 mL of 70-150-µm unloaded beads, and seven received oral sunitinib (6 mg every day). Tumor size was monitored with ultrasonography. PSC, ITSC, and phosphorylation of VEGFR2 were assessed on days 1 and 14. After the animals were sacrificed, histopathologic analysis was performed. The Kruskal-Wallis test, Mann-Whitney U test, and Fisher exact test were used to look for statistically significant differences between groups. Results Maximum PSC after TACE with 100-300-µm SEBs was 0.002 µg/mL on day 1. ITSC was 17.8 µg/g on day 1 and 0.16 µg/g on day 14. After TACE with 70-150-µm SEBs, ITSC was 40.4 µg/g on day 1 and 27.4 µg/g on day 14. Phosphorylation of VEGFR2 was inhibited until day 14 after TACE with both sizes of SEBs. The size of VX2 tumors treated with 70-150-µm SEB TACE increased less (-2%) than that of tumors treated with unloaded beads (+42%) and oral sunitinib (6 mg every day; +1853%; P = .044). Conclusion SEB TACE resulted in minimal PSC, high ITSC, and sustained VEGFR2 phosphorylation inhibition until day 14. (©) RSNA, 2016.

Comparative Chemosensitivity of VX2 and HCC Cell Lines to Drugs Used in TACE.

AIM: To compare the cytotoxic effects of 11 anticancer agents against VX2 and HepG2 cells in order to establish candidate drugs that can be tested preclinically on VX2 tumor model for transarterial chemoembolization (TACE) of hepatocellular carcinoma (HCC). MATERIALS AND METHODS: VX2 and HepG2 cells were incubated with different drug concentrations. The half-maximal inhibitory concentration (IC50) values were determined by total cell protein assay for anthracyclines, platins, irinotecan, mytomicin-C (MMC), 5-fluorouracil (5-FU) and antiangiogenics. RESULTS: IC50 values for VX2 and HepG2 were found close for doxorubicin (0.8 µM vs. 1.1 µM), MMC (13.9 µM vs. 8.7 µM), sunitinib (32.7 vs. 33.7 µM), sorafenib (10.3 vs. 8.9 µM), lapatinib (30 vs. 18.3 µM) and different for platins and irinotecan. Oxaliplatin was less active against VX2 than HepG2 (IC50=41 µM vs. 2.7 µM), cisplatin was more active against VX2 than HepG2 (IC50=8.0 µM vs. 15.9 µM), whereas carboplatin had a low toxicity against both cell lines (70.4 µM vs. 538.3 µM). The toxicity of 5-FU against VX2 and HepG2 was low (IC50=560.6 µM vs. 323.2 µM). Irinotecan was less active against VX2 vs. HepG2 (IC50=44.5 µM vs. 15.3 µM). Bevacizumab had no effect on either of the cell lines up to 6.7 µM. CONCLUSION: Drugs recommended for pre-clinical trials of TACE in the VX2 model are doxorubicin, sunitinib, sorafenib, MMC, lapatinib and 5-FU.

Automated Quantification of Tumor Viability in a Rabbit Liver Tumor Model after Chemoembolization Using Infrared Imaging.

The rabbit VX2 tumor is a fast-growing carcinoma model commonly used to study new therapeutic devices, such as catheter-based therapies for patients with inoperable hepatocellular carcinoma. The evaluation of tumor viability after such locoregional therapies is essential to directing hepatocellular carcinoma management. We used infrared microspectroscopy for the automatic characterization and quantification of the VX2 liver tumor viability after drug-eluting beads transarterial chemoembolization (DEB-TACE). The protocol consisted of K-means clustering followed by principal component analysis (PCA) and linear discriminant analysis (LDA). The K-means clustering was used to classify the spectra from the infrared images of control or treated tumors and to build a database of many tissue spectra. On the basis of this reference library, the PCA-LDA analysis was used to build a predictive model to identify and quantify automatically tumor viability on unknown tissue sections. For the DEB group, the LDA model determined that the surface of tumor necrosis represented 91.6% ± 8.9% (control group: 33.1% ± 19.6%; Mann-Whitney P = 0.0004) and the viable tumor 2.6% ± 4% (control group: 62.2% ± 15.2%; Mann-Whitney P = 0.0004). Tissue quantification measurements correlated well with tumor necrosis (r = 0.827, P < 0.0001) and viable tumor (r = 0.840, P < 0.0001). Infrared imaging and PCA-LDA analysis could be helpful for easily assessing tumor viability.

