Angiogenesis: noninvasive quantitative assessment with contrast-enhanced functional US in murine model

Quantitative Functional Evaluation of Liver Fibrosis in Mice with Dynamic Contrast-enhanced Photoacoustic Imaging

Background Dynamic contrast-enhanced (DCE) photoacoustic (PA) imaging (PAI) is a novel noninvasive imaging modality that uses the differences in optical absorption of oxyhemoglobin and deoxyhemoglobin and may be performed in a dynamic fashion to image the indocyanine green (ICG) pharmacokinetics in the liver. Purpose To determine whether DCE PAI parameters (maximum peak time [T_max] and half-life [T_1/2]) derived from the PA liver function curve correlate with fibrosis determined using histopathologic analysis. Materials and Methods Between June 2020 and October 2020, 28 male mice aged 8 weeks were intraperitoneally injected with carbon tetrachloride solution every 2 days to establish a liver fibrosis model. At the 1st, 4th, and 8th week of modeling, the changes in liver structure were monitored dynamically by using a PA technique. The T_max and T_1/2 of ICG were calculated at different pathologic stages and within a control group. Corresponding liver histopathologic results and blood biochemical data were obtained. Spearman rank correlation was used to evaluate the relationship between the DCE PAI results and histologic scores. Results The PA liver function curve showed that the T_max and T_1/2 varied among groups (mean T_max: control group, 9 seconds ± 1.8 [standard deviation]; 1 week, 51 seconds ± 4.4; 4 weeks, 73 seconds ± 5.3; 8 weeks, 104 seconds ± 6.6; P < .001) (mean T_1/2: control group, 28 seconds ± 6.5; 1 week, 201 seconds ± 12.4; 4 weeks, 285 seconds ± 11; 8 weeks, 318 seconds ± 30.5; P < .001). There was a positive correlation between the dynamic parameters (T_max and T_1/2) and the histopathologic scores; the Spearman ρ ratios for the Sirius red and α-smooth muscle actin (αSMA)-positive areas versus the T_max were 0.93 and 0.94 (P < .001 for both), and the Spearman ρ ratios for the Sirius red and αSMA-positive areas versus T_1/2 were 0.87 and 0.89 (P < .001 for both). Conclusion Dynamic contrast-enhanced photoacoustic imaging demonstrated a higher maximum peak time and half-life in mice with induced fibrosis compared with control mice without fibrosis, and these values correlated with histologic measures of fibrosis. © RSNA, 2021 Online supplemental material is available for this article.

Assessment of angiogenesis in rabbit orthotropic liver tumors using three-dimensional dynamic contrast-enhanced ultrasound compared with two-dimensional DCE-US

OBJECTIVES

To evaluate quantitative three-dimensional (3D) dynamic contrast-enhanced ultrasound (DCE-US) in the assessment of tumor angiogenesis using an orthotropic liver tumor model.

METHODS

Nine New Zealand white rabbits with liver orthotropic VX2 tumors were established and imaged by two-dimensional (2D) and 3D DCE-US after SonoVue^® bolus injections. The intraclass correlation coefficients of perfusion parameters, including peak intensity (PI), mean transit time, time to peak, and area under the curve, were calculated based on time-intensity curve. The percentage area of microvascular (PAMV) and the expression of vascular endothelial growth factor (VEGF) were both evaluated by immunohistochemical analysis and weighted by the tumor activity area ratio. Correlations between quantitative and histologic parameters were analyzed.

RESULTS

The reproducibility of 3D DCE-US quantitative parameters was excellent (ICC 0.91-0.99); but only PI showed high reproducibility (ICC 0.97) in 2D. None of the parameters of quantitative 2D DCE-US were significantly correlated with weighted PAMV or VEGF. For 3D DCE-US, there was a positive correlation between PI and weighted PAMV (r = 0.74, P = 0.04) as well as VEGF (r = 0.79, P = 0.02).

CONCLUSION

Quantitative parameters of 3D DCE-US show feasibility, higher reproducibility and accuracy for the assessment of tumor angiogenesis using an orthotropic liver tumor model compared with 2D DCE-US.

Quantitative Evaluation of Combretastatin A4 Phosphate Early Efficacy in a Tumor Model with Dynamic Contrast-Enhanced Ultrasound

Combretastatin A4 phosphate (CA4P) is a vascular disrupting agent that rapidly shuts down blood supply to tumors. Early monitoring of tumor perfusion plays a crucial role in determining the optimal strategy to managing treatment and guiding future therapy. The aim of this study was to investigate the potential value of dynamic contrast-enhanced ultrasound (CEUS) in quantitative evaluation of tumor perfusion at an early stage in CA4P therapy. Central and peripheral perfusion of tumors was detected by CEUS pre-treatment (0 h) and 2, 12 and 48 h after CA4P injection. Two perfusion parameters, maximum intensity (IMAX) and time to peak (TTP), were calculated from the time-intensity curve. After CEUS, the efficacy of CA4P was immediately confirmed by immunofluorescence assay and hematoxylin and eosin, Hoechst 33342 and fluorescein isothiocyanate-lectin staining. In CEUS of the center region of tumors, IMAX gradually decreased from 0 to 12 h and regrew at 48 h (p < 0.01). TTP increased only at 2 h. In the peripheral regions, IMAX did not change obviously from 0 to 12 h (p > 0.05) and just increased at 48 h (p < 0.01). The TTP of peripheral regions had the same tendency to vary tendency as that of center regions. In addition, microvascular density (MVD), vascular perfusion and necrotic area of the tumor were quantitatively analyzed. A close correlation between IMAX and MVD was observed in the center areas of tumors (r = 0.72, p < 0.01), whereas the correlation between IMAX and MVD in peripheral areas was weak (r = 0.37, p < 0.01). However, IMAX was positively correlated with tumor perfusion in both center and peripheral areas of tumors (r = 0.82, p < 0.01, and r = 0.63, p < 0.01, respectively). Consequently, IMAX was a reliable indicator of tumor perfusion evaluation by CEUS. The use of CEUS to quantify tumor perfusion could a promising method for the early detection of tumor responses in anti-vascular treatment.

