Vessel Fractions in Tumor Xenografts Depicted by Flow- or Contrast-Sensitive Three-Dimensional High-Frequency Doppler Ultrasound Respond Differently to Antiangiogenic Treatment

Abstract

High-frequency volumetric Power Doppler ultrasound (HF-VPDU) captures flow-dependent signals in blood vessels and can be used to assess antiangiogenic therapy effects in rodent tumors. However, the sensitivity is limited to vessels larger than capillaries. Contrast-enhanced HF-VPDU reveals all perfused vessels by assessing stimulated acoustic emissions from disintegrating microbubbles. Thus, we investigated whether flow-sensitive and contrast-enhanced HF-VPDU can depict different vessel fractions and assess their early response to antiangiogenic therapy. Mice with A431 tumors were scanned before and after administration of polybutylcyanoacrylate microbubbles by HF-VPDU. Animals received either antiangiogenic treatment (SU11248) or a control substance and were imaged repeatedly over 9 days. At each time point, tumors were removed for immunohistochemical analysis. During growth of untreated tumors, vascularization decreased correspondingly on flow-sensitive and contrast-enhanced scans. Treated tumors showed a significantly (P < 0.05) stronger decline in vascularization than controls, which was more pronounced in contrast-enhanced scans. Surprisingly, whereas vascularization remained low in contrast-enhanced scans, flow-sensitive ultrasound indicated a reincrease after day 6 with a higher vascularization than the controls at day 9. Histologic evaluation indicated that immature vessels degraded markedly on therapy, whereas large mature vessels on the tumor periphery were more therapy resistant and drew closer due to tumor shrinkage. In conclusion, contrast-enhanced HF-VPDU and flow-sensitive HF-VPDU are both capable of assessing the effects of antiangiogenic therapy. Because contrast-sensitive ultrasound is more sensitive for small immature vessels and flow-sensitive ultrasound mostly captures large vessels at the tumor periphery, the combination of both methods can provide evidence of vascular maturity in tumors. [Cancer Res 2008;68(17):7042-9]

Molecular Imaging of Changes in the Prevalence of Vascular Endothelial Growth Factor Receptor in Sunitinib-Treated Murine Mammary Tumors

“…Therefore, an approximately 2.5-fold decline in VEGFR-2 prevalence is primarily responsible for the 2.6-and 2.2-fold decline in 99m Tc-scVEGF uptake. These data are in agreement with recent reports on a dramatic and rapid decrease in CD31-positive endothelial cells induced by various VEGF-and VEGFR-targeting drugs, including sunitinib (19)(20)(21)(22)(23)(24). However, a more detailed and quantitative analysis would be necessary to establish a contribution of the changes in VEGFR-2 internalization and recycling into a decline in 99m Tc-scVEGF uptake.…”

“…Thus, we expected that a sunitinib-induced decrease in 99m TcscVEGF uptake might be due to the changes in VEGFR-2 prevalence, accessibility, or internalization or recycling in tumor endothelial cells. As sunitinib and other VEGF-and VEGFR-targeting drugs are known to induce a rather rapid regression of tumor vasculature (19)(20)(21)(22)(23)(24)(25), we assessed the effects of sunitinib on VEGFR-2 and CD31 prevalence in tumors harvested from control and treated mice. Immunostaining revealed extensive vascularization in control tumors, with somewhat higher VEGFR-2 and CD31 density at the tumor edge adjacent to the underlying muscle tissue (Supplemental Fig.…”

Tumor blood vessel visualization

“…As shown in Fig. 1 Doppler ultrasound without contrast enhancement visualizes the laminar blood flow within large tumor vessels while all vessels independent of flow velocities are displayed by contrast enhancement (Palmowski et al, 2008). Design and development of new conjugates targeting key proteins related to angiogenesis like vascular epithelial growth factor receptor (VEGFR) 2 (Pillai et al, 2010) will extend the value of contrast-enhanced ultrasound in monitoring tumor vascularization in vivo in the near future.…”

Current Perspectives on Sunitinib Targeted Therapy for Tumors

“…Interestingly, a recent case-report confirmed clinical benefit of sunitinib in a chemo-refractory adrenocortical carcinoma patient, suggesting that it may be active in a highly Pgp overexpressing tumor type [25]. Furthermore, depending on the resistance or sensitivity of specific vessels, which may occur both in one tumor, sunitinib, affecting its own delivery to remaining tumor tissue in a positive or negative way [26]. In an attempt to evaluate the possible interaction of sunitinib with P-glycoprotein (P-gp, ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), breast cancer resistance protein (BCRP, ABCG2) and lungresistance protein (LRP) in vitro.…”