Comparison of tumor vascularity and hemodynamics in three rat hepatoma models

Liver Cancer Vascularity Driven by Extracellular Matrix Stiffness: Implications for Imaging Research

BACKGROUND

Extracellular matrix stiffness represents a barrier to effective local and systemic drug delivery. Increasing stiffness disrupts newly formed vessel architecture and integrity, leading to tumor-like vasculature. The resulting vascular phenotypes are manifested through different cross-sectional imaging features. Contrast-enhanced studies can help elucidate the interplay between liver tumor stiffness and different vascular phenotypes.

PURPOSE

This study aims to correlate extracellular matrix stiffness, dynamic contrast-enhanced computed tomography, and dynamic contrast-enhancement ultrasound imaging features of 2 rat hepatocellular carcinoma tumor models.

METHODS AND MATERIALS

Buffalo-McA-RH7777 and Sprague Dawley (SD)-N1S1 tumor models were used to evaluate tumor stiffness by 2-dimensional shear wave elastography, along with tumor perfusion by dynamic contrast-enhanced ultrasonography and contrast-enhanced computed tomography. Atomic force microscopy was used to calculate tumor stiffness at a submicron scale. Computer-aided image analyses were performed to evaluate tumor necrosis, as well as the percentage, distribution, and thickness of CD34+ blood vessels.

RESULTS

Distinct tissue signatures between models were observed according to the distribution of the stiffness values by 2-dimensional shear wave elastography and atomic force microscopy ( P < 0.05). Higher stiffness values were attributed to SD-N1S1 tumors, also associated with a scant microvascular network ( P ≤ 0.001). Opposite results were observed in the Buffalo-McA-RH7777 model, exhibiting lower stiffness values and richer tumor vasculature with predominantly peripheral distribution ( P = 0.03). Consistent with these findings, tumor enhancement was significantly greater in the Buffalo-McA-RH7777 tumor model than in the SD-N1S1 on both dynamic contrast-enhanced ultrasonography and contrast-enhanced computed tomography ( P < 0.005). A statistically significant positive correlation was observed between tumor perfusion on dynamic contrast-enhanced ultrasonography and contrast-enhanced computed tomography in terms of the total area under the curve and % microvessel tumor coverage ( P < 0.05).

CONCLUSIONS

The stiffness signatures translated into different tumor vascular phenotypes. Two-dimensional shear wave elastography and dynamic contrast-enhanced ultrasonography adequately depicted different stromal patterns, which resulted in unique imaging perfusion parameters with significantly greater contrast enhancement observed in softer tumors.

Syngeneic N1-S1 Orthotopic Hepatocellular Carcinoma in Sprague Dawley Rat for the Development of Interventional Oncology-Based Immunotherapy: Survival Assay and Tumor Immune Microenvironment

Rodent HCC rat models provide advantages for interventional oncology (IO) based immunotherapy research compared to other established larger animal models or mice models. Rapid and predictable tumor growth and affordable costs permit the formation of a compelling preclinical model investigating novel IO catheter-directed therapies and local ablation therapies. Among orthotopic HCC models, the N1-S1 orthotopic HCC model has been involved in many research cases. Suboptimal tumor induction rates and potential spontaneous regression during tumor implantation procedures discouraged the use of the N1-S1 HCC model in IO-based immunotherapies. Here, N1-S1 HCC models were generated with a subcapsular implantation of two different number of N1-S1 cells using a mini-laporatomy. Tumor growth assay and immunological profiles which can preclinically evaluate the therapeutic efficacy of IO-based immunotherapy, were characterized. Finally, an N1-S1 HCC rat model generated with the proposed procedure demonstrated a representative immune suppressive HCC tumor environment without self-tumor regression. The optimized syngeneic N1-S1 HCC rat models represent an essential tool for pre-clinical evaluation of new IO immunotherapies for the treatment of HCC.

Ideal Size Range for Embolic Agents in Interventional Oncology Experiments Involving Rat Models of Hepatocellular Carcinoma

PURPOSE

To optimize future translational research, this study aimed to determine the ideal range of sizes for embolic agents in interventional oncology experiments utilizing rat models of hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Fifty-five male Sprague-Dawley rats were divided into 2 groups to evaluate the distribution of microparticles and tumor response rates. After implanting hepatoma cells into the rodent liver, fluorescent microparticles of sizes ranging from 5 to 35 μm were administered via the hepatic artery. In the first group, the distribution of microparticles was evaluated in hepatoma-free rats, and the tumor necrosis rates following administration of a predetermined aliquot of microparticles (0.4 mL) were measured in tumor-bearing rats. Thereafter, the 3 microparticle sizes associated with the best tumor response rates were chosen for analysis of the tumor necrosis rates following hepatic artery embolization until angiographic stasis is achieved in the second group.

