The role of nitric oxide synthase expressed by cytokine-induced macrophages on HIF-1 regulation in tumour cells and their response to therapy

Abstract

Murine macrophages were induced to over-express iNOS by treatment with a combination of cytokines, mixed with HT1080 and HCT116 human tumour cells and the toxicity of AQ4N was determined under normoxic or hypoxic conditions. The normoxic toxicity of AQ4N towards tumour cells was not affected through co-culturing with macrophages. However, under hypoxic conditions, the induction of iNOS activity in the macrophages was associated with an increase in AQ4N metabolism and a substantial increase in tumour cell toxicity, which was dependent upon the proportion of macrophages in the culture. This study is the first demonstration of tumour associated macrophage mediated pro-drug activation to result in bystander killing of human tumour cells. The oxygenase domain of the iNOS enzyme is responsible for the production of nitric oxide (NO), a potent biological mediator, whose complex role in tumour biology is still not fully understood as it seems to have both anti- and protumour effects. We were able to use the co-culture model of NO-producing macrophages and cancer cells to demonstrate that NO is also a potent tumour radiosensitiser under hypoxic conditions with a sparing effect on well-oxygenated tumour cells, also a characteristic of normal tissues. Additionally, NO produced by the macrophages resulted in a significant induction of hypoxia inducible factor-1 (HIF-1) driven transcriptional activity in the co-cultured tumour cells under both normoxic and hypoxic conditions. We therefore, suggest the use of HIF-1 inhibitors in combination with NO-based therapies and radiation to favour tumour regression.EThOS - Electronic Theses Online ServiceGBUnited Kingdo