Delineating the signalling interplay between mTORC1 and MET in Tuberous Sclerosis Complex

Abstract

Tuberous Sclerosis Complex (TSC) is a genetic disease caused by mutations in the TSC1 and TSC2 genes. As a result of these mutations, there is dysregulation in the TSC complex which in turn leads to downstream hyperactivation of mTOR (mechanistic target of rapamycin), a serine/threonine protein kinase. The involvement of the MET proto-oncogene, receptor tyrosine kinase (MET) in TSC pathogenesis has been explored in this project, as MET could play an important role in cell proliferation, motility, migration, and invasion. MET could be a potential therapeutic target in TSC. Ref-1 is a redox regulator involved in DNA repair and inhibition of apoptosis. This study aimed to provide confirmatory data of the link between MET and mTOR signalling, as well as providing evidence of whether MET and Ref-1 are functionally important in TSC and associated cell models of cancer. Preliminary data indicated a potential link between MET and mTOR. Dual inhibition of MET and mTOR signalling on TSC2-deficient AML cells (621-101) and Tsc2−/− mouse embryonic fibroblast (MEF) cells demonstrate greater anti-proliferative effects compared to single agent treatments. Combined blockade of MET and mTOR pathways reduced cell growth more potently than individual MET or mTOR inhibitors alone. mTOR activity was found to potently enhance hepatocyte growth factor (HGF) and autocrine signalling in TSC2-deficient model cells of TSC, which was blocked with rapamycin treatment. Data indicates that co- targeting aberrant MET, Ref-1 and mTORC1 signalling has potential as a therapeutic strategy in cancers dependent on these oncogenic pathways. Blockade of dysregulated MET and Ref-1 signalling pathways demonstrated greater anti- tumour effects compared to inhibition of mTORC1 alone in AML and MEF cells lacking functional TSC2. Combining MET and Ref-1 inhibitors with mTOR-targeted agents may provide additional therapeutic benefits for TSC. The combination of MET inhibitor, Crizotinib, and mTOR inhibitor, rapamycin, on AML, MDA-MB-231 and ST8814 cells demonstrates synergistic anti-tumour effects in preclinical cancer models. Early phase clinical trials show this drug combination is tolerable with encouraging efficacy signals in certain malignancies, yet their outcomes were not conclusive. In conclusion, this thesis demonstrates the potential of targeting MET, mTORC1, and Ref-1 signalling as an anti-cancer strategy. Further optimization of MET/mTORC1 inhibitor combination therapies inhibiting these pathways is needed to translate the findings into improved clinical outcomes for cancer patients.