Dynamic contrast-enhanced ultrasonography (D-CEUS) for the early prediction of bevacizumab efficacy in patients with metastatic colorectal cancer

OBJECTIVES

To investigate early changes in tumour perfusion parameters by dynamic contrast-enhanced ultrasonography (D-CEUS) and to identify any correlation with survival and tumour response in patients with metastatic colorectal cancer (CRC) treated with bevacizumab (B).

METHODS

Thirty-seven patients randomized to either chemotherapy (C) plus B or C alone were considered for this study. D-CEUS was performed at baseline and after the first treatment cycle (day 15). Four D-CEUS perfusion parameters were considered: derived peak intensity (DPI), area under the curve (AUC), slope of wash-in (A) and time to peak intensity (TPI).

RESULTS

In patients treated with C plus B, a ≥22.5 % reduction in DPI, ≥20 % increase in TPI and ≥10 % reduction in AUC were correlated with higher progression-free survival in the C+B arm (p = 0.048, 0.024 and 0.010, respectively) but not in the C arm. None of the evaluated parameter modifications had a correlation with tumour response or overall survival.

CONCLUSIONS

D-CEUS could be useful for detecting and quantifying dynamic changes in tumour vascularity as early as 15 days after the start of B-based therapy. Although these changes may be predictive of progression-free survival, no correlation with response or overall survival was found.

KEY POINTS

• D-CEUS showed early changes in liver metastasis perfusion in colorectal cancer. • A decrease in tumour perfusion was associated with longer progression-free survival. • The decrease in perfusion was not correlated with higher overall survival.

Hyposialylated IgG activates endothelial IgG receptor FcγRIIB to promote obesity-induced insulin resistance

Type 2 diabetes mellitus (T2DM) is a common complication of obesity. Here, we have shown that activation of the IgG receptor FcγRIIB in endothelium by hyposialylated IgG plays an important role in obesity-induced insulin resistance. Despite becoming obese on a high-fat diet (HFD), mice lacking FcγRIIB globally or selectively in endothelium were protected from insulin resistance as a result of the preservation of insulin delivery to skeletal muscle and resulting maintenance of muscle glucose disposal. IgG transfer in IgG-deficient mice implicated IgG as the pathogenetic ligand for endothelial FcγRIIB in obesity-induced insulin resistance. Moreover, IgG transferred from patients with T2DM but not from metabolically healthy subjects caused insulin resistance in IgG-deficient mice via FcγRIIB, indicating that similar processes may be operative in T2DM in humans. Mechanistically, the activation of FcγRIIB by IgG from obese mice impaired endothelial cell insulin transcytosis in culture and in vivo. These effects were attributed to hyposialylation of the Fc glycan, and IgG from T2DM patients was also hyposialylated. In HFD-fed mice, supplementation with the sialic acid precursor N-acetyl-D-mannosamine restored IgG sialylation and preserved insulin sensitivity without affecting weight gain. Thus, IgG sialylation and endothelial FcγRIIB may represent promising therapeutic targets to sever the link between obesity and T2DM.

Quantitative Analysis of Contrast-Enhanced Ultrasound Imaging in Invasive Breast Cancer: A Novel Technique to Obtain Histopathologic Information of Microvessel Density

We examined whether enhancement area ratios obtained by the new bubble detection method correlate with histologic microvessel density in invasive breast cancer. Forty consecutive patients with invasive breast cancer lesions underwent contrast-enhanced ultrasound. The ratio of enhanced area to manually segmented tumor area (enhancement area ratio) was obtained with the new method at peak and delayed phases (50-54, 55-59, 60-64 and 65-69 s). We also analyzed time-intensity curves to obtain peak intensity and area under curve. Enhancement area ratios in both peak and delayed phases (50-54, 55-59, 60-64 and 65-69 s) were significantly correlated with microvessel density (r = 0.57, 0.62, 0.68, 0.61 and 0.58; p = 0.0001, <0.0001, <.0001, <.0001 and 0.0001, respectively). In time-intensity curve analysis, peak intensity was significantly correlated (r = 0.43, p = 0.0073), whereas area under the curve was not (r = 0.29, p = 0.0769). Enhancement area ratios obtained by the new method were correlated with microvessel density in invasive breast cancer.

