Date of Award
Doctor of Philosophy (PhD)
Colon cancer progression is characterized by growth of the primary tumor in the colon followed by metastasis to distant organs. The metastatic cascade involves invasion of cells from the primary tumor into the surrounding tissue, entering into and survival of cancer cells in the circulation, arrival at the end organ and finally colonization of the end organ. The liver is the primary site of colon cancer metastatic colonization, with over 70% of colon cancer patients experiencing liver metastases. Despite current standard-of-care surgical intervention and broad spectra cytotoxic chemotherapeutics, the survival rate of patients with metastatic disease is less then 5%. A greater understanding of the biology and molecular determinants of liver colonization is therefore of great importance to the scientific and clinical community. This thesis presents unbiased approaches to identify regulators of liver metastasis in colon cancer and the elucidation of the mechanisms involved. The first part of this thesis describes the identification of two microRNAs, miR- 483-5p and miR-551a as suppressors of liver metastasis by human colon cancer cells using two parallel, complementary xenograft models of colon cancer metastasis. The first approach involved a functional library-based in vivo screen of 661 microRNAs. The second approach utilized in vivo selection of liver metastatic colon cancer cell population from poorly metastatic parental population. Functional studies revealed both microRNAs to target a common downstream effector gene, Creatine Kinase Brain (CKB). CKB was found to promote metastasis and the second part of this thesis present mechanistic studies that describe CKB-mediated modulation of intra- and extracellular energetics by colon cancer cells that contributed to colon cancer cell survival in the liver microenvironment, allowing for development of macrometastases and finally liver colonization. Further investigation identified the membrane transporter SLC6a8 as an important effector of the CKB pathway and also a promoter of colon cancer metastasis. The final part of this study reveals miR-483-5p, miR-551a, CKB and SLC6a8 to be clinically relevant across multiple patient datasets and archival patient samples. MiR-483-5p and miR-551a were found to be down-regulated in liver metastases of patients relative to primary tumors, while CKB and SLC6a8 were up-regulated. In addition, proof-of-principle therapeutic experiments involving adeno associated viral delivery of the microRNAs and small molecule inhibition of CKB and SLC6a8 demonstrated the therapeutic potential of targeting this pathway in suppressing colon cancer metastasis.
Loo, Jia Min, "Extracellular Metabolic Energetics Can Promote Cancer Progression" (2016). Student Theses and Dissertations. 308.