Abstract 491: Tumor response to cabozantinib in the TH-MYCN GEM model of neuroblastoma
Authors: Almeida Gilberto S. , King Philippa , Jamin Yann , Hallsworth Albert , Webber Hannah , Popov Sergey , Pearson Andrew D.J. , Chesler Louis , Robinson Simon P. 
Published: August 2015

Abstract
Neuroblastoma (NB) is the most common extra-cranial solid tumor in childhood. The proto-oncogene MYCN is amplified in 25% of NB, and is associated with enhanced angiogenesis and poor survival. Vascular endothelial growth factor (VEGF) is the most potent angiogenic growth factor and, with the hepatocyte growth factor (HGF)/c-MET signalling pathway, is implicated in the progression of human NB. Cabozantinib (CBZ) is a small-molecule kinase inhibitor with potent activity against VEGFR2 and MET, currently in clinical trials against NB. In this study, the efficacy of CBZ was evaluated in tumors spontaneously arising in the TH-MYCN GEM model of high-risk NB, previously shown to faithfully recapitulate the radiological and hypervascular characteristics of childhood disease.
TH-MYCN mice with spontaneous abdominal tumors were treated daily with either vehicle or 30mg/kg CBZ. Non-invasive T2-weighted anatomical MRI revealed that CBZ induced significant (p&lt;0.001) tumor growth arrest after 48 hours compared to control. Quantitative functional MRI showed this volumetric response was associated with significant decreases in both the native longitudinal MRI relaxation time T1 (p&lt;0.01) a measure of the ratio of bound to free water in tissue reflecting the increased extracellular space in tumors, and transverse MRI relaxation rate R2* (p&lt;0.05), sensitive to paramagnetic deoxyhemoglobin. Histopathological analysis revealed a significant increase in necrosis (p&lt;0.01), and significant decrease in microvessel density (p&lt;0.01) and VEGFR2 scoring (p&lt;0.02) in CBZ-treated tumors compared to control. Significant (p&lt;0.01) tumor growth delay was maintained after 7 days treatment with CBZ compared to control, which translated into a significant improvement in survival rate (p&lt;0.0001).
This study demonstrates that CBZ is efficacious against, and conveys a survival benefit for the TH-MYCN GEM model of NB. The data reinforces native T1 as a biomarker of response to anti-vascular therapy due to its sensitivity to therapy-induced damage to erythrocytes and/or cell death-mediated increase in macromolecules into the extracellular space. Relatively fast R2* rates in NB arising in the TH-MYCN model are strongly associated with vascular instability, characterised by numerous regions of aggregated paramagnetic erythrocytes (“blood lakes”), and treatment-induced thrombosis with the pan-VEGFR inhibitor cediranib which increased tumor R2*. The CBZ-induced decrease in R2* is clearly associated with vascular disruption, hence precluding the extravasation of deoxygenated red blood cells.
Citation Format: Gilberto S. Almeida, Philippa King, Yann Jamin, Albert Hallsworth, Hannah Webber, Sergey Popov, Andrew D.J. Pearson, Louis Chesler, Simon P. Robinson. Tumor response to cabozantinib in the TH-MYCN GEM model of neuroblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 491. doi:10.1158/1538-7445.AM2015-491