Angiogenesis model for ultrasound contrast research

Production and Characterization of an Integrated Multi-Layer 3D Printed PLGA/GelMA Scaffold Aimed for Bile Duct Restoration and Detection

We successfully fabricated artificial bile duct via 3D printing technique which was composed of poly (lactic-co-glycolic acid) (PLGA) and gelatin methacrylate (GelMA). The PLGA-inner layer provided sufficient strength to support the bile duct contraction, the GelMA-outer layer possessed good biocompatibility to provide a good living environment for the cells. Moreover, IKVAV laminin peptide (Ile-Lys-Val-Ala-Val) and ultrasmall superparamagnetic iron oxide (USPIO) were used to regulate scaffold cell adhesion and magnetic resonance imaging (MRI) detection, respectively. After BMSCs co-culture with IKVAV at a certain concentration, the survival rate and adhesion of BMSCs was increased obviously. Meanwhile, the fabricated scaffold exhibited the tensile modulus in the range of 17.19 - 29.05 MPa and the compressive modulus in the range of 0.042 - 0.066 MPa, which could meet the needs of human implantation. In an animal experiment in vivo pig bile duct regeneration, PLGA/GelMA/IKVAV/USPIO duct conduits could promote bile duct regeneration and enhance cytokeratin 19 (CK19) expression. In summary, the composite bile duct scaffold with excellent MRI imaging function and biocompatibility could be used to develop bioactive artificial bile ducts.

Perfusion-guided sonopermeation of neuroblastoma: a novel strategy for monitoring and predicting liposomal doxorubicin uptake in vivo

Neuroblastoma (NB) is the most common extracranial solid tumor in infants and children, and imposes significant morbidity and mortality in this population. The aggressive chemoradiotherapy required to treat high-risk NB results in survival of less than 50%, yet is associated with significant long-term adverse effects in survivors. Boosting efficacy and reducing morbidity are therefore key goals of treatment for affected children. We hypothesize that these may be achieved by developing strategies that both focus and limit toxic therapies to the region of the tumor. One such strategy is the use of targeted image-guided drug delivery (IGDD), which is growing in popularity in personalized therapy to simultaneously improve on-target drug deposition and assess drug pharmacodynamics in individual patients. IGDD strategies can utilize a variety of imaging modalities and methods of actively targeting pharmaceutical drugs, however in vivo imaging in combination with focused ultrasound is one of the most promising approaches already being deployed for clinical applications. Over the last two decades, IGDD using focused ultrasound with "microbubble" ultrasound contrast agents (UCAs) has been increasingly explored as a method of targeting a wide variety of diseases, including cancer. This technique, known as sonopermeation, mechanically augments vascular permeability, enabling increased penetration of drugs into target tissue. However, to date, methods of monitoring the vascular bioeffects of sonopermeation in vivo are lacking. UCAs are excellent vascular probes in contrast-enhanced ultrasound (CEUS) imaging, and are thus uniquely suited for monitoring the effects of sonopermeation in tumors. Methods: To monitor the therapeutic efficacy of sonopermeation in vivo, we developed a novel system using 2D and 3D quantitative contrast-enhanced ultrasound imaging (qCEUS). 3D tumor volume and contrast enhancement was used to evaluate changes in blood volume during sonopermeation. 2D qCEUS-derived time-intensity curves (TICs) were used to assess reperfusion rates following sonopermeation therapy. Intratumoral doxorubicin (and liposome) uptake in NB was evalauted ex vivo along with associated vascular changes. Results: In this study, we demonstrate that combining focused ultrasound therapy with UCAs can significantly enhance chemotherapeutic payload to NB in an orthotopic xenograft model, by improving delivery and tumoral uptake of long-circulating liposomal doxorubicin (L-DOX) nanoparticles. qCEUS imaging suggests that changes in flow rates are highly sensitive to sonopermeation and could be used to monitor the efficacy of treatment in vivo. Additionally, initial tumor perfusion may be a good predictor of drug uptake during sonopermeation. Following sonopermeation treatment, vascular biomarkers show increased permeability due to reduced pericyte coverage and rapid onset of doxorubicin-induced apoptosis of NB cells but without damage to blood vessels. Conclusion: Our results suggest that significant L-DOX uptake can occur by increasing tumor vascular permeability with microbubble sonopermeation without otherwise damaging the vasculature, as confirmed by in vivo qCEUS imaging and ex vivo analysis. The use of qCEUS imaging to monitor sonopermeation efficiency and predict drug uptake could potentially provide real-time feedback to clinicians for determining treatment efficacy in tumors, leading to better and more efficient personalized therapies. Finally, we demonstrate how the IGDD strategy outlined in this study could be implemented in human patients using a single case study.

