VEGFR2-targeted ultrasound molecular imaging of angiogenesis to evaluate liver allograft fibrosis

Novel anti-VEGFR2 antibody-conjugated nanobubbles for targeted ultrasound molecular imaging in a rabbit VX2 hepatic tumor model

Nanobubbles (NBs), as ultrasound contrast agents, possess the potential for clinical applications in targeted ultrasound molecular imaging due to their small diameters and the specific molecular markers attached. Previous research studies mainly focused on the tumor-specific recruitment capability or drug carriers based on subcutaneous tumor models. In clinical trials, orthotopic tumor models are considered more clinically relevant and better predictive models for assessing drug efficacy compared to standard subcutaneous models. Here, we first prepared uniform-sized NBs with a soft chitosan-lipid membrane containing perfluoropropane gas and then anti-VEGFR2 antibodies were incorporated into NB membranes in order to achieve targeting ability toward tumor angiogenesis. The results of physicochemical characterization (the average size of 260.9 ± 3.3 nm and a PDI of 0.168 ± 0.036, n = 3) indicated that the targeted nanobubbles (tNBsv) have a spherical morphology and a vacant core. In vitro experiments found that the contrast enhancement abilities of tNBsv are similar to those of commercial SonoVue. In in vivo experiments, the orthotopic model of the rabbit VX2 hepatic tumor was used to evaluate the targeted binding ability of tNBsv toward tumor angiogenesis. Ultrasound sonograms revealed that tNBsv achieved the peak intensity of ultrasound imaging enhancement in the region of peripheral vasculature of VX2 tumors over non-targeted NBs or SonoVue, and the imaging time was longer than that of the other two. Ex vivo fluorescence imaging and examination using a confocal laser scanning microscope further verified that tNBsv were capable of binding to tumor angiogenesis. These results from our studies suggested that tNBsv are useful to develop an ultrasound imaging probe to evaluate anti-angiogenic cancer therapy by monitoring tumor angiogenesis.

Microbubbles for human diagnosis and therapy

Microbubbles (MBs) were observed for the first time in vivo as a curious consequence of quick saline injection during ultrasound (US) imaging of the aortic root, more than 50 years ago. From this serendipitous event, MBs are now widely used as contrast enhancers for US imaging. Their intrinsic properties described in this review, allow a multitude of designs, from shell to gas composition but also from grafting targeting agents to drug payload encapsulation. Indeed, the versatile MBs are deeply studied for their dual potential in imaging and therapy. As presented in this paper, new generations of MBs now opens perspectives for targeted molecular imaging along with the development of new US imaging systems. This review also presents an overview of the different therapeutic strategies with US and MBs for cancer, cardiovascular diseases, and inflammation. The overall aim is to overlap those fields in order to find similarities in the MBs application for treatment enhancement associated with US. To conclude, this review explores the new scales of MBs technologies with nanobubbles development, and along concurrent advances in the US imaging field. This review ends by discussing perspectives for the booming future uses of MBs.

Liver Fibrosis Assessment by Viewing Sinusoidal Capillarization: US Molecular Imaging versus Two-dimensional Shear-Wave Elastography in Rats

Background US elastography is a first-line assessment of liver fibrosis severity; however, its application is limited by its insufficient sensitivity in early-stage fibrosis detection and its measurements are affected by inflammation. Purpose To assess the sensitivity of US molecular imaging (USMI) in early-stage liver fibrosis detection and to determine whether USMI can specifically distinguish fibrosis regardless of inflammation when compared with two-dimensional (2D) shear-wave elastography (SWE). Materials and methods USMI and 2D SWE were performed prospectively (January to June 2021) in 120 male Sprague-Dawley rats with varying degrees of liver fibrosis and acute hepatitis and control rats. Liver sinusoidal capillarization was viewed at CD34-targeted USMI and quantitatively analyzed by the normalized intensity difference (NID). Data were compared by using a two-sided Student t test or one-way analysis of variance. Linear correlation analyses were used to evaluate the relationships between collagen proportionate area values and NID and liver stiffness measurement (LSM) values. Receiver operating characteristic curves were used to assess the diagnostic performance in detecting liver fibrosis. Results Both NID and LSM values showed good linear correlation with collagen proportionate area values (r = 0.91 and 0.87, respectively). No difference was observed between the areas under the receiver operating characteristic curve in detecting stage F0-F1 between USMI and 2D SWE (0.97 vs 0.91, respectively; P = .20). USMI depicted liver fibrosis at an early stage more accurately than 2D SWE (area under the curve, 0.97 vs 0.82, respectively; P = .01). Rats with hepatitis had higher liver stiffness values than control rats (9.83 kPa ± 0.79 vs 6.55 kPa ± 0.38, respectively; P < .001), with no difference in the NID values between control rats and rats with hepatitis (6.75% ± 1.43 vs 6.74% ± 0.86, respectively; P = .98). Conclusion Sinusoidal capillarization viewed at US molecular imaging helped to detect early-stage liver fibrosis more accurately than two-dimensional shear-wave elastography and helped assess fibrosis regardless of inflammation. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Barr in this issue.