Angiogenesis in Ischemic Stroke and Angiogenic Effects of Chinese Herbal Medicine

Stroke is one of the major causes of death and adult disability worldwide. The underlying pathophysiology of stroke is highly complicated, consisting of impairments of multiple signalling pathways, and numerous pathological processes such as acidosis, glutamate excitotoxicity, calcium overload, cerebral inflammation and reactive oxygen species (ROS) generation. The current treatment for ischemic stroke is limited to thromolytics such as recombinant tissue plasminogen activator (tPA). tPA has a very narrow therapeutic window, making it suitable to only a minority of stroke patients. Hence, there is great urgency to develop new therapies that can protect brain tissue from ischemic damage. Recent studies have shown that new vessel formation after stroke not only replenishes blood flow to the ischemic area of the brain, but also promotes neurogenesis and improves neurological functions in both animal models and patients. Therefore, drugs that can promote angiogenesis after ischemic stroke can provide therapeutic benefits in stroke management. In this regard, Chinese herbal medicine (CHM) has a long history in treating stroke and the associated diseases. A number of studies have demonstrated the pro-angiogenic effects of various Chinese herbs and herbal formulations in both in vitro and in vivo settings. In this article, we present a comprehensive review of the current knowledge on angiogenesis in the context of ischemic stroke and discuss the potential use of CHM in stroke management through modulation of angiogenesis.

RGD-Targeted Ultrasound Contrast Agent for Longitudinal Assessment of Hep-2 Tumor Angiogenesis In Vivo

OBJECTIVE

To prepare arginine-glycine-aspartate (RGD)-targeted ultrasound contrast microbubbles (MBs) and explore the feasibility of their use in assessing dynamic changes in αvβ3 integrin expression in a murine model of tumor angiogenesis.

METHODS

RGD peptides were conjugated to the surfaces of microbubbles via biotin-avidin linkage. Microbubbles bearing RADfK peptides were prepared as controls. The RGD-MBs were characterized using an Accusizer 780 and optical microscopy. The binding specificity of the RGD-MBs for ανβ3-expressing endothelial cells (bEnd.3) was demonstrated in vitro by a competitive inhibition experiment. In an in vivo study, mice bearing tumors of three different stages were intravenously injected with RGD-MBs and subjected to targeted, contrast-enhanced, high-frequency ultrasound. Subsequently, tumors were harvested and sectioned for immunofluorescence analysis of ανβ3 expression.

RESULTS

The mean size of the RGD-MBs was 2.36 ± 1.7 μm. The RGD-MBs showed significantly higher adhesion levels to bEnd.3 cells compared to control MBs (P < 0.01). There was rarely binding of RGD-MBs to αvβ3-negative MCF-7 cells. Adhesion of the RGD-MBs to the bEnd.3 cells was significantly inhibited following treatment with anti-alpha(v) antibodies. The quantitative acoustic video intensity for high-frequency, contrast-enhanced ultrasound imaging of subcutaneous human laryngeal carcinoma (Hep-2) tumor xenografts was significantly higher in small tumors (19.89 ± 2.49) than in medium tumors (11.25 ± 2.23) and large tumors (3.38 ± 0.67) (P < 0.01).

CONCLUSIONS

RGD-MBs enable noninvasive in vivo visualization of changes in tumor angiogenesis during tumor growth in subcutaneous cancer xenografts.

Recent developments in dynamic contrast-enhanced ultrasound imaging of tumor angiogenesis

Angiogenesis is a critical process for tumor growth and metastatic dissemination. There is tremendous interest in the development of noninvasive methods for imaging tumor angiogenesis, and ultrasound (US) is an emerging platform technology to address this challenge. The introduction of intravascular microbubble contrast agents not only allows real-time visualization of tumor perfusion during an US examination, but they can be functionalized with specific ligands to permit molecular US imaging of angiogenic biomarkers that are overexpressed on the tumor endothelium. In this article, we will review current concepts and developing trends for US imaging of tumor angiogenesis, including relevant preclinical and clinicsal findings.

Imaging of thyroid tumor angiogenesis with microbubbles targeted to vascular endothelial growth factor receptor type 2 in mice

BACKGROUND

To evaluate whether Contrast Enhanced Ultrasund (CEUS) with microbubbles (MBs) targeted to VEGFR-2 is able to characterize in vivo the VEGFR-2 expression in the tumor vasculature of a mouse model of thyroid cancer (Tg-TRK-T1).

METHODS

Animal protocol was approved by Institutional committee on Laboratory Animal Care. Contrast-enhanced ultrasound imaging with MBs targeted with an anti-VEGFR-2 monoclonal antibody (UCAVEGFR-2) and isotype control antibody (UCAIgG) was performed in 7 mice with thyroid carcinoma, 5 mice with hyperplasia or benign thyroid nodules and 4 mice with normal thyroid. After ultrasonography, the tumor samples were harvested for histological examination and VEGFR-2 expression was tested by immunohistochemistry. Data were reported as median and range. Paired non parametric Wilcoxon's test and ANOVA of Kruskal-Wallis were used. The correlation between the contrast signal and the VEGFR-2 expression was assessed by the Spearman coefficient.

RESULTS

The Video intensity difference (VID) caused by backscatter of the retained UCAVEGFR-2 was significantly higher in mice harboring thyroid tumors compared to mice with normal thyroids (P < 0.01) and to mice harboring benign nodules (P < 0.01). No statistically significant differences of VID were observed in the group of mice carrying benign nodules compared to mice with normal thyroids. Moreover in thyroid tumors VID of retained VEGFR-2-targeted UCA was significantly higher than that of control UCAIgG (P <0.05). Results of immunohistochemical analysis confirmed VEGFR-2 overexpression. The magnitude of the molecular ultrasonographic signal from a VEGFR-2-targeted UCA retained by tissue correlates with VEGFR-2 expression determined by immunohistochemistry (rho 0.793, P=0.0003).

