Abstract #0556

Dual PI3K/mTOR Inhibition Induces Structural Changes in Tumor Vasculature Assessed by Vessel Size Imaging

Shelby Katherine Wyatt¹, Sharon E. Ungersma¹, Jason R. Oeh², Calvin Ho¹, Tim C. Cao¹, Hartmut Koeppen³, Lori S. Friedman², Deepak Sampath², Richard A. D. Carano¹

¹Biomedical Imaging, Genentech, Inc, South San Francisco, CA, USA; ²Translational Oncology, Genentech, Inc, South San Francisco, CA, USA; ³Pathology, Genentech, Inc, South San Francisco, CA, USA

This study aims to elucidate the role of PI3K and mTOR inhibition on vascular structure using an in-vivo multispectral vessel size index (VSI) MRI approach and ex-vivo micro-computed tomography (micro-CT) angiography. In-vivo multispectral VSI MRI demonstrated significant tumor growth suppression, reduced Q, increased VSI and decreased blood volume, while ex-vivo micro-CT angiography demonstrated decreased vascular density following PI3K/mTOR inhibition. These results are consistent with the loss of small vessels and help elucidate the effects of inhibiting the PI3K and mTOR pathways on vascular structure.