Exploring Treatments to Inhibit tumour recurrence Following Resection of Colorectal Liver Metastases
AuthorKastrappis, Georgios Loizou
AffiliationSurgery (Austin & Northern Health)
Document TypePhD thesis
Access StatusThis item is embargoed and will be available on 2023-10-13.
© 2021 Georgios Loizou Kastrappis
Background: Colorectal cancer (CRC) accounts for 9.2% of all cancer related deaths making it the second most common cause of cancer related death worldwide. The majority of CRC deaths are attributed to metastases, with liver being the most common metastatic site. Currently the best available treatment for colorectal liver metastasis (CRLM) that offers high survival rates and a potential for cure is liver resection surgery. However, only a small fraction of CRLM patients are eligible for surgery. Furthermore, liver resection and the ensuing liver regeneration (LR) upregulate growth factors and cytokines leading to a pro-inflammatory response, creating a favourable environment for any dormant tumours to grow. Thus, liver resected patients experience high tumour recurrence rates. Anti-inflammatory treatments administered perioperatively may reduce tumour recurrence. Previous experimental studies have shown that inhibition of the Renin Angiotensin System (RAS) classical pathway reduces tumour growth and accelerates liver regeneration together with a reduction in inflammation. This study investigates mechanisms by which captopril a RAS inhibitor (RASi) influences the environment of a regenerating liver to reduce inflammation. Additionally, it investigates the potential of a VEGFR-3 specific inhibitor, SAR131675, to inhibit tumour growth and reduce inflammation. Aims: 1) To investigate the effects Captopril, an angiotensin I converting enzyme (ACE) inhibitor, has on pro-inflammatory cytokines during LR. 2) To investigate the effect Captopril has on the global proteome and phosphoproteome of the liver during the early stages of LR 3) To investigate the effect SAR131675, a VEGFR-3 tyrosine kinase inhibitor, has on liver metastases in a CRLM mouse model and determine the likely mechanisms. Methods: Male CBA mice were used for all experiments in this study. For the liver regeneration study a 70% partial hepatectomy mouse model was used. Captopril (750mg/kg) was administered intraperitoneally and given daily starting 4 days before surgery until the endpoint (1 hour, 3 hours, 4 hours, 1 day and 2 days). Serum cytokine (IL-2, IL-6, IL-10, IL-12p70, IL-17A, TNF, IFNgamma and MCP-1) levels were assessed at the 1, 3 and 4 hour timepoints while liver regeneration was assessed at the day 1 and 2 timepoints, by measuring liver to body weight ratio and the liver regeneration rate. In addition, the 4 hour timepoint was used to conduct global proteomic and phosphoproteomic analyses. To investigate the effects SAR131675 had on CRLM and the mechanisms involved a mouse model of CRLM was used where metastases were established via intrasplenic injection of tumour cells. Immunohistochemistry was used for the analysis of proliferation, apoptosis, lymphatic and blood vessel densities, macrophage and T-cell tumour infiltration. Furthermore, FACS analysis was used to investigate changes in immune lymphoid and myeloid cell populations due to SAR131675 treatment. Results: Captopril treatment significantly reduced IL-6 levels in the serum of mice in the early phase of liver regeneration. This result was reinforced by the results of the global proteomic and phospho-proteomic study indicating that Captopril induced changes in a great number of proteins involved in inflammatory pathways in almost every cell process including cell proliferation, apoptosis transcription, translation and stress response. Interestingly, the largest proportion of protein changes were associated with lipid metabolism which is also closely associated with inflammatory pathways. SAR131675 treatment significantly reduced tumour growth in the mouse model of liver metastases. Mechanistically SAR131675 treatment changed the tumour microenvironment and promoted anti-tumour immune responses by modulating the tumour infiltrating immune cell composition; increasing the ratio of T lymphocytes to monocytes and by modifying the T-cell and myeloid cell subtype and activation to that favouring an anti-tumour immune response. Conclusion: Both Captopril and SAR131675 were able to modulate inflammatory pathways creating a microenvironment that is inhibitory towards tumour growth. These treatments have potential to be used in order to reduce tumour recurrence in patients that have undergone liver resection surgery.
KeywordsColorectal cancer; liver metastasis; renin-angiotensin system; VEGFR-3 inhibition; SAR131675; Cancer immunology
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