CONCLUSIONS

We demonstrated that CEUS with UCAVEGFR-2 might be used for in vivo non invasive detection and quantification of VEGFR-2 expression in thyroid cancer in mice, and to differentiate benign from malignant thyroid nodules.

Imaging of thyroid tumor angiogenesis with microbubbles targeted to vascular endothelial growth factor receptor type 2 in mice

Background

To evaluate whether Contrast Enhanced Ultrasund (CEUS) with microbubbles (MBs) targeted to VEGFR-2 is able to characterize in vivo the VEGFR-2 expression in the tumor vasculature of a mouse model of thyroid cancer (Tg-TRK-T1).

Methods

Animal protocol was approved by Institutional committee on Laboratory Animal Care. Contrast-enhanced ultrasound imaging with MBs targeted with an anti-VEGFR-2 monoclonal antibody (UCA_VEGFR-2) and isotype control antibody (UCA_IgG) was performed in 7 mice with thyroid carcinoma, 5 mice with hyperplasia or benign thyroid nodules and 4 mice with normal thyroid. After ultrasonography, the tumor samples were harvested for histological examination and VEGFR-2 expression was tested by immunohistochemistry. Data were reported as median and range. Paired non parametric Wilcoxon’s test and ANOVA of Kruskal-Wallis were used. The correlation between the contrast signal and the VEGFR-2 expression was assessed by the Spearman coefficient.

Results

The Video intensity difference (VI_D) caused by backscatter of the retained UCA_VEGFR-2 was significantly higher in mice harboring thyroid tumors compared to mice with normal thyroids (P < 0.01) and to mice harboring benign nodules (P < 0.01). No statistically significant differences of VI_D were observed in the group of mice carrying benign nodules compared to mice with normal thyroids. Moreover in thyroid tumors VI_D of retained VEGFR-2-targeted UCA was significantly higher than that of control UCA_IgG (P <0.05). Results of immunohistochemical analysis confirmed VEGFR-2 overexpression. The magnitude of the molecular ultrasonographic signal from a VEGFR-2-targeted UCA retained by tissue correlates with VEGFR-2 expression determined by immunohistochemistry (rho 0.793, P=0.0003).

Conclusions

We demonstrated that CEUS with UCA_VEGFR-2 might be used for in vivo non invasive detection and quantification of VEGFR-2 expression in thyroid cancer in mice, and to differentiate benign from malignant thyroid nodules.

Volumetric contrast-enhanced ultrasound imaging to assess early response to apoptosis-inducing anti-death receptor 5 antibody therapy in a breast cancer animal model

OBJECTIVES

The objective of this study was to determine whether volumetric contrast-enhanced ultrasound (US) imaging could detect early tumor response to anti-death receptor 5 antibody (TRA-8) therapy alone or in combination with chemotherapy in a preclinical triple-negative breast cancer animal model.

METHODS

Animal experiments had Institutional Animal Care and Use Committee approval. Thirty breast tumor-bearing mice were administered Abraxane (paclitaxel; Celgene Corporation, Summit, NJ), TRA-8, TRA-8 + Abraxane, or saline as a controlon days 0, 3, 7, 10, 14, and 17. Volumetric contrast-enhanced US imaging was performedon days 0, 1, 3, and 7 before dosing. Changes in parametric maps of tumor perfusion were compared with the tumor volume and immunohistologic findings.

RESULTS

Therapeutic efficacy was detected within 7 days after drug administration using parametric volumetric contrast-enhanced US imaging. Decreased tumor perfusion was observed in both the TRA-8-alone- and TRA-8 + Abraxane-dosed animals compared to control tumors (P = .17; P = .001, respectively). The reduction in perfusion observed in the TRA-8 + Abraxane group was matched with a corresponding regression in tumor size over the same period. Survival curves illustrate that the combination of TRA-8 + Abraxane improves drug efficacy compared to the same drugs administered alone. Immunohistologic analysis revealed increased levels of apoptotic activity in the TRA-8-dosed tumors, confirming enhanced antitumor effects.

CONCLUSIONS

Preliminary results are encouraging, and volumetric contrast-enhanced US-based tumor perfusion imaging may prove clinically feasible for detecting and monitoring the early antitumor effects in response to combination TRA-8 + Abraxane therapy.

Contrast enhanced maximum intensity projection ultrasound imaging for assessing angiogenesis in murine glioma and breast tumor models: A comparative study