RESULTS

The tendency for microparticles to distribute in nontarget organs increased as the microparticle size decreased below 15 μm. Tumor necrosis rates tended to be higher in rats treated with 15-19-μm microparticles than in those treated with 19-24-μm or 19-24-μm microparticles. The in-group deviation of the tumor necrosis rates was highest for microparticle sizes of 19-24 and 25-35 μm, which implies the proximal embolization of the hepatic artery for larger microparticle sizes. However, there was no statistical significance among the 3 groups (P = .095).

CONCLUSIONS

The 15-19-μm embolic agents were the most favorable for causing tumor necrosis without nontarget toxicity in the transarterial treatments of rat HCC models.

Drug delivery in transarterial chemoembolization of hepatocellular carcinoma: Ex vivo evaluation using transparent tissue imaging

In this study, we elucidated for the first time the role of anti-cancer drugs in transarterial chemoembolization (TACE) via direct visualization of the spatial distribution of drugs with respect to blood vessels in intact transparent hepatocellular carcinoma (HCC) tissues. To date, precise estimation of drug penetration into tumors using thin 3D tissue sections has been challenging. This study utilized the tissue optical clearing technique to resolve the lack of tissue clarity, thereby enabling deep tissue imaging for the quantitative assessment of drug delivery following TACE. We compared the drug delivery effect, time-dependent embolic effect, and immunogenic response following conventional TACE (cTACE), drug-eluting embolic TACE (DEE-TACE), and transarterial embolization (TAE) in a rat model of HCC. After each treatment, three-dimensional drug delivery was quantitatively evaluated via the transparent liver tumor imaging, and time-dependent tumor necrosis was analyzed by serial tumor harvesting and histological staining. The results showed that chemotherapeutic agents travel only short distances after cTACE (∼80µm) and DEE-TACE (∼110µm), whereas necrosis occurs extensively within 24 h of treatment (85.3-97.2% of tumor cells). In addition, the percentages of CD4 and IL-17+ CD4 T cells increased significantly following treatment; however, drug-loading did not appear to affect the immune response following TACE. In conclusion, transarterially delivered chemotherapeutic agents appeared to exert a limited role, owing to the rapid and overwhelming effect of embolization. STATEMENT OF SIGNIFICANCE: TACE has been widely used for the treatment of HCC, especially for unresectable intermediate and advanced HCCs. Drug use in TACE is expected to provide patients with synergistic therapeutic benefits with the effect of embolic agents; however, the role of chemotherapeutic agents in TACE remains controversial. This study quantitatively verified that chemotherapeutic agents travel only short distances after TACE, while necrosis occurs extensively within 24h, and drug loading does not significantly affect immune responses following TACE. Three-dimensional imaging of intact transparent HCC can contribute to a better understanding of drug delivery mechanisms associated with TACE and also reveal that drug use in TACE may need to be reconsidered and limited to situations when embolization is expected to be insufficient.

In vivo monitoring of vascularization and oxygenation of tumor xenografts using optoacoustic microscopy and diffuse optical spectroscopy

The research is devoted to comparison of the blood vessel structure and the oxygen state of three xenografts: SN-12C, HCT-116 and Colo320. Differences in the vessel formation and the level of oxygenation are revealed by optoacoustic (OA) microscopy and diffuse optical spectroscopy (DOS) respectively. The Colo320 tumor is characterized by the highest values of vessel size and fraction. DOS showed increased content of deoxyhemoglobin that led to reduction of saturation level for Colo320 as compared to other tumors. Immunohistochemical (IHC) analysis for CD31 demonstrates the higher number of vessels in Colo320. The IHC for hypoxia was consistent with DOS results and revealed higher values of the relative hypoxic fraction in Colo320.

