Whole Exome Sequencing of refractory aggressive B-cell lymphomas identified recurrent mutations of the exportin 1 gene (XPO1) in Primary Mediastinal B-cell Lymphoma subtype. A LYSA study.

Fabrice Jardin (1, 2) , Anaïs Pujals (3) , Laura Pelletier (3) , Elodie Bohers (2, 1) , Sylvain Mareschal (2, 1) , Marlène Ochmann (4) , Francois A. Lemonnier (3) , Vincent Camus (2, 1) , Philippe Bertrand (2, 1) , Alexandra Traverse-Glehen (5) , Philippe Gaulard (3) , Diane Damotte (6) , Richard Delarue (7) , Corinne Haioun (8) , Yosef Landesman (9) , Gilles Salles (10) , Jean Philippe Jais (11) , Thierry Jo Molina (12) , Jean Michel Picquenot (2, 1) , Thierry Fest (4) , Noel Milpied (13, 14) , Emilie Lemasle (15, 2, 1) , Herve Tilly (15, 2, 1) , Karen Leroy (3)

1 GPMCND - Génomique et Médecine Personnalisée du Cancer et des Maladies Neuropsychiatriques
2 GPL - Groupe d'étude des proliférations lymphoïdes
3 IMRB - Institut Mondor de Recherche Biomédicale
4 MiCa - Microenvironnement et cancer
5 CHLS - Centre Hospitalier Lyon Sud [CHU - HCL]
6 CRC (UMR_S_1138 / U1138) - Centre de Recherche des Cordeliers
7 Service d'immuno-hématologie pédiatrique [CHU Necker]
8 Service d'hématologie clinique
9 Karyopharm Therapeutics Inc., Newton, MA
10 Service d'hématologie [Hôpital Edouard Herriot - HCL]
11 Service d'informatique médicale et biostatistiques [CHU Necker]
12 Hôpital Necker - Enfants Malades [AP-HP]
13 Service d'Hématologie et Thérapie Cellulaire
14 CHU Bordeaux
15 CLCC Henri Becquerel - Centre de Lutte Contre le Cancer Henri Becquerel Normandie Rouen

Introduction: Although diffuse large B‐cell lymphoma (DLBCL) has largely benefited from immunochemotherapy combinations in the past decade, 30% to 40% of patients still do not respond to treatment or relapse rapidly, underlying the need for understanding the mechanisms involved and identifying predictive biomarkers. To address this issue, we performed whole exome sequencing (WES) in a cohort of refractory/relapsed (RR) DLBCLs included in the LYSA clinical trial program. Methods: Fourteen normal/tumoural pairs of exomes from patients who progressed or relapsed within 12 months were sequenced on a HiSeq2000 platform. These cases had been classified as GCB (n = 4), ABC (n = 4), primary mediastinal B‐cell lymphoma (PMBL) (n = 4) subtypes or unclassified (n = 2), using Affymetrix U133 + 2 arrays. To refine the results obtained with WES, we performed high‐throughput targeted resequencing in 216 patients enroled in the LNH03 LYSA (LYmphoma Study Association) clinical trial programme and sequenced additional cohorts by Sanger method to assess the frequency and specificity of the candidate mutations. Results: WES identified several recurrent somatic mutations that are under investigation. Among candidate mutations, we identified a recurrent point mutation (p.E571K) targeting the Exportin 1 gene (XPO1) in 2/4 RR PMBL. XPO1 encodes a cargo protein mediating the nuclear export of multiple tumour suppressor proteins, including p53. Targeted resequencing was performed in four cohorts including GEP‐defined PMBLs (n = 36, cohort 1), PMBLs defined by histological criteria (n = 81, cohort 2), Hodgkin lymphoma (HL) cases and gray‐zone lymphomas (GZL) (22 HLs and 19 Reed–Sternberg micro‐dissected HLs, 20 GZLs, cohort 3) and DLBCL‐NOS (n = 194, 81 ABC, 81 GCB, 32 unclassified, cohort 4). XPO1 mutations were observed in 16/36 (44%) cases of PMBL cohort 1 and 10/81cases (12%) of cohort 2. By contrast, no mutation was observed in cohort 3, and only 3 cases (1.5%) were mutated in cohort 4. Copy number gains of XPO1 were observed in 8/22 PMBL cases (3 to 7 copies). In cohort 1, XPO1 mutation was significantly associated with a decreased PFS and OS [3y OS = 74% CI95% (55–100) as compared to 3y OS = 95% (86–100), log‐rank test p = 0.04]. The highly recurrent E571K variant (27/29 mutations) is located in the NES binding groove related to the cargo function. The effects of KPT‐185, a small inhibitor of nuclear export (SINE) that blocks XPO1‐dependent nuclear export, were assessed in 3 PMBL cell lines (MedB‐1, Karpas1106 and U2940) using cell proliferation and apoptosis assays. The XPO1 E571K mutated MedB‐1 cells showed a decreased response to the compound compared to the 2 other cell lines which are XPO1 wild type. Conclusions: XPO1 mutations represent a new distinctive genetic feature of the PMBL subtype and could be a biomarker with prognostic impact. The effect of the recurrent E571K variant on the cargo function of XPO1 is currently investigated.

Domaines: Sciences du Vivant [q-bio]

Fabrice Jardin, Anaïs Pujals, Laura Pelletier, Elodie Bohers, Sylvain Mareschal, et al.. Whole Exome Sequencing of refractory aggressive B-cell lymphomas identified recurrent mutations of the exportin 1 gene (XPO1) in Primary Mediastinal B-cell Lymphoma subtype. A LYSA study.. 13th International Conference on Malignant Lymphoma (ICML), Juin 2015, Lugano (Suisse), Jun 2015, Lugano, Switzerland. ⟨hal-02483516⟩