Investigation into chemotherapeutic and chemopreventive properties of seaweeds against prostate cancer

Background: Prostate cancer (PCa) is the second most common cancer and the fifth leading cause of cancer related deaths in men worldwide, with an estimated 1.4 million cases and 375,000 deaths in 2020. PCa is a disease of older age. The late age of onset provides ample opportunity for chemoprevention. PCa incidence rates range from 6.3 to 83.4 per 100,000 men in South Central Asia and Northern Europe, respectively. The low incidence among Asian men has been connected with multiple dietary elements. Brown seaweeds have been afforded numerous health benefits and are a staple constituent of the Asian diet. Anti-cancer properties of some seaweed compounds have been previously demonstrated across different cancer types. However, knowledge on the effects of seaweeds against PCa is lacking. The aim of this thesis was to investigate the anti-cancer properties of 10 seaweed species using cell line models of prostate cancer. Methods: Ten seaweed extracts were screened for their effects on the viability of three PCa cell lines (LNCaP, PC3 and DU145) using MTT assay. To determine cancer specificity, we tested the effective species on viability of prostate non-cancerous (BPH1 and PWR-1E) cells. The effect of Fucus vesiculosus, a brown seaweed, on migration and invasion of PCa cells was measured using the wound healing and Transwell invasion assays, respectively. Fucus vesiculosus impact on LNCaP cell cycle, apoptosis, and proliferation was measured by flow cytometry. Western blotting was used to measure the expression of cell cycle proteins (CDK1, CyclinD3 and CyclinE1), apoptotic proteins (cleaved caspase 3 and PARP) in PCa cells cultured in the presence of F. vesiculosus. Regulatory protein of migration and invasion (E cadherin, vimentin, survivin) were studied in PC3 and DU145 cells. The secretion of matrix metalloproteinases (MMP1, MMP3, and MMP9) in PC3 and DU145 cells were measured by multiplex ELISA. Cytoprotective effects of F. vesiculosus against H2O2 induced PWR-1E cytotoxicity was measured by MTT assay. Glutathione levels in PWR-1E cells was measured by GSH-GLO assay. Results: Three seaweed extracts demonstrated a reduction in viability of androgen dependent LNCaP cells. LNCaP cells were more sensitive to F. vesiculosus than either of the non cancerous cells. F. vesiculosus induced apoptosis in LNCaP cells by increased cleaved caspase 3 and cell cycle arrest at G1 phase by reducing expression of Cyclin D3. F. vesiculosus had no effect on the expression of the androgen receptor. None of the seaweed extracts had any effect on the viability of the androgen independent PC3 and DU145 cells. However, F. vesiculosus did reduce the migration and invasion of PC3 cells and invasion of DU145 cells, although no mechanism could be identified. Pre-treatment of non-cancerous prostate epithelial cells PWR1E with low-dose F. vesiculosus extracts were not found to have any cytoprotective or antioxidant effects against H2O2 induced cytotoxicity. Conclusion: The work presented in this thesis provide strong evidence for therapeutic potential of the Fucus vesiculosus brown seaweed against PCa. Further research is needed to decipher the identity of the bio-active compound(s) responsible for these effects as well as to further elucidate the mechanisms of action.