A miRNA tumour signature as a prognostic biomarker to decipher the biology of Relapsed/Refractory Diffuse Large B-cell Lymphoma (R/R DLBCL) and improve treatment response

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disorder. Prognostic factors include genomic alterations and cell-of-origin (COO) subtypes, even though they cannot fully predict treatment response. MicroRNAs (miRNAs), deregulated in patient tumours and blood, are promising non-invasive biomarkers. Several circulating miRNAs were found to be correlated with progression-free survival (PFS), independently of other prognosticators. However, miRNA signatures, rather than individual miRNAs, represent more reliable biomarkers and a better mirror of the disease. In this PhD project, we identified circulating miRNAs differentially expressed between R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone) refractory and responding patients, by small-RNA sequencing on serum from 33 DLBCL samples. Among the identified miRNAs, the combined expression of three of them (miR-200c-3p, miR-324-5p, miR-421) improved the predictive performance and was correlated with PFS. Moreover, two out of three miRNAs, miR-324-5p and miR-421, were also differentially expressed in tumour tissues based on treatment response. Overexpressing the latter miRNAs reduced cell proliferation, viability and resistance to R-CHOP in the germinal centre B-like COO subtype. Through an in silico analysis, EGLN1 and TXNRD1, regulators of oxygen metabolism and redox homeostasis, were identified and validated as miRNA targets. The silencing or inhibition of these genes impaired cell viability and induced ferroptosis. On the one hand, these results support the value of a circulating three-miRNA signature as a potential predictive biomarker of treatment response. On the other hand, the results obtained strengthen the possible application of a two-miRNA signature and its targets for novel combined therapeutic interventions in DLBCL.