Enhanced efficacy of direct immunochemotherapy for hepatic cancer with image-guided intratumoral radiofrequency hyperthermia

BACKGROUND

It is still a challenge to prevent tumor recurrence post radiofrequency ablation (RFA) of medium-to-large hepatocellular carcinomas (HCC). Immunochemotherapy, a combination of immunotherapy with chemotherapy, has demonstrated a great potential in augmenting the treatment efficacy for some malignancies. In this study, we validated the feasibility of using radiofrequency hyperthermia (RFH)-enhanced intratumoral immunochemotherapy of LTX-315 with liposomal doxorubicin for rat orthotopic HCC.

METHODS

Different groups of luciferase-labeled rat HCC cells and rat orthotopic HCC models were treated by: (1) phosphate buffered saline; (2) RFH; (3) LTX-315; (4) RFH+LTX-315; (5) liposomal doxorubicin; (6) RFH+liposomal doxorubicin; (7) LTX-315+liposomal doxorubicin; and (8) RFH+LTX-315+liposomal doxorubicin. Cell viabilities and apoptosis of different treatment groups were compared. Changes in tumor sizes were quantified by optical and ultrasound imaging, which were confirmed by subsequent histopathology. The potential underlying biological mechanisms of the triple combination treatment (RFH+LTX-315+liposomal doxorubicin) were explored.

RESULTS

Flow cytometry and MTS assay showed the highest percentage of apoptotic cells and lowest cell viability in the triple combination treatment group compared with other seven groups (p<0.001). Tumors in this group also presented the most profound decrease in bioluminescence signal intensities and the smallest tumor volumes compared with other seven groups (p<0.001). A significant increase of CD8+ T cells, CD8+/interferon (IFN)-γ+ T cells, CD8+/tumor necrosis factor (TNF)-α+ T cells, and natural killer cells, and a significant decrease of regulatory T cells were observed in the tumors (p<0.001). Meanwhile, a significantly higher level of Th1-type cytokines in both plasma (interleukin (IL)-2, IL-12, IL-18, IFN-γ) and tumors (IL-2, IL-18, IFN-γ, TNF-α), as well as a significantly lower Th2-type cytokines of IL-4 and IL-10 in plasma and tumor were detected.

CONCLUSIONS

Intratumoral RFA-associated RFH could enhance the efficacy of immunochemotherapy of LTX-315 with liposomal doxorubicin for HCC, which may provide a new strategy to increase the curative efficacy of thermal ablation for medium-to-large HCC.

Gas generating microspheres for immediate release of Hsp90 inhibitor aiming at postembolization hypoxia in transarterial chemoembolization therapy of hepatocellular carcinoma

CO₂ gas generating poly(lactic-co-glycolic acid) (PLGA) microsphere (MS) was designed for rapid release of tanespimycin (17-AAG) in transarterial chemoembolization (TACE) treatment of hepatocellular carcinoma (HCC). As poorly water-soluble drug is generally released from PLGA MS in a sustained manner, the drug release profile should be controlled according to its clinical indications. In current study, responding to immediate increase in hypoxia inducible factor-1α (HIF-1α) level under hypoxia state followed by embolization of tumor feeding arteries, sodium bicarbonate (NaHCO₃) was added to PLGA/17-AAG MS for fast drug release by CO₂ gas generation in slightly acidic tumor microenvironment. With the aid of NaHCO₃, initial burst release of 17-AAG was available without losing the micron-size and spherical shape of designed MS for embolization of artery. Acid-responsive CO₂ gas generation and subsequent immediate release of 17-AAG from MS were successfully verified. PLGA/17-AAG/NaHCO₃ MS-treated group exhibited higher antiproliferation and apoptosis induction efficacies in McA-RH7777 and SNU-761 cells. McA-RH7777 tumor-implanted rats treated by TACE using PLGA/17-AAG/NaHCO₃ MS presented a complete therapeutic response. All these findings suggest that developed tumor microenvironment-responsive gas-generating MS can be efficiently applied to TACE therapy of HCC.

Combined treatment of sorafenib and doxorubicin-loaded microbubble-albumin nanoparticle complex for hepatocellular carcinoma: A feasibility study

Purpose

To assess the feasibility of the combined sorafenib (SOR) and doxorubicin-loaded microbubble-albumin nanoparticle complex (DOX-MAC) treatment effect in an orthotopic rat model of hepatocellular carcinoma (HCC).