Safety and efficacy compared between irinotecan-loaded microspheres HepaSphere and DC bead in a model of VX2 liver metastases in the rabbit.

PURPOSE: To compare irinotecan-eluting HepaSphere (BioSphere Medical, Roissy-en-France, France) and DC Bead (Biocompatibles UK Ltd, London, United Kingdom) embolization microspheres for distribution in tumors, release properties, tolerance, and antitumor effects in a model of liver metastases in the rabbit. MATERIALS AND METHODS: Multiple liver tumors were created by injection of a VX2 cell suspension in the portal vein of rabbits. After 2 weeks, embolization of the proper hepatic artery was performed with a fixed volume of bland HepaSphere (n = 5), irinotecan-loaded HepaSphere (n = 6), or irinotecan-loaded DC Bead (n = 5) microspheres. Untreated animals injected with VX2 cells served as control animals (n = 5). Plasma pharmacokinetics of irinotecan and its metabolite SN38 were assessed. Histopathology and gene expression analysis were performed 3 days after treatment. RESULTS: Among all treated groups, there was no significant difference in liver enzymes or liver damage on histology. Irinotecan-loaded HepaSphere microspheres showed a faster release of drug than DC Bead microspheres leading to a twofold higher concentration of drug in plasma for HepaSphere microspheres. HepaSphere microspheres were less frequently found inside tumor nodules on histology than DC Bead microspheres (11% vs 48%, P < .001) because of their larger size. Tumor necrosis was significantly greater for rabbits given irinotecan-loaded HepaSphere microspheres (69% of total tumor surface) and rabbits given DC Bead microspheres (50% of total tumor surface) compared with control animals (24% of total tumor surface, P = .006 and P = .047). CONCLUSIONS: HepaSphere and DC Bead microspheres loaded with irinotecan caused significant necrosis of tumor nodules in a model of VX2 liver metastases. This outcome was mostly due to irinotecan delivery rather than vascular occlusion by the microspheres and was greater for HepaSphere microspheres compared with DC Bead microspheres.

Toxicity of doxorubicin on pig liver after chemoembolization with doxorubicin-loaded microspheres: a pilot DNA-microarrays and histology study.

PURPOSE: The potential mechanisms accounting for the hepatotoxicity of doxorubicin-loaded microspheres in chemoembolization were examined by combining histology and DNA-microarray techniques. METHODS: The left hepatic arteries of two pigs were embolized with 1 mL of doxorubicin-loaded (25 mg; (DoxMS)) or non-loaded (BlandMS) microspheres. The histopathological effects of the embolization were analyzed at 1 week. RNAs extracted from both the embolized and control liver areas were hybridized onto Agilent porcine microarrays. Genes showing significantly different expression (p < 0.01; fold-change > 2) between two groups were classified by biological process. RESULTS: At 1 week after embolization, DoxMS caused arterial and parenchymal necrosis in 51 and 38 % of embolized vessels, respectively. By contrast, BlandMS did not cause any tissue damage. Up-regulated genes following embolization with DoxMS (vs. BlandMS, n = 353) were mainly involved in cell death, apoptosis, and metabolism of doxorubicin. Down-regulated genes (n = 120) were mainly related to hepatic functions, including enzymes of lipid and carbohydrate metabolisms. Up-regulated genes included genes related to cell proliferation (growth factors and transcription factors), tissue remodeling (MMPs and several collagen types), inflammatory reaction (interleukins and chemokines), and angiogenesis (angiogenic factors and HIF1a pathway), all of which play an important role in liver healing and regeneration. CONCLUSIONS: DoxMS caused lesions to the liver, provoked cell death, and disturbed liver metabolism. An inflammatory repair process with cell proliferation, tissue remodeling, and angiogenesis was rapidly initiated during the first week after chemoembolization. This pilot study provides a comprehensive method to compare different types of DoxMS in healthy animals or tumor models.

Modified model of VX2 tumor overexpressing vascular endothelial growth factor.