The purpose of this study was to prospectively compare noninvasive, quantitative measures of vascularity obtained from four contrast enhanced ultrasound (US) techniques to four invasive immunohistochemical markers of tumor angiogenesis in a large group of murine xenografts. Glioma (C6) or breast cancer (NMU) cells were implanted in 144 rats. The contrast agent Optison (GE Healthcare, Princeton, NJ) was injected in a tail vein (dose: 0.4ml/kg). Power Doppler imaging (PDI), pulse-subtraction harmonic imaging (PSHI), flash-echo imaging (FEI), and Microflow imaging (MFI; a technique creating maximum intensity projection images over time) was performed with an Aplio scanner (Toshiba America Medical Systems, Tustin, CA) and a 7.5MHz linear array. Fractional tumor neovascularity was calculated from digital clips of contrast US, while the relative area stained was calculated from specimens. Results were compared using a factorial, repeated measures ANOVA, linear regression and z-tests. The tortuous morphology of tumor neovessels was visualized better with MFI than with the other US modes. Cell line, implantation method and contrast US imaging technique were significant parameters in the ANOVA model (p<0.05). The strongest correlation determined by linear regression in the C6 model was between PSHI and percent area stained with CD31 (r=0.37, p<0.0001). In the NMU model the strongest correlation was between FEI and COX-2 (r=0.46, p<0.0001). There were no statistically significant differences between correlations obtained with the various US methods (p>0.05). In conclusion, the largest study of contrast US of murine xenografts to date has been conducted and quantitative contrast enhanced US measures of tumor neovascularity in glioma and breast cancer xenograft models appear to provide a noninvasive marker for angiogenesis; although the best method for monitoring angiogenesis was not conclusively established.

Contrast-enhanced ultrasonography of hepatocellular carcinoma: correlation between quantitative parameters and arteries in neoangiogenesis or sinusoidal capillarization

OBJECTIVE

The quantitative parameters in contrast-enhanced ultrasonography-time-intensity curve of hepatocellular carcinoma (HCC) were studied to explore their potential importance in monitoring the effects of anti-angiogenic therapy for HCC.

METHODS

115 HCC patients were studied with contrast-enhanced ultrasonography-time-intensity curve (CEUS-TIC) and with immunohistochemical analysis of tissue sections. The CEUS images were analyzed off-line to obtained quantitative parameters including maximum of intensity (IMAX), rise time (RT), time to peak (TTP), mean transit time (mTT), rise slope (RS), and washout time (WT). Monoclonal antibodies specific for smooth muscle actin and anti-CD34 were used to observe unpaired arteries (UAs) and microvessel area (MVA) of sinusoidal capillarization, respectively. The UAs and MVA of 82 HCC cases were successfully stained.

RESULTS

The number of UAs had moderate correlation with RT (r=-0.446), TTP (r=-0.432), and RS (r=0.431) (P<0.05), and it had mild correlation with IMAX (r=0.303) and WT (r=0.285) (P<0.05). MVA of sinusoidal capillarization had no correlation with perfusion parameters.

CONCLUSION

Quantitative CEUS-TIC parameters reflecting hemodynamics of tumors are correlated with UAs, but not with MVA, and they might be used to monitor the effects of anti-angiogenic therapy on HCC.

Antiangiogenic effects of pazopanib in xenograft hepatocellular carcinoma models: evaluation by quantitative contrast-enhanced ultrasonography

Background

Antiangiogenesis is a promising therapy for advanced hepatocellular carcinoma (HCC), but the effects are difficult to be evaluated. Pazopanib (GW786034B) is a pan-vascular endothelial growth factor receptor inhibitor, the antitumor effects or antiangiogenic effects haven't been investigated in HCC.

Methods

In vitro direct effects of pazopanib on human HCC cell lines and endothelial cells were evaluated. In vivo antitumor effects were evaluated in three xenograft nude mice models. In the subcutaneous HCCLM3 model, intratumoral blood perfusion was detected by contrast-enhanced ultrasonography (CEUS), and serial quantitative parameters were profiled from the time-intensity curves of ultrasonograms.

Results

In vitro proliferation of various HCC cell lines were not inhibited by pazopanib. Pazopanib inhibited migration and invasion and induced apoptosis significantly in two HCC cell lines, HCCLM3 and PLC/PRF/5. Proliferation, migration, and tubule formation of human umbilical vein endothelial cells were inhibited by pazopanib in a dose-dependent manner. In vivo tumor growth was significantly inhibited by pazopanib in HCCLM3, HepG2, and PLC/PRF/5 xenograft models. Various intratumoral perfusion parameters changed over time, and the signal intensity was significantly impaired in the treated tumors before the treatment efficacy on tumor size could be observed. Mean transit time of the contrast media in hotspot areas of the tumors was reversely correlated with intratumoral microvessel density.

Conclusions

Antitumor effects of pazopanib in HCC xenografts may owe to its antiangiogenic effects, and the in vivo antiangiogenic effects could be evaluated by quantitative CEUS.

Antiangiogenic effects of pazopanib in xenograft hepatocellular carcinoma models: evaluation by quantitative contrast-enhanced ultrasonography

BACKGROUND

Antiangiogenesis is a promising therapy for advanced hepatocellular carcinoma (HCC), but the effects are difficult to be evaluated. Pazopanib (GW786034B) is a pan-vascular endothelial growth factor receptor inhibitor, the antitumor effects or antiangiogenic effects haven't been investigated in HCC.

METHODS

In vitro direct effects of pazopanib on human HCC cell lines and endothelial cells were evaluated. In vivo antitumor effects were evaluated in three xenograft nude mice models. In the subcutaneous HCCLM3 model, intratumoral blood perfusion was detected by contrast-enhanced ultrasonography (CEUS), and serial quantitative parameters were profiled from the time-intensity curves of ultrasonograms.

