Investigations of the cancer therapeutic and protective effects of warfarin-mediated inhibition of the receptor tyrosine kinase AXL

Abstract

Cancer is a major health issue all over the world. Cancer related deaths are one of the major causes of deaths, and are in > 90 % of the cases related to metastatic development, and spread of the cancer outside the primary location. The receptor tyrosine kinase AXL is closely associated with the development of cancer and the receptor is upregulated in many different cancer forms. Upregulation is associated with increased invasiveness, and poor overall survival. Warfarin is a known anticoagulant, which also is suitable as an AXL inhibitor. The warfarin-mediated inhibition of AXL is through the depletion of Vitamin K, with a subsequent inhibition of the γ-carboxylation of the Vitamin K dependent proteins in the body. GAS6, the ligand of AXL, is vitamin K dependent and will be unable to activate the receptor following warfarin treatment. In this thesis, we have worked with the warfarin-mediated inhibition of the receptor tyrosine kinase AXL. In five different mouse model systems, we have evaluated the effect of warfarin-mediated AXL-inhibition in the development and metastasis of pancreatic ductal adenocarcinoma. We also evaluated how warfarin-mediated AXL inhibition impacts on expression of EMT markers, and the ability of the cells to migrate and form colonies, which is a hallmark of cancer with metastatic properties. Further, we performed a register based cohort study using the Norwegian National Registry, the Cancer registry of Norway and the Norwegian prescription database. We investigated the cancer incidence in warfarin users compared to non-users in a broad segment of the Norwegian population, with a cohort comprising 1,2 million persons aged 52-82 years. Our work establishes AXL as an important driver of metastatic formation in pancreatic ductal adenocarcinoma. The level of metastatic disease were significantly reduced in all warfarin treated animals. We also confirmed the close relation between AXL and EMT, as epithelial markers were upregulated when AXL was inhibited. The cells migratory and colony forming capabilities were also impaired after AXL inhibition. In the population-based register study we observed an overall cancer protective association, with lowered incidence rate ratio of cancer in warfarin users compared to non-users. This was observed both for all-site cancer, and for the most prevalent cancer diagnoses in the material. Altogether, our results emphasizes the importance of the receptor tyrosine kinase AXL in the development and progression of cancer. Warfarin-mediated AXL inhibition are shown to have a cancer protective effect, both in murine model systems and in population level studies. The results from this thesis suggest further investigations, to fully illuminate the potential use of warfarin in an anti-cancer setting.