Materials and methods

Sixty-two rats with N1-S1 hepatoma were divided into four groups according to the treatment methods, i.e. G1 (SOR and DOX-MAC; n = 12), G2 (SOR; n = 15), G3 (DOX-MAC; n = 12), G4 (DOX; n = 11), and G5 (normal saline; n = 12). We performed the theragnostic, contrast-enhanced ultrasound examination and treatment at the baseline, one-week, and two-weeks. Tumor volume and perfusion parameters were compared at each time point and the differences between all of the groups over time were analyzed using repeated measures ANOVA. We also analyzed the apoptotic index and microvessel density (MVD) per each tumor specimen in all of the groups.

Results

The tumors increased from the beginning in all of the groups to the final follow-up, whereas the tumor growth in the G1 group and the G2 group was inhibited during the treatment period compared to the baseline tumor volume (P = 0.016 and P = 0.031). The G1 group resulted in tumor growth inhibition compared to the control group (P = 0.008). The G1 group showed that the peak enhancement and wash-in area under the curve were lower than that of the G4 group (P = 0.010 and 0.022). However, there was no difference in perfusion parameters in the other treated group compared to control group. The MVD of the G1 group tumor was lower than that of the G4 group (P = .016).

Conclusion

Our results suggest that the combination therapy of SOR and DOX-MAC can cause inhibition of tumor growth after treatment and that this therapy can be adequately monitored using the theragnostic DOX-MAC agent.

Comparison of embolic effect between water-in-oil emulsion and microspheres in transarterial embolization for rat hepatocellular carcinoma model

AIM

To compare two different embolic materials, water-in-oil (W/O) emulsion followed by gelatin particles and microspheres in transarterial embolization (TAE), using a rat hepatocellular carcinoma model.

METHODS

Twenty rats bearing N1S1 cells were divided into the W/O emulsion group and Microsphere group. Water-in-oil emulsion was created by a glass membrane emulsification device. The tumor vascularity was measured by contrast-enhanced ultrasonography 24 h before and 10 min and 48 h after TAE. Tumor necrosis, hepatic infarction ratio surrounding the tumor, and locations of the embolic materials 48 h after TAE were assessed. The changes of serum liver enzymes were also evaluated. Statistical significance was determined by using either the Mann-Whitney U-test or Fisher's exact test.

RESULTS

The tumor vascularity 48 h after TAE was significantly higher in the Microsphere group (20.1 vs. 3.76%, P = 0.016). The overflow of Lipiodol into the portal veins surrounding the tumor was seen, whereas microspheres were seen only in the artery. The percentage of necrotic area and complete response ratio in the W/O emulsion group was significantly higher (99.9 vs. 87.6%, P = 0.029 and 87.5 vs. 28.6%, P = 0.041, respectively). Serum aspartate aminotransferase and serum alanine aminotransferase levels 48 h after TAE were significantly higher in the W/O emulsion group (P < 0.01).

CONCLUSIONS

The embolization using W/O emulsion followed by gelatin particles showed stronger antitumor effects with the occlusion of both the tumor feeding artery and the portal vein compared with microspheres, which occluded only the arteries.

Hyaluronic acid/doxorubicin nanoassembly-releasing microspheres for the transarterial chemoembolization of a liver tumor

Doxorubicin (DOX)-loaded, hyaluronic acid-ceramide (HACE) nanoassembly-releasing poly(lactic-co-glycolic acid) (PLGA) microspheres (MSs) were developed for transarterial chemoembolization (TACE) therapy of liver cancer. DOX/HACE MSs with a mean diameter of 27 μm and a spherical shape were prepared based on the modified emulsification method. Their in vitro biodegradability in artificial biological fluids was observed. A more sustained drug release pattern was observed from DOX/HACE MS than from DOX MS at pH 7.4. The cellular internalization efficiency of DOX of the DOX/HACE MS group was higher than that of the DOX MS group in liver cancer cells (HepG2 and McA-RH7777 cells), mainly due to CD44 receptor-mediated endocytosis of the released DOX/HACE nanoassembly. In both HepG2 and McA-RH7777 cells, the antiproliferation and apoptotic potentials of the DOX/HACE MS were significantly higher than those of the DOX MS (p < .05). Notably, in the McA-RH7777 tumor-implanted rat models, a better tumor growth suppression, a lower tumor viable portion, and a higher incidence of apoptosis were presented in the DOX/HACE MS group than in the DOX MS group after intra-arterial (IA) administration. DOX/HACE-based nanoassembly release from the DOX/HACE MS seems to elevate the cellular accumulation of DOX and its anticancer activities. The developed DOX/HACE MS can be used as a drug-loaded HA nanoassembly-releasing MS system for TACE therapy of liver cancer.

