Effect of tamoxifen in an experimental model of breast tumor studied by dynamic contrast-enhanced magnetic resonance imaging and different contrast agents

Objectives: The aim of this study was to compare the efficacy of gadoteridol, B22956/1 (a new protein binding blood pool contrast agent), and (Gd-DTPA)₃₇-albumin in detecting, by dynamic contrast-enhanced magnetic resonance imaging (MRI), the effect in vivo of tamoxifen in an experimental model of breast tumor implanted in rats. Materials and Methods: Tumors were induced by subcutaneous injection of 10⁶ mammary adenocarcinoma cells (13762 MAT B III). Treatment with tamoxifen (or vehicle) started on day 4 after implantation. On day 10 after implantation, animals were observed by MRI using B22956/1 (or gadoteridol) and, 24 hours later, using (Gd-DTPA)₃₇-albumin. Results: Dynamic contrast-enhanced magnetic resonance imaging data showed that tamoxifen treatment decreased vascular permeability to B22956/1, whereas no difference was detectable in permeability to gadoteridol or to (Gd-DTP A)₃₇-albumin. No effect on fractional plasma volume was detected with either of contrast agents. Conclusions: B22956/1 is superior to both small Gd chelates and macromolecular contrast agents in the assessment of the effect of tamoxifen treatment on tumor vasculature.