Tumour Jagged1 expression as a prognostic marker of bevacizumab response and modulation of 5-fluorouracil efficacy through γ-secretase inhibition in colorectal cancer.

BACKGROUND: 5-fluorouracil (5-FU)-based chemotherapy remains the backbone of metastatic colorectal cancer (CRC) treatment, although therapeutic resistance limits long-term benefit. Combination with bevacizumab improves outcomes in some patients, but biomarkers capable of predicting benefit are lacking. Notch signalling and altered expression of its ligand Jagged1 (JAG1) have been implicated in CRC progression, yet their relevance in bevacizumab-treated patients and their regulation by 5-FU remain unclear. METHODS: JAG1 protein levels were quantified in tumour samples from patients with metastatic CRC (n = 60) by using enzyme-linked immunosorbent assay and correlated with clinical outcomes. In vitro experiments using HCT15 and SW480 CRC cell lines were used to assess the effects of combining 5-FU and the γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl-l-alanyl)]-S-phenylglycine t-butyl ester (DAPT) on proliferation using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Notch pathway, stemness, epithelial-mesenchymal transition (EMT), and apoptosis markers were assessed by using quantitative PCR and/or Western blotting. The angiogenic capacity of the secretome was examined by using tube-formation assays. RESULTS: Among patients receiving bevacizumab, those with low tumour JAG1 expression exhibited longer progression-free survival and time to progression than patients with high JAG1 expression. In vitro, DAPT plus 5-FU synergistically reduced CRC-cell viability, enhanced apoptosis and autophagy, reduced the expression of stemness and EMT-related genes, and impaired tube formation. Soluble JAG1 was detected in conditioned media, with higher levels following combination treatment in HCT15 cells. CONCLUSIONS: High tumour JAG1 expression identifies metastatic CRC patients with poorer outcomes when treated with a bevacizumab-containing regimen, supporting its potential as a prognostic biomarker. Mechanistically, Notch inhibition enhances the antitumour effects of 5-FU, suggesting that its combination with γ-secretase inhibitors may improve therapeutic efficacy in CRC.