Improved Detection of preclinical Colorectal Liver Metastases by High Resolution Ultrasound including Molecular Ultrasound Imaging using the targeted Contrast Agent BR55

Abstract

Purpose: Aim of the present study was to investigate the sensitivity of high resolution ultrasound (HRU), standard contrast-enhanced ultrasound (CEUS) and CEUS using a novel vascular endothelial growth factor receptor 2 (VEGFR2)-targeted contrast agent for the detection of hepatic metastases in a mouse model of colorectal cancer using clinical standard technology.

Materials and Methods: The human colon cancer cell line HT29, transfected with luciferase cDNA for in vivo bioluminescence monitoring, was injected intrasplenically into CB17.SCID mice. Mice were monitored weekly by bioluminescence and after 2 and 4.5 weeks by HRU and CEUS. Contrast media (untargeted BR1, targeted BR55) was applied and digital cine loops from the arterial phase (15 – 45 sec), portal venous phase (50 – 120 s) and late phases (3 – 5 min, 1hour) of the whole liver were analyzed. Data were correlated with postmortem histopathology.

Results: Without contrast enhancement, lesions > 4 mm were reliably detected. After use of untargeted CEUS, lesions > 2 mm were reliably detected and enhanced rim vascularization and late-phase wash-out was shown. With BR55, lesions > 0.8 mm were reliably detected with excellent documentation of vascularization. A persistent contrast enhancement was seen > 30 min after injection. Contrast-enhancement patterns with BR55 significantly correlated with CD31 (R2 = 0.74) and VEGFR2-immunohistochemistry (R2 = 0.66).

Conclusion: Detection of metastases by HRU and CEUS was earlier and more accurate than monitoring via bioluminescence. In vivo monitoring of hepatic micrometastases can thus be performed without prior modification of cancer cells using standard technology.

Zusammenfassung

Ziel: Ziel der vorliegenden Studie war die Bestimmung der Sensitivität hochauflösender Sonografie, standardisierter kontrastverstärkter Sonografie und kontrastverstärkter Sonografie mittels eines den vaskulären endothelialen Wachstumsfaktor-Rezeptor 2 (VEGFR2) gezielt bindenden Ultraschallkontrastmittels in der Detektion hepatischer Metastasen im präklinischen Mausmodell des Kolonkarzinoms mithilfe klinischer Standardtechnologie.

Material und Methoden: Die humane Kolonkarzinomzelllinie HT29, transfiziert mit Luciferase cDNA zur Ermöglichung eines Biolumineszenz-Monitorings, wurde intrasplenisch in CB17.SCID Mäuse injiziert. Es erfolgten wöchentliche Biolumineszenzmessungen sowie Ultraschalluntersuchungen nach 2 und 4,5 Wochen. Als Kontrastmittel kamen BR1 und gezieltes BR55 zur Anwendung. Videosequenzen der arteriellen Phase (15 – 45 s), der portalvenösen (50 – 120 s), und zweier Spätphasen (3 – 5 min, 1 h) der gesamten Leber wurden analysiert. Die Ultraschallergebnisse wurden mit postmoraler Histologie korreliert.

Ergebnisse: Hochauflösende Sonografie ohne Kontrastmittel konnte hepatische Metastasen > 4 mm reproduzierbar detektieren. Mithilfe von BR1-Kontrastverstärkung wurden Metastasen > 2 mm zuverlässig detektiert, zudem eine verstärkte Randperfusion und Spätphasen-washout nachgewiesen. Mit BR55 konnten Metastasen ab 0,8 mm detektiert werden mit exzellenter Dokumentation der Vaskularisation. Zudem wurde hier in den Metastasen eine persistente Kontrastmittelanreicherung auch > 30 min nach Injektion detektiert. Die Kontrastmittelverteilung von BR55 korrelierte signifikant mit der Immunhistochemie für CD31 (R2 = 0,74) und VEGFR2 (R2 = 0,66).

Schlussfolgerung: Die Metastasendetektion mittels hochauflösender und kontrastverstärkter Sonografie erfolgte früher und akkurater als mittels Biolumineszenz. Somit kann ein in vivo monitoring hepatischer Metastasen in diesem Modell zukünftig auch ohne zuvor nötige Zellalteration und unter Anwendung klinischer Standardtechnologie erfolgen.

Key words

abdomen - blood vessels - ultrasound

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