Preclinical studies suggest that fasting prior to chemotherapy may be an effective strategy to protect patients against the adverse effects of chemo-toxicity. Fasting may also sensitize cancer cells to chemotherapy. It is further suggested that fasting may similarly augment the efficacy of oncolytic viral therapy. The primary mechanism mediating these beneficial effects is thought to relate to the fact that fasting results in a decrease of circulating growth factors. In turn, such fasting cues would prompt normal cells to redirect energy toward cell maintenance and repair processes, rather than growth and proliferation. However, fasting is also known to upregulate autophagy, an evolutionarily conserved catabolic process that is upregulated in response to various cell stressors. Here, we review a number of mechanisms by which fasting-induced autophagy may have an impact on both chemo-tolerance and chemo-sensitization. First, fasting may exert a protective effect by mobilizing autophagic components prior to chemo-induction. In turn, the autophagic apparatus can be repurposed for removing cellular components damaged by chemotherapy. Autophagy also plays a key role in epitope expression as well as in modulating inflammation. Chemo-sensitization resulting from fasting may in fact be an effect of enhanced immune surveillance as a result of better autophagy-dependent epitope processing. Finally, autophagy is involved in host defense against viruses, and aspects of the autophagic process are also often targets for viral subversion. Consequently, altering autophagic flux by fasting may alter viral infectivity. These observations suggest that fasting-induced autophagy may have an impact on therapeutic efficacy in various oncological contexts.

It has been demonstrated that vitamin C exhibits anti-cancer activity in various tumor cell lines; however, its specific mechanism of action remains unknown. Although the diagnosis and therapy of cancer patients have markedly improved in recent years, safer and more cost-effective treatments are still required. Therefore, the present study examined the effect of vitamin C on the induction of cell death in gastric cancer and its underlying mechanism of action. It was observed that the cytotoxicity of vitamin C on the human gastric cancer cell line AGS is dependent on the apoptotic pathway, including caspase cascades, but not on the necroptotic pathway. It was demonstrated that the vitamin C-induced calcium influx and ROS generation have critical roles in the induction of apoptosis. Furthermore, vitamin C treatment depleted adenosine triphosphate (ATP) production in AGS cells, and the autophagy pathway may be involved in this process. Taken together, the current study suggests that a high dose of vitamin C may induce gastric cancer cell apoptosis through the dysfunction of mitochondria, including calcium influx, reactive oxygen species generation and ATP depletion.