Identification of ferroptosis-sensitizers for DLBCL treatment

Abstract Diffuse large B-cell lymphoma (DLBCL) is the most common form of lymphoma in adults and represents a clinically and molecularly heterogeneous disease. Based on gene expression profiling, DLBCL can be classified into two major subtypes, the germinal center B-cell–like (GCB) and the activated B-cell–like (ABC). The standard first-line treatment for DLBCL is the immunochemotherapy regimen R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone). However, approximately 30% of patients are refractory to this treatment or relapse after an initial response. A major contributor to treatment failure is the resistance of lymphoma cells to apoptosis. To overcome this resistance, we and others have proposed the induction of ferroptosis, a form of regulated, iron-dependent cell death that is mechanistically distinct from apoptosis. Ferroptosis inducers have shown anti-lymphoma activity in vitro and in vivo, particularly in GCB-type DLBCL. However, in preclinical xenograft mouse models, these agents failed to fully eradicate tumor cells. To identify compounds that enhance ferroptosis sensitivity, we conducted a compound library screen, which revealed that inhibitors of the PI3K/Akt/mTORC1 signaling pathway significantly increase the susceptibility of the GCB DLBCL cell line DOHH2 to ferroptosis. Notably, this pathway is frequently dysregulated in DLBCL, due to either constitutive B-cell receptor (BCR) signaling or PTEN deletions. We demonstrate that PI3K/Akt/mTORC1 inhibitors synergize with multiple ferroptosis-inducing agents to effectively kill various GCB DLBCL cell lines. Mechanistically, inhibition of PI3K signaling results in the downregulation of both mRNA and protein levels of SLC7A11, a key subunit of the system xc- cystine/glutamate antiporter, which mediates cystine uptake essential for glutathione biosynthesis. Consequently, PI3K inhibition leads to a significant reduction in intracellular glutathione levels, thereby increasing ferroptosis susceptibility. Overexpression of SLC7A11 rescues this effect, confirming its central role in PI3K-mediated ferroptosis sensitization. Furthermore, we show that PI3K inhibition downregulates the transcription factor HIF-1α (hypoxia-inducible factor 1-alpha), a known positive regulator of SLC7A11 expression. These findings suggest that PI3K/Akt/mTORC1 inhibition sensitizes DLBCL cells to ferroptosis by disrupting the HIF-1α–SLC7A11–glutathione axis. Taken together, our results support a novel therapeutic strategy combining FDA-approved PI3K or mTORC1 inhibitors with ferroptosis inducers as a promising approach to eliminate apoptosis-resistant DLBCL, particularly of the GCB subtype. Disclosures: No relevant conflicts of interest to declare.