PO-273 Aldehyde dehydrogenase 7A1 (ALDH7A1) contributes to reduction of reactive oxygen species generation in colorectal tumour microenvironment

Reactive oxygen species (ROS) are reported to increase cancer cell proliferation, survival and migration. Paradoxically, high concentrations can trigger apoptotic or necrotic cell death. Mounting evidence indicates that hypoxic cancer cells undergoing exposure to oxidative stress and ROS develop adaptive strategies to survive to the hostile milieu. These are indeed antioxidant responses that may result in increased aggressiveness and resistance toward chemotherapy. Aldehyde dehydrogenase 7A1 (ALDH7A1) is a drug metabolising enzyme that has protective role against hyperosmotic stress and oxidative stress. Increased expression of ALDH7A1 was reported in different cancer types. However, its expression and role in tumour microenvironment has not been investigated. Therefore, the aim of this study was to evaluate the impact of hypoxia on the expression of ALDH7A1 and to assess the effect of ALDH7A1 on ROS generation. Material and methods Colorectal cancer (CRC) cell lines (HT29 and DLD-1) were grown as monolayer and exposed to normoxic or hypoxic conditions (0.1% O2). Multicellular spheroids (MCS) were generated in spinner flasks. ALDH7A1 gene and protein expression was evaluated using qRT-PCR and western blot, respectively. Immunohistochemistry was done to assess the expression at different depths within MCS and correlate it with hypoxia using the hypoxic marker, pimonidazole. Knockdown studies were done using siRNA and ROS was measured using carboxy-H2DCFDA. Results and discussions The gene and protein analysis data showed that ALDH7A1 was significantly upregulated in both cell lines upon exposure to hypoxia. In addition, cells residing in the hypoxic region of both MCS showed significant increase of ALDH7A1 compared to surface layer cells and monolayer cells at the gene and protein levels. ROS generation was reduced in hypoxic cells in comparison to normoxic cells, while ALDH7A1 knockdown studies showed elevation in ROS level. Conclusion Our data suggests that ALDH7A1 upregulation in CRC cells as a result of tumour hypoxia might be one of the adaptive and protective responses against oxidative stress. As a consequence, ALDH7A1 might act as a potential biomarker for aggressive cancer phenotypes and/or a target for therapeutic intervention in CRC tumour microenvironment. To fully establish the role of ALDH7A1, future work will include evaluation of its expression and distribution in relation to hypoxic areas using clinical samples from CRC patients and study its correlation with the tumour stages and drug resistance.