Angiogenesis Research in Mouse Mammary Cancer Based on Contrast-enhanced Ultrasonography: Exploratory Study

RATIONALE AND OBJECTIVES

The objective of this study was to investigate the contrast-enhanced ultrasound (CEUS) characteristics of tumor angiogenesis in mouse mammary cancer.

MATERIALS AND METHODS

Twenty-four mice were examined with ultrasound and CEUS at 2-12 days after implantation. Four to five mice were assessed daily, and one to three mice were then sacrificed for histology. All of the histologic slides were reviewed and correlated with CEUS findings.

RESULTS

A total of 46 cases of ultrasound examination had been performed in 24 mice. The mice were classified into three groups according to the tumor growth: group 1 (2~6 days after implantation, n = 20 cases), group 2 (7~9 days after implantation, n = 15 cases), and group 3 (10~12 days after implantation, n = 11 cases). In group 1, all tumors presented as a homogeneous hypoechoic mass with no color Doppler signals. However, three CEUS patterns were observed: 14 tumors presented as type I (peripheral ring enhancement with no enhancement within the tumor), 4 tumors presented as type II (peripheral ring enhancement with deep penetration), and 2 tumors presented as type III (homogeneous or heterogeneous enhancement in the entire tumor). In group 2, there was only difference in the echo (heterogeneous or not) and color Doppler signals (with or without) among the tumors in conventional ultrasound, but four CEUS patterns were observed and most presented as type III (53.3%, 8/15). In group 3, most tumors presented as a heterogeneous solid mass (81.8%, 9/11) with color signals (100%, 11/11), and almost all tumors presented as enhancement of type IV (peripheral ring enhancement with focal nodular enhancement) (90.9%, 10/11).The histologic results showed that the enhanced areas mainly corresponded to tumor cells, large tortuous vessels, and an inflammatory cell infiltrate. Nonenhanced areas corresponded to large areas of necrotic tissue or tumor cells, which arranged loosely with the small zone of necrosis.

CONCLUSIONS

CEUS could image the progression of vessel formation. Moreover, most importantly, CEUS is able to identify angiogenesis before the change of tumor color Doppler, and presents different enhanced patterns at different tumor growth times, which corresponded to tumor histologic features.

Reducing tumor growth and angiogenesis using a triple therapy measured with Contrast-enhanced ultrasound (CEUS)

Background

To evaluate the in vivo response by detecting the anti-angiogenic and invasion-inhibiting effects of a triple-combination-therapy in an experimental-small-animal-squamous-cell-carcinoma-model using the “flash-replenishment” (FR) method to assess tissue hemodynamics via contrast-enhanced-ultrasound (CEUS).

Methods

Human hypopharynx-carcinoma-cells were subcutaneously injected into the left flank of 22-female-athymic-nude-rats. After seven days of subcutaneous tumor growth, FR-measurements were performed on each rat. Treatment-group and control-group were treated every day for a period of one week, with the treatment-group receiving solvents containing a triple therapy of Upamostat®, Celecoxib® and Ilomastat® and the control-group solvents only. On day seven, follow-up measurements were performed using the same measurement protocol to assess the effects of the triple therapy. VueBox® was used to quantify the kinetic parameters and additional immunohistochemistry analyses were performed for comparison with and validation of the CEUS results against established methods (Proliferation/Ki-67, vascularization/CD31, apoptosis/caspase3).