PURPOSE: To determine whether upregulated expression of vascular endothelial growth factor (VEGF) in VX2 cells can increase vessel density (VD) and reduce tumor necrosis. MATERIALS AND METHODS: The VX2 cell line was transfected with expression vectors containing cDNA for rabbit VEGF. Stable clones producing rabbit VEGF (VEGF-VX2) were selected. VEGF-VX2 cells (n = 5 rabbits) or nontransfected VX2 cells (controls; n = 5 rabbits) were implanted into leg muscle of 10 rabbits. The animals were sacrificed at day 21. Tumor volume, percentage of necrosis, VD, and VEGF concentration in tumor protein extract were quantified. RESULTS: Overexpression of VEGF by VX2 cells augmented tumor implantation efficiency 100% and favored cyst formation. The tumor volume was significantly larger for VEGF-VX2 transfected tumors versus controls (P = .0143). Overexpression of VEGF in VX2 cells significantly increased the VD of the tumors (P = .0138). The percentage of necrosis was reduced in VEGF-VX2 tumors versus controls (19.5% vs 38.5 %; P = .002). VEGF concentration in VEGF-VX2 tumors was significantly higher than in control tumors (P = .041) and was correlated with tumor volume (ρ = .883, P = .012). CONCLUSIONS: The overexpression of VEGF increased tumor growth and vascularization, favored cyst formation, and reduced tumor necrosis. This new phenotype of the VX2 tumor may offer some advantages over classic models of VX2 tumor for evaluating anticancer therapies.

Embolization of hepatocellular carcinoma with drug-eluting beads: doxorubicin tissue concentration and distribution in patient liver explants.

BACKGROUND & AIMS: To follow the local tissue delivery of doxorubicin in HCC explants from patients embolized with drug-eluting beads and to compare it with histologic modifications. METHODS: Six patients with HCC underwent chemoembolization with doxorubicin-eluting beads (caliber 100-300 µm, dose 75-150 mg) followed by liver transplantation at different time points (8 h to 36 days). On sections of the explanted liver, the tissue concentration of doxorubicin was determined radially around bead-occluded vessels with microspectrofluorimetry. The intra/peritumoral location of the beads and the modifications of the surrounding tissue were determined on an adjacent hematein-eosin-saffron-stained section and compared to drug measurements. RESULTS: Doxorubicin was detected in the tissue surrounding the beads at all times of explantation. The drug impregnates an area of at least 1.2 mm in diameter around the occluded vessel. The tissue concentration of drug ranges from 5 µM at 8 h to 0.65 µM at 1 month. In patient transplanted at 8 h, no major tissue modification was observed and we found 42% of the beads occluding intratumoral vessels. Drug concentration was not different around intratumoral and peritumoral occluded vessels. After 9-14 days, necrosis was present around 37% of vessels and at 32-36 days, around 40% of vessels. Necrotic tissue was associated with a deeper penetration and a higher concentration of the drug than non necrotized areas, though statistically significant only at 32-36 days. CONCLUSIONS: Doxorubicin-eluting beads provide a sustained delivery of drug for a period of 1 month and local tissue concentrations above cytotoxic threshold in HCC-bearing livers.

IL6 and TNF expression in vessels and surrounding tissues after embolization with ibuprofen-loaded beads confirms diffusion of ibuprofen.

PURPOSE: In the treatment of uterine fibroid embolization related pain, the use of embolics loaded with non-steroidal anti-inflammatory drugs (NSAID) relies on an efficient delivery and impregnation of the embolized tissue. Immuno-labelling and spectroscopic techniques have demonstrated the release of ibuprofen from drug eluting beads (Wassef et al., 2008; Namur et al., 2009) but failed to demonstrate diffusion of the drug beyond the vascular wall (VW). We investigated whether ibuprofen diffused beyond the VW in surrounding tissues (ST), by tracking its biological effects through the modulation of expression of two main inflammatory cytokines. MATERIALS AND METHODS: Uterine arteries of 6 sheep were embolized with ibuprofen loaded beads (IBU-BB) or non-loaded beads (BB) and sacrificed at one week. On frozen tissue slices, VWs of occluded arteries were isolated from ST using laser capture microdissection. RNA was extracted from VW and ST samples. Gene expression of IL6 and TNFα genes was measured by quantitative real-time PCR (qPCR). RESULTS: IL6 expression was significantly increased in IBU-BB compared to BB group both in VW (VW: fold-change (FC)=4.9, p=0.0009) and ST (ST: FC=8.7, p=0.0003). In IBU-BB, IL6 was significantly more expressed in VW than in ST (FC=4.4; p=0.0009). TNFα expression was not significantly different between IBU-BB and BB groups. CONCLUSION: Using qPCR+microdissection was useful to evaluate the spread of the biological effects of drug-loaded systems which attest of the tissular release. This approach can be considered when other drug detection techniques are unsuccessful or difficult to achieve. IL6 can be used as a marker of ibuprofen released by drug eluting beads in uterus. Gradient of expression of IL6 suggests diffusion of ibuprofen across the VW into the ST.

