Hypoxia-induced redox alterations and their correlation with 99mTc-MIBI and 99mTc-HL-91 uptake in colon cancer cells

Colorectal cancer is one of the most common malignancies in the Western world and is an example of a solid tumour in which hypoxia is a common feature and develops because of the inability of the vascular system to supply adequate amounts of oxygen to growing tumours. Hypoxia effects on tumour cell biology can be detected and characterized using different methods. The use of imaging with γ-emitting radionuclides to detect hypoxic tissue was first suggested by Chapman in 1979 [N Engl J Med 301 (1979) 1429–1432]. 99mTc-4,9-diaza-3,3,10,10-tetramethyldodecan-2,11-dione dioxime, also known as 99mTc-HL-91, has been among the most studied hypoxia markers.The objective of this study was to correlate the uptake of 99mTc-HL-91 and 99mTc-MIBI in colon cancer cells under normoxic and hypoxic conditions and to compare this information with some parameters such as oxidative stress and mitochondrial dysfunction of the cells analyzed by flow cytometry.Our results show that the in vitro 99mTc-HL-91 uptake is higher in hypoxic conditions, which is confirmed by the decreased uptake of 99mTc-MIBI. Flow cytometry results demonstrate that hypoxic conditions used are not enough to induce cellular death, but are responsible for the alterations in the intracellular redox environment, namely, increase of ROS production, proteic pimonidazol-derived adduct formation and alteration in the mitochondrial membrane permeability. Therefore, these results confirm that 99mTc-HL-91 is a radiopharmaceutical with favourable characteristics for detecting hypoxia.