Evaluation of the Response of Intracranial Xenografts to VEGF Signaling Inhibition Using Multiparametric MRI.

Vascular endothelial growth factor A (VEGF-A) is considered one of the most important factors in tumor angiogenesis, and consequently, a number of therapeutics have been developed to inhibit VEGF signaling. Therapeutic strategies to target brain malignancies, both primary brain tumors, particularly in pediatric patients, and metastases, are lacking, but targeting angiogenesis may be a promising approach. Multiparametric MRI was used to investigate the response of orthotopic SF188luc pediatric glioblastoma xenografts to small molecule pan-VEGFR inhibitor cediranib and the effects of both cediranib and cross-reactive human/mouse anti-VEGF-A antibody B20-4.1.1 in intracranial MDA-MB-231 LM2–4 breast cancer xenografts over 48 hours. All therapeutic regimens resulted in significant tumor growth delay. In cediranib-treated SF188luc tumors, this was associated with lower Ktrans (compound biomarker of perfusion and vascular permeability) than in vehicle-treated controls. Cediranib also induced significant reductions in both Ktrans and apparent diffusion coefficient (ADC) in MDA-MB-231 LM2–4 tumors associated with decreased histologically assessed perfusion. B20-4.1.1 treatment resulted in decreased Ktrans, but in the absence of a change in perfusion; a non-significant reduction in vascular permeability, assessed by Evans blue extravasation, was observed in treated tumors. The imaging responses of intracranial MDA-MB-231 LM2–4 tumors to VEGF/VEGFR pathway inhibitors with differing mechanisms of action are subtly different. We show that VEGF pathway blockade resulted in tumor growth retardation and inhibition of tumor vasculature in preclinical models of pediatric glioblastoma and breast cancer brain metastases, suggesting that multiparametric MRI can provide a powerful adjunct to accelerate the development of antiangiogenic therapies for use in these patient populations.