Use of dynamic contrast-enhanced MRI to evaluate acute treatment with ZD6474, a VEGF signalling inhibitor, in PC-3 prostate tumours

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), using gadopentetate dimeglumine, was used to monitor acute effects on tumour vascular permeability following inhibition of vascular endothelial growth factor-A (VEGF-A) signal transduction. Mice bearing PC-3 human prostate adenocarcinoma xenografts were treated with ZD6474, a VEGF receptor-2 (KDR) tyrosine kinase inhibitor. The pharmacokinetic parameter K trans was obtained, which reflects vascular permeability and perfusion. Mice were imaged immediately before, and following, acute treatment with ZD6474 (12.5 - 100 mg kg(-1) orally). Whole tumours were analysed to obtain mean K trans values, and a histogram approach was used to examine intratumour heterogeneity. Reproducibility of K trans measurements gave inter- and intra-animal coefficients of variation of 40 and 18%, respectively. Dose-related reductions in K trans were evident following acute ZD6474 treatment. A K trans reduction of approximately 30% (P<0.001) was evident with 50 and 100 mg kg(-1) ZD6474, a reduction of 12.5% (P<0.05) at 25 mg kg(-1), and a reduction that did not reach statistical significance at 12.5 mg kg(-1). A correlation between this dose response and the growth inhibitory effect of ZD6474 following chronic treatment was also observed. The histogram analysis of the data indicated that ZD6474-induced a K-trans reduction in both the most enhancing rim and the core of PC-3 tumours. Dynamic contrast-enhanced magnetic resonance imaging may have a role in assessing the acute effects of VEGF signalling inhibition, in clinical dose-ranging studies.