Arterial distribution of calibrated tris-acryl gelatin and polyvinyl alcohol embolization microspheres in sheep uterus.

The purpose of this study was to compare, after embolization, the distribution in the uterine arterial vasculature of tris-acryl gelatin microspheres (TGMS) and polyvinyl alcohol microspheres (PVAMS). A limited bilateral uterine artery embolization was performed in six adult sheep under fluoroscopic control by injecting in each uterine artery 0.25 ml of 500- to 700-microm TGMS of PVAMS suspended in 50/50 saline/contrast medium. Sacrifices were performed 1 week after embolization and uteri were analyzed histologically. The number and size of microspheres and vessels were measured, as well as the histological location according to a classification in four zones of the uterus. One hundred sixty-five vessels (69 vessels occluded with TGMS and 96 vessels occluded with PVAMS) were measured. The size of the occluded vessels decreased significantly from proximal to distal zones of the uterine vasculature (P < 0.0001). The location of TGMS and PVAMS within the vasculature was significantly different (P < 0.0001) since PVAMS blocked significantly more distally than TGMS. Deformation of the microspheres within the tissue was greater for PVAMS (18.0% +/- 12.3%) than for TGMS (8.7% +/- 9.2%) (P < 0.0001). In conclusion, PVAMS have a more distal distribution in the sheep uterine vasculature, compared to TGMS. Such differences in partition, already described in the kidney embolization model, can ultimately explain the different clinical outcome reported with these two types of microspheres in uterine fibroid embolization.

Drug-eluting beads for liver embolization: concentration of doxorubicin in tissue and in beads in a pig model.

PURPOSE: To evaluate the local tissue concentrations of the antineoplastic agent doxorubicin and the amount of drug still present inside drug delivery embolization beads at different time points after embolization and to compare doxorubicin levels with histologic modifications around the beads in a pig liver model. It was hypothesized that doxorubicin-eluting beads maintain cytotoxic concentrations of drug locally over a period of several weeks, as suggested by in vitro elution tests. MATERIALS AND METHODS: Left lobe hepatic artery embolization was performed in 10 pigs with 100-300-microm or 700-900-microm beads loaded with 37.5 mg doxorubicin/mL. Control unloaded 100-300-microm beads were injected in five pigs. Livers were sampled 28 days or 90 days after embolization. The amount of drug retained inside the beads was assessed with infrared microspectroscopy. Doxorubicin concentration and distribution in the tissue around the beads were determined with microspectrofluorimetry and compared with tissue modifications on hematein eosin saffron-stained sections. RESULTS: Doxorubicin-eluting beads eluted 43% of their initial drug load after 28 days and 89% after 90 days. Doxorubicin was present in tissues around the beads at both time points, with a significant decrease over time (P = .0004). The drug was detected at distances as far as 600 microm from the bead edge. Doxorubicin tissue concentrations ranged from 0.55 microM to 6.80 microM, [corrected] which are cytotoxic levels in hepatocyte cell cultures. High concentrations of drug were associated with coagulative necrosis of liver parenchyma. Doxorubicin-eluting beads 100-300 microm in size induced more necrosis than 700-900-microm beads (P = .0036). CONCLUSIONS: Doxorubicin-eluting beads deliver high concentrations of the drug over a period of at least 3 months at several hundred micrometers from the bead, leading to significant cytotoxic effects.

Recanalization and particle exclusion after embolization of uterine arteries in sheep: a long-term study.

OBJECTIVE: To compare the long-term evolution of uterine arteries after embolization with the two most commonly used embolic agents for fibroid embolization: nonspherical polyvinyl alcohol (PVA) particles and trisacryl gelatin microspheres (TGMS). DESIGN: Prospective study. SETTING: University-based interventional radiology, pathology, and reproductive physiology units. ANIMAL(S): Two groups of 10 sheep embolized in the uterine artery. INTERVENTION(S): Embolization of the uterine artery with either 600-1000 microm nonspherical polyvinyl alcohol (PVA) particles or with 700-900 microm trisacryl gelatin microspheres (TGMS). Animals were synchronized and naturally inseminated. Animals were killed at 26 months. MAIN OUTCOME MEASURE(S): Uteri were examined pathologically for vessel size, site of occlusion, recanalization rate of vessels, and particle location within the vascular wall. RESULT(S): The PVA particles were more numerous in the vessels' lumen than the TGMS particles (13.3 +/- 20.8 vs. 2.5 +/- 2.7), were located more proximally than TGMS (97% vs. 68% in the trunk and first branches of the uterine artery), and were found almost exclusively in the intima (99.2%). In contrast, 54.4% of the TGMS particles were found in the intima, and 45.6% partially or totally excluded. The rate of recanalization was not statistically significantly different for PVA and TGMS (65.2% vs. 60.6%). CONCLUSION(S): The long-term evolution of uterine arteries was different after uterine artery embolization with PVA and TGMS because PVA particles formed large-sized aggregates that occluded proximal vessels and remained in the vessel intima. Microspheres occluded more distal vessels, and about 50% of them were partially or totally excluded from the vessel.

