Vascular Endothelial Growth Factor Receptor Type 2–targeted Contrast-enhanced US of Pancreatic Cancer Neovasculature in a Genetically Engineered Mouse Model: Potential for Earlier Detection

Abstract

Purpose To test ultrasonographic (US) imaging with vascular endothelial growth factor receptor type 2 (VEGFR2)-targeted microbubble contrast material for the detection of pancreatic ductal adenocarcinoma (PDAC) in a transgenic mouse model of pancreatic cancer development. Materials and Methods Experiments involving animals were approved by the Institutional Administrative Panel on Laboratory Animal Care at Stanford University. Transgenic mice (n = 44; Pdx1-Cre, KRasG12D, Ink4a−/−) that spontaneously develop PDAC starting at 4 weeks of age were imaged by using a dedicated small-animal US system after intravenous injection of 5 × 107 clinical-grade VEGFR2-targeted microbubble contrast material. The pancreata in wild-type (WT) mice (n = 64) were scanned as controls. Pancreatic tissue was analyzed ex vivo by means of histologic examination (with hematoxylin-eosin staining) and immunostaining of vascular endothelial cell marker CD31 and VEGFR2. The Wilcoxon rank sum test and linear mixed-effects model were used for statistical analysis. Results VEGFR2-targeted US of PDAC showed significantly higher signal intensities (26.8-fold higher; mean intensity ± standard deviation, 6.7 linear arbitrary units [lau] ± 8.5; P < .001) in transgenic mice compared with normal, control pancreata of WT mice (mean intensity, 0.25 lau ± 0.25). The highest VEGFR2-targeted US signal intensities were observed in smaller tumors, less than 3 mm in diameter (30.8-fold higher than control tissue with mean intensity of 7.7 lau ± 9.3 [P < .001]; and 1.7-fold higher than lesions larger than 3 mm in diameter with mean intensity of 4.6 lau ± 5.8 [P < .024]). Ex vivo quantitative VEGFR2 immunofluorescence demonstrated that VEGFR2 expression was significantly higher in pancreatic tumors (P < .001; mean fluorescent intensity, 499.4 arbitrary units [au] ± 179.1) compared with normal pancreas (mean fluorescent intensity, 232.9 au ± 83.7). Conclusion US with clinical-grade VEGFR2-targeted microbubbles allows detection of small foci of PDAC in transgenic mice.

Breast Cancer Detection by B7-H3–Targeted Ultrasound Molecular Imaging

“…General limitations of ultrasound as a screening tool, such as long imaging times and operator dependency, are already being addressed by the introduction of commercially available automated whole-breast ultrasound imaging systems that allow a time- and cost-efficient as well as more standardized acquisition and interpretation of breast ultrasound exams (30). In recent years, molecularly targeted ultrasound contrast agents have been developed to improve diagnostic accuracy of ultrasound in earlier detection of cancer such as pancreatic (15, 31), ovarian (32), and breast cancer (16, 19). To allow differentiation of cancer from non-cancerous tissue using ultrasound and molecularly-targeted contrast microbubbles, imaging targets have to be differentially expressed on the neovasculature of cancer compared to vessels in non-cancerous tissue.…”

Ultrasound molecular imaging: Moving toward clinical translation

“…Pysz et al . showed that VEGFR2-targeted ultrasound imaging with BR55 can visualize down to sub-millimeter sized foci of pancreatic cancer in a transgenic mouse model (Pdx1-Cre, KRas G12D , Ink4a −/− ) and the in vivo targeted ultrasound imaging signal was ~30 fold higher in tumors compared to control normal pancreatic tissue, indicating that ultrasonic molecular imaging could be used for earlier pancreatic cancer detection in a screening setting of high risk patients [33]. Besides differentiating normal from cancer tissue, ultrasound molecular imaging using BR55 has been shown to assess breast cancer progression in a transgenic mouse model of breast cancer (FVB/N-Tg(MMTV-PyMT)634Mul) [32].…”

<div>Low-intensity focused ultrasound (LIFU)-induced acoustic droplet vaporization in phase-transition perfluoropentane nanodroplets modified by folate for ultrasound molecular imaging</div>

“…This significantly narrows down the diagnostic and therapeutic options of molecular US. 9,10 Moreover, the very short circulation time of MBs (half-life of 3-15 min) prevents effective targeting imaging and MB destruction for tumor-specific drug release. All these disadvantages seriously hamper the application of MB-based US molecular imaging and therapy.…”