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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.