RESULTS

In vitro proliferation of various HCC cell lines were not inhibited by pazopanib. Pazopanib inhibited migration and invasion and induced apoptosis significantly in two HCC cell lines, HCCLM3 and PLC/PRF/5. Proliferation, migration, and tubule formation of human umbilical vein endothelial cells were inhibited by pazopanib in a dose-dependent manner. In vivo tumor growth was significantly inhibited by pazopanib in HCCLM3, HepG2, and PLC/PRF/5 xenograft models. Various intratumoral perfusion parameters changed over time, and the signal intensity was significantly impaired in the treated tumors before the treatment efficacy on tumor size could be observed. Mean transit time of the contrast media in hotspot areas of the tumors was reversely correlated with intratumoral microvessel density.

CONCLUSIONS

Antitumor effects of pazopanib in HCC xenografts may owe to its antiangiogenic effects, and the in vivo antiangiogenic effects could be evaluated by quantitative CEUS.

Trans-arterial chemoembolization as a therapy for liver tumours: New clinical developments and suggestions for combination with angiogenesis inhibitors

The liver is the primary site of metastases for many malignancies. Gastrointestinal cancers are especially prone to spread to the liver and other tumours, as breast cancer and melanoma often spread to the liver. On the other hand, hepatocellular cancer (HCC) is the fifth most common malignancy in the world due to its common etiology from chronic liver damage caused by hepatitis or cirrhosis. Treatments of liver tumours vary according to histology and liver invasion and until now trans-arterial chemoembolization (TACE) has represented a main approach in the therapy of liver tumours. This review takes into consideration: (i) the background to utilizing TACE in liver tumours; (ii) TACE methods and the biological rationale for utilizing chemotherapeutic agents coated to a new micro-particle such as DC-Beads and HepaSphere; (iii) clinical experiences employing TACE in different liver tumours; (iv) the pivotal role of angiogenesis and hypoxia-induced angiogenesis following TACE with special references to HCC. Finally, the rationale for the combination of TACE with angiogenesis inhibitors is also discussed.

Copper transporter 2 regulates endocytosis and controls tumor growth and sensitivity to cisplatin in vivo

Copper transporter 2 (CTR2) is one of the four copper transporters in mammalian cells that influence the cellular pharmacology of cisplatin and carboplatin. CTR2 was knocked down using a short hairpin RNA interference. Robust expression of CTR2 was observed in parental tumors grown in vivo, whereas no staining was found in the tumors formed from cells in which CTR2 had been knocked down. Knockdown of CTR2 reduced growth rate by 5.8-fold, increased the frequency of apoptotic cells, and decreased the vascular density, but it did not change copper content. Knockdown of CTR2 increased the tumor accumulation of cis-diamminedichloroplatinum(II) [cisplatin (cDDP)] by 9.1-fold and greatly increased its therapeutic efficacy. Because altered endocytosis has been implicated in cDDP resistance, uptake of dextran was used to quantify the rate of macropinocytosis. Knockdown of CTR2 increased dextran uptake 2.5-fold without reducing exocytosis. Inhibition of macropinocytosis with either amiloride or wortmannin blocked the increase in macropinocytosis mediated by CTR2 knockdown. Stimulation of macropinocytosis by platelet-derived growth factor coordinately increased dextran and cDDP uptake. Knockdown of CTR2 was associated with activation of the Rac1 and cdc42 GTPases that control macropinocytosis but not activation of the phosphoinositide-3 kinase pathway. We conclude that CTR2 is required for optimal tumor growth and that it is an unusually strong regulator of cisplatin accumulation and cytotoxicity. CTR2 regulates the transport of cDDP in part through control of the rate of macropinocytosis via activation of Rac1 and cdc42. Selective knockdown of CTR2 in tumors offers a strategy for enhancing the efficacy of cDDP.

Intrahepatic transit time predicts liver fibrosis in patients with chronic hepatitis B: quantitative assessment with contrast-enhanced ultrasonography

We investigated the use of contrast-enhanced ultrasonography (CEUS) with quantitative measurements to assess the stages of liver fibrosis in patients with chronic hepatitis B. One-hundred twenty-two patients with chronic hepatitis B were divided into three groups according to the Scheuer scoring system pathologically and according to clinical evidence: mild fibrosis (S0 and S1, n = 36); moderate fibrosis (S2 and S3, n = 24); and cirrhosis (S4 and clinically typical cirrhosis, n = 62). CEUS of hepatic vessels and parenchyma was performed using the Cadence contrast pulse sequencing technique, with an intravenous bolus injection of a contrast agent (SonoVue). Real-time CEUS imaging of the liver was recorded and analyzed offline. Contrast arrival time, baseline, and peak intensity in the hepatic artery, portal vein, right hepatic vein, and liver parenchyma were used to calculate intrahepatic transit times, hepatic artery to hepatic vein transit time (HA-HVTT) and portal vein to hepatic vein transit time (PV-HVTT), as well as increased signal intensity (ISI). The correlations between these quantitative parameters and the stages of fibrosis were analyzed using Spearman rank correlation coefficients. HA-HVTT and PV-HVTT were shortened gradually with the progression of liver fibrosis. PV-HVTT was statistically significant differences existed between the two paired groups (mild vs. moderate vs. cirrhosis groups, p < 0.001), whereas HA-HVTT was changed significantly between mild and moderate or cirrhosis groups (p < 0.001). HA-HVTT and PV-HVTT changes were significantly correlated with liver fibrosis severity (r = -0.5930, p < 0.001; r = -0.8215, p < 0.001). Area under receiver operating characteristic curves for HA-HVTT and PV-HVTT were 0.891 +/- 0.034 and 0.955 +/- 0.020 at fibrosis scores >or=S2, and 0.785 +/- 0.040 and 0.946 +/- 0.018 at fibrosis score >or=S4, respectively. ISI values in the portal vein and liver parenchyma decreased with the severity of fibrosis. This study demonstrated that hepatic CEUS with quantitative measurements of intrahepatic transit time reflected the severity of liver fibrosis. The real-time CEUS imaging with use of software-based quantitative analysis could provide reliable information of hepatic hemodynamic changes to noninvasively assess the severity of liver fibrosis in patients with chronic hepatitis B.

