Date of Award

2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Biochemistry & Molecular Biophysics

First Advisor

Wafik S. El-Deiry

Abstract

TNF-related apoptosis-inducing ligand (TRAIL; Apo2L) is an endogenous protein that selectively induces apoptosis in cancer cells and is a critical effector in the immune surveillance of cancer. Recombinant TRAIL and TRAIL-agonist antibodies are in clinical trials for the treatment of solid malignancies due to the cancer-specific cytotoxicity of TRAIL. Recombinant TRAIL has a short serum half-life and both recombinant TRAIL and TRAIL receptor agonist antibodies have a limited capacity to perfuse to tissue compartments such as the brain, limiting their efficacy in certain malignancies. To overcome such limitations, we searched for small molecules capable of inducing the TRAIL gene using a high throughput luciferase reporter gene assay. We selected TRAIL-inducing compound 10 (TIC10) for further study based on its induction of TRAIL at the cell surface and its promising therapeutic index. TIC10 is a potent, stable, and orally active antitumor agent that crosses the blood-brain barrier and transcriptionally induces TRAIL and TRAIL-mediated cell death in a p53-independent manner. TIC10 induces a sustained upregulation of TRAIL in tumors and proximal cells that may contribute to the antitumor activity of TIC10 through a bystander effect. Expression profiling of TIC10-induced transcriptional changes revealed changes in FOXO target genes. We found that Foxo3a undergoes a TIC10-induced nuclear translocation, binds to the TRAIL gene promoter in response to TIC10, and is responsible for TIC10-induced cell death and TRAIL production in vitro and in vivo. TIC10 activates Foxo3a through the dual inactivation of Akt and ERK, which normally phosphorylate and inactivate Foxo3a. The induction of TRAIL by TIC10 can be recapitulated using pharmacological inhibitors of Akt and ERK signaling pathways or siRNA. These mechanistic data provide a clear therapeutic strategy for targeting the TRAIL gene and suggest that Foxo3a-mediated TRAIL induction is responsible for the synergy between PI3K/Akt and MAPK pathway inhibitors. TIC10 is a potentially first-in-class antitumor therapy that utilizes the tumor microenvironment to produce TRAIL, acts as a pharmacological delivery vehicle to improve the therapeutic properties of TRAIL, and highlights Foxo3a activation as an attractive opportunity to induce TRAIL-mediated apoptosis that can be harnessed through dual inhibition of the MAPK and PI3K/Akt pathway.

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