Aldehyde metabolic reprogramming in oesophageal adenocarcinoma

Abstract

Oesophageal adenocarcinoma (OAC) has unmet clinical needs as the UK five-year survival is 14%. Efforts to enhance early diagnosis uncovered enriched volatile aldehydes in OAC patients’ breath, although their origins and fate are unknown. Following comprehensive bioinformatics analyses, it was hypothesised that detoxification loss enriches aldehydes in the transforming lower oesophagus. Pursuing this biology could help refine OAC breath testing, deepen understanding of oncogenesis and uncover therapeutic susceptibilities. This PhD aimed to describe OAC aldehyde metabolism, its genetic framework, and its oncogenic effects. A bespoke ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was validated to unambiguously quantify 43 aldehydes and ketones in tissue samples. Multiple aldehyde species were enriched in OAC tissues, suggesting active carbonyl stress, field effects, and a requirement for competent defences. Genetically, aldehyde oxidoreductase expression loss defined OAC tissues, compared to normally resident tissue. Five aldehyde dehydrogenase isoenzymes were consistently and significantly depleted (P < 10-8 to -20); these findings were validated at the RNA (n = 67) and protein (n = 412) levels in clinical samples. In particular, loss of ALDH3A2 was associated with disease progression and independently predicted poorer survival (OR = 1.64, 95% C.I. 1.13 – 2.39, P = 0.01). To explore the effects of aldehyde metabolic rewiring, a second UPLC-MS/MS method was developed, which suggested that aldehyde-DNA adducts are also enriched in OAC tissues. Mechanistic studies in vitro revealed that ALDH inhibition is sufficient to enrich metabolic aldehyde in OAC cells. Finally, stable perturbation of ALDH3A2 in OAC cells highlighted a potential tumour suppressor role for this gene, as CRISPR-Cas9 mediated knockout enhanced cell growth through cell cycle shunting and affected redox control. These data highlight genetically deregulated aldehyde metabolism as a feature of OAC, which may contribute to carcinogenesis. Clinical implications and future research directions are discussed.