Breast cancer is the second deadliest disease among women. Thanks to screening programs and advances in diagnostics and treatment, mortality rates have declined in recent decades. However, cancer stem cells remain the major challenge in effective treatment. Due to their unique abilities of self-renewal and differentiation, these cells are resistant to most current therapies, often persisting post-treatment, where they proliferate, differentiate, and metastasize, leading to reoccurrence. New treatments targeting these cells are needed. Cysteine cathepsins B and X, which are involved in all stages of cancer progression, show increased expression and activity in cancer stem cells.
In this thesis, cancer stem cells were isolated from MDA-MB-231, MCF-7, and MCF-10A neoT cell lines based on their sphere-forming abilities. Secondary tumour spheres were prepared to increase purity. The role of cathepsin B and X inhibitors in endocytosis was assessed using nitroxoline and compound Z9.
We showed that transferrin endocytosis is significantly lower in cancer stem cells than in differentiated cancer cells. Inhibition confirmed cathepsin B’s involvement in endocytosis, while cathepsin X inhibition had a lower effect. Reduced cathepsin B activity increased endocytosis capacity in cancer stem cells to levels typical of differentiated cells. Additionally, receptor-mediated transferrin endocytosis was confirmed in cancer stem cells by holotransferrin saturation.
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