Cytotoxic action of acetate on tumor cells of thymic origin: Role of MCT-1, pH homeostasis and altered cell survival regulation

Neoplastic cells display altered biosynthetic and bioenergetic machinery to support cell survival. Therefore, cancer cells optimally utilize all available fuel resources to pump their highly upregulated metabolic pathways. While glucose is the main carbon source, transformed cells also utilize other molecules, which can be utilized in metabolic pathways, designated as alternative fuels. Acetate is one of such alternative metabolic fuels, which is mainly consumed in carbohydrate and lipid metabolism. However, studies demonstrate the contradictory effects of acetate on tumor cell survival. Moreover, the mechanisms of its antitumor actions remain poorly understood. Further, the spectrum of acetate susceptible tumor targets needs to be characterized in order to optimize the use of acetate in maneuvering tumor progression as a therapeutic strategy. As the effect of acetate on survival properties of the tumor cells of thymic origin is not worked out, in the present study the effect of acetate was investigated against tumor cells derived from a murine thymoma designated as Dalton's Lymphoma (DL). Acetate treatment of tumor cells inhibited tumor cell survival accompanied by induction of apoptotic cell death, associated with modulated expression of cell survival regulatory HIF1α, ROS, p53, Caspase 3, Bax and HSP70 along with the elevated level of cytosolic cytochrome c. Acetate treatment also modulated the expression of pH regulators MCT-1 and V-ATPase accompanied by altered pH homeostasis. Expression of MDR and lipid metabolism regulatory molecules was also inhibited in tumor cells upon acetate exposure. Further, pre-exposure of tumor cells to α-CHC (α-cyano-4-hydroxycinnamate), an inhibitor of MCT-1, partially abrogated the cytotoxic action of acetate. These findings shed a new light regarding the effect and mechanisms of the exogenous acetate on the biology of tumor cells of thymic origin.