In situ validation of VEGFR-2 and α v ß 3 integrin as targets for breast lesion characterization

Vascular endothelial growth factor receptor 2 (VEGFR-2) and α v ß 3 integrin are the most frequently addressed targets in molecular imaging of tumor angiogenesis. In preclinical studies, molecular imaging of angiogenesis has shown potential to detect and differentiate benign and malignant lesions of the breast. Thus, in this retrospective clinical study employing patient tissues, the diagnostic value of VEGFR-2, α v ß 3 integrin and vascular area fraction for the diagnosis and differentiation of breast neoplasia was evaluated. To this end, tissue sections of breast cancer (n = 40), pre-invasive ductal carcinoma in situ (DCIS; n = 8), fibroadenoma (n = 40), radial scar (n = 6) and normal breast tissue (n = 40) were used to quantify (1) endothelial VEGFR-2, (2) endothelial α v ß 3 integrin and (3) total α v ß 3 integrin expression, as well as (4) the vascular area fraction. Sensitivity and specificity to differentiate benign from malignant lesions were calculated for each marker by receiver operating characteristics (ROC) analyses. Whereas vessel density, as commonly used, did not significantly differ between benign and malignant lesions (AUROC: 0.54), VEGFR-2 and α v ß 3 integrin levels were gradually up-regulated in carcinoma versus fibroadenoma versus healthy tissue. The highest diagnostic accuracy for differentiating carcinoma from fibroadenoma was found for total α v ß 3 integrin expression (AUROC: 0.76), followed by VEGFR-2 (AUROC: 0.71) and endothelial α v ß 3 integrin expression (AUROC: 0.68). In conclusion, total α v ß 3 integrin expression is the best discriminator between breast cancer, fibroadenoma and normal breast tissue. With respect to vascular targeting and molecular imaging of angiogenesis, endothelial VEGFR-2 appeared to be slightly superior to endothelial α v ß 3 for differentiating benign from cancerous lesions.

Influence of repetitive contrast agent injections on functional and molecular ultrasound measurements

Quantitative contrast-enhanced ultrasound plays an important role in tumor characterization and treatment assessment. Besides established functional ultrasound techniques, ultrasound molecular imaging using microbubbles targeted to disease-associated markers is increasingly being applied in pre-clinical studies. Often, repeated injections of non-targeted or targeted microbubbles during the same imaging session are administered. However, the influence of repeated injections on the accuracy of the quantitative data is unclear. Therefore, in tumor-bearing mice, we investigated the influence of multiple injections of non-targeted microbubbles (SonoVue) on time to peak and peak enhancement in liver and tumor tissue and of vascular endothelial growth factor receptor 2 (VEGFR2)-targeted contrast agents (MicroMarker) on specific tumor accumulation. We found significantly decreasing values for time to peak and a tendency for increased values for peak enhancement after multiple injections. Repeated injections of VEGFR2-targeted microbubbles led to significantly increased tumor accumulation, which may result from the exposure of additional binding sites at endothelial surfaces caused by mechanical forces from destroyed microbubbles.

Recent advances in molecular, multimodal and theranostic ultrasound imaging

Ultrasound (US) imaging is an exquisite tool for the non-invasive and real-time diagnosis of many different diseases. In this context, US contrast agents can improve lesion delineation, characterization and therapy response evaluation. US contrast agents are usually micrometer-sized gas bubbles, stabilized with soft or hard shells. By conjugating antibodies to the microbubble (MB) surface, and by incorporating diagnostic agents, drugs or nucleic acids into or onto the MB shell, molecular, multimodal and theranostic MBs can be generated. We here summarize recent advances in molecular, multimodal and theranostic US imaging, and introduce concepts how such advanced MB can be generated, applied and imaged. Examples are given for their use to image and treat oncological, cardiovascular and neurological diseases. Furthermore, we discuss for which therapeutic entities incorporation into (or conjugation to) MB is meaningful, and how US-mediated MB destruction can increase their extravasation, penetration, internalization and efficacy.

Establishment of functional and molecular ultrasound for breast cancer xenograft imaging

The present work was originally published in European Radiology and as a PhD thesis at the RWTH Aachen University and was conducted at the Institute for Experimental Molecular Imaging at the RWTH Aachen University.

Targeted ultrasound imaging of cancer: an emerging technology on its way to clinics

Ultrasound is one of the workhorses in clinical cancer diagnosis. In particular, it is routinely used to characterize lesions in liver, urogenital tract, head and neck and soft tissues. During the last years image quality steadily improved, which, among others, can be attributed to the development of harmonic image analysis. Microbubbles were introduced as intravascular contrast agents and can be detected with superb sensitivity and specificity using contrast specific imaging modes. By aid of these unspecific contrast agents tissues can be characterised regarding their vascularity. Antibodies, peptides and other targeting moieties were bound to microbubbles to target sites of angiogenesis and inflammation intending to get more disease-specific information. Indeed, many preclinical studies proved the high potential of targeted ultrasound imaging to better characterize tumors and to more sensitively monitor therapy response. Recently, first targeted microbubbles had been developed that meet the pharmacological demands of a clinical contrast agent. This review articles gives an overview on the history and current status of targeted ultrasound imaging of cancer. Different imaging concepts and contrast agent designs are introduced ranging from the use of experimental nanodroplets to agents undergoing clinical evaluation. Although it is clear that targeted ultrasound imaging works reliably, its broad acceptance is hindered by the user dependency of ultrasound imaging in general. Automated 3D-scanning techniques-like being used for breast diagnosis - and novel 3D transducers will help to make this fascinating method clinical reality.

Platelet-derived growth factor-B normalizes micromorphology and vessel function in vascular endothelial growth factor-A-induced squamous cell carcinomas

Vascular endothelial growth factor (VEGF), which is a key regulator of angiogenesis, often induces formation of immature vessels with increased permeability and reduced vessel functionality. Here, we demonstrate that de novo expression of murine (m)VEGF-164 induces malignant and invasive tumor growth of HaCaT keratinocytes. However, the mVEGF-164-induced tumors are ulcerated with a disorganized epithelium that is interrupted by lacunae with limited basement membrane and endothelial cell coverage. Vessel maturation is strongly impaired. Tumor and vessel micromorphology are markedly improved by the combined expression of human platelet-derived growth factor (hPDGF)-B and mVEGF-164. Although tumor size and malignancy are comparable with either mVEGF-164 alone or combined human PDGF-B and mVEGF-164 expression, combined hPDGF-B and mVEGF-164 expression leads to a more solid and compact tumor tissue with a mature functional tumor vasculature and a higher microvessel density, as demonstrated histologically and by dynamic contrast-enhanced magnetic resonance imaging. Treatment of the hPDGF-B- and mVEGF-164-expressing tumors with imatinib mesylate to block PDGF-B signaling reverses this effect. In addition, tumor cell invasion of mVEGF-164 transfectants and mVEGF-164 plus hPDGF-B transfectants in vivo is associated with a marked induction of tumor-derived matrix metalloproteinase-1 and stromal matrix metalloproteinase-9 and -13, as was confirmed in three-dimensional organotypic co-cultures with fibroblasts in vitro. These data clearly demonstrate the need for a concerted action of different growth factors in the establishment of solid tumors with functional vasculature and emphasize the need for a multifactorial therapy.