Recurrent mutations of the exportin 1 gene (XPO1) and their impact on selective inhibitor of nuclear export compounds sensitivity in primary mediastinal B-cell lymphoma

Fabrice Jardin 1, Anais Pujals 2, Laura Pelletier 2, Elodie Bohers 1, Vincent Camus 1, Sylvain Mareschal 1, Sydney Dubois 1, Brigitte Sola 3, Marlène Ochmann 4, François Lemonnier 2, Pierre-Julien Viailly 1, Philippe Bertrand 1, Catherine Maingonnat 1, Alexandra Traverse-Glehen 4, Philippe Gaulard 2, Diane Damotte 5, Richard Delarue 6, Corinne Haioun 2, Christian Argueta 7, Yosef Landesman 7, Gilles Salles 8, Jean-Philippe Jais 9, Martin Figeac 10, Christiane Copie-Bergman 2, Thierry Jo Molina 11, Jean Michel Picquenot 1, Marie Cornic 1, Thierry Fest 4, Noel Milpied 12, Emilie Lemasle 1, Aspasia Stamatoullas 1, Peter Moeller 13, Martin J S Dyer 14, Christer Sundstrom 15, Christian Bastard 1, Hervé Tilly 1, Karen Leroy 2

Abstract
Primary mediastinal B-cell lymphoma (PMBL) is a distinct subtype of B-cell lymphoma, separate from the molecular variants of diffuse large B-cell lymphoma (DLBCL), based on its unique clinicopathologic and molecular features. Unlike conventional DLBCL, PMBL primarily affects young adults—particularly women—and originates from thymic B cells in the anterior mediastinum. Although it shares histological similarities with DLBCL, PMBL is molecularly closer to classical Hodgkin lymphoma (cHL), suggesting a shared cellular origin between the two diseases.

To further characterize the molecular underpinnings of PMBL and identify potential diagnostic and therapeutic targets, we investigated mutations in XPO1, a gene encoding exportin-1—a key member of the karyopherin-β family involved in nuclear export. Exportin-1 regulates the transport of various tumor suppressors, oncogenes, and regulatory RNAs out of the nucleus, and its altered function has been linked to cancer development.

We performed sequencing on a large cohort of PMBL cases defined by either histology or gene expression profiling (GEP), and correlated XPO1 mutation status with genomic alterations, clinical features, and patient outcomes. To assess the specificity of these mutations, we also analyzed XPO1 in related lymphomas, including DLBCL, cHL, and mediastinal gray-zone lymphoma (MGZL)—a biologically intermediate lymphoma with overlapping features of PMBL and cHL.

Mutations in XPO1 were identified in 24% (28/117) of PMBL cases and in 26% (5/19) of cHL cases, but were absent or rare in MGZL (0/20) and DLBCL (3/197). This enrichment in PMBL and cHL highlights a potential role for XPO1 alterations in thymic B-cell derived malignancies. A recurrent hotspot mutation, p.E571K, was found in approximately 50% of GEP-defined PMBL cases. This mutation affects a key residue within the cargo recognition domain of exportin-1 and was associated with reduced progression-free survival (PFS), suggesting prognostic significance.

Interestingly, clinical parameters such as age, International Prognostic Index (IPI), and bulky disease status did not differ significantly between XPO1-mutant and wild-type PMBL cases, indicating that XPO1 mutation is an independent molecular marker rather than a surrogate for clinical aggressiveness.

To explore the functional impact of the XPO1 mutation—particularly E571K—we tested the response of PMBL cell lines to selective inhibitors of nuclear export (SINE) compounds, including KPT-185 and its clinically available analog, KPT-330 (selinexor). Both wild-type and mutant XPO1 cell lines exhibited a dose-dependent reduction in proliferation and increased apoptosis in response to KPT-185. Additionally, binding assays in U2OS cells expressing either wild-type or mutant XPO1 confirmed that the E571K variant does not significantly disrupt drug binding, suggesting that SINE compounds remain effective regardless of mutational status.

In summary, our results establish XPO1 E571K as a recurrent, defining genetic alteration in PMBL with potential utility as a diagnostic and prognostic biomarker. The preserved sensitivity of mutant and wild-type XPO1 to SINE compounds supports the therapeutic relevance of targeting nuclear export in PMBL. These findings underscore the broader role of nuclear export dysregulation in KPT-185 lymphoma pathogenesis and support the development of precision medicine strategies tailored to the molecular features of PMBL.