[Assessment of tumour angiogenesis using contrast-enhanced ultrasound]

Microbubbles are useful for imaging tumour angiogenesis and relatively crude forms of this approach are now routinely used for subjective diagnosis, especially in the liver. More sophisticated methods use quantitative approaches to measure the amount and the time course of bolus or reperfusion curves and have shown great promise in revealing effective tumour response to anti-angiogenic drugs in humans before tumour shrinkage occurs. These are beginning to be accepted into clinical practice. In the long term, targeted microbubbles for molecular imaging and eventually for directed anti-tumour therapy are expected to be tested.

A method for assessing the microvasculature in a murine tumor model using contrast-enhanced ultrasonography

OBJECTIVE

The purpose of this study was to develop a method for assessing tumor vascularity in a preclinical model of breast cancer using contrast-enhanced ultrasonography.

METHODS

Eight mice were injected with 67NR breast cancer cells on their hind limbs and imaged with ultrasonography 8 days later. Mice were injected with an ultrasound contrast agent (UCA), and a sequence of images of the resultant backscattered echoes was recorded before and after high-power "destruction" pulses for each of multiple parallel planes. From these, data maps of the maximum contrast enhancement (within each time course) were constructed for each pixel, which enabled reconstruction of high-resolution coregistered sections into a 3-dimensional (3D) volume reflecting tumor vascularity. Additional studies were performed to determine the duration and repeatability of image enhancement, and images were correlated with conventional 3D power Doppler measurements.

RESULTS

The lifetime of the UCA in vivo was found to be 4.3 +/- 1.09 minutes (mean +/- SD). The 3D contrast-enhanced ultrasonographic technique produced images that correlated well with power Doppler images in specific regions but also depicted additional regions of flow surrounding the power Doppler signal. The mean correlation coefficient between voxel measurements of the central slice for each animal was 0.64 +/- 0.07 (P < .01). In addition, sequential studies in each animal were reproducible.

CONCLUSIONS

A method producing high-resolution volumetric assessments of tumor vascularity in a preclinical model of breast cancer is shown that correlates with other ultrasonographic measures of blood flow, which may provide greater sensitivity to the microvasculature.

Regularized estimation of contrast agent attenuation to improve the imaging of microbubbles in small animal studies

Quantitative analysis of tissue perfusion using contrast-enhanced ultrasound is still limited by shadowing, which is caused by inadequate compensation for microbubble contrast agent attenuation. Many previous methods have been developed for attenuation correction in soft tissues. However, no method has been proposed to correct for microbubble attenuation in vivo. In this article, a model to estimate microbubble attenuation is presented, using the time-intensity variation in a highly echogenic distal area without contrast uptake. This model is based on the assumption that a linear relationship holds between local microbubble attenuation and local backscatter. The model was applied to 12 murine renal perfusion studies. Parametric images of microbubble attenuation were generated, corresponding to dynamic contrast agent-specific sequences without shadowing. Contrast uptake kinetics consistent with the physiology were retrieved in all perfused areas. This method therefore proved to be of potential interest in the quantification of tissue perfusion in small animal studies.

Relationship between retention of a vascular endothelial growth factor receptor 2 (VEGFR2)-targeted ultrasonographic contrast agent and the level of VEGFR2 expression in an in vivo breast cancer model

OBJECTIVE

The aim of this study was to characterize the relationship between retention of a vascular endothelial growth factor receptor 2 (VEGFR2)-targeted ultrasonographic contrast agent (UCA) and VEGFR2 expression in tumor vasculature of breast cancer.

METHODS

67NR breast cancer tumors implanted in mice were evaluated in vivo with both VEGFR2-targeted and nontargeted UCAs, and a high-frequency ultrasound system. A bolus of the UCA was injected and allowed to circulate for 4 minutes to allow binding of targeted microbubbles. After that, 2 sets of images before and after a high-power ultrasonic destruction sequence were acquired. The average video intensity of predestruction and postdestruction images was measured and used as a relative measure of retention of the UCA in the tumor. Levels of VEGFR2 expression and tumor vascular density were quantified by immunohistochemical staining and compared with retention of the VEGFR2-targeted UCA.

RESULTS

Retention of VEGFR2-targeted microbubbles in tumors was significantly higher than retention of nontargeted microbubbles (mean +/- SD, 47.75+/-9.85 versus 18.5+/-5.46 dB; P< .001). Retention of the VEGFR2-targeted UCA was found to correlate with the level of VEGFR2 expression in the studied tumors (r(2)=0.41). In contrast, retention of the nontargeted UCA was not correlated with the level of VEGFR2 expression (r(2)=0.08). Furthermore, retention of the VEGFR2-targeted UCA was not correlated with the level of tumor vascularity.

CONCLUSIONS

The magnitude of the molecular ultrasonographic signal from a VEGFR2-targeted UCA retained by tissue correlates with VEGFR2 expression. These results validate the use of molecular ultrasonography for in vivo detection and quantification of VEGFR2 expression in this breast cancer model.

