Investigating the effects or AKT/PKB inhibitors on [18F]-FDG uptake in cancer cells

Abstract

Increased AKT activity due to hyperactivated PI3K or inactivation of PTEN is frequently found in cancer. Thus the development of AKT inhibitors and pharmacodynamic (PO) biomarkers for AKT inhibition is of major interest for cancer therapy. [18F]-FDG PET is a non-invasive imaging technique which allows the isualization of glucose metabolism. As AKT activity has been associated with glucose uptake and phosphorylation, it has been hypothesized that CSF]-FOG PET is a potential PO biomarker for the assessment of AKT inhibitor action in the clinic. The primary aim of the work presented in this thesis was to investigate whether (18F]-FOG uptake can be used as a PO biomarker for AKT inhibition. An in vitro system was established including assembly of a gamma counter which was used to demonstrate that both ATP competitive and allosteric inhibitors of AKT block [18F]-FDG uptake in the PTEN null U87MG human glioblastoma cell line. These results led to a detailed investigation of the mechanism(s) by which the AKT inhibitors affect [18F]-FDG uptake. However, no change in expression or translocation of the glucose transporters GLUT-1 and GLUT-4, or in hexokinase phosphorylation or activity was seen after inhibitor treatment. Reduction of [18F]-FDG uptake was then confirmed with a later generation of AKT inhibitors and in a second cellular model, namely the human breast cancer cell line BT474. These results were also complimented by MRS studies of lactate production. AKT knock down studies using siRNA were also carried out. However, complete functional removal of AKT was not achieved, although AKT protein level was substantially reduced. In addition, in vivo studies demonstrated that [18F]-FDG uptake and AKT signalling were decreased in U87MG xenografts by the AKT inhibitor CCT129254. Hence, it was concluded that [18F]-FDG uptake can be used as a PD biomarker of AKT inhibition for the types of compound studied.EThOS - Electronic Theses Online ServiceGBUnited Kingdo