Kelly Harris, Xiaohuan Gao, Sara Huerta-Yepez, Payal Kapur and Sergio Huerta
Introduction: There is a wide range of responses to pre-operative chemoradiation (CRT) in patients with rectal cancer. Factors that dictate tumors response have not been identified. The objective of this study was to determine the role of hypoxia-inducible factor 1-alpha (HIF-1α) in in vitro and ex vivo models of rectal cancer. Methods: Levels of HIF-1α were assessed in radiosensitive (HCT-116) and a radioresistant (HT-29) cells. Radioresistant HT-29 cells were exposed to a potent radiosensitizing agent (a nitric oxide donor: DETANONOate [1 mM]) and IR followed by Western blot analysis with anti- HIF-1α antibodies. Patients with rectal cancer that were treated with CRT were separated based on good responders (≥ 50% reduction in tumor by comparing tumor size pre-operatively and postoperatively) compared to those that did not respond (<50% reduction in tumor). Blocks were stained for HIF-1α. Tissues collected from normal colonic epithelium from all these patients were subjected to the same treatments. Results: In vitro, radiosensitive HCT-116 colorectal cancer cells demonstrated low levels of HIF-1α following treatment IR. Western blot analysis showed high protein levels of HIF-1α in radioresistant HT-29 cells subjected to IR with induction at 2.0 and 4.0 Gy. Protein levels of HIF-1α were attenuated by treatment of cells HT-29 with the radiosensitizing agent DETANONOate following exposure to IR. Ex vivo, tissue microarrays demonstrated no difference in HIF-1α expression between patients with a poor response to CRT (418.1 ± 32.6) vs. good responders (371.1 ± 31.5; p=0.3). However, examination tumor tissue compared to normal epithelium showed an increase in HIF-1α (1.5 fold; p<0.001) in patients who responded poorly to IR. This effect was not observed in the cohort of patients who responded well to IR. Conclusions: The results of this study further support the potential role of HIF-1α in resistance to IR. This study implicates it a potential role of HIF-1α in rectal cancers.