Anti-inflammatory effect of ibuprofen-loaded embolization beads in sheep uterus.

Embolization of blood vessels may result in a variety of side effects which can include pain and inflammation. The objective of this study was to assess the release and effect of ibuprofen (IBU) from Bead Block microspheres (BB) loaded with IBU (IBU-BB) on the foreign body inflammatory reaction in a sheep uterine artery model. Both uterine arteries of 12 hormonally cycled ewes were embolized with 0.5 mL of 500-700 microm BB (n = 6) or IBU-BB (n = 6). Animals were sacrificed at 1 week (1W) or 3 weeks (3W) (n = 3 each group). The gross examination of the organs was performed and distribution of the beads in the tissue was assessed. Inflammation was estimated histologically by quantitative and semiquantitative classification of inflammatory cells on HES and MGG stains and use of videoanalysis after immunohistolabeling with CD-antibodies to a variety of inflammatory cells. At 1W, a significant decrease of inflammatory response was observed for IBU-BB relative to BB in terms of number of lymphocytes and of immunohistochemical staining for CD172a, MHC-II, CD3, and CD4. At 3W, the inflammatory response for IBU-BB was similar to that for BB at 1W in terms of cell populations and moderate intensity. There was no or low amounts of staining for CD8 and CD45RA and none for CD21 in all four groups. Immunohistochemical detection of IBU showed that some drug was still present in the beads at 1W but none was detectable at 3W suggesting it had all eluted. These results signify that the inflammatory response is dampened by the action of IBU eluted from the beads and that IBU-BB can delay postembolization inflammatory reaction.

MR imaging detection of superparamagnetic iron oxide loaded tris-acryl embolization microspheres.

PURPOSE: To assess by magnetic resonance (MR) imaging the detectability of superparamagnetic iron oxide (SPIO)-labeled microspheres (MSs) in vitro on gelose, ex vivo in kidneys from embolized sheep, and in vivo in kidneys from embolized pigs. MATERIALS AND METHODS: With various sizes of SPIO-labeled MSs, common neck and pelvic spin-echo and gradient-echo sequences were acquired on a 1.5-T MR unit. SPIO-labeled MSs of four sizes were embedded in a hydrogel as single MSs or in multiple units, or multiplets. Detection rate on MR imaging was assessed according to the real size and number of MSs. SPIO-loaded and unloaded MSs of four sizes were injected into eight sheep kidneys, which underwent MR and pathologic examinations. For each size, the location of MSs in renal vasculature was determined and compared according to the technique used. Kidneys were embolized in pigs with various amounts of MSs in three sizes. MR was performed immediately after embolization and SPIO-labeled MS detection was assessed according to size, organ, and amount injected. Results SPIO-labeled MSs provide a low signal intensity on T1-weighted sequences, without distortion. In vitro, 28% of 100-300-microm single MSs were detected and more than 80% were detected for larger sizes. MS multiplets were all detected in all sizes. Ex vivo, all sizes of MSs were detected by MR imaging in kidneys, whereas control MSs were not observed. Histologic analysis showed that there was no difference in vascular distribution between SPIO-labeled MS and control MSs, and therefore for each caliber (P > .05). Arterial location of SPIO-labeled MSs was the same on MR imaging and histologic analysis. In vivo, SPIO-labeled MS were detected in the kidney vasculature when volumes greater than 1 mL of 100-300-microm or 500-700-microm MSs were injected. Volumes lower than 1 mL SPIO-labeled MSs were hardly detected in kidneys, regardless of MS size. Conclusions SPIO-labeled MSs are detected by MR imaging with common gradient-echo sequences in vitro in gelose and ex vivo and in vivo in kidneys. SPIO-labeled MSs could allow better control of embolization and thereby enhance efficacy and safety of the procedure.