AG-013736, a novel inhibitor of VEGF receptor tyrosine kinases, inhibits breast cancer growth and decreases vascular permeability as detected by dynamic contrast-enhanced magnetic resonance imaging.
ABSTRACT Dynamic contrast-enhanced MRI (DCE-MRI) was used to noninvasively evaluate the effects of AG-03736, a novel inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases, on tumor microvasculature in a breast cancer model. First, a dose response study was undertaken to determine the responsiveness of the BT474 human breast cancer xenograft to AG-013736. Then, DCE-MRI was used to study the effects of a 7-day treatment regimen on tumor growth and microvasculature. Two DCE-MRI protocols were evaluated: (1) a high molecular weight (MW) contrast agent (albumin-(GdDTPA)(30)) with pharmacokinetic analysis of the contrast uptake curve and (2) a low MW contrast agent (GdDTPA) with a clinically utilized empirical parametric analysis of the contrast uptake curve, the signal enhancement ratio (SER). AG-013736 significantly inhibited growth of breast tumors in vivo at all doses studied (10-100 mg/kg) and disrupted tumor microvasculature as assessed by DCE-MRI. Tumor endothelial transfer constant (K(ps)) measured with albumin-(GdDTPA)(30) decreased from 0.034+/-0.005 to 0.003+/-0.001 ml min(-1) 100 ml(-1) tissue (P<.0022) posttreatment. No treatment-related change in tumor fractional plasma volume (fPV) was detected. Similarly, in the group of mice studied with GdDTPA DCE-MRI, AG-013736-induced decreases in tumor SER measures were observed. Additionally, our data suggest that 3D MRI-based volume measurements are more sensitive than caliper measurements for detecting small changes in tumor volume. Histological staining revealed decreases in tumor cellularity and microvessel density with treatment. These data demonstrate that both high and low MW DCE-MRI protocols can detect AG-013736-induced changes in tumor microvasculature. Furthermore, the correlative relationship between microvasculature changes and tumor growth inhibition supports DCE-MRI methods as a biomarker of VEGF receptor target inhibition with potential clinical utility.
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ABSTRACT: Within the past 5 years, the United States Food and Drug Administration have approved six targeted agents for the treatment of metastatic renal cell carcinoma (mRCC). While this offers great potential to patients afflicted with this disease, oncologists are faced with the challenge of applying each agent in the appropriate clinical setting. Doing so requires an intricate understanding of the pivotal trials evaluating these agents. Herein, we have provided a detailed analysis of the study design employed in these trials. Use of appropriate comparator arms for targeted therapies (i.e., interferon-alpha or placebo) is addressed. Furthermore, we discuss the relative merits of using progression-free survival (PFS) or overall survival (OS) as a primary endpoint-importantly, the two endpoints may not be precisely correlated. Strategies to appropriately interpret OS in the context of post-study therapies and crossover designs are described. Ultimately, head-to-head trials comparing targeted therapies are necessary to resolve clinical equipoise. Several ongoing efforts juxtaposing the approved agents for mRCC are discussed.Targeted Oncology 06/2010; 5(2):131-8. · 3.61 Impact Factor