Characterisation of methylglyoxal stress in human colorectal cancer and liver metastases using immunohistochemistry.

Background: Glycolysis is the principal source of energy for cancerous cells. One inevitable consequence of the elevated glycolytic rate is the production of highly reactive molecules such as methylglyoxal (MG). MG induces the glycation of proteins on lysine and arginine residues and generates protein adducts called MG-derived hydroimidazolones (MGHs). Glyoxalase 1 (GLO1) is the main detoxifying enzyme of MG. It is expressed in most eukaryotes and prokaryotes and is localized in the cytoplasmic compartment. An increase of GLO1 expression and activity is a cell defence mechanism against glycation damage induced under MG stress. Our previous studies reported the presence of MG protein adducts in CRC tumours and have linked MG stress with the resistance to targeted therapy in KRAS-mutated CRCs.

Aims: In this pilot project, we undertook the detection of MG stress in human CRC primary tumours and liver metastases lesions.

Methods: We have used immunohistochemistry and antibodies directed against MGHs protein adducts and GLO1 enzyme in CRC samples. Specific Ki67 antibodies were used for the evaluation of tumour proliferation rate.

Results: By comparison of the same histological sample for GLO1 and Ki67 immunostainings, we observed that GLO1 enzyme was strongly detectable in the nucleus of undifferentiated and highly proliferative human CRC lesions. While most of the well-differentiated CRC tumours demonstrated undetectable to low nuclear GLO1 levels in the nucleus. Cytoplasmic GLO1 was similarly distributed among differentiated and non-differentiated tumours.

Conclusion: It might be therefore interesting to explore further this peculiar GLO1 sub-localisation that could potentially indicate for the first time the presence of MG stress in the nucleus and the necessity for the nuclear translocation of GLO1 detoxifying enzyme in aggressive CRC lesions. Whether nuclear GLO1 detection could be a valuable marker in terms of unfavourable prognosis in CRC patients will be analysed on a large collection of CRC patients with documented clinical data and follow-up.