Decoy Receptors block tumour cell eradication by TRAIL - Molecular engineering of TRAIL to evade decoy receptors
O' Leary, Lynda
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Tumour necrosis factor-related apoptosis inducing ligand (TRAIL) is a cytokine expressed by immune cells which selectively eradicates a wide range of cancer cells while leaving normal healthy cells unharmed. TRAIL binds to 4 different membrane-bound receptor molecules. However, only two of these receptors, DR4 and DR5, can launch the death machinery into action leading to cancer cell death. The two remaining receptors, decoy receptor-1 (DcR1) and DcR2 can also bind TRAIL but are unable to induce apoptosis. These decoy receptors can attenuate TRAIL-induced apoptosis by competing with DR4 and DR5 for TRAIL binding or directly binding and inhibiting the death inducing receptors. Here we show that decoy receptors either expressed by the tumour cells or on the surrounding normal cells can greatly reduce the efficacy of wild type TRAIL. While TRAIL shows promise as a potential anti-cancer agent, its promiscuous receptor binding capacity limits its utilisation as a therapeutic. To address this limitation we engineered a TRAIL mutant (TRAIL-45) using computational rational design that retained the ability to bind to DR4 and DR5 with high affinity, but not to the DcRs. We found that mutating a threonine to a leucine at position 261 (T261L) could reduce binding to the DcRs without significantly reducing binding to DR4 and DR5. Furthermore, combination of T261L with G160E where glutamic acid takes the place of glycine at position 160 resulted in enhanced favourable characteristics. The mutants were capable of activating both DR4 and DR5 and proved to be potent inducers of cell death compared to WT TRAIL. Unlike native TRAIL the efficacy of the mutants was not altered in the presence of non-transformed cells overexpressing decoy receptors indicating that they can successfully evade these receptors. In this thesis it is clearly illustrated the necessity for these decoy receptor insensitive TRAIL mutants and their potential power in the clinic.