Results

Compared to the control-group, the treatment-group that received the triple-therapy resulted in a reduction of tumor growth by 48.6% in size. Likewise, the immunohistochemistry results showed significant decreases in tumor proliferation and vascularization in the treatment-group in comparison to the control-group of 26%(p≤0.05) and 32.2%(p≤0.05) respectively. Correspondingly, between the baseline and follow-up measurements, the therapy-group was associated with a significant(p ≤ 0.01) decrease in the relative-Blood-Volume(rBV) in both the whole tumor(wt) and hypervascular tumor(ht) areas (p≤0.01), while the control-group was associated with a significant (p≤0.01) increase of the rBV in the wt area and a non-significant increase (p≤0.16) in the ht area. The mean-transit-time (mTT) of the wt and the ht areas showed a significant increase (p≤0.01) in the follow-up measurements in the therapy group.

Conclusion

The triple-therapy is feasible and effective in reducing both tumor growth and vascularization. In particular, compared with the placebo-group, the triple-therapy-group resulted in a reduction in tumor growth of 48.6% in size when assessed by CEUS and a significant reduction in the number of vessels in the tumor of 32% as assessed by immunohistochemistry. As the immunohistochemistry supports the CEUS findings, CEUS using the “flash replenishment”(FR) method appears to provide a useful assessment of the anti-angiogenic and invasion-inhibiting effects of a triple combination therapy.

Type IV collagen α1-chain noncollagenous domain blocks MMP-2 activation both in-vitro and in-vivo

α1(IV)NC1 inhibits angiogenesis by regulating MAPK activation, this biological function was partly attributed α1(IV)NC1 binding to α1β1-integrin. However, its potent antiangiogenic activity and the molecular targets of α1(IV)NC1 has not been investigated. In the present study, the regulation of MMP-2 activation by α1(IV)NC1 was evaluated. α1β1-integrin which is required for inhibition of angiogenesis is not playing a role in cellular invasion and inhibition of MMP-2 activation by α1(IV)NC1. We found that α1(IV)NC1 binds the CBD of MMP-2 and forming a stable complex that prevents activation of MMP-2. The antiangiogenic activity of α1(IV)NC1 is mediated, in part, by this binding activity. In addition, up-regulation of TIMP-2 by α1(IV)NC1 led to saturation of MT1-MMP binding sites, which in turn led to inhibition of MMP-2 activation. In-vivo studies using α1-integrin null-mice treated with higher doses of α1(IV)NC1 showed integrin independent inhibition of tumor growth and active-MMP-2, without affecting MMP-9, MMP-7 and angiostatin.

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.

RALBP1/RLIP76 depletion in mice suppresses tumor growth by inhibiting tumor neovascularization

RalBP1/RLIP76 is a widely expressed multifunctional protein that binds the Ral and R-Ras small GTPases. In the mouse, RLIP76 is nonessential but its depletion or blockade promotes tumorigenesis and heightens the sensitivity of normal and tumor cells to radiation and cytotoxic drugs. However, its pathobiologic functions, which support tumorigenesis, are not well understood. Here, we show that RLIP76 is required for angiogenesis and for efficient neovascularization of primary solid tumors. Tumor growth from implanted melanoma or carcinoma cells was blunted in RLIP76(-/-) mice. An X-ray microcomputed tomography-based method to model tumor vascular structures revealed defects in both the extent and form of tumor angiogenesis in RLIP76(-/-) mice. Specifically, tumor vascular volumes were diminished and vessels were fewer in number, shorter, and narrower in RLIP76(-/-) mice than in wild-type mice. Moreover, we found that angiogenesis was blunted in mutant mice in the absence of tumor cells, with endothelial cells isolated from these animals exhibiting defects in migration, proliferation, and cord formation in vitro. Taken together, our results establish that RLIP76 is required for efficient endothelial cell function and angiogenesis in solid tumors.