Characterizing blood volume fraction (BVF) in a VX2 tumor

OBJECTIVES

Neovascular proliferation of a tumor's blood supply is an important precursor of malignant growth. Evaluation of blood volume may provide useful information for the characterization, prognosis and response of tumors to therapy. The purpose of this study was to determine and compare the blood volume of tumor tissue measured noninvasively by MRI and microbubble contrast ultrasound imaging.

MATERIALS AND METHODS

Twenty-two rabbits injected with VX2 tumors were studied. The blood volume fraction in tumor and muscle tissue was obtained from MRI T(1)-weighted images using a blood-pool agent, Clariscan, and by ultrasound using Definity and pulse inversion imaging.

RESULTS AND CONCLUSIONS

Similar results were obtained from MRI and ultrasound. Estimation of the blood volume in tissue in the rim of a VX2 tumor 1.5 to 5.0 cm in diameter relative to that in the surrounding muscle was (mean+/-S.D.) 3.31+/-1.43 by MRI and 2.99+/-1.83 by ultrasound. The blood volume in the tissue relative to the total tissue volume (relative blood volume fraction) measured by MRI was 13+/-4.1% in tumor versus 4+/-1.4% in muscle (P<.01). Our data also suggested that, compared to the distribution volume of an extracellular contrast agent, Gd-DTPA, Clariscan as an intravascular agent demonstrated high-quality depictions of vascular structure of the tumor.

Dose-response relationship of ultrasound contrast agent in an in vivo murine melanoma model

Many factors affect the sensitivity and reliability of tumor vasculature assessment at the small doses of contrast agent necessary for imaging mice. In this study we investigate the dose-response relationship of ultrasound contrast agent for a minimal exposure power Doppler technique (minexPD) in a murine melanoma model. K1735 murine melanomas grown in 25 C3H/HeN mice were imaged by power Doppler ultrasound using different doses of contrast agents, Optison(R) and Definity(R). Six mice were treated with an antivascular agent, combretastatin A4-phosphate (CA4P), and imaged before and after treatment. The color-weighted fractional area (CWFA) of the peak-enhanced image was measured to assess tumor perfusion on a relative scale of 0 to 100. CWFA increased logarithmically with dose (R(2)=0.97). Treatment with CA4P resulted in pronounced reduction in tumor perfusion 2 h after contrast injection, but perfusion recovered in the tumor periphery after 2 days. CWFA was significantly different between pre- and post-treatment for all doses at 2 h and 2 days (p < 0.05, respectively). There was no significant difference detectable between the two contrast agents, Optison(R) and Definity(R) (p = 0.46). In vivo tumor enhancement in mice increases as logarithmic function with dose. Although the extent of enhancement is dose dependent, the difference between pre- and post-therapy enhancement is relatively unchanged and uniform at varying doses. The two contrast agents tested in this study performed equally well. These results suggest that quantitative contrast-enhanced power Doppler imaging is an effective method for monitoring therapy response of tumors in mice.

Molecular imaging of vascular endothelial growth factor receptor 2 expression using targeted contrast-enhanced high-frequency ultrasonography

OBJECTIVE

The aim of our study was to investigate the use of targeted contrast-enhanced high-frequency ultrasonography for molecular imaging of vascular endothelial growth factor receptor 2 (VEGFR2) expression on tumor vascular endothelium in murine models of breast cancer.

METHODS

Highly invasive metastatic (4T1) and nonmetatstatic (67NR) breast cancer cells were implanted in athymic nude mice. Tumors were examined in vivo with targeted contrast-enhanced high-frequency ultrasonography using a scanner with a 40-MHz probe. Randomized boluses of ultrasound contrast agents (UCAs) conjugated with an anti-VEGFR2 monoclonal antibody or an isotype control antibody (immunoglobulin G) were injected into the animals. Sonograms were analyzed by calculation of the normalized video intensity amplitudes caused by backscatter of the bound UCA. After ultrasonography, the tumor samples were harvested for analysis of VEGFR2 expression by immunoblotting and immunocytochemistry.

RESULTS

The mean video intensity amplitude caused by backscatter of the retained VEGFR2-targeted UCA was significantly higher than that of the control UCA (mean +/- SD: 4T1 tumors, 15 +/- 3.5 versus 7 +/- 1.6 dB; P < .01; 67NR tumors, 50 +/- 12.3 versus 12 +/- 2.6 dB; P < .01). There was a significant difference in VEGFR2-targeted UCA retention between 4T1 and 67NR tumors (normalized video intensity amplitudes, 15 +/- 3.5 and 50 +/- 12.3 dB, respectively; P < .001), and this correlated well with relative VEGFR2 expression in the two tumor types.

CONCLUSIONS

Targeted contrast-enhanced high-frequency ultrasonography may enable in vivo molecular imaging of VEGFR2 expression on the tumor vascular endothelium and may be used for noninvasive longitudinal evaluation of tumor angiogenesis in preclinical studies.

L’échographie haute résolution de la souris

Small-animal ultrasound imaging has been made possible using high-resolution imaging devices. The spatial resolution is therefore sufficient to accurately measure anatomical parameters in mice. This paper reviews some of the main applications of high-resolution ultrasound imaging of the mouse and highlights what could be the forthcoming advances.