The catabolism of the essential amino acid tryptophan (Trp) by tumour cells expressing either IDO1/2 or TDO has been associated with malignant tumour progression and poor patient survival. Expression of these rate-limiting genes leads to both depletion of Trp and accumulation of the Trp breakdown product kynurenine (Kyn) in the tumour microenvironment. Kyn has recently been shown to act as a ligand for the aryl hydrocarbon receptor (AHR), causing its nuclear translocation and resulting in expression changes which in tumour cells result in increased survival and motility, whilst in T-cells induce anergy and apoptosis.
Although the membrane transport protein LAT1 is known to act as a Trp/Kyn exchanger, accumulating evidence from transport kinetics studies clearly indicate the presence of highly specific, as yet unidentified Trp and Kyn transporters. Identifying the transport proteins responsible would offer a significant therapeutic target not only for aggressive, hard to treat brain cancers such as gliomas, but also in a number of neurodegenerative and auto-immune disorders in which the catabolism of Trp has been shown to be altered.
I propose to do precisely this by expanding on discoveries I made during my studies of the role of the Trp catabolite 3-hydroxykynurenine in Huntington’s Disease, wherein I took advantage of unique features of Drosophila physiology to identify a number of candidate Trp/Kyn transporter proteins. To fully realise the potential of my discoveries I should like to characterise the human homologs of these transporters in glioma culture and in vivo models, which will require me to change both my scientific field and model system.
To gain the required expertise I am applying for an IEF to train with Michael Platten's group at the DKFZ in Germany, a world leading cancer research center which has developed a number of unique reporters for Trp and Kyn levels that are essential to my characterisation of the transporters identified.