Multiple myeloma (MM) is a common hematological disease characterized by the accumulation of clonal malignant plasma cells in the bone marrow. Over the past two decades, new therapeutic strategies have significantly improved the treatment outcome and patients survival. Nevertheless, most MM patients relapse underlying the need of new therapeutic approaches. Plasma cells are prone to produce large amounts of immunoglobulins causing the production of intracellular ROS. Although adapted to high level of ROS, MM cells die when exposed to drugs increasing ROS production either directly or by inhibiting antioxidant enzymes. In this review, we discuss the efficacy of ROS-generating drugs for inducing MM cell death and counteracting acquired drug resistance specifically toward proteasome inhibitors.

Multiple myeloma (MM) is a plasma cell neoplasm that remains incurable due to innate or acquired resistance. Although MM cells produce high intracellular levels of reactive oxygen species (ROS), we hypothesised that they could remain sensitive to ROS unbalance. We tested if the inhibition of ROS, on one hand, or the overproduction of ROS, on the other, could (re)sensitise cells to bortezomib (BTZ). Two drugs were used in a panel of MM cell lines with various responses to BTZ: VAS3947 (VAS), an inhibitor of NADPH oxidase and auranofin (AUR), an inhibitor of thioredoxin reductase (TXNRD1), an antioxidant enzyme overexpressed in MM cells. We used several culture models: in suspension, on a fibronectin layer, in coculture with HS-5 mesenchymal cells, and/or in 3-D culture (or spheroids) to study the response of MM primary cells and cell lines. Several MM cell lines were sensitive to VAS but the combination with BTZ showed antagonistic or additive effects at best. By contrast, in all culture systems studied, the combined AUR/BTZ treatment showed synergistic effects on cell lines, including those less sensitive to BTZ and primary cells. MM cell death is due to the activation of apoptosis and autophagy. Modulating the redox balance of MM cells could be an effective therapy for refractory or relapse post-BTZ patients.

Multiple myeloma (MM) is an incurable plasma cell malignancy with frequent patient relapse due to innate or acquired drug resistance. Cholesterol metabolism is reported to be altered in MM; therefore, we investigated the potential anti-myeloma activity of two cholesterol derivatives: the 5,6 α- and 5,6 β-epoxycholesterol (EC) isomers. To this end, viability assays were used, and isomers were shown to exhibit important anti-tumor activity in vitro in JJN3 and U266 human myeloma cell lines (HMCLs) and ex vivo in myeloma patients’ sorted CD138+ malignant cells. Moreover, we confirmed that 5,6 α-EC and 5,6 β-EC induced oxiapoptophagy through concomitant oxidative stress and caspase-3-mediated apoptosis and autophagy. Interestingly, in combination treatment a synergistic interaction was observed between 5,6 α-EC and 5,6 β-EC on myeloma cells. These data highlight a striking anti-tumor activity of 5,6 α-EC and 5,6 β-EC bioactive molecules against human myeloma cells, paving the way for their potential role in future therapeutic strategies in MM.

Exportin 1 (XPO1) is the main nuclear export receptor that controls the subcellular trafficking and the functions of major regulatory proteins. XPO1 is overexpressed in various cancers and small inhibitors of nuclear export (SINEs) have been developed to inhibit XPO1. In primary mediastinal B-cell lymphoma (PMBL) and classical Hodgkin lymphoma (cHL), the XPO1 gene may be mutated on one nucleotide and encodes the mutant XPO1 ^E571K . To understand the impact of mutation on protein function, we studied the response of PMBL and cHL cells to selinexor, a SINE, and ibrutinib, an inhibitor of Bruton tyrosine kinase. XPO1 mutation renders lymphoma cells more sensitive to selinexor due to a faster degradation of mutant XPO1 compared to the wild-type. We further showed that a mistrafficking of p65 (RELA) and p52 (NFκB2) transcription factors between the nuclear and cytoplasmic compartments accounts for the response towards ibrutinib. XPO1 mutation may be envisaged as a biomarker of the response of PMBL and cHL cells and other B-cell hemopathies, to SINEs and drugs that target even indirectly the NFκB signaling pathway.

Primary mediastinal large B-cell lymphoma (PMBL) achieves excellent outcomes with dose-dense immunochemotherapy, yet response assessment by positron emission tomography (PET) remains limited. In this prospective multicenter observational study, we evaluated the clinical relevance of circulating tumor DNA (ctDNA) minimal residual disease (MRD) in patients with newly diagnosed PMBL and assessed whether MRD enhances outcome discrimination beyond PET. Plasma and PET images were collected at baseline and after 2 and 4 cycles. ctDNA and tumor biopsy were analyzed by high-depth, error-corrected sequencing (limit of detection ∼10−3). Associations between MRD, PET response, and progression-free survival (PFS) were evaluated. Among 84 patients, baseline ctDNA was detected in 98%. After 4 cycles of treatment with R-CHOP14 (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone, administered every 14 days) or R-ACVBP (rituximab, doxorubicin, cyclophosphamide, vindesine, bleomycin, prednisone), 87.7% had undetectable MRD. Persistence of minimal residual disease after 4 cycles of therapy (MRD4) was associated with shorter PFS (hazard ratio [HR], 78.1; 95% confidence interval [CI], 9.5-641.8). The 1-year PFS was 98.4% (95% CI, 95.4%-100%) for patients with undetectable MRD4 vs 33.3% (95% CI, 13.2%-84.0%) for patients with detectable MRD4 (P < 10^-4). MRD4 showed a higher positive predictive value (89% vs 50%) for disease progression than PET4, (PET after 4 cycles of chemotherapy) maintaining a similar negative predictive value (100% vs 93%). In multivariate analysis, only PET4−/MRD4− remained associated with PFS (adjusted HR, 0.07; 95% CI, 0.01-0.90). Plasma ctDNA represents a highly abundant source of genetic markers for tumor fingerprinting and disease monitoring. MRD detection after frontline therapy strongly complements PET response criteria in predicting outcome. These findings support the use of ctDNA monitoring as a valuable tool for future risk-adapted strategies in PMBL. This trial was registered at www.clinicaltrials.gov as NCT04980222.

Primary mediastinal large B-cell lymphoma (PMBCL) is characterized by recurrent 9p24.1 alterations driving constitutive overexpression of PD-1 ligands and high sensitivity to PD-1 blockade. While PD-L1 is widely used as a biomarker, the tumor-intrinsic functions of PD-1 ligands, and particularly PD-L2, remain poorly defined. Here, we investigated the distinct roles of PD-L1 and PD-L2 in PMBCL using CRISPR-Cas9-engineered isogenic models, immune co-culture assays, an immune-interactive in ovo chorioallantoic membrane (CAM) xenograft system, and integrative transcriptomic analyses of patient datasets. PD-L1 was most strongly associated with restraint of Th1-associated immune signaling and influenced responsiveness to PD-1 blockade, whereas PD-L2 was associated with preservation of lineage-associated transcriptional programs and distinct treatment-response patterns. Combined disruption of both ligands enhanced Th1 immune activation while altering B-cell transcriptional states. Consistent with these findings, transcriptomic analyses in PMBCL cohorts linked PDCD1LG2 expression to B-cell identity and signaling modules, whereas CD274 expression aligned with interferon-responsive immune programs. Together, these results support a model in which PD-L1 and PD-L2 associate with distinct immune and lineage-associated states in PMBCL and provide a framework for exploring biologically informed stratification strategies in this disease.