The purpose of this thesis was to examine and quantify the effects of the short-chain fatty acid acetate, a by-product of the microbial fermentation of dietary fibre, on the metabolism of cancer cells, and to test whether acetate can sensitize cells to apoptosis induced by anti-cancer drugs, by a process known as priming.
To examine the effects of acetate, several markers of metabolism were assayed in 3 cell lines HCT116 (Human colon cancer), MCF7 (Human breast cancer) and the control cell line MCF10 (non-cancerous human breast) following 24-hour acetate treatment in doses ranging from 1-25 mM. Reactive oxygen species and Ca2+ were measured with fluorescent spectroscopy. Mitochondrial function was measured using the SeaHorse XFE Analyser and 2-photon-NADH FLIM. Mitochondrial morphology was assessed with confocal microscopy.
To determine whether acetate could prime cells for death, changes in proliferation were measured with the MTT cell viability assay and levels of apoptosis induction were measured with Annexin-V FITC flow cytometry.
Acetate induced a state of oxidative stress in the HCT116 and MCF7 cancer cell lines, indicated by an average 17.5% significant decrease in mitochondrial basal respiration, increased ROS production (significant 24% average increase across the two cancer cell lines), and increased Ca2+ levels (significant 22% average). Whilst ROS and Ca2+ were elevated in the non-cancerous cell line, there was no significant change in mitochondrial basal respiration, suggesting that acetate treatment did not cause oxidative stress in healthy cells.
When cancer cells were primed with 10 mM acetate 24 hours prior to treatment with cisplatin, there was an average 1.85-fold increase in apoptosis compared to treatment with the drug by itself. This effect was not observed in the non-cancerous cell line.
Priming has been shown to have the potential to improve the efficacy of pre-existing chemotherapeutic agents. With cancer incidence increasing worldwide, there is a need to improve current treatments without exacerbating side effects and impairing patient quality of life. In this thesis, I show that acetate improves the effectiveness of cisplatin in inducing apoptosis, by selectively inducing oxidative stress in a cancer cell line model. My work highlights a new mechanism for the action of acetate and adds further evidence that priming can be used as a safe, effective method to improve chemotherapeutic treatment.