[Contrast-enhanced ultrasound in animal models]

In the past the detection of tumor perfusion was achieved solely via invasive procedures, such as intravital microscopy or with the help of costly modalities, such as multidetector computed tomography (MDCT), magnetic resonance tomography (MRT) or the combined use of positron emission tomography and computed tomography (PET/CT). Ultrasound offers the non-invasive display of organs without usage of ionizing radiation and it is widely available. However, colour-coded ultrasound and power Doppler do not allow the detection of tumor microcirculation. The introduction of contrast-enhanced ultrasound (CEUS) as well as new high-frequency ultrasound probes made it possible to detect and quantify tumor microcirculation with high resolution. CEUS has been used clinically on human beings for more than 10 years. During the last years different tumor models in experimental animals were used for the establishment of this new technique, e.g. in rats, hamsters and mice. CEUS allows the detection of functional parameters, such as the angiogenetic metabolic status of tissue pretreatment and posttreatment. Further research is required to solve the problems of absolute quantification of these perfusion parameters to allow the comparison of CEUS with other modalities (e.g. MRT and CT).

Ultrasound contrast microbubbles in imaging and therapy: physical principles and engineering

Microbubble contrast agents and the associated imaging systems have developed over the past 25 years, originating with manually-agitated fluids introduced for intra-coronary injection. Over this period, stabilizing shells and low diffusivity gas materials have been incorporated in microbubbles, extending stability in vitro and in vivo. Simultaneously, the interaction of these small gas bubbles with ultrasonic waves has been extensively studied, resulting in models for oscillation and increasingly sophisticated imaging strategies. Early studies recognized that echoes from microbubbles contained frequencies that are multiples of the microbubble resonance frequency. Although individual microbubble contrast agents cannot be resolved-given that their diameter is on the order of microns-nonlinear echoes from these agents are used to map regions of perfused tissue and to estimate the local microvascular flow rate. Such strategies overcome a fundamental limitation of previous ultrasound blood flow strategies; the previous Doppler-based strategies are insensitive to capillary flow. Further, the insonation of resonant bubbles results in interesting physical phenomena that have been widely studied for use in drug and gene delivery. Ultrasound pressure can enhance gas diffusion, rapidly fragment the agent into a set of smaller bubbles or displace the microbubble to a blood vessel wall. Insonation of a microbubble can also produce liquid jets and local shear stress that alter biological membranes and facilitate transport. In this review, we focus on the physical aspects of these agents, exploring microbubble imaging modes, models for microbubble oscillation and the interaction of the microbubble with the endothelium.

Ultrasound microbubble contrast agents: fundamentals and application to gene and drug delivery

This review offers a critical analysis of the state of the art of medical microbubbles and their application in therapeutic delivery and monitoring. When driven by an ultrasonic pulse, these small gas bubbles oscillate with a wall velocity on the order of tens to hundreds of meters per second and can be deflected to a vessel wall or fragmented into particles on the order of nanometers. While single-session molecular imaging of multiple targets is difficult with affinity-based strategies employed in some other imaging modalities, microbubble fragmentation facilitates such studies. Similarly, a focused ultrasound beam can be used to disrupt delivery vehicles and blood vessel walls, offering the opportunity to locally deliver a drug or gene. Clinical translation of these vehicles will require that current challenges be overcome, where these challenges include rapid clearance and low payload. The technology, early successes with drug and gene delivery, and potential clinical applications are reviewed.

