The radiation response of cells from 9L gliosarcoma tumours is correlated with [F18]-EF5 uptake

Abstract

Purpose: Tumour hypoxia affects cancer biology and therapy-resistance in both animals and humans. The purpose of this study was to determine whether EF5 ([2-(2-nitro-1-H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide]) binding and/or radioactive drug uptake correlated with single-dose radiation response in 9L gliosarcoma tumours.

Materials and methods: Twenty-two 9L tumours were grown in male Fischer rats. Rats were administered low specific activity ¹⁸F-EF5 and their tumours irradiated and assessed for cell survival and hypoxia. Hypoxia assays included EF5 binding measured by antibodies against bound-drug adducts and gamma counts of ¹⁸F-EF5 tumour uptake compared with uptake by normal muscle and blood. These assays were compared with cellular radiation response (in vivo to in vitro assay). In six cases, uptake of tumour versus muscle was also assayed using images from a PET (positron emission tomography) camera (PENN G-PET).

Results: The intertumoural variation in radiation response of 9L tumour-cells was significantly correlated with uptake of ¹⁸F-labelled EF5 (i.e., including both bound and non-bound drug) using either tumour to muscle or tumour to blood gamma count ratios. In the tumours where imaging was performed, there was a significant correlation between the image analysis and gamma count analysis. Intertumoural variation in cellular radiation response of the same 22 tumours was also correlated with mean flow cytometry signal due to EF5 binding.

Conclusion: To our knowledge, this is the first animal model/drug combination demonstrating a correlation of radioresponse for tumour-cells from individual tumours with drug metabolism using either immunohistochemical or non-invasive techniques.

Keywords:

• EF5
• tumour hypoxia
• 9L-gliosarcoma
• predictive assay
• non-invasive molecular imaging

Acknowledgements

Thanks to Grant RO1-CA87645 and the Departments of Radiation Oncology and Radiology at the University of Pennsylvania for financial support, and to The National Cancer Institute for the supply of unlabelled EF5.

Declaration of interest: EF5 is patented (inventors include CJK, AVK, WRD) with rights assigned to the University of Pennsylvania. UPENN has a licensing agreement with Varian.