Abstract 4314: Metabolic manipulation of hypoxia and radiotherapy response by electron transport inhibitors

Abstract

The presence of hypoxia in solid tumors is correlated with poor treatment outcome. Even small population of hypoxic cells within tumors can significantly decrease the efficacy of radiation therapy. One approach to treating hypoxia in tumours is to reduce overall tumor cell oxygen consumption by modulating mitochondrial respiration. This could reoxygenate hypoxic cells within the tumor and restore radiation sensitivity. To guide in vivo application we tested the effects of three respiratory chain inhibitors; the biguanides metformin and phenformin and rotenone on oxygen consumption in 3D tissue engineered discs. Experiments were carried out to evaluate the effect of respiratory inhibition on the hypoxic fraction of HCT116 and HT29 tissue discs using immunostaining with the hypoxic cell marker pimonidazole. An oxygen sensing phosphorescence lifetime probe assessed pO2 on the basal side of the disc as a function of time after inhibitors were exposed to the apical surface. Clonogenic assays were then performed to confirm the radiosensitization of hypoxic cells within the tissue discs. Pimonidazole staining and direct pO2 sensing confirmed that all three electron transfer inhibitors decrease the hypoxic fraction by reducing cellular oxygen consumption. Rotenone was found to completely eliminate the hypoxic fraction at nanomolar concentrations compared to metformin and phenformin which require milli to micromolar concentrations respectively. Furthermore, rotenone was found to have an effect on oxygen utilization within minutes of drug exposure compared to both metformin and phenformin, which took hours to be effective. In addition, clonogenics assays determined that all three electron transfer inhibitors radiosensitize tumor cells with rotenone being the most efficient compound on a molar basis. The mitochondrial inhibitors of complex I metformin, phenformin and rotenone decrease oxygen utilization by tumor cells in a concentration dependent manner resulting in reduction of the hypoxic fraction and increased radiosensitivity. Citation Format: Maria Jose Gandolfo, Alastair H. Kyle, Andrew I. Minchinton. Metabolic manipulation of hypoxia and radiotherapy response by electron transport inhibitors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4314. doi:10.1158/1538-7445.AM2014-4314