Enhancement of cell attachment and tissue integration by a IKVAV containing multi-domain peptide

Laminin contains a number of cell binding motifs including IKVAV and some that bind heparin. We developed a multi-domain synthetic peptide, LA2, which combines IKVAV sequences with a heparin-binding domain with the goal of improving cell attachment to otherwise non-adherent substrates. LA2 was used to coat polystyrene, ethyl vinyl acetate (EVA), expanded polytetrafluoroethylene (ePTFE), polycarbonate, titanium and stainless steel. In cell attachment studies, LA2 dramatically increased cell attachment to polystyrene and EVA compared to uncoated counterparts or those coated with SIKVAV. Similar increases were observed on ePTFE and titanium. On polystyrene, LA2 enhanced the attachment of endothelial cells, smooth muscle cells, epithelial cells, myoblasts, and osteoblast progenitor cells. Following adhesion, the cells underwent proliferation to form confluent monolayers with phenotypic morphologies. Using osteoblast progenitor cells (MC3T3 cells) grown on LA2/polystyrene, the cells exhibited an increased production of a differentiation marker, alkaline phosphatase. In vivo, LA2 improved tissue integration into ePTFE when implanted subcutaneously in rats. After 2 weeks, cells had penetrated deep into the LA2 coated ePTFE implant whereas little cell penetration was found in uncoated grafts. The implant sites exhibited little inflammation or other untoward effects. The results indicated that the LA2 peptide improved cell adhesion and tissue integration and might be useful in a number of tissue engineering applications.

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

PURPOSE

To evaluate quantitative functional ultrasonography (US) in a murine gel model by using microbubble destruction kinetics to determine whether parametric indices provided with US could help assess angiogenesis.

MATERIALS AND METHODS

Institutional Animal Subjects Committee approved experiments and procedures. In 36 normal mice, two 0.4-mL gel implants were placed subcutaneously on either side of spine. One implant contained 0.5, 1.0, or 1.5 microg human basic fibroblast growth factor (bFGF) per milliliter of gel. Functional US quantitative analysis of angiogenesis with microbubble contrast agent was performed on days 3, 6, 9, and 12; histologic data were collected. Time-intensity curve of implant was fitted to mathematic decay model to calculate fractional blood volume and fraction of blood replaced per unit of time. Microvascular density (MVD) and percentage of microvascular area (MVA) were measured after anti-CD31 staining. Spearman rank order correlation was used in analyses.

RESULTS

bFGF-containing implants induced MVD of eight, 35, 42, and 42 vessels per square millimeter on days 3, 6, 9, and 12, respectively; in controls, MVD was four vessels/mm2 (P<.05 on days 6, 9, and 12). bFGF-containing implants induced percentage MVA of 2%, 5%, 20%, and 27%, respectively; in controls, it was 0.5% (P<.05). Maximum enhancement was significantly increased in bFGF implants (23.3 gray level+/-14.1 [standard deviation]) compared with controls (11.0+/-5.5, P<.001). Implants containing bFGF showed poor correlations between fractional blood volume and MVD (r2=0.42) or percentage MVA (r2=0.51) at US. There was no correlation between microbubble velocity and MVD (r2<0.05) or percentage MVA (r2<0.13).

CONCLUSION

Functional US perfusion parameters do not correlate with current histologic indices for quantifying angiogenesis. MVD, as a histologic quantitative measurement of angiogenesis, may not be an appropriate standard for contrast-enhanced imaging that relies on perfused neovessels.

Ultrasound assessment of angiogenesis in a matrigel model in rats

Matrigel, a basement membrane extract, has been extensively used in in vivo angiogenesis. Contrast ultrasound imaging (CUI) of implanted Matrigel plugs with (+bFGF) and without basic fibroblast growth factor (-bFGF) was performed 7 and 14 d after implantation, followed by histologic analysis. Statistically significant differences between +bFGF and -bFGF plugs were apparent at d 7 in both plug size and contrast enhancement (both p < 0.05). Histopathology revealed differences in microvessel density (MVD) between +bFGF and -bFGF at d 7 and d 14. A significant correlation between MVD and both power Doppler contrast-enhanced area (r = 0.65, p < 0.05) and fraction of plug enhanced (r = 0.59, p < 0.05) was present. CUI of Matrigel plugs was shown to be a robust method for distinguishing between two different angiogenic states. Ultrasound measurements of blood flow in the plugs correlated with MVD, a histologic technique used to quantify tumor angiogenesis.