Modified Rat Hepatocellular Carcinoma Models Overexpressing Vascular Endothelial Growth Factor

PURPOSE

To compare tumor vascularity in 4 types of rat hepatocellular carcinoma (HCC) models: N1S1, vascular endothelial growth factor (VEGF)-transfected N1S1 (VEGF-N1S1), McA-RH7777, and VEGF-transfected McA-RH7777 (VEGF-McA-RH777) tumors.

MATERIALS AND METHODS

The N1S1 and McA-RH7777 cell lines were transfected with expression vectors containing cDNA for rat VEGF. Eighty-eight male Sprague-Dawley rats (weight range, 400-450 g) were randomly divided into 4 groups (ie, 22 rats per model), and 4 types of tumor models were created by using the N1S1, VEGF-N1S1, McA-RH7777, and VEGF-McA-RH777 cell lines. Tumor vascularity was evaluated by perfusion computed tomography (CT), enzyme-linked immunosorbent assay of VEGF, CD34 staining, angiography, and Lipiodol transarterial embolization. Intergroup discrepancies were evaluated by Kruskal-Wallis test.

RESULTS

Arterial perfusion (P < .001), portal perfusion (P = .015), total perfusion (P < .001), tumor VEGF level (P = .002), and microvessel density (MVD; P = .007) were significantly different among groups. VEGF-McA-RH7777 tumors showed the greatest arterial perfusion (46.7 mL/min/100 mL ± 15.5), total perfusion (60.7 mL/min/100 mL ± 21.8), tumor VEGF level (3,376.7 pg/mL ± 145.8), and MVD (34.5‰ ± 7.5). Whereas most tumors in the N1S1, VEGF-N1S1, and McA-RH7777 groups showed hypovascular staining on angiography and minimal Lipiodol uptake after embolization, 5 of 6 VEGF-McA-RH7777 tumors (83.3%) presented hypervascular tumor staining and moderate to compact Lipiodol uptake.

CONCLUSIONS

McA-RH7777 tumors were more hypervascular than N1S1 tumors, and tumor vascularity was enhanced further by VEGF transfection. Therefore, the VEGF-McA-RH7777 tumor is recommended to mimic hypervascular human HCC in rats.

Translational Animal Models for Liver Cancer

Animal models have become increasingly important in the study of hepatocellular carcinoma (HCC), as they serve as a critical bridge between laboratory-based discoveries and human clinical trials. Developing an ideal animal model for translational use is challenging, as the perfect model must be able to reproduce human disease genetically, anatomically, physiologically, and pathologically. This brief review provides an overview of the animal models currently available for translational liver cancer research, including rodent, rabbit, non-human primate, and pig models, with a focus on their respective benefits and shortcomings. While small animal models offer a solid starting point for investigation, large animal HCC models are becoming increasingly important for translation of preclinical results to clinical practice.

Sorafenib and 2,3,5-triiodobenzoic acid-loaded imageable microspheres for transarterial embolization of a liver tumor

Sorafenib (SOF; an angiogenesis inhibitor) and 2,3,5-triiodobenzoic acid (TIBA; a contrast agent for computed tomography imaging)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres (MSs) were fabricated. Embolization, drug delivery, and tracing the distribution of MSs for liver cancer therapy were accomplished with the developed MSs after their intra-arterial (IA) administration. SOF/TIBA/PLGA MSs with 24.8–28.5 µm mean diameters were prepared, and the sustained release of SOF from MSs was observed. Lower systemic exposure (represented as the area under the curve [AUC]) and maximum drug concentration in plasma (C_max) values of the SOF/TIBA/PLGA MSs group (IA administration, 1 mg/kg) in the results of the pharmacokinetic study imply alleviated unwanted systemic effects (e.g., hand and foot syndrome), compared to the SOF solution group (oral administration, 10 mg/kg). In a rat hepatoma model, the increase of microvessel density (MVD) following arterial embolization (i.e., reactive angiogenesis) was partially limited by SOF/TIBA/PLGA MSs. This resulted in the SOF/TIBA/PLGA MSs group (IA administration, single dosing, 1 mg/kg) showing a smaller tumor size increase and viable tumor portion compared to the TIBA/PLGA MSs group. These findings suggest that a developed SOF/TIBA/PLGA MS can be a promising therapeutic system for liver cancer using a transarterial embolization strategy.