Effect of medium chain fatty acids on the cytotoxicity of docosahexaenoic and/orpunicic acid on FaDu cancer cells grown at physiological pH or under chronic acidosis

(eng) Cancer is the second leading cause of death worldwide. In 2018, about seventy thousand new patients have been diagnosed in Belgium, 53% being men and 47% being women. Cancer is described as an uncontrolled multiplication and growth of abnormal cells that tend to invade neighboring tissues and spread throughout the body. Cancer onset is related to mutations appearing in genes that control cell growth and division. Perturbations in the cancer microenvironment conditions may lead to modifications in cancer cell metabolism in order to allow them to survive and continue to proliferate. Acidosis, a change in cancer microenvironment characterized by a toxic decrease in tumor pH, triggers a shift in tumor metabolism from glucose to exogeneous fatty acids as energy source. Because glycolysis is then strongly decreased, proton production is reduced, and cancer cells can continue to grow and divide. As exogenous fatty acids become the main source of energy for cancer cells facing acidosis, our team has developed a particular interest in studying the impact of the addition of diverse fatty acids on cancer cells. In previous studies, docosahexaenoic acid (DHA) and punicic acid (PunA) have been shown to have a cytotoxic effect on cancer cells. Moreover, a recent study has demonstrated that the addition of medium chain fatty acids to an emulsion containing omega 3 fatty acids leads to a protective effect in patients after a stroke event. Following this observation, the idea of developing a similar approach (i.e. an emulsion rich in DHA and/or PunA with medium chain fatty acids) on cancer cells has emerged. The medium chain fatty acids capric and caprylic acids have been studied in vitro on FaDu cancer cells either grown at physiological pH (7.4) or at acidic pH (6.5) in order to evaluate their effect on DHA and/or PunA cytotoxicity. In viability experiments, capric and caprylic acids have been shown to have no inhibitory effect on DHA and/or PunA cytotoxicity, independently of the pH or the concentration. Moreover, capric and caprylic acids seem to enhance the cytotoxicity of DHA and to have a cytotoxic effect on cancer cells when applied alone. An inverse trend has been observed with palmitic acid (PAL). Indeed, the addition of PAL to DHA and/or PunA treatments led to a decrease of their cytotoxicity, characterized by an almost full recovery of viability at pH 6.5. To go a step closer to an actual tumor, a second set of experiments was carried out on three-dimensional FaDu spheroids at pH 7.4. Similar results were observed than with two-dimensional viability assays. Capric and caprylic acid non-inhibitory effect on DHA and/or PunA cytotoxicities was validated even when DHA and PunA were combined. These medium chain fatty acids have instead shown to enhance DHA cytotoxicity, leading to a greater impact on the growth and cell detachment of the spheroids. Finally, different formulations containing PunA have been studied when the FaDu cells were grown in 2D at the physiological pH (7.4) in order to evaluate the differences in the delivery form of PunA on cancer cells. These last experiments have highlighted that the triglyceride form of PunA is probably ineffective on cancer cells since the expected cytotoxicity of PunA was not verified after administration of high doses of pomegranate seed oil rich in PunA in its triglyceride form. This master’s thesis suggests that caprylic and capric acid could be used in an emulsion containing DHA and/or PunA, which aims at treating cancers. However, the emulsions have yet to be studied in order to improve their efficacity as the triglyceride form of PunA appears not to have an impact. Numerous questions are yet to be addressed to understand the different mechanisms involved in fatty acid cytotoxicity. Moreover, the cytotoxicity of DHA and PunA have to be confirmed in an actual tumor environment in vivo.