Prolonging the ultrasound signal enhancement from thrombi using targeted microbubbles based on sulfur-hexafluoride-filled gas

RATIONALE AND OBJECTIVES

The objective of this study is to develop and characterize new microbubbles based on lipids and sulfur hexafluoride (SF6) for targeting thrombi as an improved ultrasound contrast agent.

MATERIALS AND METHODS

Bioconjugate ligands were inserted into the lipid-coated membranes of SF6 gas microbubbles, and their physicochemical properties were determined. Diagnostic efficacies of SF6-filled microbubbles and the contrast agent SonoVue (Bracco Imaging, Geneve, Switzerland) were compared in dogs.

RESULTS

Suspensions of lyophilized powder were reconstituted by injecting saline containing 3.1 x 10(8) SF6 microbubbles/mL with a mean diameter of 4.4 microm. More than 90% of microbubbles had diameters between 1 and 10 microm. After reconstitution, echogenicity and microbubble characteristics were unchanged for 8 hours. Targeted microbubbles increased the echogenicity of thrombi significantly and provided a longer period of optimal signal enhancement compared with nontargeted microbubbles.

CONCLUSIONS

Our thrombus-targeting microbubble contrast agent shows high echogenicity and stability and thereby enhances the visualization of intravascular thrombi and prolongs the duration of the diagnostic window.

Contrast-enhanced computed tomography and ultrasound for the evaluation of tumor blood flow

OBJECTIVE

We evaluated implanted rat mammary adenocarcinoma tumors during a 5-week period using ultrasound, computed tomography (CT), and histology.

MATERIALS AND METHODS

Contrast-enhanced ultrasound with a destruction-replenishment imaging scheme was used to derive estimates of blood volume and flow. These ultrasound-derived measures of microvascular physiology were compared with contrast-enhanced CT-derived measures of perfusion and vascular volume made by the Mullani-Gould formula and Patlak analysis, respectively.

RESULTS

The tumor cross-sectional area and necrotic core cross-sectional area determined by the 3 methods were correlated (r>0.8, P<0.001, n=15). The spatial integral of perfusion estimated by CT correlated with the spatial integral of flow from ultrasound (P<0.05). The contrast-enhanced tumor area calculated from the ultrasound analysis was highly correlated with the contrast-enhanced area estimated by CT images (r=0.89, P<0.001, n=15). However, the fraction of the tumor area enhanced by the CT contrast agent was significantly larger than either the fraction enhanced by ultrasound contrast agent or than the viable area as estimated from histology slides.

CONCLUSION

Destruction-replenishment ultrasound provides valuable information about the spatial distribution of blood flow and vascular volume in tumors and ultrasound analysis compares favorably with a validated contrast-enhanced CT method.

Ultrasound imaging of flow patterns in liver metastases from colorectal cancer

BACKGROUND

The ability of colour Doppler, power Doppler and echo-enhanced Doppler imaging to detect the blood flow in liver metastases from colorectal cancer was investigated. An evaluation was then made to determine whether the flow pattern could be used as an indication of disease elsewhere.

METHODS

Forty-two patients with hepatic metastases from colorectal cancer were examined, 8 of whom had local recurrence of their colorectal cancer. Seventy-seven liver metastases were evaluated with colour Doppler and power Doppler, and the presence or absence of a Doppler signal in the halo or centre was noted. Forty-three of these metastases were further examined after contrast media echo-enhancement.

RESULTS

Signals from the peripheral halo were detected by colour Doppler imaging in 34% of the metastases, and in 77% by power Doppler (P < 0.001). Use of contrast media enhanced the power Doppler detection rate to 98% (P < 0.005). Central signals were detected by power Doppler in 12 patients, 8 (66%) of whom also had local recurrence. Thirty patients had neither local recurrence nor central signals, as detected by power Doppler (P < 0.001).

CONCLUSION

The results indicate that the halo in liver metastases corresponds to the vascular flow. There seems to be an association between metastases showing a central power Doppler flow and local tumour recurrence.